NASA’s Office of Space Science recently awarded a $7 million contract to the US Department of Energy’s ORNL, Boeing and Swales Aerospace to develop a potassium Rankine cycle power conversion system. The unit would convert thermal energy to electric power aboard a spacecraft.
‘The power conversion system we’re developing employs a similar approach to that used in nuclear reactors to produce electricity on Earth,’ said Sherrell Greene, who leads ORNL’s space reactors research and development activities. ‘The big difference is that this one has to operate in zero gravity, and that poses several challenges.’
When coupled with a nuclear reactor, the Rankine system would reportedly produce megawatts of power in a compact sized-unit capable of operating in hostile environments typical of outer space.
Greene added that these units boast energy densities 10 million times that of chemical propellants and can provide electrical power over the long lifetime that would be essential for exploration of distant planets like Jupiter, Saturn and Pluto.
‘To give you an idea of the distances involved, it takes nearly 71 minutes for a radio signal to travel to Saturn,’ Greene said. ‘And it takes almost five and a half hours for a radio signal to travel from Earth to Pluto.’ Radio frequency signals travel at 186,000 miles per second.
Manned and unmanned missions to the outer regions of our solar system require massive amounts of power for electrical propulsion, spacecraft command and control, and scientific research. The lack of technologies capable of generating adequate power has made it impossible to truly explore the farthest reaches of our solar system, Greene said. But that obstacle could soon fall.
The contract issued by NASA will enable principal investigator Grady Yoder and his colleagues to design and fly a low-temperature technology demonstration unit within three years.
This first system would use freon or a similar fluid to demonstrate control and management of two-phase liquid-vapour phenomena required to use the Rankine power conversion approach in space. The next step is to design and build a second, higher-temperature demonstrator using stainless steel and a liquid metal more like what would be used in the actual unit.
The first demonstration unit is scheduled to fly in space in the late spring or early summer of 2005.