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{{Short description|2015 European Space Agency spacecraft}}
{{Infobox spaceflight
{{Infobox spaceflight
| name = LISA Pathfinder
| name = LISA Pathfinder
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| mission_type = Technology demonstrator
| mission_type = Technology demonstrator
| operator = [[European Space Agency|ESA]]<ref name=ESA2>{{Cite web | title = LISA Pathfinder: Operations | publisher = [[European Space Agency|ESA]] | url = http://www.esa.int/SPECIALS/Operations/SEMR4E7DWZE_0.html | date=8 January 2010 |accessdate = 5 February 2011}}</ref>
| operator = [[European Space Agency|ESA]]<ref name=ESA2>{{Cite web | title = LISA Pathfinder: Operations | publisher = [[European Space Agency|ESA]] | url = http://www.esa.int/SPECIALS/Operations/SEMR4E7DWZE_0.html | date=8 January 2010 |access-date = 5 February 2011}}</ref>
| website =
| website =
| COSPAR_ID =
| COSPAR_ID =
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| manufacturer = [[Airbus Defence and Space]]
| manufacturer = [[Airbus Defence and Space]]
| dry_mass = {{convert|810|kg|lb|abbr=on}}
| dry_mass = {{convert|810|kg|lb|abbr=on}}
| BOL_mass = {{convert|480|kg|lb|abbr=on}}<ref name="eoPortal">{{cite web |url=http://directory.eoportal.org/web/eoportal/satellite-missions/l/lisa-pathfinder |title=LPF (LISA Pathfinder) Mission |publisher=[[ESA]] eoPortal |accessdate=2014-03-28}}</ref>
| BOL_mass = {{convert|480|kg|lb|abbr=on}}<ref name="eoPortal">{{cite web |url=http://directory.eoportal.org/web/eoportal/satellite-missions/l/lisa-pathfinder |title=LPF (LISA Pathfinder) Mission |publisher=[[ESA]] eoPortal |access-date=2014-03-28 |archive-date=2015-10-17 |archive-url=https://web.archive.org/web/20151017030659/https://directory.eoportal.org/web/eoportal/satellite-missions/l/lisa-pathfinder |url-status=dead }}</ref>
| launch_mass = {{convert|1910|kg|lb|abbr=on}}<ref name="ESA2" />
| launch_mass = {{convert|1910|kg|lb|abbr=on}}<ref name="ESA2" />
| payload_mass = {{convert|125|kg|lb|abbr=on}}
| payload_mass = {{convert|125|kg|lb|abbr=on}}
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| power = <!--end-of-life power, in watts-->
| power = <!--end-of-life power, in watts-->
<!--Launch details-->
<!--Launch details-->
| launch_date = 3 December 2015, 04:04:00 UTC<ref name="completed">{{cite web|url=http://spaceflightnow.com/launch-schedule/ |title=Launch Schedule |publisher=SpaceFlight Now |accessdate=2015-10-16 |deadurl=yes |archiveurl=https://web.archive.org/web/20161224185459/http://spaceflightnow.com/launch-schedule/ |archivedate=2016-12-24 |df= }}</ref><ref name="esapr" /><ref name=ESAlaunch>{{cite web|url=http://www.esa.int/Our_Activities/Space_Science/LISA_Pathfinder_en_route_to_gravitational_wave_demonstration|title=LISA Pathfinder enroute to gravitational wave demonstration|publisher=[[European Space Agency]]|accessdate=3 December 2015}}</ref>
| launch_date = 3 December 2015, 04:04:00 UTC<ref name="completed">{{cite web|url=http://spaceflightnow.com/launch-schedule/ |title=Launch Schedule |publisher=SpaceFlight Now |access-date=2015-10-16 |url-status=dead |archive-url=https://web.archive.org/web/20161224185459/http://spaceflightnow.com/launch-schedule/ |archive-date=2016-12-24 }}</ref><ref name="esapr" /><ref name=ESAlaunch>{{cite web|url=http://www.esa.int/Our_Activities/Space_Science/LISA_Pathfinder_en_route_to_gravitational_wave_demonstration|title=LISA Pathfinder enroute to gravitational wave demonstration|publisher=[[European Space Agency]]|access-date=3 December 2015}}</ref>
| launch_rocket = [[Vega (rocket)|Vega]]
| launch_rocket = [[Vega (rocket)|Vega]] ([[Vega flight VV06|VV06]])
| launch_site = [[Guiana Space Centre|Kourou]] [[ELA-1|ELV]]
| launch_site = [[Guiana Space Centre|Kourou]] [[ELA-1|ELV]]
| launch_contractor = [[Arianespace]]
| launch_contractor = [[Arianespace]]
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| insignia_size = 180x180px
| insignia_size = 180x180px


