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djellison
Posted on: Sep 3 2018, 11:20 PM


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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

  Forum: Opportunity · Post Preview: #240844 · Replies: 410 · Views: 487226

djellison
Posted on: Sep 1 2018, 06:10 PM


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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.
  Forum: Opportunity · Post Preview: #240831 · Replies: 410 · Views: 487226

djellison
Posted on: Aug 30 2018, 10:44 PM


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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."
  Forum: Opportunity · Post Preview: #240807 · Replies: 410 · Views: 487226

djellison
Posted on: Aug 29 2018, 05:50 AM


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There is no risk of Opportunity overheating. That would require an amount of power than would guarantee reliable communication with Earth.
  Forum: Opportunity · Post Preview: #240785 · Replies: 410 · Views: 487226

djellison
Posted on: Aug 17 2018, 03:59 AM


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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........

QUOTE
A few background details....
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/2...750/05-0557.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....

QUOTE
If the antenna is looking for MER-B, then the session on DSN Now says 'MER1'.

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.
  Forum: Opportunity · Post Preview: #240725 · Replies: 410 · Views: 487226

djellison
Posted on: Aug 10 2018, 03:52 AM


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Infact I've recently rejoined the 'Eyes...' team (only part of my time) and one of my first tasks was to take a nominal observation plan for the flyby and start parsing it down to the elements needed for 'Eyes.....' - so it's happening smile.gif
  Forum: New Horizons · Post Preview: #240678 · Replies: 578 · Views: 917311

djellison
Posted on: Aug 8 2018, 11:15 PM


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Seeing a shadow at all is awesome - we've basically not seen one since the dust storm started! It means the skies are clearing and more of the illumination is coming directly from the sun rather than the diffuse sky glow!
  Forum: MSL · Post Preview: #240670 · Replies: 685 · Views: 498516

djellison
Posted on: Aug 8 2018, 03:39 PM


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QUOTE (mcaplinger @ Aug 8 2018, 07:23 AM) *
We've had the tech for 20 years or more, if only we would choose to do it. While I have some significant concerns about whether the viewgraphs Van linked to represent the best approach, I suspect it would be workable with sufficient commitment.



This. The only thing lying between Mars 2020, and returning its samples to Earth - is the will to do so, expressed in an appropriate budget to get it done.
  Forum: Past and Future · Post Preview: #240663 · Replies: 579 · Views: 574619

djellison
Posted on: Aug 8 2018, 04:07 AM


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QUOTE (John Whitehead @ Aug 7 2018, 02:09 PM) *
Wasn't there a NASA competition about 5 years ago for "lunar landing" propulsion?


Are you thinking of the Northrop Grumman Lunar Lander XCHALLENGE ? https://lunarlander.xprize.org/

The level 2 challenge of that was specifically designed to demonstrate a Delta V of that required to take off from the moon and enter lunar orbit. To that end - it is exactly what's needed for lunar landing.

No one suggested the NGLLC was about designing vehicles for Mars ascent.

QUOTE
For lunar landing, propulsion needs to be at the best state-of-the-art ever used for spacecraft (also for other subsystems).


There is nothing state of the art required to build a lunar lander. It was done autonomously over 50 years ago with Luna 9. The surveyor spacecraft didn't even have proper onboard computers. They used a solid rocket motor to do most of the landing burn, followed by vernier thrusters for the last 7km or so. It could maybe be considered best state-of-the-art ever used....in 1966.

There is no fundamentally new technology required for a MAV. It's simply a case of spending the money to do the engineering and make it work.

It's not - for want of a better phrase - rocket science.



  Forum: Past and Future · Post Preview: #240655 · Replies: 579 · Views: 574619

djellison
Posted on: Aug 6 2018, 04:10 PM


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I think those are just symptoms of SSTV ham radio downlink.
  Forum: Chang'e program · Post Preview: #240616 · Replies: 466 · Views: 1423581

djellison
Posted on: Aug 5 2018, 05:47 PM


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QUOTE (mcaplinger @ Aug 4 2018, 11:25 PM) *
IMHO, ISRU is one of those supposedly enabling technologies that have served to distract MSR from simpler, more workable architectures for decades.


Seconded. ISRU is enabling for future human exploration architectures. It's an unnecessary source of complication and cost for sample return.

