Actually, Paolo, here in Minneapolis it's been significantly colder overall over the past couple of days than it is during midsummer at Meridiani. Overnight lows have been only a few degrees warmer than Martian midsummer, and daytime highs significantly colder.



-the other Doug

Exactly, Doc. There are limits to the compressibility of ice. Compression can compensate over a short term -- hundreds of years, maybe. But if this crustal spreading has been going on for millions of years, unless it's dramatically slower than it appears to be, I'd have to think that you'd quickly pass the limit at which compression would compensate for the spreading. You'd either have to be raising enormous ice mountains somewhere, or you'd have to have subduction going on somewhere. Neither of which is apparent in the imaging.

-the other Doug

You've got to wonder about the mechanism by which meteor fragments are emplaced on the Martian surface. At Meridiani, several of the meteor fragments (most specifically Bounce Rock, plus the couple of others I seem to recall) seem to just be lying free and open on the surface, with no apparent relationship to impact features (or any other features). They're not buried, and they seem not to have left indentations on the ground, so they seem not to have hit the ground very hard. They certainly look like they landed a lot more gently than, for example, the heat shield.

This would make a lot of sense if the meteor fragments we've seen have eroded out of local rockbeds, and were emplaced in more traditionally violent manners onto the surfaces that existed when they fell out of the sky. The rockbeds that built up around them have now eroded off, leaving the more erosion-resistant meteor sitting on the surface as if a god's hand had gently laid it there.

Swarms of small meteor fragments, and meteor frags which were badly shocked and thence broken up during the build-up and subsequent deflation of their entombing rockbeds, could account for some of the groups of cobbles that we see scattered around.

That doesn't mean that all meteor fragments are cobbles, or that all cobbles are meteor fragments. I'd bet more on the possibility that a majority of the cobbles may be examples of the otherwise-seemingly-absent impact melt from local impacts. You'd expect some impact melt to be tossed out along with the more intact local bedrock, and the melt might well be more erosion-resistant than the sulfur-rich bedrock (especially if it was glass-enriched). This mix of friable sulfur-rich bedrock and harder, fused impact melt would erode over time, the softer bedrock leaving behind little piles of impact melt.

That may not turn out to be true (though I am peplexed as to why we can't find much impact melt anywhere near Victoria), but it makes a certain amount of sense to me...

-the other Doug

OK, I'll admit my ignorance -- what was wrong with the idea of driving downhill and making our way around Home Plate on the ground below? As I recall, the parking spot was selected with the idea of driving down, not up, in mind.

-the other Doug

If Enceladus' crust is actively spreading, then either 1) the entire moon is expanding, or 2) it has subduction zones. Where would any of y'all think the subduction zones are located?

Also, doesn't subduction and surface spreading absolutely require a soft mantle upon which the crust floats? Where is all the heat coming from to keep Enceladus everything from molten (at the core, and by that I mean liquid water) to very elastic in the mantle?

Suppositions, anyone? (For myself, I wonder if there's any way that Enceladus could have been impacted by an extrasolar AL26 mass sometime within the last several thousand years, which could be powering a short-term period of activity within the moon...)

-the other Doug

OK -- I can accept that. I just thought I had remembered that the rover design was pretty well determined by late summer of 2005, when the skycrane maneuver testing was done that was to validate the concept and allow pallets and legged landers to finally be cast aside.

-the other Doug

What I got is the fact that the same size/mass rover was designed for either a pallet landing or a skycrane landing. Ergo, the mass of the pallet descent stage vs. the skycrane descent stage would have to be roughly similar.

-the other Doug

A landing platform for MSL would mass roughly the same as the skycrane descent stage. You bring the whole thing to zero velocity relative to the ground, so you're using about the same mass of propellants, etc. (in fact, the skycrane descent stage uses more propellants, since it has to hover and then fly a ways away to avoid dropping onto the rover). All you'd have to do to make the descent stage into a bottoms-down lander is add a solid top for the rover to sit on, and maybe some short, stubby legs (and maybe not, the "landing pallet" concept was just barely beat out by the skycrane maneuver for MSL, in which the descent stage simply plopped onto the surface, with MSL on top, without legs).

