SPIRE Design Description - Research Services

Draft SPIRE Design Description Document
(ii) the entrance of the strap into the 2-K detector box must not allow excessive stray light to enter. The
stray light requirements for this are far less stringent than those emplaced on the entrance of the 2-K
straps into the FPU;
(iii) the mechanical supports must positively and reliably locate the straps so the there can be no
possibility of the strap touching the surrounding structure and causing a thermal short. This
contingency is highly undesirable as it could compromise the functionality of the detectors by either
greatly reducing the hold time of the cooler at the operating temperature or preventing the cooler
from maintaining the detectors at the required 300 mK;
(iv) the suspension system must not place an excessive heat load directly to the strap. This is limited to 1
µW per strap (TBC).
The strap will be fabricated from ∅3 mm copper rod with a flexible lighter gauge copper wire running the
last tract to the BDAs. These joints are formed by electron beam welding. A Kevlar suspension system will
provide the mechanical support for the strap while maintaining a sufficient thermal impedance so as to meet
the thermal requirements.
There is a stray light baffle around the entrance of the strap into the detector box. This is to prevent
unfiltered 4-K stray from entering the detector box. It’s design will be similar to the concept illustrated in
Figure 4-49 but will be less complicated due to the less stringent shielding requirements. Several concepts of
the support structure are currently being developed.
Figure 4-50 - Routing of the 300-mK strap from the cooler tip (inside the green box) to the 2-K photometer detector
box.
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