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|publisher = [[United Launch Alliance]] |
|publisher = [[United Launch Alliance]] |
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|year = 2011 |
|year = 2011 |
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|access-date = 2 September 2011 |
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|url-status = dead |
|url-status = dead |
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|archive-url = https://web.archive.org/web/20110901221606/http://www.ulalaunch.com/site/pages/Launch.shtml#/21/ |
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|archive-date = 1 September 2011 |
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}}</ref><ref>{{cite web| title =The GRAIL Mission: A Fact Sheet| url =http://www.grailmoonkam.com/about/grail_fact_sheet| publisher =[[Sally Ride Science]]| year =2010| |
}}</ref><ref>{{cite web| title =The GRAIL Mission: A Fact Sheet| url =http://www.grailmoonkam.com/about/grail_fact_sheet| publisher =[[Sally Ride Science]]| year =2010| access-date =2010-04-15| url-status =dead| archive-url =https://web.archive.org/web/20100428001600/http://www.grailmoonkam.com/about/grail_fact_sheet| archive-date =2010-04-28}}</ref> |
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| COSPAR_ID = 2011-046 (A, B) |
| COSPAR_ID = 2011-046 (A, B) |
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| SATCAT = 37801, 37802 |
| SATCAT = 37801, 37802 |
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[[File:GRAIL MoonKAM NASA mission 15.jpg|thumb|right|MoonKAM shot]] |
[[File:GRAIL MoonKAM NASA mission 15.jpg|thumb|right|MoonKAM shot]] |
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The '''Gravity Recovery and Interior Laboratory''' ('''GRAIL''') was an American lunar science mission in NASA's [[Discovery Program]] which used high-quality [[gravitational field]] mapping of the [[Moon]] to determine its interior structure. The two small spacecraft '''GRAIL A''' ('''Ebb''') and '''GRAIL B''' ('''Flow''')<ref>{{Cite web|url=https://www.bozemandailychronicle.com/news/education/bozeman-class-wins-contest-to-name-satellites-orbiting-moon/article_e73236bc-4188-11e1-9ae2-001871e3ce6c.html|title=Bozeman class wins contest to name satellites orbiting moon|first=Gail|last=Schontzler |website=Bozeman Daily Chronicle|language=en|access-date=2018-12-18}}</ref><ref name=ebbflow>{{cite web|last=Agle|first=DC|title=Montana Students Submit Winning Names for NASA Lunar Spacecraft|url=http://www.nasa.gov/home/hqnews/2012/jan/HQ_12-019_GRAIL_Name.html|publisher=NASA JPL}}</ref> were launched on 10 September 2011 aboard a single launch vehicle: the most-powerful configuration of a [[Delta II]], the 7920H-10.<ref name=ula/><ref>{{cite paper|title=Delta II: The Industry Workhorse |publisher=United Launch Alliance |url=http://www.ulalaunch.com/site/docs/product_cards/DII_product_card.pdf |date=2010 | |
The '''Gravity Recovery and Interior Laboratory''' ('''GRAIL''') was an American lunar science mission in NASA's [[Discovery Program]] which used high-quality [[gravitational field]] mapping of the [[Moon]] to determine its interior structure. The two small spacecraft '''GRAIL A''' ('''Ebb''') and '''GRAIL B''' ('''Flow''')<ref>{{Cite web|url=https://www.bozemandailychronicle.com/news/education/bozeman-class-wins-contest-to-name-satellites-orbiting-moon/article_e73236bc-4188-11e1-9ae2-001871e3ce6c.html|title=Bozeman class wins contest to name satellites orbiting moon|first=Gail|last=Schontzler |website=Bozeman Daily Chronicle|language=en|access-date=2018-12-18}}</ref><ref name=ebbflow>{{cite web|last=Agle|first=DC|title=Montana Students Submit Winning Names for NASA Lunar Spacecraft|url=http://www.nasa.gov/home/hqnews/2012/jan/HQ_12-019_GRAIL_Name.html|publisher=NASA JPL}}</ref> were launched on 10 September 2011 aboard a single launch vehicle: the most-powerful configuration of a [[Delta II]], the 7920H-10.