Artists's Conception of Jupiter Icy Moons Orbiter

The Jupiter Icy Moons Orbiter (JIMO) was a proposed spacecraft designed to explore the icy moons of Jupiter. The main target was Europa along with Ganymede and Callisto, which are now thought to have liquid, salty oceans beneath their icy surface. This ocean is one of the places where very simple alien life is a possibility.

The JIMO mission was in its early planning stage and launch was not to be expected before 2015. It was to be the first proposed mission of NASA's Project Prometheus, a program for developing nuclear fission into a viable means of spacecraft propulsion.

However, the US president's 2006 budget request to Congress essentially cut funding for JIMO. Among other things the proposed nuclear technology was deemed too ambitious, as was the multiple-launch and in-orbit assembly mission architecture. The possibility remains that Congress might still restore funding for it.

The JIMO spacecraft

JIMO was to have a large number of revolutionary features. Throughout its main voyage to the Jupiter moons, it was to be propelled by ion propulsion and powered by a small nuclear reactor. Thermo-electric couples would convert reactor heat into electricity. A thousand times conventional spaceprobe electricity output will open up opportunities like flying a full scale ice-penetrating radar system and a strong high-bandwidth data transmitter.

Electric propulsion using 8 ion engines was meant to make it possible to go into and leave orbits around Jupiter moons, whereby more thorough observation and mapping will be possible than during short time fly-by maneuvers.

The design called for the reactor to be positioned in the tip of the spacecraft behind a strong radiation shield protecting sensitive spacecraft equipment. The reactor would only be powered up once the probe is well out of Earth orbit, so that the amount of radionuclides that must be launched into orbit is minimized. This configuration is thought to be less risky than the radioisotope thermoelectric generators (RTGs) used on previous missions to the outer solar system. RTGs contain large amounts of highly radioactive material which generate heat for the thermoelectric couples.

Northrop Grumman was selected on September 20, 2004 for a $400 million preliminary design contract, beating Lockheed Martin and Boeing IDS. The contract will run through to 2008. Separate contracts, covering construction and individual instruments, was to be awarded at a later date.

External links

• http://www.jpl.nasa.gov/jimo/
• http://www.jpl.nasa.gov/galileo/
• http://spacescience.nasa.gov/missions/prometheus.htm