London, Jun 8 (PTI) A key component of a gravitational wave observatory, scheduled to launch in 2034, has passed a series of tests, while coming closer to experiencing true free fall than any other human-made object ever, the European Space Agency said.

At the heart of the experiment is a two-kilogramme cube of a high-purity gold and platinum alloy that is currently sailing through space almost completely free of any force other than gravity.

The Laser Interferometer Space Antenna (LISA) Pathfinder mission, led by the ESA with contributions from NASA, proves that a formation of such cubes flown in space will function as a space-based gravitational wave observatory, which could detect signals from supermassive black hole collisions and other violent events that would be impossible to see on Earth.

The free-falling test mass, as the gold and platinum cube is known, is nestled inside the shell-like LISA Pathfinder spacecraft, and has been orbiting a location in space called Lagrangian Point 1 (L1) since February 2016.

At L1, the gravitational pull of the Earth and Sun are such that objects near the point execute orbits around L1 in much the same way that a satellite orbits the Earth.

The LISA Pathfinder mission is a crucial test of systems that will be incorporated in three spacecraft that will comprise the LISA gravitational wave observatory scheduled to commence in 2034.

The LISA observatory will follow an orbit around the Sun trailing fifty million kilometres behind the Earth. Each LISA spacecraft will contain two test masses like the one currently in the LISA Pathfinder spacecraft.

In order to detect gravitational waves, the LISA test masses must be protected from anything that might jostle them in flight.

Even sunlight produces forces that would disturb the masses motion enough to swamp gravitational wave signals. To test such protective systems, the LISA Pathfinder spacecraft is equipped with an array of thrusters that work to keep it properly positioned around the freely falling test mass.

Electrodes adjacent to each side of the test mass cube detect the relative locations of the test mass and the spacecraft.

The thrusters fire as necessary to ensure that the spacecraft moves in a way that allows the test mass to follow its orbital trajectory as undisturbed as possible.

In the LISA observatory mission planned for 2034, lasers will be used to measure the distance between test masses housed in spacecraft flying in a triangular configuration about a million kilometres on a side.

Tiny changes in the spacing of the test masses will indicate the passing of gravitational waves. The LISA Pathfinder spacecraft contains a second test mass that, along with the test mass in free fall, is part of a minuscule equivalent of one leg of the triangular LISA formation.

The study appears in the journal Physical Review Letters. PTI MHN SAR SAR