One thing I remember hearing at some point - something similar to an AMRAAM missile would make a capable MAV first stage. A small mono-prop upper stage for orbit insertion would finish the job quite well.
  Forum: Past and Future · Post Preview: #240605 · Replies: 579 · Views: 574619

djellison
Posted on: Aug 5 2018, 05:43 PM


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QUOTE (dvandorn @ Aug 5 2018, 09:23 AM) *
.... 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.


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.
  Forum: Opportunity · Post Preview: #240604 · Replies: 410 · Views: 487226

djellison
Posted on: Aug 4 2018, 04:00 PM


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QUOTE (dvandorn @ Aug 3 2018, 10:10 AM) *
....not so much against a date as against a tau level


That infers you know the solar array dust factor - which we do not.
  Forum: Opportunity · Post Preview: #240584 · Replies: 410 · Views: 487226

djellison
Posted on: Jul 28 2018, 06:33 AM


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QUOTE (PaulH51 @ Jul 27 2018, 03:37 PM) *
The full frame HazCams from sol 2122 may provide a few clues, but have not made it to the public server yet.


The Navcams and Hazcams get out on the public server within an hour or two (Often much less) of reaching the ground.

If they’re not on the public website, they’re almost certainly not on the ground yet.
  Forum: MSL · Post Preview: #240519 · Replies: 685 · Views: 498516

djellison
Posted on: Jul 25 2018, 11:25 PM


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Roughly speaking - the gravitational force between a 500kg spacecraft that's 10km above a 350m radius asteroid with a 2,000kg/m^3 density is just below a tenth of a millinewton.

Put another way - after 24 hours it will have accelerated to around 2cm/second and travelled around 900 meters.

It takes a very very short TCM indeed to zero out figures like that. You could zero it out for 10 years for less than 0.1km/sec of delta v.
  Forum: Hayabusa2 · Post Preview: #240494 · Replies: 983 · Views: 963142

djellison
Posted on: Jul 24 2018, 10:15 PM


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Good find. Really not that compelling when you see it in context.
  Forum: Past and Future · Post Preview: #240471 · Replies: 6 · Views: 21531

djellison
Posted on: Jul 22 2018, 05:25 AM


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Took me a second read thru to find the HiRISE image in question
https://hirise.lpl.arizona.edu/PSP_003894_1560

Where in that image it is, however, I have no idea.
  Forum: Past and Future · Post Preview: #240457 · Replies: 6 · Views: 21531

djellison
Posted on: Jul 17 2018, 05:13 PM


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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.
  Forum: Opportunity · Post Preview: #240361 · Replies: 410 · Views: 487226

djellison
Posted on: Jul 13 2018, 04:03 AM


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QUOTE (mcmcmc @ Jul 12 2018, 01:28 PM) *
3d printable model and stand.


Page not found on both those links.
  Forum: Hayabusa2 · Post Preview: #240287 · Replies: 983 · Views: 963142

djellison
Posted on: Jul 12 2018, 04:59 PM


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I'm not going to try and do another model ( and certainly there's not much point trying to texture it yet ) until we have better imagery.
  Forum: Hayabusa2 · Post Preview: #240281 · Replies: 983 · Views: 963142

djellison
Posted on: Jul 12 2018, 01:50 PM


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I used Agisoft Photoscan, and manually added about 4 tie points to seed to the process.
  Forum: Hayabusa2 · Post Preview: #240276 · Replies: 983 · Views: 963142

djellison
Posted on: Jul 11 2018, 11:59 PM


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Had a go at making a 3d model myself

https://sketchfab.com/models/44876e2f0d314b...a32b0472a1eddc6

  Forum: Hayabusa2 · Post Preview: #240268 · Replies: 983 · Views: 963142

djellison
Posted on: Jul 3 2018, 02:54 PM


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That's not 'climb the mountain'. That's 'get to the sulfates'

And that remains the long term goal.
  Forum: MSL · Post Preview: #240204 · Replies: 685 · Views: 498516

djellison
Posted on: Jul 2 2018, 01:31 AM


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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.
  Forum: Opportunity · Post Preview: #240177 · Replies: 410 · Views: 487226

djellison
Posted on: Jun 25 2018, 03:28 AM


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QUOTE (serpens @ Jun 24 2018, 05:13 PM) *
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.


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.
  Forum: Opportunity · Post Preview: #240059 · Replies: 410 · Views: 487226

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