2009-03-24

Spirit Sol 79

In my copious free time, I've been hacking on RoSE to add features that they'll need for the extended mission. So far, there hasn't been a delivery date, so I've just been working on the changes when I can. Today a delivery date crops up. They want to install it Monday.

That means I'll need every spare minute to finish the work. So I don't have time to check out an alarming observation about the failed Mazatzal drive. Mark Maimone points out that the tracks show that we passed only about 60cm from a rock called "Skull," much closer than we should have. The planned drive had about 1.5 to 2m of clearance. Skull was a large rock; if it had been a little taller, this problem might have damaged the solar panels. The positive spin on that, I guess, is that things could have been worse.

I do take time to go to the downlink assessment meeting, though. The coolest part of that is a "show and tell" moment: one of the RAT guys passes around a prototype of the RAT. It's cool to be able to hold it in my hand, press the contact switches against my palm to get a genuine feel for the instrument.

I also go to the post-SOWG science talks. Ben Clark tells us about "The Universal Soil of Mars." The soils and rocks have most elements the same; only sulfur, chlorine, and maybe potassium differ. Adirondack and Humphrey are made of virtually identical material. In order to tell whether this is only a surface phenomenon, he argues for a deep RAT grind. It might also help to do a progressive brushing: do a light brush, measure the spot afterward, then brush a little more and measure again, and so on, to see how the results change as the dust layer thins and eventually is removed entirely.

The really interesting presentation is Geoffrey Landis's exploration of the "Proposed Spirit Electrostatic Discharge Campaign." There's a lot of electrostatic charging on Mars, which comes from the sand grains being rubbed together by wind (similar to rubbing a balloon) and from the solar UV. Some of the dust adherence to rocks may be a result of this electrostatic charging.

However, because the air pressure is so low, the fields will tend to discharge easily. The ever-present dust devils, for instance, likely have strong electrostatic fields and may discharge them continuously, much as happens in tornadoes on Earth. Similarly, winds blowing into Gusev from the Ma'adim may stir the sand enough to cause electrostatic discharges. This stirring would happen at night, as katabatic winds (caused by nighttime air cooling) come whistling down the Ma'adim river valley. He suggests that we try waking up at night and looking for the glow.

It's even possible, he says, that the RAT brush would produce a friction charge. If this is permitted, we could try running the RAT brush at night and watching for discharges into the soil. Even the rover's own motion may charge the dust, simply by compressing it, though it's not clear to me how we'd test that.

Electrostatic buildup on Mars is not news. The rovers have electrostatic discharge needles for precisely that reason. (He shows a picture of the rovers during assembly, when these needles had an attached tag: "F#@!ing Sharp Hardware -- Keep Hands Out!")

Seeking and measuring the electrostatic discharges, he concludes, might help with future mission planning. There might also be a good science reason: electrostatic forces may contribute to weathering; if we measure them, we'll know more than we know now.

The science plan for tomorrow has to be radically curtailed late in the process. It turns out we have significantly less energy than predicted, and they need to conserve power for the RAT. Jeff Norris gets visibly stressed out and depressed as he cuts more and more science observations in order to get energy usage down far enough. I know he doesn't look forward to reporting what didn't make it into the plan. At one point, when he's waiting for a remodel to complete, I lay down a challenge.

"I dare you, after you list the things that didn't make it in, to say: 'But I do have some good news ... I just saved a ton of money by switching my auto insurance to GEICO.'"

This gets a big laugh from him. "You can't just dare someone to do something like that, though," he says. "You have to provide some kind of reward."

"Dude, the reward is to have done it!"

He laughs again. But when the time comes, he doesn't say it.

4 comments:

Dave said...

"In my copious free time, I've been hacking on RoSE to add features that they'll need for the extended mission."

At this point, were you assuming that you wouldn't be a part of the extended mission? It was only 10 or so sols away...or am I reading too much into that.

Anonymous said...

In the interests of posterity and extranational or extraplanetary readers it might be good to note that the GEICO references are to a television ad campaign that (I hope) had just started around the time the MERs landed. The schtick was to give someone horrible news, then say the good news is that (the person giving the news) saved money on their car insurance.

Ed said...

Perhaps "But I do have some good news ... I just saved a ton of money by switching our rover insurance to GEICO."

You weren't driving that thing around without insurance were you? What if you'd run over some innocent Martian and they'd sued?

Anonymous said...

On the basis that you cannot switch from one thing to another without first having something to switch from - it is obvious he had insurance! Doh