Posted on March 8th, 2016

Reaching Orbit – LISA Pathfinder, the Hunt for Gravitational Waves

While we are celebrating the first direct measurement of gravitational waves from a ground-based observatory, researchers are already on track to send up a space-based observatory to detect the same gravitational waves. Detecting these waves in space is the next step for this technology as there is less interference from planetary factors, like gravitation, radiation and the atmosphere. I suggest you read my Out of This World article to better understand how the ground-based system works but I’ll give a little recap here.

The ground-based interferometer is two and a half miles long and measures infinitesimally small changes in the distance between mirrors signaling a gravitational wave has passed by. Precisely placing mirrors in a fixed position to measure space distortion is relatively easy only in comparison to doing it in space. On Earth, objects stay where you put them, especially in cases such as this. In space, where objects are basically free falling and pulled by gravity, maintaining the same distance between two separate objects is a daunting task. It’s hard to imagine how sensors orbiting independently in space can maintain the accuracy required for such precise measurements. Any positional change between the mirrors will have tremendous effect on the data. However, the great benefit of a space observatory is that it can identify even larger anomalies then the collisions of two relatively small black holes, since larger gravitational waves are much longer and move more slowly. Smaller anomalies are actually easier to detect as the waves are closer together and thus they have a more distinct signature.

LISAArtist depiction of the LISA Pathfinder, the first mission to test the technology necessary to detect gravitational waves. (Credit: ESA-C.Carreau)

On December 3rd, 2015, the LISA Pathfinder spacecraft launched into orbit. Its mission is to test the main technologies that are necessary to accomplish such a feat. The spacecraft houses two masses that are in near-perfect gravitational free fall. The main technology being tested is the drag-free control system, intended to monitor the movement of the two test masses. When one mass moves away from its null position, the spacecraft adjusts to center itself on the mass and a signal is sent to the second test mass to follow the first one, thus staying in formation. The LISA Pathfinder mission is the first leg of the overall eLISA mission to put an instrument for measuring gravitational waves in space. During this test phase with the LISA Pathfinder, the two masses are only about 38-centimeters apart. For the eLISA mission, the arm length is set to be 1 million kilometers long, I can’t begin to explain how this is scientifically possible, I will leave it to more capable minds then mine. If you want more technical information, I suggest checking out the eLISA mission page.

Screen Shot 2016-03-04 at 1.41.53 PMThis video depicts the LISA Pathfinder spacecraft and its instruments in action. (Credit: ESA/ATG medialab)

This spaced-based system will someday allow researchers to probe into the depths of space and time. Gravitational waves, unlike waves found in the electromagnetic spectrum, pass through space and objects undisturbed. Once researchers can accurately measure gravitational waves, they can study astronomical phenomenon that are too distant to be seen by current technology, they may even be able to see back to the very origins of the Universe. Measuring the distortion of space and time feels like something from science fiction. The fact that this is reality is both thrilling and awe inspiring.

Katie Nelson
Geospatial Ninja
(303) 718-7163

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