LISA Pathfinder overview
LISA Pathfinder will test in flight the concept of low-frequency gravitational wave detection: it will put two test masses in a near-perfect gravitational free-fall, and control and measure their motion with unprecedented accuracy. To do this it will use inertial sensors, a laser metrology system, a drag-free control system and an ultra-precise micro-propulsion system.
LISA Pathfinder is scheduled for launch in 2015.
The aim of the LISA Pathfinder mission is to demonstrate, in a space environment, that free-falling bodies follow geodesics in space-time, by more than two orders of magnitude better than any past, present, or planned mission. Specifically, it must:
- Demonstrate drag-free and attitude control in a spacecraft with two free proof masses
- Test feasibility of laser interferometry with picometre resolution at low frequency – approaching 10-12 m Hz-1/2 in the frequency band 1-30 mHz
- Test the endurance of the different instruments and hardware in the space environment
Completely different method of observing the Universe
Virtually our entire knowledge about the Universe is based upon the observation of electromagnetic waves, such as visible light, infrared, ultraviolet, radio, X-rays and gamma rays. LISA Pathfinder will pave the way to a completely different method of observing the Universe: detecting gravitational waves. This will allow astrophysicists to address some of the most fundamental questions about the Universe and possibly raise new ones, such as the nature of inspirals and mergers of binary black holes, the most powerful transformations of energy in the Universe.
Very first detection of gravitational waves in space
With LISA Pathfinder, the technology needed to detect gravitational waves will be tested in space for the very first time.
Gravitational waves are ripples in space-time predicted by Albert Einstein’s Theory of General Relativity. Detecting gravitational waves would greatly enhance our knowledge of General Relativity and allow scientists to detect the impact of astronomical events which are thought to cause a miniscule distortion on the fabric of space itself.
Only feasible in space
LISA Pathfinder is a pioneering mission. Not only are these technologies new, they cannot be properly verified on the ground. This is because the Earth's gravity and environment would overwhelm the test results. Only in space can the subtle effects of the low frequency gravitational waves be detected with exquisitely precise instruments.
Greater accuracy than ever achieved before
In doing this, LISA Pathfinder will build an almost exact inertial frame of reference in which scientists can measure the warping of space-time many times more precisely than achieved before. This will lay the foundation for future space borne tests of General Relativity.
First-time application of a micro-Newton electric propulsion system
The LISA Pathfinder drag-free control system onboard the spacecraft consists of an inertial sensor, a proportional micro-propulsion system and a control system. The inertial sensor’s role is to monitor the micro motions of a 46mm Gold-Platinum cube. When the cube, known as the Test Mass, moves away from its null position, a signal is sent to the control system which is used to command the micro-propulsion thrusters which in turn enable the spacecraft to remain centred on the test mass. It is the very first time that ESA operates a spacecraft with such micro-Newton thrusters as the only propulsion mechanism.
LTP motion sensor – the best ever flown in space
The sensor within the LTP is sensitive to micro motions of the test mass, with respect to the spacecraft, as small as one millionth of a millimetre (one nano-metre, or 10-9m). However, the relative motion of the two test masses within the LTP can be measured, using ultra-precise laser interferometry, to a staggering one thousandth of one millionth of a millimetre (one pico-metre, or 10-12m).
LISA Pathfinder carries two advanced instruments: The LTP (LISA Technology Package), a payload developed by European institutes and industry. It contains two identical proof masses in the form of 46 mm cubes made of gold-platinum, each suspending in its own vacuum can. They shall simulate the observational arrangement for the LISA mission, with the difference that the distance between the proof masses is reduced from 5 million kilometres to 35 centimetres.
The Disturbance Reduction System (DRS) is an experiment provided by NASA's Jet Propulsion Laboratory in California, which includes also a set of micro-rockets that aim to control the spacecraft’s position to within a millionth of a millimetre.
The launch of the LISA Pathfinder is planned for 2015. The spacecraft will be launched by a VEGA rocket from Kourou, French Guiana, and will be placed into a slightly elliptical parking orbit. From there, it will use its own propulsion module to reach its final operational orbit, a 500 000 kilometres by 800 000 kilometres halo orbit around the first Sun-Earth Lagrange point, at 1.5 million kilometres from Earth. After the last transfer burn is performed, and the health of the science spacecraft is ascertained, the propulsion module will be jettisoned.
LISA Pathfinder’s operational phase will last six months, shared between 90 days LTP and 60 days DRS, and 30 days joint operations The DRS experiment will be using the European LTP sensor for its measurements. The mission itself could be extended to one year.
LISA Pathfinder was approved by the ESA Science Programme Committee (SPC) in November 2000. It was further reconfirmed by the same body and by the ESA Council in May 2002, as part of ESA’s new 'Cosmic Vision' Scientific Programme.
The name LISA originally comes from Laser Interferometer Space Antenna, which was a gravitational wave mission planned by ESA and NASA. Although this mission will not go ahead because of changes in funding commitments, the new technologies required for a similar mission will be tested by LISA Pathfinder.
Last update: 6 June 2013