LISA Pathfinder

LISA Pathfinder

LISA Pathfinder spacecraft

Artist's impression of the LISA Pathfinder spacecraft
Mission type Technology
Operator ESA[1]
Website sci.esa.int/lisa-pathfinder/
Mission duration Nominal: 1 year[1] (with sufficient Cold Gas for mission extension)
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 September 2015[3]
Rocket Vega
Launch site Kourou ELV
Contractor Arianespace
Orbital parameters
Reference system Sun–Earth L1
Regime Lissajous orbit
Periapsis 500,000 km (310,000 mi)
Apoapsis 800,000 km (500,000 mi)
Inclination 60 degrees
Epoch Planned
Transponders
Band X band
Bandwidth 7 kbit/s
Instruments
~36.7 cm Laser interferometer and Disturbance Reduction System
LISA Pathfinder logo

LISA Pathfinder, formerly Small Missions for Advanced Research in Technology-2 (SMART-2), is an ESA space probe to be launched in September 2015.[2] The mission will test technologies needed for the Laser Interferometer Space Antenna (LISA), an ESA gravitational wave observatory. Additionally, LISA Pathfinder will probe Einstein's geodesic motion at an unprecedented level.

The estimated mission cost is €400 million.[4]

Mission

LISA Pathfinder will place two test masses in a nearly perfect gravitational free-fall, and will control and measure their relative motion with unprecedented accuracy. The test masses and their environment will be the quietest place in the Solar System.

International collaboration

LISA Pathfinder is an ESA led mission. It involves European space companies and research institutes from France, Germany, Italy, The Netherlands, Spain, Switzerland and UK and the US space agency NASA.[5]

LISA Pathfinder science

The primary science objective of LISA Pathfinder is to measure deviations from geodesic motion. Much of the experimentation in gravitational physics requires measuring the relative acceleration between free-falling, geodesic reference test particles. For LISA, the test masses will be 2 kg cubes housed in separate spacecraft millions of km apart. In LISA Pathfinder, precise inter-test-mass tracking, by optical interferometry, will allow scientists to assess the relative acceleration of the two LISA test masses, situated about 38 cm apart in a single spacecraft. The science of LISA Pathfinder consists 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 the eLISA follow up mission.[6]

LISA Pathfinder will contain one arm of LISA, shortened from 5 million km to about 38 cm. In particular, it will verify:

Spacecraft design

LISA Pathfinder is being built by Airbus Defence and Space 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 an electric propulsion system[7] 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. [8]

Instrumentation

The LISA Technology Package (LTP) is being integrated by Airbus Defence and Space Germany, but the instruments and components are being supplied 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.

Environmental influences

On the upcoming LISA mission, environmental factors will influence the measurements the interferometer takes. These environmental influences include stray electromagnetic fields and temperature gradients, which could be caused by the Sun heating the spacecraft unevenly, or even by warm instrumentation inside the spacecraft itself. Therefore, LISA Pathfinder is designed to find out how such environmental influences change the behaviour of the inertial sensors and the other instruments. LISA Pathfinder will fly with an extensive instrument package which can measure temperature and magnetic fields at the test masses and at the optical bench. The spacecraft is even equipped to stimulate the system artificially: it carries heating elements which can warm the spacecraft's structure unevenly, causing the optical bench to distort and enabling scientists to see how the measurements change with varying temperatures.[9]

Orbit

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.[1][10] The results and technology of the LISA Pathfinder mission will provide the basis for a space-borne gravitational-wave observatory which will be launched in 2034 as the third L-class mission in ESA's Cosmic Vision programme addressing the science theme of "The Gravitational Universe".[11]

Spacecraft operations

Mission control for LISA Pathfinder will be at ESOC in Darmstadt, Germany with science and technology operations controlled from ESAC in Madrid, Spain.[12]

Possible mission extension

A possible mission extension would perform some measurements to confirm the general relativity theory. 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.[13]

References

  1. ↑ 1.0 1.1 1.2 1.3 "LISA Pathfinder: Operations". ESA. 8 January 2010. Retrieved 5 February 2011.
  2. ↑ 2.0 2.1 "LPF (LISA Pathfinder) Mission". ESA eoPortal. Retrieved 2014-03-28.
  3. ↑ Amos, Jonathan (28 February 2015). "Lisa Pathfinder: 'Exquisite' gravity probe leaves UK". BBC News. Retrieved 2015-02-28.
  4. ↑ "LISA Pathfinder To Proceed Despite 100% Cost Growth". Space News. 22 June 2011.
  5. ↑ "LISA Pathfinder international partners". eLISAscience.org. Retrieved 9 July 2014.
  6. ↑ "LISA Pathfinder Science". eLISAscience.org. Retrieved 9 July 2014.
  7. ↑ Ziemer, J.K.; and Merkowitz, S.M.: “Microthrust Propulsion of the LISA Mission,” AIAA–2004–3439, 40th AIAA/ASME/SAE/ASEE Joint Propulsion Conference, Fort Lauderdale FL, July 11–14, 2004.
  8. ↑ Rovey, J. "Propulsion and Energy: Electric Propulsion (Year in Review, 2009)" (PDF). Aerospace America, December 2009, p. 44.
  9. ↑ "LISA Pathfinder Technology". eLISAscience.org. Retrieved 9 July 2014.
  10. ↑ "LISA Pathfinder: Mission home". ESA. Retrieved 5 February 2011.
  11. ↑ "ESA's new vision to study the invisible universe". www.esa.int. Retrieved 26 June 2014.
  12. ↑ "LISA Pathfinder: Fact sheet". ESA. Retrieved 20 April 2009.
  13. ↑ New Scientist 2 March 2013 page 44

External links