he European Space Agency (ESA) and NASA may have just determined they have the technology needed to build a space-based observatory for detecting gravitational waves. Gravitational waves, the tiny ripples in the fabric of space, were predicted by Albert Einstein over 100 years ago and were—for the first time ever—seen by the ground-based Laser Interferometer Gravitational Wave Observatory.
Now, thanks to LISA Pathfinder, a mission led by ESA with contributions from NASA finding signals from more exotic events, such as mergers of supermassive black holes in colliding galaxies, could be possible. These kinds of discoveries require the ability to see frequencies at one hertz or less, a sensitivity level only possible from space.
A space-based observatory would work by tracking test masses that move only under the influence of gravity. Each spacecraft would fly around its test masses without disturbing them.
ESA's LISA Pathfinder mission’s primary goal is to test current technology by flying around an identical pair of 1.8-inch cubes made of a gold-platinum alloy, a material chosen for its high density and insensitivity to magnetic fields.
From their findings so far, the scientists are awestruck by the results. What they found was that non-gravitational forces on the cubes were reduced to levels far below the project's original requirements and approach the level of control needed for a full-scale observatory.
"The measurements have exceeded our most optimistic expectations," said Paul McNamara, the LISA Pathfinder project scientist at ESA's Directorate of Science, Noordwijk, the Netherlands. "We reached the level of precision originally required for LISA Pathfinder within the first day, and so we spent the following weeks improving the results a factor of five better."
"LISA Pathfinder was always intended as a stepping stone to the level of performance needed for a full-scale gravitational wave observatory, but these results tell us we've nearly made the full jump. A full-scale observatory with LISA Pathfinder's performance would achieve essentially all of the ultimate science goals," said Ira Thorpe, a team member at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "That's amazing in itself, and data from this mission will help us build on an already impressive foundation."
The test masses are included in an experiment called the LISA Technology Package (LTP), built by a combination of space agencies. The LTP employs a high-resolution laser interferometer to determine the positions of the test masses and relays the information to the spacecraft's Drag-Free and Attitude Control System, which then applies minute bursts from micro-thrusters.
This allows the spacecraft to fly in formation with the cubes and isolate them from external forces. The results show that LISA Pathfinder reduced non-gravitational forces on the test masses to a level about 10,000 times smaller than drag-free control technologies used on previous science missions.
"These impressive results show that LISA Pathfinder has successfully demonstrated some of the advanced technologies needed for a future space-based gravitational wave observatory," said Paul Hertz, Director of NASA's Astrophysics Division in Washington. "ESA is currently planning such a mission for the 2030s, and NASA is working closely with ESA in exploring how we might continue the successful LISA Pathfinder partnership in that mission."
LISA Pathfinder was launched last December. In late January, it began orbiting a point called Earth-sun L1, roughly 930,000 miles from Earth in the sun's direction.