Chapter 5 Robust Performance Tailoring with Tuning - SSL - MIT
Chapter 5 Robust Performance Tailoring with Tuning - SSL - MIT Chapter 5 Robust Performance Tailoring with Tuning - SSL - MIT
h1. h 1 w1 w 2 h 2 (a) Y (b) Figure 6-9: Schematic of TPF SCI tailoring parameters (a) XZ-plane (b) XY-plane. Geometric tailoring is also allowed in the XY-plane through the parameters w1 and w2. These parameters are the width of the batten frame at the end and in the center of the array as shown in Figure 6-9(b). The width tailoring is similar to the height tailoring in that the batten widths vary linearly in x and are symmetric about the center of the array. However, in this plane the tailoring is also symmetric about the x-axis, since the positions of the optics are not affected by the batten frame widths. There are constraints on the tailoring parameters in order to keep the design within practical limits. Both the height and width parameters are subject to a lower bound of 10 cm. In addition, the total mass of the system is constrained to be less than 4000 kg. This number is based on launch vehicle mass limits and ensures that the resulting design is realistic. 198 Z X X
6.2.2 Tuning The tuning parameters are chosen from a small subset of design variables that could practically be adjusted on hardware during component testing or on-orbit operation. Only two tuning parameters are used in order to keep the number of design variables required for the RPTT problem small. The parameters are the cross-sectional radius of the primary mirror supports, rPM and the corner frequency of the RWA isolator, fiso. The nominal tuning parameter values are listed in Table 6.11. Adjusting the parameter rPM is equivalent to changing the stiffness of the optical mount. Although the radii of the support bars are not easily adjusted on the hardware, this parameter is used to model a tunable optical mount stiffness. The isolator corner frequency parameter models a type of active isolator in which the corner frequency can be adjusted through some unspecified mechanism. Table 6.11: TPF SCI model tuning parameters. y Description y0 Units rPM XS radius of primary mirror support 0.05 m fiso RWAisolatorcornerfrequency 8 Hz The tuning parameters are subject to constraints that keep them within realis- tic limits. The radius of the primary mirror support structure is constrained by a lower bound of 1 cm to ensure that the primary mirrors stay connected to the truss. Although the radius of the optical mount supports does in fact affect the mass of the system, this parameter is not included in the mass constraint calculation. The reason for this omission is that in reality only the stiffness of the mount will change and not the physical properties of the support. The corner frequency of the RWA isolator is constrained to be between 2 and 10 Hz based on engineering judgment and experience. 6.2.3 Uncertainty The uncertainty parameters considered for the TPF SCI model are very similar to those in the development model and are listed in Table 6.12. The Young’s Modulus of 199
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h1.<br />
h<br />
1<br />
w1<br />
w 2<br />
h 2<br />
(a)<br />
Y<br />
(b)<br />
Figure 6-9: Schematic of TPF SCI tailoring parameters (a) XZ-plane (b) XY-plane.<br />
Geometric tailoring is also allowed in the XY-plane through the parameters w1<br />
and w2. These parameters are the width of the batten frame at the end and in the<br />
center of the array as shown in Figure 6-9(b). The width tailoring is similar to the<br />
height tailoring in that the batten widths vary linearly in x and are symmetric about<br />
the center of the array. However, in this plane the tailoring is also symmetric about<br />
the x-axis, since the positions of the optics are not affected by the batten frame<br />
widths.<br />
There are constraints on the tailoring parameters in order to keep the design<br />
<strong>with</strong>in practical limits. Both the height and width parameters are subject to a lower<br />
bound of 10 cm. In addition, the total mass of the system is constrained to be less<br />
than 4000 kg. This number is based on launch vehicle mass limits and ensures that<br />
the resulting design is realistic.<br />
198<br />
Z<br />
X<br />
X
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