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Black-hole sniffing 'laser combs' are go, say Brit gov boffins

Golden triangle mega space scope gets box-tick

Boffins at Blighty's National Physical Laboratory (NPL) - birthplace among other things of the internet* and the Dambusters' bouncing bomb - say they have validated a cunning super-accurate, laser-assisted space formation flying tactic. This will allow the detection of ripples in the very fabric of space-time, allowing top brainboxes to probe the deepest secrets of the cosmos.

It seems that if you want to make a group of spacecraft fly in a really, really accurate formation the way to do it is by the use of "femtosecond comb lasers". The very short, 0.000000000000001 second laser pulses are sent between the satellites or whatever, and their brevity means that accurate timing of their passage can measure the distance covered with an accuracy "of microns".

This will be particularly handy, according to the NPL, in the case of detecting gravitational waves - the propagation fronts of changes in the curvature of space-time caused by massive bodies moving about or doing things. There are already grav-wave detectors on Earth, but their performance in some frequencies is limited by masses moving about nearby - road traffic, for instance. Theory suggests that a clearer picture could be achieved by using 3 spacecraft 5 million km from each other, orbiting the sun well away from Earth in a gigantic triangle.

The three gold-platinum masses of this proposed Laser Interferometer Space Antenna (LISA) would measure tiny changes in their distance from one another using the femtosecond comb technique, so sniffing the tiny grav ripples emanating from far-off massive black holes or certain kinds of binary stars. Black holes in particular are hard to observe by normal optical means, so boffins would like to have a reliable way of detecting the lower-frequency grav waves they are thought to emit in some circumstances.

According to the NPL, the femtosecond comb tech - validated in a joint study with other organisations called HAALDM (High Accuracy Absolute Long Distance Measurement) - would also be handy in other apps such as X-ray observatory satellites. The study was carried out on behalf of the European Space Agency, which will partner with NASA on the LISA grav-scope array if it goes ahead. ®


* The NPL says (pdf p13) that it developed packet-switched networking in 1966, and that by the early 1970s it had 200 users on its proto-internet - which "provided a much needed steer to the development of the Arpanet, which would evolve into the Internet we know today".

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