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Unmanned Spaceflight.com _ Opportunity _ Dust Storm- Opportunity EOM
Posted by: djellison Jun 5 2018, 03:05 PM
Expect a quiet few sols - http://www.lpl.arizona.edu/~lemmon/mars-tau-b.html
SOL TAU
5097 0.65
5098 0.64
5099 0.67
5100 0.64
5101 0.60
5102 0.60
5103 0.61
5104 1.55
5105 ****
5106 2.12
Posted by: nprev Jun 9 2018, 06:38 AM
Breaking news: As Mars nears one of its closest perihelion passes, a large dust storm has developed. Per the https://www.jpl.nasa.gov/news/news.php?feature=7155, the storm now covers a surface area the size of North America. It may possibly grow into a global storm as has happened during previous close perihelion years (notably 1971, which coincided with Mariner 9's arrival).
Needless to say, this will produce highly challenging conditions for Oppy, and the mission team is making survival preparations. Science operations have been suspended at this time.
We wish the team the very best of luck, and GO OPPORTUNITY!!!!! 
Posted by: Sean Jun 9 2018, 11:17 AM
Oh god.
Posted by: fredk Jun 9 2018, 02:17 PM
Some details of the storm activity at the http://www.msss.com/msss_images/subject/weather_reports.html site. That's only updated weekly, on Wednesdays.
Posted by: James Sorenson Jun 9 2018, 06:44 PM
Good luck to Opportunity and to the very talented team that has brought her through obstacle after obstacle after all these wonderful and fascinating years. She will prevail with the Sun gleaming off her dust-free camera lenses and solar cells after this passes. GO OPPY!!
Posted by: Explorer1 Jun 9 2018, 07:18 PM
Given the length of the mission, it was only a matter of time until another dust storm showed up; hopefully it won't be global or very long lasting!
Posted by: marsophile Jun 10 2018, 12:46 AM
Once the dust storm per se abates, there may be a period while dust settles out of the atmosphere. I wonder if there might be some advantage at that point to positioning the rover on a slope so that it minimizes the catchment area that is presented to the falling dust. If this conflicts with maximizing the sun exposure of the solar panels, perhaps it could be done at night.
Posted by: Phil Stooke Jun 10 2018, 08:21 PM
"I wonder if there might be some advantage at that point to positioning the rover on a slope"
The rover is already on about as steep a slope as it can easily manage. But pondering the geometry, to reduce the projected area of the panel to 50% you would need a slope of 60 degrees, completely impossible. The allowable slopes are only going to cut dust deposition by a small amount. We'll have to rely on wind gusts.
Phil
Posted by: djellison Jun 10 2018, 09:03 PM
When you have skies this dusty - the single best strategy is to be flat. You're getting your power from the diffuse glow of the whole sky.....anything other than flat hurts you.
Posted by: centsworth_II Jun 10 2018, 09:21 PM
Also, with panels flat, a gust of wind from any direction will blow off dust.
Posted by: djellison Jun 10 2018, 09:34 PM
Moreover - it's not dust 'fall' that hits the arrays - it's just blowing around and sometimes you get some. Tilting at a large angle may actually put your arrays facing upwind and cause more harm than good.
Posted by: pioneer Jun 10 2018, 10:07 PM
Will Opportunity get a chance to send back images from the surface during the dust storm?
Posted by: djellison Jun 10 2018, 10:13 PM
Other than taking occasional tau measurements of the sun - no - there simply is not enough power to do so.
If you look at the MER raw image page and PanCam tracking database - you'll see the only imaging attempted since Sol 2107 has been tau measurements of one sort or another.
Posted by: ngunn Jun 10 2018, 10:29 PM
I wonder how much tilt you need to shake some dust off by jiggling around a bit. Anything worth trying there?
Posted by: djellison Jun 10 2018, 10:38 PM
The sort of slope that represents a threat to vehicle safety can cause some kinds of coarse dust, bordering on sand, to rattle down the rover deck.
This is all academic - we don't know how long this storm will last, nor what state the vehicle will be in when it ends. We may find we come out of it with hundreds of watt hour to burn.
Remember - dust on the arrays is not the problem right now. It's dust in the atmosphere. A brand new rover with clean arrays would also be in trouble right now. We went into this with a pretty clean rover. A dust factor of 0.772 ( see https://mars.jpl.nasa.gov/mer/mission/status.html#opportunity ) is remarkably clean.
Posted by: Dalhousie Jun 10 2018, 11:01 PM
Dust collects on upwind slopes, not downwind.
Posted by: ngunn Jun 10 2018, 11:11 PM
Sure, my question was not about managing the situation right now, so academic in that sense. That's good information on the sandy stuff sliding on dangerous slopes, thanks. Just one thing I'd like to add: the solar panels however they are supported must have some some natural vibration frequencies. If it were possible to drive those natural oscillations the amplitude might be enhanced to the point where more dust slides.
Posted by: marsophile Jun 10 2018, 11:38 PM
Is it still true that the prevailing wind is upslope?
Posted by: djellison Jun 11 2018, 12:30 AM
They wobble - yes - and that's caused sand to slide down them driving on dangerously steep slopes in the past.
Posted by: djellison Jun 11 2018, 12:43 AM
That's a rather simplified view of what really occurs
Papers like this : https://onlinelibrary.wiley.com/doi/pdf/10.1002/esp.1272 : go into it in more detail.
Moreover - the rover itself presents a topographic feature to the oncoming wind, whatever angle it comes from.
Posted by: pioneer Jun 11 2018, 12:55 AM
Thanks. I thought I saw an image taken by one of the MER rovers during a dust storm.
Posted by: James Sorenson Jun 11 2018, 01:15 AM
Oppy as well as Spirit did take some images of the ground to monitor pebble movement and images of the horizon during the 07 global storm when power conditions allowed it.
Posted by: serpens Jun 11 2018, 03:49 AM
Yep. Spirit provided a sequence of images that provided a short movie of dust ripples in motion, but I think this was taken towards the end of the storm as the intensity of the dust diminished.
Posted by: djellison Jun 11 2018, 04:23 AM
This mosaic is from Opportunity
https://www.nasa.gov/images/content/182691main_mer-20070719.jpg
during the 2007 storm.
They were able to execute simple Pancam observations briefly during that storm. However - even if the tau were the same now, Opportunity would be in worse shape for all sorts of reasons (11 year older batteries, on a slope, it's not high summer ).
However - the tau is a lot LOT worse right now. We've seen both record high tau's, and record low power. The vehicle is facing conditions we just have no experience with.
Posted by: James Sorenson Jun 11 2018, 04:36 AM
I am curious if the full frame wide range tau images that have been coming down shows any trace of the solar disk in the original data products, Doug? And if so, can a current estimated Tau be worked out from them, heard anything? 
Mark's site was last updated on 5106 when the last visible solar disk images were taken.
Posted by: Deimos Jun 11 2018, 11:49 AM
Hoping to see some new values added to that site soon. The combination of data from which tau may not be automatically extracted and a newsworthy event may require some permission to restart the updates.
Posted by: serpens Jun 11 2018, 12:15 PM
The Tau is about double the worst experienced by Opportunity during the last storm. With the current orientation what is the correlation between tau and Whr generated? Since the attenuation of sunlight through the atmosphere is essentially exp(-tau) the observed light intensity with tau around 10.8 must be negligible.
Posted by: Deimos Jun 11 2018, 07:32 PM
I suppose since the news is https://mars.nasa.gov/news/8348/opportunity-hunkers-down-during-dust-storm/, it is on the plot http://www.lpl.arizona.edu/~lemmon/mars-tau-b.html.
I did a very simple 2-stream model, and you can approximate total insolation (proportional to array W-hrs/sol) as varying with exp(-tau*gamma), where gamma is 0.35-0.40 or so. If you compare two sols, that's exp(-delta_tau*gamma). A lot of the extinction goes into sky light, but total light is still much reduced. At these taus, tilt is a small perturbation, I'd guess. (A chunk of sky is blocked, but that chunk is the source of a small fraction of light, and the tilt hasn't changed.)
Posted by: fredk Jun 11 2018, 07:47 PM
I guess there isn't much data from the ground during dust storms to say very accurately how much reduced the total light is. Technically the tau itself tells you how much darker the sun has become, but as Deimos says some of that will be scattered to the ground via the sky.
Anyway of course we don't need to do full scattering calculations, since what really matters is array power, which is known (if not publicly).
Posted by: MoreInput Jun 11 2018, 07:49 PM
I just can't believe how fast the tau increased. Over the years it oscillated just below 1, and now within 8 sols it increased by 18 times.
Posted by: mcaplinger Jun 11 2018, 09:52 PM
Has Opportunity ever been in a low-power fault state? I'm thinking not.
As far as I know, Spirit went into this state on sol 2210 and never came out, although this is supposed to be recoverable.
Posted by: serpens Jun 11 2018, 11:28 PM
I guess Opportunity would be better placed to come out of a low power fault state. Spirit had to try and survive the depths of winter. With the dust storm maximum temperatures will be cool but minimum temperatures will be higher than normal for this time of year and the radioisotope heaters may be able to cope.
Posted by: marsophile Jun 12 2018, 12:33 AM
https://mars.nasa.gov/mer/newsroom/pressreleases/20040526a.html
Is it cold enough to require "Deep Sleep" mode to keep the "stuck-on" heater from wasting energy? (I guess we don't have to worry about the Mini-TES any more.)
Does the loss of flash memory affect the hazard of a low-battery state?
Posted by: Hungry4info Jun 12 2018, 04:11 AM
It's apparently not as bad over Curiosity's landing site, but the air is noticeably dusty.
Sol 2077 MastCam.
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Posted by: mcaplinger Jun 12 2018, 05:47 AM
I'm not sure that the specific failure mode that got Spirit has ever really been identified. The presumption was that it was related to cold, but it would surprise me a little if there was anything about MER that could be rendered non-functional by a few deep thermal cycles. (Well, maybe the batteries, but the system would still work in the daytime.)
Hopefully there isn't some inherent flaw in the low power fault state, or better yet, that it never gets entered.
Posted by: PaulH51 Jun 12 2018, 09:36 PM
NASA will host a media teleconference at 10:30 a.m. PDT (1:30 p.m. EDT) Wednesday, June 13, to discuss a massive Martian dust storm affecting operations of the agency's Opportunity rover and what scientists can learn from the various missions studying this unprecedented event. More at link:
https://www.jpl.nasa.gov/news/news.php?feature=7158
Posted by: HSchirmer Jun 12 2018, 10:09 PM
Now that we have equipment on Mars, should global dust storms get names like Earth hurricanes or typhoons?
Guess the 2007 storm would be "Ashes" and this would be "Bowie"?
Posted by: MahFL Jun 12 2018, 10:39 PM
Sol 2077 MastCam.
Can only imagine what it's like at Oppy.
Posted by: xflare Jun 12 2018, 11:32 PM
Has there been any further communication from Opportunity since Sunday morning?
Posted by: RoverDriver Jun 13 2018, 12:46 AM
There will be a telecon tomorrow (Wednesday June 13, 2018) at 10:30am PDT
https://www.jpl.nasa.gov/news/news.php?feature=7158
Paolo
Posted by: mcaplinger Jun 13 2018, 12:50 AM
I don't know. I happened to notice a DSN track on DSN Now this morning but nothing was received while I was watching.
Posted by: jccwrt Jun 13 2018, 03:05 AM
The JPL news story on the dust storm was updated this evening to say that the rover failed to check in today and is likely in low-power fault mode.
https://www.jpl.nasa.gov/news/news.php?feature=7155
Posted by: mcaplinger Jun 13 2018, 03:45 AM
Bummer. Per https://trs.jpl.nasa.gov/handle/2014/37750 (assuming there are no changes to the fault response), if it gets enough power to boot back up, comm is limited to one LGA DTE per day at 11 LST, unless the ops team can get commands in to alter this behavior and enable UHF comm. I'm sure this will all be described tomorrow.
Posted by: serpens Jun 13 2018, 04:15 AM
Thanks for that link. I guess all that can be done now is sit back, cross all available fingers and hope that this amazing feat of engineering design can astound us one more time.
Posted by: RoverDriver Jun 13 2018, 04:21 PM
On Si=ol 4311 we "drove" uphill at 32 degrees and excited the vehicle with quite large values of vibration and very little dust was moved. We tried on Spirit as well back on a slope (also at 30deg) before leaving the north side of Home Plate and there was no measurable effect on dust factor. I think one has to consider we are talking DUST, not sand.
Paolo
Posted by: SpaceListener Jun 13 2018, 04:31 PM
Are the solar panels able to raise up? I say this when MER traveled thru the space, the solar panels was inside in compact mode before it landed.
During the process of closing (raising) and opening (lowering) solar panels might shake due to the motor vibration or also due to the slope, some
dust will slip down.
Posted by: Explorer1 Jun 13 2018, 04:35 PM
No, those were a one-time use, though good thinking outside the box!
Telecon starting now....
Posted by: djellison Jun 13 2018, 05:52 PM
People should think of their TV screen. It has dust on it. It's vertical. The dust just sits there.
Posted by: Art Martin Jun 13 2018, 06:22 PM
The news conference was upbeat. They expect the rover to survive based on observations so far. Good news is this is happening during the summer so battery temps aren't as much of a concern. (I was unaware there were warming plutonium sources inside the battery compartments). Very little power is required to run the onboard clock and even if it stops, the rover can awake again from new solar input and go into a search mode to contact Earth. Fascinating. Such amazing engineering and staff.
Posted by: MahFL Jun 13 2018, 10:48 PM
During the process of closing (raising) and opening (lowering) solar panels might shake due to the motor vibration or also due to the slope, some
dust will slip down.
The wind blows the panels clean from time to time.
Posted by: mcaplinger Jun 13 2018, 11:24 PM
The good news from the press conference is that the low-power fault state is basically the same thing as deep sleep, which they use all the time.
I don't know two things: first, how long it has until it loses its mission clock, which complicates the situation, and second, how the stuck-on IDD heater that deep sleep was added to get around will affect the recovery -- since that's a 0.5A load that will start as soon as the battery controller comes up.
Posted by: PaulH51 Jun 14 2018, 12:35 AM
ICYMI : Here is a link to the YouTube recording of the 'Dust Storm' teleconference: https://youtube.com/watch?v=fIKxdRFx2Wo#
Posted by: serpens Jun 14 2018, 02:13 AM
The extent of this dust storm seems to be emulating the 1971 Mariner global dust storm. That storm lasted over three months so we could be in for a long wait as the atmospheric transfer between poles slows down and the dust settles.
Posted by: jccwrt Jun 14 2018, 02:55 AM
Another potential alternative is the 1977 dust storms observed by Viking. There was an early season storm that followed the Acidalia storm track (started in Mare Acidalium, crossed south across Chryse and Thaumasia, and exploded in the southern hemisphere) that cleared by mid-summer, followed by an even more intense storm in late summer originating from the Hellas Basin.