<ref name=ula/><ref>{{cite paper|title=Delta II: The Industry Workhorse |publisher=United Launch Alliance |url=http://www.ulalaunch.com/site/docs/product_cards/DII_product_card.pdf |date=2010 |access-date=2 August 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110930102552/http://www.ulalaunch.com/site/docs/product_cards/DII_product_card.pdf |archive-date=30 September 2011 }}</ref><ref>{{cite web | author=Grey Hautaluoma | title=New NASA Mission to Reveal Moon's Internal Structure and Evolution | url=http://www.nasa.gov/home/hqnews/2007/dec/HQ_07274_Grail_Mission.html | publisher=NASA | date=10 December 2007 | access-date=31 August 2011}}</ref> GRAIL A separated from the rocket about nine minutes after launch, GRAIL B followed about eight minutes later. They arrived at their orbits around the Moon 25 hours apart.<ref>[http://earthsky.org/space/moon-bound-twin-grail-spacecraft-launch-success Moon-bound twin GRAIL spacecraft launch success]</ref><ref>[http://www.spaceflight101.com/grail-mission-updates.html Spaceflight101] {{webarchive|url=https://web.archive.org/web/20150211061336/http://www.spaceflight101.com/grail-mission-updates.html |date=2015-02-11 }}</ref> The first probe entered orbit on 31 December 2011 and the second followed on 1 January 2012.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/grail/news/grail20111231.html|title=First of NASA's GRAIL Spacecraft Enters Moon Orbit|publisher=[[NASA]]|access-date=1 January 2012}}</ref> The two spacecraft impacted the Lunar surface on December 17, 2012.<ref>[http://www.spaceflight101.com/grail-mission-updates.html GRAIL Twins crash into the Moon to complete highly successful Mission] {{webarchive|url=https://web.archive.org/web/20150211061336/http://www.spaceflight101.com/grail-mission-updates.html |date=2015-02-11 }}</ref> |
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==Overview== |
==Overview== |
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[[File:Ebb and flow.jpg|thumb|Fourth grade students at [[Emily Dickinson Elementary School]] in [[Bozeman, Montana]] who suggested names ''Ebb'' and ''Flow''.<ref name=ebbflow/>]] |
[[File:Ebb and flow.jpg|thumb|Fourth grade students at [[Emily Dickinson Elementary School]] in [[Bozeman, Montana]] who suggested names ''Ebb'' and ''Flow''.<ref name=ebbflow/>]] |
||
[[Maria Zuber]] of the [[Massachusetts Institute of Technology]] is GRAIL's principal investigator. [[NASA]]'s [[Jet Propulsion Laboratory]] manages the project. {{As of|2011|8|5|df=US}}, the program had cost US$496 million.<ref>{{cite news | work=Yahoo News | title=NASA Spacecraft Begins 5-Year Trip to Jupiter | author=Marcia Dunn, AP Aerospace Writer | date=5 August 2011| url=https://news.yahoo.com/nasa-spacecraft-begins-5-trip-jupiter-211124283.html | |
[[Maria Zuber]] of the [[Massachusetts Institute of Technology]] is GRAIL's principal investigator. [[NASA]]'s [[Jet Propulsion Laboratory]] manages the project. {{As of|2011|8|5|df=US}}, the program had cost US$496 million.<ref>{{cite news | work=Yahoo News | title=NASA Spacecraft Begins 5-Year Trip to Jupiter | author=Marcia Dunn, AP Aerospace Writer | date=5 August 2011| url=https://news.yahoo.com/nasa-spacecraft-begins-5-trip-jupiter-211124283.html | access-date=7 September 2011}}</ref> Upon launch the spacecraft were named GRAIL A and GRAIL B and a contest was opened to school children to select names. Nearly 900 classrooms from 45 states, Puerto Rico and the District of Columbia, participated in the contest. The winning names, Ebb and Flow, were suggested by 4th grade students at [[Emily Dickinson Elementary School]] in [[Bozeman, Montana]].<ref name=ebbflow/> |
||
