jimlux@earthlink.net said: > If it gets cold enough (without power from solar cells, it won't generate > enough internal heat to keep warm), it will die. That's probably what > happened to Spirit on Mars. It got cold enough during the Martian winter, > and with not enough solar power, enough things drifted cold enough that we > couldn't get commands in. What stops working when things get cold? On Mars, the solar cells are pointed in the right direction. Why doesn't it recover when the sun comes back in the Spring? -- These are my opinions. I hate spam.

On 9/21/13 6:40 PM, Hal Murray wrote: > > jimlux@earthlink.net said: >> If it gets cold enough (without power from solar cells, it won't generate >> enough internal heat to keep warm), it will die. That's probably what >> happened to Spirit on Mars. It got cold enough during the Martian winter, >> and with not enough solar power, enough things drifted cold enough that we >> couldn't get commands in. > > What stops working when things get cold? Lots of things. Mars gets *really cold* in the winter (-50C and lower) There's an issue with plastic packages where it gets brittle. CTE mismatches cause cracks, etc. Electrolytic capacitors freeze. > > On Mars, the solar cells are pointed in the right direction. Why doesn't it > recover when the sun comes back in the Spring? for Spirit, because of the issues with the wheel drive motors, it couldn't get into the right position to face the sun (on a south facing hillside, basically) That 10-20 degrees makes a big difference because of the cosine (angle) problem/ > >

On Sat, Sep 21, 2013 at 6:40 PM, Hal Murray <hmurray@megapathdsl.net> wrote: > > What stops working when things get cold? > > On Mars, the solar cells are pointed in the right direction. Why doesn't it > recover when the sun comes back in the Spring? They run out of power for running the battery heaters, then the battery freezes and fails. The batteries get to such a low temperature that they are unable to be charged. The rover was never designed so that it could move and operate under solar power. It is really battery powered and uses the panel for charging. This is the biggest reason the newest rover, "Curiosity" is powered by an RTG, not solar cells. The RTG is powered by radioactive decay. The thing makes a lot of heat and should last 15 to 20 years. Likely longer than all the moving parts like motors and so on. -- Chris Albertson Redondo Beach, California

There is a major problem with Radioisotope Thermoelectric Generators Our stocks of Plutonium-238 are very low -- less than 40 pounds remain available to NASA and this is all spoken for future missions. We are restarting the manufacture and it is supposed to come online sometime around 2017. One gram of Plutonium-238 gives about 0.5 watts of deliverable electricity. Half-life of 87.7 years. P-238 does not go KaBoom! -- you are thinking of P-239. http://en.wikipedia.org/wiki/Plutonium-238 http://www.space.com/20290-plutonium-spacecraft-nasa-fuel.html http://www.wired.com/wiredscience/2013/09/plutonium-238-history-timeline/ > -----Original Message----- > From: time-nuts-bounces@febo.com > [mailto:time-nuts-bounces@febo.com] On Behalf Of Chris Albertson > Sent: Saturday, September 21, 2013 20:34 > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Space mission comes to an end > becuase of a "computer time tagging" problem > > On Sat, Sep 21, 2013 at 6:40 PM, Hal Murray > <hmurray@megapathdsl.net> wrote: > > > > > What stops working when things get cold? > > > > On Mars, the solar cells are pointed in the right > direction. Why doesn't it > > recover when the sun comes back in the Spring? > > They run out of power for running the battery heaters, then the > battery freezes and fails. The batteries get to such a low > temperature that they are unable to be charged. The rover was never > designed so that it could move and operate under solar power. It is > really battery powered and uses the panel for charging. > > This is the biggest reason the newest rover, "Curiosity" is powered by > an RTG, not solar cells. The RTG is powered by radioactive decay. > The thing makes a lot of heat and should last 15 to 20 years. Likely > longer than all the moving parts like motors and so on. > -- > > Chris Albertson > Redondo Beach, California > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.