Ulysses Status Report - November 2004
As a result of the poor link margins, the possible data rates were lower than usual, although actual data losses were kept to a minimum. Routine operations commenced once again on 8 September, with a return to normal data recovery.
Following the approval by SPC at its February 2004 meeting to extend spacecraft operations until March 2008, steps have been initiated to extend the ESA-NASA Memorandum of Understanding for Ulysses accordingly. The current MOU is valid until the end of the year.
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. A core set of instruments providing the key science measurements is being operated continuously, together with one or more discretionary instruments depending on the thermal conditions and available power. In accordance with cost-saving measures agreed at the time of the 2003 Senior Review at NASA, as of 1 October 2004, the baseline telemetry coverage via the DSN will be reduced from 70 hrs per week to 35 hrs per week on average. Normal coverage will resume in November 2006 to support the 3rd set of polar passes. The ESA Ulysses archive is accessible via the World Wide Web at URL: http://helio.esa.int/ulysses.
Following the interesting Jupiter Distant Encounter earlier this year, the scientific focus of the mission has returned to the Sun and the evolution of the solar wind in the approach to activity minimum. As the spacecraft heads further south, it is expected to encounter relatively stable solar wind stream structures that co-rotate with the Sun, similar to those seen in 1992/93. A major difference, however, will be the polarity of the Sun's magnetic field that underwent a reversal during the recent solar maximum period.
Another topic of continuing interest, and one to which Ulysses is making unique contributions, is the study of so-called "inner-source" pick-up ions. In contrast to pick-up ions of interstellar origin that are created through ionisation of neutral interstellar gas that penetrates the heliosphere, the precise origin of the inner-source ions remains uncertain. Among the possible candidates are neutral solar wind atoms that are implanted in, and subsequently released from, dust grains close to the Sun. The composition of the inner source is certainly not cometary in nature, making Sun-grazing comets an unlikely progenitor. Ulysses measurements have demonstrated clearly that the population of inner-source ions extends out as far as the orbit of Jupiter, suggesting that several different sources may be contributing. In addition to the intrinsic interest in these ions, they also form a potentially important seed population for injection into shock acceleration processes that give rise to fluxes of energetic particles of non-solar origin found throughout the heliosphere.