| programme = '''[[List of European Space Agency programs and missions#Horizon 2000+|Horizon 2000+]]'''
| programme = '''[[European Space Agency Science Programme#Horizon 2000 Plus|Horizon 2000 Plus]]'''
| previous_mission = ''[[Gaia (spacecraft)|Gaia]]''
| previous_mission = ''[[Gaia (spacecraft)|Gaia]]''
| next_mission = ''[[BepiColombo]]''
| next_mission = ''[[BepiColombo]]''
}}
}}
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'''LISA Pathfinder''', formerly '''Small Missions for Advanced Research in Technology-2''' ('''SMART-2'''), was an [[ESA]] spacecraft that was launched on 3 December 2015.<ref name="completed" /><ref name="esapr">{{cite web | url=http://sci.esa.int/lisa-pathfinder/56897-call-for-media-lisa-pathfinder-launch/ | title=Call for Media: LISA Pathfinder launch | publisher=ESA | date=23 November 2015}}</ref><ref name="ESAlaunch" /> The mission tested technologies needed for the [[Evolved Laser Interferometer Space Antenna]] (eLISA), an ESA [[gravitational wave]] observatory planned to be launched in 2034. The scientific phase started on 8 March 2016 and lasted almost sixteen months.<ref>{{cite web|url=https://www.elisascience.org/news/top-news/lpfscienceoperationsbegin|title=News: Top News - LISA Gravitational Wave Observatory|publisher=}}</ref> In April 2016 ESA announced that LISA Pathfinder demonstrated that eLISA mission is feasible.


⚫
'''LISA Pathfinder''', formerly '''Small Missions for Advanced Research in Technology-2''' ('''SMART-2'''), was an [[ESA]] spacecraft that was launched on 3 December 2015 on board [[Vega flight VV06]].<ref name="completed" /><ref name="esapr">{{cite web | url=http://sci.esa.int/lisa-pathfinder/56897-call-for-media-lisa-pathfinder-launch/ | title=Call for Media: LISA Pathfinder launch | publisher=ESA | date=23 November 2015}}</ref><ref name="ESAlaunch" /> The mission tested technologies needed for the [[Laser Interferometer Space Antenna]] (LISA), an ESA [[gravitational wave]] observatory planned to be launched in 2035. The scientific phase started on 8 March 2016 and lasted almost sixteen months.<ref>{{cite web|url=https://www.elisascience.org/news/top-news/lpfscienceoperationsbegin|title=News: Top News - LISA Gravitational Wave Observatory|url-status=dead|archive-url=https://web.archive.org/web/20160419224526/https://www.elisascience.org/news/top-news/lpfscienceoperationsbegin|archive-date=2016-04-19}}</ref> In April 2016 ESA announced that LISA Pathfinder demonstrated that the LISA mission is feasible.
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The estimated mission cost is €400 million.<ref name=SpaceNews>{{Cite web | title = LISA Pathfinder To Proceed Despite 100% Cost Growth | work=Space News | url = http://www.spacenews.com/article/lisa-pathfinder-proceed-despite-100-cost-growth | date =22 June 2011}}</ref>

⚫
The estimated mission cost was €400 million.<ref name=SpaceNews>{{Cite web | title = LISA Pathfinder To Proceed Despite 100% Cost Growth | work=Space News | url = http://www.spacenews.com/article/lisa-pathfinder-proceed-despite-100-cost-growth | date =22 June 2011}}</ref>


==Mission==
==Mission==
LISA Pathfinder placed two test masses in a nearly perfect gravitational free-fall, and controlled and measured their relative motion with unprecedented accuracy. The [[Interferometry|laser interferometer]] measured the relative position and orientation of the masses to an accuracy of less than 0.01&nbsp;nanometres,<ref>{{cite press release |url=http://spaceref.com/news/viewpr.html?pid=47419 |title=LISA Pathfinder Ready for Launch from Kourou |via=SpaceRef |publisher=Airbus Defence and Space |date=November 30, 2015}}</ref> a technology estimated to be sensitive enough to detect gravitational waves by the follow-on mission, the [[Laser Interferometer Space Antenna]] (LISA).
LISA Pathfinder placed two test masses in a nearly perfect gravitational free-fall, and controlled and measured their relative motion with unprecedented accuracy. The [[Interferometry|laser interferometer]] measured the relative position and orientation of the masses to an accuracy of less than 0.01&nbsp;nanometres,<ref>{{cite press release |url=http://spaceref.com/news/viewpr.html?pid=47419 |title=LISA Pathfinder Ready for Launch from Kourou |via=SpaceRef |publisher=Airbus Defence and Space |date=November 30, 2015 }}{{Dead link|date=September 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> a technology estimated to be sensitive enough to detect gravitational waves by the follow-on mission, the [[Laser Interferometer Space Antenna]] (LISA).


The interferometer was a model of one arm of the final LISA interferometer, but reduced from millions of kilometers long to 40&nbsp;cm. The reduction did not change the accuracy of the relative position measurement, nor did it affect the various technical disturbances produced by the spacecraft surrounding the experiment, whose measurement was the main goal of LISA Pathfinder. The sensitivity to gravitational waves, however, is proportional to the arm length, and this is reduced several billion-fold compared to the planned LISA experiment.
The interferometer was a model of one arm of the final LISA interferometer, but reduced from millions of kilometers long to 40&nbsp;cm. The reduction did not change the accuracy of the relative position measurement, nor did it affect the various technical disturbances produced by the spacecraft surrounding the experiment, whose measurement was the main goal of LISA Pathfinder. The sensitivity to gravitational waves, however, is proportional to the arm length, and this is reduced several billion-fold compared to the planned LISA experiment.


