SPIRE Design Description - Research Services

Draft SPIRE Design Description Document
temperature immediately outside the FPU is at a temperature of between 10 and 15 K and is therefore
radiating strongly in the frequency band of the detectors. A stray light baffle is therefore required to greatly
attenuate this stray light from entering the FPU close to the detectors. Two possible
‘Add-on’
Structure
Thermal Strap
Aramide cable
suspension
107
Aramide cable
suspension
‘Part of the structure’
Figure 4-49 – Conceptual design of the stray light baffle on the 2-K straps entering the FPU.
light baffle on 2-K straps
power limits on 2-K strap during recycle (IID-B Ch 5)
FIRST Interface SPIRE Interface IID-A
(Sect. 5-26)
4.12.2 300 mK
Instrument Temperature
Requirement
Instrument
Conductance
Requirement
L2 Photometer JFET Enclosure T < 15K - TBD
L2 Spectrometer JFET Enclosure T < 15K - TBD
L1 FPU 4K Optical Bench T < 6K T < 3.5K (at FPU Flange) TBD
L0 FPU 1.8K Boxes T < 2K T < 1.75K (at FPU Flange) TBD
L0 Cooler Evaporator T < 2K T < 1.75K (at FPU Flange) G>100mW/K
@ 2K
L0 Cooler Pump T < 2K T < 1.75K (at FPU Flange) G>50mW/K @
2K
For the photometer and spectrometer detectors to operate correctly, they have to be maintained below a
temperature of 300 mK during operation. Power is constantly being dissipated within the bolometers due to
ohmic heating caused by the bias current and power is being absorbed due to photon thermailization, and
conduction from warmer parts of the instrument. This heat needs to be carried away from the bolometers to
prevent them from heating up. Two 300-mK straps between the photometer and spectrometer BDAs to the
3 He cooler conduct this heat away. The routing of the photometer 300mK strap is shown in Figure 4-50 and
Figure 4-51 shows the routing of the spectrometer strap.
The design of these straps is challenging. They have the following requirements:
(i) the straps need to be supported rigidly so that the first mode of vibration is above 120 Hz (TBC);