WEBVTT FILE

1
00:00:00.010 --> 00:00:04.010
(music)

2
00:00:04.030 --> 00:00:08.030
Today is Sunday, January, 11th

3
00:00:08.050 --> 00:00:12.070
2015. we're in the SSDIF cleanroom. We're here to

4
00:00:12.090 --> 00:00:16.110
do some model testing on the pathfinder structure. My name is Brian

5
00:00:16.130 --> 00:00:20.120
Ross, I'm the lead test engineer for JWST.

6
00:00:20.140 --> 00:00:24.150
And what we're doing today, we've hooked up a model shaker to part of the

7
00:00:24.170 --> 00:00:28.170
structure and we're going to drive it with a random signal, and collect response

8
00:00:28.190 --> 00:00:32.190
data from almost 400 channels of accelerometers that are

9
00:00:32.210 --> 00:00:36.200
attached to the structure will be taking data in a couple of different

10
00:00:36.220 --> 00:00:40.250
frequency bands. We'll start with a low frequency band goes out to 80 herrtz.

11
00:00:40.270 --> 00:00:44.270
We're driving it with very low levels

12
00:00:44.290 --> 00:00:48.300
for the large set of data we're going to collect it's only a half a pound RMS.

13
00:00:48.320 --> 00:00:52.330
So it's a very low force input.

14
00:00:52.350 --> 00:00:56.360
They're trying to correlate their fine line element models do to

15
00:00:56.380 --> 00:01:00.380
jitter analysis for the deploy on orbit

16
00:01:00.400 --> 00:01:04.420
configuration of the observatory and so they're interested in

17
00:01:04.440 --> 00:01:08.450
particular modes of the mirrors and there's a

18
00:01:08.470 --> 00:01:12.490
handful of target modes of the mirror themselves and then the entire structure

19
00:01:12.510 --> 00:01:16.540
has lots of modes in the bandwidth we're looking at.

20
00:01:16.560 --> 00:01:20.570
We collect frequency response functions which is a ratio of the

21
00:01:20.590 --> 00:01:24.590
acceleration at all the points we've got accelerometers to the input

22
00:01:24.610 --> 00:01:28.610
force. And we can take that data and

23
00:01:28.630 --> 00:01:32.650
curve fit that data and extract what we call mobile parameters which is

24
00:01:32.670 --> 00:01:36.670
frequency, damping, and what we call mode shapes.

25
00:01:36.690 --> 00:01:40.690
We collect all that

26
00:01:40.710 --> 00:01:44.720
data, provide the results to the analysts that create the fine

27
00:01:44.740 --> 00:01:48.740
line element models. And they use that to tweak their models.

28
00:01:48.760 --> 00:01:52.760
So it's accurately representing the structure.

29
00:01:52.780 --> 00:01:56.780
(music)

30
00:01:56.800 --> 00:02:00.100
(music)