2009-02-03

Spirit Sol 31

I check the Web site before going to work. It's bad news: there were no changes to the joint angles. The IDD didn't move at all.

I can't think of what I could possibly have done wrong, but it's obviously my fault -- I wrote the sequences. Still at home, I download and print out the sequences I wrote and start staring at them, trying to figure out what could possibly have gone wrong. I find nothing. It has to be something that occurs before the first attempt to move the IDD, because the joint angles didn't change. There is one unusual feature of the sequence early on, an IDD motion command that doesn't actually move anything -- by design; it's just intended to force the IDD to remember its starting position for use later in the sequence. But since it was an unusual thing to do, I confirmed it was OK with two flight software developers, plus the simulation. I don't think that's the problem, but I don't see anything else it could be, either.

Grumpy and worried, I get ready and go to work.

Where I learn, to my everlasting relief, that it's not my fault. The IDD didn't move, that's true (and it's bad news), but not because of something I did (or failed to do). The rover needs to know exactly where it is before it will move, and to do that it needs to find the sun. The sun-find failed -- we don't know why -- so the rover did the right thing in response, deciding it was in an unknown state and refusing to move. The failure of the sun-find is a puzzler, since we got back images showing that it actually took pictures of the sun. The prevailing theory is that this is connected to our flash problems -- because of the weird state the flash is in, it took too long to write the image file on-board, and this caused the sun-find to time out. Or something. I'm so relieved that it's not my fault, I don't even pay attention to the explanation.[1]

Instead I sit around chatting with the guys in the SMSA. Randy Lindemann describes a proposed late-'80s Mars mission, back when the technology wasn't good enough to build autonomy into a rover. Instead, they were going to build all of the intelligence into an orbiting Mars telescope, which would beam instructions to a surface rover with which it would stay in constant contact. The telescope would constantly scan the area around the rover -- with 10-cm resolution -- and direct its movement from orbit. Weird, wild stuff.

That breaks up just in time for the downlink assessment meeting, which doesn't have much to discuss: because the sun-find failed yesterday, we got no science done, and since the flash reformat will take all day tomorrow, they don't have much to plan. The instruments are healthy, for what that's worth, and they got the needed MEX overflight data.

They also have a complaint: not that it ended up mattering, but stuff was cut from yesterday's plan unnecessarily. The data and energy reported in SAP badly overestimated the requirements for a couple of the experiments, so they got dropped later in the planning process. There's a fix in the works, though.

Amazingly, the first third of the nominal mission is now over. Arvidson points out that this is bad news, because it means we've missed the prime driving period. Every day, we have less energy than the day before, as the sun wanders farther away from us, not to mention the problem of dust buildup. ("Time's a-runnin' and the sun's goin' and the dust's comin'," are his exact words.) Arvidson says he's working with Jake Matijevic to see how much driving we can do per sol, and he promises the results will be sobering. As a back-of-the-envelope number, it takes 80W-h to drive 40m, and we only have 150W-h available now -- a number that declines daily. Arvidson follows up his colloquial description of the problem with an equally colloquial solution: "Put it in gear and pop a wheelie and get out of here." It's fine to tell the scientists this, but what can they do about it? It's not their fault we've been stuck in one spot for almost two weeks now.

Along those lines, Diana Blaney points out that we shouldn't be too hasty to drive; we need to finish up at Adirondack first. Arvidson doesn't disagree, but he says to bear in mind that Adirondack may not be the rock that tells us whether there was water in this spot on Mars. ("Where is that rock?" someone asks. He's joking, but we'd all like to know.)

I'm off shift today, so I don't hang out for too much longer. I check out Opportunity's latest images before I leave; the best is a beautifully clear microscopic image of the soil, showing a smooth surface dusted with tiny white pebbles. Hoping to better understand the sun-find problem that cost us yesterday's science (which would have included our first use of the RAT, bringing us one important step closer to full mission success), I also read yesterday's downlink reports for Spirit. Craig Leff's report aptly quotes Robert Burns:


... In proving foresight may be in vain,
The best-laid plans of mice ["and RATs", Craig adds] and men
Gang aft agley,
An' lea'e us nought but grief an' pain;
For promis'd joy!





Courtesy NASA/JPL-Caltech. An early MI image from Opportunity.






Footnotes:

[1] It wasn't the last time I'd have this response, but I'm ashamed of it now. The sol's still lost, no matter whose fault it was, or even if it was nobody's fault. This was the wrong attitude.

4 comments:

Jet said...

Scott, I have a question concerning the solar power issues that are always mentioned in connection with Martian dust: why not simply have some sort of windshield-wiper-type blade or brush that could clean off the panel periodically?

Anonymous said...

Jet, I am not Scott but the response I've always seen is that it's weight that can be used for a scientific instrument instead.

Plus it's something extra that can break. Woe to the poor bastard whose solar panel is permanently eclipsed by the thing that's supposed to be cleaning it.

Scott Maxwell said...

@Jet You raise a good question, but "Anonymous" has it exactly right. We believed we could survive the 90-sol required mission without a wiper (or a similar system, such as a compressed-air blower), so we couldn't justify throwing off a science instrument for it.

Incidentally, there's another issue with wipers, in addition to weight and risk. The Martian dust is very fine, and also electrostatically charged, so it tends to be "sticky." If you try to wipe it off the solar panels, you end up with badly scratched solar panels, leaving you possibly worse than if you'd done nothing at all. How annoying!

Jet said...

Ah weight, our constant foe. Thanks for the insight, both of you.