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{{Short description|American robotic space probe launched in 1996 to study the near-Earth asteroid 433 Eros}}
{{Short description|American space probe to asteroid (1996–2001)}}
{{Redirect|NEAR|other uses|Near (disambiguation){{!}}Near}}
{{Redirect|NEAR|other uses|Near (disambiguation){{!}}Near}}
{{Use mdy dates|date=May 2020}}
{{Use mdy dates|date=May 2020}}
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| name = ''NEAR Shoemaker''
| name = ''NEAR Shoemaker''
| image = NEAR Shoemaker spacecraft model.png
| image = NEAR Shoemaker spacecraft model.png
| image_caption = Model of the ''NEAR Shoemaker'' spacecraft
| image_caption = Artist's rendering of the ''NEAR Shoemaker'' spacecraft
| image_alt = Model of a cylindrical spacecraft with four square-shaped solar panels at one of the craft's edges
| image_alt = Model of a cylindrical spacecraft with four square-shaped solar panels at one of the craft's edges


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| manufacturer =
| manufacturer =
| launch_mass = 805 kg<ref>{{cite web|url=https://solarsystem.nasa.gov/missions/near-shoemaker/in-depth/ |title=NEAR Shoemaker |publisher=NASA's Solar System Exploration website |access-date=December 1, 2022}}</ref>
| launch_mass = ~{{convert|800|kg|lb}}
| dry_mass = {{convert|487|kg|lb}}
| dry_mass = {{convert|487|kg|lb}}
| power = 1,800 [[Watt|W]]
| power = 1,800 [[Watt|W]]
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| insignia = NEAR Shoemaker insignia.png
| insignia = NEAR Shoemaker insignia.png
| insignia_caption = Official insignia of the ''NEAR Shoemaker'' mission
| insignia_caption = Official insignia of the ''NEAR Shoemaker'' mission
| insignia_alt = An artwork of a spacecraft hovering above an asteroid, enclosed in an equilateral triangle with thick, red border. The words "JHU/APL", "NASA", and "NEAR" are printed in bold white font, on the left, right, and bottom sides of the triangle's borders.
| insignia_alt = An artwork of a spacecraft hovering above an asteroid, enclosed in an equilateral triangle with a thick, red border. The words "JHU/APL", "NASA", and "NEAR" are printed in bold white font, on the left, right, and bottom sides of the triangle's borders.


| programme = '''[[Discovery program]]'''
| programme = '''[[Discovery program]]'''
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}}
}}


'''''Near Earth Asteroid Rendezvous – Shoemaker''''' ('''''NEAR Shoemaker'''''), renamed after its 1996 launch in honor of planetary scientist [[Eugene Merle Shoemaker|Eugene Shoemaker]], was a [[Robotic spacecraft|robotic]] [[space probe]] designed by the [[Johns Hopkins University]] [[Applied Physics Laboratory]] for [[NASA]] to study the [[near-Earth asteroid]] [[433 Eros|Eros]] from close orbit over a period of a year. It was the first spacecraft to successfully orbit an asteroid and also land on an asteroid.<ref name=twofirsts>{{cite news|url=https://solarsystem.nasa.gov/missions/near-shoemaker/in-depth/|title=NEAR Shoemaker|publisher=NASA|accessdate=April 26, 2021}}</ref> In February 2000, the mission succeeded in closing in with the asteroid and orbited it several times, finally terminating just over two weeks after touching down on the asteroid on February 12, 2001.<ref name=twofirsts />
'''''Near Earth Asteroid Rendezvous – Shoemaker''''' ('''''NEAR Shoemaker'''''), renamed after its 1996 launch in honor of planetary scientist [[Eugene Merle Shoemaker|Eugene Shoemaker]], was a [[Robotic spacecraft|robotic]] [[space probe]] designed by the [[Johns Hopkins University]] [[Applied Physics Laboratory]] for [[NASA]] to study the [[near-Earth asteroid]] [[433 Eros|Eros]] from close orbit over a period of a year. It was the first spacecraft to orbit an asteroid and land on it successfully.<ref name=twofirsts>{{cite news|url=https://solarsystem.nasa.gov/missions/near-shoemaker/in-depth/|title=NEAR Shoemaker|publisher=NASA|accessdate=April 26, 2021}}</ref> In February 2000, the mission closed in on the asteroid and orbited it. On February 12, 2001, Shoemaker touched down on the asteroid and was terminated just over two weeks later.<ref name=twofirsts />


