Thoughts on a space station at L2 of the Earth-Moon system

An interesting article appeared recently "NASA considers orbital outpost near moon as next big project" The article says it would be a gateway for missions to the Moon and Mars. The project would be to put a space station at the L2 point in the Earth-Moon system.

Some points not mentioned in the article, provide some evocative scenarios.

L2 is a hover point above the center of the far side of the Moon. One thing that this means, is that it is out of direct sight, and radio communication, with the Earth. Thus what goes on there, we can only find out indirectly, if at all. The Moon between L2 and the Earth also provides shielding from the electromagnetic smog exuding from our civilization, and could be a quiet place from which to do radio astronomy.

But also, being permanently hidden from the eyes and ears of people on Earth, for war-defense-minded folks, it could be an even better hideout for storing the nuke-carrying rockets that once were feared were going to be put on the Moon's surface, that brought forth the Apollo Project in the Space Race.

L2 is the balance point between the combined gravitational force from the Earth plus that of the Moon, by the outward force centrifugal force generated by the angular velocity of orbiting around the Earth at the same orbital period as the Moon, about 28.25 days per orbit. (The reference article was incorrect in saying that L2 was the balance point between the Earth and the Moon; that balance point is called L1.)

Being a balance point, it means it would require ever vigilant station-keeping externally supplied station-keeping energy. Not much energy; but if ever not fully compensated, it would build up speed that would rapidly require ever increasing amounts of energy to get it put back at the balance point. From L2, a bit of outward shift and the station heads for more distant space; a shift toward the Moon, heads for the moon.

Similar to a station put at the L1 balance point between the Moon and the Earth, if it loses station-keeping balance, it would head either toward the Moon or toward the Earth; neither is a desirable prospect. But from L2, the option of heading away from the Moon, suggests to me that such a station have mounted on it a set of emergency rockets to push it back through L2 and out toward distant space, if ever station-keeping was lost and it was headed down toward the Lunar surface. That would give people time to arrange some kind of rescue mission.

A related concept could provide station keeping without addition of energy, but would have its own considerations. That is to have the L2 "Gateway Spacecraft" (as the reference article called it) part of a lunar space elevator through L2 from the Lunar surface. Such an anchored tether space elevator would provide the L2 space station with station keeping force, and also L2 being the balance point between the sum of the Lunar-ward gravitational-dominant force on the mass of the part of the tether between the Moon and L2, and the centrifugal-force dominant part of the tether space elevator, that is beyond L2 as it swings around in the lunar-period Earth orbit.

Hydrocarbon-based materials probably exist for making such a space elevator through L2. Space-rated fiberglass was shown to be strong enough, for its density, to be used for a Lunar anchored tether space elevator through L1, back in 1972 (reference "The Mooncable: A profitable Transportation System in Space" and The Mooncable: Gravitational-Electric Siphon in Space" and NASA ICB's reply to it on June 23, 1972) using a constant-stress cross-section tapered configuration; and recently a different material has been proposed by the LiftPort group, currently making a new push for such a project, using a hydrocarbon-based tether material.

Space technology project concepts that are not in line with current corporate business plan territories, have little opportunity to become reality. There remains one outlet for the resulting frustrations endured by an author of such a concept, and that is to incorporate the concepts into science fiction stories. That way it becomes non-threatening to corporate managers and investors - although suppression of the distribution of such sci fi novels might still happen. In this case, for some thoughts about how to deal with establishing communication between Earth and L2, see "The Torus City Ice Shields Returning Home" 2008 novel, as well as for some more thoughts regarding an anchored tether Lunar space elevator through L2. (And see it also for lots more thoughts about an anchored Lunar tether through L1, too, if that is of any interest.)

The prospect of creating a space station at L2, provides lots of new and interesting factors in the exploration and utilization of space.

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