Artist's impression of a large radio dish built into a crater next to 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. This large radio antenna would be used for communication and tracking purposes. The US Space Commission has recommended that a lunar base should be built by 2005, with a manned mission to Mars in 2015.