1. Lunar propellant manufacture and its economic benefits for space transportation;Rosenberg,1991
2. Mars direct: combining nearterm technologies to achieve a two-launch manned Mars mission;Baker,1990
3. Mars direct: a simple, robust, and cost-effective architecture for the space exploration initiative;Zubrin,1991
4. America on the threshold: report of the Synthesis Group on America's Space Exploration Initiative;Stafford,1991