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Because everything you take to mars costs ~68% more fuel to get off of earth. Getting off of Earth is much harder than getting off of the moon, which has ~86% l
by chisleu 11y ago
Because everything you take to mars costs ~68% more fuel to get off of earth. Getting off of Earth is much harder than getting off of the moon, which has ~86% less gravity.
If you only take enough fuel to get to the moon, then you can load up there and enjoy a significantly easier time to get up to speed on the way to Mars.
I didn't see how much of a percentage difference it is in total fuel though, in the article. I'm expecting it is pretty close or they would have cited it instead of the Earth liftoff reduction.
- Cshelton 11y agoWell another consideration is the additional time added to the Mars trip. Right now, going directly from Earth, around Earth a bunch of times, then straight to Mars will be 6-9 months one way, which I believe the opportunity to come back would be ~2 years after arriving (I may be wrong here). So, assuming we are doing a round trip and not one way, it's already a 3 year trip ish? Either way, I see building a launching space station orbiting earth as the best way. Use smaller rockets like the falcon 9, get a bunch of fuel into orbit, build the ship from many parts and trips, then launch from Earths orbit. Make the built ship reusable for many Mars trips. Like in the Martian...
- TeMPOraL 11y agoA fuel station in LEO may be convenient, but it will still be much cheaper to ship fuel from the Moon than from the surface, Δv-wise. Per a handy Δv map[0], it's about 2.5km/s (if you aerobrake) vs. almost 10km/s to lift fuel from Earth. [0] - http://i.imgur.com/SqdzxzF.png http://i.imgur.com/SqdzxzF.png
- sandworm101 11y agoAerobrake a couple tons of liquid H2 and O2 in earth's atmosphere? Assuming it doesn't all boil off, it would certainly make for some nice fireworks.
- TeMPOraL 11y agoAdd moar heatshields, eh? ;). Also, I was thinking more about dipping in the atmo a little, doing the kind of aerobraking the ISS has to fight all the time. You don't have to make the entire insertion in one orbit.
- deciplex 11y agoYou have to at least aerobrake enough on the first pass to get into some orbit, and it's preferable if the orbital period isn't a few months before you get the second pass.
- sandworm101 11y agoIf you are returning from the moon, capture isn't the issue. You are already captured because the moon is captured. You are in a highly elliptical orbit around earth. So aerobraking is still an option, as opposed to the more violent aerocapture maneuver where it all has to happen in the first pass.
- deciplex 11y agoAh sorry I didn't pay enough attention :-( I thought we were talking about returning from Mars, not insertion into Earth orbit from the Moon.
- sandworm101 11y agoA slow series of aerobrakes would run up against the time factor. Today's H2 storage boils off about 1% per day. So if you spend a few weeks slowing things down gradually you quickly defeat the advantage as much of your fuel has escaped.
- TeMPOraL 11y agoDidn't consider that. Thanks! EDIT: Maybe there are some improvements for storage available that don't make sense on Earth given H₂ prices? A magnetic containment field, perhaps? Or whatever chemistry shenanigans are used for hydrogen fuel cells? You would be trading the time factor for mass and volume (the latter doesn't matter that much in space, and could even help with aeroinsertion), but it may still add up moneywise.
- sandworm101 11y agoOh it is more than 68%. That 68% gets you a flyby of Mars, landing is another issue. There are limits to what heatshields and parachutes can do in a thin atmosphere. If you wanted to accurately land something truly heavy you will have to bring fuel for the descent stage. Even just achieving a stable orbit would probably mean doubling that 68%.