The Twenty-Five-Foot Space Simulator is a chamber for testing spacecraft in space-like conditions, including extreme cold, high radiation, and near-vacuum pressure.

It has been used to prepare many American space probes for their launches, including the Ranger, Surveyor, Mariner, and Voyager spacecraft.

The first facility of its type, the chamber served as an example for other countries seeking to establish space programs.

Its walls and floor are lined with cooling shrouds that help provide a controllable temperature range from −320 °F (−195.6 °C) to 200 °F (93 °C).

A series of lamps, lenses, and mirrors can irradiate the chamber with a directed beam of simulated solar energy in a variety of patterns and strengths.