Nearly two months after the vibration testing on the James Webb Space Telescope was stopped, NASA has restarted the testing stating that they are now fully aware of what caused the previous automatic shut down of the testing and that they have implemented changes to the test profile to prevent it from happening again.
In early December – December 3 to be precise – the vibration testing of the James Webb telescope ceased automatically because of some sensor readings that exceeded predicted levels. Investigation revealed that the testing stopped because of extremely small motions of the numerous “launch restraint mechanisms” that keep one of the telescope’s mirror wings folded-up for launch.
These extremely small motions were caused by strong input vibration and high resonance of the telescope at specific vibration frequencies. Lee Feinberg, an engineer and James Webb Space Telescope Optical Telescope Element Manager at Goddard, said that after having determined the cause, they have implemented the necessary changes to ensure that these small motions do not happen again.
The testing was restarted last week and the tests that were left because of the December automatic shut down were completed. Now with the test complete along one direction, the team will commence testing in the other two directions to confirm that the telescope can withstand vibrations in all three dimensions.
Because of the sheer size of the telescope, it can’t be launched in an unfolded condition. It has to be folded up so as to fit it inside the rocket fairing. This effectively means that the telescope will have to withstand tremendous forces in this folded state and this is where the testing helps determine if the telescope is ready for launch and if not, where it could faulter and solution applied.
Because the mirror of the James Webb Telescope is larger NASA will fold the whole structure for launch. In addition to the mirror, many other parts of JWST must deploy, and each have their own unique set of challenges for testing and launch.
NASA is working with ESA and their launch company, Arianespace, to ensure that the adjustments just made to Webb’s vibration testing adequately envelopes the launch vibration environment, plus some margin. The mission continues to be on track and within budget for a 2018 launch.
The James Webb Space Telescope is the world’s most advanced space observatory. This engineering marvel is designed to unravel some of the greatest mysteries of the universe, from discovering the first stars and galaxies that formed after the Big Bang to studying the atmospheres of planets around other stars. Before the Webb is declared ready for launch, engineers and technicians rigorously test it to demonstrate all aspects of the mission and launch survivability.