Editing NEAR Shoemaker (section)

==Mission profile==
[[File:Eros - PIA02923 (color).jpg|thumb|330x330px|Near-Earth asteroid [[433 Eros|Eros]] as seen from the ''NEAR'' spacecraft.]]

===Summary===
The mission's primary goal was to study the near-Earth asteroid [[433 Eros]] from orbit for approximately one year. Eros is an [[S-type asteroid]] approximately 13 × 13 × 33&nbsp;km in size, the second largest near-Earth asteroid. Initially, the orbit was circular with a radius of 200&nbsp;km. The orbit radius was brought down in stages to a 50 × 50&nbsp;km orbit on April 30, 2000, and decreased to 35 × 35&nbsp;km on July 14, 2000. The orbit was raised over succeeding months to a 200 × 200&nbsp;km orbit and then slowly decreased and altered to a 35 × 35&nbsp;km retrograde orbit on December 13, 2000. The mission ended with a touchdown in Eros's "saddle" region on February 12, 2001.

Some scientists claim that the mission's ultimate goal was to link Eros, an asteroidal body, to meteorites recovered on Earth. With sufficient data on chemical composition, a causal link could be established between Eros and other S-type asteroids, and those meteorites believed to be pieces of S-type asteroids (perhaps Eros itself). Once this connection is established, meteorite material can be studied with large, complex, and evolving equipment, and the results can be extrapolated to bodies in space. ''NEAR'' did not prove or disprove this link to the satisfaction of scientists.<!-- However, it is undeniable that ''NEAR'' data advanced the field of asteroidal studies tremendously.{{citation needed|date=August 2014}} Please do not uncomment this without finding a reference. -->

Between December 1999 and February 2001, ''NEAR'' used its gamma-ray spectrometer to detect [[gamma-ray bursts]] as part of the [[InterPlanetary Network]].<ref name=Trombka />

===The journey to Mathilde===
[[File:NEARlaunch.jpg|thumb|left|Launch of ''NEAR'', February 1996]]
After launching on a Delta 7925-8 (a [[Delta II]] launch vehicle with nine strap-on solid-rocket boosters and a [[Star 48]] (PAM-D) third stage) on February 17, 1996, and exited from Earth orbit, ''NEAR'' entered the first part of its cruise phase. ''NEAR'' spent most of the cruise phase in a minimal activity "hibernation" state, which ended a few days before the flyby of the 61&nbsp;km diameter asteroid [[253 Mathilde]].<ref name="NSSDC" />

[[File:(253) mathilde crop.jpg|thumb|right|One of the images from the flyby of [[253 Mathilde]]]]
On June 27, 1997, ''NEAR'' flew by Mathilde within 1200&nbsp;km at 12:56 UT at 9.93&nbsp;km/s, returning imaging and other instrument data. The flyby produced over 500 images, covering 60% of Mathilde's surface,<ref name="flyby">{{cite web | last=Williams | first=David R. | date=December 18, 2001 | url=http://nssdc.gsfc.nasa.gov/planetary/mission/near/near_mathilde.html | title=NEAR Flyby of Asteroid 253 Mathilde | publisher=[[NASA]] | access-date=August 10, 2006 }}</ref> as well as gravitational data allowing calculations of Mathilde's dimensions and mass.<ref name="Yeomans 1997">{{cite journal | author=D. K. Yeomans |display-authors=etal | title=Estimating the mass of asteroid 253 Mathilde from tracking data during the NEAR flyby | journal=[[Science (journal)|Science]] | volume=278 | issue=5346 | date=1997 | pages=2106–9 | pmid=9405343 | url=http://www.sciencemag.org/cgi/content/full/278/5346/2106 | access-date=August 29, 2007 | doi=10.1126/science.278.5346.2106 | bibcode=1997Sci...278.2106Y}}</ref>

===The journey to Eros===
On July 3, 1997, ''NEAR'' executed the first major deep space maneuver, a two-part burn of the main 450&nbsp;N thruster. This decreased the velocity by 279&nbsp;m/s and lowered [[perihelion]] from 0.99&nbsp;[[astronomical unit|AU]] to 0.95&nbsp;AU. The Earth [[gravity assist]] swingby occurred on January 23, 1998, at 7:23 UT. The closest approach was 540&nbsp;km, altering the orbital [[inclination]] from 0.5 to 10.2&nbsp;degrees and the [[aphelion]] distance from 2.17 to 1.77&nbsp;AU, nearly matching those of Eros. Instrumentation was active at this time.<ref name="NSSDC" />