LISA Pathfinder was an ESA-led mission. It involved European space companies and research institutes from France, Germany, Italy, The Netherlands, Spain, Switzerland, UK, and the US space agency NASA.<ref name=LPFpartners>{{Cite web | title = LISA Pathfinder international partners | work=eLISAscience.org | url = https://www.elisascience.org/articles/lisa-pathfinder/lpf-partners | accessdate =7 September 2015}}</ref>
LISA Pathfinder was an ESA-led mission. It involved European space companies and research institutes from France, Germany, Italy, The Netherlands, Spain, Switzerland, UK, and the US space agency NASA.<ref name=LPFpartners>{{Cite web | title = LISA Pathfinder international partners | work = eLISAscience.org | url = https://www.elisascience.org/articles/lisa-pathfinder/lpf-partners | access-date = 7 September 2015 | archive-url = https://web.archive.org/web/20150926180758/https://www.elisascience.org/articles/lisa-pathfinder/lpf-partners | archive-date = 26 September 2015 | url-status = dead }}</ref>


==LISA Pathfinder science==
==LISA Pathfinder science==
LISA Pathfinder was a proof-of-concept mission to prove that the two masses can fly through space, untouched but shielded by the spacecraft, and maintain their relative positions to the precision needed to realise a full gravitational wave observatory planned for launch in 2034. The primary objective was to measure deviations from [[Geodesics in general relativity|geodesic motion]]. Much of the experimentation in [[gravitational physics]] requires measuring the relative acceleration between free-falling, geodesic reference test particles.<ref>[https://www.elisascience.org/articles/lisa-pathfinder/lpf-science science objective of LISA Pathfinder].</ref>
LISA Pathfinder was a proof-of-concept mission to prove that the two masses can fly through space, untouched but shielded by the spacecraft, and maintain their relative positions to the precision needed to realise a full gravitational wave observatory planned for launch in 2035. The primary objective was to measure deviations from [[Geodesics in general relativity|geodesic motion]]. Much of the experimentation in [[gravitational physics]] requires measuring the relative acceleration between free-falling, geodesic reference test particles.<ref>[https://www.elisascience.org/articles/lisa-pathfinder/lpf-science science objective of LISA Pathfinder] {{Webarchive|url=https://web.archive.org/web/20141021163912/https://www.elisascience.org/articles/lisa-pathfinder/lpf-science |date=2014-10-21 }}.</ref>


In LISA Pathfinder, precise inter-test-mass tracking by optical [[interferometry]] allowed scientists to assess the relative acceleration of the two test masses, situated about 38&nbsp;cm apart in a single spacecraft. 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 the [[Evolved Laser Interferometer Space Antenna|eLISA]] follow up mission.<ref name=LPFscience>{{Cite web | title = LISA Pathfinder Science | work=eLISAscience.org | url = https://www.elisascience.org/articles/lisa-pathfinder/lpf-science | accessdate =9 July 2014}}</ref>
In LISA Pathfinder, precise inter-test-mass tracking by optical [[interferometry]] allowed scientists to assess the relative acceleration of the two test masses, situated about 38&nbsp;cm apart in a single spacecraft. 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 the [[Laser Interferometer Space Antenna|LISA]] follow-up mission.<ref name=LPFscience>{{Cite web | title = LISA Pathfinder Science | work = eLISAscience.org | url = https://www.elisascience.org/articles/lisa-pathfinder/lpf-science | access-date = 9 July 2014 | archive-url = https://web.archive.org/web/20141021163912/https://www.elisascience.org/articles/lisa-pathfinder/lpf-science | archive-date = 21 October 2014 | url-status = dead }}</ref>


In particular, it verified:
In particular, it verified:
* Drag-free [[attitude control]] of a spacecraft with two proof masses,
* Drag-free [[Spacecraft attitude control|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 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.
* The reliability and longevity of the various components—capacitive sensors, microthrusters, lasers and optics.


For the follow-up mission, [[Evolved Laser Interferometer Space Antenna|eLISA]],<ref>{{cite web|url=https://www.elisascience.org/|title=LISA Gravitational Wave Observatory - We will observe gravitational waves in space - New Astronomy - LISA Pathfinder|publisher=}}</ref> the test masses will be 2&nbsp;kg cubes housed in two separate spacecraft one million kilometers apart.
For the follow-up mission, [[Laser Interferometer Space Antenna|LISA]],<ref>{{cite web|url=https://www.elisascience.org/|title=LISA Gravitational Wave Observatory - We will observe gravitational waves in space - New Astronomy - LISA Pathfinder}}</ref> the test masses will be pairs of 2&nbsp;kg gold/platinum cubes housed in each of three separate spacecraft 2.5 million kilometers apart.<ref>Official design proposal at https://www.elisascience.org/files/publications/LISA_L3_20170120.pdf</ref>


