ESA runs final tests as LISA Pathfinder spacecraft readies for shutdown

DARMSTADT, Germany. The final days of the European Space Agency (ESA) LISA Pathfinder mission have actually been some of its busiest, as controllers on the ground conduct final tests and get ready to switch off the gravitational-testing craft on July 18 after 16 months of scientific effort.

The LISA -- or laser interferometer space antenna -- Pathfinder craft completed its stated proof-of-concept mission on June 30, having demonstrated the technology the needs to operate its future LISA space observatory to study gravitational waves, or the ripples in spacetime predicted by Albert Einstein in his General Theory of Relativity.

ESA's team is now using the spacecraft’s last days to conduct a series of technical tests on components and devices, making full use of every remaining minute; such tests could not be performed previously on the craft because meeting the missin's science goals required a very stable and "quiet" environment. In its last days, engineers been directing the craft to turn to assess thermal effects on its systems, particularly the micropropulsion system, from solar illumination; analyzing the effect of magnetic interference, from the operation of pressure-regulation valves in the cold-gas thruster system, on the spacecraft’s magnetic momentum, external forces, and test mass control; and pushing the micropropulsion system and test-mass electrostatic sensing and control systems to their limits.

Ground teams are getting ready to shut off or "passivate" LISA Pathfinder, eliminating radio transmissions from the spacecraft and switching off most of the units. In April 2017, the spacecraft used its thrusters over five days to nudge itself into a safe orbit around the sun; the orbit shift minimizes any probability that the Pathfinder will return to the vicinity of the earth or moon in the next 100 years, in accordance with ESA's requirement for space-debris mitigation.

The full LISA mission, an ESA/ joint venture that is expected to launch in the early 2030s, will comprise three spacecraft orbiting about 2.5 million km (1.55 million miles) apart in a triangular formation, with their test masses isolated from all external forces bar gravity and linked by laser beams.

Paolo Ferri, head of mission operations for ESA, said of the mission: “Before LISA Pathfinder, gravitational wave astronomy from space was a theoretical possibility, with its future implementation hidden behind a thick, dark wall. 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.”

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