Lasso the Moon

presentation set-05.ai

I have been a personal fan of the concept of the Space Elevator (SE) since attending a talk by Bradley Edwards describing his work developing the concept. From that time I have always thought it was self-evident that this was the method that eventually most of the mass traveling between Earth and the rest of space would use. The problem to this point is that currently there is no material in commercial production that could be used to build the elevator. I have faith that material sciences will eventually resolve this issue but this could be decades away. There is a variation on the concept that is currently feasible, a Moon SE.

The Slow Boat to Luna

Currently the LiftPort Group is promoting the concept of and SE stretching from the surface of the Moon through the first Lagrange point (L1). Unlike the Earth based elevator this would not require a yet undeveloped material but would be possible with various existing materials such as Kevlar. Several modern synthetic fibers could be used because of the lower lunar gravity even though L1 is about 30% further from the surface of the Moon than GEO is from the surface of Earth.

Another difference is that while a SE from the surface of Earth is able to “self-counterweight”. A cable/ribbon of consistent cross section would need to extend almost 240,000 km beyond L1 to just counterweight the cable/ribbon to the Moon. For every 1 kg of payload to be lifted from the Moon you would need 33 kg in counterweight. A cable/ribbon of this length would possibly conflict with an Earth based elevator when one is built.

One advantage of a cable/ribbon this long is that a payload released from the end would come within 15,000 km of Earth. This could make returning to Earth from the Moon fairly cheap. If some way could be developed to capture payloads from the Earth any rocket able to deliver a payload to GEO would be able to deliver it to the Moon.

Like all space elevators the one to the Moon would be ideal for moving cargo. What it will not be very good for is moving people. Even if the climber moved at an average 1,000 km/h it would take over 2 days to make the trip between L1 and the Moon’s surface. The reality is the top speed will likely be less than half of that making the trip more like a week. A climber would be an extremely cramped space to live in for a week. It is unlikely that until space elevators are built for loads of at least 50 tons of mass that it will be used to transport people except in dire emergency.

What Good is It

A lunar space elevator would enable much more extensive exploration of the Moon’s surface. Exploration vehicles could be much more complex because their landing would be very soft and because potentially they can be returned from the surface for repairs and maintenance. It would be far cheaper to supply a permanent human habitation on the Moon. It would provide an ideal opportunity to develop a permanent habitation at L1. It would greatly simplify returning payloads from the Moon to the Earth; first scientific samples and later products of commercial value.

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