==Spacecraft design==
==Spacecraft design==
LISA Pathfinder was built by [[Airbus 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 on [[Gaia (spacecraft)|Gaia]]), and a US-built 'Disturbance Reduction System' using the European sensors and an [[electric propulsion]] system that uses ionised droplets of a colloid accelerated in an [[electric field]].<ref>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.</ref> The [[colloid thruster]] (or "[[electrospray]] thruster") system was built by [[Busek]] and delivered to [[JPL]] for integration with the spacecraft.<ref>{{cite web |last=Rovey, J.| title= Propulsion and Energy: Electric Propulsion (Year in Review, 2009) |url=http://www.aerospaceamerica.org/Documents/Aerospace%20America%20PDFs%20(2009)/Aerospace%20America_DEC2009.pdf |publisher=Aerospace America, December 2009, p. 44}}</ref>
LISA Pathfinder was assembled by [[Airbus 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 on [[Gaia (spacecraft)|Gaia]]), and a US-built "Disturbance Reduction System" using the European sensors and an [[electric propulsion]] system that uses ionised droplets of a colloid accelerated in an [[electric field]].<ref>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.</ref> The [[colloid thruster]] (or "[[electrospray]] thruster") system was built by [[Busek]] and delivered to [[JPL]] for integration with the spacecraft.<ref>{{cite web|last=Rovey, J.|title=Propulsion and Energy: Electric Propulsion (Year in Review, 2009)|url=http://www.aerospaceamerica.org/Documents/Aerospace%20America%20PDFs%20(2009)/Aerospace%20America_DEC2009.pdf|publisher=Aerospace America, December 2009, p. 44|access-date=2012-10-26|archive-url=https://web.archive.org/web/20151208101354/http://www.aerospaceamerica.org/Documents/Aerospace%20America%20PDFs%20(2009)/Aerospace%20America_DEC2009.pdf|archive-date=2015-12-08|url-status=dead}}</ref>

[[File:LISA Pathfinder exploded view.jpg|thumb|LISA Pathfinder exploded view]]


===Instrumentation===
===Instrumentation===
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.
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.


===Environmental influences===
===Environmental influences===
On the follow-up mission, eLISA, 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 was designed to find out how such environmental influences change the behaviour of the inertial sensors and the other instruments. LISA Pathfinder flew with an extensive instrument package which can measure temperature and magnetic fields at the test masses and at the optical bench. The spacecraft was even equipped to stimulate the system artificially: it carried 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.<ref name=LPFtechnology>{{Cite web | title = LISA Pathfinder Technology| work=eLISAscience.org | url = https://www.elisascience.org/articles/lisa-pathfinder/lpf-technology| accessdate =9 July 2014}}</ref>
On the follow-up mission, eLISA, 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 was designed to find out how such environmental influences change the behaviour of the inertial sensors and the other instruments. LISA Pathfinder flew with an extensive instrument package which can measure temperature and magnetic fields at the test masses and at the optical bench. The spacecraft was even equipped to stimulate the system artificially: it carried 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.<ref name=LPFtechnology>{{Cite web| title = LISA Pathfinder Technology| work = eLISAscience.org| url = https://www.elisascience.org/articles/lisa-pathfinder/lpf-technology| access-date = 9 July 2014| archive-url = https://web.archive.org/web/20141021204854/https://www.elisascience.org/articles/lisa-pathfinder/lpf-technology| archive-date = 21 October 2014| url-status = dead}}</ref>

== Lissajous orbit ==
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The spacecraft was first launched into an elliptical [[Low Earth Orbit|LEO]] parking orbit. From there it executed a short burn each time [[perigee]] was passed, slowly raising the [[apogee]] closer to the intended [[halo orbit]] around the Earth–Sun {{L1}} point.<ref name=ESA2/><ref name=ESA1>{{Cite web | title = LISA Pathfinder: Mission home | publisher = [[European Space Agency|ESA]] | url = http://sci.esa.int/science-e/www/area/index.cfm?fareaid=40 | accessdate = 5 February 2011}}</ref><ref>{{cite web| title=ESA's new vision to study the invisible universe| url=http://www.esa.int/Our_Activities/Space_Science/ESA_s_new_vision_to_study_the_invisible_Universe |website=www.esa.int| accessdate=26 June 2014}}</ref>


==Spacecraft operations==
==Spacecraft operations==
Mission control for LISA Pathfinder was at [[European Space Operations Centre|ESOC]] in [[Darmstadt, Germany]] with science and technology operations controlled from [[European Space Astronomy Centre|ESAC]] in [[Madrid|Madrid, Spain]].<ref name=ESA3>{{Cite web | title = LISA Pathfinder: Fact sheet | publisher = [[European Space Agency|ESA]] | url = http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31714 | accessdate = 20 April 2009}}</ref>
Mission control for LISA Pathfinder was at [[European Space Operations Centre|ESOC]] in [[Darmstadt, Germany]] with science and technology operations controlled from [[European Space Astronomy Centre|ESAC]] in [[Madrid|Madrid, Spain]].<ref name=ESA3>{{Cite web | title = LISA Pathfinder: Fact sheet | publisher = [[European Space Agency|ESA]] | url = http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31714 | access-date = 20 April 2009}}</ref>


