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[[File:James Webb Space Telescope in NASA’s giant thermal vacuum chamber (17006918727).jpg|thumb|OTE Pathfinder in a test chamber]]
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[[File:James Webb Space Telescope in NASA’s giant thermal vacuum chamber (17006918727).jpg|thumb|OTE Pathfinder in a test chamber]]
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The ”’OTE Pathfinder”’ (for ”’Optical Telescope Element Pathfinder”’), or ”’JWST Pathfinder”’, is a [[technology demonstration|technology demonstrator]]/[[test article (aerospace)|test article]] for the [[James Webb Space Telescope]].<ref name=”auto”>{{cite web |url=http://spie.org/Publications/Proceedings/Paper/10.1117/12.2054782 |title=James Webb Space Telescope (JWST) Optical Telescope Element (OTE) Pathfinder status and plans |first1=Lee D. |last1=Feinberg |first2=Ritva |last2=Keski-Kuha |first3=Charlie |last3=Atkinson |first4=Andrew |last4=Booth |first5=Tony |last5=Whitman |publisher= |accessdate=5 December 2016 |doi=10.1117/12.2054782}}</ref> It is a non-flight replica of the actual backplane, but only includes the center section not the two “Wings” on the side the extend and have additional segments on the actual JWST.<ref name=”nasa.gov”>{{Cite news |url=https://www.nasa.gov/content/goddard/james-webb-space-telescope-pathfinder-backplanes-path-to-nasa/ |title=James Webb Space Telescope “Pathfinder” Backplane’s Path to NASA |last=Jenner |first=Lynn |publisher=NASA |date=12 August 2014 |access-date=6 February 2017}}</ref> It has been used for various tests and has some different configurations, but some of the major tests have been practicing installing mirror segments with non-flight hardware as well as thermal tests.<ref name=thermalpath>{{Cite news |url=https://www.nasa.gov/image-feature/testing-the-james-webb-space-telescope-pathfinder |title=Testing the James Webb Space Telescope Pathfinder |last=Loff |first=Sarah |publisher=NASA |date=29 September 2016 |access-date=27 January 2017}}</ref><ref name=”Jenner”>{{Cite news |url=https://www.nasa.gov/content/goddard/james-webb-space-telescope-pathfinder-backplanes-path-to-nasa/ |title=James Webb Space Telescope “Pathfinder” Backplane’s Path to NASA |last=Jenner |first=Lynn |date=12 August 2014 |publisher=NASA |access-date=27 January 2017}}</ref> The Pathfinder has also been tested in conjunction with flight hardware including the Aft Optics System.<ref name=”jwst.nasa.gov”>{{Cite web |url=https://jwst.nasa.gov/recentaccomplish.html |title=Recent Accomplishments JWST/NASA |publisher=NASA |access-date=6 February 2017}}</ref> One of the goals and uses of the pathfinder is risk reduction for JWST program.<ref name=”Matthews 957505″>{{Cite journal |last=Matthews |first=Gary W. |last2=Scorse |first2=Thomas R. |last3=Spina |first3=John A. |last4=Noël |first4=Darin M. |last5=Havey |first5=Keith A. |last6=Huguet |first6=Jesse A. |last7=Whitman |first7=Tony L. |last8=Wells |first8=Conrad |last9=Walker |first9=Chanda B. |date=1 August 2015 |title=JWST pathfinder telescope risk reduction cryo test program |bibcode=2015SPIE.9575E..05M |volume=9575 |pages=957505 |doi=10.1117/12.2188793 |issn=0277-786X|hdl=2060/20150018095 |hdl-access=free }}</ref> The pathfinder allows practicing integration and testing procedures, and for risk mitigation<ref>[http://www.northropgrumman.com/MediaResources/Pages/Photo.aspx?pid%3DJW-12013_035%26rel%3D%2F%26name%3DPhotos]</ref><ref>{{Cite web|url=https://www.spiedigitallibrary.org/conference-proceedings-of-spie/7731/77313T/Use-of-a-pathfinder-optical-telescope-element-for-James-Webb/10.1117/12.855800.full|title=Use of a pathfinder optical telescope element for James Webb Space Telescope risk mitigation|first1=Lee D.|last1=Feinberg|first2=Ritva|last2=Keski-Kuha|first3=Charlie|last3=Atkinson|first4=Scott C.|last4=Texter|date=11 August 2010|publisher=SPIE|volume=7731|pages=1347–1355|via=www.spiedigitallibrary.org|doi=10.1117/12.855800}}</ref> With the Pathfinder it was possible to test [[Phase (waves)|phasing]] two mirrors together and also to do tests with the Aft Optical System.<ref>[https://www.cosmos.esa.int/documents/739790/758041/ClampinM.pdf/ab03f396-5d69-4495-bfe4-c226d5642f42]</ref> The OTE Pathfinder was part of the plan for integration and testing of JWST, and in particular supported the [[Optical Telescope Element]] (primary mirror, backplane, etc.).<ref>[https://jwst.nasa.gov/resources/caa_2006/sabelhaus_projectstatus.pdf]</ref>