Each [[spacecraft]] transmitted and received [[telemetry]] from the other spacecraft and Earth-based facilities. By measuring the change in distance between the two spacecraft, the gravity field and geological structure of the Moon was obtained. The two spacecraft were able to detect very small changes in the distance between one another. Changes in distance as small as one [[micrometre]] were detectable and measurable.<ref>[https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20120009915_2012010042.pdf GRAVITY RECOVERY AND INTERIOR LABORATORY (GRAIL) MISSION: STATUS AT THE INITIATION OF THE SCIENCE MAPPING PHASE, 43rd Lunar and Planetary Science Conference (2012)]</ref><ref>[https://www.washingtonpost.com/blogs/innovations/post/nasa-to-crash-probes-into-the-moon/2012/12/17/2f2d2b80-4871-11e2-b6f0-e851e741d196_blog.html Washington Post December 17, 2012]</ref> The [[gravitational field]] of the Moon was mapped in unprecedented detail.<ref name="AboutGRAIL">{{cite web |
Each [[spacecraft]] transmitted and received [[telemetry]] from the other spacecraft and Earth-based facilities. By measuring the change in distance between the two spacecraft, the gravity field and geological structure of the Moon was obtained. The two spacecraft were able to detect very small changes in the distance between one another. Changes in distance as small as one [[micrometre]] were detectable and measurable.<ref>[https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20120009915_2012010042.pdf GRAVITY RECOVERY AND INTERIOR LABORATORY (GRAIL) MISSION: STATUS AT THE INITIATION OF THE SCIENCE MAPPING PHASE, 43rd Lunar and Planetary Science Conference (2012)]</ref><ref>[https://www.washingtonpost.com/blogs/innovations/post/nasa-to-crash-probes-into-the-moon/2012/12/17/2f2d2b80-4871-11e2-b6f0-e851e741d196_blog.html Washington Post December 17, 2012]</ref> The [[gravitational field]] of the Moon was mapped in unprecedented detail.<ref name="AboutGRAIL">{{cite web | title=About GRAIL | publisher=Massachusetts Institute of Technology | url=http://moon.mit.edu/index.html | access-date = 2011-03-12}}</ref><ref>{{cite journal |last1=Lemoine |first1=Frank G. |last2=Goossens |first2=Sander |last3=Sabaka |first3=Terence J. |last4=Nicholas |first4=Joseph B. |last5=Mazarico |first5=Erwan |last6=Rowlands |first6=David D. |last7=Loomis |first7=Bryant D. |last8=Chinn |first8=Douglas S. |last9=Neumann |first9=Gregory A. |last10=Smith |first10=David E. |last11=Zuber |first11=Maria T. |title=GRGM900C: A degree 900 lunar gravity model from GRAIL primary and extended mission data |journal=Geophysical Research Letters |date=28 May 2014 |volume=41 |issue=10 |pages=3382–3389 |doi=10.1002/2014GL060027|pmc=4459205 }}</ref> |
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==Objectives== |
==Objectives== |
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===Instruments=== |
===Instruments=== |
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[[Image:GRAIL's gravity map of the moon.jpg|thumb|Gravity map of the Moon by GRAIL]] |
[[Image:GRAIL's gravity map of the moon.jpg|thumb|Gravity map of the Moon by GRAIL]] |
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* [[Ka band|K<sub>a</sub> band]] Lunar Gravity Ranging System (LGRS), derived from the [[Gravity Recovery and Climate Experiment]] instrument.<ref name=spacecraft /> 90% of the GRACE software was reused for GRAIL.<ref name="Operations MIT">{{cite web | title= GRAIL: Mission Operations & Data Processing | url= http://moon.mit.edu/operations.html | publisher= [[Massachusetts Institute of Technology|MIT]] | |
* [[Ka band|K<sub>a</sub> band]] Lunar Gravity Ranging System (LGRS), derived from the [[Gravity Recovery and Climate Experiment]] instrument.<ref name=spacecraft /> 90% of the GRACE software was reused for GRAIL.<ref name="Operations MIT">{{cite web | title= GRAIL: Mission Operations & Data Processing | url= http://moon.mit.edu/operations.html | publisher= [[Massachusetts Institute of Technology|MIT]] | access-date= 2012-12-14 | archive-url= https://web.archive.org/web/20120305034145/http://moon.mit.edu/operations.html | archive-date= 2012-03-05 | url-status= dead }}</ref> |
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* Radio science beacon (RSB) |
