CloudSat Lights Out - End of Life Operations

Abstract The CloudSat Mission proposal was selected by National Aeronautics and Space Administration (NASA) in 1999 from an Announcement of Opportunity for the Earth Science System Pathfinder program. CloudSat was proposed to fly as part of a joint mission between NASA and the Centre National D'Etudes Spatiales (CNES), where CNES provided the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite. They were designed to be launched together and flown in on-orbit formation to provide near-coincident observations. Cloudsat carried a single science instrument payload, the Cloud Profiling Radar (CPR), capable of observing the vertical distribution of all but the thinnest clouds, while CALIPSO carried a Lidar instrument used to study thinner clouds and aerosols. The satellites were co-manifested and launched on April 28, 2006 from Vandenburg Air Force Base in California. Following launch, both spacecraft were maneuvered into the NASA’s Afternoon Constellation of satellites (A-Train), where they operated for many years. Originally designed for a 22-month mission, CloudSat far exceeded expectations and ultimately operated for nearly eighteen years. CloudSat had a complicated on-orbit operational history due to spacecraft anomalies that frequently challenged the operations team. The inflight anomalies necessitated changes to spacecraft operations, changes to formation flying with CALIPSO and finally changes to the orbits of both satellites. Through it all, CloudSat continued formation flying operations with CALIPSO until both satellites reached end of life. When CALIPSO’s mission ended in mid-2023, the combined radar-lidar measurements could no longer be achieved and plans for CloudSat End of Mission (EOM) activities began. There was a strong desire to perform an engineering test on the redundant CPR subsystems, as the instrument had operated exclusively on the primary hardware side since launch. EOM plans were carefully laid out to include a 3-month CPR engineering test on the redundant hardware and a 2-month orbit lowering campaign. The success-oriented plan had sufficient margin to ensure successful execution within the required schedule. EOM activities were challenged by operating an aging spacecraft and altered concepts of operations to deal with limitations imposed by previous inflight anomalies. True to the history of the CloudSat mission, the plan encountered an additional obstacle that interrupted the orbit lowering and satellite disposal campaign. This paper will provide a brief overview of the mission, but discussion will focus on the decision to terminate the CloudSat mission, planning for and execution of the CPR engineering test, the orbit lowering maneuver campaign and finally spacecraft passivation.