SAFER backpack test. Astronauts Carl Meade (left) and Mark Lee (right, on RMS arm) seen testing the Simplified Aid for EVA Rescue (SAFER) system during Shuttle Mission STS-64. In this test Meade was evaluating SAFER's automatic stabilising system after Lee span him round. SAFER is a scaled-down version of the Manned Manoeuvring Unit (MMU) used in Shuttle space walks, and is intended to provide emergency free-flying mobility or a self-rescue capability to astronauts during extravehicular activity (EVA). SAFER clips around the normal life-support backpack, and is powered by 24 fixed nitrogen thrusters. STS-64 flew on 9- 20 September 1994.