* Radio science beacon (RSB) |
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* Moon Knowledge Acquired by Middle school students (MoonKAM).<ref>{{cite web | title = About GRAIL MoonKAM | url = http://www.grailmoonkam.com/about | publisher = Sally Ride Science | date = 2010 | |
* Moon Knowledge Acquired by Middle school students (MoonKAM).<ref>{{cite web | title = About GRAIL MoonKAM | url = http://www.grailmoonkam.com/about | publisher = Sally Ride Science | date = 2010 | access-date = 2010-04-15 | url-status = dead | archive-url = https://web.archive.org/web/20100427105214/http://www.grailmoonkam.com/about | archive-date = 2010-04-27 }}</ref> Each MoonKAM system (one per spacecraft) consists of a digital video controller and four camera heads.<ref name=PressKit>{{cite web | title = GRAIL Launch Press Kit| url= http://solarsystem.nasa.gov/grail/docs/GRAIL%20launch%20press%20kit1.pdf | publisher= NASA| access-date = 31 August 2011}}</ref> Click here [http://www.nasa.gov/mission_pages/grail/multimedia/pia15514.html] for a MoonKAM photo from lunar orbit. |
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===Propulsion=== |
===Propulsion=== |
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{{LaunchAttempt |
{{LaunchAttempt |
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| date1 = 2011-09-08 08:37:06 |
| date1 = 2011-09-08 08:37:06 |
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| result1 = scrubbed<ref name=LaunchCBS>{{cite news | last=Harwood | first=William | title= NASA launches GRAIL lunar probes | url=http://www.cbsnews.com/stories/2011/09/10/scitech/main20104282.shtml |work=CBS News | |
| result1 = scrubbed<ref name=LaunchCBS>{{cite news | last=Harwood | first=William | title= NASA launches GRAIL lunar probes | url=http://www.cbsnews.com/stories/2011/09/10/scitech/main20104282.shtml |work=CBS News | access-date = 11 September 2011}}</ref> |
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| reason1 = high level winds |
| reason1 = high level winds |
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| decision_date1 = 2011-09-08 08:30:00 |
| decision_date1 = 2011-09-08 08:30:00 |
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[[File:GRAIL-transit-Earth-Moon.png|thumb|GRAIL-transit-Earth-Moon]] |
[[File:GRAIL-transit-Earth-Moon.png|thumb|GRAIL-transit-Earth-Moon]] |
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[[File:Animation of GRAIL-A trajectory around Moon.gif |thumb |right |Animation of GRAIL-A{{'s}} trajectory around [[Moon]] from 31 December 2011 to 30 April 2012<br>{{legend2|magenta| GRAIL-A}}{{·}}{{legend2| DarkKhaki|[[Moon]]}}]] |
[[File:Animation of GRAIL-A trajectory around Moon.gif |thumb |right |Animation of GRAIL-A{{'s}} trajectory around [[Moon]] from 31 December 2011 to 30 April 2012<br>{{legend2|magenta| GRAIL-A}}{{·}}{{legend2| DarkKhaki|[[Moon]]}}]] |
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Unlike the [[Apollo program]] missions, which took three days to reach the Moon, GRAIL made use of a three- to four-month low-energy trans-lunar cruise well outside the Moon's orbit and passing near the Sun-Earth [[Lagrange point#L1|Lagrange point L1]] before looping back to rendezvous with the Moon. This extended and circuitous trajectory enabled the mission to reduce fuel requirements, protect instruments and reduce the velocity of the two spacecraft at lunar arrival to help achieve the extremely low {{convert|50|km|abbr=on}} orbits with separation between the spacecraft (arriving 25 hours apart) of {{convert|175|to|225|km||abbr=on}}.<ref name="MIT-overview">{{cite web | title=GRAIL: Mission Overview | publisher = [[Massachusetts Institute of Technology|MIT]] | url=http://moon.mit.edu/overview.html | |