===Status===
=== Lissajous orbit ===
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The spacecraft reached its operational location in orbit around the [[Lagrange point]] L1 on 22 January 2016, where it underwent payload commissioning.<ref name="commissioning">{{cite news |url=http://sci.esa.int/jump.cfm?oid=57290 |title=First locks released from LISA Pathfinder's cubes |work=ESA |publisher=ESA Press Release |date=February 3, 2016 |accessdate=2016-02-12 }}</ref> The testing started on 1 March 2016.<ref>{{cite news |last=Amos |first=Jonathan |url=http://www.bbc.com/news/science-environment-35689814 |title=Gravitational waves: Tests begin for future space observatory |work=BBC News |date=1 March 2016 |accessdate=2016-03-01 }}</ref> In April 2016 ESA announced that LISA Pathfinder demonstrated that eLISA mission is feasible.<ref name="Final report">{{cite conference |title=The ESA–L3 Gravitational Wave Mission - Final Report |url=http://www.cosmos.esa.int/documents/427239/653121/goat-final-submitted1.pdf/10eaf634-e7df-4db2-921b-43d930993101 |format=PDF |conference=ESA–L3 Final Report |editor-last=Gravitational Observatory Advisory Team |date=28 March 2016 |page=4 }}</ref>


⚫
The spacecraft was first launched by [[Vega flight VV06]] into an elliptical [[Low Earth Orbit|LEO]] parking orbit. From there it executed a short burn each time [[perigee]] was passed, slowly raising the [[apogee]] closer to the intended [[halo orbit]] around the Earth–Sun {{L1}} point.<ref name=ESA2/><ref name=ESA1>{{Cite web | title = LISA Pathfinder: Mission home | publisher = [[European Space Agency|ESA]] | url = http://sci.esa.int/science-e/www/area/index.cfm?fareaid=40 | access-date = 5 February 2011}}</ref><ref>{{cite web| title=ESA's new vision to study the invisible universe| url=http://www.esa.int/Our_Activities/Space_Science/ESA_s_new_vision_to_study_the_invisible_Universe |website=www.esa.int| access-date=26 June 2014}}</ref>
⚫
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.<ref>{{cite journal |title=Sub-Femto-g Free Fall for Space-Based Gravitational Wave Observatories: LISA Pathfinder Results| author=M. Armano| journal=[[Physical Review Letters]]|year=2016|volume=116| issue=23|url=http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.231101| doi=10.1103/PhysRevLett.116.231101|display-authors=etal| bibcode=2016PhRvL.116w1101A| pmid=27341221| page=231101}}</ref><ref>{{cite web| title=LISA Pathfinder exceeds expectations| publisher=ESA| url=http://www.esa.int/Our_Activities/Space_Science/LISA_Pathfinder_exceeds_expectations| date=7 June 2016| accessdate=7 June 2016}}</ref><ref>{{cite web| title=LISA Pathfinder exceeds expectations |publisher=elisascience.org| work=Benjamin Knispel| url=https://www.elisascience.org/news/top-news/lisa-pathfinder-exceeds-expectations| date=7 June 2016| accessdate=7 June 2016}}</ref> In February 2017, BBC News reported that the gravity probe had exceeded its performance goals.<ref>{{cite web| title=Gravity probe exceeds performance goals |work=Jonathan Amos, BBC Science Correspondent, Boston | url=http://www.bbc.com/news/science-environment-38897697?SThisFB| date=18 February 2017| accessdate=20 February 2017}}</ref>

{{multiple image | align =center| direction = horizontal| width =
| header = Animation of LISA Pathfinder {{'s}} trajectory
| image1 = Animation of LISA Pathfinder trajectory - Polar view.gif
| caption1 = Polar view
| image2 = Animation of LISA Pathfinder trajectory - Equatorial view.gif
| caption2 = Equatorial view
| image3 = Animation of LISA Pathfinder trajectory viewed from the Sun.gif
| caption3 = Viewed from the Sun
| footer ={{legend2| RoyalBlue| Earth}}{{·}}{{legend2|Magenta|LISA Pathfinder}}
}}

=== Chronology and results ===
[[File:LISA Pathfinder final results.png|thumb|right|300px|The final results (red line) far exceeded from the initial requirements.]]
⚫
The spacecraft reached its operational location in orbit around the [[Lagrange point]] L1 on 22 January 2016, where it underwent payload commissioning.<ref name="commissioning">{{cite news |url=http://sci.esa.int/jump.cfm?oid=57290 |title=First locks released from LISA Pathfinder's cubes |work=ESA |publisher=ESA Press Release |date=February 3, 2016 |access-date=2016-02-12 }}</ref> The testing started on 1 March 2016.<ref>{{cite news |last=Amos |first=Jonathan |url=https://www.bbc.com/news/science-environment-35689814 |title=Gravitational waves: Tests begin for future space observatory |work=BBC News |date=1 March 2016 |access-date=2016-03-01 }}</ref> In April 2016 ESA announced that LISA Pathfinder demonstrated that the LISA mission is feasible.<ref name="Final report">{{cite conference |title=The ESA–L3 Gravitational Wave Mission - Final Report |url=http://www.cosmos.esa.int/documents/427239/653121/goat-final-submitted1.pdf/10eaf634-e7df-4db2-921b-43d930993101 |format=PDF |conference=ESA–L3 Final Report |editor-last=Gravitational Observatory Advisory Team |date=28 March 2016 |page=4 }}</ref>

