JWST in Kourou
The James Webb Space Telescope is now in a payload processing facility at the spaceport in Kourou, French Guiana, and on schedule for a launch Dec. 18. Credit: NASA/Chris Gunn

WASHINGTON — NASA announced Nov. 22 that it is delaying the launch of the James Webb Space Telescope by at least four days to investigate an incident that took place preparing the spacecraft for launch in French Guiana.

NASA said that, working in conjunction with the European Space Agency and Arianespace, it has delayed the launch of JWST on an Ariane 5 from Dec. 18 to no earlier than Dec. 22 to perform additional testing of the spacecraft after the incident.

In that incident, according to the NASA statement, a “sudden, unplanned release of a clamp band” that secures JWST to its launch vehicle adapter “caused a vibration throughout the observatory.” Those activities, the statement added, were the responsibility of Arianespace.

It’s not clear exactly when the incident took place other than in the last few days. NASA officials did not mention it during a pair of Nov. 18 briefings about the science and instruments of JWST, saying at the time that the mission was still on schedule for a Dec. 18 launch.

“Of course, when you work on a $10 billion telescope, conservatism is the order of the day,” Thomas Zurbuchen, NASA associate administrator for science, said when asked about the incident during a Nov. 22 press conference about the upcoming launch of the agency’s Double Asteroid Redirection Test (DART) mission.

He said that, because JWST is so close to launch, it did not have sensors that had been in place when it was transported to French Guiana to measure the effect of the clamp release on the spacecraft, leaving only calculations estimating the force imparted on it. “For sheer caution, what we have done after these calculations is gone back to a small number of subsystems and just do the functional tests to make sure that, with all of that conservatism, to be sure that nothing happened.”

“It’s just the right thing to do right now, to do these tests, to make sure everything is as ready as we hope they are,” he said. “I hope that, in just a few days here, we will be in good shape.”

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...