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The ”’OTE Pathfinder”’ (for ”’Optical Telescope Element Pathfinder”’), or ”’JWST Pathfinder”’, is a [[technology demonstration|technology demonstrator]]/[[test article (aerospace)|test article]] for the [[James Webb Space Telescope]].<ref name=”auto”>{{cite web |url=http://spie.org/Publications/Proceedings/Paper/10.1117/12.2054782 |title=James Webb Space Telescope (JWST) Optical Telescope Element (OTE) Pathfinder status and plans |first1=Lee D. |last1=Feinberg |first2=Ritva |last2=Keski-Kuha |first3=Charlie |last3=Atkinson |first4=Andrew |last4=Booth |first5=Tony |last5=Whitman |publisher= |accessdate=5 December 2016 |doi=10.1117/12.2054782}}</ref> It is a non-flight replica of the actual backplane, but only includes the center section not the two “Wings” on the side the extend and have additional segments on the actual JWST.<ref name=”nasa.gov”>{{Cite news |url=https://www.nasa.gov/content/goddard/james-webb-space-telescope-pathfinder-backplanes-path-to-nasa/ |title=James Webb Space Telescope “Pathfinder” Backplane’s Path to NASA |last=Jenner |first=Lynn |publisher=NASA |date=12 August 2014 |access-date=6 February 2017}}</ref> It has been used for various tests and has some different configurations, but some of the major tests have been practicing installing mirror segments with non-flight hardware as well as thermal tests.<ref name=thermalpath>{{Cite news |url=https://www.nasa.gov/image-feature/testing-the-james-webb-space-telescope-pathfinder |title=Testing the James Webb Space Telescope Pathfinder |last=Loff |first=Sarah |publisher=NASA |date=29 September 2016 |access-date=27 January 2017}}</ref><ref name=”Jenner”>{{Cite news |url=https://www.nasa.gov/content/goddard/james-webb-space-telescope-pathfinder-backplanes-path-to-nasa/ |title=James Webb Space Telescope “Pathfinder” Backplane’s Path to NASA |last=Jenner |first=Lynn |date=12 August 2014 |publisher=NASA |access-date=27 January 2017}}</ref> The Pathfinder has also been tested in conjunction with flight hardware including the Aft Optics System.<ref name=”jwst.nasa.gov”>{{Cite web |url=https://jwst.nasa.gov/recentaccomplish.html |title=Recent Accomplishments JWST/NASA |publisher=NASA |access-date=6 February 2017}}</ref> One of the goals and uses of the pathfinder is risk reduction for JWST program.<ref name=”Matthews 957505″>{{Cite journal |last=Matthews |first=Gary W. |last2=Scorse |first2=Thomas R. |last3=Spina |first3=John A. |last4=Noël |first4=Darin M. |last5=Havey |first5=Keith A. |last6=Huguet |first6=Jesse A. |last7=Whitman |first7=Tony L. |last8=Wells |first8=Conrad |last9=Walker |first9=Chanda B. |date=1 August 2015 |title=JWST pathfinder telescope risk reduction cryo test program |bibcode=2015SPIE.9575E..05M |volume=9575 |pages=957505 |doi=10.1117/12.2188793 |issn=0277-786X|hdl=2060/20150018095 |hdl-access=free }}</ref> The pathfinder allows practicing integration and testing procedures, and for risk mitigation<ref>[https://web.archive.org/web/20190416152142/http://www.northropgrumman.com/MediaResources/Pages/Photo.aspx?pid%3DJW-12013_035%26rel%3D%2F%26name%3DPhotos Optical Telescope Element Pathfinder]</ref><ref>{{Cite web|url=https://www.spiedigitallibrary.org/conference-proceedings-of-spie/7731/77313T/Use-of-a-pathfinder-optical-telescope-element-for-James-Webb/10.1117/12.855800.full|title=Use of a pathfinder optical telescope element for James Webb Space Telescope risk mitigation|first1=Lee D.|last1=Feinberg|first2=Ritva|last2=Keski-Kuha|first3=Charlie|last3=Atkinson|first4=Scott C.|last4=Texter|date=11 August 2010|publisher=SPIE|volume=7731|pages=1347–1355|via=www.spiedigitallibrary.org|doi=10.1117/12.855800}}</ref> With the Pathfinder it was possible to test [[Phase (waves)|phasing]] two mirrors together and also to do tests with the Aft Optical System.<ref>[https://www.cosmos.esa.int/documents/739790/758041/ClampinM.pdf/ab03f396-5d69-4495-bfe4-c226d5642f42 Status of the James Webb Space Telescope (JWST) Observatory]</ref> The OTE Pathfinder was part of the plan for integration and testing of JWST, and in particular supported the [[Optical Telescope Element]] (primary mirror, backplane, etc.).<ref>[https://jwst.nasa.gov/resources/caa_2006/sabelhaus_projectstatus.pdf Phil Sabelhaus: JWST Project Status for the CAA, May 20, 2006]</ref>
