Over one month ago, the European Space Agency (ESA) announced that the Herschel space observatory had run out of liquid helium coolant. The coolant was necessary to cool the telescope’s instruments to near absolute zero. As planned, the powerful infrared observatory quickly became useless as an astronomy tool.

Today, the ESA announced that mission controllers have sent their the very last command to Herschel. The command was the final step in moving the satellite out of its L2 Sun-Earth Lagrange Point orbit. Over the past month the observatory has been given complex flight commands designed to deplete its fuel while maneuvering it into a safe heliocentric disposal orbit. On May 13 and 14, Herschel completed a record 7-hour and 45-minute thruster burn as part of these commands.

While maneuvering the satellite into this safe orbit and depleting its fuel, researchers were also using the defunct observatory to conduct software and hardware tests.

“Normally, our top goal is to maximise scientific return, and we never do anything that might interrupt observations or put the satellite at risk,” said Micha Schmidt, spacecraft operations manager for Herschel at the European Space Operations Centre in Darmstadt, Germany. “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.”

Other ESA teams, such as the ExoMars rover team and the Euclid Dark Universe Mission, used Herschel to test components that will also be a part of their missions.

“Herschel has not only been an immensely successful scientific mission, it has also served as a valuable flight operations test platform in its final weeks of flight,” said Paolo Ferri, the ESA’s head of Mission Operations. “This will help us increase the robustness and flexibility of future missions operations.”

(Image courtesy ESA)