The European Space Agency’s LISA Pathfinder lifted off earlier today on a Vega rocket from Europe’s spaceport in Kourou, French Guiana, on its way to demonstrate technology for observing gravitational waves from space.
Gravitational waves are ripples in the fabric of spacetime, predicted a century ago by Albert Einstein’s General Theory of Relativity, published on 2 December 1915.
Einstein’s theory predicts that these fluctuations should be universal, generated by accelerating massive objects. However, they have not been directly detected to date because they are so tiny. For example, the ripples emitted by a pair of orbiting black holes would stretch a million kilometre-long ruler by less than the size of an atom.
LISA Pathfinder will test the extraordinary technology needed to observe gravitational waves from space. At its core is a pair of identical 46 mm gold–platinum cubes separated by 38 cm, which will be isolated from all external and internal forces acting on them except one: gravity.
The mission will put these cubes in the purest free-fall ever produced in space and monitor their relative positions to astonishing precision, laying the foundations for gravitational wave observatories in space.
Such future missions will be key partners to the ground sites already searching for these elusive cosmic messengers. Space and ground experiments are sensitive to different sources of gravitational waves, both opening up new possibilities to study some of the most powerful phenomena in the Universe.
The Vega launcher lifted off at 04:04 GMT (05:04 CET 3 December 2015). About seven minutes later, after separation of the first three stages, the first ignition of Vega’s upper stage propelled LISA Pathfinder into a low orbit, followed by another ignition about one hour and forty minutes into the flight.
The spacecraft separated from the upper stage at 05:49 GMT (06:49 CET). Controllers at ESA’s operations centre in Darmstadt, Germany then established control.
Over the next two weeks, the spacecraft will reach the orbit’s highest point in six critical burns. The final burn will propel the spacecraft towards its operational location, orbiting around a stable virtual point in space called L1, some 1.5 million kilometres from Earth towards the Sun.
LISA Pathfinder is expected to reach its operational orbit about 10 weeks after launch, in mid-February. After final checks, it will begin its six-month scientific mission at the beginning of March.
En route to the final orbit, the two cubes will be released from the locking mechanisms that hold them during launch and cruise. Once in orbit around L1, the final mechanisms will be unlocked and the cubes will no longer be in mechanical with the spacecraft.
A complex system of laser beams bouncing between the two cubes will measure how close to true free-fall they are to within a billionth of a millimetre – never previously achieved in space.
University of Birmingham physicists were involved in the design and build of the Phasemeter – an electronic box which measures the separation between two test masses linked by laser beams. This mission will allow scientists to search for any spurious influences on the measurements between the masses that might hinder the future detection of gravitational waves.
‘Fundamental research tries to understand our world,’says Johann-Dietrich Woerner, ESA’s Director General. ‘Einstein’s theoretical findings are still very impressive. With LISA Pathfinder we will try to take a further step towards confirmation of one of Einstein’s predictions: gravitational waves.’
Professor Mike Cruise , lead investigator from the University of Birmingham’s School of Physics and Astronomy , said: ‘Birmingham scientists have developed the sensitive electronics that will allow LISA Pathfinder to take the first step toward gravitational wave detection from space, opening a new window on the Universe. This mission has been launched a hundred years after Einstein’s prediction of gravitational waves and will confirm that the precision required to detect these waves is now achievable.’
The spacecraft itself will be an active part of the experiment, firing tiny thrusters about 10 times a second to adjust its position and avoid making with the cubes, thus shielding them from any forces that would prevent them from moving under the effect of gravity alone.
If these extraordinarily high-precision measurements and operations can be achieved by LISA Pathfinder, the door will be open to building a future space observatory, capable of detecting the minute disturbances in spacetime produced by gravitational waves, which are expected to be a few tens of a billionth of a millimetre over distances of millions of kilometres.
LISA Pathfinder will operate as a physics laboratory in space. Over an intense period of six months, mission scientists will analyse the data received on Earth from each day’s operations to plan the experiments to be performed on the satellite during the following days.