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The OTE pathfinder uses two additional mirror segments, an additional [[secondary mirror]], and puts together various structures to allow testing of various aspects of the section, including Ground Support Equipment.<ref name=”auto”/> This supports the GSE being used on the JWST itself later on, and allows testing of mirror integration.<ref name=”auto”/> OTE pathfinder has 12 rather than 18 cells compared to the full telescope, but it does include a test of the backplane structure.<ref>[http://www.aura-astronomy.org/news/2012/SatMagazine_Feb2012_Webb_complete.pdf]</ref> The pathfinder allowed practicing installing mirror segments with a non-flight mirror and non-flight backplane.<ref name=”nasa.gov”/> Mirror installation is a task that necessitated practice due to the high-precision required.<ref name=”Jenner”/>
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The OTE pathfinder uses two additional mirror segments, an additional [[secondary mirror]], and puts together various structures to allow testing of various aspects of the section, including Ground Support Equipment.<ref name=”auto”/> This supports the GSE being used on the JWST itself later on, and allows testing of mirror integration.<ref name=”auto”/> OTE pathfinder has 12 rather than 18 cells compared to the full telescope, but it does include a test of the backplane structure.<ref>[https://web.archive.org/web/20161011061920/http://www.aura-astronomy.org/news/2012/SatMagazine_Feb2012_Webb_complete.pdf SatMagazine, February 2012: The Untold Story Of NASA’s James Webb Space Telescope]</ref> The pathfinder allowed practicing installing mirror segments with a non-flight mirror and non-flight backplane.<ref name=”nasa.gov”/> Mirror installation is a task that necessitated practice due to the high-precision required.<ref name=”Jenner”/>
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The Pathfinder backplane was completed in 2011.<ref>{{Cite web |url=https://www.nasa.gov/topics/technology/features/webb-2011progress.html |title=NASA – NASA’s James Webb Space Telescope: A Year of Achievement and Success |publisher=NASA |access-date=6 February 2017}}</ref> Three tests planned for the OTE Pathfinder were Optical Ground Support Equipment 1 (OGSE1), Optical Ground Support Equipment 2 (OGSE2), and Thermal Pathfinder.<ref name=”optics.msfc.nasa.gov”>[https://web.archive.org/web/20161204015402/https://optics.msfc.nasa.gov/sites/optics.msfc.nasa.gov/files/18%20NASA%20JWST%20Pathfinder%20Testing%20at%20JSC.pdf]</ref>
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The Pathfinder backplane was completed in 2011.<ref>{{Cite web |url=https://www.nasa.gov/topics/technology/features/webb-2011progress.html |title=NASA – NASA’s James Webb Space Telescope: A Year of Achievement and Success |publisher=NASA |access-date=6 February 2017}}</ref> Three tests planned for the OTE Pathfinder were Optical Ground Support Equipment 1 (OGSE1), Optical Ground Support Equipment 2 (OGSE2), and Thermal Pathfinder.<ref name=”optics.msfc.nasa.gov”>[https://web.archive.org/web/20161204015402/https://optics.msfc.nasa.gov/sites/optics.msfc.nasa.gov/files/18%20NASA%20JWST%20Pathfinder%20Testing%20at%20JSC.pdf James Webb Space Telescope (JWST) Optical Telescope Element (OTE) Pathfinder Status and Plans]</ref>
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The Pathfinder was used with the Beam Image Analyzer (BIA) and another important related device is the AOS Source Plate Assembly (ASPA).<ref name=”optics.msfc.nasa.gov”/> ASPA provides infrared sources for doing optical testing.<ref name=”optics.msfc.nasa.gov”/>
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The Pathfinder was used with the Beam Image Analyzer (BIA) and another important related device is the AOS Source Plate Assembly (ASPA).<ref name=”optics.msfc.nasa.gov”/> ASPA provides infrared sources for doing optical testing.<ref name=”optics.msfc.nasa.gov”/>