The primary scientific objective of ''NEAR'' was to return data on the bulk properties, composition, [[mineral]]ogy, morphology, internal [[mass]] distribution and [[magnetic field]] of Eros. Secondary objectives include studies of [[regolith]] properties, interactions with the [[solar wind]], possible current activity as indicated by dust or gas, and the asteroid spin state. This data will be used to help understand the characteristics of [[asteroid]]s in general, their relationship to [[meteoroid]]s and [[comet]]s, and the conditions in the early Solar System. To accomplish these goals, the spacecraft was equipped with an [[X-ray spectroscopy|X-ray]]/[[gamma-ray spectrometer]], a near-infrared imaging spectrograph, a multi-spectral camera fitted with a [[CCD imaging]] detector, a [[laser range-finder|laser rangefinder]], and a [[magnetometer]]. A radio science experiment was also performed using the ''NEAR'' tracking system to estimate the [[gravitational|gravity]] field of the asteroid. The total mass of the instruments was {{cvt|56|kg}}, requiring 80 watts of power.
The primary scientific objective of ''NEAR'' was to return data on the bulk properties, composition, [[mineral]]ogy, morphology, internal [[mass]] distribution, and [[magnetic field]] of Eros. Secondary objectives include studies of [[regolith]] properties, interactions with the [[solar wind]], possible current activity as indicated by dust or gas, and the asteroid spin state. This data was used to help understand the characteristics of [[asteroid]]s in general, their relationship to [[meteoroid]]s and [[comet]]s, and the conditions in the early Solar System. To accomplish these goals, the spacecraft was equipped with an [[X-ray spectroscopy|X-ray]]/[[gamma-ray spectrometer]], a near-infrared imaging spectrograph, a multi-spectral camera fitted with a [[CCD imaging]] detector, a [[laser range-finder|laser rangefinder]], and a [[magnetometer]]. A radio science experiment was also performed using the ''NEAR'' tracking system to estimate the [[gravitational|gravity]] field of the asteroid. The total mass of the instruments was {{cvt|56|kg}}, requiring 80 watts of power.


==Development==
==Development==
A previous plan for the mission was for it to go to [[4660 Nereus]] and do a flyby of [[2019 van Albada]] en route.<ref name=ads/> In January 2000 it would rendezvous with Nereus but instead of staying it would visit multiple asteroids and comets.<ref name=ads/> Some of the choices that were discussed were [[2P/Encke]], [[433 Eros]] (which became the mission's primary target), [[1036 Ganymed]], [[4 Vesta]], and [[4015 Wilson–Harrington]].<ref name=ads/>
NEAR was the first robotic [[space probe]] built by [[Johns Hopkins University]]'s [[Applied Physics Laboratory]] (APL).<ref name="lawler20020104">{{Cite journal |last=Lawler |first=Andrew |date=2002-01-04 |title=Lab Rivalry Spices Up Solar System Exploration |url=https://www.science.org/doi/10.1126/science.295.5552.33 |journal=Science |language=en |publication-date=2002-01-04 |volume=295 |issue=5552 |pages=33 |doi=10.1126/science.295.5552.33 |pmid=11778023 |s2cid=109108852 |issn=0036-8075 |access-date=2022-11-16}}</ref> A previous plan for the mission was for it to go to [[4660 Nereus]] and do a flyby of [[2019 van Albada]] en route.<ref name=ads/> In January 2000, it would rendezvous with Nereus, but instead of staying, it would visit multiple asteroids and comets.<ref name=ads/> Some of the choices that were discussed were [[2P/Encke]], [[433 Eros]] (which became the mission's primary target), [[1036 Ganymed]], [[4 Vesta]], and [[4015 Wilson–Harrington]].<ref name=ads/>
The Small-Body Grand Tour was a plan for visiting two asteroids and two comets over a span of a decade with the spacecraft.<ref name=ads>[http://adsabs.harvard.edu/abs/1993STIA...9581370F Extended-mission opportunities for a Discovery-class asteroid rendezvous mission]</ref>
The Small-Body Grand Tour was a plan to visit two asteroids and two comets over a decade with the spacecraft.<ref name=ads>[http://adsabs.harvard.edu/abs/1993STIA...9581370F Extended-mission opportunities for a Discovery-class asteroid rendezvous mission]</ref>


==Mission profile==
==Mission profile==
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===Summary===
===Summary===
The primary goal of the mission was to study the near-Earth asteroid [[433 Eros]] from orbit for approximately one year. Eros is an [[S-type asteroid]] approximately 13 &times; 13 &times; 33&nbsp;km in size, the second largest near-Earth asteroid. Initially the orbit was circular with a radius of 200&nbsp;km. The radius of the orbit was brought down in stages to a 50 &times; 50&nbsp;km orbit on April 30, 2000 and decreased to 35 &times; 35&nbsp;km on July 14, 2000. The orbit was raised over succeeding months to a 200 &times; 200&nbsp;km orbit and then slowly decreased and altered to a 35 &times; 35&nbsp;km retrograde orbit on December 13, 2000. The mission ended with a touchdown in the "saddle" region of Eros on February 12, 2001.
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 ultimate goal of the mission 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 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. -->
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 />
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 />
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===The journey to Mathilde===
===The journey to Mathilde===
[[File:NEARlaunch.jpg|thumb|left|Launch of ''NEAR'', February 1996]]
[[File:NEARlaunch.jpg|thumb|left|Launch of ''NEAR'', February 1996]]
After launch 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 exit 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" />
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]]]]
[[File:(253) mathilde crop.jpg|thumb|right|One of the images from the flyby of [[253 Mathilde]]]]
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===The journey to Eros===
===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" />
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===
===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 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 | 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 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. Images of Eros were taken by the camera, 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" />
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===

⚫
[[File:NEARtrajectory.jpg|thumb|right|275px|Trajectory graphic depicting the voyage of the ''NEAR'' spacecraft.]]
⚫
[[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" />
⚫
[[File:Animation of NEAR Shoemaker trajectory.gif|275px|thumb|right|Animation of ''NEAR Shoemaker''{{'s}} trajectory from February 19, 1996, to February 12, 2001{{hlist|{{legend2|magenta|''NEAR Shoemaker''}}|{{legend2|lime|Eros}}|{{legend2|RoyalBlue|Earth}}|{{legend2|cyan|Mathilde}}|{{legend2|yellow|Sun}}}}]]

