Artist's impression of a manned lunar base. Permanently-manned bases on the Moon have been proposed to support a manned mission to the planet Mars. The low-gravity environment on the Moon could allow materials processing and construction projects that would be impractical on Earth. The objects and structures made on the Moon could be very easily launched into orbit for final construction of the Mars spaceship. The Moon has also been seen as an easy source of liquid oxygen. The US Space Commission has recommended that a lunar base should be built by 2005, with a manned mission to Mars in 2015.