dietz%usc-cse%USC-ECL%SRI-NIC@sri-unix.UUCP (01/11/84)
Last month I sent a message describing an idea by Krafft Ehricke to land payloads on the lunar surface. It involved skidding the payloads on a long strip of lunar soil at orbital velocity (about 1650 m/sec). A difficulty is sifting the lunar soil to remove rocks from the top 1/2 to 1 meter. But this may not be necessary. The rocks could be removed by a special vehicle. The vehicle would have pipes that would be extended several meters into the lunar soil. Around the outside of the vehicle is a gas-tight skirt that would be anchored in the soil. Gas would be injected into the lunar soil through the pipes. Sufficient gas flow would liquify the soil, causing large objects such as rocks to sink. Smaller soil particles would be buoyed by the gas flow. Gas would be collected under the skirt for recirculation. Care must be taken not to let the vehicle sink. Subsurface lunar soil is quite cold, so the gas will have to reheated, probably with sunlight. Or, the cold gas could be used as a heat sink to increase the efficiency of solar powered heat engines. Another way to sift the soil would be to give the soil particles electrical charges. The particles repel one another, allowing large rocks to sink. This suggest a novel form of earth moving possible only in a vacuum: spray the soil to be removed with an electron beam while giving a soil collector a positive charge. Lack of moving parts should help reliability. I previously proposed using an aluminum strip to levitate rockets for lunar launches. Samarium-cobalt magnets should be sufficiently light to make the scheme practical. For extra efficiency, high launch accelerations could be used (10 gee's, say), and the strip could be covered by a gas-tight tunnel ~14 km long. The rocket would use lunar oxygen and imported hydrogen as fuel; the water produced by combustion would be trapped in the tunnel, recovered and the hydrogen recycled. The tunnel would have gas tight doors on the east end which would close after launch to trap the water. This scheme will help keep a lunar atmosphere from developing.
kcarroll@utzoo.UUCP (Kieran A. Carroll) (01/16/84)
* I see a problem, with both of the suggestions given for "sifting" lunar soil. Both methods are ways of fluidizing the soil, to allow larger rocks to sink far below the surface. However, at least if the rocks and soil are of similar densities, fluidizing the soil may make the larger rocks rise up, instead. Simple experiment: next time you're making instant coffee, put a spoonful of sugar and one of coffee crystals into the cup, before you add the water. Put the codffee in first, and the sugar afterwards. To start with, the sugar is then above the coffee. Now, shake the cup for a couple of seconds. If the coffee crystals are larger than the sugar grains, you'll (probably) find that the coffe crystals tend to rise to the top of the mix. I don't know what the relative densities are in this case, but you'll find that this works for differen-sized particles of identical densities. For example, if you (or your little brother) has a bag of marbles (remember those?), put a coupl of big ones in the middle of a jar full of little ones. After shaking, the big ones tend to rise to the top. The reason I've heard for this is that, when shaken, the small particles in these mixtures tend to fall into the small gaps underneath the large particles, making the large ones migrate upwards. I don't know if the same effect would be observed in the proposed lunar schemes, but I suspect that it would. Question: just how deep is the lunar "soil"? (of course, it's not real soil). -Kieran A. Carroll ...decvax!utzoo!kcarroll
eder@ssc-vax.UUCP (01/16/84)
From Dani Eder at Boeing Aerospace
16 January 1984
Another method of getting stuff to and from the lunar surface is a
rotating cable. Since the Moon is much smaller than the Earth, material
strengths can be lower for cable type systems. For example, suppose you
have a cable orbiting the Moon at 1650 meters/sec. It is spinning so that
it's outer tip is moving at lunar escape velocity (2333 meters/sec),
and its inner tip is moving at a corresponding amount slower(966 meters/
sec).
On your way from Earth, you come in at escape velocity, grab on for
half a rotation of the cable, then let go. You have reduced your velocity
from 2333 meters/sec to 966 meters/ sec. You do the rest with rockets.
Compared with pure rockets, you have to do only 41% as much velocity
change. If you are using LOX-Hydrogen rockets your fuel use goes from
.677 times landed weight to .239 times landed weight, only 35% as much
fuel. You don't have to have any special facility on the lunar surface.
On the way up, you drop off some oxygen or aluminum to feed an ion
thruster or mass driver at the center of the cable. This is required
to balance any net momentum change if the payload to the moon does not
equal the payload from the moon.