Achieving a working main mirror was considered one of the greatest challenges of JWST development. Part of the JWST development included validating and testing JWST on various
testbeds of different functions and sizes. Some types of development items include
pathfinders,
test beds, and
engineering test units. Sometimes a single item can be used for different functions, or it may not be a physically created item at all, but rather a software simulation. It was lighter, so it was envisioned it could be launched as early as 2004 on a Delta 2 launch rocket. At that time NGST/JWST was still a design, with an area of , a few years later this was reduced eventually to the design, with an area of .
OTE Pathfinder One part of JWST development was the production of the Optical Telescope Element Pathfinder. The OTE pathfinder uses two additional mirror segments, and additional secondary mirror, and puts together various structures to allow testing of various aspects of the section, including Ground Support Equipment.
Additional tests/models (JWST) and
Hubble Space Telescope (HST) There are many test articles and developmental demonstrators for the creation of JWST. Another optics testbed is called JOST, which stands for JWST Optical Simulation Testbed, and uses an MEMS with hexagonal segments to simulate the degrees of freedom of the primary mirror alignment and phasing. The SBMD was a half-meter diameter mirror made from powdered beryllium. The SBMD had to meet the requirements for a space-based mirror, and these lessons were important to the development of the JWST. The tests were conducted at the X-Ray Calibration Facility (XRCF) at
Marshall Space Flight Center (MSFC) in the U.S. State of Alabama. The AMSD results were utilized in construction of beryllium mirrors. ==Diagram 1==