.jpg) Model of theLISA Pathfinder spacecraft | |
| Mission type | High-precision metrology, Technology demonstrator for gravitational-wave observation |
|---|---|
| Operator | ESA[1] |
| COSPAR ID | 2015-070A |
| SATCATno. | 41043 |
| Mission duration | 576 days |
| Spacecraft properties | |
| Manufacturer | Airbus Defence and Space |
| Launch mass | 1,910 kg (4,210 lb)[1] |
| BOL mass | 480 kg (1,060 lb)[2] |
| 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 | 3 December 2015, 04:04:00 UTC[3][4][5] |
| Rocket | Vega (VV06) |
| Launch site | KourouELV |
| Contractor | Arianespace |
| End of mission | |
| Disposal | Decommissioned |
| Deactivated | 30 June 2017 |
| Orbital parameters | |
| Reference system | Sun–Earth L1 |
| Regime | Lissajous orbit |
| Periapsis altitude | 500,000 km (310,000 mi) |
| Apoapsis altitude | 800,000 km (500,000 mi) |
| Inclination | 60 degrees |
| Epoch | Planned |
| Transponders | |
| Band | X band |
| Bandwidth | 7 kbit/s |
| Instruments | |
| ~36.7 cm Laserinterferometer | |
 ESA astrophysics insignia forLISA Pathfinder ← Gaia | |
LISA Pathfinder (LPF) was a space mission by theEuropean Space Agency (ESA). It was launched on 3 December 2015 on boardVega flight VV06, and operated until July 2017.[3][4][5] The mission tested key technologies needed for theLaser Interferometer Space Antenna (LISA), an ESAgravitational wave observatory planned to be launched in 2035.[6] Formerly, the mission was known as Small Missions for Advanced Research in Technology-2 (SMART-2) of theSmall Missions for Advanced Research in Technology ESA scientific programme. The LISA Pathfinder scientific phase started on 1 March 2016 and lasted almost sixteen months.[7][8] In June 2016, ESA announced that LISA Pathfinder demonstrated that the LISA mission is feasible,[9] paving the way for the official adoption of the LISA mission.[10]
The mission cost was €490 million.[11] It involved research institutes and space companies from many European countries, as well as the AmericanNational Aeronautics and Space Administration (NASA).[12][13]
LISA Pathfinder was a proof-of-concept mission, to prove that the two masses (known as test masses) can fly through space, untouched but shielded by the spacecraft, and maintain their relative positions to the precision needed to realize a full gravitational wave observatory. The primary objectives were to minimize the external forces acting on the test masses, guaranteeing small deviations fromgeodesic motion, and to measure their relative displacement with high precision. Much of the experimentation ingravitational physics requires measuring the relative acceleration between free-falling, geodesic reference test particles.[14]
LISA Pathfinder hosted the first sub-picometerlaserinterferometer ever flown in space,[15] capable of tracking the relative displacement of the two test masses, situated about 38 cm apart in a single spacecraft. For the gravitational wave observatoryLISA,[16] each of three separate spacecraft will host two test masses, 2.5 million kilometers apart.[17] The science of LISA Pathfinder consisted of measuring and creating an experimentally-anchored physical model for all the spurious effects – including stray forces and optical measurement limits – that limit the ability to create, and measure, the perfect constellation of free-falling test particles that would be ideal for theLISA follow-up mission.[18]
LISA will have its test mass pairsfree falling along the spacecraft-to-spacecraft axes, with micro-Newtonthrusters controlling the spacecraft motion to follow the test masses. In LISA Pathfinder, however, the complete free fall was not possible, as the two test masses were enclosed in the same spacecraft. Hence, the spacecraft could follow only one of the two masses in its free fall, and was forced to applyfeedback forces to the second test mass. This way, the spacecraft acted as an active shield to external noisy forces, especially the solar radiation pressure, whose magnitude would prevent the mission to reach its requirements. The main LISA Pathfinder science measurement was therefore the out-of-loop differentialacceleration between the two test masses.
LISA Pathfinder was assembled byAirbus Defence and Space in Stevenage (UK), under contract to the European Space Agency. It carried 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 onGaia), and a US-built "Disturbance Reduction System" using the European sensors and anelectric propulsion system that uses ionised droplets of a colloid accelerated in anelectric field.[19] Thecolloid thruster (or "electrospray thruster") system was built byBusek and delivered toJPL for integration with the spacecraft.[20]
The LISA Technology Package (LTP) was integrated by Airbus Defence and Space Germany, but the instruments and components were supplied by contributing institutions across Europe. The noise rejection technical requirements on the interferometer were very stringent, which means that the physical response of the interferometer to changing environmental conditions, such as temperature, must be minimised.
Mission control for LISA Pathfinder was atESOC inDarmstadt, Germany with science and technology operations controlled fromESAC inMadrid, Spain.[21]
The spacecraft was first launched byVega flight VV06 into an ellipticalLEO parking orbit. From there it executed a short burn each timeperigee was passed, slowly raising theapogee closer to the intendedhalo orbit around the Earth–SunL1 point.[1][22][23]
The spacecraft reached its operational location in orbit around theLagrange point L1 on 22 January 2016, where it underwent payload commissioning.[24] The testing started on 1 March 2016.[25] In April 2016 ESA announced that LISA Pathfinder demonstrated that the LISA mission is feasible.[26]
On 7 June 2016, ESA presented the first results of two months' worth of science operation showing that the technology developed for a space-based gravitational wave observatory was exceeding expectations. The two cubes at the heart of the spacecraft are falling freely through space under the influence of gravity alone, unperturbed by other external forces, to a factor of 5 better than requirements for LISA Pathfinder.[27][28][29] In February 2017, BBC News reported that the gravity probe had exceeded its performance goals.[30]
LISA Pathfinder was deactivated on 30 June 2017.[31]
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