Optical Telescope Element
[4] The main three-mirror telescope is a Korsch-type design,[5] and it feeds into the Aft Optics Subsystem (part of OTE), which in turn feeds into the Integrated Science Instrument Module which holds the science instruments and fine guidance sensor.
[7] The OTE combines a large amount of the optics and structural components of the James Webb Space Telescope, including the Main mirror.
[8] Then for finer alignment, special optical devices inside NIRCam are used to conduct a phase retrieval technique, to achieve designed wavefront error of less than 150 nm.
[8] This needs to be done in outer space, so extensive testing on Earth is required to ensure that it will work properly.
[8] Although in the essentially weightless environment of space the mirror will weigh hardly anything, it needs to be very stiff to maintain its shape.
[12] The metal beryllium was chosen for a number of reasons including weight, but also for its low-temperature coefficient of thermal expansion compared to glass.
[12] The Subscale Beryllium Model Demonstrator (SBMD) was successfully tested at cryogenic temperatures, and one of the concerns was surface roughness at low kelvin numbers.
[12] The beryllium mirrors are coated with a very fine layer of gold to reflect infrared light.
[12][14] There are 18 hexagonal segments that are grouped together to create a single mirror with an overall diameter of 6.5 metres (21 ft).
[15] The sunshield segment has multiple components, including six spreaders at the outer edge to spread the layers out at the six extremities.
[15] The DTA is extended by an electric motor that rotates a ball screw nut which pushes the two tubes apart.
[16] The DTA tubes are made of graphite-composite carbon fiber, and it is intended that they will be able to survive the conditions in space.
[31] OTE pathfinder as 12 rather than 18 cells compared to the full telescope, but it does include a test of the backplane structure.
[34] The tests were conducted at the X-Ray Calibration Facility (XRCF) at Marshall Space Flight Center (MSFC) in the U.S. State of Alabama.
[33] The OTS included a WaveScope Shack-Hartmann sensor and a Leica Disto Pro distance measurement instrument.
