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Comment by Sir_Cmpwn | Hacker News Reader

Another issue with this would be that a Mars vehicle would probably be big, and to a large extent designed to never land on anything. Getting it down to the Moon safely and back out again would be very complicated. The solution is to do a fuel run with a smaller craft that can disengage from the main craft several times, but then you're doing several landings and takeoffs and that's going to shoot the risk WAY up.

I think that we would be wise to invest in a space elevator on the Moon. We can't support one on Earth with currently understood technology, but the Moon is different and it could be done with modern materials. A plan of this sort would seriously reduce the cost of lunar development and increase the viability of the plan in the article.

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From the 4th paragraph:

>They found the most mass-efficient path involves launching a crew from Earth with just enough fuel to get into orbit around the Earth. A fuel-producing plant on the surface of the moon would then launch tankers of fuel into space, where they would enter gravitational orbit. The tankers would eventually be picked up by the Mars-bound crew, which would then head to a nearby fueling station to gas up before ultimately heading to Mars.

TLDR, the main Mars vehicle wouldn't land on the moon.

The risk of multiple moon landings and takeoffs is really quite small as the moon has no atmosphere.

Perhaps not mission critical small, it might be in the range of 0.1-2% risk for each landing/takeoff cycle. So if you require 10 refuelling launches, your total risk is 1-20%.

Say you had a large moon lander, or multiple landers that make up a robotic fuel collection and refining system. Then you have a reusable lander-launcher that lands, collects the fuel and delivers whatever it doesn't use for takeoff/landing into a orbital fuel deport orbiting either the moon or earth. Actually might be best to have your deport orbiting the moon until it's full then send it on a slow, low-fuel, multi-month path back to earth orbit, perhaps you meet the Mars transfer vehicle there.

If at any point the fuel transfer lander-launcher fails, you can launch a new one from earth and push back your Mars mission. Perhaps you have multiple fuel transfer landers as a contingency, or to increase throughput (fuel in orbit isn't just useful for a single Mars mission)

Only once you have your fuel ready, do you launch your Mars crew.

You could do a similar setup at Mars to collect fuel for your trip and avoid having to drag that fuel from the moon. But a Mars fuel transfer lander-launch would be much more complex and risky, and it would be a lot harder to land the fuel collection/refining facility.

Don't forget to add the rendezvous risk. It would also be extremely difficult to try and send it to meet the vehicle during the Mars transfer - the launch window eventually closes, and even during the launch window the ideal trajectories are quite different.

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