View source for Gravity Field and Steady-State Ocean Circulation Explorer

{{short description|ESA satellite intended to map in the Earth's gravity field. Part of the  Living Planet Programme}}
{{Redirect| GOCE}}
{{Infobox spaceflight |auto=all
| name                  = Gravity Field and Steady-State Ocean Circulation Explorer
| image                 = GOCE.jpg
| image_caption         = Artist's view of GOCE. Its sleek, aerodynamic design led it to be dubbed the 'Ferrari of space'<ref name="Esa.int">{{cite web |url=http://www.esa.int/Our_Activities/Observing_the_Earth/GOCE/GOCE_completes_its_mission |title=GOCE completes its mission |publisher=European Space Agency |access-date=11 November 2013}}</ref>
| image_size            = 285px

| mission_type          = Gravitational research
| operator              = [[ESA]]
| COSPAR_ID             = 2009-013A
| SATCAT                = 34602
| website               = http://www.esa.int/GOCE
| mission_duration      = Planned: 20 months <br /> Final: {{time interval|17 March 2009 14:21|21 October 2013|show=ymd|sep=,}}

| manufacturer          = [[Thales Alenia Space]]<br />[[EADS Astrium]]
| launch_mass           = {{convert|1077|kg|lb|abbr=on}}
| dry_mass              = {{convert|872|kg|lb|abbr=on}}
| dimensions            = {{convert|5.3|x|2.3|m|ft|abbr=on}}
| power                 = 1,600&nbsp;watts

| launch_date           = {{start-date|17 March 2009, 14:21}}&nbsp;UTC<ref name="goceLaunch">{{cite web |url=http://www.esa.int/Our_Activities/Observing_the_Earth/GOCE/Entry_23_GOCE_launched_and_in_orbit |title=GOCE launched and in orbit |publisher=European Space Agency |date=17 March 2009 |access-date=10 October 2013}}</ref>
| launch_rocket         = [[Rockot]]/[[Briz-KM]]
| launch_site           = [[Plesetsk Cosmodrome]]
| launch_contractor     = [[Eurockot Launch Services]]
| entered_service       = <!--date on which the spacecraft entered service, if it did not do so immediately after launch-->

| disposal_type         = Orbital decay
| declared              = {{end-date|21 October 2013}}&nbsp;UTC<ref name="esa20131021">{{cite press release |url=http://www.esa.int/For_Media/Press_Releases/ESA_s_GOCE_mission_comes_to_an_end |title=ESA's GOCE mission comes to an end |publisher=European Space Agency |date=21 October 2013 |access-date=10 July 2017 |id=No. 33-2013}}</ref>
| last_contact          = 10 November 2013, 22:42&nbsp;UTC<ref name="esoc.lastpass">{{cite web |url=http://blogs.esa.int/rocketscience/2013/11/11/esoc-update-2350cet/ |title=ESOC update – 23:50CET |publisher=European Space Agency |first=Daniel |last=Scuka |date=11 November 2013 |access-date=28 December 2016}}</ref>
| decay_date            = 11 November 2013, 00:16&nbsp;UTC<ref name="esoc.interface">{{cite web |url=http://blogs.esa.int/rocketscience/2013/11/11/goce-re-entry-region/ |title=GOCE re-entry region |publisher=European Space Agency |first=Daniel |last=Scuka |date=11 November 2013 |access-date=28 December 2016}}</ref>

| orbit_reference       = [[Geocentric orbit|Geocentric]]
| orbit_regime          = [[Sun-synchronous orbit|Sun-synchronous]]<ref name="insights">{{cite web |url=http://www.esa.int/Our_Activities/Observing_the_Earth/GOCE/GOCE_giving_new_insights_into_Earth_s_gravity |title=GOCE giving new insights into Earth's gravity |publisher=European Space Agency |date=29 June 2010 |access-date=29 June 2010}}</ref>
| orbit_semimajor       = 
| orbit_eccentricity    = 
| orbit_periapsis       = {{convert|254.9|km|mi|abbr=on}}<ref name="insights" />
| orbit_apoapsis        = {{convert|254.9|km|mi|abbr=on}}<ref name="insights" />
| orbit_inclination     = 96.7&nbsp;degrees
| orbit_period          = 
| orbit_epoch           = 29 June 2010<ref name="insights" />
| apsis                 = gee

