A mission planner’s perspective: Planning, development, and verification of the new horizons Pluto flyby command sequences

Abstract

The New Horizons Spacecraft, part of the NASA New Frontiers Program, launched on January 19, 2006 to conduct a flyby of the Pluto-Charon system in 2015. The full science campaign spanned seven months beginning in January 2015, culminating with a nine-day encounter period encompassing closest approach on July 14th. Departure science observations continued through the end of July. The launch trajectory included a Jupiter gravity assist early in 2007; without the gravity assist the Pluto arrival would have been no earlier than 2019. The successful Jupiter flyby proved to be a valuable lesson to the team. Executing flybys are complex with only one chance for mission success. The Pluto flyby was highly constrained by long round trip light time, and limited thruster cycles, propellant, navigation, power, downlink, command memory space, and recorder space. To reduce risk and help ensure success, the New Horizons team elected to begin work on the Pluto flyby in 2008 with the intent to have the command sequence “on the shelf and ready to fly” prior to 2015. Starting in 2008, the spacecraft mission profile was to spend most of its journey to Pluto in a hibernation mode. The hibernation periods enabled the team to focus on the flyby sequencing during a period in which spacecraft operations were at a minimum. In the six years that followed, the team planned, developed, and tested seven command sequences associated with the flyby. These sequences consisted of the Core Encounter Sequence, two sequences preceding Core Encounter Sequence, the first sequence after Encounter, and three contingency sequences. Two operational flight tests were also conducted. There were several elements that had to be coordinated when planning and developing the flyby sequences, including science observations, optical navigation imaging, trajectory correction maneuvers, ephemeris management, uplink command windows, downlinking telemetry and recorder data, and contingency preparedness. The early builds of the command sequences did contribute to the success of the flyby. The Core Encounter Sequence itself was built and reviewed twenty times. This would not have been feasible in a nominal operational command sequence build schedule. Managing and executing a multi-year build cycle presented its own challenges. The team still had to conduct ongoing spacecraft operations; track, test, and review changes to the Pluto flyby sequences; and manage a configured area for spacecraft command sequencing and a test area for Pluto flyby sequencing. This paper will discuss from a mission operations viewpoint how the command sequences were built within the requirements and how the challenges were addressed and managed.