Unlike the [[Apollo program]] missions, which took three days to reach the Moon, GRAIL made use of a three- to four-month low-energy trans-lunar cruise well outside the Moon's orbit and passing near the Sun-Earth [[Lagrange point#L1|Lagrange point L1]] before looping back to rendezvous with the Moon. This extended and circuitous trajectory enabled the mission to reduce fuel requirements, protect instruments and reduce the velocity of the two spacecraft at lunar arrival to help achieve the extremely low {{convert|50|km|abbr=on}} orbits with separation between the spacecraft (arriving 25 hours apart) of {{convert|175|to|225|km||abbr=on}}.<ref name="MIT-overview">{{cite web | title=GRAIL: Mission Overview | publisher = [[Massachusetts Institute of Technology|MIT]] | url=http://moon.mit.edu/overview.html | access-date = 10 September 2011}}</ref><ref name="MissionDesign">{{cite web | title=Mission Design | url=http://solarsystem.nasa.gov/grail/missiondesign.cfm | publisher=NASA | access-date=10 September 2011 | url-status=dead | archive-url=https://web.archive.org/web/20111003144042/http://solarsystem.nasa.gov/grail/missiondesign.cfm | archive-date=3 October 2011 }}</ref> The very tight tolerances in the flight plan left little room for error correction leading to a launch window lasting one second and providing only two launch opportunities per day.<ref name='launch windows'>{{cite news | author= Justin Ray | title=GRAIL Launch Window Chart | url=http://www.spaceflightnow.com/delta/d356/windows.html | work=SpaceFlight Now | date=17 August 2011 | access-date=9 September 2011}}</ref> |
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===Science phase=== |
===Science phase=== |
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The primary science phase of GRAIL lasted for 88 days, from 7 March 2012 to 29 May 2012. It was followed by a second science phase starting on 8 Aug. |
The primary science phase of GRAIL lasted for 88 days, from 7 March 2012 to 29 May 2012. It was followed by a second science phase starting on 8 Aug. |
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The gravity mapping technique was similar to that used by [[Gravity Recovery and Climate Experiment]] (GRACE), and the spacecraft design was based on [[XSS-11]].<ref>{{cite news | author= Taylor Dinerman | title = Is XSS-11 the answer to America’s quest for Operationally Responsive Space? | work=The Space Review | date= 31 December 2007 | url= http://www.thespacereview.com/article/1026/1 | |
The gravity mapping technique was similar to that used by [[Gravity Recovery and Climate Experiment]] (GRACE), and the spacecraft design was based on [[XSS-11]].<ref>{{cite news | author= Taylor Dinerman | title = Is XSS-11 the answer to America’s quest for Operationally Responsive Space? | work=The Space Review | date= 31 December 2007 | url= http://www.thespacereview.com/article/1026/1 | access-date=31 August 2011}}</ref> |
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The orbital insertion dates were {{Start date|2011|12|31}} (for GRAIL-A) and {{Start date|2012|01|01}} (for GRAIL-B).<ref name=LaunchCBS/> |
The orbital insertion dates were {{Start date|2011|12|31}} (for GRAIL-A) and {{Start date|2012|01|01}} (for GRAIL-B).<ref name=LaunchCBS/> |
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===Final experiment and mission end=== |
===Final experiment and mission end=== |
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At the end of the science phase and a mission extension, the spacecraft were powered down and decommissioned over a five-day period. The spacecraft impacted the lunar surface on December 17, 2012.<ref name="design MIT"/><ref>{{cite web | title= NASA GRAIL Twins Complete Their Moon Impact | url= http://www.nasa.gov/mission_pages/grail/news/grailstatus20121217.html |
At the end of the science phase and a mission extension, the spacecraft were powered down and decommissioned over a five-day period. The spacecraft impacted the lunar surface on December 17, 2012.<ref name="design MIT"/><ref>{{cite web | title= NASA GRAIL Twins Complete Their Moon Impact | url= http://www.nasa.gov/mission_pages/grail/news/grailstatus20121217.html |
