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Ulysses Status Report April 2005

Status Report From: European Space Agency
Posted: Thursday, May 12, 2005

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The spacecraft and its scientific payload are in good health, and no anomalies have occurred during the reporting period. The situation concerning the budget for NASA's contribution to the mission remains a concern.

NASA has requested that the JPL Project formulate a Closeout Plan for Ulysses as a contingency measure in case funds are not restored. The project team at JPL has thus been instructed to draft a plan based on an assumed termination of routine spacecraft operations on 31 December 2005. The ESA Mission Operations Team members, located at JPL, have provided technical input where appropriate. This includes preparation of detailed end-of-mission procedures for spacecraft switch-off that is in any case required for the nominal end of mission in 2008.

On 1 May 2005, Ulysses will be at a radial distance of 5.1 AU from the Sun, and heliographic latitude 22° south of the solar equator.

Operations and Archive

All science operations during the reporting period have been nominal. Payload operations are being conducted according to the pre-determined power-sharing plan. The proposed switchon of the Ulysses Gamma-ray Burst instrument to support post-launch calibrations of instruments on NASA's Swift gamma-ray burst satellite was deemed unnecessary based on the satisfactory in-orbit performance of the Swift payload. The Ulysses GRB instrument will therefore remain off until the on-board power/thermal situation improves (probably not before April 2007). The ESA Ulysses archive is accessible on-line at: http://helio.esa.int/ulysses.

Science Highlights

The location of Jupiter with respect to the structure of the heliospheric magnetic field is precisely determined and non-central. This makes electrons emitted by Jupiter ideal tracers for studying particle propagation throughout the inner heliosphere. In mathematical terms, the propagation is usually characterized by a diffusion tensor. In recent work, Ulysses electron observations during the close (1992) and distant (2004) Jupiter encounters were analyzed to study the time dependence of the diffusion parameters. Since the observations from both periods were obtained during the declining phase of the solar cycle, it was expected that the electron intensities in 2004 would vary in the same way as the 1992 observations. This was found not to be the case, however. During the 2004 encounter, in contrast to 1992, Ulysses did not enter the Jovian magnetosphere but remained upstream of it. In mid-2002, the electron flux started increasing and displaying large short-term variations. These features lasted throughout the encounter, making the electron intensities less obviously correlated with the proximity to Jupiter compared with the first Jovian encounter. The suggestion is that the diffusion coefficients, and in particular perpendicular diffusion in the polar direction, are highly time-dependent.

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