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How the 'LHC in space' lost its British 'engine'

Jonathan Amos | 01:06 UK time, Friday, 27 August 2010

The mythical beast has been sighted. The Alpha Magnetic Spectrometer (AMS) has finally arrived at the Kennedy Space Center in Florida to begin final checks before being launched to the International Space Station (ISS) in February.

The AMSThe AMS has variously been described as the "LHC in space" and the "world's most expensive space experiment", besides a few other derogatory labels that have played on its $1.5bn price tag.

The machine will be placed atop the station's starboard truss to undertake a comprehensive survey of cosmic rays - the storm of high-energy particles (mostly protons and helium nuclei) that are accelerated in our direction from supernovas, black holes and who knows what other exotic corners of the cosmos.

It promises remarkable new discoveries about the origin and make-up of the Universe.

There's a chance it could find anti-matter, the mirror of the material from which we're all made; and even identify the mysterious "dark matter" that scientists say makes a bigger contribution to the mass of the cosmos than all the stuff we see through telescopes. That's a big billing.

For those involved in the project, though, getting to Kennedy must have a slightly surreal feel about it given the number of times AMS has flirted with cancellation.

Its most serious crisis followed the Columbia tragedy when Nasa wrote the detector out of the shuttle launch manifest, saying all remaining flights had to be used to complete the space station and stock it with essential supplies.

Studies were done to see if AMS could launch on an expendable rocket like an Atlas or Delta instead. But this route threatened to add hundreds of millions of dollars on to the existing project budget and might only have got the experiment to the ISS in time to be chucked in the Pacific Ocean along with a decommissioned station (at the time expected to occur at the end of 2015).

And then Congress stepped in and mandated Nasa to fly an extra shuttle. AMS was back on.

What's more, US President Obama said he wanted to extend the life of the space station to at least 2020... and that presented the 16-nation AMS collaboration with a dilemma.

The AMS arrives at Kennedy

At the core of the machine is a magnet that bends particles as they enter through the top. The way they bend reveals their charge, a fundamental property that together with information from a slew of detectors tells scientists precisely what they're dealing with - very probably only a boring proton but just possibly a strange piece of matter never witnessed before.

The original intention was to fly a superconducting magnet, a frigid and very powerful device but one that loses its edge when its liquid helium refrigerant runs dry.

Without a top-up (and this can't be done in space), the superconducting device would give AMS only about three good years.

The assembled UK magnetWhen the station was going to be ditched in 2016, this didn't much matter but with an extended platform operating until deep into the 2020s, it suddenly represented a wasted opportunity.

So the AMS scientists decided to remove the superconducting magnet and replace it with a less powerful permanent one.

The swap-out would reduce the machine's sensitivity slightly but give it many more years of service. And for an experiment which relies on statistics, on getting millions of particle measurements - length of service is really important.

But here's the thing for those who follow UK efforts in space: the superconducting magnet was a British-designed and built technology. It was made at Scientific Magnetics (formerly Space Cryomagnetics) of Culham, in Oxfordshire.

Steve Harrison at the company gave 12 years of his life to the magnet, and this week he watched as AMS arrived at Kennedy without his "engine". AMS now uses a Chinese-built device instead. He told me:

"It was always a very risky proposition. To be quite honest, most of the time I was expecting AMS never to fly anyway because the shuttle programme was in such doubt. Yes, I was gutted; but it was one of those things. There's now a project under way to transfer some of the technology into the European Space Agency so that it can be used for other purposes. It's not all lost. Esa are interested in using it for magnetic shielding of astronauts on interplanetary missions. Magnetic shielding from cosmic rays is one possible application."

The UK is not involved in the AMS collaboration at a programmatic level; but just as in several other areas of space activity where Britain chooses to stand aside, one of its companies was still called upon at contractor level to fulfil tasks no-one else could do.

It's good to see that the effort Scientific Magnetics put into AMS will live on, even if its superconducting magnet only ever makes it into a museum.

spectro595x306.gif

Transition Radiation Detector determines highest-energy particle velocities
Silicon trackers follow particle paths; how they bend reveals their charge
Permanent magnet is core component of AMS and makes particles curve
Time-of-flight counters determine lowest-energy particle velocities
Star trackers scan star fields to establish AMS's orientation in space
Cerenkov detector makes accurate velocity measurements of fast particles
Electromagnetic calorimeter measures energy of impacting particles
Anti-coincidence counter filters signal from unwanted side particles

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