Posted by: marsophile Jun 14 2018, 03:17 AM
If it gets no power from the solar panels, is there a ball-park figure on how long the pre-existing battery charge could keep the clock going? Days or weeks?
[EDIT: Based on figures here:
https://trs.jpl.nasa.gov/bitstream/handle/2014/38400/05-3884.pdf
and some assumptions, my own rough estimate is 8 days if zero power from the solar panels.]
Posted by: elakdawalla Jun 14 2018, 03:27 AM
Because a lot of questions being asked here were answered in the press briefing, I'm going to break my usual practice and link to my own writing, in this case https://threadreaderapp.com/thread/1006952540234059776.html.
Posted by: mcaplinger Jun 14 2018, 04:09 AM
John Callas said "If rover is generating less than 22Wh, then it won't have enough power to maintain clock". I'm not sure how to parse this. AFAIK, the mission clock is powered directly from the batteries during sleep and will presumably drain them down to some minimum voltage cutoff. 22Wh per sol would be a little under 1 watt of power, which is a heck of a high power draw for a simple clock.
At any rate, I think it's safe to assume that over the next few days there will be essentially no power generated.
Posted by: Explorer1 Jun 14 2018, 04:33 AM
The main thought I keeping coming back to is that Oppy has been out of contact for much longer stretches of time during conjunctions (though obviously this is a very different circumstance in other respects!) We know the rover won't suffer some cold-related issue as Spirit did; it's just a matter of crossing our fingers and waiting it out...
Posted by: mcaplinger Jun 14 2018, 03:05 PM
https://trs.jpl.nasa.gov/handle/2014/43244 "The effects of clock drift on the Mars Exploration Rovers" is an interesting paper about the MER clock architecture. It didn't really have anything germane to the issue of losing time reference but it has a lot of detail about how the mission clock works.
Posted by: mcaplinger Jun 14 2018, 03:11 PM
During conjunction the rover has still been powered, of course. The most worrisome thing about this is whether there's some issue associated with losing the mission clock (go back through all the Spirit status reports after loss of comm for lots of discussion about various permutations there). We can assume that Spirit just got too cold, but there's no proof of that I'm aware of. And then there's the possibility that the panels will be so dusty after the storm clears that they won't produce a useful amount of power (although I think that's probably unlikely.)
Posted by: elakdawalla Jun 14 2018, 04:36 PM
At any rate, I think it's safe to assume that over the next few days there will be essentially no power generated.
He said that below 22Wh they would likely have a clock fault, so the fact that 22 was the last number reported from the rover made him think it very likely that they had already triggered that fault.
Posted by: Gerald Jun 14 2018, 05:30 PM
If the dust will settle uniformly, the panels will be just as dusty as the sky will have been during the storm. So, a cleaning event will be required after or near the end of the dusty sky phase.
Posted by: Deimos Jun 14 2018, 05:59 PM
Not strictly true, at least if you're referring to how dusty the local skies were. The very high opacity the rover last saw is quite localized. The planet-encircling dust event, by its nature, distributes dust geographically. When local lifting stops, Meridiani could see rapid clearing that is not dust settling on panels. Then, a long slow period of sedimentation will get things dusty, but I imagine the Meridiani winds will not let too much dust accumulate (Mars may imagine differently, of course).
Posted by: marsophile Jun 14 2018, 08:02 PM
New MARCI weather report:
http://www.msss.com/msss_images/latest_weather.html
It includes a link to this "Storm Watch" website:
https://mars.nasa.gov/weather/storm-watch-2018/
Posted by: Steve G Jun 15 2018, 03:19 AM
To add a layman's context to the amount of sunlight blocked from the dust storm, if I was standing next to Opportunity, how dark would it be to my human eyes? (Bright as a full moon on Earth? for example)
Posted by: serpens Jun 15 2018, 06:38 AM
There are a lot of variables to consider there Steve and the human eye has remarkable adaptability to light intensity. To put this in context the difference in intensity between a really bright sunlit day in a high albedo environment and a moonlit night is around 9 or 10 million to 1. The eye doesn't mind whether it gets its lumens by the bucket load or with a tea spoon provided it gets enough. But since the impact of tau on solar intensity is a negative exponential function with a tau of 10.8+ you probably wouldn't be able to see your hand in front of your face.
Posted by: Don1 Jun 15 2018, 09:02 AM
OK, so according to the source linked below, a sunny day on earth is about 100,000 lux, while a moonlit night is about 0.25 lux.
At Mars distance the sun will be about 1/4 brightness compared to Earth, so say 25000 lux under clear skies. A tau of 10 means a reduction of about 50,000 fold in the light intensity, so I would estimate about 0.5 lux. This is comparable to a moonlit night on Earth.
https://answers.yahoo.com/question/index?qid=20081208165331AA8eZWH&guccounter=1
Posted by: Gerald Jun 15 2018, 12:03 PM
If I understand it correctly, tau measurements are performed by considering only the sun or another small apparent source of light.
https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1998JE900017
Scattered light seems to be neglected. This approach tells something about the total incoming light, if tau is small. But for large values of tau, most of the light is scattered. So, it doesn't need to be much darker than it would be, if the whole sky would be as bright as the moon on Earth.
More useful, in this case, would probably be the comparison of about 700 Wh with 22 Wh, which is about a factor of 34 darker than under clear sunshine. Reduce this factor a bit by the dust layer on the panels. It may still be bright enough to read newspapers easily, like on a cloudy or very cloudy day on Earth.
Posted by: Deimos Jun 15 2018, 01:46 PM
Exactly! The Sun itself was fainter than a full moon on Earth on Sunday. But in each photon-dust interaction the extinction (which tau measures) is <10% absorption and >90% scattering to sky light. The scattering is ~85% downward, 15% upward. There would be 10-11 extinction events (more like 14-15 at the time Opportunity was awake, with the Sun not vertical). Modeling literally the round numbers I just used, I get 98% loss of light at the surface (i.e., sky light >10,000 times direct sun light); you got 97% (and I believe the panels more than made up numbers).
What did it look like? Other than the decidedly ruddy to brownish tint, it looked like a somewhat overcast day. The sort of mid-afternoon when you can just barely see (or not quite see) the Sun through clouds that stretch from horizon to horizon. When the world would be black through eclipse glasses, but easily visible without. Normal human vision would adapt well--it's not night, moonless or moonlit, or even sunset. Solar panels, however, are not known for being so dark-adaptable. So the drama is real, even if people seem to want to describe it in terms that would be as dramatic for people as the actual situation is dramatic for the rover.
This weekend, I expect tau of several hundred. Not on Mars, but at home, where we expect thunderstorms.
PS, scattered light is not 'neglected'. In photometrically measuring opacity it is hunted and eliminated with extreme prejudice. 
Posted by: mcaplinger Jun 15 2018, 02:26 PM
As a data point, I have solar panels on my house. On a typical day in March they generate about 30 kW-h. During the cloudiest, lowest-production day this March, I got about 3 kW-h, about 10x worse.
700/22 is 32x less production, so this would be a really cloudy day, at least by SoCal standards. (Solar distance is already scaled out so don't complain about that.)
Posted by: fredk Jun 15 2018, 04:37 PM
Another example that people may have witnessed is being under heavy smoke from forest fires. The sun may be just barely visible as a dull orange disk (so a huge tau), but the landscape will be as bright as some level of cloudy day due to light scattered from the sky (smoke).
I don't know how smoke particle size compares with Martian dust, which would affect the details of the scattering (how much into what angles vs frequency), so the details may be different.
Still it's worth pointing out that so far 22 Whrs/sol is an upper limit...
Posted by: hendric Jun 15 2018, 07:19 PM
On the 22 WH just to keep the clock alive, maybe that number is accounting for the stuck IDD heater?
From the paper - "The Mission Clock in the MER rovers uses a custom hybrid crystal oscillator from Q-Tech Corporation. " which however is proprietary, at least at the time the paper was published. The skew of +-10s over 10 sols with temperature is pretty reasonable for a typical +-50 ppm crystal oscillator. (~900,000s for 10 sols, so about +- 10ppm with 10s drift). To get better PPMs clocks in your phones use temperature compensation, ie they adjust the voltage based on temp, with <2 ppm or less commercially available. Of course, that costs power too (~mA), and isn't space rated. A COTS RTC (real-time clock, think wrist-watch in a tiny package) without temperature compensation can be < 1uA though, again not space rated.
Posted by: Roby72 Jun 15 2018, 09:56 PM
just as a reminder how Mars looked in 2001 fully in dust - shots with the MGS orbiter camera:
https://photojournal.jpl.nasa.gov/catalog/pia03170
Posted by: siravan Jun 15 2018, 10:10 PM
Regarding tau and the efficiency of solar panels, another issue is that Oppy's solar panels are of triple-junction type. This allows a wider spectral coverage and improved efficiency (each junction works at a different part of the spectrum). But this increased efficiency comes with a drawback as the junctions are in series. During a dust storm, the light is likely skewed toward red. Hence, not much blue is left and the blue junction becomes the limiting factor.
Posted by: mcaplinger Jun 15 2018, 10:26 PM
I don't see how, that heater is turned off when the battery controller is turned off, that being the whole point of deep sleep.
Posted by: serpens Jun 16 2018, 01:13 AM
As siravan noted the spectrum at the surface would be skewed towards the red. The spectral response of Opportunities solar cells extends into the near infrared and it would not surprise if this is where the remnant charge is coming from. While comparing Earth to Mars is a bit chalk and cheese the attached link shows the effect on visible light of a dust storm in my old stamping ground. https://www.youtube.com/watch?v=BrlD22HwPvI
The descriptions of current (human) visibility on Mars as a cloudy day may be a trifle optimistic, even given the range of visibility of the human eye:
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Posted by: marsophile Jun 16 2018, 02:58 AM
According to the paper cited here:
the stuck on heater causes a drain of 0.5 amps, but it is actually really only on when the temperature drops sufficiently. The paper estimated a cost of 180 WH per day at the time the anomaly occurred.
Assuming 24 volt battery power, 1 watt corresponds to around 40 milliamps, which doesn't seem too unreasonable for the mission clock (plus alarm mechanism).
Posted by: Deimos Jun 16 2018, 01:30 PM
Not sure what is meant. The chart describes a factor of ~30 below full sun (ok, a factor of 60 below given Mars-Sun distance) as 'near windows'. Moreover, overcast days on Earth literally have optical depth >10 quite frequently (well, frequency is location dependent, but I grew up in Seattle).
If blue is the limiting factor for the triple junction cells (per siravan), the light providing array energy cannot be all IR; frankly, there should be more red light available than IR (per unit wavelength) given the Sun's spectrum and the albedo of dust in the red.
Posted by: mcaplinger Jun 16 2018, 04:01 PM
Normally you don't use linear regulation from battery voltage, because most of the power is used in the regulator. 40 mA at 5V is only 200 mW (which is still a lot for a simple clock -- for example, a Chronodot RTC http://docs.macetech.com/doku.php/chronodot_v2.0 -- admittedly not rad-hard -- uses 840 nanoamps in standby timekeeping!). But it's not impossible that in this case they did use linear regulation because it's simpler and losing all solar power wasn't really a credible fault for the short mission design life.
At any rate, if the clock is lost, we may see a lot of X-band "sweep & beep" commanding once there's any expectation that the rover is getting enough power during the day to communicate. On Spirit they started this about 4 months after the loss of comm. See https://mars.nasa.gov/mer/mission/status_spiritAll_2010.html for some descriptions of this.
Posted by: Don1 Jun 16 2018, 09:20 PM
I did try to estimate the illumination based on the solar panel output, and I was puzzled by why that was coming out so differently from the estimate based on tau. What bothers me about the 22 Watt-hr quoted for the solar panel production is that seems way too much to just run a clock. Are we certain that number is accurate?
Also, if there was a break in the storm the rover might have gotten half an hour of sun which would charge the battery a little. We don't know how much the panels were producing at the time the tau was measured.
On a different topic, the 8 RHUs are providing 192 Watt-hours of energy in the form of heat. If I remember correctly, sunny day production from the panels is about 600 Watt-hours of electricity. So a big chunk of the energy budget of this "solar" powered rover is actually from nuclear sources, even when it is sunny. That surprised me when I worked out the numbers.
Posted by: fredk Jun 16 2018, 11:30 PM
Another point is that if blue limits the power, and the sky is very red, then estimates of the overall brightness on the ground based on the 22/700 ratio will be underestimates, due to the extra red light not contributing to array power. Probably not a huge factor, though.
Posted by: mcaplinger Jun 16 2018, 11:38 PM
No, and it was a bit of an off-the-cuff answer, but barring some additional information from the project it's all we have to go on, and it's not implausible given what details of the design we do know. For example, some types of Q-Tech oscillators really do draw 40 mA just for the oscillator, and then for a complete clock there has to be a counter and maybe some other stuff -- the fault protection paper references a "mission clock FPGA".
I also don't fully understand how the scheduling of transmission and reception periods happens if the mission clock is lost. This seemed to introduce a lot of complexity into the attempted recovery process for Spirit. Presumably without the mission clock there's no way for the rover to figure when 11 LST is (in theory it could do with from solar power production but that would vary a lot based on tau, tilt, dust on the panels, etc.); AFAIK this scenario isn't described in the fault protection paper.
Posted by: MahFL Jun 17 2018, 08:44 AM
I also don't fully understand how the scheduling of transmission and reception periods happens if the mission clock is lost. This seemed to introduce a lot of complexity into the attempted recovery process for Spirit. Presumably without the mission clock there's no way for the rover to figure when 11 LST is (in theory it could do with from solar power production but that would vary a lot based on tau, tilt, dust on the panels, etc.); AFAIK this scenario isn't described in the fault protection paper.
The rover transmits roughly around midday on Mars, so the orbiters listen then. Once the signal is received they can send commands to the rover, which listens periodically, eventually getting back into sync with Earth.
Posted by: Don1 Jun 17 2018, 09:05 AM
The only thing I got from the press conference is that when the rover detects sunlight it sets a timer so that it can wake up periodically to attempt to phone home. I think it is a 4 hour interval, so presumably the DSN will listen for 4 hours during daylight to see if it hears from the rover.
Posted by: serpens Jun 17 2018, 12:48 PM
While the GaInP top cell is the limiting (short circuit) control its spectral response extends out to 750nm with a high response out to 600nm. So low levels of solar power will continue to be generated when much of the visible spectrum is suppressed. This link provides some information on MER solar panel performance https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20070010752.pdf
Absorption due to dust is highest towards the blue, decreasing to level out around 650 nm. Scattering increases with wavelength. So with the optical depths over the course of the day with tau of 10.8 it is possible that the small charging occurred around midday and if the tau has increased, has terminated.
Posted by: mcaplinger Jun 17 2018, 02:21 PM
As noted before, if it was that easy, then how do you explain the need for the "sweep&beep" campaign done for months with Spirit?
Posted by: hendric Jun 17 2018, 02:31 PM
Yes, but when the rover wakes up to phone home/listen, the IDD current draw could be a factor then if the temp is low enough to turn it on uncommanded.
