Lisa Pathfinder’s success boosts likelihood of future gravity-wave observatory
PARIS — European scientists on June 7 said the Lisa Pathfinder technology-demonstrator satellite, launched in December to determine if current technologies were sufficient to justify investment in a full-scale gravitational-wave observatory, has far surpassed expectations and should lead to a larger mission around 2034.
The 22-nation European Space Agency has said a laser-interferometry mission featuring three spacecraft millions of kilometers apart and linked by lasers is their preferred next selection for Large-class mission.
But while Lisa Pathfinder’s ability to eliminate most surrounding noise, including that caused by gas molecules, during its nearly three months of operations argues heavily in favor of a full-blown Lisa mission, other technologies need to be proven before the full observatory is given go-ahead approval.
Fabio Favata, head of the coordination office at ESA’s science directorate, told a briefing on Lisa Pathfinder results that requirements for a telescope of unprecedented stability is one of the technology hurdles a future Lisa will need to clear in addition to those proven on the Pathfinder.
Asked whether a national 2034 date could not be moved forward by five years, to 2029, Favata said the technologies challenges remaining are probably too formidable to make the earlier date.
Favata said ESA will spend the next three or four years examining how close they are to reaching the technology readiness level for the Lisa mission components. Once a go-ahead is decided, a 10-year development effort would begin.
Lisa Pathfinder, budgeted at 450 million euros ($503 million), has a nominal six-month life. The first three months, beginning in March, were dedicated to proving whether the satellite’s design to seal off the test bed from exterior nose. The test bed consists of two two-kilogram, 46-centimeter-diameter gold-platinum cubes.
The cubes are spaced just 38 centimeters from each other – too close to detect gravitational waves even in the best of circumstances.
But after less than three months’ operations, project scientists said the Pathfinder results were far better than imagined and more than enough to begin the full Lisa observatory with confidence.
“On March 1 we turned the toy on and immediately realized that it was much better than expected, with lower than expected noise,” said Stefano Vitale, Lisa Pathfinder’s principal investigator. One early concern was thermal “noise” coming from gas molecules around the test bed. These were pumped out into space. “We are now at Lisa requirements,” Vitale said.
With the primary mission now completed, a NASA-furnished experiment, called the Disturbance Reduction System, will take over as Lisa Pathfinder’s principal experiment for three months beginning in July.
NASA’s Jet Propulsion Laboratory provided its own set of Lisa Pathfinder thrusters to test their ability to keep the test masses as still as possible.
The eight NASA electrospray thrusters on board Lisa Pathfinder were built by Busek Co. Inc. of Natick, Massachusetts, under a NASA contract.
Lisa Pathfinder program managers expect to request a mission extension once NASA’s work is done.
Favata said ESA expects NASA will also be a partner on the full Lisa observatory for 2034. Details are yet to be finalized. ESA’s Large-class missions are budgeted at aroun 900 million euros, plus whatever contributions are made by national European laboratories and national space agencies in Europe.
ESA will issue a call for mission ideas for the next Large-class mission, called L3, “as soon as feasible,” Favata said. “At that point the community will have to bring forward their concept — or concepts. If more than one concept is proposed we will have to have a selection. It appears likely that the front-runner will be [Lisa]. But, it will be an open process, giving all the chance to have their day in court.”
The Lisa Pathfinder contracting team, led by Airbus Defence and Space Ltd. of Stevenage, England, and Friedrichshafen, Germany, included more than 40 companies from 14 nations in Europe, plus the NASA contribution.
Christian Trenkel, Airbus’s Lisa Pathfinder program manager, said the main challenge for the program was controlling the gravity environment on the spacecraft to minimize perturbations – with no way of testing it on the ground.
Paul McNamara, ESA’s Lisa Pathfinder project scientist, said the program benefited from what he called an exceptionally accurate launch from Europe’s Vega small-satellite launch vehicle, which was making its sixth launch. Satellite injection occurred within 100 meters of the target, “which is better than we could have dreamed of,” he said.