⚫
[[File:Animation of NEAR Shoemaker trajectory around 433 Eros.gif |275px|thumb |right |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 mode=packed heights=200px>
⚫
[[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 chances of 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 10 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" />
⚫
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===
===Orbits and landing===
[[File:Erosregolith.jpg|thumb|left|200px|Eros asteroid from approximately 250&nbsp;meters altitude (area in image is roughly 12&nbsp;meters across [http://near.jhuapl.edu/iod/20010214/index.html]). This image was taken during ''NEAR''{{'s}} descent to the surface of the asteroid.]]
[[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|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 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>
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>
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>


==Spacecraft and subsystems==
==Spacecraft and subsystems==
[[File:NEARCraft.jpg|thumb|right|200px|''NEAR'' spacecraft inside its [[Delta II]] rocket.]]
[[File:NEARCraft.jpg|thumb|right|200px|''NEAR'' spacecraft inside its [[Delta II]] rocket.]]


===Spacecraft===
The spacecraft has the shape of an octagonal prism, approximately 1.7 m on a side, with four fixed [[gallium arsenide]] [[Photovoltaic module|solar panel]]s in a windmill arrangement, a fixed 1.5 m [[X band|X-band]] high-gain radio antenna with a [[magnetometer]] mounted on the antenna feed, and an X-ray solar monitor on one end (the forward deck), with the other instruments fixed on the opposite end (the aft deck). Most electronics were mounted on the inside of the decks. The propulsion module was contained in the interior. The decision to mount instruments on the body of the spacecraft rather than using booms resulted in the gamma-ray spectrometer needing to be shielded from noise generated by the craft.<ref name=Trombka /> A [[bismuth germanate]] shield was used although this proved only moderately effective.<ref name=Trombka />
The spacecraft has the shape of an octagonal prism, approximately 1.7 m on a side, with four fixed [[gallium arsenide]] [[Photovoltaic module|solar panel]]s in a windmill arrangement, a fixed 1.5 m [[X band|X-band]] high-gain radio antenna with a [[magnetometer]] mounted on the antenna feed, and an X-ray solar monitor on one end (the forward deck), with the other instruments fixed on the opposite end (the aft deck). Most electronics were mounted on the inside of the decks. The propulsion module was contained in the interior. The decision to mount instruments on the body of the spacecraft rather than using booms resulted in the gamma-ray spectrometer needing to be shielded from noise generated by the craft.<ref name=Trombka /> A [[bismuth germanate]] shield was used, although this proved only moderately effective.<ref name=Trombka />


The craft was three-axis stabilized and used a single [[bipropellant rocket|bipropellant]] ([[hydrazine]] / [[nitrogen tetroxide]]) 450 [[newton (unit)|newton]] (N) main thruster,<ref>{{Cite web |url=https://nssdc.gsfc.nasa.gov/planetary/mission/near/near_traj.html |title=NEAR Mission Profile |last=Williams |first=David R. |date=February 8, 2000 |website=NASA Goddard Space Flight Center |access-date=February 5, 2019 }}</ref> and four 21&nbsp;N and seven 3.5&nbsp;N hydrazine thrusters for propulsion, for a total [[delta-V]] potential of 1450&nbsp;m/s. Attitude control was achieved using the hydrazine thrusters and four reaction wheels. The propulsion system carried 209&nbsp;kg of hydrazine and 109&nbsp;kg of NTO oxidizer in two oxidizer and three fuel tanks.<ref name="NSSDC">{{Cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1996-008A |title=NEAR Shoemaker |website=NASA Space Science Data Coordinated Archive |access-date=February 5, 2019}}</ref>
The craft was three-axis stabilized and used a single [[bipropellant rocket|bipropellant]] ([[hydrazine]] / [[nitrogen tetroxide]]) 450 [[newton (unit)|newton]] (N) main thruster,<ref>{{Cite web |url=https://nssdc.gsfc.nasa.gov/planetary/mission/near/near_traj.html |title=NEAR Mission Profile |last=Williams |first=David R. |date=February 8, 2000 |website=NASA Goddard Space Flight Center |access-date=February 5, 2019 }}</ref> and four 21&nbsp;N and seven 3.5&nbsp;N hydrazine thrusters for propulsion, for a total [[delta-V]] potential of 1450&nbsp;m/s. Attitude control was achieved using the hydrazine thrusters and four reaction wheels. The propulsion system carried 209&nbsp;kg of hydrazine and 109&nbsp;kg of NTO oxidizer in two oxidizer and three fuel tanks.<ref name="NSSDC">{{Cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1996-008A |title=NEAR Shoemaker |website=NASA Space Science Data Coordinated Archive |access-date=February 5, 2019}}</ref>


