Ulysses hanging on valiantly (7/6/2008)

The orbit of Ulysses was chosen so as to chart the heliosphere - the sphere of influence of the Sun carved out by the solar wind that extends beyond the outer fringes of the Solar System - at all solar latitudes. Ulysses’s orbit is an ellipse with the Sun at one focus (heliocentric), and is inclined 80° with respect to the Sun’s equator (polar). The orbital period is 6.2 years. Maximum distance from the Sun (aphelion) is reached at about 810 million km (or 5.4 AU; one AU or Astronomical Unit equals the average distance between Earth and the Sun, or about 150 million km) and minimum distance (perihelion) is at about 200 million km (or 1.3 AU). Ulysses was launched on 6 October 1990. It then headed out to Jupiter, arriving on 8 February 1992 for the gravity-assist manoeuvre that swung the craft into its unique solar orbit. Over more than 17 years of operation, Ulysses orbited the Sun three times and performed six polar passes, during which the spacecraft was above 70° heliospheric latitude in either hemisphere (South pole: June-November 1994, September 2000 - January 2001, November 2006 - April 2007. North pole: June-September 1995, August-December 2001, November 2007 - March 2008). During its mission, Ulysses has travelled 8.6 thousand million km (or 57.65 AU) at an average speed of 56 000 km/hr. Credits: ESA (image by C.Carreau)

The Ulysses spacecraft, whose mission was expected to end on 1 July 2008, is hanging on valiantly as spacecraft controllers wait for a sign of the fuel freeze that would end the mission. This could happen any time now.

Controllers will know that the fuel needed to keep the antenna pointing towards Earth has started to freeze when Earth-pointing manoeuvres become less efficient and the radio signals from the spacecraft grow weaker.

In the meantime, Ulysses is still providing important science data as it pursues its exploration of the heliosphere, the sphere of influence of our star.

Although the spacecraft can now transmit data only in real time, the amazing 17.5-year-old mission is using all the time it has left to add to the wealth of information collected so far.

Ulysses is a joint mission between ESA and NASA. ESA provided the spacecraft, built by Astrium GmbH, Friedrichshafen, Germany (formerly Dornier Systems). NASA provided the Space Shuttle launch, the inertial upper stage and the payload assist module to put Ulysses into its correct orbit. NASA also provided the Radioisotope Thermoelectric Generator (RTG) to power the craft and its payload.

ESA's European Space Research and Technology Centre (ESTEC) and European Space Operations Centre (ESOC) have been managing the mission in coordination with NASA's Jet Propulsion Laboratory (JPL). Ulysses is tracked by NASA's Deep Space Network. A joint ESA/NASA team at JPL has overseen spacecraft operations and data management. Teams from universities and research institutes in Europe and the United States provided the 10 instruments on board.

Note: This story has been adapted from a news release issued by the ESA

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