Ulysses spacecraft retires after 17 year mission

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Tuesday, July 1, 2008

Ulysses before launch

The Ulysses spacecraft has been retired from service today, following a successful 17-year mission. The probe was launched aboard Space Shuttle Discovery, in October 1990. Following separation from Discovery, Ulysses was boosted into a Heliocentric orbit by an Inertial Upper Stage, and a Payload Assist Module.

Ulysses was a joint venture between the European Space Agency (ESA), and the United States National Aeronautics and Space Administration (NASA). Its primary mission was to study the Sun. It made several significant discoveries, including that the density of dust particles in the solar wind was over 30 times what scientists had expected, and that the solar magnetic field was weaker, and more complex, than expected.

Over the last few years, the spacecraft has started to show its age, and several major systems have failed. When one of the high-band communications antenna was shut down to conserve power, technicians were unable to restart it, and from January onwards, the low-band antenna had to be used to relay all data to and from the probe. When the main power system started to fail, the decision was taken to retire the spacecraft before its propellant froze, making it completely inoperable.

Ulysses operated for over three times its design life. It was originally planned to survive for five years, and make a single orbit of the Sun. Its seventeen year mission duration made it one of the oldest spacecraft in service at the time of its retirment, along with the Hubble Space Telescope, which was launched just six months earlier, the Voyager probes, and the much older Pioneer Solar probes. It was also one of a handful of spacecraft to use a nuclear radioisotope thermoelectric generator to generate power.