What the skycrane maneuver buys you is instant mobility. You don't have to have deployable ramps or any other means of driving the rover off of the top of its lander, the rover is plopped onto the surface on its six wheels, and can immediately drive away.

When you trade the extra fuel needed to hover and fly away from the rover for the solid deck and ramps of the pallet, you get roughly the same mass.

-the other Doug

Just to get it all somewhat straight...

The "full Moon" occurs when the Moon is 180 degrees around from the Sun in Earth's skies. That doesn't happen at sunset/moonrise at every point on Earth. In fact, the Moon is only exactly 180 degrees around from the Sun for a split-second. Of course, the *apparent* amount of the visible lunar surface that is sunlit is such that the Moon *appears* full for most everyone around the globe for 15 or so hours on either side of its exact moment of "fullness."

Which brings us to "appear." The verb doesn't just mean to become visible after not having been visible. It also is used to specify in what particular place you can see an object. For example, you often see picture captions with language like "Dione appears in the lower left portion of the image, with Saturn's cloudtops in the background." Or "The rock in question appears in the right-center portion of this image, taken on Sol 743."

When I walk outside well after sunset and see the Moon high in the sky, I can say that "the Moon appears very high, large and bright tonight" without the Moon having been invisible to everyone, everywhere up until the moment I stepped out the door...

-the other Doug

We have normality. We have normality. Anything you can't handle from this point on is your own lookout.

Now -- off to find a really *hot* cup of tea!



-the other Doug

The SLA panels were jettisoned on every lunar flight, and what's more, the entire stack was on a trajectory to miss the Moon when they were dropped. They were spring-loaded and separated at a good meter per second, so they weren't anywhere near the spacecraft when it reached the Moon... but they likely didn't impact the Moon, either. Or at least, certainly most of them missed the Moon.

Nine sets of four SLA panels, 36 in total, were let loose early on in a translunar trajectory. Some few hit the Moon, I'm sure, and some others likely ended up being swept back in by the Earth. But I'd bet several of them are still out there. And harder to find than a needle in a haystack...

-the other Doug

An infinite number of me really got that remark, and found it hilarious. Another infinite number of me just sat and scratched my head, wondering what you meant. Yet another infinite number of me never read it...



-the other Doug

I just realized I mis-stated something. At the time of ascent/descent stage separation, Snoopy was actually in an orbit of roughly 300 by 10 miles, not 70 by 10. For reasons of aligning the craft properly to simulate a Constant Delta Height rendezvous sequence after two low passes over the landing site, they had to enlarge the orbit between passes to place the LM and CSM in the proper locations.

This impacts this discussion in that a 300 by 10 mile orbit might have taken longer to decay than a 70 by 10 orbit. Depending on how the mascons affected the descent stage, the dynamic may well have raised the periselene a bit before dropping it back down again.

I do know that NASA wasn't at all concerned that this piece of space flotsam might be yet in orbit when they launched Apollo 11 into an almost identical orbit two months later, though. So, the descent stage must have been assumed to have impacted by then. Of course, with no electronic tracking (and skin tracking being nearly impossible at that distance), and with no seismometers emplaced as of yet, it would be nearly impossible to figure out where and when it actually impacted. Same with Apollo 11's ascent stage, the impact of which was never observed on the EASEP seismometer.

The impact speeds were indeed not incredibly high, especially for the orbital assets like the Apollo 10 descent stage and all of the ascent stages from the landing missions. The materials would be broken up a lot but not vaporized. Many small but recognizable pieces of terrestrial technology are scattered around the lunar surface in a variety of locations; some impact sites will likely only be found when someone on the surface runs across one of these pieces.

But truly, is it certain that artificial craters are necessarily indistinguishable from natural ones? The images I've seen from known spacecraft/booster impacts tend to have dark haloes -- at least I recall this from at least two of the S-IVB impact craters and at least one of the Ranger impacts. It was speculated at the time that this might be due to the interaction of remnant volatiles within the impactors with the lunar ejecta, an effect that was most obvious with the S-IVB impacts but still noticeable in some other impacts, including one of the Ranger impacts, if my memory isn't fooling me again...

I know dark haloes are not a definite or ubiquitous trait of spacecraft impact craters, but wouldn't a look through the existing imagery of the "target" areas in question for fresh-looking dark halo craters be something worthwhile to try?

