On Monday at 12:25 GMT, the European Space Agency (ESA) executed final shutdown on the Herschel space telescope after shooting it into solar orbit. This shutdown marks the end of Herschel’s successful four-year mission of deep space observation, which was terminated when it ran out of liquid helium in April. Without liquid helium to cool its super-sensitive infrared instrument, Herschel was unable to continue its mission, but it was otherwise fully functional, so ESA took the opportunity to use the probe to carry out technical tests that couldn't be done earlier.
“Normally, our top goal is to maximize scientific return, and we never do anything that might interrupt observations or put the satellite at risk,” says Micha Schmidt, Herschel’s Spacecraft Operations Manager. “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.”
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Once these tests were completed, Herschel was put through a series of flight control activities and thruster maneuvers, which moved it out of its position at the Lagrangian point L2 1,500,000 km (930,000 mi) from Earth. Its final maneuver was executed on May 13 to 14 when it exhausted its fuel tanks in a record 7-hour, 45-minute thruster burn. This sent the craft into a heliocentric orbit before being completely turned off.
Though deactivated, Herschel’s solar power cells are still charging its batteries, so it could be restarted by a command from Earth, though ESA has no intentions to do so.
The video below shows the construction of Herschel.