 Phobos has also been proposed as an early target for a manned mission to Mars because a landing on Phobos would be considerably less difficult and expensive than a landing on the surface of Mars itself.A lander bound for Mars would need to be capable of atmospheric entry and subsequent return to orbit, without any support facilities (a capacity that has never been attempted in a manned spacecraft), or would require the creation of support facilities in-situ (a "colony or bust" mission); a lander intended for Phobos could be based on equipment designed for lunar and asteroid landings.Additionally, the delta-v to land on Phobos and return is only 80% of that for a trip to and from the surface of the Moon, partly due to Phobos's very weak gravity.