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The SpaceX system, which consists of the re-useable Dragon capsule and the Falcon 9 launch system is the most promising of all commercial designs. The Falcon 9 rocket, which has undergone 2 successful independent launch tests, has been cleared by NASA for a launch and docking mission to the International Space Station on April 30, 2012.The Dragon is currently a unmanned capsule designed for re-supply missions to the ISS, but two derivatives which can carry three or seven (The "Super Draco") astronauts are currently under development.The Falcon 9 rocket is a two-stage system which has been designed to be re-useable. As of the current date, SpaceX has not been able to recover the stages of the booster. Future versions of the Dragon capsule and the Falcon 9 stages, codenamed "Grashopper" are supposed to be able to launch, return from orbit and land vertically under their own power, sans parachute, a la "Buck Rogers", however SpaceX has not yet started testing of these radical design improvements in either the Dragon or the Falcon.Vital Specs: Falcon 9 Rocket
Boeing's CST-100 (Crew Space Transportation) is a large capsule capable of supporting up to 7-man crews and is designed to remain in orbit for up to 7 months at a time, and can be re-useable for up to 10 missions.The capsule is currently under preliminary development and has had mock-ups undergo parachute drop testing in the Nevada desert in April of 2012.NASA has leased space at the Orbiter Processing Facility in Kennedy Space Center for further manufacturing and tests of the CST-100.The CST-100 was designed to be compatible with several launch systems, including Atlas V, Delta 4, and SpaceX's Falcon 9.
MPCV (Multi-Purpose Crew Vehicle) is an outgrowth of the CEV (Crew Exploration Vehicle) of President George W. Bush's Vision for Space Exploration initiative that was announced in January of 2004. Various design changes have resulted in a capsule that can carry up to four astronauts, and is similar in outward appearance to the Apollo capsule from the 1960s.The Orion was originally designed to sit atop the Ares V booster system, which has since been cancelled by the Obama administration. Lockheed plans to do an initial unmanned flight test of the Orion using a Delta IV Heavy booster in 2014.