Ulysses Status Report - January 2009
02 February 2009 13:06
On 14 January 2008, during the mission's third north polar pass, the spacecraft reached maximum northern latitude on its third solar orbit. Around the same time the X-band transmitter onboard the spacecraft failed after its power supply could not be switched on again following what was planned to be a temporary switch off. This unfortunately has left the mission with S-band-only communication. The temporary switch off of the X-band transmitter was part of a plan to manage the naturally decreasing amount of available power from the spacecraft's generator after, at that time, more than 17 years of operations.
Operations and Archiving
The spacecraft no longer has enough power to run all of its communications, heating and scientific equipment simultaneously. Predictions regarding the remaining operational lifetime of Ulysses made earlier in the year following the loss of the X-band transmitter in January 2008 have proven to be pessimistic: the science mission is still ongoing, despite the low on-board temperatures. This is largely due to the introduction of "fuel bleeding", whereby two oppositely-directed thrusters are fired simultaneously every two hours, causing hydrazine fuel to move through a short length of pipework where fuel is likely to freeze.
Spacecraft operations and science data acquisition will continue using this same strategy until no more fuel remains or freezing occurs. Because of the increasing distance between the spacecraft and Earth, the S-band downlink can be used for playback of recorded data for very limited periods only. In general, spacecraft data received in real-time during a tracking pass are all that can be acquired.
With the spacecraft still sending back scientific data, albeit at a slower rate, the mission is not over yet: October 2008 marked the 18th anniversary of Ulysses in orbit. On 31 December 2008 Ulysses was at 32° N solar latitude and 4.1 AU from the Sun. All data is publicly available through the ESA Ulysses archive at: http://helio.esa.int/ulysses.
Among the latest Ulysses science results is the finding that the solar wind is currently at its weakest since the start of the space age. The observed long-term trend of lower dynamic pressures implies that the extent of the heliopause - the Solar System's buffer against galactic cosmic rays - has been shrinking.
The 2nd Heliospheric Network Workshop was held on 5-9 May in Kefalonia, Greece.
More than 1450 publications have been published by the end of 2008.