They showed an animation of the cleaning event. Immediately after showing the real images of DDs tracking across the plain, they showed an animation that depicted the dust on Spirit being lifted off of it in a vortex-shaped wind. My feeling was that Maas was trying to make the movement of the dust raised off Spirit look like the movement of dust seen at the base of the DDs just displayed.

It wasn't a definitive statement that a DD cleaned Spirit, but it was highly suggestive of it.

-the other Doug

Excellent, excellent piece. Brought us fully up to date with the entire mission. The biggest lack in existing documentaries on the MERs was that they focused on the landing and the primary mission, and in the case of the MERs, there has been so much more.

Of course, it *did* sort of violate the well-known UMSF axiom that dust devils don't clean rovers... I guess it's just too prosaic to talk about regular old wind gusts. There's a lot more drama in a dust devil.

But the CGI work by Maas is just outstanding. I thought I would weep when the point of view swiveled around Spirit sitting atop Husband Hill and the Inner Valley laid itself out, with Home Plate nestled at its far end. It was in all ways a visually perfect representation of the scene.

-the other Doug

You know, that bring up a good semantic nit -- is it only "photographic" if it involves film? Is there another term if the light is recorded via CCDs and not film? Electronic light capture vs. photographic light capture vs. biologic (i.e., eyeball) light capture? I guess in that case, "visual" contact would only apply to the third of those options.

I find it interesting that by 2061 it's possible that Halley might not again be lost -- that we may have instruments sensitive enough to maintain electronic (if not "visual") contact all the way out to its next aphelion and back.

-the other Doug

I have a feeling that the Wikipedia reference is for the first eyeball-to-eyepiece *visual* (not photographic) recovery of Halley prior to its 1986 perihelion, and that Mike is referring to the first *photographic* recovery of the comet.

-the other Doug

Really? We need to go fix Wikipedia, then...



This was footnoted:



-the other Doug

Thanks, Doug. I remembered it was in the single thousands.

The battery system for the MERs reminds me of the axiom that you always prepare to fight the last war, not the next one. Everything on Mars Pathfinder was working pretty well, when the battery system started having problems. It died from battery failure before dust accumulation could kill it. I can just imagine the MER designers, with far better battery technology available, said to themselves "these things won't die because their batteries failed!"

-the other Doug

Yeah, very true. Well, last time Halley was spotted telescopically just more than a year before its perihelion. It had a rather poor geometry for Earth-based observation last time, but that was during perihelion. I really don't know how the far-approach geometry compares in 2061 to what it was in 1986.

BTW, as per wiki, next perihelion is July 28, 2061. No info readily available on the approach or viewing geometry, though.

-the other Doug

Isn't Halley supposed to return in 2061? It's period is some fraction greater than 75 years, right? And it last appeared in 1986, the time before that it was here in 1910, and the time before that in 1835. It's either slated for late '61 or early '62, from that reckoning. At which time I would be somewhere around 106 years old. YMMV.

Fairly easy to predict in rough terms, though, eh?

-the other Doug

Hmmmm.. my admittedly imperfect memory does recall something along those lines. Something about 2,000 cycles being what the MER batteries were rated for. As I recall, it was discussed in the same context as the death of Viking 1, where the batteries were actually deteriorating, their shortening charging cycles were creating a low-energy state, and the attempt to rework the charging cycles via a software update resulted in overwriting antenna pointing information in its limited memory and thus broke off its ability to communicate.

Anyone else remember that discussion? I'm positive it had to be here on this forum somewhere...

-the other Doug

I stand corrected!



-the other Doug

I'm not trying to belabor a point, here, but it's the "20x" statement that's specious. The MERs have *NOT* performed 20x longer than they were designed to perform. They have performed 20X longer than the primary mission, but they were designed to perform for far longer than their primary mission. Again according to Steve Squyres, when his team figured out how to get the extra solar cell strings onto the rovers, he knew he had a pair of vehicles designed to last not just for 90 sols, but until dust accumulation killed them -- which they thought would be at least 200 sols, and with some luck perhaps as much as 400 sols.

They were *designed* to last far longer than 90 sols. To say that they have outperformed their design lifetimes is valid -- to say that they have outperformed their design lifetimes by a factor of 20 is specious. The factor that they have outperformed the lifetimes *actually* envisioned by their creators is more like 4x to 8x. Still impressive -- but not 20x.

