Re: Mars Rover Windshield Wiper

John Doe wrote:
Derek Lyons wrote:
Because we don't have a battery that can hold sufficient charge across
the winter

Geez, the poster said POWER DOWN the unit. There is thus no need to have power available throughout the winter (except perhaps just a clock).

No actually, you are wrong. The units must remain powered (or if unpowered kept warm) or they will be destroyed. Your experience of electronic devices surviving the environment on earth does not give you sufficient information to what happens to electronics on Mars. At night the temperature on Mars can be as low as -220ºF. The differing thermal expansion coefficients of the component parts will cause mechanical stresses to set up which will cause breakage of the connections (solder joints, electric welds, etc.) which will render the electronics useless.


And there is that newphangled thing called flash memory that can hold the data even withough power. Shirley they can make RAD versions for space travel. Or does NASA insist on using 1960s technology even for ships they design today ?

Actually more modern silicon devices are more prone to radiation induced faults and failures. At the smaller geometries of modern active devices (we're getting into the 10's of nanometer size features now) it simply takes less energy to flip a bit or cause device destruction. There are things you can do to make this better but at some point you simply decide that you don't need to use the latest 18 nanometer process processor. This is not a big deal since most probes just don't need the processing power the average PC gamer has at hand. And one more thing, don't call me Shirley.



and because it's awfully hard to design electronics that
will power down into a deterministic state that will power up reliably
when the solar panels are illuminated again in the spring.

Ahh, typical NASA "can't be done" explanation. Consider the millions of people who turn off their computers at night by just flicking the switch, and turn it back on the next morning by again just flicking the switch ?

Consider that even residential UPS systems are able to warn a computer when power is getting low so that the computer can shutdown. (and I strongly suspect that the rovers already have that built-in).


Then there
is the (AIUI) high probability of damage caused by differential
contraction as the lander cools.


Aren't these ships designed to widthstand even greater temperature ranges during the space travel portion of their journey ?

None of the above applies. The problem with letting your electronics box power down is not saving the state and booting reliably, it is actual physical breakage caused by low temperature. When the solder pad that connects the LSB of your address bus to your main memory breaks free your lander/probe/rover is technically what we in the industry like to call "dead" (yes, you can add redundant electronics but at -220ºF so many component bonds are going to fail that you will never add enough redundancy to live through more than a couple of Martian winter nights). The way deep space probes avoid this is they simply don't power down because they use RTGs that supply continuous power for decades. The electronics assembly is in an insulated container an it general the inherent power dissipation of the electronics inside this well insulated box is enough to keep the temperature to something survivable. If necessary you can add a heater but this too needs a continuous source of power.



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