| instruments_list      = {{Infobox spaceflight/Instruments
  | acronym1 = EGG  | name1 = Electrostatic Gravity Gradiometer
  | acronym2 = SSTI | name2 = Satellite-to-Satellite Tracking Instrument
  | acronym3 = LRR  | name3 = Laser Retroreflector
 }}

| trans_band            = [[S band]]
| trans_frequency       = 2 GHz
| trans_bandwidth       = up to {{nowrap|1.2 Mbit/s}} download<br />up to {{nowrap|4 kbit/s}} upload

| insignia              = Goce_logo.png
| insignia_caption      = Insignia for the ''GOCE'' mission
| insignia_alt          = ''GOCE'' mission insignia
| insignia_size         = 160x160px

| programme             = '''[[Living Planet Programme]]'''
| previous_mission      = 
| next_mission          = ''[[Soil Moisture and Ocean Salinity|SMOS]]''
}}

The '''Gravity Field and Steady-State Ocean Circulation Explorer''' ('''GOCE''') was the first of [[European Space Agency|ESA]]'s [[Living Planet Programme]] [[satellite|heavy satellite]]s intended to map in unprecedented detail the [[Earth's gravity field]]. The spacecraft's primary instrumentation was a highly sensitive gravity [[Gravity gradiometry|gradiometer]] consisting of three pairs of [[accelerometer]]s which measured gravitational gradients along three [[orthogonal]] axes.

Launched on 17 March 2009, GOCE mapped the deep structure of the Earth's [[Mantle (geology)|mantle]] and probed hazardous volcanic regions. It brought new insight into ocean behaviour; this in particular, was a major driver for the mission. By combining the gravity data with information about [[sea surface height]] gathered by other satellite altimeters, scientists were able to track the direction and speed of [[Geostrophic current|geostrophic ocean currents]]. The low orbit and high accuracy of the system greatly improved the known accuracy and spatial resolution of the [[geoid]] (the theoretical surface of equal gravitational potential on the Earth).

The satellite's unique arrow shape and [[fins]] helped keep GOCE stable as it flew through the [[thermosphere]] at a [[Low Earth orbit#Orbital characteristics|comparatively low altitude]] of {{convert|255|km|mi}}. Additionally, an [[ion propulsion]] system continuously compensated for the variable deceleration due to air [[Drag (physics)|drag]] without the vibration of a conventional chemically powered [[rocket engine]], thus limiting the errors in gravity gradient measurements caused by non-gravitational forces and restoring the path of the craft as closely as possible to a purely [[inertial]] trajectory.

After running out of propellant, the satellite began dropping out of orbit and made an uncontrolled re-entry on 11 November 2013.<ref name="Esa.int"/>

== Discoveries and applications ==

=== Mission objectives ===
* To determine gravity-field anomalies with an accuracy of {{val|e=-5|ul=m/s2}} (1&nbsp;[[Gal (unit)|mGal]]).<ref name="home"/><ref>{{cite journal |url=http://www.esa.int/esapub/bulletin/bulletin133/bul133b_drinkwater.pdf |title=GOCE: Obtaining a Portrait of Earth's Most Intimate Features |journal=Bulletin |publisher=European Space Agency |first1=Mark |last1=Drinkwater |first2=Roger |last2=Haagmans |first3=Michael |last3=Kern |first4=Danilo |last4=Muzi |first5=Rune |last5=Floberghagen |issue=133 |pages=4–13 |date=February 2008}}</ref><ref>{{cite journal |url=http://earth.esa.int/goce04/Documents/From-Sensors-to-Earth-Science_ISSI_Mar03.pdf |title=GOCE: ESA's First Earth Explorer Core Mission |journal=Space Science Reviews |publisher=Kluwer Academic |first1=M. R. |last1=Drinkwater |first2=R. |last2=Floberghagen |first3=R. |last3=Haagmans |first4=D. |last4=Muzi |first5=A. |last5=Popescu |volume=108 |issue=1–2 |pages=419–432 |date=July 2003 |doi=10.1023/A:1026104216284 |bibcode=2003SSRv..108..419D|s2cid=121029480 }}</ref><ref>{{cite journal |url=http://archimer.ifremer.fr/doc/2003/publication-493.pdf |title=The European Gravity Field and Steady-State Ocean Circulation Explorer Satellite Mission: Its Impact on Geophysics |journal=Surveys in Geophysics |first1=J. A. |last1=Johannessen |first2=G. |last2=Balmino |first3=C. |last3=Le Provost |first4=R. |last4=Rummel |first5=R. |last5=Sabadini |display-authors=etal |volume=24 |issue=4 |pages=339–386 |date=July 2003 |doi=10.1023/B:GEOP.0000004264.04667.5e |bibcode=2003SGeo...24..339J|hdl=1956/3796 |s2cid=55391538 |hdl-access=free }}</ref> To increase resolution, the satellite flew in an unusually low orbit.
* To determine the [[geoid]] with an accuracy of 1–2&nbsp;cm.
* To achieve the above at a spatial resolution better than 100&nbsp;km.