Power was provided by four 1.8 by 1.2&nbsp;meter [[gallium arsenide]] solar panels which could produce 400&nbsp;[[watt]]s at 2.2&nbsp;[[Astronomical unit|AU]] (329,000,000&nbsp;km), ''NEAR''{{'s}} maximum distance from the Sun, and 1800 watts at one AU (150,000,000&nbsp;km). Power was stored in a nine-ampere-hour, 22-cell rechargeable super [[nickel-cadmium]] battery.<ref name="NSSDC"/>
Power was provided by four 1.8 by 1.2&nbsp;meter [[gallium arsenide]] solar panels, which could produce 400&nbsp;[[watt]]s at 2.2&nbsp;[[Astronomical unit|AU]] (329,000,000&nbsp;km), ''NEAR''{{'s}} maximum distance from the Sun and 1800 watts at one AU (150,000,000&nbsp;km). Power was stored in a nine-ampere-hour, 22-cell rechargeable super [[nickel-cadmium]] battery.<ref name="NSSDC"/>


⚫
Spacecraft guidance was achieved through the use of a sensor suite of five digital solar attitude detectors, an inertial measurement unit (IMU), and a star tracker camera pointed opposite the instrument pointing direction. The IMU contained hemispherical resonators [[gyroscope]]s and accelerometers. Four [[reaction wheel]]s (arranged so that any three can provide complete three-axis control) were used for normal attitude control. The thrusters were used to dump [[angular momentum]] from the reaction wheels, as well as for rapid slew and propulsive maneuvers. Attitude control was to 0.1 degree, line-of-sight pointing stability is within 50 microradians over one second, and post-processing attitude knowledge is to 50 microradians.<ref name="NSSDC"/>
⚫
[[File:NEAR Spacecraft Configuration.jpg|thumb|left|Diagram showing location of ''NEAR'' science instruments.]]

⚫
Spacecraft guidance was achieved through the use of a sensor suite of five digital solar attitude detectors, an inertial measurement unit (IMU), and a star tracker camera pointed opposite the instrument pointing direction. The IMU contained hemispherical resonator [[gyroscope]]s and accelerometers. Four [[reaction wheel]]s (arranged so that any three can provide complete three-axis control) were used for normal attitude control. The thrusters were used to dump [[angular momentum]] from the reaction wheels, as well as for rapid slew and propulsive maneuvers. Attitude control was to 0.1 degree, line-of-sight pointing stability is within 50 microradians over one second, and post-processing attitude knowledge is to 50 microradians.<ref name="NSSDC"/>


The command and data handling subsystem was composed of two redundant command and telemetry processors and solid state recorders, a power switching unit, and an interface to two redundant [[MIL-STD-1553|1553 standard data buses]] for communications with other subsystems.
The command and data handling subsystem was composed of two redundant command and telemetry processors and solid state recorders, a power switching unit, and an interface to two redundant [[MIL-STD-1553|1553 standard data buses]] for communications with other subsystems.
Line 119: Line 122:
</ref>
</ref>


The solid state recorders are constructed from 16 Mbit [[International Business Machines|IBM]] Luna-C [[DRAM]]s. One recorder has 1.1 [[gigabit]]s of storage, the other has 0.67 gigabits.<ref name="NSSDC"/>
The solid-state recorders are constructed from 16 Mbit [[International Business Machines|IBM]] Luna-C [[DRAM]]s. One recorder has 1.1 [[gigabit]]s of storage, and the other has 0.67 gigabits.<ref name="NSSDC"/>

⚫
The ''NEAR'' mission was the first launch of NASA's [[Discovery Program]], a series of small-scale spacecraft designed to proceed from development to flight in under three years for a cost of less than $150 million. The construction, launch, and 30-day cost for this mission is estimated at $122 million. The final total mission cost was $224 million, which consisted of $124.9 million for spacecraft development, $44.6 million for launch support and tracking, and $54.6 million for mission operations and data analysis.<ref name=FAQ>{{Cite web | title = NEAR: FAQ | publisher = [[Applied Physics Lab]] | url = http://near.jhuapl.edu/intro/faq.html}}</ref>


===Scientific payload and experiments===
⚫
The ''NEAR'' mission was the first launch of NASA's [[Discovery Program]], a series of small-scale spacecraft designed to proceed from development to flight in under three years for a cost of less than $150 million. The construction, launch, and 30-day cost for this mission is estimated at $122 million. The final total mission cost was $224 million which consisted of $124.9 million for spacecraft development, $44.6 million for launch support and tracking, and $54.6 million for mission operations and data analysis.<ref name=FAQ>{{Cite web | title = NEAR: FAQ | publisher = [[Applied Physics Lab]] | url = http://near.jhuapl.edu/intro/faq.html}}</ref>
⚫
[[File:NEAR Spacecraft Configuration.jpg|thumb|right|Diagram showing location of ''NEAR'' science instruments.]]
The science payload includes:<ref>{{cite journal |last1=Santo |first1=A. G. |last2=Lee |first2=S. C. |last3=Gold |first3=R. E. |title=NEAR spacecraft and instrumentation. |journal=Journal of the Astronautical Sciences |date=1995 |volume=43 |issue=4 |pages=373–397}}</ref>
* The Multi-Spectral Imager (MSI), designed and built by the [[Johns Hopkins University]] [[Applied Physics Laboratory]], provided visible images of the asteroid's surface.
* The NEAR IR Spectrograph (NIS) covers a 0.8 to 2.6-micrometer spectral range in 62 bins.
* A three-axis fluxgate magnetometer supplied by NASA's [[Goddard Space Flight Center]] can measure the asteroid's magnetic field from DC to 10&nbsp;Hz.
* The X-ray/Gamma-Ray Spectrometer (XGRS) is two instruments. The x-ray spectrometer measures x-ray fluorescence on the asteroid excited by solar flare x-rays. The gamma-ray spectrometer is a NaI scintillator with an active BGO shield.
* The laser rangefinder (NLR) is a direct-detection single-pulse rangefinder.


