Todd J. Barber, Cassini lead propulsion engineer




Todd Barber
Todd Barber

One part of the Cassini team at JPL receives perhaps less attention outside the project than the science, navigation, or engineering teams. However, their contribution is absolutely critical to the success of this mission, in every respect. I recently sat down with the head of Uplink Operations (ULO), Bill Heventhal, to learn more about this critical function that literally enables everything we do.

Bill received an electrical engineering degree from San Diego State and started his career at JPL as a mission controller or “ace” on the Magellan mission to Venus. The ace position is a demanding one, worthy of its own “Insider’s Cassini” column, but suffice it to say that it involves more second-shift and third-shift work than any other position on the project. Once Bill and his wife were expecting, he gave nine months notice, seeking a job with less off-shift work, understandably. After a stint as a Sequence Event Generation (SEG) software engineer on Magellan, including learning to program in PERL, Mr. Heventhal moved on to the Mars Observer, Mars Pathfinder, and Cassini missions, also as a SEG software engineer. In late 1996, less than a year before launch, he became a Sequence Virtual Team Lead (SVTL), finally culminating in his promotion to ULO Manager in 2002.

Bill manages a team of nine engineers—two Deep Space Network (DSN) schedulers and seven SVTLs. He remarked that his two DSN schedulers have the “non-enviable” task of negotiating DSN tracking passes for Cassini, while roughly two dozen other spacecraft teams jockey equally as fervently for precious minutes of downlink time on the heavily used DSN antennas. I understood this function well enough, but I wanted to dig more deeply into the job of the SVTLs. Mr. Heventhal boiled it down to the level a “rocket jock” could understand, pointing out that SVTLs receive inputs from twelve orbiter science instruments and the spacecraft engineering teams, integrate them into a single, cohesive, integrated, flyable sequence of commands, and then approve them to be sent to the spacecraft. These sequences are typically 4-6 weeks in duration, and they are thoroughly checked against mission flight rules and constraints before being blasted out to Saturn at the speed of light. Fortunately for Bill and his team, most of the inevitable “clashes” between science demands and engineering realities happen upstream of the SVTLs, but occasionally he deals with these issues, too.

On the downlink side, the SVTLs respond to any alarms in telemetry, verify proper “clocking out” of the active sequence on board Cassini, and recover from anomalies, including restarting science instruments. They also build real-time commands, should they prove necessary, and provide flight rule checks for the integrated sequence to be flown (i.e., the combination of the real-time commands overlaid upon the background sequence). These downlink anomalies lead to the occasional late-night phone call, but there’s still much less off-shift work than when Bill was an ace. I asked Mr. Heventhal about the role of the sequence team during cruise, tour, the extended mission (which we refer to as XM, but has been officially called the Equinox Mission), and the doubly extended mission (which we refer to as XXM, but has been officially called the Solstice Mission). Interestingly enough, these duties evolved quite a bit. Cruise was punctuated by quiet science sequences, but this allowed time for the development of SVTL software, scripts, etc. During tour and the Equinox mission, with the same-sized flight team, Bill and his group have been “crazy-busy” with the endless deluge of science executed by Cassini. The Solstice mission, no doubt, will offer new challenges as Bill’s team will be consolidating with the Science Planning Team, with a reduction in staff consistent with the Solstice mission guidelines. Even a dozen years after launch, there will still be new and exciting challenges for Bill and his team as they cross-train to tackle science planning assignments (and vice versa).

As we closed off this enlightening interview, I asked Mr. Heventhal about his favorite memories at JPL. He mentioned Cassini’s Saturn Orbit Insertion (SOI) and Magellan’s Venus Orbit Insertion (VOI), the latter of which sparked a smile on my part, as that auspicious day (August 10, 1990) was the day I interviewed at JPL to accept permanent employment here. He compared the gradual climax as Cassini patiently burned its main engine for 96 minutes, getting us ever closer to orbit insertion, with Magellan. In contrast, Magellan’s VOI happened during Venus eclipse from Earth, so this enabled one euphoric moment when tracking data resumed and orbit insertion was verified in an instant. I also asked Bill about his feelings on working at JPL, and shared his sentiments (which I wholeheartedly echo) that we have very rewarding jobs and that we play a very small but vital part in each and every one of the fantastic images returned by Cassini. He also mentioned the great privilege of working with literally the “world’s experts” on the project, labeling them the true “crème de la crème.” It was a distinct honor to interview Bill and learn more about the sequence team, and I hope you enjoyed this glimpse into yet another critical piece of the puzzle that makes Cassini’s mission possible and ultimately successful.