SPIRE Design Description - Research Services

Draft SPIRE Design Description Document
means of several hollow pins. These pins ensure that in case of dismounting of the mirror, it will be
reassembled in the same position. During integration of the mirrors in the SPIRE structure, the mirrors are
mounted on brackets. The mirror mounts are designed to have the first natural mode of vibration above
200 Hz. Figure 4-23 below shows a drawing of the CM5 mirror, which is the heaviest one.
For the mechanical interface between the mirror mounts and the SPIRE optical bench, the technique of using
a hollow dowel pin as illustrated in Figure 4-40 is adopted. The mounting accuracy is nominally within 0.5
arc minute and 0.05 mm linearly. The mechanical interface between the mirror and the mirror mount is
illustrated in Figure 4-24. This technique ensures that the rotational and translational degrees of freedom for
the mirror are tightly constrained in a repeatable fashion.
The finish of the mirrors is to optical quality. This is to permit the alignment of the mirrors to be performed
within the optical wave lengths (< 10 nm RMS, specular reflectivity > 80%). The emissivity of the surfaces
within the sub-millimetre wavelength is to be less than 1% to minimise the spurious emissions transmitted to
the detectors. The specular reflectivity in the same wavelength is in excess of 99%.
All the common mirrors, the photometer mirrors and the spectrometer mirrors are listed and briefly
described in Table 4-3. The locations of the mirrors with respect to the other optical components are
illustrated in Figure 4-25 and Figure 4-26. Information on the optical alignment of the instrument, and
details of the corner cubes is found in the FIRST SPIRE: Optical alignment verification plan, (Origne and
Dohlen 2000).
Figure 4-22 – Example of mirror mounts.
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