=== Gravity map and model ===
The final gravity map and model of the geoid will provide users worldwide with well-defined data product that will lead to:
* A better understanding of the physics of the Earth's interior to gain new insights into the geodynamics associated with the [[lithosphere]], mantle composition and rheology, uplift and subduction processes.
* A better understanding of the ocean currents and heat transport.
* A global height-reference system, which can serve as a reference surface for the study of topographic processes and sea-level change.
* Better estimates of the thickness of polar ice-sheets and their movement.<ref>{{cite web |url=http://www.esa.int/Our_Activities/Observing_the_Earth/The_Living_Planet_Programme/Earth_Explorers/GOCE/Objectives |title=GOCE scientific objectives |publisher=European Space Agency |access-date=11 November 2013}}</ref>

=== Findings ===
The first Earth global gravity model based on GOCE data was presented at ESA's Living Planet Symposium, in June 2010.<ref name="insights" />

Initial results of the GOCE satellite mission were presented at the [[American Geophysical Union]] (AGU) 2010 Fall (Autumn) Meeting by Dr Rory Bingham from Newcastle University, UK. 
The maps produced from the GOCE data show ocean currents in much finer detail than had been available previously.<ref>{{cite conference |title=Using GOCE to estimate the mean North Atlantic circulation (Invited) |conference=American Geophysical Union, Fall Meeting 2010. 13–17 December 2010. San Francisco, California. |first1=R. J. |last1=Bingham |first2=P. |last2=Knudsen |first3=O. B. |last3=Andersen |first4=R. |last4=Pail |date=December 2010 |bibcode=2010AGUFM.G33B..08B}}</ref>
Even very small details like the [[Mann Eddy]] in the [[North Atlantic]] were visible in the data,<ref>{{cite news |url=https://www.bbc.com/news/science-environment-11867162 |title=Goce gravity mission traces ocean circulation |work=BBC News |first=Jonathan |last=Amos |date=21 December 2010 |access-date=21 December 2010}}</ref> as was the effect of [[Hurricane Igor]] in 2010.<ref>{{cite web |url=http://www.esa.int/Our_Activities/Observing_the_Earth/GOCE/ESA_missions_highlighted_at_world_s_largest_scientific_conference |title=ESA missions highlighted at world's largest scientific conference |publisher=European Space Agency |date=17 December 2010 |access-date=22 December 2010}}</ref> Detailed analysis of GOCE's thruster and accelerometer data [[Role of chance in scientific discoveries|serendipitously]] revealed that it had detected the [[infrasound]] waves generated by the [[2011 Tōhoku earthquake and tsunami|2011 Tōhoku earthquake]] (whereupon it inadvertently became the first [[seismograph]] in orbit).<ref>{{cite news |url=http://www.cbc.ca/news/technology/1-tonne-goce-satellite-falls-to-earth-sunday-night-1.2419729 |title=1-tonne GOCE satellite falls to Earth Sunday night |work=CBC News |date=21 March 2009 |access-date=11 November 2013}}</ref>

Later results from the GOCE data exposed details in the Earth's mantle including mantle plumes, ancient subduction zones, and remnants of the [[Tethys Ocean]].<ref>{{cite news |url=https://www.bbc.com/news/science-environment-25911846 |title=Europe's Goce gravity satellite probes Earth's mantle |work=BBC News |first=Jonathan |last=Amos |date=27 January 2014 |access-date=27 January 2014}}</ref>

