Artist's impression of a LISA Pathfinder spacecraft
|Mission duration||Nominal: 1 year (with sufficient Cold Gas for mission extension)|
|Launch mass||1,910 kilograms (4,210 lb)|
|BOL mass||480 kg (1,060 lb)|
|Dry mass||810 kg (1,790 lb)|
|Payload mass||125 kg (276 lb)|
|Dimensions||2.9 m × 2.1 m (9.5 ft × 6.9 ft)|
|Start of mission|
|Launch date||July 2015|
|Launch site||Kourou ELV|
|Reference system||Sun–Earth L1|
|Periapsis||500,000 km (310,000 mi)|
|Apoapsis||800,000 km (500,000 mi)|
|35 cm Laser interferometer and Disturbance Reduction System|
LISA Pathfinder is the revised name for SMART-2 or Small Missions for Advanced Research in Technology-2, an ESA/NASA space probe to be launched in 2015. The estimated cost for the mission is 400 million Euros, and the aim is to test technologies needed for the Laser Interferometer Space Antenna (LISA), a joint ESA/NASA gravitational wave detector. It will contain one arm of LISA, shortened from 5 Gm (5 million km) to 35 cm. In particular, it will verify:
- Drag-free attitude control of a spacecraft with two proof masses,
- The feasibility of laser interferometry in the desired frequency band (which is not possible on the surface of Earth), and
- The reliability and longevity of the various components—capacitive sensors, microthrusters, lasers and optics.
LISA Pathfinder is being built by EADS Astrium Ltd. of Stevenage, UK under contract to the European Space Agency. It will carry a European 'LISA Technology Package' comprising inertial sensors, interferometer and associated instrumentation as well as two drag-free control systems: a European one using Cold Gas Micro thrusters (similar to those used on GAIA), and a US-built 'Disturbance Reduction System' using slightly different sensors and colloid thrusters that use ionised droplets of a colloid accelerated in an electric field. The colloid thruster system was built by Busek and delivered to JPL for integration with the spacecraft. 
The LISA Technology Package is being integrated by Astrium Germany, but the instruments and components are being supplied to Astrium by contributing institutions across Europe. The noise rejection technical requirements on the interferometer are very stringent, which means that the physical response of the interferometer to changing environmental conditions, such as temperature, must be minimised.
The spacecraft will first be launched into an elliptical LEO parking orbit. From there it will execute a short burn each time perigee is passed, slowly raising the apogee closer to the intended halo orbit around the Earth–Sun L1 point. If this mission is successful, it is hoped that the LISA mission will be launched a few years later, current estimates are around 2018.
Possible Mission Extension
A possible mission extension could be to perform some measurements to confirm whether gravity is all general relativity says it is. By flying through the 'Saddle Point' where the Earth and Sun's gravity cancel out, the spacecraft might probe whether Einstein's theory still holds when gravitational accelerations are incredibly small. If it does, these gravitational lacunae will be the last resting place of other occasionally fashionable theories, such as Modified Newtonian Dynamics (MOND) and TeVeS.
- "LISA Pathfinder: Operations". ESA. 8 January 2010. Retrieved 5 February 2011.
- "LPF (LISA Pathfinder) Mission". ESA eoPortal. Retrieved 2014-03-28.
- "LISA Pathfinder factsheet". ESA. 11 June 2012. Retrieved 26 June 2012.
- "LISA Pathfinder To Proceed Despite 100% Cost Growth". Space News. 22 June 2011.
- Rovey, J. "Propulsion and Energy: Electric Propulsion (Year in Review, 2009)". Aerospace America, December 2009, p. 44.
- "LISA Pathfinder: Mission home". ESA. Retrieved 5 February 2011.
- "LISA Pathfinder: Fact sheet". ESA. Retrieved 20 April 2009.
- New Scientist 2 March 2013 page 44