===Failure of first attempt at orbital insertion===
The first of four scheduled rendezvous burns was attempted on December 20, 1998, at 22:00 UT. The burn sequence was initiated but immediately aborted. The spacecraft subsequently entered [[safe mode (spacecraft)|safe mode]] and began tumbling. The spacecraft's [[Rocket engine|thrusters]] fired thousands of times during the anomaly, which expended 29&nbsp;kg of propellant, reducing the program's propellant margin to zero. This anomaly almost resulted in the loss of the spacecraft due to a lack of solar orientation and subsequent battery drain. Contact between the spacecraft and mission control could not be established for over 24 hours. The root cause of this incident has not been determined, but software and operational errors contributed to the severity of the anomaly.<ref>{{cite web | url=http://near.jhuapl.edu/anom/Hoffman.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://near.jhuapl.edu/anom/Hoffman.pdf |archive-date=2022-10-09 |url-status=live | title=The NEAR Rendezvous Burn Anomaly of December 1998  |date=November 1999 | publisher=Final Report of the NEAR Anomaly Review Board | access-date=February 2, 2017}}</ref>

The original mission plan called for the four burns to be followed by an orbit insertion burn on January 10, 1999, but the abort of the first burn and loss of communication made this impossible. A new plan was put into effect in which ''NEAR'' flew by Eros on December 23, 1998, at 18:41:23 UT at a speed of 965&nbsp;m/s and a distance of 3827&nbsp;km from the center of mass of Eros. The camera took images of Eros, data were collected by the near [[Infrared|IR]] spectrograph, and radio tracking was performed during the flyby. A rendezvous maneuver was performed on January 3, 1999, involving a thruster burn to match ''NEAR''{{'s}} orbital speed to that of Eros. A [[hydrazine]] thruster burn took place on January 20 to fine-tune the trajectory. On August 12, a two-minute thruster burn slowed the spacecraft velocity relative to Eros to 300&nbsp;km/h.<ref name="NSSDC" />

===Orbital insertion===

[[Orbital insertion]] around Eros occurred on February 14, 2000, at 15:33 UT (10:33 EST) after ''NEAR'' completed a 13-month heliocentric orbit which closely matched the orbit of Eros. A rendezvous maneuver was completed on February 3 at 17:00 UT, slowing the spacecraft from 19.3 to 8.1&nbsp;m/s relative to Eros. Another maneuver took place on February 8, increasing the relative velocity slightly to 9.9&nbsp;m/s. Searches for satellites of Eros took place on January 28 and February 4, and 9; none were found. The scans were for scientific purposes and to mitigate any possible collision with a satellite. ''NEAR'' went into a 321×366&nbsp;km elliptical orbit around Eros on February 14. The orbit was slowly decreased to a 35&nbsp;km circular polar orbit by July 14. ''NEAR'' remained in this orbit for ten days and then was backed out in stages to a 100&nbsp;km circular orbit by September 5, 2000. Maneuvers in mid-October led to a flyby of Eros within 5.3&nbsp;km of the surface at 07:00 UT on October 26.<ref name="NSSDC" />

<gallery mode=packed heights=200px>
File:NEARtrajectory.jpg|Trajectory graphic depicting the voyage of the ''NEAR'' spacecraft
File:Animation of NEAR Shoemaker trajectory.gif|Animation of ''NEAR Shoemaker''{{'s}} trajectory from February 19, 1996, to February 12, 2001{{hlist|{{legend2|magenta|''NEAR Shoemaker''}}|{{legend2|lime|[[433 Eros|Eros]]}}|{{legend2|RoyalBlue|[[Earth]]}}|{{legend2|cyan|[[253 Mathilde|Mathilde]]}}|{{legend2|yellow|[[Sun]]}}}}
File:Animation of NEAR Shoemaker trajectory around 433 Eros.gif|Animation of ''NEAR Shoemaker''{{'s}} trajectory around Eros from April 1, 2000, to February 12, 2001{{hlist|{{legend2|magenta|''NEAR Shoemaker''}}|{{legend2|Lime|[[433 Eros]]}}}}
</gallery>

