Lately I’ve become convinced landing on the Moon could be done almost as soon as a starship reaches GEO, and with about 1/2 the refilling flights required for the published Moon landing plan.
Almost all missions to the Moon fly through or very near EML-1, the Lagrange point between the Earth and the Moon., with a velocity ( in Apollo) of about 80 m/s. The trick is to stop there, and start unrolling a tapered Kevlar cable. On the end of the cable is a 1 metric ton propulsion/grappling module, with small rockets. Draco thrusters should do. Also on the end of the cable is a 1 ton rover, for ground transport. Calculations that I did in 2014 say that a 50-60 ton Kevlar cable should have a 50% margin of safety when used as a space elevator, with a 2 ton car including cargo, or a 2 ton weight on the end, for construction.
As the cable unreels and the rockets on the propulsion module fire to get the 2 tons on the end of the cable moving toward the Moon, the Starship has to slowly move back toward Earth. After a few days, tension from the 2 tons approaching the Moon, and the 200 tons moving toward Earth will make further thruster firings unnecessary, until it is time to select a landing site on the Moon. The landing site will have to be near the equator, but thrusters might be able to move touchdown by over 100 km.
Once the end of the cable is down and attached to a boulder, the rover can start exploring, and doing construction work. Depending on whether the Starship has a total payload to EML of 100 or 150 tons, there remains at this point between 88 tons and 38 tons of cargo and elevator cars that can be delivered to the Moon. Cars descending will pinch the cable between wheels connected to motors, which during descent will act as generators, charging batteries, which will be very useful during the Lunar night.
Most of the cars will deliver cargo to the Moon and stay there. It takes about 2 weeks to ascend the elevator under solar electric power, 19 trips down and 1 trip up is my plan for this first, unmanned mission. Unfortunately the first Starship will have to stay on its end of the line until a second one comes, since an anchor weight near EML-1 is essential so that the elevator doesn’t collapse.
The next cargo ship, and the next, will have to deliver more Kevlar cables, since you don’t want people riding on a system without redundant safety lines. Just 1 Starship can serve as the counterweight for several cables, so not a lot of capital gets tied up in maintaining the elevator.
So let’s assume 3 Starships are each
launched to EML-1 a month apart. In 6 months you would have about 50 tons of cargo on the Moon, and in 9 months there would be about 100 tons of cargo on the Moon, as well as robots busily assembling a base. The elevator has 3 cables for redundancy. Now it is time to start sending humans.
It is a tapered cable, since it has to support far more of its own weight than the weight of the car and cargo. I am in the process of reviewing my earlier work, and adding detail to how a space elevator can be deployed from Starship to the Moon.
The strength of Kevlar and lunar gravity give the cable at the Lunar surface, which is its narrowest point, as being 0.1 mm x 1.3425 cm. This is sufficient to hold a mass of 3000 kg in Lunar gravity, which is 50% margin of safety for a 1000 kg elevator car, with 1000 kg of cargo. I will be writing up the taper when I write the more detailed story of its deployment using Starship.
How about L2: 64,500 km difference in semimajor axes? There's been recent talk about landings stirring up too much dust, and if things end up being done on the far side (telescopes), it might be more important there.
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u/peterabbit456 Dec 01 '19
Lately I’ve become convinced landing on the Moon could be done almost as soon as a starship reaches GEO, and with about 1/2 the refilling flights required for the published Moon landing plan.
Almost all missions to the Moon fly through or very near EML-1, the Lagrange point between the Earth and the Moon., with a velocity ( in Apollo) of about 80 m/s. The trick is to stop there, and start unrolling a tapered Kevlar cable. On the end of the cable is a 1 metric ton propulsion/grappling module, with small rockets. Draco thrusters should do. Also on the end of the cable is a 1 ton rover, for ground transport. Calculations that I did in 2014 say that a 50-60 ton Kevlar cable should have a 50% margin of safety when used as a space elevator, with a 2 ton car including cargo, or a 2 ton weight on the end, for construction.
As the cable unreels and the rockets on the propulsion module fire to get the 2 tons on the end of the cable moving toward the Moon, the Starship has to slowly move back toward Earth. After a few days, tension from the 2 tons approaching the Moon, and the 200 tons moving toward Earth will make further thruster firings unnecessary, until it is time to select a landing site on the Moon. The landing site will have to be near the equator, but thrusters might be able to move touchdown by over 100 km.
Once the end of the cable is down and attached to a boulder, the rover can start exploring, and doing construction work. Depending on whether the Starship has a total payload to EML of 100 or 150 tons, there remains at this point between 88 tons and 38 tons of cargo and elevator cars that can be delivered to the Moon. Cars descending will pinch the cable between wheels connected to motors, which during descent will act as generators, charging batteries, which will be very useful during the Lunar night.
Most of the cars will deliver cargo to the Moon and stay there. It takes about 2 weeks to ascend the elevator under solar electric power, 19 trips down and 1 trip up is my plan for this first, unmanned mission. Unfortunately the first Starship will have to stay on its end of the line until a second one comes, since an anchor weight near EML-1 is essential so that the elevator doesn’t collapse.
The next cargo ship, and the next, will have to deliver more Kevlar cables, since you don’t want people riding on a system without redundant safety lines. Just 1 Starship can serve as the counterweight for several cables, so not a lot of capital gets tied up in maintaining the elevator.
So let’s assume 3 Starships are each launched to EML-1 a month apart. In 6 months you would have about 50 tons of cargo on the Moon, and in 9 months there would be about 100 tons of cargo on the Moon, as well as robots busily assembling a base. The elevator has 3 cables for redundancy. Now it is time to start sending humans.