Editing GRACE and GRACE-FO (section)

== GRACE Follow-On ==
{{Infobox spaceflight |auto=all
| name                  = GRACE-FO
| names_list            = {{unbulleted list|
* GRACE-FO 1<ref name="NSSDCA GFO1">{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=2018-047A |title=GRACE-FO 1 |work=[[National Space Science Data Center]] |publisher=NASA |access-date=23 May 2019}}</ref>
* GRACE-FO 2<ref name="NSSDCA GFO2">{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=2018-047B |title=GRACE-FO 2 |work=[[National Space Science Data Center]] |publisher=NASA |access-date=23 May 2019}}</ref>
}}
| image                 = GRACE-FO.jpg
| image_size            = 275px
| image_caption         = Illustration of the twin GRACE-FO satellites

| mission_type          = Gravitational science
| operator              = [[NASA]]{{·}}[[German Aerospace Center|DLR]]<ref>{{cite web |title=Twin Spacecraft Launch to Track Earth's Water Movement |url=https://www.nasa.gov/press-release/twin-spacecraft-launch-to-track-earth-s-water-movement |website=NASA |date=22 May 2018 |access-date=28 May 2019}}</ref>
| COSPAR_ID             = {{unbulleted list|2018-047A|2018-047B}}
| SATCAT                = 43476 and 43477
| website               = {{URL|nasa.gov/missions/grace-fo/}}
| mission_duration      = Planned: 5 years <br /> Elapsed: {{time interval|22 May 2018 19:47:58|show=ymd|sep=,}}

| spacecraft_bus        = Flexbus<ref name="gunters-FO">{{cite web |url=http://space.skyrocket.de/doc_sdat/grace.htm |title=GRACE-FO |work=Gunter's Space Page |access-date=23 May 2019}}</ref>
| manufacturer          = [[Airbus Defence and Space]] (formerly [[Astrium]])<ref>{{cite web |title=GRACE-FO |url=https://directory.eoportal.org/web/eoportal/satellite-missions/g/grace-fo |website=eoPortal |access-date=26 May 2019}}</ref>
| launch_mass           = {{convert|600|kg|lb|abbr=on}} each<ref name="presskit-launch-FO">{{cite web |url=https://www.jpl.nasa.gov/news/press_kits/grace-fo/download/grace-fo_launch_press_kit.pdf |title=GRACE-FO Launch Press Kit |publisher=NASA |date=May 2018 |access-date=23 May 2019}}</ref>
| dry_mass              = 
| dimensions            = {{convert|1.943|xx|3.123|xx|0.78|m|ft|1|abbr=on}}<ref name="presskit-launch-FO" />
| power                 = <!--end-of-life power, in watts-->

| launch_date           = {{start-date|22 May 2018, 19:47:58}}&nbsp;UTC
| launch_rocket         = [[Falcon 9 Block 4]] [[List of Falcon 9 first stage boosters#B1043|B1043-2]]
| launch_site           = [[Vandenberg AFB]], [[California]]
| launch_contractor     = [[SpaceX]]
| entered_service       =

| declared              = 
| decay_date            =

| orbit_reference       = [[Geocentric orbit|Geocentric]]
| orbit_regime          = 
| orbit_semimajor       = {{convert|6872.2|km|abbr=on}}
| orbit_eccentricity    = 0.00179
| orbit_periapsis       = {{convert|481.7|km|mi|abbr=on}}
| orbit_apoapsis        = {{convert|506.3|km|mi|abbr=on}}
| orbit_inclination     = 89.0°
| orbit_period          = 94.5 minutes
| orbit_epoch           = 29 September 2019, 15:36:45&nbsp;[[UTC]]<ref name="habove-gfo1">{{cite web |url=https://heavens-above.com/orbit.aspx?satid=43476 |title=GRACE-FO 1 – Orbit |website=Heavens-Above.com |date=29 September 2019 |access-date=29 September 2019}}</ref>
| apsis                 = gee

