The Twenty-Five-Foot Space Simulator is an -foot-high () stainless-steel cylinder at the Jet Propulsion Laboratory in Pasadena, California, that is foot (m) in diameter. It was declared a National Historic Landmark in 1985 and is on the National Register of Historic Places. It is used for testing spacecraft in space-like conditions of extreme cold, near-vacuum pressure, and high radiation. Ranger, Surveyor, Mariner, and Voyager spacecraft were all tested in this facility.