-the other Doug

Yep -- but only Snoopy's ascent stage survives. The descent stage crashed into the Moon in May or June, 1969. (No one is sure of the exact date, but it was dropped when the LM was in a 70 by 10 mile orbit, it had to have decayed pretty quickly.)

-the other Doug

Yeah... for instance, the full image from which the detail is taken shows a similar-looking black dot several kilometers to the south of the dot in question, which looks quite similar to this purported shadow.

Of course, this image was taken at about 80,000 feet, and I have often been flying at 35,000 feet in an airliner and been able to see the shadow of the airplane on the ground, looking quite large to my eye. So, it's not intrinsically impossible. Just unlikely.

-the other Doug

Oh, agreed. And obviously, according to the formula itself, the amount of time charged for each chargeable comm pass is a maximum of 8 hours per day ("the lesser of the spacecraft’s view period, the scheduled pass duration plus calibration times, or 8 hours"). MER DTE sessions would be liable for the full cost of such a comm pass, obviously, but that's a tiny fraction of the communications with the rovers. (It's hard from the information I found to tell how much of the calibration times are required for each Mars asset pass even though your dish is already pointed at Mars; I imagine some of that calibration time is necessary each time you shift from one asset to another, but again we don't have enough operational detail to tell for sure.)

The important information missing is the prorate of relay DSN costs that are passed on to the MERs. But you're absolutely right in this case -- you wouldn't be saving any of that money, since you'd be using pretty much the same amount of DSN time whether or not the MERs are reporting data through the relays. You'd have to cancel one or more of the orbiter DSN passes per day (or simply cancel the extended missions of MODY or MRO entirely) in order to save any money from the DSN side of things, and since that would, in effect, be canceling the extended missions of the orbiters *and* the rovers, I don't see that happening. That's too much loss of bang per buck saved. And I, for one, would be pretty durned uncomfortable with a decision to put one or both orbital assets into "cold storage" for several years just to save the DSN charges.

So, as you've noted, it's unlikely that NASA will cancel or curtail the extended missions of MER-A, MER-B, MODY or MRO to find the extra money needed for MSL. I think a delay of MAVEN is more likely, but it's hard to say. We really just need to see what the numbers come out like over the next several months; speculation at this point as to what might be cut or delayed isn't very useful, since we don't have enough information yet to make intelligent guesses.

-the other Doug

Here is a detail of the image Kenny is talking about:



There is indeed a black dot in a position where you would expect the CSM shadow to be cast. I've often wondered, as well, if this is indeed a shadow. Sure looks like one.

-the other Doug

You betcha!


-the other Doug

I will point out that Endurance is characterized by incipient "bay" formation that looks for all the world as if the crater wall had been undercut by erosion (likely aeolian) and the upper surface had collapsed in a sheet into the now-enlarged crater. This fits is rather well with the description of Victoria's bay formation.

-the other Doug

I just went looking for a rate table of DSN fees, and found the following item in a .pdf file ( http://deepspace.jpl.nasa.gov/advmiss/docs...MEX_AO_2007.pdf ) that describes, among other things, the services and rates for the DSN. There was no actual rate chart; there was a formula for calculating what is called the Aperture Fee:

AF = RB [AW (0.9 + FC / 10)]
where:
AF = weighted Aperture Fee per hour of use.
RB = contact dependent hourly rate, adjusted annually ($1057/hr. for FY08).
AW = aperture weighting:
= 0.80 for 34-meter High-Speed Beam Waveguide (HSB) stations.
= 1.00 for all other 34-meter stations (i.e., 34 BWG and 34 HEF).
= 4.00 for 70-meter stations.
FC = number of station contacts, (contacts per calendar week).

The weighting factor seems to be a multiplier based on a function of aperture size (34m vs. 70m) and number of weekly contacts. An accompanying chart shows the weighting factor for a 70m dish used 28 times per week (i.e., 4 times per day), for example, is 15. The same dish used 14 times a week (twice a day) has a weighting multiplier of a little more than 9. The same numbers of weekly contacts using a 34m dish give you weighting mutiplier of 9 for 28 contacts and 2.5 for 14 contacts.

