Trip to Jovian moons faces delay, but JIMO's nuclear power key to NASA's strategy
Launch of NASA's Jupiter Icy Moons Orbiter (JIMO) looks likely to be delayed from 2011-12 to 2015, but the nuclear-powered deep space probe is taking on increased importance under the agency's new space exploration vision.
The JIMO mission to explore the Jovian moons Callisto, Europa and Ganymede will pioneer nuclear power and electric propulsion technologies that are key to NASA's emerging plans for robotic and human missions to the Moon, Mars and beyond.
A nuclear fission reactor will provide power for electric propulsion, allowing a direct flight to Jupiter, with ample electricity available once in orbit to power a large scientific payload, probably including a radar to measure ice thickness and laser to map surface elevation as well as visible and infrared imagers and other instruments.
Teams led by Boeing, Lockheed Martin and Northrop Grumman are studying concepts for the mission, with a winning design to be selected in November. Even then, a number of design options will remain open for several months, says Boeing's JIMO programme manager, Dr Joe Mills. "The biggest trade space is the power conversion option, whether it is thermoelectric or dynamic rotating," he says.
The choice has a big impact on mission design. The JIMO is a large spacecraft, measuring 40-50m (130-165ft) from reactor to payload when fully deployed, and launch options depend on reactor type and power conversion technology. As thermoelectric is 4-5% efficient compared with 20% for more complex dynamic conversion, "for the same power level you need a significantly different reactor size", says Mills.
"They have to be packaged differently. In some cases they can be packaged for existing launch vehicles. In some cases they are too big," says Mills. Launch in a couple of pieces and assembly in a 1,000km (620 miles)-high nuclear-safe orbit is being looked at as an alternative to developing a larger launch vehicle.
"Safety is the number one requirement," he says, with the reactor being launched in a cold state and only being turned on once in a safe orbit.
GRAHAM WARWICK / WASHINGTON DC
Source: Flight International
