Astronaut Mark Lee floats freely as he tests the new backpack called the Simplified Aid for EVA Rescue (SAFER) system. SAFER is designed for use in the event a crew member becomes untethered while conducting an EVA. The STS-64 mission marked the first untethered U.S. EVA in 10 years, and was launched on September 9, 1994, aboard the Space Shuttle Orbiter Discovery.