A Gravitational Wave Observatory in Space

The first engineering problem I see in this project is getting the blocks in a "free fall" state. Particularly with such a relatively short resonant cavity length of just 38 cm. LIGO used interferometers with 4 kilometer lengths to detect spatial anomalies at a resolution "1/10,000th the width of a proton!" This arm is 10,000 times shorter than LIGO. Any release mechanism to "free fall" these cubes will certainly jostle the cubes in a random fashion much more than 1/(10,000*10,000) of the width of a proton.

I realize the mission of this satellite based instrument is not to directly measure gravity wave distortions of space only 38 cm long but to hopefully codify most of the error mechanisms a network of satellites will produce when arms longer than the Earth are attempted. I wonder if they plan on running LIGO while this experiment runs. It will be interesting to see if any of the results correlate outside of nominal statistical probabilities.

I was also thinking 38 cm is a pretty short reference length for such an experiment. Maybe with them moving the spacecraft around the cube(s) to get both cubes perfectly normal to the laser beam, they know something about this we do not?

I do not really get it, how any motion of the cubes is really cancelled out to the point where they will rest in a static position until a gravitational disturbance comes by.

Oh, no. The sides of this will be massive...5000 km. Here's an article that does a better job explaining the experiment - http://www.nature.com/news/2008/080305/full/452018a.html

Unaided earthly eyes will never actually see the Laser Interferometer Space Antenna (LISA), as this artificial constellation is to be named. Its three component spacecraft will be too small, and the light with which they shine will be invisible infrared. Unseen as it may be, though, it will still be humanity's largest ever creation - 5 million kilometres on a side.

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Using freely falling objects to spot gravitational waves in this way, as LISA is intended to do, is a three-step process. First you set up a situation in which masses can fall freely along their geodesics without being disturbed by magnetic fields or other spurious forces. Then you must measure with extraordinary precision how the distance between their geodesics changes when passing gravitational waves distort the local curvature of space. The last step is analysing these changes to determine the exact shape, frequency and intensity of the distortions to the curvature of space, so as to learn about the nature of distant events producing them.

To provide Vitale's geodesic-joining rays of light, LISA uses neodymium-YAG lasers, which shine at a wavelength of a little more than a micrometre, a wavelength they stick to with extreme precision. These will illuminate cubes four kilograms in mass but just four centimetres on a side - polished 'test masses' of gold-coated gold-platinum alloy as beautiful as fine jewellery and much more costly. The test masses respond to gravity and not much else. "The gold-platinum alloy has a magnetic susceptibility almost as low as glass," explains Paul McNamara, an ESA project scientist in Noordwijk, the Netherlands. Once in space, the test masses' sole purpose is to follow their own paths, each falling freely along its geodesic within one of the LISA spacecraft while reflecting the laser light with which the other spacecraft illuminate it.

LISA will be arranged so that these geodesics are 5 million kilometres apart, with the spacecraft falling around the Sun 20° behind the Earth in the same orbit. That will put them about 50 million kilometres from their planet of origin. Once during every annual orbit the triangle will 'breathe', its sides taking turns to grow and shrink by about 50,000 kilometres.