NASA: The development of the ESA portable sleep restraint system is described. The system was developed to simulate certain earthbound sleep conditions in microgravity. The restraint is a bag made of two sheets of Nomex(R) cloth stretched over a tubular tension device and provides the astronaut with feedback pressure similar to bedding on Earth. The final prototype of the bag was tested on the German Spacelab-D1 mission and during a six-month mission aboard MIR. Positive feedback from astronauts suggests the need for further evaluation during space flight.