Subsequent analysis of GOCE data has also provided new information about the geological makeup of the Antarctic continent, including the detection of ancient continent remnants and at least three [[craton]]s beneath the Antarctic ice.<ref>{{cite web |url=http://www.esa.int/Our_Activities/Observing_the_Earth/GOCE/ESA_s_gravity-mapper_reveals_relics_of_ancient_continents_under_Antarctic_ice |title=ESA's gravity-mapper reveals relics of ancient continents under Antarctic ice |publisher=[[ESA]] |date=7 November 2018 |access-date=13 March 2019}}</ref><ref>{{cite web |last=Andrews |first=Robin George |url=https://www.nytimes.com/2018/11/23/science/east-antarctica-supercontinent.html |title=Beneath Antarctica's Ice Is a Graveyard of Dead Continents |work=[[New York Times]] |date=23 November 2018 |access-date=13 March 2019 |url-access=limited}}</ref><ref>{{cite journal |last1=Ebbing |first1=Jörg |last2=Haas |first2=Peter |last3=Ferraccioli |first3=Fausto |last4=Pappa |first4=Folker |last5=Szwillus |first5=Wolfgang |last6=Bouman |first6=Johannes |title=Earth tectonics as seen by GOCE - Enhanced satellite gravity gradient imaging |journal=[[Scientific Reports]] |publisher=[[Nature Research]] |volume=8 |issue=1 |pages=16356 |date=5 November 2018 |doi=10.1038/s41598-018-34733-9|pmid=30397250 |pmc=6218487 |bibcode=2018NatSR...816356E }}</ref>

== Operations ==

=== Launch ===
The first launch attempt on 16 March 2009 was aborted due to a malfunction with the launch tower.<ref>{{cite web |url=http://www.esa.int/Our_Activities/Observing_the_Earth/GOCE/Launch_of_ESA_s_gravity_mapping_satellite_delayed |title=Launch of ESA's gravity mapping satellite delayed |publisher=European Space Agency |first=Franco |last=Bonacina |date=16 March 2009}}</ref>

GOCE was launched on 17 March 2009 at 14:21&nbsp;UTC from the [[Plesetsk Cosmodrome]] in northern Russia aboard a [[Rokot]]/[[Briz-KM]] vehicle.<ref>{{cite web |url=http://www.esa.int/Our_Activities/Observing_the_Earth/GOCE/ESA_launches_Earth_Explorer_mission_GOCE |title=ESA launches first Earth Explorer mission GOCE |publisher=European Space Agency |first=Franco |last=Bonacina |date=17 March 2009}}</ref> The Rokot is a modified [[UR-100N]] intercontinental ballistic missile that was decommissioned after the Strategic Arms Reduction Treaty. The launcher used the two lower liquid fuel stages of the original missile and was equipped with a Briz-KM third stage developed for precise orbit injection. GOCE was launched into a [[Sun-synchronous orbit|Sun-synchronous]] dusk-dawn orbit with an inclination of 96.7° and an ascending node at 18:00. Separation from the launcher was at 295&nbsp;km. The satellite's orbit then decayed over a period of 45 days to an operational altitude, planned at 270&nbsp;km. During this time, the spacecraft was commissioned and the electrical propulsion system checked for reliability in [[Spacecraft attitude control|attitude control]]{{Update after|2009|03}}.<ref>{{cite journal |url=http://www.esa.int/esapub/bulletin/bulletin133/bul133c_fehringer.pdf |title=A Jewel in ESA's Crown |journal=Bulletin |publisher=European Space Agency |first1=Michael |last1=Fehringer |first2=Gerard |last2=Andre |first3=Daniel |last3=Lamarre |first4=Damien |last4=Maeusli |issue=133 |pages=14–23 |date=February 2008}}</ref>

=== Operation ===
[[File:GOCE scale 1 4 (7628217840) (2).jpg|thumb|Model of GOCE]]

In February 2010 a fault was discovered in the satellite's computer, which meant controllers were forced to switch control to the backup computer.

