Advanced propulsion researchers at NASA are a step closer to solving the challenge of safely sending human explorers to Mars and other solar system destinations. 

By using an innovative test facility at NASA's Marshall Space Flight Center in Huntsville, Ala., researchers are able to use non-nuclear materials to simulate nuclear thermal rocket fuels -- ones capable of propelling bold new exploration missions to the Red Planet and beyond. 

The Nuclear Cryogenic Propulsion Stage team is tackling a three-year project to demonstrate the viability of nuclear propulsion system technologies. A nuclear rocket engine uses a nuclear reactor to heat hydrogen to very high temperatures, which expands through a nozzle to generate thrust. Nuclear rocket engines generate higher thrust and are more than twice as efficient as conventional chemical rocket engines. 

The team recently used Marshall's Nuclear Thermal Rocket Element Environmental Simulator, or NTREES, to perform realistic, non-nuclear testing of various materials for nuclear thermal rocket fuel elements. In an actual reactor, the fuel elements would contain uranium, but no radioactive materials are used during the NTREES tests. Among the fuel options are a graphite composite and a "cermet" composite -- a blend of ceramics and metals. Both materials were investigated in previous NASA and U.S. Department of Energy research efforts. 

Nuclear-powered rocket concepts are not new; the United States conducted studies and significant ground testing from 1955 to 1973 to determine the viability of nuclear propulsion systems, but ceased testing when plans for a crewed Mars mission were deferred. 

The NTREES facility is designed to test fuel elements and materials in hot flowing hydrogen, reaching pressures up to 1,000 pounds per square inch and temperatures of nearly 5,000 degrees Fahrenheit -- conditions that simulate space-based nuclear propulsion systems to provide baseline data critical to the research team.

Source:-http://www.nasa.gov/topics/technology/features/ntrees.html