Two More Years at Saturn
The Cassini mission at Saturn is going swimmingly, as my father would have said. The spacecraft is healthy, the instruments are healthy (yes, we do tend to attach human attributes to these machines), and the discoveries are piling up more quickly than we can report. One of the things that has struck me about the UVIS observations I work with is the tremendous advantage it is to have multiple observations from different vantage points, and at different times. The combination of the observations is truly greater than the sum of the parts. So I am hopeful that an “extended mission” or “XM” will be approved for Cassini to continue observing Saturn and its family of rings and moons for another two years after the nominal mission ends June 30, 2008.
In anticipation of such an extension, the project has been working on the trajectory the spacecraft will fly for the two year XM. The trajectory, called a “tour”, determines the viewing geometry available to the spacecraft. Because Cassini’s targets include Saturn’s many icy moons, the giant moon Titan, as well as the rings and magnetosphere, a wide variety of viewing geometries are desired. Clever use of gravity assists by Titan and natural perturbations to Cassini’s orbit due to Saturn’s aspherical gravitational field (Saturn is squashed by about 10% in the North-South direction because it (a) rotates in only 10.6 hours, and (b) is a big floppy gas-bag sort of a planet, with a bulk density less than water; this causes Cassini’s orbit to precess around Saturn rather than repeating perfectly) allow the tour designers at JPL to come up with a wide variety of tour options and to meet the observation requirements of a highly diverse set of scientific goals. A final decision on the XM tour is expected in early February. The two-year XM will allow Cassini to continue observations of all its science targets at Saturn in the same style that it is currently operating, namely very productively.
The spacecraft will still have power and fuel available after a two year XM, so I’m also hopeful for an XXM.