Todd J. Barber, Cassini lead propulsion engineer
Happy 2008 from the Cassini team at NASA's Jet Propulsion Laboratory! I can't believe this last calendar year of the prime mission has begun. At times during our seven-year, two-billion-mile cruise from Earth to Saturn, it seemed as if the ringed planet were always out of grasp. Now nearly ninety percent into our four-year tour, it truly feels as if time is accelerating. Perhaps the steady barrage of fundamental science discoveries just makes it difficult to keep pace.
Our campaign to crank up the orbital inclination of Cassini continues with frequent Titan flybys. One perk of this more polar geometry is a deluge of radio science occultations, both of Saturn and its glorious ring system. When these entities come between Earth and Cassini, the radio signal may actually be used as a science instrument, probing Saturn's atmosphere, ring structure, etc. A series of eight occultations are planned during the last seven months of Cassini's prime mission, and I'm sure our radio science team is "licking their chops" for the data that is to come.
On the engineering front, the flight team was finally able to cancel an Orbit Trim Maneuver, just before the holiday period at JPL. OTM-140 ended up being a mere 0.4 millimeters per second (or 0.0009 mph), a far smaller velocity change than we can accurately implement on the spacecraft. This was great news for a busy flight team, for before OTM-140 we muscled through a dozen propulsive maneuvers in a row without a cancellation. I'm not sure if that was a record, but it certainly felt like one!
The new year is off to a busy start, with a couple of very interesting science press releases. A close flyby of the irregular moon Epimetheus last month yielded curious science results and the best images to date. The ghostly remains of an ancient impact crater appear to cover much of the body. In addition, two distinct types of terrain were visible -- smoother and darker areas juxtaposed with brighter terrain scarred with fractures. As much as I love engineering, I think in another life I would chose to study the icy satellites of the outer solar system. They never fail to grab my attention, with every precious pixel returned to Earth.
I'll close this column with the stunning surprise of a warm north polar vortex in Saturn's atmosphere. The south polar region now has company in this regard, but this is perplexing because Saturn's north pole hasn't seen the sun since before Cassini launched over a decade ago. There's nothing like a good planetary science mystery to kick off a new year.