IF-MOS trade-off study: Operational issues


Two significant aspects of spacecraft operation are relevant here:

A consideration of the first of these issues is beyond the scope of this study except to point out that an IFS is likely to have fewer moving parts than a MOS but that, in the current designs, the IFS has a larger total detector array.

The MOS concept implies a requirement for prior imaging to a depth sufficient to identify targets. This may be done with a camera or with the spectrograph itself. If this imaging is carried out with broadband filters, it will discriminate in favour of continuum and against emission line sources. Once objects have been identified, their positions have to be transferred to the micro-mirror/shutter array with a precision which depends on the smallest of the synthesised apertures. Fine adjustments to the pointing can be carried out either with the spacecraft pointing system (using the fast steering mirror) or internal to the MOS by readdressing apertures. Insofar as the whole process can be carried out autonomously, the instrument could be used in a parallel mode with long camera exposures.

The IFS-LR is essentially a 'point and shoot' instrument with no requirement for field pre-imaging. Given the discrimination against the sky provided by a spectral dispersion, it is sensitive to emission line sources which which may not appear in broadband images.


Modified by Bob Fosbury on July 19, 1999.
For more information, please send mail to Bob Fosbury.