Life Beyond the Leak for ESA's CryoSat
Life Beyond the Leak for ESA's CryoSat
Spacecraft Switched to Backup Propulsion System
On November 21, 2023, ESA’s CryoSat satellite switched over to its back-up propulsion system after a fuel leak threatened to bring the mission to an end in 2025.
“Since 2010, CryoSat has used its Synthetic Radar Altimeter (SAR) to monitor land and sea ice everywhere on Earth to help scientists demonstrate the important role ice plays in regulating climate."
Tommaso Parrinello, CryoSat Mission Manager
The swap has the potential to extend the life of the satellite by as much as 5 to 10 years. But the back-up thrusters had never been used before. If something had damaged them during CryoSat’s 13 years in orbit, there was a small chance that the mission would come to an immediate end after the switch.
CryoSat is ESA’s satellite dedicated to measuring the thickness of polar sea ice and monitoring changes in the ice sheets that blanket Greenland and Antarctica.
The mission was designed to last roughly 5 years. It has now spent over 13 years in orbit. “Since 2010, CryoSat has used its Synthetic Radar Altimeter (SAR) to monitor land and sea ice everywhere on Earth to help scientists demonstrate the important role ice plays in regulating climate and being affected by global warming,” says Tommaso Parrinello, CryoSat Mission Manager. "Its thirteen-year climate record of global ice and sea levels is unparalleled, and long may it continue."
CryoSat’s nitrogen propellant is stored in a fuel tank at high pressure. A pressure regulator converts the high-pressure air into much lower pressure for use by the thrusters. Together with the experts at the satellite’s manufacturer, Airbus, the ESA team has pinpointed the location of the leak to one of CryoSat’s smaller attitude thrusters.
At first, the leak rate was small, but it increased over the first few years and has reached a stable rate that would still bring the CryoSat mission to the end in 2025. One explanation for this could be that a small crack appeared somewhere and grew to a certain size before stopping. But it is difficult to diagnose this kind of problem from the ground, and it’s impossible to know for sure.
CryoSat has a secondary, back-up propulsion system connected to its fuel tank. Leaving the primary thrusters connected, operators at ESOC in Germany opened the main valve to the back-up propulsion system for the first time in CryoSat’s 13 years in space. The pressure in the back-up system stabilized – indicating that it was not suffering from any major issues of its own – and the satellite’s onboard computer was instructed to use the back-up thrusters instead of the primary thrusters that it has used since launch.
The next day the flight control team at ESA conducted an ‘orbital control maneuver’ to test the two larger thrusters in the back-up system. As no issues were found during or after the maneuver, CryoSat’s back-up thrusters are now officially commissioned, and the satellite is capable of continuing scientific activities to the end of the decade and possibly beyond.
The swap to CryoSat’s back-up thrusters was a success. But it is not yet know exactly how much this could extend the mission. Only by monitoring the fuel reserves over the next few days and weeks will the CryoSat team know if there are any smaller leaks or issues in the back-up system.