Twenty-Five-Foot Space Simulator, Space simulation facility at Jet Propulsion Laboratory in Pasadena, United States.

The Twenty-Five-Foot Space Simulator is a large testing chamber at the Jet Propulsion Laboratory in Pasadena that recreates the conditions of space. The facility contains a steel cylinder with aluminum components and a system designed to produce extreme cold, heat, and near-perfect vacuum.

Built in 1961 at the Jet Propulsion Laboratory in Pasadena, the stainless-steel chamber was the first facility of its type and became a model for other countries establishing space programs. It prepared the Ranger, Surveyor, Mariner and Voyager probes for launch, and Ingenuity, the first helicopter to fly on Mars, was tested inside it. It was declared a National Historic Landmark in 1985 and is listed on the National Register of Historic Places.

The simulator's name comes from its 25-foot interior diameter. Its role in testing Ranger, Surveyor, Mariner and Voyager probes made it a model for other nations starting space programmes. The Mars helicopter Ingenuity, which flew from 2021 to 2024, was also prepared here. A clean room beside the chamber is where equipment is readied before testing.

The chamber stands 85 feet tall and 27 feet in diameter, with a 15-foot-wide, 25-foot-high doorway for test objects and a personnel door built into it. Reaching space-like conditions takes about 75 minutes; returning to normal takes about two and a half hours. A clean room next to the chamber is used to prepare equipment for testing.

The chamber's walls and floor are lined with cooling shrouds that hold a controllable range from −320 °F to 200 °F. Reaching a space-like environment takes about 75 minutes, while returning to normal conditions takes about two and a half hours. A clean room next to the chamber prepares equipment for testing.