Transcripts of JWST Machine Vibration Test Snapshot H264

(music) Today is Sunday, January, 11th 2015, we're in the SSDIF cleanroom. We're here to do some model testing on the pathfinder structure. My name is Brian Ross, I'm the lead test engineer for JWST. And what we're doing today, we've hooked up a model shaker to part of the structure and we're going to drive it with a random signal, and collect response data from almost 400 channels of accelerometers that are attached to the structure will be taking data in a couple of different frequency bands. We'll start with a low frequency band goes out to 80 herrtz. We're driving it with very low levels for the large set of data we're going to collect it's only a half a pound RMS. So it's a very low force input. They're trying to correlate their fine line element models do to jitter analysis for the deploy on orbit configuration of the observatory and so they're interested in particular modes of the mirrors and there's a handful of target modes of the mirror themselves and then the entire structure has lots of modes in the bandwidth we're looking at. We collect frequency response functions which is a ratio of the acceleration at all the points we've got accelerometers to the input force. And we can take that data and curve fit that data and extract what we call mobile parameters which is frequency, damping, and what we call mode shapes. We collect all that data, provide the results to the analysts that create the fine line element models. And they use that to tweak their models. So it's accurately representing the structure. (music) (music)