SPIRE Design Description - Research Services

Draft SPIRE Design Description Document
covers are created by screwing a series of lightweighted, 12mm thick plates together in the manner shown in
Figure 4-40-B. The integration plan for the FPU structure sees the covers being loosely assembled with the
screws not being fully tightened. The covers are then screwed tightly onto the SOB and the cover screws
fully tightened thus forming a monocoque cover structure that will not be subsequently disassembled.
Access to the SOB with integrated optical components will be done by removing either the photometer or
the spectrometer covers. The remaining cover and optical bench give the required stiffness to the structure.
The two covers and the SOB are machined from Al-6082. After final machining, it is passivated with
Aluchrome treatment.
The FPU structure is connected to the Herschel Optical Bench via three feet structures. These feet have to:
(i) provide a rigid connection between SPIRE and Herschel so that the first natural frequency of the
integrated instrument is higher than 100 Hz and prescribed in the IRD.
(ii) provide adequate thermal isolation between the 10K HOB and the FPU structure so that the heat
load requirements are met and that the temperature of the structure does not rise above the nominal
operating temperature;
(iii) allow for contraction and expansion between the FPU and the Herschel optical bench without
inducing high stresses.
This is achieved through the use of two struts illustrated in Figure 4-41 attached to the covers and a single
conical pin joint attached to the central SPIRE optical bench. Each of these three supports have a high
thermal impedance and help to isolate the FPU structure from the HOB. The conical pin joint restrains the
three translation degrees of freedom of the structure. The two struts in combination with the pin restrain the
three rotational degrees of freedom. Vespel washers electrically isolate the
Figure 4-42 - View of the Lakeshore, Cernox SD hermetically sealed RTD thermometers.
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