Google has launched an “X-Prize” like contest to reward the first private company that manages to land a mobile probe successfully on the moon with $20 million.

Welcome to a new kind of space race, where the earthly guest will be a machine and the goal is as much exploration as seeking out new business ventures.

The quest is part of the Google Lunar X Prize, which will put $20 million into the hands of the first privately funded team that can land a rover on the moon, have it travel on the surface for 500 meters or more, send back data, photos and video, and do it all by December 31, 2012.

As they point out in the story, the effort is likely to cost many times more than the prize money, but it’s still an impressive chunk of change to give incentives to companies that are already considering such an endeavor. I’m all for it.

Now, if it were me, I would rent existing heavy-lift capability to get something up into near earth orbit, maybe two launches, one for a large container of fuel, and one for the probe itself. The Shuttle is probably too expensive so I’d end up looking at Arianne or a delta rocket launch to get the stuff up there. I would make the probe as small as possible, and since there doesn’t seem to be any requirement to have the probe come back to earth, all it needs to do is land softly enough to remain mobile while on the lunar surface.

So, what is the biggest technical hurdle to overcome?

Probably landing the thing softly enough to avoid damaging it’s moving parts or its communication gear. Otherwise its really a fairly routine remote-controlled vehicle exercise. The moon is close enough that you can control the thing from earth quite reasonably. All you really need on it are some basice scientific testing devices, a camera and communication gear.

So how DO you land softly on the moon? Parachutes won’t work, obviously, and the precision required for a soft landing such as the Phoenix accomplished on Mars is highly complex and risky.

So, what is the cheapest and most reliable way to achieve a soft landing on the moon?

We did it with the Apollo missions by having computer controlled attitude and retro-rockets (which Neil Armstrong overrode and accomplished manually in what is still one of the most incredible piloting jobs ever done, possibly only matched by the Apollo 13 re-entry to earth piloting, also done manually).

I’ve always wondered if there is a more brute-force, total ignorance way to do such a landing while still maintaining the structural integrity of the delicate mechanisms of a probe.

On Mars they did a sort of brute-force, total ignorance method with the martian rovers. But they were able to do the bulk of the deceleration using the thin Martian atmosphere. From there they essentially dropped the probe in the middle of a bunch of air bags and let it bounce and roll until it stopped.

I wonder if a similar approach wouldn’t work on the moon. You can’t use a parachute, but you can use retro-rockets to slow the thing down to almost a full stop, and let the balloon drop approach take care of the final settling down onto lunar soil. It’s that last bit of coming to a complete stop without jarring the probe that is so difficult to achieve, it is much easier to get the descent down to a near-stop a reasonable height up from the surface, and let the air bags protect it from there. You also have the benefit of a lunar gravity that is less than half of martian gravity, so it would not fall nearly as quickly as on Mars.

That’s what I’d probably do, if it were me….

I like the air bag thing so much, I’d probably design the probe with big fluffy inflatable tires too. I might even have redundant tire tubes that could be inflated if one popped. I’d also probably have six, not four tires….

Sigh, I’m in the wong job….