Mars Direct is a 1990 proposal by Robert Zubrin and David Baker for a manned Mars exploration program. Mars Direct focuses on getting to Mars quickly using current space technologies, a direct launch from Earth, and using the Martian atmosphere instead of chemicals brought from Earth. NASA and Stanford University later reviewed Mars Direct, and while several NASA plans based on it have been published, none has been given official status as NASA’s plan for getting humans to Mars.
Under Mars Direct, the vehicle that will return to Earth is launched two years ahead of the crew. This vehicle, which carries a crew compartment, rocket engines, and a nuclear reactor, arrives on Mars well ahead of the crew’s arrival and immediately begins producing rocket fuel for the return journey. Methane, or natural gas, is the fuel, which can be made using hydrogen from Earth and carbon dioxide from the Martian atmosphere. On Mars, methane can be used to power generators and engines, and chemical reactions can produce oxygen for the crew to breathe.
The Mars Direct crew would launch two years later, on a heavy-lift vehicle similar to Project Apollo’s Saturn V. Instead of being assembled in space, the crew’s spaceship is launched in one piece from Earth’s surface and lands in one piece on Mars’ surface. After the crew has completed their Mars exploration, they drive to the return vehicle, which is now fully fueled, and take off for Earth.
NASA and others have proposed several different versions of Mars Direct. The NASA version of Mars Direct employs three launches, one of which is used to place an Earth return vehicle in Mars orbit, which the crew would dock with as they ascended from the Martian surface. Although Mars Direct avoids speculative or undeveloped technologies in order to keep the mission simple to execute, several untested technologies, such as nuclear thermal rockets and artificial gravity, can be incorporated into the design if they are available.