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OTE Pathfinder
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OTE Pathfinder
The OTE Pathfinder (for Optical Telescope Element Pathfinder), or James Webb Space Telescope Pathfinder, is a technology demonstrator and test article for the James Webb Space Telescope. It is a non-flight replica of the actual backplane, but only includes the center section, not the two "wings" on the side that extend and have additional segments on the actual JWST. 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. The Pathfinder has also been tested in conjunction with flight hardware including the Aft Optics System. One of the goals and uses of the pathfinder is risk reduction for JWST program. The pathfinder allows practicing integration and testing procedures, and for risk mitigation With the Pathfinder it was possible to test phasing two mirrors together and also to do tests with the Aft Optical System. 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.).
The OTE pathfinder uses two additional mirror segments and an additional secondary mirror, and puts together various structures to allow testing of various aspects of the section, including Ground Support Equipment. This supports the GSE's use on the JWST itself later on, and allows testing of mirror integration. OTE pathfinder has 12 rather than 18 cells compared to the full telescope, but it does include a test of the backplane structure. The pathfinder allowed practicing installing mirror segments with a non-flight mirror and non-flight backplane. Mirror installation is a task that necessitated practice due to the high-precision required.
The Pathfinder backplane was completed in 2011. Three tests planned for the OTE Pathfinder were Optical Ground Support Equipment 1 (OGSE1), Optical Ground Support Equipment 2 (OGSE2), and Thermal Pathfinder.
The Pathfinder was used with the Beam Image Analyzer (BIA) and another important related device is the AOS Source Plate Assembly (ASPA). ASPA provides infrared sources for doing optical testing.
The flight-replica backplane was assembled in Redondo Beach, California, at the NASA contractor Northrop Grumman facility there. The flight backplane has two wings and a center section, whereas the pathfinder just as center section. The backplane was transported across country (see Continental United States) in a C-5 Galaxy transport aircraft to Joint Base Andrews, and to GSC by road. The section is contained with the Space Telescope Transporter for Air Road and Sea (STTARS), which was designed for the project. This facilitates hauling items around the country for different tests or assembly for the JWST project.
The backplane is constructed out of graphite composite, titanium, and invar. Invar is an iron-nickel alloy with a low coefficient of thermal expansion (CTE or α), which means it does not significantly change size during temperature changes. One of the important features of the backplane is that it is thermally stable at low temperatures, because it is holding the main mirror, it must change size less than one-ten-thousandth of a human hair (32 nm) at −240 °C (−400 °F). Another test of the backplane design was the Backplane Structure Test Article, which was a one sixth portion of the full backplane.
In 2014 the pathfinder was transported from California to Maryland. In Maryland it was used for practicing mirror installation at Goddard Space Flight Center. It arrived at GSC in Maryland in July 2014. Mirror segments were installed on the Pathfinder, which allowed the procedure to be practiced.
At Goddard Spaceflight Center the two spare main mirror segments and a spare secondary mirror were installed on the pathfinder. The full James Webb Space Telescope main mirror has 18 segments (primary). It was considered to use silver, however gold is more durable than silver as a coating even though it is used for reflecting down to 400 nm wavelength light; JWST is primarily for 800 nm to 29000 nm.
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OTE Pathfinder
The OTE Pathfinder (for Optical Telescope Element Pathfinder), or James Webb Space Telescope Pathfinder, is a technology demonstrator and test article for the James Webb Space Telescope. It is a non-flight replica of the actual backplane, but only includes the center section, not the two "wings" on the side that extend and have additional segments on the actual JWST. 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. The Pathfinder has also been tested in conjunction with flight hardware including the Aft Optics System. One of the goals and uses of the pathfinder is risk reduction for JWST program. The pathfinder allows practicing integration and testing procedures, and for risk mitigation With the Pathfinder it was possible to test phasing two mirrors together and also to do tests with the Aft Optical System. 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.).
The OTE pathfinder uses two additional mirror segments and an additional secondary mirror, and puts together various structures to allow testing of various aspects of the section, including Ground Support Equipment. This supports the GSE's use on the JWST itself later on, and allows testing of mirror integration. OTE pathfinder has 12 rather than 18 cells compared to the full telescope, but it does include a test of the backplane structure. The pathfinder allowed practicing installing mirror segments with a non-flight mirror and non-flight backplane. Mirror installation is a task that necessitated practice due to the high-precision required.
The Pathfinder backplane was completed in 2011. Three tests planned for the OTE Pathfinder were Optical Ground Support Equipment 1 (OGSE1), Optical Ground Support Equipment 2 (OGSE2), and Thermal Pathfinder.
The Pathfinder was used with the Beam Image Analyzer (BIA) and another important related device is the AOS Source Plate Assembly (ASPA). ASPA provides infrared sources for doing optical testing.
The flight-replica backplane was assembled in Redondo Beach, California, at the NASA contractor Northrop Grumman facility there. The flight backplane has two wings and a center section, whereas the pathfinder just as center section. The backplane was transported across country (see Continental United States) in a C-5 Galaxy transport aircraft to Joint Base Andrews, and to GSC by road. The section is contained with the Space Telescope Transporter for Air Road and Sea (STTARS), which was designed for the project. This facilitates hauling items around the country for different tests or assembly for the JWST project.
The backplane is constructed out of graphite composite, titanium, and invar. Invar is an iron-nickel alloy with a low coefficient of thermal expansion (CTE or α), which means it does not significantly change size during temperature changes. One of the important features of the backplane is that it is thermally stable at low temperatures, because it is holding the main mirror, it must change size less than one-ten-thousandth of a human hair (32 nm) at −240 °C (−400 °F). Another test of the backplane design was the Backplane Structure Test Article, which was a one sixth portion of the full backplane.
In 2014 the pathfinder was transported from California to Maryland. In Maryland it was used for practicing mirror installation at Goddard Space Flight Center. It arrived at GSC in Maryland in July 2014. Mirror segments were installed on the Pathfinder, which allowed the procedure to be practiced.
At Goddard Spaceflight Center the two spare main mirror segments and a spare secondary mirror were installed on the pathfinder. The full James Webb Space Telescope main mirror has 18 segments (primary). It was considered to use silver, however gold is more durable than silver as a coating even though it is used for reflecting down to 400 nm wavelength light; JWST is primarily for 800 nm to 29000 nm.
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