Lisa Pathfinder launches to test space 'ripples' technology

Lisa Pathfinder's Vega rocket clears the pad at the Kourou spaceport

Europe has launched the Lisa Pathfinder satellite, an exquisite space physics experiment.

It will test the technologies needed to detect gravitational waves - the warping of space-time produced by cataclysmic events in the cosmos.

Having such a capability would make it possible to detect the merger of monster black holes - a marker for the growth of galaxies through time.

Lisa Pathfinder went into orbit on a Vega rocket from French Guiana.

It lifted away from the Kourou spaceport at 01:04 local time (04:04 GMT).

The satellite is being sent in the direction of the Sun, to a point some 1.5 million km from Earth.

The expectation is that the European Space Agency (Esa) mission will operate for about a year.

Pathfinder contains just the single instrument, which is designed to measure and maintain a 38cm separation between two small gold-platinum blocks.

These "proof masses" will be allowed to free-fall inside the spacecraft, and a laser system will then attempt to monitor their behaviour, looking for path deviations as small as a few picometres. This is well less than the diameter of an atom.

Scaled up, it is like tracking the distance between the tops of London's Shard skyscraper and New York's One World Trade Center, and noticing any changes down to just fractions of the width of a human hair.

"We use the laser interferometer to bounce light between the proof masses and the optical structure that we built in Glasgow," says Dr Harry Ward from Glasgow University, UK.

"We then read out the phase of the laser beams as we recombine them, and motion of the proof mass translates into phase changes in the light - essentially, the light gets brighter or dimmer."

Lisa Pathfinder has been more than 10 years in development

While this precision performance is relatively routine in Earth labs, it is very exacting to try to demonstrate it in space.

But if Pathfinder can prove the technology, it will pave the way for an even bigger Esa mission in the 2030s that will aim to study gravitational waves.

These are a prediction of Einstein's Theory of General Relativity, and describe the rippling that occurs in the very fabric of space and time when masses accelerate, such as when stars explode.

The signal, though, is expected to be extremely subtle - hence the requirement for a super-sensitive laser interferometer like the one being trialled by Pathfinder.

And while efforts are under way right now to try to detect gravitational waves on the Earth, only an orbiting observatory would ever be able to identify the long-wavelength, low frequency signals that emanate from truly gargantuan events - like the coming together of the supermassive black holes in merging galaxies.

"Gravitational waves propagate, we believe, at the speed of light, and they carry with them knowledge about the event that caused them," explained Prof Mike Cruise from Birmingham University.

"If that's two black holes crashing into one another, we would often times be able to tell the spin of the black holes, their mass and how far apart they are; and many other details of the collision."

Scientists are particularly keen to study supermassive black holes because their creation and evolution seems to be tied inextricably to that of the galaxies that host them, and probing their properties would therefore reveal details about how the great structures we see on the sky took shape through cosmic history.

Pathfinder's cost to Esa is put at about 450m euros. However, this figure omits a lot of work funded in member states by national space agencies, and so the real price tag is much higher.

The project has experienced severe delay over the years (one previous schedule had it launching in 2008) and came seriously close to cancellation in 2007.

But such is the interest in gravitational waves that Esa member states have persisted with Pathfinder, and look certain to make the formal call for its follow-on mission at the end of next year. Only a launch failure or significant in-orbit under-performance from the demonstrator are likely to disrupt the momentum.

Prof Tim Sumner is an experimental astrophysicist at Imperial College London. He commented: "Since the mid-1990s, we've been studying the concept of using proof masses with laser interferometry between them.

"That has been developed to a stage of maturity where we think it is ready for flight in 2034. There are other technologies being developed, such as atom interferometry that are making great progress, but to adopt that right now for a mission in 2034 would be a bit of a gamble."

Lisa Pathfinder is particularly noteworthy from a British perspective, being the first Esa mission to be led industrially by the UK since the Giotto probe was sent to Halley's Comet in the 1980s. Engineers at Airbus Defence and Space in Stevenage assembled Pathfinder and have been at the Kourou spaceport for the past month and a half, getting it ready to ride on the Vega rocket.

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