LISA Pathfinder mission terminated
Over a period of 16 months, the spacecraft, a preliminary proof-of-mission project, tested technologies aimed at studying gravitational waves in a follow-up mission, the Laser Interferometer Space Antenna (LISA), scheduled for launch in 2034.
First proposed as part of Albert Einstein’s theory of general relativity over a century ago, gravitational waves result from major space events, such as mergers of two black holes or supernova explosions.
Because only some types of gravitational waves can be detected by ground-based observatories, scientists had to create and launch a space-based observatory that would not be vulnerable to phenomena on Earth, such as seismic activity.
“We’re looking for the universe vibrating from these mergers, these big, big events,” said LISA Pathfinder project scientist Paul McNamara in an ESA video about the mission. “From the operations to the hardware to the development, it’s just been a wonderful mission.”
Video courtesy of European Space Agency (ESA)
Two gold-platinum cubes, each with a weight of 4.3 pounds (2 kilograms) and a diameter of about 1.8 inches (4.6 centimeters), suspended inside LISA Pathfinder, served as its primary technology. A 1.5-inch (3.8-centimeter) laser measured the distances between the cubes to vary their positions, distance, and orientation.
During its period of operation, LISA Pathfinder had to be held steady to prevent its sensitive motion detector from being influenced by photons coming from the Sun. This was accomplished by thrusters that exerted tiny reactive forces to the probe, keeping it in a near-perfect gravitational orbit.
Keeping the spacecraft stable was so important that two separate systems, one designed by ESA and the other by NASA, were placed and used on board.
“We were trying to hold it as stable as the width of a DNA helix. And we went down from there to the width of part of a DNA helix,” explained John Ziemer of NASA’s Jet Propulsion Laboratory (JPL) and systems lead for the NASA thruster system on the probe.
Known as the Space Technology 7 Disturbance Reduction System (ST7-DRS), the thruster system was developed by the company Busek Co. Inc. with assistance from JPL.
Algorithms developed by NASA’s ST7 project were used in conjunction with ESA’s commands and input from ESA’s sensors to guide LISA Pathfinder during its U.S. operations phase.
While the spacecraft completed its primary mission in the fall of 2016, tests of various algorithms to stabilize it continued into March and April of this year.
“The main goal for us was to show we can fly the spacecraft drag-free,” Ziemer said. “The main force on the spacecraft comes from the Sun, from photons with [an] extremely tiny force that can subtly move the spacecraft.”
Engineers hope that the new steady thrusters could eventually replace reaction wheels, currently used to point and rotate spacecraft, on other probes, such as telescopes designed to hunt for exoplanets, he added.
Turned off on Tuesday, July 18, 2017, LISA Pathfinder will remain in a parking orbit, where it will coast while continuing to circle the Sun. Its 2034 successor will be composed of three separate spacecraft positioned in a triangle, with each one 1.55 million miles (2.5 million km) from its partners.
The three LISA probes will use technology much like LISA Pathfinder’s cubes and will detect gravitational waves by the minute distortion (only one trillionth of a meter) the waves exert on the distances between them.
Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.