Handling Late Changes to Titan Science

Abstract

The Cassini mission has been in orbit for eight years, returning a wealth of scientific data from Titan and the Saturnian system. The mission, a cooperative undertaking between NASA, ESA and ASI, is currently in its second extension of the prime mission. The Cassini Solstice Mission (CSM) extends the mission's lifetime until Saturn's northern summer solstice in 2017. The Titan Orbital Science Team (TOST) has the task of integrating the science observations for all 56 targeted Titan flybys in the CSM. In order to balance Titan science across the entire set of flybys during the CSM, to optimize and influence the Titan flyby altitudes, and to decrease the future workload, TOST went through a "jumpstart" process before the start of the CSM. The "jumpstart" produced Master Timelines for each flyby, identifying prime science observations and allocating control of the spacecraft attitude to specific instrument teams. Three years after completing this long-range plan, TOST now faces a new challenge: incorporating changes into the Titan Science Plan without undoing the balance achieved during the jumpstart. Some changes add additional science opportunities on top of existing observations, as when we devised a new way to gather additional gravity data without impact to the originally planned science observations, using the spacecraft's Low Gain Antenna. Balance can also be impacted when instrument anomalies threaten the loss of a unique high-priority science opportunity. In response to one such situation, we created an alternative flyby timeline while keeping the original timeline viable late in the sequence planning process. As the aging spacecraft's capabilities change, we respond by tweaking long-planned observations. And as our consumables run low and project management scrutinizes their use ever more carefully, we add early detailed analysis of hydrazine use during Titan flybys, allowing us the option of redesigning (and thus saving) observations that might otherwise be removed during sequence development as being too "expensive". All this must be accomplished with a smaller workforce than was available during the Prime and first Extended mission. This paper looks at how TOST handles these and other late changes to Titan science