Posted by: fredk Jun 17 2018, 02:34 PM
I guess the question is: how does the rover decide if it's midday? One idea would be exceeding some minimum power level. More elaborate would be to take several power level samples over at least a day and fit a sinusoid. If it's something like the former it may get stuck thinking it's not midday until tau drops sufficiently.
Posted by: mcaplinger Jun 17 2018, 03:36 PM
I expressed the same concern back in post #51, yes.
Posted by: mcaplinger Jun 17 2018, 03:41 PM
Perhaps, but this kind of elaborate solution that requires state to be recorded and used from sol to sol is usually not used in deep fault responses, because it's really hard to test all the possible permutations.
Posted by: marsophile Jun 17 2018, 06:57 PM
Not to mention the fact that flash memory is unavailable, so only measurements from a single Sol could be considered, and the CPU would have to stay on throughout the Sol.
In principle, the rover might be able to autonomously reset its clock if there was enough energy to take images of the sun position but (as the previous post points out) such complex algorithms would be unlikely in fault protection. Waking up every 4 hours is a simple and seemingly adequate solution.
The biggest danger I see from the dust storm is a poor dust factor going into the winter season leading to desperate measures. If I recall, the issue with Spirit was precipitated by over-winter issues that upset the original plan of driving along Home Plate. Hopefully we will get cleaning after the current dust storm but we may also get a second dust storm in the current summer season.
Posted by: scalbers Jun 17 2018, 07:55 PM
How severe is this dust storm compared with others weathered by Opportunity? Estimating the total solar radiation in heavy dust conditions is an interesting exercise and the scattered light will be the main contributor when the direct radiation diminishes. I'm trying to model all this with my simulated weather imagery package. A key factor would be how much light gets absorbed for each scattering event (a single scattering albedo of about .90 in green light and .97 in the IR https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2009JE003350). A tau of around 10 would only cut the light down about 50% if absorption wasn't a factor. I can note a Titan analog with a tau of around 8 and estimates of 10% of the visible band light getting through when absorption is factored in. Deimos' formulation in post #28 is reasonable. As mentioned more light in the IR will help for the solar panels. Serpens' YouTube video is pretty impressive.
Posted by: mcaplinger Jun 17 2018, 08:11 PM
The worst previous was back in 2007: "Due to extensive dust storms in Mars' southern hemisphere causing record atmospheric opacity levels, Opportunity is currently experiencing its lowest power levels to date. The tau measurement as of sol 1225 is 4.12, resulting in a mere 280 watt-hours of array energy. A tau measurement of 5.0 would result in approximately 150 watt-hours."
https://mars.nasa.gov/mer/mission/status_opportunityAll_2007.html#sol1382
Keep in mind that we have two competing measurements, the tau determined by analysis from Pancam images, and the actual solar production. From an engineering perspective, only the second one is of direct interest. I'm sure they have a model to go from the first to the second, but once you have an actual number for the second you should use it. And of course for any model, you not only have to know the irradiance but also how much dust is on the panels.
Posted by: djellison Jun 17 2018, 11:42 PM
It doesn't. Assuming a loss of clock fault - it simply boots up when 2 amps are on the array. The IDD heater is not a significant concern when you're at 2 amps.
Posted by: mcaplinger Jun 18 2018, 12:11 AM
While the flash is not available, the rover also has 11MB of EEPROM thst could be used to store state information. I think, for example, that this is where Earth position as a function of SCLK is kept. Without time reference, no HGA comm will work until this can be updated.
Posted by: serpens Jun 18 2018, 12:19 AM
This may help (or not). https://www.swsc-journal.org/articles/swsc/full_html/2015/01/swsc150027/swsc150027.html
The maximum tau assessed by Opportunity in 2007 was 5.5. The maximum assessed this time around before she went dark was 10.8 and this may have increased. This doubling of the tau, ignoring the airmass variable means that direct insolation would be 0.005 that enjoyed by opportunity at the height of the 2007 storm.
EDIT. An update by A.J.S. Rayl. http://www.planetary.org/explore/space-topics/space-missions/mer-updates/2018/06-mer-update-opportunity-dust-storm-sleep.html
An interesting extract: “The dust here is thicker than anything I have ever encountered, going back to Viking missions,” said MER Deputy Principal Investigator Ray Arvidson ........It’s dark, like the end of twilight dark.”
Paolo. described it as basically "the difference between a full sunshine day and a full moon night kind of state". Even a minor increase in tau over the 10.8 value and all ambient light would go.
Posted by: fredk Jun 20 2018, 05:35 PM
From the http://www.msss.com/msss_images/2018/06/20/:
Posted by: mcaplinger Jun 20 2018, 09:57 PM
http://www.planetary.org/explore/space-topics/space-missions/mer-updates/2010/06-30-mer-update.html has some discussion with John Callas about the consequences of the mission clock fault on Spirit.
It might be interesting if someone from TPS sat down with him to discuss the recovery of Opportunity in light of that experience. (Edit: I note that there's a little bit of that in http://www.planetary.org/explore/space-topics/space-missions/mer-updates/2018/06-mer-update-opportunity-dust-storm-sleep.html linked upthread.)
Posted by: djellison Jun 20 2018, 10:31 PM
"The Martian dust storm has grown in size and is now officially a "planet-encircling" (or "global") dust event."
https://www.jpl.nasa.gov/news/news.php?feature=7164
Posted by: JRehling Jun 21 2018, 03:29 AM
Christopher Go is the ace of [superior planet] astrophotography and his latest Mars picture (as of now; his page updates in case anyone is reading this weeks from now) gives an outstanding idea of how devastating this storm is:
http://astro.christone.net/mars/
Looking down on what should be extremely high-contrasty terrain and seeing that blankness might communicate the intensity more clearly (no pun intended) than stats re: sunlight.
Posted by: vjkane Jun 21 2018, 06:32 AM
Forgive me, I'm traveling and can't always check the website. Wanted a reply up so I can get email notifications of new posts.
Posted by: mcaplinger Jun 21 2018, 09:51 PM
It's about 11:30 LST at Opportunity as I post this, and I see that DSN Now says they are uplinking to MER1 from Canberra. I wonder what they're trying to do? I thought they were in listen-only mode.
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Posted by: RoverDriver Jun 22 2018, 01:51 AM
I believe they are trying to solicit a beep.
Paolo
Posted by: djellison Jun 22 2018, 01:53 PM
The fault modes open a comm window - you have to Uplink to get a response as Paolo said
As a heads up to people watching DSN Now - you may, quite often, see what appears to be MER 1 transmitting to the ground for a few seconds, maybe half a minute. That’s not Opportunity. That’s the DSN getting a false lock on noise from MRO.
Were we to get a response from Oportunity - it would more than likely be a complete 5 minute beep.
Posted by: mcaplinger Jun 22 2018, 02:41 PM
Really? There's never any attempt to send anything on the X-band LGA autonomously? The fault protection paper implies that there is:
communication window at a predetermined hour (11:00 LST) to report
to Earth. No UHF windows are attempted because these usually occur
in the early morning or late afternoon, when the available solar
power is low. The vehicle remains in this configuration
(with autonomous shutdown mode active, in receive mode via the
LGA, performing one DTE window per day) until the operations
team reconfigures the vehicle to resume normal operations.
I read that as meaning that it's in receive mode as long as it's powered up and that it tries to send at 11 LST even if it hasn't heard anything. But I may be misinterpreting what "schedules a communication window" means.
In my experience it would be unusual to never transmit autonomously, since that would mean that if there was a receiver failure, you'd never hear anything even if the transmitter was healthy.
Posted by: marsophile Jun 22 2018, 03:40 PM
https://forum.nasaspaceflight.com/index.php?PHPSESSID=pu9bu28dqkcua6s5350qjn8000&topic=4075.msg1559668#msg1559668
Being designated as the uplink in an MSPA can be an artifact of the way the MSPA is set up. Uplink means that it gets the only two-way channel in the MSPA group. AFAIK, this doesn't preclude doing only downlink.
Posted by: mcaplinger Jun 22 2018, 04:11 PM
You'll have to explain what you meant by this. I don't know exactly how DSN Now works as far as MSPA is concerned. When DSN is looking for a signal from a drifting frequency reference (which may be the case here), I think they often record in wideband and don't even try to lock up in real time, and I suspect this doesn't show up on DSN Now as a downlink (Doug would know for sure.)
However, if DSN Now says the uplink is to a specific spacecraft, I'm pretty sure it really is to that spacecraft.
Posted by: xflare Jun 22 2018, 04:22 PM
Hopeful tweet from yesterday
https://twitter.com/AnthonyJCook2/status/1009920728546754561
Posted by: djellison Jun 22 2018, 04:31 PM
Really. To be specific, we are commanding 5 minute beeps when we believe every fault window opens.....the expected behavior is thus just 5 minute beeps to preclude a lengthy power hungry DTE.
Posted by: scalbers Jun 22 2018, 09:11 PM
Interesting paper. I coded up the equations and tested it to reproduce tables 2 and 3, so now I can plug in additional values. A tau of 10.8 still seems to be a few percent for green light depending on solar elevation angle. For practical powering up purposes it is rather dark, though quite a brighter than the full moon. With tau=15 I get between 0.4% and 1.2%.
The maximum tau assessed by Opportunity in 2007 was 5.5. The maximum assessed this time around before she went dark was 10.8 and this may have increased. This doubling of the tau, ignoring the airmass variable means that direct insolation would be 0.005 that enjoyed by opportunity at the height of the 2007 storm.
EDIT. An update by A.J.S. Rayl. http://www.planetary.org/explore/space-topics/space-missions/mer-updates/2018/06-mer-update-opportunity-dust-storm-sleep.html
An interesting extract: “The dust here is thicker than anything I have ever encountered, going back to Viking missions,” said MER Deputy Principal Investigator Ray Arvidson ........It’s dark, like the end of twilight dark.”
Paolo. described it as basically "the difference between a full sunshine day and a full moon night kind of state". Even a minor increase in tau over the 10.8 value and all ambient light would go.
Posted by: marsophile Jun 22 2018, 09:36 PM
https://mars.nasa.gov/mer/mission/status.html#opportunity
Posted by: RoverDriver Jun 23 2018, 03:15 AM
though quite a brighter than the full moon.
...
You are right, I thought that day/moonlight difference was corresponding to a Tau of 14 or thereabouts but it was the closest thing I could find. I would not be surprised if Oppy experienced a Tau at that level anyway.
Paolo
Posted by: scalbers Jun 23 2018, 03:26 PM
As a bit of nuance, a Tau of 14 sounds about right to make the direct solar illumination match the full moon, so one could look for an (Earth) moonlike orb to be somewhat visible through the dust. Otherwise there is brighter overall illumination from diffuse scattered light. How about a full Phobos ?
The faint sun appearance shows up in a sky that is not quite black on the right panel of the second picture shown in http://www.planetary.org/explore/space-topics/space-missions/mer-updates/2018/06-mer-update-opportunity-dust-storm-sleep.html posted earlier. Turning up the monitor brightness helps to see this. This is a useful example for expanding the envelope with my sky simulation software.
Posted by: Deimos Jun 23 2018, 08:13 PM
As further nuance, exp(-tau) is only appropriate when the Sun is straight up. Later in the mid-afternoon, a (normal) tau of 10.8 might have an effective extinction of, say, exp(-14.5). That would seem very similar to the right-most frame in the panel from that link--if you look very closely, the Sun is still visible as a faint, bluish disk.
Posted by: serpens Jun 23 2018, 11:51 PM
Remember that the panel view in the link is a simulation. The other point is that the brightness of the sun in any "real" image will be a function of the exposure time.
Posted by: scalbers Jun 24 2018, 01:48 AM
Comparing simulations, mine so far is rather simplified given the high Tau values, though I'm getting a notably redder sky color than the one posted by the team. I'm pretty much developing a sky hue from color ratios derived using the paper discussed in post #110. This is reminiscient of the YouTube video posted earlier from a dust storm on Earth, and consistent if we extrapolate some of the redder colors in Curiosity images to higher Tau.
Posted by: mwolff Jun 24 2018, 01:31 PM
you have to remember that the values quoted in that paper, at least the one relevant for the visible, is actually only appropriate for red, and for diffuse dust. you need to adjust the single scattering albedo for blue and green (and particle size, though not a huge change here). The single scattering albedo values for 400 nm, 500 nm, 600nm, and 700nm assuming the average (cross section-weighted mean) particle size is 2.0 micron
0.716001 0.816507 0.938796 0.968714
respectively.
Posted by: scalbers Jun 24 2018, 02:02 PM
The three wavelengths I've been using for calculations are 615nm, 551nm, and 450nm with corresponding single scattering albedo (SSA) values of .958, .904, and .800. This can be checked with the values you're mentioning and the figure I referenced in post #92. There is some subsequent interpolation that is done when estimating a full spectrum to convolve with the CIE color matching functions. Angstrom exponent is assumed to be -0.05. Would you happen to have SSA values for the three wavelengths I'm using?
Here's my http://stevealbers.net/ast/mars/sky_2018_duststorm/allsky_rgb_cyl_mars_1045.gif of thickening dust with Tau ranging from 0.5 to 10.0. The sun is 45 degrees up.
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As a more general comment I wonder if there are single scattering phase functions vs wavelength published anywhere? This could help me get the chromaticity better when using the quoted SSA values. For some reason I can tend to show a grayer sky.
Posted by: marsophile Jun 24 2018, 09:11 PM
I'm wondering about the effect of the dust storm on the atmospheric pressure at the surface of Mars. Given that the force exerted by the atmosphere on a square meter of surface depends on the weight of the atmospheric column over that surface, does it follow that the added weight due to suspended dust will increase that pressure?
Would such an increase be sufficient to extend significantly the range of temperatures at which ephemeral liquid water (just after dawn) could exist? The newly added dust on rocks might provide a convenient probe for testing this hypothesis; presumably a brief wetting would affect the texture of the dust deposits in a way that might be observable.
Posted by: Gerald Jun 24 2018, 11:02 PM
The additional weight of the dust is certainly less than 1/1000 of the weight of the atmosphere. But it might drive a greenhouse effect or increase albedo in the polar regions, and result in additional sublimation of CO2 or water near the poles.
MSL REMS should be able to test this hypothesis.
Posted by: serpens Jun 25 2018, 12:13 AM
The effect of dust storms is to loft water vapor into the middle atmosphere, with a significant decrease in absolute humidity near the ground. This reduction in the amount of water vapor means that the formation of films or brines is even less likely during a dust storm despite higher minimum temperature or minor variations in atmospheric pressure.
Posted by: marsophile Jun 25 2018, 12:38 AM
I am more interested in the aftermath of the dust storm, when (hopefully) Opportunity will be able to observe changes in the resultant dust deposits. Is the above hypothesis still applicable at that point?