⚫
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.<ref>{{cite journal |title=Sub-Femto-g Free Fall for Space-Based Gravitational Wave Observatories: LISA Pathfinder Results| author=M. Armano| journal=[[Physical Review Letters]]|year=2016|volume=116| issue=23| doi=10.1103/PhysRevLett.116.231101|display-authors=etal| bibcode=2016PhRvL.116w1101A| pmid=27341221| page=231101| doi-access=free| hdl=2117/102419| hdl-access=free}}</ref><ref>{{cite web| title=LISA Pathfinder exceeds expectations| publisher=ESA| url=http://www.esa.int/Our_Activities/Space_Science/LISA_Pathfinder_exceeds_expectations| date=7 June 2016| access-date=7 June 2016}}</ref><ref>{{cite web| title=LISA Pathfinder exceeds expectations| publisher=elisascience.org| work=Benjamin Knispel| url=https://www.elisascience.org/news/top-news/lisa-pathfinder-exceeds-expectations| date=7 June 2016| access-date=7 June 2016| url-status=dead| archive-url=https://web.archive.org/web/20160803124722/https://www.elisascience.org/news/top-news/lisa-pathfinder-exceeds-expectations| archive-date=3 August 2016}}</ref> In February 2017, BBC News reported that the gravity probe had exceeded its performance goals.<ref>{{cite web| title=Gravity probe exceeds performance goals |work=Jonathan Amos, BBC Science Correspondent, Boston | url=https://www.bbc.com/news/science-environment-38897697?SThisFB| date=18 February 2017| access-date=20 February 2017}}</ref>


LISA Pathfinder was deactivated on 30 June 2017.<ref>{{cite web
LISA Pathfinder was deactivated on 30 June 2017.<ref>{{cite web
| url =http://sci.esa.int/lisa-pathfinder/59238-lisa-pathfinder-to-conclude-trailblazing-mission/
| url =http://sci.esa.int/lisa-pathfinder/59238-lisa-pathfinder-to-conclude-trailblazing-mission/
| title =LISA Pathfinder Will Concludee Trailblazing Mission
| title =LISA Pathfinder Will Concludee Trailblazing Mission
| last =
| first =
| date =20 June 2017
| date =20 June 2017
| website =ESA Science and Technology
| website =ESA Science and Technology
| publisher =ESA
| publisher =ESA
| access-date =17 August 2017
| access-date =17 August 2017
| quote = }}</ref>
}}</ref>

On 5 February 2018, ESA published the final results. Precision of measurements could be improved further, beyond current goals for the future LISA mission, due to venting of residue air molecules and better understanding of disturbances.<ref>{{cite web |url=http://www.esa.int/Our_Activities/Space_Science/ESA_creates_quietest_place_in_space |language=en |title=ESA creates quietest place in space |date=2018-02-05 |access-date=2018-02-07}}</ref>


==See also==
==See also==
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* [[GEO600]], a gravitational wave detector located in Hannover, Germany
* [[GEO600]], a gravitational wave detector located in Hannover, Germany
* [[LIGO]], a gravitational wave observatory in USA
* [[LIGO]], a gravitational wave observatory in USA
* [[Taiji Program in Space|Taiji]] 1, a Chinese technology demonstrator for gravitational wave observation launched in 2019
* [[Virgo interferometer]], an interferometer located close to Pisa, Italy
* [[Virgo interferometer]], an interferometer located close to Pisa, Italy


Line 121: Line 139:
==External links==
==External links==
{{commons category|LISA Pathfinder}}
{{commons category|LISA Pathfinder}}
* [https://www.elisascience.org/ eLISA and LISA Pathfinder's Homepage]
* [https://www.elisascience.org/ LISA and LISA Pathfinder's Homepage]
* [http://sci.esa.int/lisa-pathfinder/ LISA Pathfinder mission home at ESA]
* [http://sci.esa.int/lisa-pathfinder/ LISA Pathfinder mission home at ESA]
* [http://directory.eoportal.org/web/eoportal/satellite-missions/l/lisa-pathfinder LISA Pathfinder at eoPortal]
* [http://directory.eoportal.org/web/eoportal/satellite-missions/l/lisa-pathfinder LISA Pathfinder at eoPortal] {{Webarchive|url=https://web.archive.org/web/20151017030659/https://directory.eoportal.org/web/eoportal/satellite-missions/l/lisa-pathfinder |date=2015-10-17 }}
* [http://www.aei.mpg.de/14026/AEI_Hannover Max Planck Institute for Gravitational Physics (Albert Einstein Institute Hannover)]
* [http://www.aei.mpg.de/14026/AEI_Hannover Max Planck Institute for Gravitational Physics (Albert Einstein Institute Hannover)] {{Webarchive|url=https://web.archive.org/web/20160517102903/http://www.aei.mpg.de/14026/AEI_Hannover |date=2016-05-17 }}


{{ESA projects}}
{{ESA projects}}
{{Space observatories}}
{{Space observatories}}
⚫
{{Gravitational waves}}
{{Solar System probes}}
{{Orbital launches in 2015}}
{{Orbital launches in 2015}}
{{2015 in space}}
{{2015 in space}}
⚫
{{Gravitational waves}}