===Orbits and landing===
[[File:Erosregolith.jpg|thumb|right|200px|Eros from approximately 250&nbsp;meters altitude (area in image is roughly 12&nbsp;meters across). This image was taken during ''NEAR''{{'s}} descent to the surface of the asteroid.<ref>{{cite web |title=Final Images from 2001 Feb 12 |url=http://near.jhuapl.edu/iod/20010214/index.html |website=near.jhuapl.edu |access-date=17 April 2022}}</ref>]]

Following the flyby, ''NEAR'' moved to a 200&nbsp;km circular orbit and shifted the orbit from [[direct motion|prograde]] near-polar to a retrograde near-equatorial orbit. By December 13, 2000, the orbit was shifted back to a circular 35&nbsp;km low orbit. Starting on January 24, 2001, the spacecraft began a series of close passes (5 to 6&nbsp;km) to the surface and, on January 28, passed 2 to 3&nbsp;km from the asteroid. The spacecraft then made a slow controlled descent to the surface of Eros, ending with a touchdown just to the south of the saddle-shaped feature Himeros on February 12, 2001, at approximately 20:01 UT (3:01&nbsp;p.m. EST). To the surprise of the controllers, the spacecraft was undamaged and operational after the landing at an estimated speed of 1.5 to 1.8&nbsp;meters per second (thus becoming the first spacecraft to soft-land on an asteroid).<ref>{{cite book|url=https://www.nasa.gov/sites/default/files/atoms/files/beyond-earth-tagged.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.nasa.gov/sites/default/files/atoms/files/beyond-earth-tagged.pdf |archive-date=2022-10-09 |url-status=live|title=Beyond Earth: A Chronicle of Deep Space Exploration, 1958–2016|page=2|last1=Siddiqi|first1=Asif A.|lccn=2017059404|isbn=9781626830424|publisher=NASA History Program Office|edition=second|year=2018|id=SP2018-4041|series=The NASA history series|location=Washington, DC}}</ref> After receiving an extension of antenna time on the [[Deep Space Network]], the spacecraft's gamma-ray spectrometer was reprogrammed to collect data on Eros's composition from a vantage point about {{convert|4|in}} from the surface where it was ten times more sensitive than when it was used in orbit.<ref name=phone>{{Cite news | title = The End of an Asteroidal Adventure: NEAR Shoemaker Phones Home for the Last Time | last = Worth | first = Helen | date = February 28, 2001 | publisher = [[Applied Physics Lab]] | url = http://near.jhuapl.edu/news/flash/01feb28.html}}</ref> This increase in sensitivity was in part due to the increased ratio of the signal from Eros compared to the noise generated by the probe itself.<ref name=Trombka /> The impact of cosmic rays on the sensor was also reduced by about 50%.<ref name=Trombka>{{cite journal |author=Trombka, J. I. |display-authors=4 | author2=Nittler, L. R. |author3=Starr, R. D. |author4=Evans, L. G. |author5=Mccoy, T. J. |author6=Boynton, W. V. |author7=Burbine, T. H. |author8=Brückner, J. |author9=Gorenstein, P. |author10=Squyres, S. W. |author11=Reedy, R. C. |author12=Goldsten, J. O. |author13=Lim, L. |author14=Hurley, K. |author15=Clark, P. E. |author16=Floyd, S. R. |author17=Mcclanahan, T. P. |author18=Mccartney, E. |author19=Branscomb, J. |author20=Bhangoo, J. S. |author21=Mikheeva, I. |author22=Murphy, M. E. | name-list-style=amp |date=2001 |title=The NEAR-Shoemaker x-ray/gamma-ray spectrometer experiment: Overview and lessons learned |journal=Meteoritics & Planetary Science |volume=36 |issue=12 |pages=1605–1616 | doi=10.1111/j.1945-5100.2001.tb01852.x |bibcode = 2001M&PS...36.1605T |doi-access=free }}</ref>

At 7 p.m. EST on February 28, 2001, the last data signals were received from ''NEAR'' Shoemaker before it was shut down. A final attempt to communicate with the spacecraft on December 10, 2002, was unsuccessful. This was likely due to the extreme −279&nbsp;°F (−173&nbsp;°C, 100 [[kelvin|K]]) conditions the probe experienced while on Eros.<ref name=silent>{{Cite news | title ='NEAR Shoemaker's Silent Treatment | date = February 23, 2001 | publisher = [[Applied Physics Laboratory]] | url = http://near.jhuapl.edu/news/flash/02dec12_1.html}}</ref>