ESA’s LISA Pathfinder mission may have officially ended on June 30, but the trio of unmanned spacecraft are as busy as ever in the runup to their shutdown on Tuesday. The technology demonstrator constellation for studying gravitational waves completed its 16-months of science experiments last month and now mission control in Darmstadt is putting the spacecrafts’ systems through their paces in a series of component tests before final disposal.
Launched on December 3, 2015 from the Guiana Space Centre in French Guiana, The three Pathfinder spacecraft were sent into orbit around Lagrange point L1, where they flew in triangular formation about 2.5 million km (1.5 million mi) apart. At this distant point where the gravity of the Earth and the Sun cancel one another out, the three probes used laser interferometry to demonstrate how the ripples in spacetime, called gravitational waves, that were predicted by Einstein’s Special Theory of Relativity can be studied.
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The infrared lasers were beamed from one spacecraft to the next to form a gigantic triangle. The manner in which these lasers interfered with one another allowed scientists back on Earth to minutely measure how far the cubical “test masses” held inside each spacecraft, and isolated from all external forces except gravity, shifted in response to gravitational waves.
X-ray viewing showing the test masses inside a LISA Pathfinder spacecraft
(Credit: ESA/ATG medialab)
ESA regards the LISA Pathfinder mission a success, but that doesn’t mean there isn’t still work to do. While the science mission was underway, it wasn’t possible for the engineers to carry out the sort of detailed systems checks they need to design the next gravitational wave mission. Now that the need to keep the experiments in an absolutely stable environment no longer applies, it’s time for the engineers to let their hair down.
During the days before final shutdown, mission control is turning the spacecraft in the sunlight and firing their microthrusters to assess thermal effects on the systems. In addition, they’re looking at magnetic interference caused by the pressure regulators in the cold-gas thruster system, as well as seeing how far they can push the micropropulsion system and test-mass electrostatic sensing and control systems to see how much they’ve degraded since launch.
Once these tests have been completed, the LISA Pathfinder spacecraft will be ready for disposal. In April, they fired their thrusters for five days to send them into an orbit around the Sun that will keep them away from the Earth for at least a century. At 18:00 GMT on July 18, the final commands ordering the spacecraft to shut down most of their systems and cease all radio transmissions will be sent.
“Before LISA Pathfinder, gravitational wave astronomy from space was a theoretical possibility, with its future implementation hidden behind a thick, dark wall,” says ESA’s Paolo Ferri, head of mission operations. “This mission has opened a ‘door’ in this wall. The road to achieving a future mission that will detect gravitational waves is still very long, but we can see it and we can now start planning our long journey to reach it.”
The video below outlines the LISA Pathfinder mission
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