That's all I'm saying...

-the other Doug

EDIT: It also just occurred to me that you also have to ask at what point does reduced functionality cause you to say that a vehicle has stopped performing, at least in a given area? Neither MER is currently operating up to spec -- Spirit is so power-starved she's a barely-active rover, and has had no RATting capability for quite some time now. Neither mini-TES is working at the moment, though my understanding is that Oppy's may be revived at some point. The radioactive sources for the APXS and Mossbauer have faded so far back that integrations that used to take a few hours would now take many, many sols, and the quality of the results goes downhill as time goes on. Has a MER that is at, say, 50% of its design operational capability actually still outperforming its design lifetime? How about 20% Or less? Do we consider a MER that can take a single image a month and can no longer move a still-operational MER? Just wondering... dvd

I will disagree slightly with Doug here on his elevation of the MERs because they've outperformed their design criteria.

For one thing, the MERs were *not* designed to complete the 90-day primary mission. They were designed to last far longer, per Steve Squyres in his memoirs. According to the best thinking and best knowledge of Martian conditions (based on some hard data from other landers), the MERs were designed to operate until the dust accumulation on the solar panels drove power levels below a sustainable level, and that period of time was reliably determined to be somewhere between 200 and 400 sols. According to everything we knew about Mars, there should have been no way for the MERs to last longer than that -- surviving a Martian winter, for example, was considered an impossible task, preflight.

We found out about cleaning events when the girls were getting into some pretty power-strapped states, though to their credit they had lasted longer at that point than was predicted. The periodic cleaning of the solar panels was an unforeseen boon. The MERs would never have lasted as long as they have had not Mars provided them with an unpredicted gift of cleaning winds.

So, the extreme longevity of the MERs is more due to serendipity than to their admittedly excellent designs.

And, to be fair, because they have lived far longer than their creators ever intended, they're both showing signs of old age. Instead of dying gracefully under predicted dust accumulation conditions, they are developing bum wheels, arthritic joints, blurred vision and low-energy listlessness. They are more like denizens of a senior citizen's home than noble explorers by now... which makes every byte of data we get back from them that much more sweet.

I'm impressed and pleased by how much information our intrepid rovers have amassed. But I don't credit the engineers who built them, or even the rovers themselves, for their great longevity. I view *that* as a series of gifts from the gods.

-the other Doug

So, Rui -- "The crater's alive with the sound of music"?

Or "How do you stop a rover like our Oppy?"

Or even "Carbonates, carbonates, our instruments cannot see them..."



-the other Doug

It would be easier to be equanimous about TEGA if it weren't for the development history of the instrument. I seem to recall that the sample delivery system went through several design iterations.

First, IIRC, there was just an open path for soil to travel to the ovens. Then the concern was raised that larger particles might block the soil chutes, so the screens were added to block all but the particles of appropriate size to successfully reach the ovens. Then it was determined that the desired soil grains wouldn't just fall through the screen, the larger grains would block up the screens, so the vibration motors were added. Then someone noticed that the ice that could be scraped by the rim of the RA scoop wouldn't pass through the screens, so the rasp was added to the scoop to break ice down to particle sizes small enough to pass through the screens (which also served to increase the surface area of the ice enough that it measurably increased the sublimation rate, making it that much more difficult to get it from the ground into the ovens before it all sublimated away).

See where I'm headed with this? The design concept itself started out rather short of being functional, even based on estimates of soil properties that we could easily determine pre-flight, and the instrument design was tweaked several times to try and make it work. Rather than starting with an instrument that was designed from inception to be able to handle everything we could imagine with a good amount of performance margin, we started with an instrument that failed to handle anticipated conditions and was tweaked several times to, with its best possible operation, push performance so that it could achieve its desired function -- with very little margin for error or unanticipated soil conditions.

I'm not finding fault here so much as I'm pointing out that, with extremely tight mass and monetary budgets, it is absolutely essential that you design your systems from the get-go with as much margin for error as possible if you're going to assure successful operation. If the last phases of design and development are spent pushing the system just far enough that its best possible operation just barely covers the requirements for success, you're courting failure. I mean, just look at the number of single-point-failure systems (particularly pyro events) that could have transformed either or both MERs from the incredible successes they have been into short-lived, frustratingly unproductive stationary lander missions. That's a good example of a design that required best operation for success -- and it was the element of the mission that probably caused the greatest intake of antacids amongst the MER team members prior to having all 12 wheels in the dirt.

