SPIRE Design Description - Research Services

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Draft SPIRE Design Description Document Figure 4-39 - Simulated spectrum of the 80 K telescope seen through the SPIRE FTS with representation optical filtering. The black line is before applying the frequency response of the detectors the red line after. Note the much larger rate of change of the sign 4.10 FPU structure Parameter Specification L1 Heat leak to FPU from FIRST Optical Bench L0 Conductive heat leaks down 2K box supports 300mK Parasitic heat leak on 300mK detector stage 300mK Heat leak down the Photometer 300mK strap supports 300mK Heat leak down the Spectrometer 300mK strap supports The structure has three main requirements: 1. To mechanically support and positively locate the components (optical or otherwise) of the photometer and the spectrometer; 2. To provide the correct thermal isolation between the various temperature stages of the instrument; and 98 6mW (for ∆T = 11-4.2 = 6.8K) 1mW (for ∆T = 4.2 - 1.7 = 2.5K)
Draft SPIRE Design Description Document 3. To provide adequate EM shielding and stray light shielding to the photometer and spectrometer such that the detectors see no spurious sources of EM power. The structure is comprised of three main components; the Spire Optical Bench (SOB), the photometer cover and the spectrometer cover. The Spire Optical Bench is machined from a single block of Al-6061 approximately 675 mm long (aligned with the Spacecraft Z axis, See Figure 2-2) by 410mm high (aligned in the X axis) and 50 mm thick. All the optical components of the spectrometer are located on the +Y side of the SOB while all the components of the photometer are located on the –Y side. The mass of the SOB is minimised by machining ribbed pockets (nominally 70 x 70 mm) on both sides. The nominal thickness of the ribs is 2 mm and the centreline plane of the bench is 2 mm (TBC) as shown in Figure 4-40-A. Optical Component SPIRE OPtical Bench 8-32 UNC Thru bored Hollow dowel pin 8-32 UNC Helicoli Screw Insert 3 70 Nom. A B Figure 4-40 Details of (A) SOB lightweighting and optical component interfaces and (B) cover joint design. The optical components are located on the bench by hollow dowel pins and 8-32 UNC screws provide positive the mechanical attachment. The SOB is manufactured and toleranced in such a way so that the position of the components located on the bench are in the correct position when the bench has undergone the contraction during cooling from room temperature to the nominal operating temperature of 4K. Figure 4-41 - FPU/HOB interface strut. The ribbed design of the SOB gives it excellent bending stiffness but it will have a relatively low torsional stiffness. The required torsional stiffness is achieved through the photometer and spectrometer covers. The 99 3 50 3 6 2 2 12
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SPIRE Design Description - Research Services

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