{{DEFAULTSORT:Lisa Pathfinder}}
{{DEFAULTSORT:Lisa Pathfinder}}
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[[Category:Spacecraft using halo orbits]]
[[Category:Spacecraft using halo orbits]]
[[Category:Spacecraft launched by Vega rockets]]
[[Category:Spacecraft launched by Vega rockets]]
[[Category:Interferometers]]
[[Category:Space telescopes]]
[[Category:Gravitational-wave telescopes]]
[[Category:Technology demonstrations]]
[[Category:Artificial satellites at Earth-Sun Lagrange points]]

Revision as of 17:04, 25 April 2024

LISA Pathfinder
LISA Pathfinder spacecraft
Model of the LISA Pathfinder spacecraft
Mission typeTechnology demonstrator
OperatorESA[1]
COSPAR ID2015-070A Edit this at Wikidata
SATCAT no.41043Edit this on Wikidata
Mission duration576 days
Spacecraft properties
ManufacturerAirbus Defence and Space
Launch mass1,910 kg (4,210 lb)[1]
BOL mass480 kg (1,060 lb)[2]
Dry mass810 kg (1,790 lb)
Payload mass125 kg (276 lb)
Dimensions2.9 m × 2.1 m (9.5 ft × 6.9 ft)
Start of mission
Launch date3 December 2015, 04:04:00 UTC[3][4][5]
RocketVega (VV06)
Launch siteKourou ELV
ContractorArianespace
End of mission
DisposalDecommissioned
Deactivated30 June 2017
Orbital parameters
Reference systemSun–Earth L1
RegimeLissajous orbit
Periapsis altitude500,000 km (310,000 mi)
Apoapsis altitude800,000 km (500,000 mi)
Inclination60 degrees
EpochPlanned
Transponders
BandX band
Bandwidth7 kbit/s
Instruments
~36.7 cm Laser interferometer
LISA Pathfinder insignia
ESA astrophysics insignia for LISA Pathfinder
← Gaia
BepiColombo →

LISA Pathfinder, formerly Small Missions for Advanced Research in Technology-2 (SMART-2), was an ESA spacecraft that was launched on 3 December 2015 on board Vega flight VV06.[3][4][5] The mission tested technologies needed for the Laser Interferometer Space Antenna (LISA), an ESA gravitational wave observatory planned to be launched in 2035. The scientific phase started on 8 March 2016 and lasted almost sixteen months.[6] In April 2016 ESA announced that LISA Pathfinder demonstrated that the LISA mission is feasible.

The estimated mission cost was €400 million.[7]

Mission

LISA Pathfinder placed two test masses in a nearly perfect gravitational free-fall, and controlled and measured their relative motion with unprecedented accuracy. The laser interferometer measured the relative position and orientation of the masses to an accuracy of less than 0.01 nanometres,[8] a technology estimated to be sensitive enough to detect gravitational waves by the follow-on mission, the Laser Interferometer Space Antenna (LISA).

The interferometer was a model of one arm of the final LISA interferometer, but reduced from millions of kilometers long to 40 cm. The reduction did not change the accuracy of the relative position measurement, nor did it affect the various technical disturbances produced by the spacecraft surrounding the experiment, whose measurement was the main goal of LISA Pathfinder. The sensitivity to gravitational waves, however, is proportional to the arm length, and this is reduced several billion-fold compared to the planned LISA experiment.

LISA Pathfinder was an ESA-led mission. It involved European space companies and research institutes from France, Germany, Italy, The Netherlands, Spain, Switzerland, UK, and the US space agency NASA.[9]

LISA Pathfinder science

LISA Pathfinder was a proof-of-concept mission to prove that the two masses can fly through space, untouched but shielded by the spacecraft, and maintain their relative positions to the precision needed to realise a full gravitational wave observatory planned for launch in 2035. The primary objective was 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.[10]

In LISA Pathfinder, precise inter-test-mass tracking by optical interferometry allowed scientists to assess the relative acceleration of the two test masses, situated about 38 cm apart in a single spacecraft. 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 the LISA follow-up mission.[11]

In particular, it verified:

  • 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.

For the follow-up mission, LISA,[12] the test masses will be pairs of 2 kg gold/platinum cubes housed in each of three separate spacecraft 2.5 million kilometers apart.[13]

Spacecraft design

LISA Pathfinder was assembled by Airbus 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 on Gaia), and a US-built "Disturbance Reduction System" using the European sensors and an electric propulsion system that uses ionised droplets of a colloid accelerated in an electric field.[14] The colloid thruster (or "electrospray thruster") system was built by Busek and delivered to JPL for integration with the spacecraft.[15]

LISA Pathfinder exploded view

Instrumentation

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.

Environmental influences

On the follow-up mission, eLISA, 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 was designed to find out how such environmental influences change the behaviour of the inertial sensors and the other instruments. LISA Pathfinder flew with an extensive instrument package which can measure temperature and magnetic fields at the test masses and at the optical bench. The spacecraft was even equipped to stimulate the system artificially: it carried 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.[16]

Spacecraft operations

Mission control for LISA Pathfinder was at ESOC in Darmstadt, Germany with science and technology operations controlled from ESAC in Madrid, Spain.[17]

Lissajous orbit

The spacecraft was first launched by Vega flight VV06 into an elliptical LEO parking orbit. From there it executed a short burn each time perigee was passed, slowly raising the apogee closer to the intended halo orbit around the Earth–Sun L1 point.[1][18][19]

Animation of LISA Pathfinder 's trajectory
Polar view
Equatorial view
Viewed from the Sun
   Earth ·   LISA Pathfinder

Chronology and results

The final results (red line) far exceeded from the initial requirements.

