Ulysses and IDL Explore Interplanetary Space above the Poles of the Sun

In October 1990, the Space Shuttle Discovery lifted off from the Kennedy Space Center on mission STS-41, carrying the ESA-NASA spacecraft, Ulysses, into orbit to begin its journey charting the region of interplanetary space above the poles of the Sun. Just like its namesake from Greek mythology, Ulysses has had to endure many difficulties along its voyage of discovery. The spacecraft had to carefully navigate the damaging radiation environment of Jupiter in a swing-by manoeuvre designed to escape the confines of the ecliptic plane by making use of the planet's immense gravity. Shortly after launch, Ulysses developed an unexpected wobble caused by uneven heating of one of its booms by the Sun. This has made it necessary for the Mission Operations team at the Jet Propulsion Laboratory in California to monitor and regularly correct the spacecraft pointing to Earth in order to maintain vital communication links during the near-Sun portion of the orbit. An additional challenge the team have had to face is the steadily declining output from the radioactive source used to power Ulysses and protect its sub-systems and scientific instruments from the freezing cold of deep space. Having survived all of these hardships, the mission is now in its 17th year of continuous operation. In the spring of 2008, Ulysses will complete its third set of polar passes, possibly marking the end (barring any future extensions by ESA and NASA) of a truly collaborative venture.

Ulysses provides scientists with unique measurements made by a suite of sophisticated instruments designed and built by teams from leading space physics centres in both Europe and the US. The payload chosen to fly on Ulysses comprises: a magnetometer (VHM/FGM); two solar wind plasma instruments (SWOOPS and SWICS); a combined radio/plasma wave experiment (URAP); three energetic charged particle instruments (EPAC, HI-SCALE and COSPIN); an interstellar neutral gas sensor (GAS); a solar X-ray/cosmic gamma-ray burst telescope (GRB); and a cosmic dust detector (DUST). In addition, the ground communications system allowed Ulysses to perform two radio science investigations to study the solar corona and to search for gravitational waves.

Ulysses data, documentation and data products are disseminated to interested users through the mission data archives. In Europe, the archive is the Ulysses Data System (UDS) which is maintained at ESTEC, ESA's technology centre in Noordwijk, the Netherlands. Currently, plots of selected data parameters from each experiment are made available to visitors of the archive website to browse the data for periods of interest. These plots also serve as a check on the quality of the data provided by the experimenter teams to the mission archives. A limitation of the plots is that they are pre-generated and do not combine parameters from different instruments in the same diagram. 'As part of an evolving archive, we would like to offer the user the possibility to interactively select arbitrary time periods and to plot a combination of parameters from several instruments in one figure' says Cecil Tranquille, the coordinator for the UDS. To this end, CREASO was contracted to provide the UDS with an interactive IDL application capable of providing exactly this functionality. The product is called UDS Viewer, a GUI application, developed using an object oriented approach, allowing the user to select a mix of Ulysses data from the many instruments, and to create specific tailored plots. An added advantage of this tool is the possibility to export the plot into the iPlot environment, allowing the user to modify the final product for inclusion in presentations and publications.

The IDL application is currently available from the UDS website (http://helio.esa.int/ulysses/archive/) as a SAV file for free-of-charge use with the IDL Virtual Machine. In the near future, the application will be integrated into a new look mission archive website providing interactive selection of data and the capability of on-the-fly graphics.