In an emergency, crew would board the Crew Return Vehicle, undock from the ISS and begin its descent to Earth in a shirtsleeves environment. Its landing will be completely automated, but the crew will be able to override the automation system. A Russian Soyuz spacecraft will serve as the Crew Return Vehicle during early ISS assembly. When a crew of seven is able to work on the ISS beginning in 2003, a larger vehicle will be needed. The X-38's capacity and ability to remain docked at the Station for three years will provide the efficiency and reliability that will be required when the ISS is fully operational.
Plans call for four of the spacecraft initially to be produced.
NASA began study of the X-38 concept in 1995 at Johnson Space Center. Free-flight drop tests began the following year, 1998. Testing includes use of a 5,500 sq.-ft. Drop tests using Navstar GPS signals for guidance will continue through 1999. NASA's Johnson Space Center is planning an unpiloted space flight test from the Space Shuttle in 2001.