In July 2010, GOCE suffered a serious communications malfunction, when the satellite suddenly failed to downlink scientific data to its receiving stations. Extensive investigations by experts from ESA and industry revealed that the issue was almost certainly related to a communication link between the processor module and the telemetry modules of the main computer.<ref>{{cite news |url=https://www.bbc.com/news/science-environment-11044470 |title=Computer blow to Europe's Goce gravity satellite |work=BBC News |first=Jonathan |last=Amos |date=21 August 2010 |access-date=22 August 2010}}</ref> The recovery was completed in September 2010: as part of the action plan, the temperature of the floor hosting the computers was raised by some {{convert|7|C-change|F-change}}, resulting in restoration of normal communications.<ref>{{cite web |url=http://www.esa.int/Our_Activities/Observing_the_Earth/GOCE/GOCE_gravity_mission_back_in_action |title=GOCE gravity mission back in action |publisher=European Space Agency |date=7 September 2010 |access-date=29 September 2010}}</ref>

In November 2010, the due completion date for the original 20-month mission before it was delayed by the glitches, it was decided to extend the mission lifetime until the end of 2012 in order to complete the original work and carry out a further 18-month mission to improve the collected data.<ref>{{cite web |url=http://www.esa.int/Our_Activities/Observing_the_Earth/GOCE/ESA_s_gravity_mission_granted_18-month_extension |title=ESA's gravity mission granted 18-month extension |publisher=European Space Agency |date=25 November 2010}}</ref>

In November 2012 the orbit was lowered from {{convert|255|to|235|km|mi|abbr=on}} to get higher resolution data, at which time fuel remained for another 50 weeks.<ref name=Nov2012>{{cite news |url=http://www.universetoday.com/98542/goce-how-low-can-it-go/ |title=GOCE – How Low Can It Go? |work=Universe Today |first=Jenny |last=Winder |date=19 November 2012}}</ref>

=== End of mission and re-entry ===
In May 2013 a further lowering to {{convert|229|km|mi|abbr=on}} took place.

The satellite ran out of its xenon propellant in October 2013, at which time it would take {{nowrap|2–3 weeks}} to re-enter.<ref>{{cite web |url=http://www.esa.int/Our_Activities/Observing_the_Earth/GOCE/ESA_s_GOCE_mission_to_end_this_year |title=ESA's GOCE mission to end this year |publisher=European Space Agency |date=13 September 2013 |access-date=11 November 2013}}</ref> On 18 October 2013, [[European Space Agency|ESA]] reported that the pressure in the fuel system of GOCE's ion engine had dropped below 2.5 bar, which is the nominal operating pressure required to fire the engine.<ref>{{cite web |url=http://blogs.esa.int/rocketscience/2013/10/18/goce-fuel-steadily-runs-out/ |title=GOCE fuel steadily runs out |publisher=European Space Agency |first1=Daniel |last1=Scuka |first2=Christoph |last2=Steiger |date=18 October 2013 |access-date=11 November 2013}}</ref> Subsequently, end of mission was formally declared on 21 October when the spacecraft ran out of fuel; deprived of xenon, the ion drive stopped working at 03:16&nbsp;UTC.<ref name="esa20131021" /><ref name="esablog20131021">{{cite web |url=http://blogs.esa.int/rocketscience/2013/10/21/update-on-goce/ |title=Update on GOCE |publisher=European Space Agency |first1=Daniel |last1=Scuka |first2=Christoph |last2=Steiger |date=21 October 2017 |access-date=10 July 2017}}</ref>

On 9 November 2013, a published report indicated that the satellite was expected to re-enter within a day or two.<ref>{{cite news |url=https://www.bbc.com/news/av/science-environment-24879140/don-t-panic-one-tonne-satellite-falling-to-earth |title='Don't panic': One-tonne satellite falling to Earth |work=BBC News |first=Tim |last=Allman |date=9 November 2013 |access-date=11 November 2013}}</ref><ref name="npr">{{cite news |url=https://www.npr.org/blogs/thetwo-way/2013/11/09/244213231/ferrari-of-space-crashing-back-to-earth-maybe-tomorrow |title='Ferrari Of Space' Crashing Back To Earth — Maybe Tomorrow |work=[[NPR]] |last=Henderson |first=Greg |date=9 November 2013 |access-date=10 November 2013}}</ref> By this date, the [[Apsis|perigee]] altitude had decayed to {{convert|155|km|mi|abbr=on}}.<ref>{{cite web |url=http://www.heavens-above.com/orbit.aspx?satid=34602 |title=GOCE - Orbit |work=Heavens Above |access-date=11 November 2013}}</ref>

