NASA boosts nuclear propulsion plans

From New Scientist: Link= www.newscientist.com...



"NASA has requested a "very significant" increase in funding for the development of nuclear propulsion systems for spacecraft, according to Sean O'Keefe, the administration's chief.

Existing chemical rocket technologies have restricted missions to the same speed for 40 years, he said. "With the new technology, where we go next will only be limited by our imagination."

O'Keefe revealed the significant new emphasis in an interview with Los Angeles Times: "We're talking about doing something on a very aggressive schedule to not only develop the capabilities for nuclear propulsion and power generation, but to have a mission using the new technology within this decade."

The request has been approved by US President George Bush and will now pass to Congress for approval. NASA's Nuclear Systems Initiative will also be renamed Project Prometheus.


Triple speed


Researchers believe new nuclear propulsion systems could triple the current speed limit for space travel of 29,000 kilometres per hour. This would make it possible, for example, get to Mars in two months, rather than six. But NASA has dismissed media speculation that it is planning a nuclear-fuelled mission to take astronauts to Mars.

O'Keefe's statement emphasised the technology, rather than any specific destinations. "The laws of physics are the only things controlling how fast we go anywhere," he said. "So until we beat the technical limitations ... you basically end up arguing about fantasy missions."

NASA's last budget request for its nuclear propulsion and power programme was $800 million over five-years. The value of the new, increased request has not yet been revealed.


Continual thrust


The power available from chemical propulsion systems is limited by the quantity of fuel that can be lifted out of Earth's gravity and into space. Spacecraft therefore use short bursts of power and coast towards their destination. Nuclear devices would deliver thrust continually, building up to much faster speeds.

The type of nuclear technology NASA plans to develop is not clear. In May 2002, O'Keefe told Senators: "We have got to find a 'leap ahead' technology."

Possibilities include improved ion drives. These use a nuclear reactor to supply electrically charged particles, which are expelled to drive a craft travelling through space. Such engines have already been used on NASA spacecraft like Deep Space One.




Fission reactor


NASA researchers have also suggested "nuclear-enhanced air-breathing rockets" to launch spacecraft from Earth. In these, a uranium dioxide fission reactor would heat hydrogen from an on-board tank to 2500�C. The hot hydrogen would then be mixed with air from outside the rocket and combusted at almost 4000 �C.

NASA launched one rocket with a nuclear fission unit in 1965. The Soviet Union is believed to have made 33 such launches. Despite billions of dollars of research in the 1950s and 1960s, nuclear propulsion was abandoned due to technical and political difficulties.

Nuclear generators already provide compact and long-lasting power sources for electronics aboard spacecraft too far from the Sun to rely on solar power. These radioisotope thermoelectric generators (RTGs) provide power by converting heat, produced through the natural decay of a radioactive isotope, into electricity. RTGs have been used on 25 different NASA spacecraft including Viking, Galileo, Cassini and Voyager. "


Will Knight and Damian Carrington