==References==
==References==
Line 127: Line 139:


* Text adapted from public domain NASA [https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1996-008A webpage].
* Text adapted from public domain NASA [https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1996-008A webpage].
* {{cite journal | title= The elemental composition of asteroid 433 Eros: Results of the NEAR-Shoemaker x-ray spectrometer |author=Trombka JI |display-authors=4 | author2=Squyres SW |author3=Bruckner J |author4= Boynton WV |author5= Reedy RC |author6=McCoy TJ |author7=Gorenstein P |author8=Evans LG |author9=Arnold JR |author10=Starr RD |author11=Nittler LR |author12=Murphy ME |author13=Mikheeva I |author14=McNutt RL |author15=McClanahan TP |author16=McCartney E |author17=Goldsten JO |author18=Gold RE |author19= Floyd SR |author20=Clark PE |author21=Burbine TH |author22=Bhangoo JS |author23=Bailey SH |author24= Petaev M|journal=Science|volume= 289 |pages=2101–2105 | date=2000 | doi =10.1126/science.289.5487.2101 | pmid= 11000107 | issue= 5487|bibcode = 2000Sci...289.2101T |s2cid=29691912 |url=https://semanticscholar.org/paper/7f5ef06fcce521aa62fcdb203efa87b8a6a40720 }}
* {{cite journal | title= The elemental composition of asteroid 433 Eros: Results of the NEAR-Shoemaker x-ray spectrometer |author=Trombka JI |display-authors=4 | author2=Squyres SW |author3=Bruckner J |author4= Boynton WV |author5= Reedy RC |author6=McCoy TJ |author7=Gorenstein P |author8=Evans LG |author9=Arnold JR |author10=Starr RD |author11=Nittler LR |author12=Murphy ME |author13=Mikheeva I |author14=McNutt RL |author15=McClanahan TP |author16=McCartney E |author17=Goldsten JO |author18=Gold RE |author19= Floyd SR |author20=Clark PE |author21=Burbine TH |author22=Bhangoo JS |author23=Bailey SH |author24= Petaev M|journal=Science|volume= 289 |pages=2101–2105 | date=2000 | doi =10.1126/science.289.5487.2101 | pmid= 11000107 | issue= 5487|bibcode = 2000Sci...289.2101T |s2cid=29691912 }}
* {{cite journal| title= The shape of 433 Eros from the NEAR-Shoemaker Laser Rangefinder |author= Zuber MT |display-authors=4 | author2= Smith DE |author3=Cheng AF |author4=Garvin JB |author5=Aharonson O |author6=Cole TD |author7=Dunn PJ |author8=Guo YP |author9=Lemoine FG |author10=Neumann GA |author11=Rowlands DD |author12=Torrence MH |journal=Science|volume= 289 |pages=2097–2101 | date=2000| doi= 10.1126/science.289.5487.2097| pmid= 11000106| issue= 5487 |bibcode = 2000Sci...289.2097Z |s2cid= 20553832 |url= https://semanticscholar.org/paper/5bfdfe35de11e40e64eaeed21e1330a96bfe9f3b }}
* {{cite journal| title= The shape of 433 Eros from the NEAR-Shoemaker Laser Rangefinder |author= Zuber MT |display-authors=4 | author2= Smith DE |author3=Cheng AF |author4=Garvin JB |author5=Aharonson O |author6=Cole TD |author7=Dunn PJ |author8=Guo YP |author9=Lemoine FG |author10=Neumann GA |author11=Rowlands DD |author12=Torrence MH |journal=Science|volume= 289 |pages=2097–2101 | date=2000| doi= 10.1126/science.289.5487.2097| pmid= 11000106| issue= 5487 |bibcode = 2000Sci...289.2097Z |s2cid= 20553832 }}
* {{cite journal| title= Radio science results during the NEAR-Shoemaker spacecraft rendezvous with Eros |author=Yeomans DK |display-authors=4 | author2=Antreasian PG |author3=Barriot JP |author4=Chesley SR |author5=Dunham DW |author6=Farquhar RW |author7=Giorgini JD |author8=Helfrich CE |author9=Konopliv AS |author10=McAdams JV |author11= Miller JK |author12=Owen WM |author13=Scheeres DJ |author14=Thomas PC |author15=Veverka J |author16=Williams BG |journal=Science|volume= 289 |pages=2085–2088 | date=2000| doi= 10.1126/science.289.5487.2085| pmid= 11000104| issue= 5487 |bibcode = 2000Sci...289.2085Y }}
* {{cite journal| title= Radio science results during the NEAR-Shoemaker spacecraft rendezvous with Eros |author=Yeomans DK |display-authors=4 | author2=Antreasian PG |author3=Barriot JP |author4=Chesley SR |author5=Dunham DW |author6=Farquhar RW |author7=Giorgini JD |author8=Helfrich CE |author9=Konopliv AS |author10=McAdams JV |author11= Miller JK |author12=Owen WM |author13=Scheeres DJ |author14=Thomas PC |author15=Veverka J |author16=Williams BG |journal=Science|volume= 289 |pages=2085–2088 | date=2000| doi= 10.1126/science.289.5487.2085| pmid= 11000104| issue= 5487 |bibcode = 2000Sci...289.2085Y }}