Posted by: mcaplinger Jun 25 2018, 01:17 AM
I don't think there's really an appreciable pressure signature from dust storms, but this has been measured. Note that some of the graphs below are more about diurnal variation in pressure and less about absolute pressure.
https://www-k12.atmos.washington.edu/k12/resources/mars_data-information/overlay.gif
https://mars.nasa.gov/resources/4902/atmospheric-pressure-patterns-before-and-during-dust-storm/
Posted by: marsophile Jun 25 2018, 02:57 AM
https://mars.nasa.gov/msl/mission/instruments/environsensors/rems/
Dates (2018) Mean Pressure (Pascals)
June 05--June 10
758 756 758 762 764 765
June 11--June 16
766 767 768 770 768 769
June 17--June 21
771 772 776 780 778
Looks quite suggestive. Of course it might be just the normal seasonal signal.
Posted by: djellison Jun 25 2018, 03:28 AM
And the maximum temperatures are also decreased, dramatically, during the storm. Rendering windows when such events might occur astonishingly small, if they existed at all.
Posted by: serpens Jun 25 2018, 07:39 AM
The second linked graph measures atmospheric pressure hundreds of miles from a dust storm and compares pressure changes above the daily minimum. Given the general atmospheric heating and the localised heating referred to wouldn't the minimum absolute pressure be different for each of the graphs, possibly implying that the absolute maximum temperatures would tend to align?
Posted by: mcaplinger Jun 25 2018, 02:54 PM
Of course. Without finding the raw data I can only show what the team chose to plot. My only point in posting this was to indicate that the pressure was being measured and eventually we would be able to see those measurements (see http://pds-atmospheres.nmsu.edu/data_and_services/atmospheres_data/Mars/Mars.html although if this page is right the REMS team is way behind on releasing data.)
Going back to the Viking 1 data would be the best way to look at the pressure through a dust storm as of today, probably.
Posted by: scalbers Jun 25 2018, 03:58 PM
This simulated version shows the blue scattering surrounding the sun a bit better. Tau ranges from 0.5 to 10. I'll try to make a plot of the phase functions being used for this.
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Posted by: Deimos Jun 25 2018, 04:03 PM
Pressure is of course modified by the storm--but there is no measurable enhancement from the dust loading, the original question (I think). The modification is not as simple as a perturbation to the existing profile (e.g., shifting the absolute minimum pressure up or down or compressing/expanding the range of variation).
There are many modes, and they interfere. There's a diurnal tide--the surface gets warmer and heats the air, warm air rises, circulation happens--that can be diminished by the the diminished temperature cycle, but also by more complex interactions (VL1 diurnal tide went away, http://science.sciencemag.org/content/213/4506/437--at least the abstract can be seen). There's a semi-diurnal tide from heating by dust in the air and can be seen from orbit and the ground (http://www.planetary.org/blogs/guest-blogs/2013/mysterious-tides-martian-atmosphere.html). It increases in amplitude significantly when there is a lot of dust in the hemisphere or globe (Fig. 2 in https://journals.ametsoc.org/doi/full/10.1175/JAS3718.1)
The tides are enhanced in Gale as opposed to Meridiani; they correlate with dust as seen by Curiosity--two pay-walled papers discuss this: https://www.sciencedirect.com/science/article/pii/S0019103516000531?via%3Dihub and https://www.sciencedirect.com/science/article/pii/S0019103515005850?via%3Dihub. It might be cool if Scott (or Scot) would do a blog post at Planetary Society.
To visualize the modes, see Figs. 3, 9, 10 in http://sirius.bu.edu/withers/pppp/pdf/withers_nsfaag2014atmo_v02.pdf.
So, there is no particular effect from the dust mass; but there will be a substantial impact from the dust heating and cooling effects, and those would be expected to significantly alter the shape of the pressure wave, based on how much the first two modes would be expected to change with tau>5 over possibly large regions.
Posted by: marsophile Jun 27 2018, 02:11 AM
https://mars.nasa.gov/mer/home/
Sol: 5127 Time: 12:51
Spirit at Gusev
Sol: 5148 Time: 14:18
http://www.planetary.org/multimedia/space-images/charts/mars_landing_site_map_lakdawalla.html
This doesn't seem right---Opportunity is at the opposite side of the planet from Spirit, so the LST times should be around 12 hours apart. Having the correct local time for Oppy is useful for checking the DSN Now comm schedule.
Posted by: marsophile Jun 27 2018, 02:59 AM
According to this article
http://curious.astro.cornell.edu/physics/64-our-solar-system/planets-and-dwarf-planets/mars/101-why-does-mars-have-a-dusty-atmosphere-intermediate
the atmospheric dust in a Martian dust storm would correspond to a layer about 3mm thick if deposited on the surface.
Assuming the dust has a density of about 1.5 gm/cc, a 3mm layer over 1 cc of surface would weigh about 1.5 x 1/3 x 3 x 1/10 = 0.15 gm on Mars. Thus, all else being equal, the pressure due to dust loading should be about 0.15 gm per sq. cm, which is equal to about 0.15 x 98 = 14.7 pascals. That is small but it should be measurable by the REMS instrument.
[EDIT: Perhaps the article linked above is confusing mm with microns (mu-m). Indeed a layer only 3 microns thick would not contribute significant loading.]
[EDIT: As a clarification, the "1/3" factor in the formula "1.5 x 1/3 x 3 x 1/10" is the correction for Mars gravity (with a slight abuse of units).]
Posted by: mcaplinger Jun 27 2018, 05:35 AM
On Mars, 0.15*38 = 5.7 pascals, I believe, unless you tried to compensate for this in your gram number (improperly, since a gram is a unit of mass, not weight.)
The article you linked cites https://www.sciencedirect.com/science/article/pii/S0019103506002855?via%3Dihub which is behind a paywall, although I guess I could walk upstairs and get a copy from the author
I think unit confusion is likely.
Posted by: xflare Jun 27 2018, 12:14 PM
For amateur observations and updates on Mars during the dust storm, keep an eye on these sites:
https://britastro.org/node/10908
http://alpo-j.asahikawa-med.ac.jp/indexE.htm
Posted by: Deimos Jun 27 2018, 12:39 PM
Note that the Cornell link got to the estimate of a few mm thick using dust diameter of 3 mm. Using a more traditional 3 microns, you can take the result down 3 orders of magnitude. I get close to 1 mPa per unit optical depth (order of magnitude), which ends up in the same ballpark.
Even at a few Pa, I'd be skeptical--certainly REMS could measure a few Pa, but I'm not sure it could measure a few Pa of dust. There are many thermal perturbations. There are tidal perturbations, changing stationary and traveling waves. The polar cap sublimation rate and mass transport rate in the atmosphere may be affected.
[For tau=1, there is 0.5 m^2 per m^2 of dust (dust area fraction) given a likely extinction efficiency of ~2. Volume is roughly cross-sectional area times 4/3 R. So, tau=1 implies 1 micron thickness for dust that is uniformly 3 microns in diameter. Being generous, since we're talking cohesive dust particles, not the actual thickness a powdery pile would have, 3000 kg/m^3 implies 0.003 kg/m^2, or 0.001 Pa in Mars gravity.]
Posted by: xflare Jun 27 2018, 01:26 PM
http://www.planetary.org/multimedia/space-images/charts/mars_landing_site_map_lakdawalla.html
This doesn't seem right---Opportunity is at the opposite side of the planet from Spirit, so the LST times should be around 12 hours apart. Having the correct local time for Oppy is useful for checking the DSN Now comm schedule.
This site http://www.dmuller.net/spaceflight/realtime.php?mission=opportunity&mode=planet lists the current time as Sol 5127, 23:32. The MER site has Sol 5128, 22:51
Posted by: Deimos Jun 27 2018, 02:46 PM
It's all good, until you look at more than one clock. The http://www.lpl.arizona.edu/~lemmon/mars-tau-b.htmlsite has a reasonably accurate clock, just checked against NAIF. If you change '-b' to '-a' or '-c' in the URL, the clocks are off by several seconds due to lack of leap second correction, and maybe due to precision issues for Spirit. The Opportunity version seems to agree with the dmuller.net link to <10 sec, too.
Posted by: mcaplinger Jun 27 2018, 03:12 PM
Maybe overkill, but I use https://www.giss.nasa.gov/tools/mars24/ -- right now it says it's 11:24 at Meridiani and 01:14 at Gale, which sounds about right.
Posted by: Phil Stooke Jun 27 2018, 03:21 PM
So, if we can just get Spirit to Gale everything will fit.
Phil
Posted by: mcaplinger Jun 27 2018, 03:34 PM
Pedantic much?
They're at about the same longitude and who cares what time it is at Gusev? [Well, in fairness, they're not that close -- Mars24J says there's about 2 hours different between Gale and Gusev. If it's right.]
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Posted by: mcaplinger Jun 28 2018, 01:06 AM
I'm going to blame either Deimos or bad typesetting at Science for this -- in http://science.sciencemag.org/content/306/5702/1753 the abstract says "The dust's cross section weighted mean radius was 1.47 ± 0.21 micrometers (mm) at Gusev and 1.52 ± 0.18 mm at Meridiani." "mm" is, as far as I know, not a valid SI abbreviation for micrometer, which is mu-m. https://en.wikipedia.org/wiki/Micrometre
Posted by: Phil Stooke Jun 28 2018, 02:15 AM
Pedantic, moi?
You're right of course, I was pedantic! It was a slow morning... but the discussion arose out of this recent post:
-------------------------------------------------------------
marsophile: (post 130 above)
https://mars.nasa.gov/mer/home/
QUOTE
Opportunity at Meridiani
Sol: 5127 Time: 12:51
Spirit at Gusev
Sol: 5148 Time: 14:18
This doesn't seem right---Opportunity is at the opposite side of the planet from Spirit, so the LST times should be around 12 hours apart. Having the correct local time for Oppy is useful for checking the DSN Now comm schedule.
--------------------------------------------------------------
So it really did concern Gusev, not Gale.
However, I will try not to give in to temptation in future, unless it's a really big juicy temptation.
Phil
Posted by: PaulH51 Jun 28 2018, 04:23 AM
MRO MARCI Weather report for the week of 18 June 2018 – 24 June 2018. Published June 28, 2018.
http://www.msss.com/msss_images/2018/06/27/
Posted by: serpens Jun 28 2018, 06:28 AM
I was always taught that the symbol for a micron or micrometre is μm. In fact the link confirms this and the SI spelling convention, although I appreciate that this is one of the words where US spelling deviates. Personally I feel that errors in nomenclature or symbols should be considered more than just a passing annoyance given the fate of the Mars Climate Orbiter.
Posted by: nprev Jun 28 2018, 12:23 PM
[ADMIN MODE]...and on that note we're done with the abbreviation debate, or 'abd'. Moving on...
Posted by: marsophile Jul 2 2018, 01:02 AM
https://mars.nasa.gov/mer/mission/status_spiritAll_2008.html
It could be said that the great dust storm of 2007 indirectly led to the loss of Spirit in 2010. As the sky cleared, dust falling on the solar panels forced Spirit to seek an extreme slope of 25 degrees at "Winter Haven 3" on the northern edge of Home Plate for the subsequent Martian winter. When spring came, Spirit was unable to climb back onto Home Plate, which caused it to take an alternative route below, which ultimately proved fatal.
To ensure a similar fate does not befall Opportunity. it may be worthwhile to seek immediate cleaning of the solar panels in the aftermath of the storm. Perhaps observing wind trails in the new dust deposits would provide information about the current wind regime at Perseverance so that Oppy could position itself where cleaning is most likely in the months before the coming of winter. It is true, though, that Opportunity is closer to the equator so maybe, hopefully, that will not be an issue.
Posted by: djellison Jul 2 2018, 01:31 AM
Opportunity experienced a major cleaning event in Perseverance Valley at the end of 2017. The rover couldn't be in a better place to get cleaned than it is now.
Posted by: marsophile Jul 2 2018, 05:55 AM
http://www.spaceflightinsider.com/space-flight-history/inside-opportunity-oppy-fights-for-its-life-in-massive-martian-dust-storm/
July 1 update.
Posted by: marsophile Jul 5 2018, 08:03 AM
http://www.planetary.org/explore/space-topics/space-missions/mer-updates/2018/06-mer-update-planet-encircling-dust-cloud.html
The monthly MER update.
This might be a good theme song for Oppy under current circumstances:
https://www.youtube.com/watch?v=gYkACVDFmeg
"I Will Survive"
Posted by: scalbers Jul 8 2018, 02:46 PM
Here is an updated simulation with Tau ranging from 0.5 to 11.0 in 0.5 steps. This shows the reversal to a darker horizon somewhat better. The software roughly estimates solar horizontal irradiance, ranging from 360 W/m^2 down to 13.5 W/m^2. The solar elevation angle is 45 degrees.
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I'll consider adding a strip of land at the bottom next. Below is a table of the estimated global horizontal irradiance.
Tau GHI (W/m^2)
--- -----------
0.5 360.4
1.0 311.3
2.0 230.6
3.0 169.7
4.0 124.4
5.0 90.9
6.0 66.2
7.0 48.2
8.0 35.1
9.0 25.5
10.0 18.5
11.0 13.5
Posted by: JRehling Jul 12 2018, 03:57 PM
I had some excellent terrestrial weather last night for observing the Opportunity site which still has terrible martian weather. Meridiani is near the left side of the disc here, and the state of the dust storm is evident in the wispiness of the dark areas, including Syrtis Major at right. However, it's not quite a blank disc, which is a hopeful sign.
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Posted by: Tom Dahl Jul 12 2018, 04:03 PM
Wow, an amazing image to have captured yourself!
Posted by: JRehling Jul 13 2018, 03:42 AM
Thanks! I wish the dust storm had not been in the way, and I know that many others feel the same. Perhaps it will fade soon.
Posted by: marsophile Jul 15 2018, 01:28 AM
Hmm. Although the seasonal upward trend is similar, the pressure during this dust storm, as measured by REMS, is about 20 pascals lower than at a similar period during the last three Martian years.
Pressure (pascals) for LS 198-208:
2018 779-807
2016 798-823
2014 802-829
2012 805-830
Sources:
https://mars.nasa.gov/msl/mission/instruments/environsensors/rems/
https://github.com/the-pudding/data/blob/master/mars-weather/mars-weather.csv
Posted by: serpens Jul 15 2018, 06:33 AM
I wouldn't read too much into this. The Gale crater temperature/pressure during the course of a sol is governed by the crater topography so that during the day as temperature increases atmosphere flows out of the crater reducing the air pressure while at night colder air settles into the crater from the rim. The drop in upper atmosphere temperatures and increase in lower atmosphere temperatures due to the dust storm has probably had an effect on this cycle.
Posted by: marsophile Jul 15 2018, 06:08 PM
The lower pressure this Mars year seems to have preceded the dust storm by several months.
For example at LS 135:
2018 727
2016 747
2014 750
2012 N/A
The 2018 LS 135 was on 02-27. Perhaps an overall lower pressure is predictive of the year in which a major dust storm is likely to occur?
