SPIRE Design Description - Research Services

Draft SPIRE Design Description Document
5. INSTRUMENT OPERATING MODES
The operational modes of the SPIRE instrument are documented in detail in the OMD. These operating
modes can be summarised as being the sequence adopted to turn the instrument on, preparing it for scientific
observations, making the observations, the recycling of the cryogenic cooler and the abnormal and normal
shut down. The implementation of the astronomical observing modes will be briefly described here.
5.1 Spacecraft pointing
It is assumed that SPIRE pointing will be defined with respect to the telescope boresight by two offset
positions, one for the centre of the photometer arrays and one for the centre of the spectrometer arrays, as
shown below. When the telescope is pointed at a source at the request of SPIRE, it shall be aligned on one of
the two positions defined in Figure 5-1 below. Any offsetting by the SPIRE BSM or the AOCS shall then be
defined with respect to this position.
θ Z
Centre of
Herschel
focal plane
θ Y
115
Centre of photometer fov
Coordinates:(θ YP =0º,
θ ZP =0º10’59”)
Centre of Spectrometer fov
Coordinates: (θ YS = 0º7’23”,
θ ZS=0º10’59”)
Figure 5-1 - Definition of SPIRE pointing offsets with respect to the telescope boresight.
5.2 Spacecraft movements during SPIRE observing
The Herschel spacecraft is capable of executing various controlled movements to allow observations of
various kinds by the three instruments. These are described in detail in the IID-A. SPIRE will mainly use the
following spacecraft movements.