Tuesday, July 31, 2007

more web diversions

Click to view my Personality Profile page
No matter how many different tests I take, how many questions they have, or what the questions are, I always turn out INTJ. Sigh.

Monday, July 30, 2007

Dark days

Despite my asking the HiRISE team to find and kill an apparent background process called HiOPACITY (heh, geek humor), the dust storms continue to give the rovers a tought time. Spirit experienced a record high tau of 4.738 on Sol 1265 with a corresponding solar array energy of 261 watt-hours. The most recent tau for Spirit on Sol 1269 was 4.322 with a solar array energy of 274 watt-hours.

Spirit still remains power positive, but things are tougher for Opportunity on the other side of the planet. Because we have been saving energy on Opportunity by not making science observations, the rover isn't generating waste heat. The waste heat normally goes into heating up the electronics box to keep the electronics warm. No activities means no waste heat means the temperature is dropping in the electronics box, about 1 degree C per sol. At a certain point, the rover will automatically turn on emergency heaters for the electronics, but they suck up a lot of power - power that Opportunity doesn't have right now. So we're now trying to strike a balance by having the rover stay on longer each sol to expend more heat, raising the electronics temperatures and avoiding the survival heater turn on. But the price is that the rover will now start draining power and risks tripping a low-power fault sometime during this plan.

When a low-power fault is tripped, the rover's systems take the batteries off-line putting the rover to sleep and then checking each sol to see if there is sufficient available energy to wake up and perform communications. If there is not sufficient power, Opportunity will stay asleep. Depending on the weather conditions Opportunity could stay asleep for days, weeks or even months, all the while trying to charge her batteries with whatever available sunlight there might be. At this point the ground team will be unable to help and Opportunity would be completely on her own. When skies clear Opportunity would wake up and service her normal communication passes (if within about 5 weeks) or listen each day to see if we are there trying to talk to her (if beyond about 5 weeks).

Oooooh, hang on little rover!!!!!!

Saturday, July 14, 2007

Dust bedevils Mars

I've been having a great couple of weeks with a MER team meeting and the 7th International Conference on Mars (ok, it was *about* Mars, not *on* Mars, sadly). A MER team meeting is a really fun thing to attend. First of all, the scientific team is pretty large, when you tally up the principal investigators, their postdocs and students, and technical staff support. We're spread out over the US, Canada, Germany, Denmark, and France, so we don't see each other much except for conferences. So a MER team meeting gives us all the chance to catch up on what we're all doing science-wise. Team members give talk about what they are thinking about these data on those rocks, or the results from those soil experiments we did, etc. and then everyone gets to ask whatever zany questions they think of. Unlike at a larger conference, people don't feel as self-conscious about thinking out loud, and it's a wonderful sounding board to toss ideas around and have the whole team's expertise brought to bear. Not surprisingly, the hot topic at this meeting were the high-silica story emerging near Home Plate. Do the high-Si rocks occur in conjunction with the high-sulfur soils? Are they remnants of fumaroles or hot springs? How could volcanic activity nearby at Home Plate have contributed? When did all these form? Could we be looking at the most habitable place on Mars we've ever seen? Fun stuff!

While the science team was debating, the rovers weren't doing very much. For the last couple of weeks, there have been some massive dust storms on Mars, accompanied by some alarmist headlines, like "Martian dust storm could destroy rovers" and "Mars dust storms suck life out of rovers". Yes, it's scary for our little dudes, but they're not dead yet. Check out this JPL video discussing the storms and the mission.

Dust storms on Mars are a common thing. They actually appear in cycles, every few years there seems to be a period of increased dust storm activity, and sometimes the entire planet can be enveloped by swirling dust. The storms start when the ground and atmosphere heat up during the change of seasons. This thermal energy causes winds to blow, and the wind lofts the fine Martian dust. The individual storms can be long-lived, similar to hurricanes on Earth, where an individual storm can last for weeks.

Underneath the storm, sunlight is blocked from entering by the opaque dust. In the image above, you can see the sky over Opportunity get darker and darker. This is a problem for the rovers, because they generate their own power using solar panels. Fully clean solar panels on each rover can generate about 800 Watt-hours per sol. That's enough to light one 100-watt light bulb for 8 hours. That is also enough to operate all our tiny instruments that look at the sky and the ground, drill into rocks, and measure elements and minerals. The dust storms have reduced the amount of sunlight getting to the ground to something like 1% of normal, so that diminishes the rovers' ability to generate energy for themselves.

In terms of science, it's perfectly ok for us to give the little dudes a break and tell them just to sit tight until the storms dissipate. Of course, we are anxious, with Opportunity perched right on the edge of Victoria Crater and Spirit just about to drive up onto Home Plate, but we want these vehicles to continue to work so we don't have to push them. The real issue is how much power does it take to stay alive? The Martian surface is really really cold, which is really really bad for electronic parts. The fear is that if the rovers don't have enough power to keep their heaters on, the electronics will freeze and break, and then it's anyone's guess whether we can still operate them. Fortunately, for Opportunity, which is experiencing the worst of it, it is the height of summer (warm), near the equator (warm), and under an insulating dust blanket (warm), so the amount of power it needs to stay warm is significantly less than it might be at other times. The engineering and science teams worked hard last week to make a low-power plan for Opportunity, where it just tries to keep itself warm, and we had telemetry today that indicates it is working well. Unfortunately, we'll only hear from the rover every 3 days or so, so that keeps everyone on edge.

But other Mars missions are on the case. You can see images of the dust cover and storm activity with THEMIS and MARCI. Also some people are actually interested in dust storms on Mars and for them they've got their instruments going full blast. We're just keeping our fingers crossed for the weather and working hard on the ground to keep this mission going a little while longer.