Spacecraft Launches to Test the Hunt for Ripples in the Fabric of Spacetime

The European Space Agency successfully launched the LISA Pathfinder, a spacecraft designed to demonstrate technology for observing gravitational waves in space. The launch took place at Europe’s spaceport in Kourou, French Guiana on a Vega rocket, at 4:04 GMT on December 3, (10:04 pm EST Dec 2), 2015.

Gravitational waves are ripples in the fabric of spacetime, which were predicted by Albert Einstein in his General Theory of Relativity. So far, because they are extremely tiny and incredibly faint, gravitational waves have proved to be elusive. The technology needed to detect them is highly sensitive and therefore has been difficult to conceive, plan and build.

The LISA Pathfinder mission is only testing the technology to see if it will be possible to detect the waves caused by a gravitational event such as the collision of two black holes, a supernova or a star with a wobbly spin.

Such an event should cause a minute distortion in the fabric of space, and it is predicted that these tiny changes should be detectable. However, the accuracy needed to detect any gravitational waves is extraordinary. An example of how tiny gravitational waves are: the ripples emitted by a pair of orbiting black holes would stretch a million kilometer-long ruler by less than the size of an atom.

LISA Pathfinder will use a specialized laser and interfermeter to measure the distance between two free-floating gold–platinum cubes that will be released into two separate vacuum chambers that are 38 cm apart. Between these chambers is the interferometer detectors. The cubes will be in the equivalent of freefall, and therefore be free from all external and internal forces acting on them, except for gravity. The detectors will monitor the cubes’ relative positions to high precision. These tests will lay the foundations for future gravitational wave observatories in space.

See the video below for a detailed description and visualization of how LISA Pathfinder will work:

Helping the spacecraft remain stable is the utmost importance for detecting gravitational waves, so also being tested on this mission is NASA’s Disturbance Reduction System (DRS), a thruster technology that allows the spacecraft’s position to be continuously adjusted so that the system stays centered about the test cubes. Using lasers, the position of the freely floating test masses will be measured by the interferometer instrument to an accuracy of 100,000th of the width of a human hair.

Again, LISA Pathfinder will not directly detect gravitational waves, but it will demonstrate technologies necessary to observe them. The spacecraft will now undergo a six-week commissioning period as it heads toward the Lagrange Point L1, about 930,000 miles (1.5 million kilometers) from Earth in the direction of the Sun. Then eight months of technology demonstration will take place.

If all goes well, a future full-scale spacecraft observatory could use the same kind of sensors, but they would be housed in three individual spacecraft separated by about 600,000 miles (1 million kilometers). Scientists could then measure how gravitational waves change the distance between the test masses, which would be a difference on the scale of picometers (one picometer is one trillionth of a meter).

More information: ESA LISA Pathfinder Fact Sheet, JPL,