PARIS, June 17 (UPI) -- European Space Agency controllers sent a final command to the Herschel satellite Monday, marking the end of operations for the successful space observatory.
Herschel's science mission ended April 29 when the liquid helium that cooled the observatory's instruments close to absolute zero ran out, but the satellite has been kept active since then as an orbiting test bed for control techniques that can't normally be tested in flight, a release from ESA headquarters in Paris said.
Engineers at ESA's European Space Operations Centre in Darmstadt also seized the rare opportunity to conduct a series of technology tests on the satellite, which remained fully functional although no longer capable of scientific observation.
"Normally, our top goal is to maximize scientific return, and we never do anything that might interrupt observations or put the satellite at risk," Micha Schmidt, Herschel's Spacecraft Operations Manager at ESOC, said.
"But the end of science meant we had a sophisticated spacecraft at our disposal on which we could conduct technical testing and validate techniques, software and the functionality of systems that are going to be reused on future spacecraft. This was a major bonus for us."
The final command issued Monday was the last step in a complex series of flight control activities and thruster maneuvers designed to take Herschel into a safe disposal orbit around the Sun and deactivate its systems, controllers said.
"Europe really received excellent value from this magnificent satellite," Paolo Ferri, ESA's Head of Mission Operations, said.