3 min read

Annual Solar Conjunction

Todd J. Barber, Cassini lead propulsion engineer

With mere days before Saturn and its orbiting companion, Cassini, disappear behind the sun, the mission continues to return a rich scientific harvest. Recently, Saturn and its perplexing magnetosphere played starring roles in movies of the ringed planet taken by the Imaging Science Subsystem (ISS), the Ultraviolet Imaging Spectrograph (UVIS), and the Magnetospheric Imaging Instrument (MIMI). In addition, the Radio Science Subsystem (RSS) began its roughly annual solar conjunction experiment as radio signals from Cassini to Earth pass ever closer to our nearest star. For roughly one month, two radio frequency bands (X and Ka) will be dissected by engineers firmly planted on terra firma to help understand the solar corona, typically only visible on the third rock during total solar eclipses.

Cassini's maneuver schedule will be pleasantly light during the month of August, again thanks to the geometry of the spacecraft and its two favorite planets. However, before solar conjunction, and near the Titan-34 to Titan-35 apoapsis point, OTM-123 was required and was ready to be uplinked on Sunday, August 5th, 2007. Ground station antenna issues precluded the flight team from uplinking the requisite commands to our robotic emissary, so we opted to use the maneuver back-up window one day later. Even though this was a first-time event for the flight team (requiring the use of a background maneuver window), it's standard procedure for our engineers as we routinely plan for anomalies and contingencies. This back-up OTM executed without a hitch on Monday the 6th (during prime shift in Pasadena, no less), serendipitously saving us some weekend work for a change!

Through this busy period, other missions marked major milestones as well. Most visibly, the Phoenix mission bound for the equivalent of the Arctic Circle of Mars set forth from Florida on August 4th. Our scientists and engineers had to carefully plan the playback of the non-stop flood of science data from Cassini given the potential for Phoenix launch slips, but we're happy to say this process went well. We wish our Martian cousins every success in their epochal mission to explore the potential habitability of the red planet via investigation of possible organic molecules and water ice. Not to take anything away from Phoenix, but Cassini also received some notable press around the same time. This, however, was for an event many months in the future -- the third Enceladus (E3) flyby in March of 2008. A final decision on the closest flyby altitude will be made this autumn, but there is a chance Cassini may plunge through one of this curious moon's icy plumes following a closest approach of a mere 31 kilometers (19 miles) above the Enceladus surface. I converted this number to (roughly 100,000) feet and then realized Cassini may buzz this icy Saturnian moon nearly 1.5 billion kilometers (900 million miles) from Earth below the maximum altitude of an SR71 airplane above Earth! Talk about the right stuff!