SPIRE Design Description - Research Services

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Draft SPIRE Design Description Document (v) the FTS is less vulnerable to degradation in performance arising from stray light and out-of-band leaks which can be problematic with a low-background grating instrument; (vi) practical implementation of either a grating or an F-P instrument within the constraints of the Herschel system would have posed serious accommodation problems (grating) or risk of FPU failure due to having multiple mechanisms in series (F-P). 2.3 Instrument functional block diagram Figure 2-1 shows a functional block diagram of the SPIRE instrument. The subsystems are prefixed HS standing for Herschel-SPIRE. The focal plane unit is mounted on the Herschel Optical Bench as shown in Figure 2-2. It is approximately 690 x 410 x 410mm in size, and has three separate temperature stages at nominal temperatures of 4 K, 2 K (both provided by the Herschel cryostat) and 300 mK (provided by SPIRE's internal cooler). The main 4-K structural element of the FPU is an optical bench panel which is supported from the 10-K cryostat optical bench by stainless steel blade mounts. The photometer and spectrometer are located on either side of this panel. The majority of the optics are at 4 K, but the detector arrays and final optics are contained within 2-K enclosures. The 3 He refrigerator cools all of the five detector arrays to 0.3 K. Two JFET preamplifier boxes (one for the photometer and one for the FTS) are attached to the 10-K optical bench close to the 4-K enclosure, with the JFETs heated internally to their optimum operating temperature of ~ 120 K. Note that the shutter is not designed for flight operation and is controlled by SPIRE EGSE. The SPIRE warm electronics consist of a Detector Readout Unit (DCU), a FPU Control Unit (FCU) and a Digital Processing Unit (DPU). The DCU provides bias and signal conditioning for the arrays and cold readout electronics and reads out the detector signals; the FCU controls the FPU mechanisms, the 3 He cooler and the internal calibrators, and housekeeping thermometers. The DPU acts as the interface to the spacecraft, including instrument commanding, and formats science and housekeeping data for telemetry to the ground. SPIRE EGSE SPIRE HSFPU Shutter RF Filter SMEC RF Filter Spacecraft Electronics BSM Phot. Cal. Source FTS Cal. Source RF Filter SPIRE Warm Electronics on SVM Cooler RF Filter FPU Control Unit (HSFCU) Spacecraft Power Distribution Unit FPU Structure RF Filter 10 Thermometers RF Filter Optics Mirrors Baffles Filters, Beam dividers, Dichroics Detector Arrays (0.3 K) P1 P2 P3 S3 S3 FTBp FTBs Detector Control Unit (HSDCU) JFET Boxes Opt. Bench CVV Wall Warm Interconnect Harness (HSWIH) Digital Processing Unit (HSDPU) Spacecraft Command and Data Management System (CDMS) Figure 2-1 - Functional block diagram of the SPIRE instrument
Draft SPIRE Design Description Document +Z +Y +X out of page Definition of FIRST axes directions - for SPIRE (0,0,0) is taken at position of the telescope axial focal point Diameter of optical bench 815 mm Edge of HIFI envelope at base of their mirror is at -22.5 mm Z and - 95 mm Z Indicative shape of FIRST telescope focal plane. The on axis focus position is at a defined height above the FIRST optical bench - the detailed shape of the "bowl"depends on the final design of the FIRST telescope 815 mm Telescope FOV diameter 248 mm Edge of HIFI will be 132 mm from the telescope optical axis in -Y direction on SPIRE (-Z) side Distance to edge of SPIRE box 37.5 mm from optical axis 95 mm 105 mm 170 mm 11 132 mm 192 mm 306 mm +X 202 mm Nominal envelope for the SPIRE FPU Edge of HIFI will be 170 mm from the telescope optical axis in -Z direction +Y SPIRE Envelope - view towards +Z 306 mm 192 mm Nominal envelope for the SPIRE FPU Figure 2-2 Location of the SPIRE FPU on the Herschel Optical Bench 452 mm Cryostat radiation shield envelope. Rotationally symmetric. 504 mm
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SPIRE Design Description - Research Services

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