The spacecraft reached its operational location in orbit around the Lagrange point L1 on 22 January 2016, where it underwent payload commissioning.[20] The testing started on 1 March 2016.[21] In April 2016 ESA announced that LISA Pathfinder demonstrated that the LISA mission is feasible.[22]

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.[23][24][25] In February 2017, BBC News reported that the gravity probe had exceeded its performance goals.[26]

LISA Pathfinder was deactivated on 30 June 2017.[27]

On 5 February 2018, ESA published the final results. Precision of measurements could be improved further, beyond current goals for the future LISA mission, due to venting of residue air molecules and better understanding of disturbances.[28]

See also

  • Einstein Telescope, a European gravitational wave detector
  • GEO600, a gravitational wave detector located in Hannover, Germany
  • LIGO, a gravitational wave observatory in USA
  • Taiji 1, a Chinese technology demonstrator for gravitational wave observation launched in 2019
  • Virgo interferometer, an interferometer located close to Pisa, Italy

References

  1. ^ a b c "LISA Pathfinder: Operations". ESA. 8 January 2010. Retrieved 5 February 2011.
  2. ^ "LPF (LISA Pathfinder) Mission". ESA eoPortal. Archived from the original on 2015-10-17. Retrieved 2014-03-28.
  3. ^ a b "Launch Schedule". SpaceFlight Now. Archived from the original on 2016-12-24. Retrieved 2015-10-16.
  4. ^ a b "Call for Media: LISA Pathfinder launch". ESA. 23 November 2015.
  5. ^ a b "LISA Pathfinder enroute to gravitational wave demonstration". European Space Agency. Retrieved 3 December 2015.
  6. ^ "News: Top News - LISA Gravitational Wave Observatory". Archived from the original on 2016-04-19.
  7. ^ "LISA Pathfinder To Proceed Despite 100% Cost Growth". Space News. 22 June 2011.
  8. ^ "LISA Pathfinder Ready for Launch from Kourou" (Press release). Airbus Defence and Space. November 30, 2015 – via SpaceRef.[permanent dead link]
  9. ^ "LISA Pathfinder international partners". eLISAscience.org. Archived from the original on 26 September 2015. Retrieved 7 September 2015.
  10. ^ science objective of LISA Pathfinder Archived 2014-10-21 at the Wayback Machine.
  11. ^ "LISA Pathfinder Science". eLISAscience.org. Archived from the original on 21 October 2014. Retrieved 9 July 2014.
  12. ^ "LISA Gravitational Wave Observatory - We will observe gravitational waves in space - New Astronomy - LISA Pathfinder".
  13. ^ Official design proposal at https://www.elisascience.org/files/publications/LISA_L3_20170120.pdf
  14. ^ 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.
  15. ^ Rovey, J. "Propulsion and Energy: Electric Propulsion (Year in Review, 2009)" (PDF). Aerospace America, December 2009, p. 44. Archived from the original (PDF) on 2015-12-08. Retrieved 2012-10-26.
  16. ^ "LISA Pathfinder Technology". eLISAscience.org. Archived from the original on 21 October 2014. Retrieved 9 July 2014.
  17. ^ "LISA Pathfinder: Fact sheet". ESA. Retrieved 20 April 2009.
  18. ^ "LISA Pathfinder: Mission home". ESA. Retrieved 5 February 2011.
  19. ^ "ESA's new vision to study the invisible universe". www.esa.int. Retrieved 26 June 2014.
  20. ^ "First locks released from LISA Pathfinder's cubes". ESA. ESA Press Release. February 3, 2016. Retrieved 2016-02-12.
  21. ^ Amos, Jonathan (1 March 2016). "Gravitational waves: Tests begin for future space observatory". BBC News. Retrieved 2016-03-01.
  22. ^ Gravitational Observatory Advisory Team, ed. (28 March 2016). The ESA–L3 Gravitational Wave Mission - Final Report (PDF). ESA–L3 Final Report. p. 4.
  23. ^ M. Armano; et al. (2016). "Sub-Femto-g Free Fall for Space-Based Gravitational Wave Observatories: LISA Pathfinder Results". Physical Review Letters. 116 (23): 231101. Bibcode:2016PhRvL.116w1101A. doi:10.1103/PhysRevLett.116.231101. hdl:2117/102419. PMID 27341221.
  24. ^ "LISA Pathfinder exceeds expectations". ESA. 7 June 2016. Retrieved 7 June 2016.
  25. ^ "LISA Pathfinder exceeds expectations". Benjamin Knispel. elisascience.org. 7 June 2016. Archived from the original on 3 August 2016. Retrieved 7 June 2016.
  26. ^ "Gravity probe exceeds performance goals". Jonathan Amos, BBC Science Correspondent, Boston. 18 February 2017. Retrieved 20 February 2017.
  27. ^ "LISA Pathfinder Will Concludee Trailblazing Mission". ESA Science and Technology. ESA. 20 June 2017. Retrieved 17 August 2017.
  28. ^ "ESA creates quietest place in space". 2018-02-05. Retrieved 2018-02-07.
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