So, a probe that requires four comm passes a day using a 70m dish looks like it would cost something on the order of $15,865 per hour. That's 28 times $15,865 per week, times 52 per year. That would be $444,220 per month, and $23,990,440 per year. That's based on a reading of the chart, not by plugging numbers into the above formula.

A twice-a-day contact through a 70m dish, again based on the chart, would cost $9,500 or so per comm pass, times 14 passes per week ($133,000), for an annual cost of $6,916,000.

And that all assumes that you're only paying for a single hour of DSN time per pass. In actuality, with calibration times, you're likely going to have pay for a minimum of two hours' worth per pass, possibly more (*). So you might have to double those numbers.

However you slice it up between the various data sources coming through on a MODY or MRO comm pass, total DSN costs add up to millions of dollars a year. So I still think one of the biggest chunks (if not the biggest) of mission operations, extended or otherwise, is DSN time.

-the other Doug

* -- the assumption that each comm pass lasts *at least* an hour is built into the rate structure, I think. At least it says in there: "A station contact may be any length but is defined as the lesser of the spacecraft’s view period, the scheduled pass duration plus calibration times, or 8 hours. For a standard pass, a 45-minute set-up and a 15-minute tear-down time must be added to each scheduled pass to obtain the station contact time (other calibration times apply to Beacon Monitoring and Delta-DOR passes). Note that scheduled pass-lengths should be integer multiples of 1-hour." So even if your comm pass only lasts 12 minutes, it doesn't look like you get the benefit of a pro-rate... dvd

Speaking of which -- I once spent a week in Buenos Aires. It was late April, so the length of day at that latitude in Argentina was similar to that in North America in late October, i.e., it got dark pretty early in the evening.

So I enjoyed several strolls down the streets under dark skies. Now, it's a big city, with lots of light pollution, but the Moon shone through quite nicely.

And, from my lifetime-of-experence, it was upside-down.

You spend eight hours on an airplane, and you don't feel like you've gone all that far... until you look up in the sky, and the Moon is upside-down. Then you get this odd feeling, deep in your gut, that you're really a long way from home...

-the other Doug

That's actually triscadecaphobia (sp?). Tridecaphobia would be the fear of the number 30.



-the other Doug

I agree, the design of the Beagle package is ingenious. But so was Phoenix's, and it did not completely succeed. I think perhaps *any* design that requires transport of samples into a test chamber of any kind might need to be revisited, just in case.

-the other Doug

At the risk of continuing this divergence in the thread, I'll point out that extended mission ops are the cheapest portion of a planetary mission. The biggest costs are for the DSN time to get the data back to Earth. The remaining costs are mostly for the manpower -- the salaries and benefits of the teams working the missions. And in the case of the MERs, many of those are only working part-time on Oppy and Spirit, spending much of their time on MSL and other projects, as well. (Amortized costs of things like the computers used by the MER teams, the office space they take up, etc., are really pretty irrelevant, after all; it's not like they buy new equipment and rent new facilities for each mission extension. Those capital investments have long since been paid for and depreciated in the bookkeeping.)

Extended ops are the biggest "bang for the buck" you can get out of these things, and NASA has been pretty good about avoiding the penny-wise, pound-foolish approach of cutting $10 million from extended ops to try and make up a $400 million shortfall elsewhere. They're more likely to delay or cancel whole programs before they start racking up their major design and construction costs than they are to cut off assets already in place.

That said, there may be pressure to cut back on Spirit operations if she continues to be power-starved and barely mobile. I don't foresee a project shutdown for Spirit, but you have to admit, we're not getting a huge amount of science data from her recently. Then again, we're not spending nearly as much time (and therefore money) on her as we are on Oppy, either.

-the other Doug

I'll weigh in on this one. A few do's and dont's for you, here -- mostly dont's, I'm afraid. These are sort of general guidelines, not comments on your story, sorry to say.

- Don't just film it in the desert and then tint everything red. That's really hokey and looks terrible.

- Don't have lots of free pieces of fabric flapping in the breeze. Martian winds are normally rather benign, and as thin as the air is, it takes a really good gust to make something like a flag or a tent whip around noticeably. Very small threads and other very light things (like the wind telltale on Phoenix) move around a good deal, but, for example, instead of showing a flag rippling in the wind, you'd show a flag twitching a bit around the edges and threads hanging off the flag moving more quickly.

