Perpetual Lunar Rover

TheBigDog · #1 (**permalink**) 03-28-2008

I had this idea a while ago and dismissed it as nothing more than a bit of a joke, but after some more thought I think it might be a good idea. Follow me on this...

The moon rotates very slowly. It does one revolution every 27.5 days. That means that at its equator the shadow of night/day is moving at 16.53 km/h. Given the low gravity, good sunlight, and lack of clouds; would it be possible too build a lunar rover that could operate on solar power, self navigate obstacles, and be fast enough to stay in the sunlight long enough to circle the moon? What I am suggesting is an autonomous rover that circumnavigates the moon.

What would the engineering challenges of that be? I don't know exactly why a person would want to do it other than because it is a damn cool idea. I am going to mull over the engineering and come back with some ideas.

Bill

UncleAl · #2 (**permalink**) 03-29-2008

Lunar dust has the dimensions of cigarette smoke - and there is about a foot of it most everywhere front side. Nasty for all things mechanical. Other problems with boulders and craters on the front side. The lunar back side is all spiked mountains and deep gorges from when low-melting lava shifted to the front side after orbital locking.

Janus · #3 (**permalink**) 03-29-2008

Quick correction. While the Moon's Sidereal(fixed star to fixed star) period is 27.5 days, the synodic (local noon to local noon) period is 29.531 days. The day/night terminator thus travels at 15.4 km/h. Not much of a difference, but every little bit could help.

For comparison, the Apollo mission rovers had a top speed of 13 km/hr and and averaged 9.6 km/h.

The rover used about 1000w for the drive and steering motors and massed (fullly loaded) 700kg.

After a little search I found some 80w solar panels, each weighing 7.7 kg, you would need 13 of these to provide 1000w (with some reserve) bringing the mass of the panels to 100 kg. The panels cover an area of 7.8 m² or about 3 m x 2.6 m. The rover was 3m x 2.3m. The panels would extend just a little past the rover main body. This seems reasonable.

This is, of course, only gets you the top speed of the rover running at full tilt, which is about 18% shy of the average speed you would need to maintain. Since you need to allow for time to circumnavigate large obstacles (and thus a higher max speed), and extra power requirements for climbing inclines, etc., you will want to scale up the solar panels (add in the fact that the panels are only warranted for 76w max power.)

Then there is the consideration of just maintaining 15.4 km/hr over the rough Lunar surface. At 1/6g hitting a bump will cause 2.5 times more "bounce" than hitting the same bump at the same speed on Earth. Or put another way, it would be the equivalent of hitting the same bump at 38.5 km/hr on the Earth. And remember, this is the average speed you must maintain. at times you will have to travel faster to make up for detours etc.

OTOH, if you want to make just one trip around the Moon, and can tilt your panels to catch the most sunlight, you can try this trick:

Start your rover about 45° "ahead" of the Sun and then allow the Sun to creep forward to 45° ahead of the rover. This gives you 40 days of Sunlight to run on, bringing your required average speed down to 11.4 km/sec.

Janus · #4 (**permalink**) 03-29-2008

Uncle Al brings up a point I wasn't going to yet; The fact that some of the "obstacles" you will have to circumnavigate are going to be really large, this will make it hard to keep ahead of the terminator.

Jay-qu · #5 (**permalink**) 03-30-2008

Janus beat me to mentioning an important point that would make it much easier. If you land the rover in the dark and start its trip when the sun hits it, it will have much more than its 29 day period to make the distance.

You could also increase the latitude slightly to make the trip shorter.

The other side of the moon isnt as bad as Al makes out - but even the side facing us is covered in obstacles, its this part that makes it impractical. Why not just image the moon in high-res from a low orbiting satellite.