Todd J. Barber, Cassini lead propulsion engineer
As it has many times since 16-day Saturnian orbits began in January, Cassini zipped by Titan on Wednesday, June 13, 2007. This flyby took place at a mere 965 kilometers (600 miles) above this otherworldly surface. Originally, Cassini would have passed by this moon at 975 kilometers (606 miles), but our OTM-115 approach maneuver deftly targeted a closer flyby. This actually offered an improvement for the Ion and Neutral Mass Spectrometer (INMS), the prime science instrument during this Titan pass. INMS "sniffs" the Titan atmosphere to ferret out chemical composition, so as a rule it prefers lower altitudes in order to "breathe in" more of the perplexing Titan atmosphere. Ordinarily, such a change would not have been undertaken so late in the process, but as it happens this altitude adjustment actually returned Cassini more nearly to its reference trajectory around Saturn! In fact, this minor maneuver adjustment saved 2.6 meters per second of Delta-V, a rather substantial number. Such Delta-V and thus propellant savings enable more science to be executed as Cassini continues its orbital ballet within the Saturnian system.
The Cassini flight team is eagerly anticipating a first break in the demanding 16-day orbit schedule commencing in July. It has definitely been a long haul since January of this year, but the myriad of Cassini science results constantly returning to Earth always puts smiles on our tired faces. With no rest for the weary, we are currently executing the Titan-32 clean-up maneuver, OTM-116, as I write this on Saturday, June 16, 2007. I wouldn't say Isaac Newton seems to have it out for Cassini, but we do seem to have a disproportionate number of propulsion maneuvers scheduled for second and third shifts, weekends and holidays. However, I'm sure I speak for the entire Cassini team when I say it's a labor of love for our robotic emissary encircling the ringed planet some 1.5 billion kilometers (930 million miles) from home.