4 ms·

LEO is the most expensive part, but we know how to do it pretty well at this point. Landing something big enough to carry humans on Mars, on the other hand, is

by rquantz 11y ago

LEO is the most expensive part, but we know how to do it pretty well at this point. Landing something big enough to carry humans on Mars, on the other hand, is a problem we haven't solved yet.

rbanffy 11y ago
Landing won't be the hardest part - any Earth-rated capsule with rockets like the human-rated Dragon can do the last leg provided you are leaving Martian orbit with some rocket to slow you down. You may need parachutes to slow the craft to the point the rockets can make their part. Curiosity was complicated because they didn't want to touchdown on rockets. Now, accelerating a Mir-sized craft towards Mars and decelerating it to orbit while keeping the crew alive for a year outside the Earth's benevolent magnetic field and having enough fuel to accelerate back to Earth (even assuming we'll throw out the interplanetary craft and get to Earth on a capsule) is quite an impressive engineering feat. I'm inclined to suggest that, instead of building a vehicle like that we build one or more cyclers that will orbit the Earth-Mars-Sun system periodically and astronauts would only need to reach them in order to get back and forth. This way we pack all shielding for the long-duration trip into the cyclers and astronauts only need to carry the consumables they'll use. Since reaching them would be time-critical (they won't stop), I would suggest building a similar one that could be stationed in Martian orbit to serve as a fallback plan in case a crew misses the one cycler and has to wait a couple months for the next bus home. These two spacecraft are, essentially, space stations with clever orbits we could maintain with regular resupply missions just as we do with the ISS, but we'd need beefier rockets because the delta-v is the same as a craft going to Mars (because that's what it's doing). Luckily, we'd only need to accelerate the resupply craft - living space is "free" after the first burn. I am uncertain if these craft are more or less complicated than building and landing the Mars ascent vehicle (much worse than landing a crew capsule, for sure). This sounds very complicated to me.
- redahs 11y ago
  > accelerating a Mir-sized craft towards Mars and decelerating it to orbit while keeping the crew alive ... and having enough fuel to accelerate back to Earth ... You don't need to ship enough fuel to return to Earth in the same trip as a manned crew. You can send orbital depots for return fuel and ascent\descent vehicles ahead of time in unmanned missions. This could be done multiple years in advance. When you are launching the crew and interplanetary habitat, you only need to bring enough fuel for a one way trip.
  - rbanffy 11y ago
    It's true, and a clever approach. Since the orbiting propellant depots on Mars would have gotten there with engines, the simplest approach would be to dock the Mars departure vehicle (which could just be the service module of the Mars ascent vehicle) and dock it to the propellant depot and use it as a propulsion stage to match the trajectory of the next cycler passing by. Docking that vehicle with the cycler would allow any extra fuel to be used for trajectory corrections. As long as the mass you are adding to the cycler has propellant and an engine, there is no big issue with adding it.

by rquantz 11y ago

LEO is the most expensive part, but we know how to do it pretty well at this point. Landing something big enough to carry humans on Mars, on the other hand, is a problem we haven't solved yet.

rbanffy 11y ago

Landing won't be the hardest part - any Earth-rated capsule with rockets like the human-rated Dragon can do the last leg provided you are leaving Martian orbit with some rocket to slow you down. You may need parachutes to slow the craft to the point the rockets can make their part. Curiosity was complicated because they didn't want to touchdown on rockets. Now, accelerating a Mir-sized craft towards Mars and decelerating it to orbit while keeping the crew alive for a year outside the Earth's benevolent magnetic field and having enough fuel to accelerate back to Earth (even assuming we'll throw out the interplanetary craft and get to Earth on a capsule) is quite an impressive engineering feat. I'm inclined to suggest that, instead of building a vehicle like that we build one or more cyclers that will orbit the Earth-Mars-Sun system periodically and astronauts would only need to reach them in order to get back and forth. This way we pack all shielding for the long-duration trip into the cyclers and astronauts only need to carry the consumables they'll use. Since reaching them would be time-critical (they won't stop), I would suggest building a similar one that could be stationed in Martian orbit to serve as a fallback plan in case a crew misses the one cycler and has to wait a couple months for the next bus home. These two spacecraft are, essentially, space stations with clever orbits we could maintain with regular resupply missions just as we do with the ISS, but we'd need beefier rockets because the delta-v is the same as a craft going to Mars (because that's what it's doing). Luckily, we'd only need to accelerate the resupply craft - living space is "free" after the first burn. I am uncertain if these craft are more or less complicated than building and landing the Mars ascent vehicle (much worse than landing a crew capsule, for sure). This sounds very complicated to me.

redahs 11y ago
> accelerating a Mir-sized craft towards Mars and decelerating it to orbit while keeping the crew alive ... and having enough fuel to accelerate back to Earth ... You don't need to ship enough fuel to return to Earth in the same trip as a manned crew. You can send orbital depots for return fuel and ascent\descent vehicles ahead of time in unmanned missions. This could be done multiple years in advance. When you are launching the crew and interplanetary habitat, you only need to bring enough fuel for a one way trip.
- rbanffy 11y ago
  It's true, and a clever approach. Since the orbiting propellant depots on Mars would have gotten there with engines, the simplest approach would be to dock the Mars departure vehicle (which could just be the service module of the Mars ascent vehicle) and dock it to the propellant depot and use it as a propulsion stage to match the trajectory of the next cycler passing by. Docking that vehicle with the cycler would allow any extra fuel to be used for trajectory corrections. As long as the mass you are adding to the cycler has propellant and an engine, there is no big issue with adding it.