On 10 November, ESA expected re-entry to occur between 18:30 and 24:00&nbsp;UTC that day, with the most probable impact ground swath largely running over ocean and polar regions.<ref>{{cite web |url=http://blogs.esa.int/rocketscience/2013/11/10/goce-re-entry-forecast-from-esas-space-debris-office/ |title=GOCE re-entry forecast from ESA's Space Debris Office |publisher=European Space Agency |first1=Daniel |last1=Scuka |first2=Heiner |last2=Klinkrad |date=10 November 2013 |access-date=11 November 2013}}</ref>

Its descending orbit on 11 November 2013 passed over [[Siberia]], the western [[Pacific Ocean]], the eastern [[Indian Ocean]] and [[Antarctica]].<ref>{{cite web |url=http://www.esa.int/Our_Activities/Observing_the_Earth/GOCE/GOCE_gives_in_to_gravity |title=GOCE gives into gravity |publisher=European Space Agency |date=11 November 2013 |access-date=11 November 2013}}</ref><ref>{{cite news |url=http://www.cnn.com/2013/11/09/tech/satellite-falling |title=Falling European satellite burns up upon re-entry |work=CNN |first=Matt |last=Smith |date=10 November 2013 |access-date=11 November 2013}}</ref> The satellite finally disintegrated around 00:16&nbsp;[[UTC]] on 11 November near the  [[Falkland Islands]].<ref name="esoc.interface" /><ref>{{cite news |url=http://news.discovery.com/space/twitter-goce-burned-up-over-falkland-islands-131111.htm |title=Twitter: GOCE Burned Up Over Falkland Islands |work=Discovery News |first=Ian |last=O'Neill |date=11 November 2013 |archive-url=https://web.archive.org/web/20131112070621/http://news.discovery.com/space/twitter-goce-burned-up-over-falkland-islands-131111.htm |archive-date=12 November 2013 |url-status=dead |df=dmy-all }}</ref>

== Design ==

=== Payload ===
The satellite's main payload was the Electrostatic Gravity Gradiometer (EGG) to measure the [[Physical geodesy|gravity field of Earth]]. This instrument consisted of three pairs of capacitive accelerometers arranged in three dimensions that responded to tiny variations in the 'gravitational tug' of the [[Earth]] as it traveled along its orbital path. Because of their different position in the gravitational field they all experienced the gravitational acceleration of the Earth slightly differently. The three axes of the [[Gravity gradiometry|gradiometer]] allowed the simultaneous measurement of the five independent components of the [[gravity gradient tensor]].

Other payload was an onboard [[GPS]] receiver used as a Satellite-to-Satellite Tracking Instrument (SSTI); a compensation system for all non-gravitational forces acting on the spacecraft. The satellite was also equipped with a [[laser]] [[retroreflector]] to enable tracking by ground-based [[Satellite laser ranging]] stations.<ref>{{cite journal |title=Characteristics of GOCE orbits based on Satellite Laser Ranging |journal=Advances in Space Research |publisher=Elsevier |first1=Dariusz |last1=Strugarek |first2=Krzysztof |last2=Sosnica |first3=Adrian |last3=Jaeggi |issue=1 |pages=417–431 |date=January 2019|volume=63 |doi=10.1016/j.asr.2018.08.033 |bibcode=2019AdSpR..63..417S |s2cid=125791718 }}</ref>

=== Power and propulsion ===
[[File:GOCE 03012010.jpg|thumb|GOCE flares to magnitude +2 as the 67.5&nbsp;degree solar panel briefly mirrors sunlight (3 January 2010, 17:24:23.15 UTC).]]

GOCE's {{convert|5|xx|1.1|m|ft|0|abbr=on}} frame had fixed [[Photovoltaic system|solar panels]] covering its sun-facing side, which produced 1,300&nbsp;[[watt]]s of power.<ref>{{cite news |url=http://news.bbc.co.uk/2/hi/science/nature/7592689.stm |title=Goce gravity flight slips to 2009 |work=BBC News |first=Jonathan |last=Amos |date=24 October 2008 |access-date=26 October 2008}}</ref> The panels were shaped to act as fins, stabilising the spacecraft while it orbited through the residual air in the [[thermosphere]].

