During routine testing of NASA’s James Webb Space Telescope in December, an unexpected response occurred from several of the more than 100 devices designed to detect small changes in the motion of the structure, prompting engineers at Goddard Space Flight Center to put the vibration tests on hold to determine the cause.
“This is why we test—to know how things really are, as opposed to how we think they are,” says Paul Geithner, technical deputy project manager for the Webb Telescope at Goddard.
Since the December stoppage, NASA engineers and scientists have analyzed many potential scenarios for the measured responses and have successfully conducted three low-level vibrations of the telescope. All visual and ultrasonic examinations of the structure continue to show it to be sound, according to NASA.
“Currently, the team is continuing their analyses with the goal of having a review of their findings, conclusions and plans for resuming vibration testing in January,” says Eric Smith, program director for NASA’s James Webb Space Telescope at NASA Headquarters in Washington.Vibration and acoustics test facilities provide vibration and shock testing of spaceflight hardware to ensure that severe launch and landing environments don’t impair functionality. Launches create high levels of vibration in spacecraft and equipment and ground testing is done to simulate that launch-induced vibration. Engineers conduct vibration testing on components as small as a few ounces to as large as complete structures or systems. By performing the vibration testing on NASA’s James Webb Space Telescope, scientists and engineers can ensure that the spacecraft and all of its instruments will endure the launch and maintain functionality when it is launched from French Guiana in 2018.
During vibration testing on Dec. 3 at NASA Goddard, accelerometers attached to the telescope detected unexpected responses and consequently the test shut itself down to protect the hardware. The shutdown came in the fraction of a second after the system recorded a higher-than-expected response at a particular frequency of vibration, about one note lower than the lowest note on a piano.
Further testing may or may not reveal additional unexpected responses, but NASA says that is the purpose of these tests and if additional anomalies are detected the agency will correct them before launch.