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| publisher= NASA | date=17 December 2012| |
| publisher= NASA | date=17 December 2012| access-date = 2012-12-17}}</ref><ref>{{cite news | last=Wall | first= Mike | title= Twin GRAIL probes readied for crash into Moon | url= http://www.nbcnews.com/id/50192371 | work=NBC News | date=13 December 2012 | access-date=18 February 2013}}</ref><ref>{{cite news | last=Wall | first=Mike| title=Twin NASA Probes to Crash into Moon Next Week | url=http://www.space.com/18845-nasa-grail-mission-crash-moon.html | work= Space.com | date=11 December 2012 | access-date=18 February 2013}}</ref><ref>{{cite news | title=Twin NASA spacecraft prepare to crash into moon | url=http://phys.org/news/2012-12-twin-nasa-spacecraft-moon.html | work=Phys.org | date=13 December 2012 | access-date=13 December 2012}}</ref><ref>{{cite news | last=Knapp | first=Alex | title=NASA Prepares To Crash Its Probes Into The Moon | url=https://www.forbes.com/sites/alexknapp/2012/12/14/nasa-prepares-for-its-probes-to-crash-into-the-moon/ | work=Forbes | date=14 December 2012| access-date=2012-12-13}}</ref> Both spacecraft impacted an unnamed lunar mountain between [[Philolaus (crater)|Philolaus]] and [[Mouchez (crater)|Mouchez]] at {{Lunar coords and quad cat|75.62|N|26.63|W}}. Ebb, the lead spacecraft in formation, impacted first. Flow impacted moments later. Each spacecraft was traveling at {{convert|3760|mph|km/s}}. A final experiment was conducted during the final days of the mission. Main engines aboard the spacecraft were fired, depleting remaining fuel. Data from that effort will be used by mission planners to validate fuel consumption [[computer models]] to improve predictions of fuel needs for future missions.<ref>{{cite web | title=NASA Probes Prepare for Mission-Ending Moon Impact| url=http://www.jpl.nasa.gov/news/news.php?release=2012-396&cid=release_2012-396 | publisher=NASA, Jet Propulsion Laboratory| access-date=18 February 2013}}</ref> NASA has announced that the crash site will be named after GRAIL collaborator and first American woman in space, [[Sally Ride]].<ref>{{cite web | author=Mike Wall | title=Moon Probes' Crash Site Named After Sally Ride | url=http://www.space.com/18944-nasa-grail-moon-crash-sally-ride.html | work=Space.com | date=17 December 2012 | access-date=18 February 2013}}</ref> |
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{{multiple image|total_width=600|align=center |
{{multiple image|total_width=600|align=center |
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|header=Moon – [[Oceanus Procellarum]] ("Ocean of Storms")|width1=614 |height1=228 |image1=14-236-LunarGrailMission-OceanusProcellarum-Rifts-Overall-20141001.jpg|caption1=Ancient [[rift valley]]s – rectangular structure (visible – topography – GRAIL gravity gradients) (October 1, 2014).|width2=1500 |height2=1500 |image2=PIA18822-LunarGrailMission-OceanusProcellarum-Rifts-Overall-20141001.jpg|caption2=Ancient [[rift valley]]s – context.|width3=1546 |height3=905 |image3=PIA18821-LunarGrailMission-OceanusProcellarum-Rifts-Closeup-20141001.jpg|caption3=Ancient [[rift valley]]s – closeup (artist's concept).}} |
|header=Moon – [[Oceanus Procellarum]] ("Ocean of Storms")|width1=614 |height1=228 |image1=14-236-LunarGrailMission-OceanusProcellarum-Rifts-Overall-20141001.jpg|caption1=Ancient [[rift valley]]s – rectangular structure (visible – topography – GRAIL gravity gradients) (October 1, 2014).|width2=1500 |height2=1500 |image2=PIA18822-LunarGrailMission-OceanusProcellarum-Rifts-Overall-20141001.jpg|caption2=Ancient [[rift valley]]s – context.|width3=1546 |height3=905 |image3=PIA18821-LunarGrailMission-OceanusProcellarum-Rifts-Closeup-20141001.jpg|caption3=Ancient [[rift valley]]s – closeup (artist's concept).}} |
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Artist's interpretation of the GRAIL tandem spacecraft above the lunar surface.
