I Joined the Wiki at Team FREDNET, the 'Open Source Team' at the Google Lunar X-prize.
I had an idea.
"The Google Lunar X PRIZE is a $30 million international competition to safely land a robot on the surface of the Moon, travel 500 meters over the lunar surface, and send images and data back to the Earth. Teams must be at least 90% privately funded and must be registered to compete by December 31, 2010. The first team to land on the Moon and complete the mission objectives will be awarded $20 million; the full first prize is available until December 31, 2012. After that date, the first prize will drop to $15 million. The second team to do so will be awarded $5 million. Another $5 million will awarded in bonus prizes. The final deadline for winning the prize is December 31, 2014."
They're probably well along in their engineering of a Moon Rover, with the dealine only 2 years to go, but looking at video of Joshua Tristancho's "Picorover" - I was inspired - and imagined this:
Using the difference between shaded and not shaded temperatures on the moon as a motive force.
The 'thermal motor' is a number of thermometer-like tubes, inside the skin of a ball, that travel 1/4 (for example) around the diameter of the ball. The 'thermometers' contain a liquid that at 107°C (moon sunny-side temperature) expands to almost fill the length of the tube - while at -153°C (the shadow side moon temperature) must shrink to fill less than half of the tube.
Through the use of Smart Glass membranes on the skin of the ball, the tubes are alternately exposed to sun light and then not, the resultant movement of the liquid up their tubes, around the inside of the skin of the ball, causes the ball to roll.
I don't know what that liquid is yet.
Also 'chambers' could be added to the ends of these thermometers, the idea being to change the position of as much liquid mass via warming and cooling by solar radiation as possible.
To add steering to this thermal motor driven rover, layers of tubes running at right angles to the first layer are shielded by a separate layer of Smart Glass screening - by exposing elements of the second layer you would create momentum at right angles to the forward inertia, thus causing angular momentum which would cause the ball to change direction.
As the relative position of everything is changing all the time when the ball is in motion, one would need to have position technology of some sort, so the on-board computer, that controls the smart glass screening could maintain a relative position in space. The position technology could be as simple as a flies eye cluster of light sensors - for direction only - plus solar astrometric data.
(It cannot roll into shadowed areas, or it's 'off' until the moon's rotation brings it into the sun again.)
An area of the ball will need to be covered with photoelectrics to supply electricity to a series of capacitors as the energy required to change the opaqueness of the screens is a voltage burst, plus the on board processor requires a steady voltage, so battery storage is also required.
The vehicle could be made of a polysilicon of some sort or perhaps polyurethane.
Now, somebody make a prototype and get famous. :)
The Google Lunar X-prize, Team FREDNET Wiki - User: Michael Holloway Page.
Joshua Tristancho's "Picorover"