The [[ion propulsion]] electric engine, designed and built at [[QinetiQ]]'s space centre in Farnborough, England, ejected [[xenon]] ions at velocities exceeding {{convert|40000|m/s|km/h mph|abbr=on}}, which compensated for the orbital decay losses. GOCE's mission ended when the {{convert|40|kg|lb|abbr=on}} xenon fuel tank emptied.<ref name=home >{{cite web |url=http://www.esa.int/Our_Activities/Observing_the_Earth/The_Living_Planet_Programme/Earth_Explorers/GOCE/ESA_s_gravity_mission_GOCE |title=ESA's Gravity Mission GOCE |publisher=European Space Agency |date=16 October 2008 |access-date=26 October 2008 |archive-date=10 September 2014 |archive-url=https://web.archive.org/web/20140910080826/http://www.esa.int/Our_Activities/Observing_the_Earth/The_Living_Planet_Programme/Earth_Explorers/GOCE/ESA_s_gravity_mission_GOCE |url-status=dead }}</ref> The dual Kaufman-type ion thrusters could produce up to {{convert|20|mN|lbf|lk=in}} of thrust.<ref>{{cite web |url=http://www.esa.int/Our_Activities/Observing_the_Earth/The_Living_Planet_Programme/Earth_Explorers/GOCE/Satellite |title=GOCE Mission |publisher=European Space Agency |access-date=16 April 2017}}</ref>

Although its predicted lifetime was 20 months, an ESA report in June 2010 suggested that unusually low solar activity (meaning a calmer upper atmosphere, and hence less drag on the craft) meant the fuel would last longer than its predicted 20 months—possibly into 2014. In reality, the end of mission was formally declared on 21 October 2013 after 55 months, with the final 11 months in a lower orbit (with greater air density and therefore greater fuel use).<ref name=BBCGOCE >{{cite news |url=http://news.bbc.co.uk/1/hi/sci/tech/8767763.stm |title=Goce satellite views Earth's gravity in high definition |work=BBC News |first=Jonathan |last=Amos |date=28 June 2010 |access-date=30 June 2010}}</ref>

== See also ==
{{Portal|Spaceflight}}
* [[Gravity Recovery and Climate Experiment|GRACE]] (NASA; DLR; in orbit 2002–2017) and the follow-up mission GRACE-FO
* [[Super Low Altitude Test Satellite|SLATS]] (JAXA), also used ion thrusters to maintain altitude, 2017-2019
* [[Satellite gravimetry]]
<!--- redundant list ----
* ESA's [[Living Planet Programme]]
** [[Soil Moisture and Ocean Salinity|SMOS]]
** [[CryoSat]] & [[CryoSat-2]]
** [[Swarm (spacecraft)|Swarm]]
** [[ADM-Aeolus]]
** [[EarthCARE]]
** [[BIOMASS]]
** [[FLEX (satellite)|FLEX]]
------------>

== References ==
{{Reflist|colwidth=30em}}

== External links ==
* [http://www.esa.int/GOCE GOCE site] by the European Space Agency
* [http://www.esa.int/Our_Activities/Observing_the_Earth/The_Living_Planet_Programme/Earth_Explorers/GOCE GOCE site] by ESA Earth Explorers
* [http://www.esa.int/Our_Activities/Operations/GOCE GOCE site] by ESA Operations
* [https://earth.esa.int/eogateway/missions/goce GOCE site] by ESA Earth Online
* [https://directory.eoportal.org/web/eoportal/satellite-missions/g/goce GOCE site] by ESA eoPortal

{{ESA projects}}
{{Orbital launches in 2009}}

{{Use British English|date=January 2014}}
{{Use dmy dates|date=July 2017}}

[[Category:Earth observation satellites of the European Space Agency]]
[[Category:Satellites in very low Earth orbit]]
[[Category:Spacecraft launched in 2009]]
[[Category:Spacecraft which reentered in 2013]]
[[Category:Spacecraft launched by Rokot rockets]]
[[Category:Gravimetry satellites]]