| |
Operator | NASA / JPL[1][2] |
---|---|
COSPAR ID | 2011-046 (A, B) |
SATCAT no. | 37801, 37802 |
Website | moon |
Mission duration | 1 year, 3 months, 7 days, 9 hours |
Spacecraft properties | |
Manufacturer | Massachusetts Institute of Technology, LMSS |
Launch mass | 307 kg (677 lb) |
Dry mass | 132.6 kg (292 lb) |
Power | (Solar array / Li-ion battery) |
Start of mission | |
Launch date | September 10, 2011, 13:08:52.775 (2011-09-10UTC13:08:52Z) UTC |
Rocket | Delta II 7920H-10 D-356 |
Launch site | Cape Canaveral SLC-17B |
Entered service | December 31, 2011 (Ebb) January 1, 2012 (Flow) |
Orbital parameters | |
Reference system | Selenocentric |
Regime | Polar orbit |
Semi-major axis | 1,788.0 kilometres (1,111.0 mi) |
Periselene altitude | 25 kilometres (16 mi) |
Aposelene altitude | 86 kilometres (53 mi) |
Period | 113 minutes |
Lunar impactor | |
Impact date | GRAIL A: December 17, 2012, 22:28:51 UTC |
Impact site | 75°36′30″N 33°24′15″E / 75.6083°N 33.4043°E / 75.6083; 33.4043 |
Lunar impactor | |
Impact date | GRAIL B: December 17, 2012, 22:29:21 UTC |
Impact site | 75°39′01″N 33°09′51″E / 75.6504°N 33.1643°E / 75.6504; 33.1643 |
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← Kepler
InSight →
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The Gravity Recovery and Interior Laboratory (GRAIL) was an American lunar science mission in NASA's Discovery Program which used high-quality gravitational field mapping of the Moon to determine its interior structure. The two small spacecraft GRAIL A (Ebb) and GRAIL B (Flow)[3][4] were launched on 10 September 2011 aboard a single launch vehicle: the most-powerful configuration of a Delta II, the 7920H-10.[1][5][6] GRAIL A separated from the rocket about nine minutes after launch, GRAIL B followed about eight minutes later. They arrived at their orbits around the Moon 25 hours apart.[7][8] The first probe entered orbit on 31 December 2011 and the second followed on 1 January 2012.[9] The two spacecraft impacted the Lunar surface on December 17, 2012.[10]
Maria Zuber of the Massachusetts Institute of Technology is GRAIL's principal investigator. NASA's Jet Propulsion Laboratory manages the project. As of August 5, 2011[update], the program had cost US$496 million.[11] Upon launch the spacecraft were named GRAIL A and GRAIL B and a contest was opened to school children to select names. Nearly 900 classrooms from 45 states, Puerto Rico and the District of Columbia, participated in the contest. The winning names, Ebb and Flow, were suggested by 4th grade students at Emily Dickinson Elementary SchoolinBozeman, Montana.[4]
Each spacecraft transmitted and received telemetry from the other spacecraft and Earth-based facilities. By measuring the change in distance between the two spacecraft, the gravity field and geological structure of the Moon was obtained. The two spacecraft were able to detect very small changes in the distance between one another. Changes in distance as small as one micrometre were detectable and measurable.[12][13] The gravitational field of the Moon was mapped in unprecedented detail.[14][15]
The data collection phase of the mission lasted from 7 March 2012 to 29 May 2012, for a total of 88 days. A second phase, at a lower altitude, of data collection began 31 August 2012,[16] and was followed by 12 months of data analysis.[14] On 5 December 2012 NASA released a gravity map of the Moon made from GRAIL data.[17] The knowledge acquired will aid understanding of the evolutionary history of the terrestrial planets and computations of lunar orbits.[18]
