This article is from the Space FAQ, by Jon Leech leech@cs.unc.edu and Mark Bradford tla@surly.org with numerous contributions by others.
Robert Zubrin and collaborators have developed several proposals for
near-term, low cost manned missions to Mars and the Moon. These
proposals center around the use of "indigenous propellants" to reduce
the mass which must be launched from Earth - for example, sending a
robotic "mining" vehicle to Mars before the astronauts arrive, which
would extract methane from the atmosphere for use on the return trip.
Some references are:
Zubrin, R. and Baker, D., "Mars Direct: A Simple, Robust, and Cost
Effective Architecture for the Space Exploration Initiative, AIAA
paper 91-0326, 29th Aerospace Science Meeting, Reno, Nevada, Jan.
7-10, 1991.
Zubrin, R. and Baker, D., "Humans to Mars in 1999", Aerospace
America, Aug. 1990, p. 30-32, 41.
Walberg, G., "Ho Shall We Go to Mars? A Review of Mission
Scenarios", Journal of Spacecraft and Rockets, Vol. 30, No. 2,
Mar.-Apr. 1993, p.129-139.
 
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