Chapter 5 Robust Performance Tailoring with Tuning - SSL - MIT

PSD OPD14 [m 2 /Hz]
CumulativeOPD14 [m 2 ]
2
1
0
10 −15
10 −20
10 −25
10 −30
x 10 −16
10 −2
10 −1
3.06 Hz
10 0
Frequency [Hz]
10 1
6 Hz
7.55 Hz
Figure 6-7: Output PSD and cumulative variance from nominal TPF SCI design.
Table 6.9: Critical modes of nominal TPF SCI design.
Mode # Freq. [Hz] % Energy (app.). Description
4 1.07 < 1 truss 1 st bending
7 3.06 88.00 truss 2 nd bending
13 5.99 2.42 collector 1 st bending (potato-chip)
18 7.55 16.7 truss 3 rd bending
2 Hz, but does not contribute appreciably to the OPD since it is symmetric and the
path lengths change equally on each arm of the interferometer. Additional critical
modes under 10 Hz are listed in Table 6.9. The cluster of modes around 6Hz are
due to local bending modes of the primary mirrors as shown in Figure 6-8(c). The
third bending mode at 7.55 Hz (Figure 6-8(d)) is also a significant contributor. It is
interesting to note that, although this model is higher-fidelity than the development
model presented in Chapter 2, the global behavior is similar in that the second bending
mode is the most critical.
195
10 2