Thrusters aboard each spacecraft were capable of producing 22 newtons (4.9 lbf).[19] Each spacecraft was fueled with 103.5 kilograms (228 lb) of hydrazine to be used by the thrusters and main engine to enable the spacecraft to enter lunar orbit and transition to the science phase of its mission. The propulsion subsystem consisted of a main fuel tank and a Re-repressurization system which were activated shortly after lunar orbit insertion.[23]
Attempt | Planned | Result | Turnaround | Reason | Decision point | Weather go (%) | Notes |
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1 | 8 Sep 2011, 8:37:06 am | scrubbed[24] | — | high level winds | 8 Sep 2011, 8:30 am | 40% | A weather balloon was released minutes before the decision point to take the latest readings of upper level winds and Air Force weather reconnaissance aircraft were aloft beginning at 7 am. |
2 | 8 Sep 2011, 9:16:12 am | scrubbed[24] | 0 days, 0 hours, 39 minutes | high level winds | 8 Sep 2011, 9:07 am | 40% [25] | Range was reconfigured for omni antennae instead of tracked ones to support 99 degree azimuth. |
3 | 9 Sep 2011, 8:33:25 am | abandoned[24] | 0 days, 23 hours, 17 minutes | rocket propulsion | 40% | An issue with the rocket's propulsion system was detected while the Delta 2 rocket was drained of fuel. | |
4 | 10 Sep 2011, 8:29:45 am | scrubbed[24] | 0 days, 23 hours, 56 minutes | high level winds | 10 Sep 2011, 8:21 am | 60% | |
5 | 10 Sep 2011, 9:08:52 am | Success[24] | 0 days, 0 hours, 39 minutes |
Unlike the Apollo program missions, which took three days to reach the Moon, GRAIL made use of a three- to four-month low-energy trans-lunar cruise well outside the Moon's orbit and passing near the Sun-Earth Lagrange point L1 before looping back to rendezvous with the Moon. This extended and circuitous trajectory enabled the mission to reduce fuel requirements, protect instruments and reduce the velocity of the two spacecraft at lunar arrival to help achieve the extremely low 50 km (31 mi) orbits with separation between the spacecraft (arriving 25 hours apart) of 175 to 225 km (109 to 140 mi).[18][26] The very tight tolerances in the flight plan left little room for error correction leading to a launch window lasting one second and providing only two launch opportunities per day.[25]
The primary science phase of GRAIL lasted for 88 days, from 7 March 2012 to 29 May 2012. It was followed by a second science phase starting on 8 Aug.
The gravity mapping technique was similar to that used by Gravity Recovery and Climate Experiment (GRACE), and the spacecraft design was based on XSS-11.[27]
The orbital insertion dates were December 31, 2011 (2011-12-31) (for GRAIL-A) and January 1, 2012 (2012-01-01) (for GRAIL-B).[24]
The spacecraft were operated over the 88-day acquisition phase, divided into three 27.3 day long nadir-pointed mapping cycles. Twice each day there was an 8-hour pass in view of the Deep Space Network for transmission of science and "E/PO MoonKam" data.[28]
At the end of the science phase and a mission extension, the spacecraft were powered down and decommissioned over a five-day period. The spacecraft impacted the lunar surface on December 17, 2012.[28][29][30][31][32][33] Both spacecraft impacted an unnamed lunar mountain between Philolaus and Mouchezat75°37′N 26°38′W / 75.62°N 26.63°W / 75.62; -26.63. Ebb, the lead spacecraft in formation, impacted first. Flow impacted moments later. Each spacecraft was traveling at 3,760 miles per hour (1.68 km/s). A final experiment was conducted during the final days of the mission. Main engines aboard the spacecraft were fired, depleting remaining fuel. Data from that effort will be used by mission planners to validate fuel consumption computer models to improve predictions of fuel needs for future missions.[34] NASA has announced that the crash site will be named after GRAIL collaborator and first American woman in space, Sally Ride.[35]
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