-the other Doug

Hey, Nick -- tried to leave you a PM and your mailbox is full!

Here's a brief precis of what I wrote (and will send to you once you clean out your mailbox a bit):

Good luck! I'm sure everything will turn out fine!

And avoid watching really funny things for the first week or so after the surgery. You don't want to indulge in a lot of energetic laughter. Trust me, I know...

-the other Doug

As someone who survived hernia repair 20 years ago, I can tell you that it's not all that uncomfortable -- they work through a relatively small incision, and depending on the location of the hernia, the healing repair is often (and was for me) less painful than the hernia itself is.

Have you heard if the surgery has been moved up? I'm sure I'm not the only one who wants to know when you're going under the old knife.

I've had two full-on operations in my adult life, where I was put completely out with drugs. One was the hernia repair 20 years ago, the other was the emergency removal of my appendix about five years ago. My one best memory from both is the completely relaxed and relief-drenched feeling of waking up in the recovery room, in no pain and with a drug-supplied sense of self-satisfaction at surviving the pain and coming out the other side.

Vaya con dios, my friend...

-the other Doug

What really causes me a wonderment is that these same two images, the electron miscroscope image of the terrestral soil and the AFM image of Martian soil, was used at a press conference back in September to show that *carbonates* were seen in Martian soil.

Is the phyllosilicate composed of carbonate minerals? Or did I hear something entirely wrong?

-the other Doug

I almost decided it was a chance alignment of craters, too -- but my eye keeps going back to the dark-albedo arcs to the north and south. Those seem to be independent of the craters in the area, and their arc shapes define a big circular feature. Now, it seems to me that a big circular feature like that would have to be either the degraded remnants of a huge shield volcano or the degraded remnants of a basin. Since we've seen a lot of the latter and no other indications of the former, I sort of get led down the garden path to Skinakas...

-the other Doug

Hmmm... no Skinakas? I see arc-shaped lobes of dark material, in some areas bounded by what appear to be old, degraded arcs of rimwall massif. I'm not a consummate image manipulator, but look within the crudely drawn red circle below:



I really do see a structure there that seems to be roughly concentric with that very roughly drawn red circle. Very degraded, yes -- the southern rim seems to have been obliterated by subsequent large craters. But this might be a basin, after all...

-the other Doug

Well, see, that's one of the things I'm talking about. Does the observed amount of carbonate in this soil, if applied globally, require massive ocean beds of limestone as the source of the now-pulverized carbonate remnants? What are the upper and lower limits of globally distributed soil carbonates of the range that absolutely requires such a large source? How many locations do we have to visit and test to determine just how ubiquitous this admixture of carbonates in the soil really is?

Also... I know there are people who are applying the observation of perchlorates in the Phoenix soils to the life detection experiments on both Viking landers. If you're going to speculate that the Phoenix soils are ubiquitous in composition to the extent of the distribution of perchlorates, you sort of have to admit the possibility that carbonates are similarly ubiquitous.

I guess one of the things I'm thinking is that this line of inquiry leads to definition of the type of sensors you need to deploy, and the results you would expect to see from them, so that you can begin to actually establish useful estimate ranges for the total amount of carbonates mixed into the soils.

-the other Doug

Well, we've known for a century that the "north polar hood" of clouds and haze forms every Martian spring and fall. But I'll tell you, I'm *really* pumped to see it floating overhead like the leaden lid of an overcast day. That really makes Mars a familiar-looking place, to me.

I just worry a bit about how much energy-delivering sunlight those clouds are blocking.

-the other Doug

We don't see this admixture of carbonates from orbit in this area. That tells me that mixing the carbonates into the regolith at this kind of level (five to six percent) effectively hides it from orbital sensing. We needed something like TEGA and the AFM, working together, to make a positive identification of carbonates in this soil. So, that answers why we don't see it elsewhere -- it can't be seen easily from orbit, and nowhere else on Mars have we landed the kind of instruments that can actually detect this level of finely ground carbonate "flakes" in the soil.

