The five tennis-court sized sunshield layers that will protect NASA's Webb telescope mirrors and instruments from the heat of the sun have entered an important new test phase. The sunshield is the key design element that allows the Webb telescope to cool to its 40 K. cryogenic operating temperature, necessary to image faint infrared objects in the early universe.

The start of 3-D shape testing will tell engineers how the full-size sunshield layers will behave in orbit. Northrop Grumman is the prime contractor for NASA's Goddard Space Flight Center.

"Testing the full-size sunshield in a fully simulated flight configuration and comparing test results to our computer models is a very significant step forward in validating the sunshield's predicted performance," said Jim Flynn, Webb telescope Sunshield manager, Northrop Grumman Aerospace Systems.

"The size of the sunshield mandates the use of computer models to verify performance, and this test represents the next level of analysis on a full-size membrane."

"The completion and testing of this full size layer is the final step of the Sunshield's development program and provides the needed confidence and experience needed to manufacture the five flight layers," said Keith Parrish, Webb telescope Sunshield manager at NASA's Goddard Space Flight Center, Greenbelt, Md.

The month-long testing began in early September at teammate ManTech International Corporation's Nexolve facility in Huntsville, Ala., using flight-like material for the sunshield, and a full-scale test frame and hardware attachments.

The test sunshield layer is made of Kapton, a very thin, high-performance plastic with a reflective metallic coating, similar to a mylar balloon. Each sunshield layer thickness is less than half the thickness of a sheet of paper. It is stitched together like a quilt from over 52 individual pieces because no manufacturer makes Kapton sheets as big as a tennis court.

Test engineers used a high precision laser radar tool to measure the layer every few inches at room temperature and pressure, creating a 3-D map or picture of the material surface, which is curved in multiple directions. The map made during the test will be compared to computer models to see if the material behaved as the model predicted, and whether critical clearances with adjacent hardware are achieved.

"The completion of the assembly and the start of shape testing for the first flight-like sunshield layer is the culmination of over five years of work for our ManTech engineering team," said Greg Laue, ManTech's sunshield program manager at Nexolve.

"Over this period, we have developed a significant number of innovative design, modeling and manufacturing technologies for the sunshield. Some of these include computer modeling and design of the curved 3-D shape of the sunshield as well as manufacturing techniques that include an innovative welding technology that allows us to accurately join multiple Kapton sheets together to form the large tennis court-sized sunshield membrane structure."

The test will be done on all five layers of the sunshield to give engineers a very precise idea of how the entire sunshield will behave once in orbit.

Last year, a one-third-scale model of the sunshield was tested in a chamber that simulated the extreme temperatures the sunshield will experience in space, and confirmed that the sunshield will allow the telescope to cool to its operating temperature. The shape changes under temperature were also compared to computer models to validate predictions.

After all five layers of the full-size sunshield complete testing and model analysis, they will be sent to Northrop Grumman's high bay in Redondo Beach. The sunshield layers are folded, much like a parachute, so they can be safely stowed for launch. In the high bay, engineers verify the process of unfurling the sunshield layers after launch.