The Value of Low Lunar Orbit Space Stations

Background on Lunar Material Lifting

Rockets suck, and they suck uniquely when they have to carry all their propellant with them for a high Delta-V trip. The only time they suck even more than this is when the rockets have to be thrown away at the end of the trip.

Gas Stations in Space

I really can’t do any better to argue this than linking to the following graphics. If you read these that and still don’t see the central problem of space development, then I’m sorry, you’re wrong.

Building Materials and Mass Drivers

This is a case where I believe existing literature is wildly inconsistent. In the 1970s, among the great exuberance for the seemingly inevitable migration into space, authors wrote about mass drivers on the Moon with language such as this.

Lunar Mass Driver, old NASA Work

Lunar Orbital Industry

A reasonable catcher/launcher-based lunar transportation system would involve a massive LLO orbiting station. Why? Firstly, it’s cheaper than doing the same things on the lunar surface. Landing on the moon is another stage in the Delta V math. Secondly, micro-gravity is the point of going into space in the first place, and may be better suited for rocket building. Thirdly, it’s the only place in the solar system that a mass-driver makes any near-term sense.

Details of the scheme

Necessarily, the lunar surface mass-driver must be on the Moon’s equator, and the orbital catcher must also be orbiting exactly along the equator.

Local Industrial Environment Around Time of Firing
Fine Velocity Adjustment

Margins of Error

I went into detail in the linked notebook what tolerances are needed in order to get the payload to the station. Some summaries:

  • An anomaly of just 0.01 m/s in the muzzle velocity will cause the rendezvous location to shift by 44 meters. This is considered to be on the borderline of acceptability.
  • A 0.1 degree right/left misalignment in the mass-driver would only add roughly 2.5 m/s to the rendezvous velocity.
  • Variations in the timing would have very little impact on the rendezvous location, roughly approximating a parabolic free-fall trajectory of 1/2 a t², where a is the lower 1/6th lunar gravity.
  • Variations up/down in the angle which the mass-driver acts at are very easily minimized (by a simple level), and will have a very small effect on the rendezvous location by a similar argument to the timing — the orbit is nearly circular and the altitude changes very little with respect to angle around apogee.

Safety

In the event of a failed launch, this scheme has simply the case of Newton’s Cannonball. If velocity is insufficient, it just hits the ground. If velocity is too much, the payload will hit the shield behind the mass-driver.

Industrial Value

What it would be used for? If we would ever want to do zero-gravity manufacture of spacecraft parts, this would be the place to do it. Material availability and proximity is ideal. You would only export high-value items out of the lunar gravity well (things which will ultimately make many trips, so the maiden trip is no big deal), although the station itself could take on a massive amount of mass.

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Alan

Alan

Obligatory analytical writing, online participation account for Medium. Engineering, software, books, space, constant daydreaming.