So, indeed, it's possible that all of the soils on Mars contain a similar amount of carbonate material. We simply don't have the ability to detect it with the instruments currently deployed.

On the question of how representative this soil is, and whether or not local impact events have controlled its composition, there are a lot of ways to go with that. For one thing, Mars has for some time been spoken of as having a "ubiquitous dust layer" that is pretty much homogenous in composition and character everywhere on the planet, spread over the top of every landform by the global air circulation. It's very difficult to separate the soil components at any given location that are primarily derived locally, and the components that have been blown in on the wind.

Also, the polar regions build up layer after layer of accreted dust every year; Phoenix is only a few hundred kilometers from places where alternating layers of water ice and dust are being laid down, year after Martian year. We don't have a theory that even begins to address how long these polar soils at the Phoenix site have been in situ (though the lack of smaller impact craters hints that this terrain is being renewed pretty regularly). And if these soils are being actively renewed, how much of the material we see in place right now can have been locally derived?

There are a lot of questions to answer. I think it shows that my original set of four questions has to have been a pretty good starter set, since even setting limits on the estimate ranges seems to be bringing up other really good questions.

-the other Doug

Um, yeah.... Miranda, that's the ticket...



the other Doug

If you have a reliable committment to fly a rover mission every 'n' years, it does make sense to design a standard rover "bus" that can be mass-produced.

Things that can easily be standardized and identical on any rover mission you'll want to fly over the next 20 years would include:

- suspension, wheels, motors, and the standardized data connections for the engineering functions of steering, moving the wheels, etc.

- power generation and distribution.

- descent stage / EDL technology.

- standardized data paths to all engineering controls.

This gives you a rover with (after MSL flies) a proven EDL architecture, a demonstrated ability to deliver and provide power to a given instrument suite, and a design lifetime, range and landing site accessibility around which individual missions can be structured.

Every PI bidding for the next rover mission would simply need to design an instrument suite that connects into the existing power supply and that is capable of operating the standardized engineering controls used to drive and manage the rover. Your computer power and control architecture, which would be part of each individual mission proposal, can be upgraded on every mission to keep up with current technology.

So, for example, if the MSL team had been given the task of creating a decent and well-defined hardware interface between the science/control functions and the main engineering functions, they could have built a dozen of the standardized pieces in about the same amount of time it's taken to build one.

But if you're going to spend the money to build all that hardware, you have to be sure it's going to work the way it's designed, and you have to be sure you'll have the money to fly the follow-on missions. Make no mistake, designing the rovers the way I describe *would* be more expensive than it has been to build a single MSL, we might have spent more than $2 billion by now, with more to come. The only way to justify the extra expense is if you know you'll be able to amortize these costs over a series of missions. Without the firm committment to fly as many missions as the number of rovers you build, it gets really hard to justify the expense.

-the other Doug

OK -- there are a few reasons why, at the end of a spacecraft's mission, you would want to shut it down and turn off its systems, including its radio transmitter/receiver.

It's true that funding only really pays for the ground support of a mission. Extended missions are funded to pay for the DSN time it takes to communicate with the spacecraft, and to pay the people tending the spacecraft, both in an engineering and in a scientific sense.

Turning off the spacecraft may just be a formality on a vehicle that is nearly out of RCS fuel, for example, or a vehicle that is about to go into a power-negative state for longer than it can ever be expected to recover from. Each of these things happens with fair frequency.

Another reason to turn off a spacecraft is to shut down any further requests for an extended mission. On a political level, someone in management somewhere may be sick to death of seeing extension after extension to a given mission drain funds off from projects that manager is more interested (or invested) in. A final directive to a final mission extension is often "shut down the spacecraft in such a way that it cannot be revived," or words to that effect. It's a way of stating with certainty that *no* further extensions will be allowed.

And, if you have no further interest in using the spacecraft, there is a legal principle that suggests you want to deny that resource to anyone who might want to use it for purposes of which our country may not approve. Now, I grant you, there is very little one could do with a 30-year-old probe that would violate America's interests... but, as with a lot of legal principles, it looks at low-likelihood events with very large consequences and decides what actual preventive measures are warranted. In some cases, you want to shut down your spacecraft at the end of their missions just to make sure no one else tries to use them.

-the other Doug