| instruments           = <!--a list of instruments on the satellite-->
}}

The GRACE-FO mission, a collaboration between NASA and [[GFZ German Research Centre for Geosciences|GFZ]], was launched on 22 May 2018 aboard a [[SpaceX]] [[Falcon 9]] rocket from Vandenberg AFB, California, sharing the launch with five [[Iridium satellite constellation|Iridium NEXT]] satellites.<ref name="FO launch">{{cite web |url=https://gracefo.jpl.nasa.gov/mission/overview/ |title=GRACE-FO Mission |publisher=NASA/JPL |access-date=19 November 2017}}</ref><ref name="space20180522">{{cite news |url=https://www.space.com/40672-spacex-launches-grace-fo-iridium-satellites.html |title=SpaceX Launches Twin NASA Probes to Track Earth's Water (and Satellites Hitch a Ride) |work=Space.com |first=Hanneke |last=Weitering |date=22 May 2018 |access-date=22 May 2018}}</ref> During in-orbit checks, an anomaly was discovered in the primary system component of the microwave instrument (MWI), and the system was temporarily powered down on 19 July 2018.<ref name="nasa20181101">{{cite web |url=https://www.nasa.gov/feature/jpl/grace-fo-resumes-data-collection |title=GRACE-FO Resumes Data Collection |publisher=NASA |last=Rasmussen |first=Carol |date=1 November 2018 |access-date=2 November 2018}}</ref> After a full investigation by an anomaly response team at JPL, the backup system in the MWI was powered up on 19 October 2018 and GRACE-FO resumed its in-orbit checks.<ref name="nasa20181101" /><ref name="nasa20180914">{{cite web |url=https://www.jpl.nasa.gov/news/news.php?feature=7236 |title=GRACE-FO Satellite Switching to Backup Instrument Processing Unit |publisher=NASA/JPL |first=Esprit |last=Smith |date=14 September 2018 |access-date=14 September 2018}}</ref>  GRACE-FO entered the science phase of its mission on 28 January 2019.<ref name="Webb2019">{{cite journal |url=https://media.gfz-potsdam.de/gfz/sec12/pdf/GRACE_FO_SDS_newsletter_No2.pdf |title=GRACE Follow-On Science Team & Highlights |journal=Science Data System Newsletter |first1=Frank |last1=Webb |first2=Frank |last2=Flechtner |first3=Felix |last3=Landerer |first4=Michael |last4=Watkins |first5=Himanshu |last5=Save |first6=Christoph |last6=Dahle |display-authors=1 |issue=2 |date=January–March 2019}}</ref>

