Chapter 5 Robust Performance Tailoring with Tuning - SSL - MIT

Table 6.6: Primary mirror properties.
Name Description Value Units Source
dPM mirror diameter 3.5 m JPL
ρM material density 2210 kg/m 3 ULE Glass
EM Young’s Modulus 67.6 GPa ULE glass
νM Poisson’s Ratio 0.17 none ULE glass
ρa areal density 40 kg/m 2 JPL estimate
mount properties are listed in Table 6.7 for reference.
Table 6.7: Primary mirror mount properties.
Name Description Value Units Source
ρPM material density 1830 kg/m 3 low CTE MJ55
EPM Young’s Modulus 111.7 GPa low CTE MJ55
νPM Poisson’s Ratio 0.3 none low CTE MJ55
rPM cross-sectional radius .05 m frequency estimates
The combiner consists of the combining optics, supporting structure, a cryo-cooler,
and thermal and mechanical controls and is located at the center of the interferometric
array. All of these elements are modelled together as a concentrated mass (250 kg)
with no inertia. The mass of the combiner is based on the CBE from JPL. The
combiner mass is located at the origin of the spacecraft coordinate system and is
connected to the bus with a rigid element. All of the finite elements that make up
the instrument model are listed in Table 6.8.
Optical Performance
The performance metrics of interest are the optical path differences (OPD) between
the reference collector, collector 1, and the other three apertures as shown schemati-
cally in Figure 6-6. Similar to the development model the OPD calculation is based
only on the perturbations of the center node of the collector primary mirrors since
there is no optical train detail in the model.
When the interferometer is in its nominal configuration, i.e. the collectors and
combiners are not perturbed from their locations, the path lengths from the star to
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