>>11751988a voyage with chemical propellants going in the best windows doesnt take months, it takes closer to 2 years. consider:
- the food which needs to last the entire round trip
- the space. on the ISS the astronauts spend 5-6 months, and even that is a little cramped.
- the resources for the ECLSS, which runs at nowhere close to 90% efficient in a zero g environment
- the bone mass loss and muscle atrophy of a crew spending all that time in a zero g environment
- or, if you have a rotating spacecraft, the mass for that system. even something as simple as a long tube rotating still has mass.
- the mass of the radiation shielding needed to protect the astronauts outside the earth's magnetosphere (an inch of lead, if I recall)
- the mass of the experiments and the entertainent equipment needed for the crew to not kill each other out of boredom
- etc etc
lowest estimate, using aerocapture/-braking all over (unrealistic but whatever), you're still looking at 5 km/s dv roundtrip. of course, you'll also want the vessel to be 100% reusable, or you'll have to manufacture and launch this hardware (or stages) every single time you want to go to mars.
lets say 70 tons of sheer payload to serve the crew? the iss is 420 tons, so i doubt that we'd make 70 tons for this considering the duration of the trip and the lagt of magnetosphere, but whatever. plug that into the rocket equation and you'll probably get a completely ridiculous fuel mass. now you gotta factor in the tank mass too, which becomes especially demanding when the vessel needs to be reusable (unless you're using balloon tanks, which have issues of their own).
i don't know what fuel we intend to run with, but all of them have their issuess, mostly regarding the tradeoff between ISP and the boiloff of cryogenic fuels.
Chris Hadfield agrees with the following conclusion: we are not going to Mars with chemical engines.