Posted by: mcaplinger Jul 15 2018, 11:31 PM
According to http://cab.inta-csic.es/rems/wp-content/uploads/2013/04/REMS_CALIBRATION_PLAN.pdf the pressure sensor is only required to be accurate to 10 Pa at beginning of life and 20 Pa at end of life (end of the primary mission, I presume.) It may be doing better than that, but I'd be reluctant to draw any conclusions from absolute pressure measurements over long time scales without taking possible instrument drift into account.
Posted by: marsophile Jul 17 2018, 01:44 AM
Good point! Based on your comment I took a look at when the larger pressure differential occurred.
Earth_date ls month pressure
2017-08-18 048 Month 2 881
2015-10-01 048 Month 2 901
2016-09-12 220 Month 8 859
2014-10-24 220 Month 8 862
The deficit in pressure from the previous year seems to have gradually widened over a period of about a half Martian year, and to have stayed roughly constant since then. This could be consistent with instrument drift. It will be interesting to see where it goes from here. It's a pity there is no ongoing way of calibrating the instrument.
Posted by: JRehling Jul 17 2018, 01:56 AM
Can radio occultation measurements from orbiters be used to measure pressure? That was how atmospheric density was measured in many other cases in the past, e.g., Voyager 1 and Titan.
Posted by: Deimos Jul 17 2018, 04:31 AM
The interpretation of the pressure differences above might be different if the altitude change were considered: ~225 m in the Ls 48 comparison, but only ~89 m in the Ls 220 comparison. One would expect a more than 2% drop in the first case (little residual), but <1% in the second (residual increases slightly with time between those two specific points). Given the possibility for drift, interpreting any residual variation seems sporty.
Posted by: marsophile Jul 17 2018, 04:12 PM
Just saw what looked like a brief downllink from Opportunity on DSN Now:
DOWN SIGNAL
SOURCE
OPPORTUNITY
TYPE
CARRIER
DATA RATE
1.10 Mb/sec
FREQUENCY
8.45 GHz
[EDIT: Now it is showing MAVEN as the source with similar data rate and frequency. Maybe it was some kind of switch-over glitch.]
Posted by: djellison Jul 17 2018, 05:13 PM
You will regularly see very brief appearances of Opportunity 'locking up' briefly.
It's usually side bands from MRO, and less frequently MAVEN drifting thru the frequency we're looking at - and the receiver incorrectly locking up on it. We have to manually drop lock and then carry on looking - so briefly, it appears Opportunity is transmitting when it isn't.
Posted by: marsophile Jul 20 2018, 07:26 PM
https://mars.nasa.gov/mer/home/
New status report and press release about the dust storm posted at the MER home page.
Misfortune for Opportunity but an opportunity for MAVEN.
Posted by: fredk Jul 25 2018, 07:52 PM
Glimmer of hope from the latest http://www.msss.com/msss_images/2018/07/25/ that things might start improving:
Posted by: PaulM Jul 26 2018, 08:25 PM
When spirit failed to restart when the spring came I was convinced by the official explanation that the electronics had been damaged by low temperatures. However it was also possible that spirit did not restart correctly because of an error in the software or hardware designed to carry out this recovery. I realize that insight has different hardware but I wonder if there has been a full end to end test of recovery from a flat battery and no sunlight using the insight reference hardware. The insight radio science experiment simply requires radio communications over more than two years to be successful. I wonder if insight would recover correctly in a similar scenario to that currently being endured by opportunity?
Posted by: mcaplinger Jul 27 2018, 12:34 AM
No idea. Probably Giang Q. Lam, Scott Billets, Timothy Norick, and Richard Warwick. "Solar Array Design For The Mars InSight Lander Mission", 14th International Energy Conversion Engineering Conference, AIAA Propulsion and Energy Forum, (AIAA 2016-4520), https://arc.aiaa.org/doi/abs/10.2514/6.2016-4520 has some information, but it's behind a paywall.
I'm not sure if a worst-case global dust storm was a credible contingency for InSight planning; I suspect not.
Posted by: mcaplinger Jul 27 2018, 04:35 PM
See "Energy management operations for the Insight solar-powered mission at Mars" https://ieeexplore.ieee.org/document/7943965/
Article is paywalled but the figures suggest that all of this analysis was done before the current dust storm, and the maximum tau value shown in the figures was about 5 IIRC.
Posted by: vjkane Jul 28 2018, 04:37 AM
Article is paywalled but the figures suggest that all of this analysis was done before the current dust storm, and the maximum tau value shown in the figures was about 5 IIRC.
It looks like the design team is, reasonably, planning to survive under then worst-case conditions:
"The lander and its unique suite of instruments - a 3-axis
precision seismometer and a self-drilling heat probe both
deployed with a robotic arm onto the Martian soil - have been
designed to operate and/or survive while maintaining a
margined battery-charging energy balance every sol, even
under the combined effect of worst-observed atmospheric dust
opacity (“tau”), worst-case tilt of the solar arrays and a
conservative dust accumulation rate on the solar panels that
assumes no wind cleanings dur
ing the entire mission. '
Posted by: vjkane Jul 28 2018, 04:42 AM
A major design challenge for dust storms could be the Mars sample return lander and fetch rover. The current working date for landing, 2026, puts the landing in the dust storm period. Both the lander and fetch rover would be solar powered. Presentations on design considerations for both highlight the need to survive the dust storm.
The lander will have a need to keep the fuel in the Mars ascent vehicle above a minimum temperature, likely creating a design challenge in the case of a major dust storm.
The presentations on the fetch rover discuss the need to survive a prolonged dust storm without including any radioisotope heating units in the rover.
Posted by: mcaplinger Jul 28 2018, 06:01 AM
under the combined effect of worst-observed atmospheric dust
opacity (“tau”)...
As I indicated, though, that appears to have been only the worst-observed prior to the recent dust storm.
Posted by: JRehling Jul 29 2018, 10:47 PM
Insight will land on November 26, 2018. That is virtually simultaneous with the next southern summer solstice – November 28.
A previous monster dust storm, in 1971, began about three weeks before that southern summer solstice.
This one began about six months before southern summer solstice.
So one thing we can hope for, at minimum, is that Insight will get through nearly an entire martian year before the next dust storm would likely begin.
Is the radio science experiment seriously compromised if it completes a bit less than one martian year?
It seems like the baseline failure rate of missions to the surface of Mars is much higher than the risk Insight faces due to a dust storm, but it's a good issue to bring up. Unlike purely engineering-based risks, this one (given solar panels for power) is beyond our control. It seems like landing right at southern summer solstice is a fortuitous design (or chance circumstance), though.
Note: If Insight had launched at its originally planned date of March 2016, it would have landed in September 2016 and had approximately 18 months of operations before this dust storm. The 2018 launch date reduced the risk. (Which, in hindsight, is more than risk for the voided 2016 dates.)
Posted by: PaulM Jul 30 2018, 06:19 PM
Opportunity parked from sol 2795 to 2963 to conduct a 5 month mars radio science experiment. I remember at the time that it was said that extending this period would not have provided any more accurate radio science data unless opportunity parked for two full earth years. From this I presumed that insight would need to operate for at least two years to better opportunity's radio science data.
Posted by: serpens Aug 2 2018, 05:07 AM
An information packed update on the dust storm in general and Opportunity in particular.
http://www.planetary.org/explore/space-topics/space-missions/mer-updates/2018/08-mer-update-opportunity-sleeps.html
Posted by: marsophile Aug 3 2018, 01:51 AM
"In the Dust Storm, the mighty Dust Storm, the rover sleeps tonight"
Thanks Serpens for that link. It seems hopeful that the rover may be waking up before too long.
In the early days of the MER mission, the ground ops team used to play "wake-up" songs for the rovers.
http://www.mit.edu/~jfc/MER%20Soundtrack.html
That tradition seems to have faded away after the prime mission, but given the long sleep now, it might be appropriate to revive it just once when the rover does wake, for public outreach purposes.
Possible choices (recycled from the list in the link) might be:
Oh What a Beautiful Mornin'
Soak Up the Sun
I Can See Clearly Now
Wake Up Little Susie [Oppy]
...
Posted by: fredk Aug 3 2018, 02:45 PM
http://www.planetary.org/explore/space-topics/space-missions/mer-updates/2018/08-mer-update-opportunity-sleeps.html
Good to see some tau estimates in that report, based on MARCI data:
And some values from MSL:
Posted by: dvandorn Aug 3 2018, 05:10 PM
So, at what point does it become concerning that we have not yet re-established contact with Oppy?
There has to be some point at which orbital and telescopic data would indicate tau in Meridiani is at a low enough level that, if Oppy is going to be recoverable, we would begin to expect to hear from it. My guess is that a fair number of people working on Oppy have a good idea of what this timeframe is -- or, failing a timeframe, at least at what level of clearing we ought to start reasonably expecting contact -- but as of yet, I've seen nothing, not even speculation, as to when this might occur.
Again, not so much against a date as against a tau level -- at what level of clearing do y'all think JPL begins to seriously expect to regain contact, if such will be possible?
-the other Doug
Posted by: Deimos Aug 3 2018, 05:50 PM
I think the article suggests tau needs to be near 2 before expectations of success rise significantly. It could be sooner (or even later), depending on cleaning events and other specifics, but that is the gap between hope and expectation. While lack of communication is always frustrating, I do not think that it becomes a specific source of concern until well into next month; maybe even later. Then, Callas described a long process of bringing the rover back to a normal mode of operations.
After the 2007 peak, communications occurred consistently after tau dropped to around 3.8, and mobility after 2.5. But the rover's mode and state of charge were in entirely different places then.
Posted by: fredk Aug 3 2018, 05:54 PM
Yeah, from the report we had:
In a comparison with the 2001 dust storm, scientists corroborate that estimate, predicting that the opacity at Endeavour Crater should drop down to 2 or so sometime in September – “if things track the way they did in that storm,” qualified Zurek.
Obviously huge uncertainty in any such projections...
Posted by: mcaplinger Aug 4 2018, 04:47 AM
Despite trying as hard as I could to figure out exactly what the recovery process might look like from public information, I haven't been able to figure this out from the papers or what various project people are quoted as saying.
EDIT: I did run across this -- http://www.planetary.org/explore/space-topics/space-missions/mer-updates/2010/09-30-mer-update.html -- which has more detail about the need for "sweep and beep" than I had previously run across.
Posted by: djellison Aug 4 2018, 04:00 PM
That infers you know the solar array dust factor - which we do not.
Posted by: mcaplinger Aug 4 2018, 04:47 PM
Well, it's somewhere between 0 and 1.
One could figure out based on season and a range of dust loading what the tau needed to get into "solar groovy" (1.1A of production) would be -- then it's a matter of hitting the narrow window when the rover would be responsive to commanding in that mode.What I don't understand about solar groovy is what the battery SoC has to do with it -- is the 1.1A after whatever the battery charging is using? What happens if the battery just refuses to charge?
Posted by: RoverDriver Aug 4 2018, 05:20 PM
IIRC once the clock is lost (which is a likely event) the BCB needs at least a 2A current from the array and 27V on the batteries before attempting to beep.
Paolo
Posted by: marsophile Aug 5 2018, 01:48 AM
The sporadic nature of the Martian dust storms reminds me of the sporadic occurrences of wildfires (which are currently raging here in California). Apologies if this seems like a far-out idea, but I'm wondering if combustion ever occurs on Mars and whether it might be related in some way to the dust storms.
The regolith is now known to contain organics and perchlorate, which may build up over time. This might conceivably form a combustable mixture in some places. Given the frigid Martian temperatures, combustion would be rare but perhaps a meteor strike could trigger ignition? Combustion could raise dust (and smoke) into the atmosphere which might be enough to trigger a positive-feedback process. Such events would tend to be self-limiting, though, given the depletion of the consumable resource.
Of course, this suggestion could easily be falsified by Maven observations, which presumably could detect the products of combustion.
Posted by: RoverDriver Aug 5 2018, 04:38 AM
My chemistry is not so hot (pun intended), but combustion doesn't it require an oxidizer?
Paolo
Posted by: marsophile Aug 5 2018, 06:04 AM
https://en.wikipedia.org/wiki/Perchlorate
The perchlorate serves as the oxidizer.
Posted by: nprev Aug 5 2018, 08:28 AM
Open question as to whether deposits of organics of sufficient mass in close proximity to large concentrations of perchlorates exist anywhere on Mars for this to occur to say nothing of the probability of an ignition event, but I gotta rate such a confluence of favorable circumstances as unlikely to the point of 'ain't gonna happen' (yes, that's a technical term ).
Moving on...
Posted by: dvandorn Aug 5 2018, 04:23 PM
Thanks, guys. The technical discussions thus far available had not been much help for me to understand what the thresholds are for a MER re-animation after a major dust storm event. I've got a much better idea now. This is exactly the discussion I was hoping to see, again much thanks.
And yes, we don't know the dust loading, but as Mike pointed out, it's got to be between 0 and 1, thus providing a range on a graph that must, when added to the tau range and the minimum charge required for the rover to start up again, define the conditions required to get to a re-activation of Oppy.
In my mind's eye, there is a graph, sort of a Venn diagram, of those three sets -- tau, dust loading and resultant power -- and the area where they overlap is the area in which we can expect a successful re-activation. And it would surprise me no end if such a graph does not exist for all you JPL types to see. I was just trying to get some insight on what the ranges are in each of the major categories, and how each sort of generally plots against time, is all.
But, yeah, planetary exploration via Venn diagramming...
p.s. -- Even with all the times lately (and yet upcoming) I have had to undergo surgeries, and get another few million brain cells whacked by the anesthesia, I am still swift enough to understand that there is not a magic date on a calendar beyond which the situation goes from "we're confident and optimistic" of recovery to "let's declare Oppy finally dead and have a wake for her". Like I say, I was just trying to get the shape of that Venn diagram I mentioned straight in my head. Again, thanks!
Posted by: djellison Aug 5 2018, 05:43 PM
Power models are run based on presumed battery voltage ( all we know is it is < power fault voltage ) dust loading (which we don't know with any accuracy ), presumed Tau ( which we don't know either - we can sort of infer from MSL, and MARCI when MER gets occasional updates from that team ) - but they're little more than educated guesses.
You could run the numbers and argue the vehicle should have woken up last week, or not until October. It's almost as bad as running the Drake Equation. You put in the numbers to get the answer your want.
Moreover - tau varies, a lot, during a storm decay. We might see enough power on the arrays on one day to start charging the battery back up but not hear anything...but then have three days of worse conditions. There are also fault recoveries where we might be listening at the wrong time, etc etc etc.
In short - tomorrow is better than today, generally speaking. The story only really gets worse when next winter arrives - many, many months from now.
Posted by: dvandorn Aug 7 2018, 04:02 PM
Thanks much, Doug!
Posted by: marsophile Aug 12 2018, 01:20 AM
https://mars.nasa.gov/msl/mission/instruments/environsensors/rems/
Some new readings from REMS. The pressure now seems to be running about 30 pascals lower than the average for previous Mars years.
Perhaps due to a further increase in altitude by Curiosity?
Posted by: Explorer1 Aug 12 2018, 02:56 AM
Something to do with the dust storm, perhaps? How much higher has the rover climbed since landing? I recall seeing a 'side chart' detailing this somewhere on the board a while back...
