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Wednesday, 8 June 2016

LISA Pathfinder mission demonstrates ways 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 ublished 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.

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