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LISA Pathfinder



LISA Pathfinder was a mission to demonstrate in orbit the technologies for LISA, the ESA/NASA Laser Interferometry Satellite Antenna gravitational wave observatory.

LISA Pathfinder, originally named SMART 2 (one of ESA's Small Missions for Application Research and Technology), was a new ESA space science mission. Launched in 2015, LISA Pathfinder was packed with radical instrumentation and technology to prepare the way for LISA, the world's first space-based gravitational wave detector.

The LISA Pathfinder mission tested a series of ultra-high precision technologies that will be used on a later and much larger international project called LISA

The basic principle of LISA will be to measure the changes in distance between freely floating 'test masses', small gold blocks held in place by carefully controlled electrostatic fields. The six test masses will be contained in three separate spacecraft (two each) arranged in an equilateral triangle with sides of 5 million km! Each of the three arms of the constellation will be optically linked by a system of lasers ('laser interferometer') and a software control system so as to form a ‘rigid' structure.

LISA Pathfinder was an in-orbit demonstrator of the key technologies for LISA. It tested the gravitational reference sensors, the laser interferometry and the micro-Newton thrusters. But instead of a separation of 5 million km, LISA Pathfinder used test masses only 30 cm apart and placed on a single spacecraft. In fact, because the technology is so challenging, LISA Pathfinder only carried two alternative packages of sensors, lasers and micro-thrusters. One (provided by European institutes and ESA) was called the LISA Test Package (LTP), while the other, the Disturbance Reduction System (DRS), was provided by NASA under the New Millennium program as ST 7.

After the inertial sensor systems, the micro-propulsion was the most innovative technology to be tested on LISA Pathfinder. Two types of micro-Newton thrusters are under development in Europe. Field Emission Electric Thrusters are a type of electric propulsion which use very large electric fields to almost instantly accelerate tiny droplets of electrically conducting-metal up to high velocity. In contrast, micro-cold gas thrusters are tiny proportional valves; in essence, a controlled leak of inert high pressure gas (typically nitrogen).

LISA Pathfinder was launched into a 207 km × 1540 km, 5.96° low-Earth Orbit. To transfer the spacecraft into its operational orbit a conventional chemical propulsion system, based on the Eurostar-2000 propulsion system, was needed, but this was ejected after use, because even a few kilograms of left-over fuel sloshing around within the emptied tanks could disturb the experiments.

The operational orbit was a stable and eclipse-free orbit around the L1 Lagrange point, 1.5 million km from Earth towards the Sun. This location helped to minimize disturbances from the Earth's gravity, magnetic field and atmosphere. The nominal mission life was just over one year, allowing the DRS and the LTP to be separately tested and also allowing special experiments where one system will monitor the performance of the other. This in-orbit feedback was to help the detailed design of LISA.

Alternate Names

  • 41043
  • LISAPathfinder

Facts in Brief

Launch Date: 2015-12-03
Launch Vehicle: Vega
Launch Site: Kourou, French Guiana
Mass: 1910 kg

Funding Agencies

  • European Space Agency (International)
  • National Aeronautics and Space Administration (United States)


  • Technology Applications
  • Astronomy

Additional Information

Questions and comments about this spacecraft can be directed to: Coordinated Request and User Support Office

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