Posted by: PaulH51 Aug 12 2018, 04:07 AM
I believe the landing elevation was in the order of -4501 meters. The current elevation (reached on sol 2132) is shown as -4170 meters on the JPL traverse map. However the rover drove downslope from its higher elevation on the ridge to reach this drill target. So are you looking for the max elevation or current elevation.
Posted by: serpens Aug 12 2018, 09:06 AM
The month 11 weather report attributes the drop in pressure compared to last year to Curiosity's increased elevation and also notes the effect on pressure of the reduced temperature range due to the dust storm.
Posted by: marsophile Aug 16 2018, 06:32 AM
Is anything known about the after-effects of a major dust storm on the global distribution of dust? For example, would it tend to move dust from lower elevations to higher elevations or vice versa?
Posted by: JRehling Aug 16 2018, 06:31 PM
It's been observed since before people knew what they were looking at that summer moves dust from darker, warmer landscapes, clearing them of dust, lowering their albedo, and thus raising the local daytime temperature some more. On an aggregate level, this moves dust from the summer tropics to the other hemisphere. Overall, there is presumably a long-term equilibrium over millennia.
If you look at Mars' albedo on a very coarse level, there is a dark belt around 30° south. This happens to be the sub solar latitude at a time near perihelion and martian southern summer solstice, thus the hottest latitude on Mars.
All of this is what led Percival Lowell, et al, to conclude that dark vegetation was spreading in local summer. What they were actually seeing was dark martian regolith being cleared of dust.
Posted by: Phil Stooke Aug 16 2018, 10:41 PM
Don't be misled by reports floating around now that Opportunity has been communicating. JPL has confirmed that this is not correct, and it is thought to be a misinterpretation of the DSN activity graphics.
Phil
Posted by: djellison Aug 17 2018, 03:59 AM
Yeah - someone saw Opportunity in lock on eyes.nasa.gov/dsn and told the world the spacecraft was clearly alive, talking to us a 6 megabits per second.
This is the bulk of what I said to correct him........
Comm subsystems for both MER and MRO here : https://descanso.jpl.nasa.gov/DPSummary/summary.html
MER fault protection primer here : https://trs.jpl.nasa.gov/bitstream/handle/2014/37750/05-0557.pdf
Opportunity is in a low power fault or loss of clock fault - neither of these attempt to use the high gain antenna. Expect data rates of 10bps or so in this scenario. Even if it were somehow using the HGA - you would never ever see a data rate from it at more than 28,800 bps - never 6 megabits per second.
What does talk at 6 megabits per second is MRO with its 3m wide HGA.
I'm afraid what you saw was an antenna briefly locking up on MRO as its orbital motion put it's nominal downlink frequency on top of the expected MER frequency due to Doppler shift.
All the 8 Ghz X-Band frequencies for these spacecraft are pretty close together and so it's easy to see why a spacecraft in orbit that is sometimes coming 'towards' Earth in that orbit, and sometimes going 'away' from Earth in that orbit could very easily have it's carrier frequency pass through the expected MER frequency twice per orbit - and that's what you saw. The antenna will briefly acquire 'lock' on that passing signal and follow it until the receiver is commanded to drop lock and start looking back at the proper frequency for a signal to acquire.
If you watch DSN Now enough - you'll have seen this has been happening a lot over the past 2 months.
Sadly what you saw was NOT a signal from Opportunity
Someone still wasn't sure....so....
If MRO comes along and dumps it's enormous power downlink right where that antenna is looking - DSN Now will still report that it's looking for MER1 - but show there is a signal. That's what DaveS saw. It's been happening on an almost daily basis for two months.
The spacecraft names on DSN Now are essentially what's "booked" on that antenna at that time - it's not responsive to where a signal is coming from. You'll notice - it will happily put a label over an antenna when neither uplink nor downlink are occuring - it's because the antenna is booked for that spacecraft and is either setting up for it, cleaning up after a pass, or looking for a signal. At the time I'm posting this - that is true for OSIRIS-REX on DSS55, STEREO-A on DSS14, Voyager 2 on DSS43 and MRO on DSS46.
Posted by: marsophile Aug 22 2018, 09:21 PM
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In this screen capture from the NASA Mars report
https://www.youtube.com/watch?v=IJtjJSHsm9c
it appears that the global dust has diminished considerably.
In the weekly weather report
https://www.msss.com/msss_images/latest_weather.html
the area at the location of the rovers may be transmitting more light, although not yet clear.
Posted by: Explorer1 Aug 22 2018, 10:27 PM
2nd last paragraph of this update says Tau is still around 2.1 to 2.5, still too high for charging to start.
I wonder what HiRISE could see at Perseverance Valley by this point... is it still too opaque to make out the rover from orbit?
Posted by: nprev Aug 23 2018, 02:22 AM
Interesting thought. I wonder how much dust deposition there's been; might be a bit difficult to pick her out from the surroundings at first.
Posted by: JRehling Aug 23 2018, 08:13 PM
I can see from my own photos that the dust storm appears to be essentially done in the vicinity of Syrtis Major. After months of Mars looking weird, it's now totally or almost totally normal. How clear Opportunity's solar panels are (about 90° west of there) is anybody's guess.
Posted by: marsophile Aug 29 2018, 12:20 AM
https://mars.nasa.gov/msl/mission/instruments/environsensors/rems/
Maximum daily ground temperature from REMS now above freezing. This suggests a clearing at least at the Curiosity site. Being a worry wart, I am now wondering if, ironically, Opportunity might overheat the warm electronics box while in fault mode with no human supervision. 
Posted by: djellison Aug 29 2018, 05:50 AM
There is no risk of Opportunity overheating. That would require an amount of power than would guarantee reliable communication with Earth.
Posted by: Fran Ontanaya Aug 29 2018, 06:13 PM
As a side note, those conditions are above the triple point aren't they? Above 611 pascals and 0ºC during the day.
Posted by: mcaplinger Aug 29 2018, 07:20 PM
It's a sol-average pressure so you can't tell if the triple point was exceeded at some point diurnally, not that it would be so amazing if it was.
Posted by: serpens Aug 29 2018, 11:17 PM
Even of it is the important variable is the absolute humidity. The actual amount of water vapour in the atmosphere so in this environment being above the triple point for a brief period would be of passing interest only.
Posted by: xflare Aug 30 2018, 11:59 AM
I wonder if we will get another twitter/internet false alarm today 
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Posted by: djellison Aug 30 2018, 10:44 PM
https://www.jpl.nasa.gov/news/news.php?feature=7227
"When the tau level [a measure of the amount of particulate matter in the Martian sky] dips below 1.5, we will begin a period of actively attempting to communicate with the rover by sending it commands via the antennas of NASA's Deep Space Network. Assuming that we hear back from Opportunity, we will begin the process of discerning its status and bringing it back online........
.....If we do not hear back after 45 days, the team will be forced to conclude that the Sun-blocking dust and the Martian cold have conspired to cause some type of fault from which the rover will more than likely not recover," said Callas. "At that point our active phase of reaching out to Opportunity will be at an end. However, in the unlikely chance that there is a large amount of dust sitting on the solar arrays that is blocking the Sun's energy, we will continue passive listening efforts for several months."
Posted by: Explorer1 Sep 1 2018, 03:31 AM
Reading https://www.theatlantic.com/science/archive/2018/08/opportunity-mars-rover-nasa/569071/a quote stuck out:
Can't MRO just take a picture? I can guess that HiRISE is either in the wrong orbit to attempt imaging, or the resolution isn't quite high enough to resolve the rover as dust-covered or not, so it's not worth bothering to do? Would the surface be visible from orbit by now?
Posted by: mcaplinger Sep 1 2018, 05:28 AM
Have you looked at the images of Opportunity already taken by HiRISE? They are useless, IMHO, for assessing anything about the dust loading.
Posted by: marsophile Sep 1 2018, 05:58 AM
I think the answer is yes. AFAIK MRO is in a sun-synchronous orbit, so it should pass over every part of Mars in due course. It used to pass always at 2pm local time, but that may have changed. Even if the dust completely settles, there should be only a couple of microns of dust cover (as discussed in a previous post). I can't believe that would blanket the terrain in a way that would make the rover invisible. The only caveat I can think of is that Oppy is on a slope, which may help rather than hinder. IMHO, the only scenario in which Opportunity should be unrecoverable is if some combination of fault modes conspired somehow to place Oppy in an infinite loop of recovery efforts.
[EDIT: Evaluating the dust loading is a very different matter. Maybe it might be possible to look for a glint (specular reflection) from the solar panels?]
Posted by: fredk Sep 1 2018, 03:31 PM
I suppose you may not need to resolve Oppy. In principle I could imagine comparing images of Perserverance Valley now with images before the storm under the same lighting conditions, and looking for signs of increased dust on the ground more generally. In principle.
In practice this sounds hard if not impossible. Can images at sufficiently similar lighting be obtained, especially given the changing season? And a current tau above the pre-storm level will surely confound a fair comparison due to the atmospheric dust contribution. And it's not clear how much of an increase of dust cover on the panels would be implied by some increase on the ground, due to the different surface characteristics.
Posted by: mcaplinger Sep 1 2018, 03:44 PM
I think that's not possible given the orbital geometry; given the low tilt the imaging would have to happen around local noon, and MRO is in a roughly 3 PM orbit.
Posted by: djellison Sep 1 2018, 06:10 PM
The one time we’ve seen a ‘glint’ via HiRise was off Spirit years after it died. And it was just lucky. I don’t believe it can be used quantitatively.
There is a huge back catalog of dust factor and tau data that’s been collated by people here.....one could quite easily see when cleaning events occur by plotting dust factor against Ls and looking for periods of general improvement.
Posted by: marsophile Sep 2 2018, 12:13 AM
I think if an orbital pass was chosen to be about 22.5 degrees to the east of Opportunity, the geometry might be about right to hope for a reflection, since 3pm should mean a sun angle of 45 degrees from the zenith. Of course it would still take careful planning and a lot of luck.
Posted by: mcaplinger Sep 2 2018, 12:23 AM
I think that would be way off nadir, since from the MRO orbit the limb is only about 27 degrees of longitude from nadir. But I haven't studied the geometry carefully, and if there was an observed glint from Spirit there must be some way to make it work, though I don't remember what Spirit's tilt was.
However, I still argue that it's not diagnostic at all anyway.
Posted by: serpens Sep 2 2018, 01:11 AM
Well we know that Opportunity is in a good position for panel cleaning events which is a plus. I would have thought that the real danger period would be as the dust settles and minimum temperatures start dropping while power levels are insufficient to recharge the batteries for heating.
Posted by: marsophile Sep 3 2018, 10:41 PM
Is it possible that the same thing could happen in reverse? That a low bit/sec signal from Opportunity might go unnoticed because it is misidentified as being from MRO or another mission? Something like this, for example:
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Posted by: djellison Sep 3 2018, 11:20 PM
No - 11b/sec on MAVEN is a regular LGA telemetry only check in. Moreover - in the same way we can go 'that's a false lock on MRO while looking for MERB' it's also similarly obvious if there's a false lock on MERB when looking for something else.
The data rate for Opportunity in various fault modes would also be unique compared to other Martian spacecraft.
Recommended reading - the DESCANSO Design and Performance Summary Series
https://descanso.jpl.nasa.gov/DPSummary/summary.html
Posted by: mcaplinger Sep 4 2018, 01:08 AM
Being "in lock" is only a very early step in the whole decoding process that ends with digital packet data being produced. If a signal makes it all the way to the end, it has a unique spacecraft ID in it AFAIK, and shouldn't be confusable with anything else; even without the unique ID it's hard to confuse one spacecraft's packets with another's.
In listen-only mode, signals are recorded in wideband, not decoded in real time, and can be combed through later in much more detail than real time will permit. So if there's a signal in there, it will be found.
Posted by: marsophile Sep 6 2018, 12:55 AM
Apart from the luminance, the color spectrum might also provide useful information on the combined attenuation due to the tau and the dust factor. If a glint could be obtained, even if it proved not to be diagnostic, I think the general public might be excited by the daring and audacity of the attempt.
However, the existing tilt of the rover (is it known?) might render the task impossible. A tilt in the wrong direction would be doubled in terms of the needed offset to get a reflection.
Posted by: djellison Sep 6 2018, 05:44 AM
The exact pitch/roll/yaw are known.
Posted by: Explorer1 Sep 9 2018, 04:10 PM
From A.J.S. Rayl'shttp://www.planetary.org/explore/space-topics/space-missions/mer-updates/2018/08-mer-update-nasa-focuses-on-recovering-opportunity.html:
I'm sure we're all looking forward to seeing Opportunity, even if it remains silent at the time of the imagery.
Posted by: mcaplinger Sep 9 2018, 05:20 PM
Maybe a lot of people don't realize that because it's never been written down anywhere publicly before now, at least as far as I know.
Posted by: fredk Sep 9 2018, 09:17 PM
It's good to finally read some detail on the active/passive distinction. From the report:
Posted by: marsophile Sep 9 2018, 11:52 PM
Is this the issue? (From the MER update from 2010 that you cited above.)
Posted by: marsophile Sep 11 2018, 11:53 PM
https://mars.nasa.gov/mer/home/
The 45 day period of "active listening" has apparently begun.
Reevaluation at the end of that period?
Posted by: atomoid Sep 12 2018, 05:15 PM
According to the https://www.cnet.com/news/nasa-ramps-up-efforts-to-reach-opportunity-rover-on-mars/ i've seen "It's now sending commands multiple times per day", now if it were only possible to pull the queue or history list on https://eyes.nasa.gov/dsn/dsn.html..
Posted by: djellison Sep 12 2018, 05:35 PM
Best way to see the DSN Now history is to look at the timeline of DSN Status - https://twitter.com/dsn_status
It's not an official NASA thing - but does the job.
Posted by: marsophile Sep 15 2018, 05:26 AM
Was this a hit? (Now 10:25pm PDT.)
https://twitter.com/dsn_status/status/1040813778147926016
1h1 hour ago
More
DSS 35 carrier lock on Opportunity
Frequency: 8.4068GHz
Signal strength: -139dBm
IDLE OFF 1 MCD3
Would have been around 11am LST at Opportunity location.
Posted by: akuo Sep 15 2018, 05:27 AM
Thanks Doug for that link.
Just now I noticed:
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Just now, there isn't a live signal or carrier, but DSS 35 is sending a data signal to Oppy.
Posted by: xflare Sep 15 2018, 07:59 AM
The frequency is different to MRO too?
Posted by: akuo Sep 15 2018, 08:31 AM
Different from MRO, but looking at the history, Odyssey's frequency is almost the same (8.4067GHz vs 8.4068GHz above), so not sure if there is some possibility of confusion there for a carrier lock.
