Solar Conjunction

Todd J. Barber, Cassini lead propulsion engineer

Hello from Saturn, essentially on the opposite side of the sun as seen from Earth! This annual occurrence called solar conjunction, when Saturn (and Cassini) nearly disappear behind the sun, is quite an interesting time. First off, the project strongly encourages vacation during this period, and given an impending three-day weekend, my arm didn't have to be twisted in the slightest. Every year, Saturn moves a bit farther along its plodding 29.46-year orbit, so Earth has to travel a wee bit longer before the sun lines up between the two planets. This causes the date of solar conjunction (Saturn's opposition) to advance about two weeks per year.

This year's conjunction is not a particularly "bad" one in terms of the separation of Saturn and the sun in the sky--it never dips below about 1.75 degrees. As such, some of the usual conjunction issues including a lack of uplink capability (commandability) and noisy or ratty downlink data (telemetry) should be mitigated this year. Even so, I can think of no better time for a brief respite before a demanding series of Titan and Enceladus flybys very soon. The only downside of solar conjunction is I'm unable to observe Saturn through a telescope for some months, a geometric hindrance not shared by Cassini.

The spacecraft has been quite busy the last few weeks, which is likely of little surprise to regular readers of this column. We executed a rather large main-engine maneuver after our successful E4 (Enceladus-4) flyby, and we've also cycled the main-engine cover a few times to protect against dust hazards. Superposed with these engineering events and others, too, Cassini has managed to continue blasting a steady stream of new and exciting science results to the home planet and its scientists.

The spacecraft dutifully executed non-targeted flybys of the small moons Methone, Mimas, and Daphnis around the time of E4. There was even a distant non-targeted flyby of Titan itself, a moon not exactly neglected in our ambitious two-year extended mission trajectory.

Results from E4 continue to astound and befuddle, thanks largely to a very clever but harrowing "point and shoot" imaging technique called "skeet shooting." Without its success, the glorious E4 close-ups we've all been enjoying would have been impossible.

Finally, I have to close with a jaw-dropping image just added to the Cassini website ( /resources/14205). It's always thrilling to peek in and see what gravitational mischief Prometheus has been wreaking on Saturn's F-ring. Even as a small part of the Cassini team and a non-scientist to boot, I feel as if a few of those pixels are mine. Nothing brings me greater pleasure than being a member of this fantastic team at NASA and JPL.