Re: A case for the eradication of unmanned Mars missions

Jeff Davis (
Fri, 10 Dec 1999 11:31:03 -0800

On Wed, 08 Dec 1999 18:58:23 -0800

Doug Jones <> writes:

>The tradeoffs are not immediately obvious. I think the moon's south pole
>might be best *if* volatiles can be extracted, since it would have frequent
>launch windows, short travel times, and reliable power (if only in limited
>geographical locations). While the delta-V for landing is high, the short
>trip time allows use of high performance cryo stages.

At the risk of seeming crackpottish, I have an exploratory suggestion re the lunar landing delta v problem and the scarcity of water, etc. (hydrogen, oxygen, and carbon) problem. Since, sans atmosphere, it is possible to orbit the moon mere millimeters above the surface, might it not be possible to set up a "landing system", ie, a moonport equipped with a mechanism to catch and decelerate inbound vehicles? Vis the system employed on aircraft carriers.

If the inbound vehicle was, at the same time, equipped with a "conventional" liquid oxygen and liquid hydrocarbon fuel rocket braking/landing system, for backup/safety/redundancy, then, when the vehicle lands by "capture" the rocket fuel becomes cargo, which can be used first as fuel, and then as water and a source of carbon.

This might kill two birds with one stone,... or at least scare the hell out of them.

I did some math last night to figure out the lunar orbital velocity. Came up with 3725 mph. If earth orbital velocity is 17,500, then a lander inbound from lunar orbit has a "mere"

( 3725 / 17,500 )^2 = 0.0453

of the kenetic energy of the same item inbound from earth orbit.

Now if the capture cable was bungi cord, with the other end attached to an outbound vehicle, you could catch one and launch one at the same time. :-)

Hmmm. A bungi cord launch system? Setting aside the excessive complexity of a simultaneous capture and launch arrangement, I wonder if this has any merit. It certainly is elegant in its simplicity. I like elegant. I'll have to do some calcs. In fact, I'm thinking that a mass driver may be a bit more tech than is needed (though I'd be delighted to here of the elegance available in mass driver designs). I wonder what other low tech options are available for getting a lunar vehicle up to the not-very-intimidating-speed of 3745 mph. Suggestions, anyone?

Best, Jeff Davis

	   "Everything's hard till you know how to do it."
					Ray Charles