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==Texas (Johns Space Center)==
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==Texas (Johns Space Center)==
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After the work done in Maryland at Goddard, the pathfinder was taken to Johnson Space Center in Texas, for cold environment testing.<ref name=”Jenner”/> The Pathfinder was delivered to JSC by early February 2015.<ref name=”jwst.nasa.gov”/> In preparation for its arrival, in 2014 Optical Ground Support Equipment was installed at the cryogenic test chamber at Johnson Space Center.<ref name=”Matthews 957505″/> The ground support equipment was tested during the OGSE-1 in Chamber A at JSC, after which the Aft Optical Subsystem and Beam analyzer were installed and tested in OGSE-2.<ref>
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After the work done in Maryland at Goddard, the pathfinder was taken to Johnson Space Center in Texas, for cold environment testing.<ref name=”Jenner”/> The Pathfinder was delivered to JSC by early February 2015.<ref name=”jwst.nasa.gov”/> In preparation for its arrival, in 2014 Optical Ground Support Equipment was installed at the cryogenic test chamber at Johnson Space Center.<ref name=”Matthews 957505″/> The ground support equipment was tested during the OGSE-1 in Chamber A at JSC, after which the Aft Optical Subsystem and Beam analyzer were installed and tested in OGSE-2.<ref>{{cite journal |last1=Feinberg |first1=Lee D. |last2=Keski-Kuha |first2=Ritva |last3=Atkinson |first3=Charlie |last4=Booth |first4=Andrew |last5=Whitman |first5=Tony |title=James Webb Space Telescope (JWST) Optical Telescope Element (OTE) Pathfinder status and plans |date=2 August 2014 |pages=91430E |doi=10.1117/12.2054782}}</ref> The first test was completed by June 2015, and the second test was completed by November 2015.<ref name=”auto1″>{{Cite web|url=http://www.nasa.gov/feature/goddard/nasas-webb-pathfinder-telescope-successfully-completes-second-super-cold-optical-test|title=NASA’s Webb Successfully Completes Second Super-Cold Optical Test|first=Lynn|last=Jenner|date=30 November 2015|website=NASA}}</ref> The third major test, which involves even more modifications to pathfinder is called Thermal Pathfinder.<ref name=”auto1″/> During the optical tests the mirrors had to be “phased” or aligned to a distance less than the wavelength of light, thousands of times smaller than the thickness of a human hair at a temperature hundreds of degree below zero.<ref>{{Cite news |url=https://www.nasa.gov/feature/goddard/nasas-webb-pathfinder-telescope-successfully-completes-first-super-cold-optical-test |title=Webb “Pathfinder Telescope” Has Super-Cold Optics Test Success |last=Jenner |first=Lynn |publisher=NASA |date=15 October 2015 |access-date=8 February 2017}}</ref>
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{{quote|Practice makes perfect. Since we will be testing the world’s largest ever cryogenic telescope for the first time in the world’s largest cryogenic test chamber, we need to be experienced in using our test equipment so we can focus on the performance of the telescope| Webb telescope Observatory Project Scientist<ref name=”auto1″/>}}
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{{quote|Practice makes perfect. Since we will be testing the world’s largest ever cryogenic telescope for the first time in the world’s largest cryogenic test chamber, we need to be experienced in using our test equipment so we can focus on the performance of the telescope| Webb telescope Observatory Project Scientist<ref name=”auto1″/>}}
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By the end of October 2015 the second round of testing with JWST was completed.<ref>{{Cite web |url=https://jwst.nasa.gov/recentaccomplish.html |title=Recent Accomplishments JWST/NASA |publisher=NASA |access-date=27 January 2017}}</ref> The flight Aft Optics System was tested with the Pathfinder, and it was delivered for testing in May 2015.<ref name=”jwst.nasa.gov”/> The Aft Optics System is part of the [[Optical Telescope Element]] in the flight telescope.