Posted by: xflare Sep 15 2018, 08:48 AM
Yes. I think we've been mistaken again, this time with Odyssey rather than MRO, here's a tweet from 16th August https://twitter.com/dsn_status/status/1030026880068595712
Here are the results when you search the DSN twitter timeline for Opportunity
https://twitter.com/search?f=tweets&vertical=default&q=opportunity%20from%3Adsn_status&src=typd
Most of the frequency's for Opportunity are 8.4358GHz
edit: confirmed false alarm : https://twitter.com/AstroStaab/status/1040845967233150976
Posted by: Explorer1 Sep 15 2018, 01:42 PM
Were any false alarms during the Spirit listening campaign? The DSN Now site didn't exist, so it wasn't all over Twitter if any happened, but the same orbiters were around the planet with the same potential for "mimicry".
Posted by: xflare Sep 15 2018, 02:09 PM
And what exactly will a DSN signal from Opportunity look like on the DSN website/twitter feed? Such as signal strength, data rate, frequency etc?
If you look back to May 2nd we see this:
DSS 24 carrier lock on Opportunity
Frequency: 8.4072GHz
Signal strength: -125dBm
With the next tweet being:
DSS 24 receiving data from Opportunity at 142.2kb/s.
IN LOCK OFF 1 MCD3
Which is quite similar to what we saw this morning, minus the data tweet ofcourse.
Posted by: mcaplinger Sep 15 2018, 02:49 PM
The bit rate would be very low for starters (<10 bps IIRC). If you don't see "receiving data" then I would assume it's a false alarm.
If a real signal is seen I don't think the team will keep it a secret.
Posted by: marsophile Sep 15 2018, 04:50 PM
The signal strength should be consistent with the low gain antenna (LGA) on Opportunity.
For comparison, this shows an example of an LGA comm from Maven:
https://twitter.com/dsn_status/status/1040572487174639617
Here is an example attributed to Mars Odyssey with an even lower signal strength:
https://twitter.com/dsn_status/status/1040558512282259457
This old one from Opportunity is almost identical to last night's.
https://mobile.twitter.com/dsn_status/status/760400607412912128?p=v
I assume without data being transferred, there is no way to verify, but we can hope that initial abortive attempts might be indications of Oppy struggling to come back...
Posted by: dvandorn Sep 15 2018, 06:19 PM
IIRC, false alarms are not only possible because of false contacts that end up being chatter with other assets in the region. I recall that there was a repeated set of false alarms during the active contact attempt phase with MPL back in '99, up to the point of a news release that there had been a signal detected that could well be from MPL. And all it ended up being was a reflection of the signal being sent out to MPL, not anything back from the crashed lander.
As Mike and Doug and others keep preaching, false alarms are quite possible, anything that appears to be a contact needs to be verified as two-way and containing at least valid headers in the downloaded data stream. In other words, while you may get a heads-up looking at the DSN status, the real proof of the pudding will be when downlinked data, if any, is analyzed and found to have valid headers. And valid engineering status data, hopefully...
And, guys? If the worst has happened and Oppy has finally gone on to meet her sister in whatever afterlife exists for such entities, it's not a sad time. Fourteen years of impressive and fundamentally game-changing data from a rover designed to last 90 days is not something to mourn. It's something to celebrate! Oppy doesn't deserve a dirge, she deserves a happy, rollicking Dixieland funeral parade!
-the other Doug
Posted by: xflare Sep 15 2018, 06:46 PM
For comparison, this shows an example of an LGA comm from Maven:
https://twitter.com/dsn_status/status/1040572487174639617
Here is an example attributed to Mars Odyssey with an even lower signal strength:
https://twitter.com/dsn_status/status/1040558512282259457
So maybe something more like this from Feb 2nd
https://twitter.com/dsn_status/status/959285817138008065
https://twitter.com/dsn_status/status/959286333024776192
Posted by: mcaplinger Sep 15 2018, 07:19 PM
If you see a "receiving data at 10 bps", then that might be a real signal. (They've transmitted from the LGA at higher rates but I don't think that the fault modes will ever try this.) My advice is to ignore all carrier lock messages.
There's a good chance that the first signals will only be seen in radio science recordings, which won't show up in the realtime DSN status anyway.
Posted by: marsophile Sep 17 2018, 05:55 AM
The DSN Now display shows 4 antennas at each complex. However, there may actually be more than 4. For example, Goldstone seems to have 8.
https://en.wikipedia.org/wiki/Goldstone_Deep_Space_Communications_Complex#Antennas
Are the antennas that are not displayed idle, or are they doing stuff that we can't see, such as attempts to transmit commands to Opportunity? This might explain why we don't see the every-day attempts discussed in the most recent MER press release.
[EDIT] Uplink to MER1 from Goldstone now (12:30am). Maybe the action just happens while I'm asleep...
Posted by: djellison Sep 17 2018, 03:18 PM
They are no longer used for routine DSN operations.
Posted by: xflare Sep 18 2018, 07:53 AM
arggh you're right, was just watching the DSN status page and their twitter page, and another false alarm, this time with Maven.
edit: Here is the History of MAVEN from the DSN status twitter feed https://twitter.com/search?f=tweets&q=MAVEN%20from%3Adsn_status&src=typd
And Opportunity's last DSN comm from June 10th? https://twitter.com/dsn_status/status/1005823559166459908
Posted by: akuo Sep 18 2018, 08:02 AM
Well, that momentary carrier lock at 8.4351GHz was a lot closer to the expected Oppy frequency (8.4358GHz you pointed before), than Maven's 8.4454GHz... But yeah, maybe it's the doppler shift around the orbit.
Posted by: djellison Sep 18 2018, 03:20 PM
-148dBm is FAR too strong for a MER LGA on the surface. That last DSN Now entry was a high gain antenna. Not the low gain that will be used now. Expect something more like -160 dBm.
Honestly - given the idiosyncrasies of how the DSN works - it is unlikely you're gonna be able to identify a successful vehicle recovery via DSN Now.
Posted by: akuo Sep 19 2018, 07:12 AM
DSN has brought out the big guns tonight. The 70 metre DSS 14 "Mars" in action with MER1 now
Posted by: xflare Sep 19 2018, 08:37 AM
Still up linking, although it did disappear for about 15 minutes then come back.
EDIT: About 2 hours now, maybe trying to cover the whole window where Oppy might be awake with the larger antenna?
Posted by: marsophile Sep 23 2018, 06:01 AM
That would be lower even than the signal strength from the Voyagers at around 10 billion miles!
https://twitter.com/dsn_status/status/1043512420768120833
https://twitter.com/dsn_status/status/1043219216659361793
Admittedly, they would be using high-gain antennas and the bit rate is around 160 b/sec.
https://twitter.com/dsn_status/status/1043220222327627776
Posted by: djellison Sep 23 2018, 03:54 PM
The Voyagers all transmit with large high gain antennas that are VERY directional and pointed at Earth. At X Band they have a beam width of half a degree and 48db of gain.
Opportunity will be using its low gain antenna that transmits to 180 degrees of the sky and has only 7 dB of gain
Physics is mean like that.
Posted by: fredk Sep 23 2018, 06:47 PM
In defence of physics, I've never known it to be mean. It just doesn't care.
Posted by: marsophile Sep 24 2018, 02:19 AM
Hypothetically, if the low gain transmitter were non-functional, but the receiver and other communication assets (UHF, high gain) were ok, could the rover still be recovered? From a practical standpoint, would recovery be unlikely in that case?
Posted by: mcaplinger Sep 24 2018, 02:53 AM
There's only one X-band transmitter (though there are redundant solid-state power amplifiers) that can be switched between the LGA and the HGA. The HGA can't be pointed at the Earth in a clock fault because the rover doesn't know what time it is and therefore where the Earth is. So the HGA path is useless for recovery unless the clock can be updated. See https://descanso.jpl.nasa.gov/DPSummary/MER_article_cmp20051028.pdf Figure 3-1 on page 17.
In theory both transmit and receive could happen via the UHF. With a clock fault, though, the exact time of UHF comm windows is moving around in a hard-to-predict manner and it's unlikely that an orbiter pass will happen to coincide with one of these windows, though I expect this is being tried.
Posted by: climber Sep 25 2018, 06:42 PM
Hi Oppy, we can at least see you again: https://www.jpl.nasa.gov/news/news.php?feature=7245
Posted by: Explorer1 Sep 25 2018, 08:24 PM
Glad to see the old girl... a poignant image if there ever was one!
Posted by: Sean Sep 26 2018, 01:09 AM
Full res blend of HiRISE RGB mapped to gray pass, Oppy is centered.
https://flic.kr/p/28FaqA1
Posted by: PaulH51 Sep 27 2018, 02:42 AM
How a Tiny Curiosity Motor Identified a Massive Martian Dust Storm https://www.nasa.gov/feature/goddard/2018/how-a-tiny-curiosity-motor-identified-a-massive-martian-dust-storm
Posted by: marsophile Sep 27 2018, 02:45 AM
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Looks like Oppy has taken on a lot more dust than its immediate surroundings (unless the area around it is in darkness and the rover is poking into the light). It would be nice to have a stereo pair---the brain does a great job of combining information from the two eyes.
Posted by: mcaplinger Sep 27 2018, 05:32 AM
I don't think that follows, as the color and reflectivity of the rover is obviously different than the surroundings regardless of the dust loading.
https://www.uahirise.org/ESP_056955_1775 says
Posted by: xflare Sep 28 2018, 08:10 AM
I wondered if the dust would fall out of the atmosphere at around the same rate globally if a dust storm turns into a global one? Maybe it might be possible to use Curiosity to give some idea of how much dust is settling on the rovers.
Posted by: RoverDriver Sep 28 2018, 09:03 AM
Given that there are dustier (Gale and Gusev) environments than others (Meridiani), I would be surprised if that was the case. Even after the 2007 PEDE, the amount of dust accumulation on the two MER vehicles was different. Keep in mind that even a 0.1 difference on the dust factor can have a significant impact on solar array output.
Paolo
Posted by: marsophile Sep 28 2018, 03:47 PM
The DSN is currently transmitting an UP signal to Opportunity at a data rate of
2.00 kb/sec. Isn't that a little high for trying to send to the LGA?
[EDIT: I guess it is the DSN power level that matters, not the rover's].
Posted by: mcaplinger Sep 28 2018, 04:54 PM
From https://descanso.jpl.nasa.gov/DPSummary/MER_article_cmp20051028.pdf
20-kW transmitters supported 2000 bps (highest uplink rate available) on the cruise MGA and the rover HGA during the primary mission.
So it seems very unlikely that they are sending 2K to the LGA. I don't know what they're doing. It's possible that DSN Now gets confused about uplink in MSPA or something, I suppose.
Posted by: djellison Sep 28 2018, 06:30 PM
Uplink rate in a fault mode to the LGA is 7.8125 bps
See https://www.cs.princeton.edu/courses/archive/fall14/cos109/mars.rover.pdf
2 kbps is the sort of into-an-HGA nominal upilnk data rate one might expect for many spacecraft. Certainly not what was happening today for MERB.
Posted by: marsophile Sep 29 2018, 12:17 AM
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Screen capture from DSN Now this morning.
Could the MER team be trying to rouse the rover via the HGA, on the theory that the LGA is not working? It may be that there was a known occurrence where by chance the HGA was pointed towards Earth.
Is it even possible to communicate using the HGA when the rover is in fault mode?
Posted by: mcaplinger Sep 29 2018, 01:23 AM
Sigh. I think a more likely explanation is that this was an uplink to some other spacecraft, and DSN Now got confused.
I suppose it's possible that there could be a switch fault that would preclude connecting the LGA to the SDST, but then I wouldn't expect them to use the highest-possible uplink rate to command, even if the HGA happened to be pointed at the Earth.
Posted by: James Sorenson Sep 29 2018, 01:34 AM
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Is it even possible to communicate using the HGA when the rover is in fault mode?
The HGA requires a mission clock and knowledge of where the Sun and Earth are in the sky for pointing the HGA. It's pretty safe to assume that the clock faulted, the rover hasn't woken up yet as the sky has cleared to levels to where a healthy and clean rover should automatically power up and start sending beeps on schedule. That is, if the clock didn't fault...in a perfect world. So, as I understand it, once 1.1 amps hits the array, the rover should wake up and start beeping on the only antenna that doesnt need any knowlege of orbiter overpasses or where the Earth is in the sky. That is the LGA, which is omni-directional.
By the way. I've been watching DSN now quite a lot lately during the attempts. Manage your expectations with it. Take everything Oppy related with a grain of salt. Don't get to excited if something appear's like Oppy is talking. These false alarms further highlights it to be super cautious. Any news of possible com with Oppy will come from the rover team and a press release. Not DSN now....
Posted by: djellison Sep 29 2018, 03:03 AM
It is not.
This was not a 2kbps uplink to Opportunity.
It was some idiosyncrasy in the way the various antennas report data to the server that collates data into the form DSN Now uses.
I know it's tempting but please stop trying to infer something about recovery efforts via DSN Now. It's not what it was designed for. It's going to be wrong more than it's right.
Source : I work on Opportunity and worked on DSN Now.
Posted by: Gerald Sep 29 2018, 07:50 AM
https://meetingorganizer.copernicus.org/EPSC2018/EPSC2018-117.pdf, but don't seem to be publicly accessible, yet.
Posted by: akuo Sep 29 2018, 06:00 PM
https://twitter.com/dsn_status/status/1046058741974609920
DSS 36 carrier lock on Opportunity
Frequency: 8.4351GHz
Signal strength: -164dBm
IDLE OFF 1 MCD2
8:26 AM - 29 Sep 2018 from Paddys River, Canberra
Ticks more of the criteria set in this thread, but just a carrier lock.
Posted by: dvandorn Sep 29 2018, 07:13 PM
Hopefully, this means we just got at least 1.1 amps out of the solar array.
Here's hoping this is a start to recovery. No way a sure thing yet, but fingers and toes all crossed...
-the other Doug
Posted by: James Sorenson Sep 29 2018, 08:58 PM
Likely another false carrier lock. Like I said with DSN Now above, take anything Oppy related with a grain of salt. To be honest, I'd just pretty much ignore the Opportunity DSN status twitter messages because of the high potential for false locks with other orbiting assets.
Posted by: MarkG Sep 30 2018, 12:52 AM
Just for curiousity (the mental attitude, NOT the robotic craft), what help could the currently-orbiting assets be to this effort? They all have there regular jobs to do, and limited capabilities, and limited time in view of Opportunity, but their one-over-R-squared advantage is significant over earthbound resources......
Posted by: RoverDriver Sep 30 2018, 01:15 AM
DTE LGA passes have been used in the past and the DSN is well capable of detecting and carrying those passes. Either the rover has enough energy to start a comm pass or it does not, it is binary, not analog where the transmitted power varies according to the energy level.
Paolo
Posted by: mcaplinger Sep 30 2018, 01:44 AM
This has been discussed several times in this thread, look for "UHF".
The bottom line is that in this particular fault it doesn't help very much.
Posted by: marsophile Sep 30 2018, 05:56 AM
https://en.wikipedia.org/wiki/Snowdrift
If there is any wind when the dust is being deposited, then perhaps it would depend on the local topography, like a snowdrift. Some kind of barrier that abruptly slows the wind might form a relative drift. For example, if the rover deck were tilted in the windward direction, then it might receive a lot of dust.
