Vibration testing on the James Webb Space Telescope, the multibillion-dollar successor to Hubble, has resumed after engineers traced a problem that cropped up last month to a restraint holding part of the observatory’s giant segmented mirror in place for launch.
The quick diagnosis keeps JWST on track for launch in October 2018, and engineers still have several months of time reserved in the schedule leading up to launch late next year to handle any more unexpected problems.
In a status report posted to the JWST web site this week, NASA said numerous tests and analysis of data and modeling led engineers to attribute an anomaly during vibration testing Dec. 3 to “gapping,” or extremely small motions, in a launch restraint mechanism holding back the wings of the telescope’s primary mirror, which are folded and stowed to fit inside the rocket for liftoff, then unfurl once the observatory is in space.
Eric Smith, JWST’s program director at NASA Headquarters, said in an interview last month that accelerometers near the launch restraint mechanisms detected unexpected readings during vibration testing intended to ensure the telescope and its instruments can survive the shaking of launch.
“During what’s called proto-flight level testing — this is where you test it to a little bit more than you expect from the launch vehicle just to make sure you have safety margin — we noticed that two of the accelerometers were giving us readings of much higher acceleration than were predicted,” Smith told Spaceflight Now last month. “When the software that runs the shaker tables detected this, they properly shut everything down safely so the team would have the time to look at these data and try to figure out why we’re getting these readings.”
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