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==External links==
==External links==
{{commons category|NEAR}}
{{Portal|Spaceflight}}
{{Portal|Spaceflight}}
* [https://solarsystem.nasa.gov/missions/near-shoemaker/in-depth/ ''NEAR'' Shoemaker Profile] by [http://solarsystem.nasa.gov NASA's Solar System Exploration]
* [https://web.archive.org/web/20180629020614/https://solarsystem.nasa.gov/missions/near-shoemaker/in-depth/ ''NEAR'' Shoemaker Profile] by [http://solarsystem.nasa.gov NASA's Solar System Exploration]
* [https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1996-008A NSSDC Master Catalog: Spacecraft – ''NEAR'' Shoemaker]
* [https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1996-008A NSSDC Master Catalog: Spacecraft – ''NEAR'' Shoemaker]
* [http://nssdc.gsfc.nasa.gov/planetary/near.html NASA GSFC: ''NEAR'' Shoemaker, Near Earth Asteroid Rendezvous]
* [http://nssdc.gsfc.nasa.gov/planetary/near.html NASA GSFC: ''NEAR'' Shoemaker, Near Earth Asteroid Rendezvous]

Latest revision as of 10:58, 25 October 2023

"NEAR" redirects here. For other uses, see Near.

NEAR Shoemaker
Model of a cylindrical spacecraft with four square-shaped solar panels at one of the craft's edges
Artist's rendering of the NEAR Shoemaker spacecraft
Mission typeOrbiter (433 Eros)
OperatorNASA · APL
COSPAR ID1996-008A Edit this at Wikidata
SATCAT no.23784Edit this on Wikidata
WebsiteOfficial website
Mission duration5 years, 21 days
Spacecraft properties
Launch mass805 kg[1]
Dry mass487 kilograms (1,074 lb)
Power1,800 W
Start of mission
Launch dateFebruary 17, 1996 (1996-02-17) 20:43:27 UTC
RocketDelta II 7925-8
Launch siteCape Canaveral LC-17B
End of mission
Last contactFebruary 28, 2001 (2001-02-28) ~00:00 UTC
Landing dateFebruary 12, 2001 (2001-02-12) 20:01 UTC
Landing siteSouth of Himeros crater, 433 Eros
Flyby of 253 Mathilde
Closest approachJune 27, 1997 (1997-06-27) 12:56 UTC
Distance1,212 kilometers (753 mi)
433 Eros orbiter
Orbital insertionFebruary 14, 2000 (2000-02-14) 15:33 UTC
Orbits230 orbits[2]
An artwork of a spacecraft hovering above an asteroid, enclosed in an equilateral triangle with a thick, red border. The words "JHU/APL", "NASA", and "NEAR" are printed in bold white font, on the left, right, and bottom sides of the triangle's borders.
Official insignia of the NEAR Shoemaker mission  

Near Earth Asteroid Rendezvous – Shoemaker (NEAR Shoemaker), renamed after its 1996 launch in honor of planetary scientist Eugene Shoemaker, was a robotic space probe designed by the Johns Hopkins University Applied Physics Laboratory for NASA to study the near-Earth asteroid Eros from close orbit over a period of a year. It was the first spacecraft to orbit an asteroid and land on it successfully.[3] In February 2000, the mission closed in on the asteroid and orbited it. On February 12, 2001, Shoemaker touched down on the asteroid and was terminated just over two weeks later.[3]

The primary scientific objective of NEAR was to return data on the bulk properties, composition, mineralogy, morphology, internal mass distribution, and magnetic field of Eros. Secondary objectives include studies of regolith properties, interactions with the solar wind, possible current activity as indicated by dust or gas, and the asteroid spin state. This data was used to help understand the characteristics of asteroids in general, their relationship to meteoroids and comets, and the conditions in the early Solar System. To accomplish these goals, the spacecraft was equipped with an X-ray/gamma-ray spectrometer, a near-infrared imaging spectrograph, a multi-spectral camera fitted with a CCD imaging detector, a laser rangefinder, and a magnetometer. A radio science experiment was also performed using the NEAR tracking system to estimate the gravity field of the asteroid. The total mass of the instruments was 56 kg (123 lb), requiring 80 watts of power.

Development

[edit]

NEAR was the first robotic space probe built by Johns Hopkins University's Applied Physics Laboratory (APL).[4] A previous plan for the mission was for it to go to 4660 Nereus and do a flyby of 2019 van Albada en route.[5] In January 2000, it would rendezvous with Nereus, but instead of staying, it would visit multiple asteroids and comets.[5] Some of the choices that were discussed were 2P/Encke, 433 Eros (which became the mission's primary target), 1036 Ganymed, 4 Vesta, and 4015 Wilson–Harrington.[5] The Small-Body Grand Tour was a plan to visit two asteroids and two comets over a decade with the spacecraft.[5]

Mission profile

[edit]
Near-Earth asteroid Eros as seen from the NEAR spacecraft.