The orbit and design of GRACE-FO is very similar to its predecessor.<ref name="gfo_brochure">{{cite web |url=https://www.jpl.nasa.gov/news/brochure/gracefo_brochure.pdf |title=GRACE-FO: Tracking Earth's Mass in Motion |publisher=NASA |date=2017 |id=NP-2017-4-002-GSFC |access-date=7 March 2019 |archive-date=26 January 2021 |archive-url=https://web.archive.org/web/20210126201514/https://www.jpl.nasa.gov/news/brochure/gracefo_brochure.pdf |url-status=dead }}</ref> GRACE-FO employs the same two-way microwave-ranging link as GRACE, which will allow for similar inter-satellite ranging precision. In addition, GRACE-FO employs laser-ranging interferometry (LRI) as a technological experiment in preparation for future satellites.<ref>{{cite press release |url=http://www.space-airbusds.com/en/press_centre/airbus-defence-and-space-to-build-two-new-research-satellites-for-nasa.html |title=Airbus Defence and Space to build two new research satellites for NASA |publisher=Airbus Defence and Space |date=29 November 2012 |archive-url=https://web.archive.org/web/20140720205747/http://www.space-airbusds.com/en/press_centre/airbus-defence-and-space-to-build-two-new-research-satellites-for-nasa.html |archive-date=20 July 2014 |url-status=dead}}</ref><ref>{{cite web |url=https://gracefo.jpl.nasa.gov/mission/spacecraft/microwaves-and-lasers/ |title=Spacecraft: Microwaves and Lasers |series=GRACE-FO |publisher=NASA/JPL |access-date=11 December 2017}}</ref><ref>{{Cite web |url=https://gracefo.jpl.nasa.gov/laser-ranging-interferometer/ |title=Laser Ranging Interferometer |series=GRACE-FO |publisher=NASA/JPL |access-date=29 September 2019}}</ref> The LRI allows for more accurate inter-satellite ranging due to the shorter wavelength of light, and additionally allows the angle between the two spacecraft to be measured as well as their separation via differential wavefront sensing (DWS).<ref name="gtel_gfo">{{Cite news |url=https://grace.jpl.nasa.gov/mission/grace-fo/ |title=GRACE Tellus: GRACE-FO |series=GRACE Tellus |publisher=NASA/JPL |access-date=18 April 2018}}</ref><ref>{{Cite web |url=https://earth.esa.int/web/eoportal/satellite-missions/g/grace-fo |title=GRACE-FO |work=eoPortal |publisher=European Space Agency |access-date=7 May 2020}}</ref><ref name="Abich2015">{{cite journal |last1=Abich |first1=Klaus |last2=Bogan |first2=Christina |last3=Braxmaier |first3=Claus |last4=Danzmann |first4=Karsten |last5=Dehne |first5=Marina |last6=Gohlke |first6=Martin |last7=Görth |first7=Alexander |last8=Heinzel |first8=Gerhard |last9=Herding |first9=Mark |last10=Mahrdt |first10=Christoph |last11=Müller |first11=Vitali |last12=Nicklaus |first12=Kolja |last13=Sanjuan |first13=Josep |last14=Schütze |first14=Daniel |last15=Sheard |first15=Benjamin |last16=Stede |first16=Gunnar |last17=Voss |first17=Kai |display-authors=1 |title=GRACE-Follow On Laser Ranging Interferometer: German contribution |journal=Journal of Physics: Conference Series |volume=610 |issue=1 |at=012010 |date=11 May 2015 |doi=10.1088/1742-6596/610/1/012010 |bibcode=2015JPhCS.610a2010A|doi-access=free |hdl=21.11116/0000-0003-655A-7 |hdl-access=free }}</ref> Using the LRI, scientists have improved the precision of the separation distance measurements by a factor of more than 20 relative to the GRACE mission.<ref name="gfo_brochure" /><ref name="physworld20190723">{{cite news |url=https://physicsworld.com/a/distance-between-spacecraft-measured-at-the-atomic-scale/ |title=Distance between spacecraft measured at the atomic scale |work=PhysicsWorld |first=Hamish |last=Johnston |date=23 July 2019 |access-date=29 September 2019}}</ref> Each laser on the LRI has about the same power as four laser pointers.<ref name=":0">{{Cite web |url=https://gracefo.jpl.nasa.gov/news/128/lasers-in-space-grace-fo-tests-new-technology |title=Lasers in Space: GRACE-FO Tests New Technology |website=GRACE-FO |publisher=NASA |date=8 May 2018 |access-date=5 March 2020}}</ref> These lasers must be detected by a spacecraft about {{convert|220|km|mi}} away.<ref name=":0" /> This laser approach will generate much more accurate measurements than the previous GRACE satellite mission.<ref>{{Cite web |url=https://gracefo.jpl.nasa.gov/mission/spacecraft/overview |title=Spacecraft Overview |website=GRACE-FO |publisher=NASA |access-date=5 March 2020}}</ref>

The GRACE-FO satellites obtain electricity from gallium arsenide solar cell array panels covering the outside of each satellite.<ref>{{Cite web |url=https://gracefo.jpl.nasa.gov/solar-cells-battery |title=Solar Cell Arrays |website=GRACE-FO |publisher=NASA |access-date=27 February 2020}}</ref>

GRACE-FO will continue to monitor Earth's gravity and climate. The mission will track gravitational changes in global sea levels, glaciers, and ice sheets, as well as large lake and river water levels, and soil moisture.<ref name="gtel_gfo" /> In addition, each of the satellites will use GPS antennas to create at least 200 profiles per day of atmospheric temperature distribution and water vapor content, a first for the GRACE mission.<ref name="gfo_brochure" />

GRACE-FO has a design life of 5 years.<ref name="gfo_brochure" /><ref name=":1">{{cite web |url=https://www.jpl.nasa.gov/news/fact_sheets/GracefoFactSheet.pdf |title=GRACE-FO |series=NASA Facts |publisher=NASA |access-date=29 September 2019 |archive-date=15 June 2021 |archive-url=https://web.archive.org/web/20210615035957/https://www.jpl.nasa.gov/news/fact_sheets/GracefoFactSheet.pdf |url-status=dead }}</ref>