spirit and opportunity

i went to this tonight. really enjoyed it. here are a few interesting facts:

• every night on mars the temperature drops to -110 degrees C. this temperature would freeze and crack the electronics and machinery so the most important function on the rovers is the heaters. they run at night to keep the temperature above about -30 degrees C.
  
• their primary mission is do geological analysis of mars to see if there really used to be water on mars. (rock analysis has proved that there was water on mars).
  
• opportunity is still kicking along after 6 years. spirit is currently out of contact (but there's is still hope for it, see below). they were originally expected to last 90 days.
  
• the rovers are sent navigation instructions once per day but then move autonomously. they can move about 4cm per second but a range of about 100m per day is safer so that operators can visually see dangers by looking at the previous day's images
• the rovers are solar powered and have had problems with dust building up on the solar panels. strong winds sometimes blows the dust off, which improves the charging rates
  
• spirit lost a front wheel motor in 2006 and has been driving backwards since then, dragging one wheel like a lame paw
• it got stuck in some soft sand in january. engineers were working on getting it out with some success when the onset of winter meant that there was longer enough battery charge to keep trying (and still have enough power to run the heaters). at some point later it shut down it's radio contact. when summer comes around in a few months from now it might be able to build up enough charge to make contact again, and even (say the more optimistic) finish getting itself unstuck.
• the routes travelled by the rovers are pretty interesting. spirit has spent a lot of time at 'home plate' which is geologically interesting and thought to be an ancient volcanic hotspring. opportunity has been visiting craters to look at the rock features and is currently on it's way to a really big crater. see here and here. (a sol is a mars day which is just a little longer than an earth day, so each white dot there is like an overnight camp)
• the landing method is pretty interesting. they come down inside a big cusion of air bags and bounce several times. (you can probably find a video of this on youtube)
• read more at http://marsrovers.jpl.nasa.gov/home/index.html and http://en.wikipedia.org/wiki/Spirit_rover and http://en.wikipedia.org/wiki/Opportunity_rover