Slashdot Mirror
Going To Mars Via the Moon (mit.edu)
An anonymous reader writes: Getting anywhere in space is a difficult proposition — at least, if you want to get there in a timely manner. Rocket propulsion requires combustion mass. The more mass you take, the more you need. A team at MIT has found that establishing fuel-generating infrastructure on the Moon could reduce launch mass for missions to Mars by up to 68%. "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 (PDF), which would then head to a nearby fueling station to gas up before ultimately heading to Mars." The technology to make this happen is not difficult to build; it just requires a lot of money. Once it's in place, it'll cut down on expensive launch costs. As the commercial space industry gets going and launches happen more often, such an investment starts to make more and more sense.
I would rather NASA goes somewhere, even the Moon, than plans to go somewhere even better, such as Mars, but never gets off the ground. The Mars discussions are like the Wright Brothers complaining it's not worth building the Wright Flyer until they solve how to cross the Atlantic, because who really wants to fly 259.7 meters on a sandy beach.
Of course the rich Republicans drive around in $80,000 luxury pickups to try and show that they're from a working class country background.
I think the idea is to launch the fuel into orbit FROM the moon.
1.) Goto Moon
2.) Mine/Generate fuel
3.) Launch fuel into orbit - this step is key
4.) Launch smaller payload from Earth
5.) Payload meets fuel in orbit around the Moon
6.) Payload continues to Mars
If you only have to launch the payload with limited fuel, you don't need to use fuel to get other fuel into orbit. Also, the Moon has a much smaller gravity well and NO air resistance so launching anything into orbit around the moon is much more efficient than launching something into Earth orbit - this step 3 and I think where the 68% savings is supposed to come from. You only need rockets big enough to get a payload off the Earth and fuel into Lunar orbit - there is no need for the one big rocket launching everything at once.
Another good thing about that way of doing it is that by the time you've built the fuel-making plant, you've had to learn how to live there without constant resupply of air and food. Once you've done that, you have the beginnings of a colony there, and you can use what you've learned once you reach Mars. And, building a self-sustaining base on Mars will be easier than on the Moon because Mars has an atmosphere, making pressure issues simpler and giving you some protection against the smaller micrometeorites.
Good, inexpensive web hosting
While the lead comment of this particular thread is funny, there actually is fuel on the Moon, in the form of oxygen in rocks, and hydrogen from the Solar Wind. There is also plenty of solar energy available, for cracking oxygen loose from the rocks, and for collecting/concentrating the hydrogen. Let us imagine a Moon-girdling system of solar power collectors and hydrogen collectors, plus power transmission lines so a single large oxygen-extraction plant can operate continuously even when it is night on the Moon.
NOW imagine we aren't the only species in the Universe that does something like that. If they use Alternating Current in those power-transmission lines, then we could put radio telescopes on the Moon and detect radio waves of the AC-power frequency from distant civilizations. (Can't detect any AC from a home-world that has an ionosphere; can only detect AC from airless worlds.) If they use Superconducted Direct Current, we are out of luck with respect to detecting them. Note AC could be cheaper than SDC, but SDC will be more energy-efficient --yet stellar energy is "free" after the capital cost of infrastructure, so some alien civs might use AC and others might use SDC (and I have no idea which we might use, unless we decided to be paranoid and use SDC to be less detectable).
An asteroid mining tug can bring back about 200 times it's starting mass over a reasonable operating life, making multiple trips. The right kind of asteroid is 20% carbon compounds and water, which can be reformed to hydrocarbons + oxygen, i.e. high thrust rocket fuel. So the fuel return ratio is 40:1. Extracting the carbon compounds and water requires an oven, which is pretty easy to do with sunlight and mirrors. You also need an electrolyzer, to split the water, refrigeration to liquefy the oxygen, and hydro-cracking unit to add the Hydrogen to the carbon compounds (they are typically polycyclic aromatics).
If you do the processing in high orbit near the Moon, like the L2 point, you can skip the launch step and just dock and tank up.
Most people also don't know you can "scoop mine" the Earth's upper atmosphere from orbit. Skimming air at 200 km altitude requires adding 7.5 km/s of velocity to bring it to orbit, but electric thrusters have exhaust velocity of ~30-50 km/s. Therefore a fraction of the air you scoop up can make up the drag you create. You need lots of solar arrays to power the thrusters, but they can power bringing multiple times their own mass in air to orbit. The part you keep can be used as additional propellant for other missions, or as air for breathing, or as 8/9ths of the mass of water (you still need to bring the Hydrogen somehow).