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 late 2015.
The aim of the LISA Pathfinder mission is to demonstrate, in a space environment, that free-falling bodies follow geodesics – the equivalent of straight lines in a curved space – in spacetime, 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 binary black holes and their mergers, which are among the most powerful events 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 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 minuscule 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 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 use of micro-newton electric propulsion
The LISA Pathfinder drag-free control system consists of an inertial sensor, a set of micro-newton thrusters and a control system. The inertial sensor’s role is to monitor the tiny movements of a 46 mm gold–platinum cube. When this test mass moves from its null position, a signal is sent to the control system which is used to command the microthrusters 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.
LTP motion sensor – the best ever flown in space
The sensor within the LISA Technology Package (LTP) is sensitive to micro motions of the test mass, with respect to the spacecraft, as small as one millionth of a millimetre (one nanometre, 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 picometre, or 10-12m).
LISA Pathfinder carries two advanced instruments. The LTP was 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 enclosure. They 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 38 cm.
The Disturbance Reduction System (DRS) was provided by NASA’s Jet Propulsion Laboratory in California. It includes a set of microthrusters to control the spacecraft’s position to within a millionth of a millimetre.
The launch of the LISA Pathfinder is planned for late 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 km by 800 000 km halo orbit around the first Sun–Earth Lagrange point, 1.5 million kilometres from Earth. After the last transfer burn is performed, and the health of the 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 in November 2000. It was 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, an earlier concept for a spaceborne observatory for gravitational waves, and now used to describe a class of missions based on the original LISA concept. LISA Pathfinder will test key technology for future LISA-like space missions to study the gravitational Universe.
Last update: 3 September 2015