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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.
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