Saturn: The sixth planet in order from the sun. It is one of the five outer planets of the solar system. Its twelve natural satellites include Phoebe and Titan.Spacecraft: Devices, manned and unmanned, which are designed to be placed into an orbit about the Earth or into a trajectory to another celestial body. (NASA Thesaurus, 1988)Extraterrestrial Environment: The environment outside the earth or its atmosphere. The environment may refer to a closed cabin (such as a space shuttle or space station) or to space itself, the moon, or other planets.Atmosphere: The gaseous envelope surrounding a planet or similar body. (From Random House Unabridged Dictionary, 2d ed)Ice: The solid substance formed by the FREEZING of water.