The mark of a very fine scientific instrument isn't usually how well it can fall, but in the case of the LISA Pathfinder spacecraft, that one metric could help astrophysicists decode the very fabric of the universe. Fortunately after just two months of testing, the tech aboard LISA has done exceptionally well in free falling – performing much better than expected and boosting hopes that we can soon have a powerful tool to capture gravitational waves.
The LISA (Laser Interferometer Space Antenna) mission began operations on March 1. It consists of two 4.6-centimeter (about 1.8-inch) cubes made from gold and platinum, floating in vacuum chambers and placed in free fall through space. As the objects and their container fall, highly sensitive lasers measure their distance relative to one another to an accuracy of a billionth of a millimeter. If there is a change in the distance, then it would mean that a gravitational wave had acted upon them.
Predicted by Einstein, gravitational waves are ripples in spacetime caused by massive objects like black holes. The most common analogy to help understand them is the way in which a bowling ball (the black hole) would warp the surface of a trampoline (spacetime).
Because the waves are super faint, highly precise equipment like LISA is necessary. While the ESA theorized that LISA could get the job done, the degree to which the spacecraft performed has been truly impressive.
According to the ESA and a paper published June 7 in Physical Review Letters, the equipment performed five times better than expected, keeping the cubes virtually motionless in respect to each other and showing that they are unperturbed by any other force than gravity. In fact, the amount of difference between the two cubes comes down to the amount of weight a virus on Earth would exert, according to the Max Planck Institute for Gravitational Physics, home to co-principal investigator of the LISA Technology Package, Karsten Danzmann.
The instrumentation has proven to be so precise that it can take measurements less than the diameter of a single atom.
"With LISA Pathfinder we have created the quietest place known to humankind," says Danzmann. "Its performance is spectacular and exceeds all our expectations by far. Only by reducing and eliminating all other sources of disturbance we could observe the most perfect free fall ever created. And this has shown us that we can build LISA, a space-based gravitational-wave observatory."
As Danzmann points out, the goal of this first launch was to make sure the technology would work. Now that it has, the next step would be to build a full-scale gravitational wave detector.
The very first gravitational waves ever recorded were picked up by ground-based Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors in the United States in September 2015. While that facility will keep searching for gravitational waves, it takes a space-based observatory to search for waves with lower frequencies, which is what a future full-scale LISA observatory could do.
"At the precision reached by LISA Pathfinder, a full-scale gravitational wave observatory in space like LISA would be able to detect fluctuations caused by the mergers of supermassive black holes in galaxies anywhere in the Universe," says Danzmann.
Sources: Max Planck Institute for Gravitational Physics, ESA