Solar Satellite Near Death

Feb. 25, 2008 -- A pioneering solar probe that gave scientists their first look at what the sun was doing above its polar regions is about to enter an orbital grave after 17 years of ground-breaking research.

The spacecraft, named Ulysses, was launched aboard a space shuttle in 1990 and traveled 16 months to reach a vantage point near Jupiter to provide the first three-dimensional view of the heliosphere.

Several previous probes had looked at the solar equator, but only Ulysses, named after the Greek hero in Homer's "Odyssey," looked at the sun from midsection to poles in an orbit inclined 80 degrees to the sun's equator. It took Ulysses 6.3 years to make a pass around the sun at distances that ranged from 1.3- to 5.3 times the distance of Earth to the sun.

The probe measured the wild streams of particles gushing from the sun's poles during highly active and relatively quiescent phases of its 11-year cycles. It discovered the sun's magnetic flux was the same at all latitudes and that dust and helium atoms from outside the solar system were mingling with the natives.

"Ulysses has set the bar on solar science data collection quite high," said project manager Ed Massey, with NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Ironically, the distance that gave Ulysses its unprecedented view of the sun is what will be the death of it. A heater to warm the fuel for its thruster rockets no longer has enough power to operate. Engineers expect Ulysses' fuel to freeze as it is carried back out to Jupiter's orbit.

Power supplies are low because the spacecraft’s supply of radioactive plutonium is about spent.

NASA and the European Space Agency, which are partners on the project, turned off Ulysses main communications transmitter to try to stretch the power supply, but when they attempted to turn the radio back on last month, Ulysses remained silent.