High precision laser interferometry for space

High precision laser interferometry for space

Spaceborne experiments that probe subtle gravitational effects often involve picometre-scale measurements over timescales of minutes to hours and over long baselines.

Current examples include LISA/NGO, a spaceborne gravitational waves mission which involves inter-spacecraft ranging over millions of kilometres, its precursor technology demonstrator mission, LISA Pathfinder, which requires distance monitoring over tens of centimetres within a single spacecraft, and GRACE II, a proposed follow-on to the GRACE gravity and climate explorer mission, which features inter-spacecraft distance monitoring over hundreds of kilometres.

Only laser interferometry offers the required precision of measurement over such baselines.

Our approach

As part of our longer term scientific goal of playing a lead role in a future LISA/NGO mission, our recent work has focused on LISA Pathfinder, for which we developed and prototyped the measurement “heart” of the spacecraft – a 20cm square block of low expansion material to which are attached multiple silica mirrors and beamsplitters.

For the component mounting we developed a technique – hydroxy-catalysis bonding – that forms an ultra–strong and dimensionally stable bond but which allows a period of adjustment of component alignment prior to a bond forming.

We also developed component manipulation and beam measurement techniques that allow absolute location of interferometer beams at the 10 micron level, and pointing with better than a few tens of microradian accuracy. With our custom designed and developed optical fibre systems we have demonstrated excellent interferometer alignment stability over the often harsh temperature, radiation and vibration conditions involved in spaceflight.

As the culmination of this work we have essentially completed the build of the flight optical benches for LISA Pathfinder and we have now embarked on development of the much more complex optical systems that will be required for the LISA mission.

Why is this research important?

The advent of a spaceborne gravitational wave detector will reveal directly for the first time extreme astrophysical events such as supermassive black hole collisions, enhancing greatly our understanding of the Universe.

Undertaking such technologically challenging projects necessarily requires invention of novel assembly methods and innovative hardware solutions, and applications of our spaceborne interferometry capabilities are expected to grow significantly.

Furthermore we have already seen industrial interest beyond the space sector – e.g. in areas such as high power lasers. Such lasers are of great interest for manufacturing, in defence and for communications.

Researchers

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