Summary

[edit]

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 km in size, the second largest near-Earth asteroid. Initially, the orbit was circular with a radius of 200 km. The orbit radius was brought down in stages to a 50 × 50 km orbit on April 30, 2000, and decreased to 35 × 35 km on July 14, 2000. The orbit was raised over succeeding months to a 200 × 200 km orbit and then slowly decreased and altered to a 35 × 35 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.

Between December 1999 and February 2001, NEAR used its gamma-ray spectrometer to detect gamma-ray bursts as part of the InterPlanetary Network.[6]

The journey to Mathilde

[edit]
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 km diameter asteroid 253 Mathilde.[7]

One of the images from the flyby of 253 Mathilde

On June 27, 1997, NEAR flew by Mathilde within 1200 km at 12:56 UT at 9.93 km/s, returning imaging and other instrument data. The flyby produced over 500 images, covering 60% of Mathilde's surface,[8] as well as gravitational data allowing calculations of Mathilde's dimensions and mass.[9]

The journey to Eros

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

Failure of first attempt at orbital insertion

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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 and began tumbling. The spacecraft's thrusters fired thousands of times during the anomaly, which expended 29 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.[10]

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 m/s and a distance of 3827 km from the center of mass of Eros. The camera took images of Eros, data were collected by the near 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 km/h.[7]

Orbital insertion

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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 m/s relative to Eros. Another maneuver took place on February 8, increasing the relative velocity slightly to 9.9 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 km elliptical orbit around Eros on February 14. The orbit was slowly decreased to a 35 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 km circular orbit by September 5, 2000. Maneuvers in mid-October led to a flyby of Eros within 5.3 km of the surface at 07:00 UT on October 26.[7]

  • Trajectory graphic depicting the voyage of the NEAR spacecraft
    Trajectory graphic depicting the voyage of the NEAR spacecraft
  • Animation of NEAR Shoemaker's trajectory from February 19, 1996, to February 12, 2001   NEAR Shoemaker   Eros   Earth   Mathilde   Sun
    Animation of NEAR Shoemaker's trajectory from February 19, 1996, to February 12, 2001
    •   NEAR Shoemaker
    •   Eros
    •   Earth
    •   Mathilde
    •   Sun
  • Animation of NEAR Shoemaker's trajectory around Eros from April 1, 2000, to February 12, 2001   NEAR Shoemaker   433 Eros
    Animation of NEAR Shoemaker's trajectory around Eros from April 1, 2000, to February 12, 2001

Orbits and landing

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Eros from approximately 250 meters altitude (area in image is roughly 12 meters across). This image was taken during NEAR's descent to the surface of the asteroid.[11]

Following the flyby, NEAR moved to a 200 km circular orbit and shifted the orbit from prograde near-polar to a retrograde near-equatorial orbit. By December 13, 2000, the orbit was shifted back to a circular 35 km low orbit. Starting on January 24, 2001, the spacecraft began a series of close passes (5 to 6 km) to the surface and, on January 28, passed 2 to 3 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 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 meters per second (thus becoming the first spacecraft to soft-land on an asteroid).[12] 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 4 inches (100 mm) from the surface where it was ten times more sensitive than when it was used in orbit.[13] 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.[6] The impact of cosmic rays on the sensor was also reduced by about 50%.[6]

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 °F (−173 °C, 100 K) conditions the probe experienced while on Eros.[14]

Spacecraft and subsystems

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NEAR spacecraft inside its Delta II rocket.

Spacecraft

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The spacecraft has the shape of an octagonal prism, approximately 1.7 m on a side, with four fixed gallium arsenide solar panels in a windmill arrangement, a fixed 1.5 m X-band high-gain radio antenna with a magnetometer mounted on the antenna feed, and an X-ray solar monitor on one end (the forward deck), with the other instruments fixed on the opposite end (the aft deck). Most electronics were mounted on the inside of the decks. The propulsion module was contained in the interior. The decision to mount instruments on the body of the spacecraft rather than using booms resulted in the gamma-ray spectrometer needing to be shielded from noise generated by the craft.[6] A bismuth germanate shield was used, although this proved only moderately effective.[6]

The craft was three-axis stabilized and used a single bipropellant (hydrazine / nitrogen tetroxide) 450 newton (N) main thruster,[15] and four 21 N and seven 3.5 N hydrazine thrusters for propulsion, for a total delta-V potential of 1450 m/s. Attitude control was achieved using the hydrazine thrusters and four reaction wheels. The propulsion system carried 209 kg of hydrazine and 109 kg of NTO oxidizer in two oxidizer and three fuel tanks.[7]

Power was provided by four 1.8 by 1.2 meter gallium arsenide solar panels, which could produce 400 watts at 2.2 AU (329,000,000 km), NEAR's maximum distance from the Sun and 1800 watts at one AU (150,000,000 km). Power was stored in a nine-ampere-hour, 22-cell rechargeable super nickel-cadmium battery.[7]

Spacecraft guidance was achieved through the use of a sensor suite of five digital solar attitude detectors, an inertial measurement unit (IMU), and a star tracker camera pointed opposite the instrument pointing direction. The IMU contained hemispherical resonators gyroscopes and accelerometers. Four reaction wheels (arranged so that any three can provide complete three-axis control) were used for normal attitude control. The thrusters were used to dump angular momentum from the reaction wheels, as well as for rapid slew and propulsive maneuvers. Attitude control was to 0.1 degree, line-of-sight pointing stability is within 50 microradians over one second, and post-processing attitude knowledge is to 50 microradians.[7]

