The two hearts of LISA Pathfinder

As you might already know, LISA, a joint mission from ESA and NASA which is scheduled for 2014, will test the fundamental theories of gravitation, including Einstein's General Relativity. This mission relies on two small hearts, two cubes, just 5 centimeters across, but they will look at three spacecrafts positioned five million kilometers away.

As you might already know, LISA, a joint mission from ESA and NASA which is scheduled for 2014, will test the fundamental theories of gravitation, including Einstein's General Relativity. In "The day LISA Pathfinder hung in the balance," the European Space Agency reminds us that this mission relies on two small hearts. The Laser Interferometer Space Antenna (LISA) hearts are two cubes, just 5 centimeters across, but will look at three spacecrafts positioned five million kilometers distant from one another. But read more...

Here is a short description of these 'hearts' which will be used to check if our current concept of relativity is valid or not.

A cornerstone of relativity is the concept of a frame of reference. This is a set of bodies relative to which any motion can be measured. Without a reference frame, no motion through space can be detected. Scientists call a frame of reference 'inertial' if unperturbed objects appear in that frame, either at rest or moving at a constant velocity.
To make this measurement, LISA Pathfinder uses two 'proof-masses'. Each is a small cube of a gold and platinum alloy, whose relative motion is measured by a laser beam. Once in space, the proof-masses will float freely within the spacecraft. When subtle forces act on the proof-masses, the laser beam will detect the way they change position to within a few thousandths of a billionth of a meter, and will be able to detect forces as small as the weight of a typical bacterium.

Here are more details about the goal of the joint ESA/NASA LISA mission? Here is the answer, provided by ESA in LISA in a new light (September 22, 2005).

[The mission,] envisaged to launch in the 2014 timeframe and designed for the purpose of detecting Einstein’s gravitational waves, relies on the use of laser light to measure the tiny distance variations that a passing gravitational wave will induce between separated masses. To this end, the LISA laser interferometer, which is formed by a triangular constellation of three spacecraft positioned five million kilometres distant from one another, will have to detect relative displacements over this enormous distance with an accuracy of less than a tenth of an atom’s diameter.

Below is an illustration showing how these future three satellites will help to "detect and observe gravitational waves from massive black holes and galactic binaries with periods in the range of a few seconds to a few hours (i.e. in the frequency range 10-4 to 10-1 Hz)." Credits: ESA-C. Vijoux

LISA's triangulation

And below, this photograph shows the LISA Pathfinder gold-platinum proof-mass being placed over the high sensitivity balance used at the International Bureau of Weights and Measures (BIPM, France) to measure the proof-mass's magnetic susceptibility. (Credits: Courtesy of M. Hueller (University of Trento)/R. Davis (BIPM))

LISA Pathfinder proof-mass under test

If you want more information about this future space mission, here is a link to a LISA overview, from which the top illustration was picked, and which gives additional details about this future space mission.

Detecting gravitational waves is the goal of ESA's future LISA mission. LISA will search for gravitational radiation from astronomical sources, testing the fundamental theories of gravitation.
The Laser Interferometer Space Antenna (LISA) is a joint mission with NASA. It is a three-spacecraft mission, designed to detect the 'ripples' in space given out when very massive objects undergo strong acceleration. For example, they are produced when a black hole swallows a massive neutron star. Such ripples are called 'gravitational waves' and LISA will be the first mission to try and detect them from space.

Finally, here is the conclusion of the ESA news release which served as the basis for this post: "LISA Pathfinder [scheduled for 2009] paves the way for LISA, three spacecraft that will work together to detect Einstein's predicted ripples, known as gravitational waves, in the fabric of spacetime.

Sources: European Space Agency news release, via EurekAlert!, October 11, 2006 ESA pages

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