Jupiter Icy Moons Orbiter
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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 2017. 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. NASA is instead considering a demonstration mission to a target closer to earth to test out the reactor and heat rejection systems. The spacecraft would possibly be scaled down from its original size as well.
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. A Brayton power conversion system 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, along with Hall thrusters of varying sizes was meant to make it possible to go into and leave orbits around Jupiter's 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, were to be awarded at a later date.
Preliminary design specifications
- Science payload mass: 1500 kg
- Electric turboalternators: multiple 104 kW (440 V AC)
- Deployable radiator: 422 m² surface area
- Electric Herakles ion thrusters: multiple 30 kW high efficiency, specific impulse 7000 lbf·s/lb (69 kN·s/kg)
- Hall thrusters: high power, higher thrust
- Telecommunications link: 10 Mbit/s (4×250 watt TWTA)
- Deployed size: 58.4 m long × 15.7 m wide
- Stowed size: 19.7 m long × 4.57 m wide
- Mission design life: 20 years
- Launch date: 2017
Source (http://www.st.northropgrumman.com/capabilities/Content.cfm?ContentID=348)
External links
- Northrop Grumman website for Prometheus I (JIMO) (http://www.st.northropgrumman.com/capabilities/Content.cfm?ContentID=348)
- JIMO webpage at NASA JPL (http://www.jpl.nasa.gov/jimo/)
- Project Prometheus overview (http://prometheus.jpl.nasa.gov/)de:Jupiter Icy Moons Orbiter