SPIRE Design Description - Research Services

Draft SPIRE Design Description Document
Power absorbed by det. (pW)
10
P250( Tshut)
P350( Tshut)
P500( Tshut)
6.712 10 5 −
×
10
9
8
7
6
5
4
3
2
1
0
4 6 8 10 12 14 16 18 20 22 24
4 Tshut
Shutter Temperature (K)
250 um
350 um
500 um
Figure 4-55 - Detector power vs. shutter temperature for the three photometer bands.
The telescope power levels that must be reproduced are nominally 3.9, 3.2 and 2.4 pW at 250, 350 and 500
µm, respectively (see §6). These correspond to shutter temperatures of approximately 17, 14.5, and 12 K.
The effective emissivity of the telescope in-orbit is highly uncertain, and the instrument will be tested in the
AIV facility over a range of backgrounds. Allowing for a factor of at least two in the power levels to be
reproduced, the shutter is therefore designed to operate at up to 25 K. Note that the shutter is not required to
reproduce the correct background levels on all arrays at the same time.
With the shutter thus providing a representative background radiation flux, the photometer and spectrometer
calibration sources can be used to stimulate the detectors and the resulting signal read out from the read out
electronics. These tests can be carried out in the AIV facility and again in the Herschel cryostat, to ensure
that the system is operating nominally.
The baseline location of the shutter is shown in Figure 4-56. As this shutter is only used in the pre-launch
testing of the detectors there is a launch lock device that will prevent the shutter from closing during flight.
This launch lock mechanism is a passive device, in that it requires no power to keep the shutter in the locked
open position.
The other components of the shutter are described below.
Vane: A metal vane blackened on one side is used to block off the input radiation.
Heater: An electrical heater mounted on the vane of the shutter provides power to heat the vane up to the
design temperature.
Temperature sensor: A single Lakeshore Cernox thermistor is mounted on the shutter vane to monitor its
temperature.
Actuator: A single rotary stepper motor is used to actuate the shutter vane. It can be driven by a primary set
of two windings or alternatively by a separate set of two windings.
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