The command and data handling subsystem was composed of two redundant command and telemetry processors and solid state recorders, a power switching unit, and an interface to two redundant 1553 standard data buses for communications with other subsystems. NEAR was the first APL spacecraft to use significant numbers of plastic encapsulated microcircuits (PEMs), and the first to use solid-state data recorders for mass storage—previous APL spacecraft used magnetic tape recorders or magnetic cores.[16]

The solid-state recorders are constructed from 16 Mbit IBM Luna-C DRAMs. One recorder has 1.1 gigabits of storage, and the other has 0.67 gigabits.[7]

The NEAR mission was the first launch of NASA's Discovery Program, a series of small-scale spacecraft designed to proceed from development to flight in under three years for a cost of less than $150 million. The construction, launch, and 30-day cost for this mission is estimated at $122 million. The final total mission cost was $224 million, which consisted of $124.9 million for spacecraft development, $44.6 million for launch support and tracking, and $54.6 million for mission operations and data analysis.[2]

Scientific payload and experiments

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Diagram showing location of NEAR science instruments.

The science payload includes:[17]

  • The Multi-Spectral Imager (MSI), designed and built by the Johns Hopkins University Applied Physics Laboratory, provided visible images of the asteroid's surface.
  • The NEAR IR Spectrograph (NIS) covers a 0.8 to 2.6-micrometer spectral range in 62 bins.
  • A three-axis fluxgate magnetometer supplied by NASA's Goddard Space Flight Center can measure the asteroid's magnetic field from DC to 10 Hz.
  • The X-ray/Gamma-Ray Spectrometer (XGRS) is two instruments. The x-ray spectrometer measures x-ray fluorescence on the asteroid excited by solar flare x-rays. The gamma-ray spectrometer is a NaI scintillator with an active BGO shield.
  • The laser rangefinder (NLR) is a direct-detection single-pulse rangefinder.

References

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  1. ^ "NEAR Shoemaker". NASA's Solar System Exploration website. Retrieved December 1, 2022.
  2. ^ a b "NEAR: FAQ". Applied Physics Lab.
  3. ^ a b "NEAR Shoemaker". NASA. Retrieved April 26, 2021.
  4. ^ Lawler, Andrew (January 4, 2002). "Lab Rivalry Spices Up Solar System Exploration". Science. 295 (5552): 33. doi:10.1126/science.295.5552.33. ISSN 0036-8075. PMID 11778023. S2CID 109108852. Retrieved November 16, 2022.
  5. ^ a b c d Extended-mission opportunities for a Discovery-class asteroid rendezvous mission
  6. ^ a b c d e Trombka, J. I.; Nittler, L. R.; Starr, R. D.; Evans, L. G.; et al. (2001). "The NEAR-Shoemaker x-ray/gamma-ray spectrometer experiment: Overview and lessons learned". Meteoritics & Planetary Science. 36 (12): 1605–1616. Bibcode:2001M&PS...36.1605T. doi:10.1111/j.1945-5100.2001.tb01852.x.
  7. ^ a b c d e f g h "NEAR Shoemaker". NASA Space Science Data Coordinated Archive. Retrieved February 5, 2019.
  8. ^ Williams, David R. (December 18, 2001). "NEAR Flyby of Asteroid 253 Mathilde". NASA. Retrieved August 10, 2006.
  9. ^ D. K. Yeomans; et al. (1997). "Estimating the mass of asteroid 253 Mathilde from tracking data during the NEAR flyby". Science. 278 (5346): 2106–9. Bibcode:1997Sci...278.2106Y. doi:10.1126/science.278.5346.2106. PMID 9405343. Retrieved August 29, 2007.
  10. ^ "The NEAR Rendezvous Burn Anomaly of December 1998" (PDF). Final Report of the NEAR Anomaly Review Board. November 1999. Archived (PDF) from the original on October 9, 2022. Retrieved February 2, 2017.
  11. ^ "Final Images from 2001 Feb 12". near.jhuapl.edu. Retrieved April 17, 2022.
  12. ^ Siddiqi, Asif A. (2018). Beyond Earth: A Chronicle of Deep Space Exploration, 1958–2016 (PDF). The NASA history series (second ed.). Washington, DC: NASA History Program Office. p. 2. ISBN 9781626830424. LCCN 2017059404. SP2018-4041. Archived (PDF) from the original on October 9, 2022.
  13. ^ Worth, Helen (February 28, 2001). "The End of an Asteroidal Adventure: NEAR Shoemaker Phones Home for the Last Time". Applied Physics Lab.
  14. ^ "'NEAR Shoemaker's Silent Treatment". Applied Physics Laboratory. February 23, 2001.
  15. ^ Williams, David R. (February 8, 2000). "NEAR Mission Profile". NASA Goddard Space Flight Center. Retrieved February 5, 2019.
  16. ^ Ronald K. Burek. "The NEAR Solid-State Data Recorders". Johns Hopkins APL Technical Digest. 1998
  17. ^ Santo, A. G.; Lee, S. C.; Gold, R. E. (1995). "NEAR spacecraft and instrumentation". Journal of the Astronautical Sciences. 43 (4): 373–397.

Public Domain This article incorporates public domain material from websites or documents of the National Aeronautics and Space Administration.

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