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Crash Course in Safely Crashing on Mars
An anonymous reader writes "NASA described today how they
prepared for the twin air-bag crash landings on Mars. The sites are Gusev Crater on January 4th and Terra Meridiani on January 25th. The golfcart-sized rovers have double-lined bladders, that must protect against: the equivalent of a forty mile-per-hour crash, compression against a surface of unknown sharpness, impacts repeated in rapid succession up to sixteen times, and the big bounce covering more than half-a-mile. Airbag landings are considered easier than retro-rocket or soft landings."
Uh... you've got your units a bit off. 40 is "miles/hour", that g is "meters/second^2" (which is incorrect for Mars), and you somehow wind up with units of feet when you multiply them?
Yes, they do. They are solar powered; in fact, the mission lifetime is determined by how long it will take for the solar panels to become degraded by dust cover.
I attended a lecture about sleep & human performance recently, and this question came up. The best strategy would be to keep the workers in an environment with a light pattern synched to mars time. Unfortunately, this would be very expensive. Even more unfortunately, since Spirit and Opportunity are landing at very different longitudes, they would need two.
That's not going to happen, so they're just using blackout shades, and telling the engineers not to spend much time in the Big Blue Room.
The problem with parachutes on Mars is not so much the wind as the air pressure (or lack thereof). Parachutes in the thin atmosphere have to be very big to slow things down. You also can't pop out a large chute when you are burning in at 20,000 mph. There is a ton of design, testing and re-testing to run up the mission cost. Materials are also more expensive for them. Single point failures also have a larger potential for disaster with a chute system. Recall the air force guy that did the skydive from 100,000 ft... he needed something like 4 parachutes to safely land: pilot chute (slows you down to a safe speed to open main chute), main chute, reserve chute (I read once that the main failed) with a pilot chute for it. In my senior design class we had to land a nuclear generator on Mars (something you wouldn't want to bounce around too much), and chutes were the only way to go. The only way we were able to land it was using ring chutes (very interesting opening mechanism) for the first section of the descent, then a normal chute for the second portion. Airbag systems seem to me to be MUCH simpler (therefore cheaper mission cost) and safer.
The flip side to all of this is that airbags have only limited use. Precise landing area requirements, manned vehicles, "this side up ^" payloads, etc. all are better with chutes and/or retro rockets.
IANAL, but I play one on