November 25, 2010

What was the best way to use the Saturn V to reach the Moon-- in retrospect?

Lunar Surface Rendezvous as an Exploration Strategy

Hi, everybody, Joseph Friedlander here in a guest post on Next Big Future. Everybody who is into the history of space knows the CSM-LM (Command and Service Module/Lunar Module) Lunar Orbit Rendezvous method that was finally chosen as payload aboard the Saturn V, but was that really the best way to have done it? It certainly was not the cheapest, using a Gemini and Centaur could have done a variant of the Apollo 8 mission a couple years in advance... but people in NASA had a strong desire to go a certain way, and anything not using Apollo-Saturn hardware was not as favored (Orion, the nuclear launch method, lost NASA support for that reason-- they were obsessed with developing chemical boosters at that time, and particularly the Saturns.)

In 1966, Douglas Aircraft, builder of the DC-9, (prime contractor on the Saturn V third stage, the S-IV-B) suggested a lunar lander variant. "Lunar Application of a Spent S-IVB Stage (LASS)" (for more details see the Astronautix page on that proposal)

I have done a Photoshop mashup of various real and projected hardware proposals from that time. LASS is on the right.

On the left bottom is the projected Apollo Venus flyby.

Basically the idea is to take a modified CSM and turn around and dock with an S-IVB and colonize the former fuel tank (the so-called 'wet workshop' concept when in Earth orbit)

Variants of this idea would have been possible in geostationary orbit and lunar orbit (a lunar orbital Skylab). the Earth-Moon L-4 and L-5 points, and indeed the Sun-Earth L1 and L2 points.
Various scientific justifications can be given for all these locations; some are long-term stable, others are not without small corrections year by year.

The ISS has one major virtue-- it is easy to reach. It also has a major vice-- it requires large amounts of station keeping delta-v to counteract orbital decay from residual atmospheric friction. In low lunar orbit things can crash within a year because of the mascons (mass concentrations ) but a very high lunar orbit presumably would be much longer-lived. (The key concern is that if the perilune touches the ground-- the orbiter loses. Every time. If the perilune still is well above the ground, even perturbed--- things go on orbiting...)

Imagine however a lunar base derived from S-IVB lander stages, as mentioned above. Each station would be the colonizable equivalent of Skylab on the ground-- coverable with lunar regolith for radiation protection. With two men landing in the S-IVB, a very minimal 2 man personal reentry vehicle, imagine a version of the MOOSE (upper right) and a small two stage booster (perhaps the equivalent of the LESS on top of the MOBEV, see top center) with one of the reentry protection concepts from upper right, about 3.5 tons of the landed 7 ton payload would be the direct up return craft and reentry vehicle, (this is only HALF the weight of the 3 man Command Module alone that actually flew!) the rest supplies for expedition and colonizing the LASS lander.

The second expedition might land at the same site, with another module for expansion (the LASS booster) and perhaps a rover; the third might carry a small foundry kit to melt down one of the boosters (each with 13 tons of metal) and using the motors and bearings from the rover, make a much more comfortable and larger rover. Six lunar landings (the same as actually happened) would have built up quite a lunar infrastructure, most of which would still be there for recolonization even after a hiatus of 40 years (not necessarily operational, in the case of the rovers, but very probably the buried base modules would be in good shape).

Actually, a number of the moonbound S-IVB stages were targeted to hit the moon to test the new lunar seismograph network (turned off on September 30th, 1977), for example the Apollo 14 stage hit with just over 10 tons of TNT equivalent and the 35 meter diameter crater and the rays around it presumably would be mine-able for aluminum metal dust. So with a very large number of incoming LASSES it would have paid to soft-land more cargo in a smaller sub-stage and let the main stage crash in a heap at a little over a kilometer a second. Presumably the soft-landed cargo would have been over 10 tons a landing-- some use the figure of 16-18 tons a landing. and if the men could stay longer and not leave on every mission, saving another 3.5 tons for the return vehicle (using the 2 man ultralight direct ascent method explained above) we could have had a very nice moon base network (probably at more than one site for access to different science and mineral opportunities) by now (particularly if the financial equivalent of say 50 shuttle missions had been, over the decades, diverted to this kind of moon landing instead.) A similar lost opportunity-- we could have brought to orbit nearly 100 30 ton External Tanks of the Space Shuttle to make a station 6 times the size of the ISS-- but we did not, because NASA did not want to concentrate on doing that rather than on their pre-set agenda. Frankly, it would have needed at least 2 tons of fuel each, and they would have needed orbital maintenance-- but a module on the lunar surface landed as part of getting the payload down needs neither.

The key thing is-- the Moon will stop an incoming impactor for you, give you free radiation shielding if you pile it on, and give you mine-able resources—and those resource piles and all your scrap landed boosters do not need to have their orbit maintained at the expense of fuel. It is not difficult to imagine mining and processing 10 to 100 times what you landed with even in the early stages. So instead of the International Space Station, we would possibly have the distributed equivalent of an aircraft carrier of structure on the Moon today...

To answer the title question, this is the strategy of 'Lunar Surface Rendezvous'-- and is my nominee for what to have done in hindsight.

The road not taken....

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