OTE Pathfinder

[9] 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.).

[1] OTE pathfinder has 12 rather than 18 cells compared to the full telescope, but it does include a test of the backplane structure.

[13] The Pathfinder was used with the Beam Image Analyzer (BIA) and another important related device is the AOS Source Plate Assembly (ASPA).

[13] The flight-replica backplane was assembled in Redondo Beach, California, at the NASA contractor Northrop Grumman facility there.

[15] The section is contained with the Space Telescope Transporter for Air Road and Sea (STTARS), which was designed for the project.

[18] 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).

[23] After the work done in Maryland at Goddard, the pathfinder was taken to Johnson Space Center in Texas, for cold environment testing.

[5] In preparation for its arrival, in 2014 Optical Ground Support Equipment was installed at the cryogenic test chamber at Johnson Space Center.

[25] 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.

[28] The thermal test will take similar hardware on cool down time line, which allows heat flow to be studied.

[29] The flight JWST primary mirror is designed to be cooled down to 55 K (−218 °C; −361 °F) for operation, and the thermal tests on the pathfinder support this goal.