Mission

LISA Pathfinder

LISA Pathfinder will pave the way for a major ESA/NASA mission planned for the near future: LISA (Laser Interferometer Space Antenna), aimed at detecting gravitational waves generated by very massive objects such as black holes. Detecting gravitational waves will tell us more about the way space and time are interconnected.

The mission consists of placing two test-masses in a nearly perfect gravitational free-fall, and of controlling and measuring their motion with unprecedented accuracy. This is achieved through state-of-the-art technology comprising inertial sensors, a laser metrology system, a drag-free control system and an ultra-precise micro-propulsion system.

All these technologies are essential not only for LISA; they also lie at the heart of any future space-based test of Einstein's General Relativity. LISA Pathfinder is scheduled for launch in 2014.

Objectives

LISA Pathfinder

• Demonstrate drag-free and attitude control in spacecraft with two test masses
• Test feasibility of laser interferometry at the level of accuracy envisaged for LISA
• Test endurance of the different instruments and hardware in the space environment
• Validate the new technologies and measurement strategies to ensure the success of LISA

What’s special?

LISA Pathfinder

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. Using this technology, LISA will be able to show whether a key prediction of Albert Einstein’s, put forward more than 90 years ago in his General Theory of Relativity, is indeed correct. The prediction is that ripples in space-time, known as gravitational waves, criss-cross the Universe, however, these waves have never been detected directly. By detecting these ripples, LISA will tell us more about the way in which space and time are interwoven. LISA will detect these waves, their intensity, properties and direction in order to investigate elusive objects such as black holes and neutron star binary systems within our galaxy that we would otherwise have no way of observing.

Only feasible in space
LISA relies on technologies that have never been built before. 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 not just for LISA, but for any future space borne test 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).

Spacecraft

LISA Technology Package

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. Once validated by this mission, the technology on LISA Pathfinder will be ready to be used in the more complex and further-reaching mission LISA. There the relative movement of two spacecrafts located 5 million kilometres apart will be measured to an accuracy of 10 picometres (1 picometre is equal to one millionth of a millionth of a metre).

Journey

LISA Pathfinder propulsion module

The launch of the LISA Pathfinder is planned for 2014. 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.

History

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.