Posted by: RoverDriver Sep 30 2018, 02:19 PM
For example, if the rover deck were tilted in the windward direction, then it might receive a lot of dust.
You are correct, the local topography greatly affects the dust deposition but your example is backwards, I think. The side facing the wind sees the highest pressure and wind speed, therefore lower dust deposition. As an example, if you remember the dune field we have traversed before and after Victoria, had an asymmetric dust deposition. Even when the crest was about 20cm taller than the trough there was a noticeable difference in dust. This is why we were usually driving on the West side of the trough, and why the Sol 833 embedding happened (Jammerbugt).
In fact, the current rover position is probably one of the best possible to expose the deck to cleaning events. If you look at the surface (before the PEDE) there wasn't much dust drifts around.
Paolo
Posted by: RoverDriver Sep 30 2018, 04:29 PM
That said -- in fact, what ARE reliable sources in this matter? Don't take this the wrong way, but I doubt you're the one and only reliable source here.
...
Probably a public announcement on JPL or NASA sites. Also, if you see me heading for the liquor store, that might be a good sign.
Paolo
Posted by: Explorer1 Sep 30 2018, 04:35 PM
Paolo
That's what I figured, but the trouble is that there are seemingly so many ways the news of Opportunity waking up could be disseminated: could it be a rover team member's social media account, a press release from NASA/JPL as you said, some lucky person looking at DSN Now at the right moment, or a 'leak' to a space news reporter?
There's no technical disclaimer on the DSN Now interface, and I'm not sure what the NASA PR rules are about private social media accounts apart from 'opinions are my own'. The chance of false alarms are still too high...
Posted by: mcaplinger Sep 30 2018, 04:46 PM
As far as I know the automated DSN twitter account is basically getting the same information as DSN Now. Many of us have said over and over again that this is not a reliable source of information with regard to the Opportunity recovery, and you can appreciate that there might be a certain amount of frustration when these caveats are ignored.
I've tried to figure out what an unambiguous detection might look like on DSN Now, but the initial contacts will likely just be beeps (carrier only) and with just this, my criterion of actually seeing data flowing at 10 bits/sec will never be met. Read https://descanso.jpl.nasa.gov/DPSummary/MER_article_cmp20051028.pdf 5.1.6 X-Band Carrier-Only Beeps for more information. It may be that once the recovery is well underway, DSN Now will be a viable way of seeing how it's progressing, but not initially.
The bottom line is that an official announcement is the only reliable way to know if something has been detected. AFAIK, team members are not supposed to be unofficially posting status information on social media. I don't think the team will sit on the news for any length of time, but it has to be coordinated with JPL PIO so I wouldn't expect it to happen over a weekend.
Posted by: marsophile Sep 30 2018, 05:56 PM
Perhaps one way of ruling out false contacts might be to look at the Local Solar Time at the Opportunity location for when they occurred. As an example, if my calculations are correct, the 3 most recent candidate "beeps" occurred at 13:28:42, 12:50:19, and 13:45:57 LST. (I assumed the times given by the twitter reports were Pacific Time.) If the onboard clock were still working, then (according to the fault protection documentation) the spontaneous beeps should be at 11:00:00 LST.
Posted by: mcaplinger Sep 30 2018, 06:10 PM
The clock has almost certainly faulted, and even if it hasn't, I don't think one can presume anything close to the level of accuracy that you're suggesting.
The fact that there is no public source that says how long a particular signal is in carrier lock makes it impossible to tell a short transient from a longer, more plausible actual contact.
Posted by: djellison Sep 30 2018, 07:25 PM
I see people are still trying to use DSN Now as some way of detecting an Opportunity recovery. Some of these points have been made earlier but just so people are clear....
https://twitter.com/dsn_status
This is an unofficial bot written by the awesome Russ Garrett. It says so right in the accounts profile. It is not a NASA account. It is simply a bot posting every time it detects a change to the XML file that drives the DSN Now website.
I get it - we all want to hear from Opportunity - but believe me, you've not going to figure it out with DSN Now. I worked on it for years, and it is a victim of many idiosyncrasies in how the DSN operates, how the network reports its status internally and - to be brutal - a lack of resources to engineer a level of robustness into its pipeline to avoid all those idiosyncrasies.
Seriously people - I know watching DSN Now like a hawk may feel like a way of getting ahead of an official press release, but you're largely wasting your time.
The way we're going to hear that Opportunity has been heard from is via a NASA and/or JPL press release. Not an overly enthusiastic fan reading too much into DSN Now.
Posted by: nprev Sep 30 2018, 07:26 PM
ADMIN MODE: This thread has become beyond overheated, and we're turning the flames down right now. Three particularly inflammatory posts hidden.
New info/rules for this discussion to continue:
1. It has been stated. And stated. And stated. REPEATEDLY...that the DSN Now interface cannot be considered an authoritative source to determine whether or not any sort of signal has been received from Oppy. Therefore, there will be no more excited future posts claiming to have seen such a signal nor passionate defenses of one's 'find'.
2. There has also been an exhaustive explanation from persons in positions to know the many technical reasons why this is, as well as the various possible failure modes that are causing the silence (all of which are at this stage possibilities, not confirmed hypotheses). Nobody else here is in a position to question their opinions.
3. Unless and until NASA/JPL makes an official announcement that Oppy has been heard from we will not know anything at all. If anyone begins claiming some sort of conspiracy about this they will be immediately and permanently banned.
Most of all, let's keep it civil. Many people here are, naturally enough, emotionally invested in this situation. Let's please not let that concern and frustration overwhelm our good sense (and I really don't wanna hear any "but s/he started it!" cries of protest--just knock it off. Now.)
Back to our regular programming.
Posted by: serpens Sep 30 2018, 10:39 PM
Bravo Zulu nprev. Not before time.
Posted by: RoverDriver Sep 30 2018, 10:52 PM
could it be a rover team member's social media account,...
My relationship with JPL media has always been difficult at best. I'm pretty sure that if I made an anouncement before they did, it would be my last post as a JPL employee.
I am also sure that JPL/NASA would not hide or delay such news. Yes, there will likely be some handshake with teh rover to make sure she's still up and running. Mars works slowly. Be patient, and watch where I'm heading ;-)
Paolo
Posted by: James Sorenson Oct 1 2018, 04:36 AM
Me and I'm sure all of us here wouldn't want that to happen to you Paolo.
So yes, please don't.
Posted by: marsophile Oct 2 2018, 02:47 AM
https://static.uahirise.org/images/2014/details/cut/ESP_035408_1775-1.jpg
Happier times for Opportunity! Hirise image from Valentine's Day 2014.
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Oppy seems much clearer in the old Hirise. We can see a shadow cast by the rover.
Is the lesser clarity in the new image due to lighting, or dust? Of course Oppy is now in a valley sloping to the East, while the Sun is in the West at 3 pm local time.
Posted by: RoverDriver Oct 2 2018, 03:07 AM
Is the lesser clarity in the new image due to lighting, or dust? Of course Oppy is now in a valley sloping to the East, while the Sun is in the West at 3 pm local time.
There's about a 30 degrees delta rover attitude between the two pictures, almost entirely to the East. Same holds true for the terrain. If you look at the Sun elevation angle for the two pictures, you can figure out the difference in lighting conditions.
Paolo
Posted by: marsophile Oct 3 2018, 01:54 AM
Perhaps snow was the wrong analogy; being pelted by rain or hail might be a better one. The dust is already falling so the carrying capacity of the wind may not be the significant factor. Instead, the angle of the fall (modified by the wind) may be the important issue. If the trajectory of the falling dust is exactly perpendicular to the plane of the tilted deck, then the deck will pick up more dust than if it had no tilt.
I think, surprisingly it may even pick up more dust than if the deck was level and the dust was falling staight down. The reason is that the angled dust will be packed the same on a level deck as if it were falling straight down, and thus more tightly on the perpendicular deck.
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Posted by: Gerald Oct 3 2018, 09:50 AM
The size of the dust grains is on the order of one micron. Therefore aerodynamical considerations will be the most relevant ones regarding dust settlement. Air is moving parallel to surfaces. and so do mostly the aerosols, not perpendicular like rain or hail. If it would be otherwise, the dust would have settled within hours after the storm, and wouldn't have been able to spread globally.
Posted by: marsophile Oct 4 2018, 01:47 AM
You make a good point. However, if the local wind is slow enough, in the tenuous Martian atmosphere, then the ability of the wind to push dust uphill on the rover deck may be limited. One would expect a critical wind speed below which dust settlement will be more like a rain of dust. Stronger winds at high altitudes may have kept the overall dust from settling more quickly.
Also the tendency of Martian dust to form aggregates of size ~100 microns or more may be a relevant factor. See
http://www.marsjournal.org/contents/2010/0005/files/vaughan_mars_2010_0005.pdf
Theory is nice but have there been any wind tunnel experiments to investigate dust deposition under
simulated Martian conditions?
Posted by: Deimos Oct 4 2018, 02:51 AM
Strong winds don't keep the dust from settling, although turbulence does; they just change where it falls. For winds of 1 mm/s or more, the dust moves much more with the wind than down, even though the average velocity is down in the post-storm environment. Look at the cal target post to see evidence of dust moving with the wind.
The large aggregates form on surfaces not in the air, so they matter for cleaning events. But we see cleaning events. Aerodynamics matters quite a bit there too, since the wind on a rough surface (rover deck, not necessarily solar cells) is much less at 100 microns than at 10 meters.
Posted by: marsophile Oct 4 2018, 05:27 AM
Some quotes from
http://www.marsjournal.org/contents/2010/0005/files/vaughan_mars_2010_0005.pdf
form, get suspended, grow to a size where they are below the
suspension threshold,....
Seems to imply possibility of growth while suspended in the atmosphere.
might equate this with dust grains becoming electrically
charged in a dust storm or any large wind event and forming
aggregates in the air. There is no way to be certain whether
the aggregates observed in this work were formed in situ or
while airborne, although it is interesting that the MI images
acquired around and after the 2007 dust storm (peaking
around Sol 1250) show the most dust aggregates.
Suggests a mechanism.
Posted by: Gerald Oct 4 2018, 12:26 PM
Nevertheless, dust will prefer to settle and remain at locations, where wind velocities are lowest. That's usually on the lee side of an obstacle, especially in concavities.
Your rain or hail analog would apply to saltating grains. But for a tilted surface, these usually rounded larger grains tend to roll downslope, and will mostly end up in concavities, too.
Posted by: Deimos Oct 4 2018, 03:29 PM
I don't like the rain analogy--nothing falls like that. Rather than further picking that nit, here's what I see as ways stuff does fall.
(1) There is the background of globally homogenized atmospheric dust. The Lemmon et al. (2004) reference above, and many others before and after, have put that dust in the vicinity of 3 micron diameter. This is in no way a lower limit. That is a measurement of the dust, while it is suspended, in bulk. The 3-micron number is a cross-section weighted mean diameter: the vast majority of dust particles are smaller than this, and some are significantly larger. The width of the distribution is difficult to pin down, and even then it would be an 'effective' width. One cannot say precisely how many 20-micron diameter particles there are (but not many).
(2) That dust (from 1) looks a lot like the globally homogenized post-storm dust. After the 2007 storm, when dust had mixed around the planet about as much as it was going to, and lifting had stopped, the dust settled (as opposed to 'was advected away'). At both rover sites, Lemmon et al. (2015) the dust opacity decayed exponentially with a 43 sol timescale (1/43 of the dust was removed each sol). That's close to the Pollack et al. (1979) values for Viking or 51 sols. We know the timescale for dust falling. We know the spatial scale is around the 10-11 km scale height. So the characteristic mean fall speed has to be in the ball park of 3 mm / s (I think I somehow got 10x lower, before). Sure, it is different high vs. low and day vs. night, but the average sedimentation speed cannot get far from this. Since the start of July, this is what has been happening, based on close analogy with measurements from the Martian surface in similar circumstances.
(1) and (2) describes dust falling like Martian dust. I don't have a good analogy. I don't have data, but I'll assert dust in my living room falls much faster. Volcanic dust could ... but the fine component that usually falls literally as rainfall far from the eruption.
(3) At the other end, there is ballistic material. This is saltating sand. Lots has been reported. Maybe during the storm, this scoured the already clean rover deck. Maybe it piled up on parts of the panels. When the wind stopped blowing, this stopped within seconds.
(4) In between, you have the gradation of stuff falling at a terminal velocity that is significantly greater than eddy speeds. Maybe one could say it falls like snow, or maybe volcanic ash. (4a) Some stuff is big when lifted, but not sand sized. It has a short residence time in the atmosphere, so it does not contribute significantly to the 'global' dust. It is likely not there most of the time. But Opportunity was in the middle of lifting areas. Did big stuff fall out as dust that settled by one to a few km in hours to a few sols? Possibly (personally, I think it is quite likely). (4b) Some stuff may have grown to 100-micron sizes and then fallen. Large aggregates fall slowly (snow, not rain). If the fractal dimension is ~2, their cross-section grows as fast as their mass, so they don't even speed up. If the fractal dimension is ~3, it falls like rain; and if this is an important mechanism, the skies clear much faster than we see happening on Mars. I guess one may speculate; but I have not seen any evidence of this stuff in the atmosphere, or clear examples of stuff that fell out (let alone that this is an important mechanism). (4c) Stuff certainly gets to 100-micron sizes on surfaces, likely growing there but maybe falling there. (I figure this is a good thing, as this stuff sticks up more into the wind and becomes easier to clean.)
But overall, there are lots of mechanisms that get the deck dusty as the various sizes interact with different winds and terrains. There are many unknowns, since we've never had active measuring happening inside that kind of storm; MSL didn't see the same activity. I'm not sure it is worth drilling deeply into one unknown without rover data.
Posted by: marsophile Oct 5 2018, 03:05 AM
http://www.planetary.org/explore/space-topics/space-missions/mer-updates/2018/09-mer-update-team-initiates-plan-to-recover-opportunity.html
A.J.Rayl's Planetary Society update, Oct 4.
Posted by: mcaplinger Oct 5 2018, 03:21 AM
Selective quoting on your part?
The fact of the matter is that not much can be determined from the HiRISE image, but clearly people want to believe that the rover is very dusty, since that's an explanation for why it hasn't woken up yet.
Posted by: marsophile Oct 5 2018, 04:32 AM
I could say the same. The bulk of opinion expressed in the article favored this view, although there were caveats.
Of more interest are the detailed descriptions of the recovery attempts.
Posted by: Gerald Oct 5 2018, 03:48 PM
... the rover is very dusty ...
Taking your words out of context...
This will be the case, even if only a fraction of the atmospheric dust column settled on the solar panels.
Let's hope for a few gusts in time.
Posted by: serpens Oct 6 2018, 03:01 AM
As I understand it, for a global dust storm the tropics and the low to mid latitudes are the sinks for dust deposition, so as far as dust fallout is concerned Opportunity is pretty well positioned.
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