Cassini PSG Report from Athens
After almost 17 years working on Cassini it is hard to believe that we are now starting to talk about the end of the mission. At the Cassini Project Science Group meeting in Athens this week the segmentation of the extended mission (called the “XM”) was nearly settled, and work on integrating the XM will start in August. Segmentation is the allocation of different phases of the XM to the different Target Working Teams (TWTs, or “twits”, as they are affectionately known). Each twit is responsible for integrating different segments of the XM tour. I work on the Rings twit (and yes, this is what we actually call these groups), and starting in August our weekly telecons will resume where integrate our segments: we hash out between the different instrument teams what observations will be made at each time during our segments.
It took us about a year and a half to get to this point on the two-year XM, so we will need to start working on the XXM - the phase of the mission after the XM - next January with the science objectives for the period after June 2010 when the XM ends. The complicating factors are that we will not have as much maneuvering fuel to work with for the XXM as for the XM, and there are also “end-of-mission” considerations that have to be taken into account. What should be the fate of Cassini? NASA has a Planetary Protection Officer whose duty is to insure that we do not contaminate any object that may or might have harbored life with terrestrial organisms. No determinations have been made yet on the protection requirements for the Saturn system. Possible scenarios for Cassini include a plunge into Saturn like Galileo’s end at Jupiter, a long-term stable orbit that has no chance of impacting anything for centuries, escaping the Saturn system and crashing into Jupiter itself, escaping the Saturn system and going into a long-term heliocentric orbit, crashing into a small icy satellite of Saturn, or perhaps escaping Saturn toward Uranus. Some of those options require significant amounts of fuel, so the determination on the end-of-mission will affect the science options for the XXM.