- Do try and at least suggest the .38 Earth gravity. Things fall more slowly than they do on Earth, but not as slowly as they do on the Moon. And try to avoid just having people move normally and suggest low gravity by slowing down the film. The juxtaposition of people moving at normal speed and things falling slowly is important in suggesting low gravity.

- Don't show big fluffy cumulous clouds in the sky. Martian clouds tend to resemble cirrus clouds more than anything else, though they're not nearly as far above the ground as cirrus clouds are here on Earth. Think light and feathery.

- Make the sky pinkish-orangish, and make the brightening of the sky near the horizon more pronounced than you would see on Earth. The sky doesn't get tremendously dark at zenith, but especially during spring and summer at low latitudes, there's a lot more dust entrained in the air in the first couple thousand feet above the ground than there is above that. Looking horizontally towards the horizon, you're looking through more dust, which backscatters the light and makes the sky near the horizon look brighter.

- The Sun looks pretty white up high in the sky, with a slightly reddish tinge. It looks more bluish, and the sky around the Sun looks bluish, at sunrise and sunset. It's the opposite of what you see on Earth, when the sky is reddish at sunrise and sunset and blue when the Sun is high in the sky.

- While this isn't ubiquitous, a lot of the soils on Mars have a somewhat hardened "armoring" layer on the very top surface. It's been called a duricrust, and while it's present in a lot of places, it's not seen on every single example of Martian soil. When it does occur, it's very thin, but it can push away from the underlying soil in somewhat choesive, through crumbley, sheets. Think of snow drifts after a day when it gets up to about 38 degrees Fahrenheit (or 3 or so degrees Celsius), where the very upper layer of snow has slightly melted and re-frozen as the day grew cooler.

- Don't forget that it's very cold on Mars. Even in those places where the daytime high temperatures reach up to 60 or 70 degrees F, it can get down well below zero F at night, even in the summer. And the warmest temperatures usually only occur in the first foot or two over the ground. The air thins out rapidly and it cools down rapidly as you disengage from the ground warming effect -- the air is so thin that mixing doesn't occur as efficiently as it does on Earth. In short, standing on Mars your feet can be comfortable while your head is quite chilly. And at night, no matter where you are, it's *really* cold.

- Martian dust devils are not tornados. They can pick up dust and maybe sand-sized grains, but most aren't powerful enough to pick up something the size of a pebble. They seem to clean dust *off* of pebbles, in fact. The blow away dust -- not houses. They generally pose very little physical threat to humans or their equipment. They look dramatic, but they're mostly harmless.

- Lots of places on Mars are very rocky, but some aren't nearly as rocky as others. The rockiest terrain we've ever landed on was at the Viking 2 landing site, followed by the Pathfinder site and then the Viking 1 site. It's still rocky at the Spirit site, though not as much so as at the previous three. And there are very, very few rocks littering the surface where Opportunity landed, or where Phoenix landed (though the polar terrain at the Phoenix site does have more surface rocks than Oppy's Meridiani site, which has the fewest surface rocks of anywhere we've seen from the surface). In actuality, a lot of Mars is covered with ancient sand dunes and dust ripples.

- There are a lot of craters on Mars, but not nearly as many per acre (or hectare) as on the Moon. Most of the Moon's surface is at crater saturation on most every scale -- every new crater obliterates an older one, so additional cratering doesn't much increase the total count. Mars isn't like that, and has relatively few small craters of less than 100 meters or so in diameter. That's because Mars' thin atmosphere burns up the smaller impactors, removing much of the small-to-tiny end of the cratering range.

- Liquid water can only exist on the surface of Mars in a very small number of locations, and even then only during the warmest parts of the day. Most of Mars' surface is below the "triple point" of pressure and temperature that allows water to exist. Ice doesn't melt most places on Mars, it mostly sublimates directly into vapor. The places where water could exist for brief periods while on the surface tend to be very low areas where the air pressure is highest, such as on the floor of the giant impact basin Hellas.

I imagine that's enough for now. Hopefully at least some of these items are useful to your endeavour... *grin*...

-the other Doug