Overview of SPIRE
The Spectral and Photometric Imaging REceiver (SPIRE) instrument is one of three instruments which will be used with the Herschel telescope and has been optimised for science which can only be done from space and for the two most important scientific goals of Herschel. By measuring the far infra-red and sub-millimetre emission radiated by gas and dust heated by young stars SPIRE will help us understand the physics of how stars form and will enable us to detect galaxies forming in the very early Universe.
SPIRE is really two instruments fitted into one: a 3 colour camera designed for sensitive imaging over as wide a field of view as possible, and an imaging Fourier Transform Spectrometer (FTS). For maximum sensitivity the optics and detectors have to be very cold - the optics are cooled to approximately 2 degrees Kelvin and the bolometers to 0.03 degrees Kelvin, and it is a considerable engineering challenge to design and build an instrument that will operate in such an extreme environment.
The camera will be used to carry out deep surveys of the universe in the still poorly known wavelength region between 200 and 700 microns, to discover new proto-galaxies and young stars. The far-infrared colours derived from the camera images will identify the most exciting new sources. These can then be measured with the FTS to obtain the crucially important measurements of their energy distribution.
These two images (courtesy of MSSL) show the layout of the two sides of the SPIRE instrument – in these views it has the external covers removed to show either side of the main structural bench. On one side, shown above right, the camera optics will be mounted and the other half will contain the FTS optics as shown below right. The detectors for both the camera and the FTS are mounted next to each other at one end.
A very important part of the SPIRE instrument is the "chopper" or Beam Steering Mirror (BSM). The first mirror the infrared light from the telescope will encounter when it enters the instrument can be oscillated rapidly back and forth between two positions, so that the detectors measure alternatively the astronomical source and a nearby region of sky. This chopping motion is necessary because it means that changes in the background infrared radiation entering the telescope can be removed from the astronomical signal, improving the accuracy and sensitivity of the measurements.
The chopping mirror is nominally 32mm diameter, and when built the whole BSM mechanism will be about the size of a child's juice carton.
2 axis prototype assembly, Jul01 (one motor in, no harness).
Structural Thermal Model & optical alignment tool (OGSE), Nov02.
Development Model 2: Front, prior to fitting baffle
Development Model 2: Rear, prior to fitting PCAL
Upscreen rigs mounted to an interface cube ready for a shake test. These rigs mount and load a set of flex pivots in a representative way for cost-effective shake tests.