A new discovery made to detect gravitational waves

LISA Pathfinder Mission successfully tested a key technology needed to build a space-based observatory for detecting gravitational waves. The Mission was led by the European Space Agency (ESA) scientists with the contribution of NASA.

This research was published in Physical Review Letters on 7 June 2016.

Key finding of the Research
• The Mission demonstrated that two test masses can be put in free fall with a relative acceleration sufficiently free of noise to meet the requirements needed for space-based gravitational-wave detection.
• These tiny ripples in the fabric of space were first seen in 2015 by the ground-based Laser Interferometer Gravitational-Wave Observatory (LIGO).
• These ripples were predicted by Albert Einstein a hundred years ago.
• The frequency of the Seismic, thermal and other noise sources limit LIGO to higher-frequency gravitational waves was around 100 cycles per second (hertz).
• But finding signals from mergers of supermassive black holes in colliding galaxies requires the ability to see frequencies at 1 hertz or less.
• A space-based observatory would work by tracking test masses that move only under the influence of gravity.
• Each spacecraft would gently fly around its test masses without disturbing them, a process called drag-free flight.
• The primary goal of ESA's LISA Pathfinder mission is to test current technology by flying around an identical pair of 1.8-inch (46 millimeter) cubes made of a gold-platinum alloy, a material chosen for its high density and insensitivity to magnetic fields.

About LISA Pathfinder mission
• LISA Pathfinder was launched on 3 December 2015, and began orbiting a point called Earth-sun L1, roughly 930000 miles (1.5 million kilometers) from Earth in the sun's direction since late January 2016.
• LISA stands for Laser Interferometer Space Antenna, a space-based gravitational wave observatory concept that has been studied in great detail by both NASA and ESA.
• The mission 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
• The Mission reduced non-gravitational forces on the test masses to a level five times better than the mission required and within 25 percent of the requirement for a future space-based gravitational wave detector.
LISA Pathfinder also carries a NASA experiment called the ST-7 Disturbance Reduction System. Managed by NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, the experiment combines novel electrospray thrusters with drag-free control software provided by Goddard on a dedicated computer.

LISA Technology Package (LTP)
• The test masses are housed in an experiment called the LISA Technology Package (LTP).
• It was built by a consortium of European national space agencies and ESA.
• The LTP uses 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 microthrusters.
• In this way, the spacecraft flies in formation with the cubes and isolates them from external forces.
• The results show that LISA Pathfinder reduced non-gravitational forces on the test masses to a level about 10000 times smaller than drag-free control technologies used on previous science missions.
• At frequencies between 1 and 60 millihertz, control over the test masses is affected by a small number of gas molecules bouncing off the cubes.
• The effect became less prominent over time as molecules escaped into space, and it is expected to improve further in the following months.