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By the end of October 2015 the second round of testing with JWST was completed.<ref>{{Cite web |url=https://jwst.nasa.gov/recentaccomplish.html |title=Recent Accomplishments JWST/NASA |publisher=NASA |access-date=27 January 2017}}</ref> The flight Aft Optics System was tested with the Pathfinder, and it was delivered for testing in May 2015.<ref name=”jwst.nasa.gov”/> The Aft Optics System is part of the [[Optical Telescope Element]] in the flight telescope.
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In 2016 the pathfinder was used for the Pathfinder Thermal Test at Johnson Space Center in Texas.<ref name=”thermalpath”/> At this time it had two spare flight-rated [[beryllium]] mirrors (one gold-coated) and ten non-flight gold-coated aluminum test segments functioning as thermal simulators.<ref name=”thermalpath”/> In 2016 the pathfinder underwent thermal and vacuum tests that the actual JWST was planned to also go through in 2017.<ref name=”Preparing JWST for launch”>{{Cite news |url=http://www.spacedaily.com/reports/Preparing_JWST_for_launch_999.html |title=Preparing JWST for launch |newspaper=Space Daily |access-date=27 January 2017}}</ref> The test chamber was originally built to test [[Apollo program]] hardware, but was refurbished for testing in the JWST program.<ref name=”Preparing JWST for launch”/> The thermal test will take similar hardware on cool down time line, which allows heat flow to be studied.<ref name=”ttu-ir.tdl.org”>[https://ttu-ir.tdl.org/ttu-ir/bitstream/handle/2346/67729/ICES_2016_429.pdf?sequence=1]</ref> The flight JWST primary mirror is designed to be cooled down to {{convert|55|K|C F|0}} for operation, and the thermal tests on the pathfinder support this goal.<ref name=”ttu-ir.tdl.org”/> The pathfinder had to be modified for the thermal tests, including the thermal simulators to stand in for the mirrors, but also insulation.<ref name=”ttu-ir.tdl.org”/> There is also an Aft Optical Subsystem Geometry Simulator and an ISIM Electronics Compartment Simulator.<ref name=”ttu-ir.tdl.org”/> The thermal test also demonstrates the Space Vehicle Thermal Simulator (SVTS) and the Deep Space Edge Radiation Sinks (DSERS).<ref name=”ttu-ir.tdl.org”/>
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In 2016 the pathfinder was used for the Pathfinder Thermal Test at Johnson Space Center in Texas.<ref name=”thermalpath”/> At this time it had two spare flight-rated [[beryllium]] mirrors (one gold-coated) and ten non-flight gold-coated aluminum test segments functioning as thermal simulators.<ref name=”thermalpath”/> In 2016 the pathfinder underwent thermal and vacuum tests that the actual JWST was planned to also go through in 2017.<ref name=”Preparing JWST for launch”>{{Cite news |url=http://www.spacedaily.com/reports/Preparing_JWST_for_launch_999.html |title=Preparing JWST for launch |newspaper=Space Daily |access-date=27 January 2017}}</ref> The test chamber was originally built to test [[Apollo program]] hardware, but was refurbished for testing in the JWST program.<ref name=”Preparing JWST for launch”/> The thermal test will take similar hardware on cool down time line, which allows heat flow to be studied.<ref name=”ttu-ir.tdl.org”>[https://ttu-ir.tdl.org/ttu-ir/bitstream/handle/2346/67729/ICES_2016_429.pdf?sequence=1 James Webb Space Telescope Thermal Pathfinder Test Development, International Conference on Environmental Systems]</ref> The flight JWST primary mirror is designed to be cooled down to {{convert|55|K|C F|0}} for operation, and the thermal tests on the pathfinder support this goal.<ref name=”ttu-ir.tdl.org”/> The pathfinder had to be modified for the thermal tests, including the thermal simulators to stand in for the mirrors, but also insulation.<ref name=”ttu-ir.tdl.org”/> There is also an Aft Optical Subsystem Geometry Simulator and an ISIM Electronics Compartment Simulator.<ref name=”ttu-ir.tdl.org”/> The thermal test also demonstrates the Space Vehicle Thermal Simulator (SVTS) and the Deep Space Edge Radiation Sinks (DSERS).<ref name=”ttu-ir.tdl.org”/>
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==Components==
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==Components==
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