A final farewell to LISA Pathfinder

July 25, 2017, Jet Propulsion Laboratory
An artist's concept of the European Space Agency's LISA Pathfinder spacecraft, designed to pave the way for a mission detecting gravitational waves. NASA/JPL developed a thruster system on board. Credit: Jet Propulsion Laboratory

With the push of a button, final commands for the European Space Agency's LISA Pathfinder mission were beamed to space on July 18, a final goodbye before the spacecraft was powered down.

LISA Pathfinder had been directed into a parking orbit in April, keeping it out of Earth's way. The final action this week switches it off completely after a successful 16 months of science measurements.

While some are flashy, never sitting still as they zip across the solar system, LISA Pathfinder was as steady as they come—literally.

It housed a space-age motion detector so sensitive that it had to be protected against the force of photons from the Sun. That was made possible thanks to a system of thrusters that applied tiny reactive forces to the spacecraft, cancelling out the force of the Sun and allowing the spacecraft to stay within 10 nanometers of an ideal gravitational orbit.

These requirements for Pathfinder were so challenging and unique that LISA Pathfinder flew two independent systems based on different designs - one provided by NASA and one by ESA - and ran tests with both during its 16-month mission.

"We were trying to hold it as stable as the width of a DNA helix," said John Ziemer, systems lead for the U.S. system at NASA's Jet Propulsion Laboratory in Pasadena, California. "And we went down from there to the width of part of a DNA helix."

JPL managed development of the thruster system, formally called the Space Technology 7 Disturbance Reduction System (ST7-DRS). The thrusters were developed by Busek Co., Inc., Natick, Massachusetts, with technical support from JPL. During the U.S. operations phase, Pathfinder was controlled using algorithims developed by ST7 team members at NASA's Goddard Space Flight Center in Greenbelt, Maryland. This control system took inputs from the European sensors and sent commands to the thrusters to precisely guide the spacecraft along its path.

JPL finished primary mission experiments in the fall of 2016. In March and April of this year, they continued validating the algorithms used in stabilizing the spacecraft. They improved them through a number of tests.

"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 extremely tiny force that can subtly move the spacecraft."

So why build something this sensitive to begin with?

LISA Pathfinder was just a starting point. The mission was led by ESA as a stepping-stone of sorts, proving the technology needed for an even more ambitious plan, the Laser Interferometer Space Antenna (LISA): a trio of spacecraft proposed to launch in 2034. With each spacecraft holding as still as possible, they would be able to detect the ripples sent out across space by the merging of black holes.

These ripples, known as gravitational waves, have been a source of intense scientific interest in recent years. The ground-based Laser Interferometry Gravitational Wave Observatory detected gravitational waves for the first time in 2015.

But there's a bigger role for thrusters like the ones on LISA Pathfinder. Ziemer said the operation of super-steady thrusters could serve as an alternative to reaction wheels, the current standard for rotating and pointing spacecraft.

"This kind of technology could be essential for space telescopes," Ziemer said. "They could potentially hold them still enough to image exoplanets, or allow for formation flying of a series of spacecraft."

The thrusters are an enabling technology, opening up a magnitude of precision that simply wasn't available before.

Explore further: Tiny thrusters demonstrate a capability needed to detect gravitational waves

Related Stories

LISA Pathfinder—bake, rattle and roll

July 14, 2017

The final days of the LISA Pathfinder mission are some of the busiest, as controllers make final tests and get ready to switch off the gravitational pioneer next Tuesday.

LISA pathfinder thrusters operated successfully

January 22, 2016

While some technologies were created to make spacecraft move billions of miles, the Disturbance Reduction System has the opposite goal: To keep a spacecraft as still as possible.

Good night, LISA Pathfinder

July 20, 2017

After 16 months of science measurements an international team deactivated the LISA Pathfinder satellite on the evening of the 18th of July 2017. The gravitational-wave laboratory in space powered down after receiving the ...

Recommended for you

Coffee-based colloids for direct solar absorption

March 22, 2019

Solar energy is one of the most promising resources to help reduce fossil fuel consumption and mitigate greenhouse gas emissions to power a sustainable future. Devices presently in use to convert solar energy into thermal ...

Paleontologists report world's biggest Tyrannosaurus rex

March 22, 2019

University of Alberta paleontologists have just reported the world's biggest Tyrannosaurus rex and the largest dinosaur skeleton ever found in Canada. The 13-metre-long T. rex, nicknamed "Scotty," lived in prehistoric Saskatchewan ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.