10.1 Introduction to the FGS

The Instrument Configurations and Operating Modes described in the following section are used for the Visit and Exposure Specifications. A summary of the legal Visit and Exposure Specifications entries is provided; more complete descriptions of Instrument Configurations, Modes, Apertures, Spectral Elements, etc. are available in the FGS Instrument Handbook.

Note that many of the Optional Parameters have default values; in such cases, an Optional Parameter entry in the Visit and Exposure Specifications is necessary only if it is desired to override the default value. In the STScI proposal system the physical units of Optional Parameter quantities are always implicit and should never be entered by the observer.

Optional Parameters whose descriptions begin with the phrase “USE WITH CAUTION” pose a risk to the intended science if a non-default value is used inappropriately. These parameters are italicized in Table 10.1. You may wish to discuss the use of these parameters with your Contact Scientist, if you have one, or with an Instrument Scientist via help@stsci.edu.

Please note that spatial scans are not permitted with the FGSs. Also note that only FGS1 will be calibrated as a science instrument for Cycle 20.

Table 10.1 lists the permitted Instrument Configuration, Operating Modes, Fields of View, Spectral Elements, and Optional Parameters for the FGS.

Table 10.1: Supported Instrument Parameters for the FGS

Config	Mode	Field of View	Spectral Elements	Optional Parameters
FGS	POS 10.2	1, 2, 3	FGS 1, 2, and 3: F583W, F5ND, F550W, PUPIL FGS 1 and 3: F605W; FGS 2 only: F650W	NULL, ACQ-DIST, COUNT, FES-TIME
	TRANS 10.3	1, 2, 3	FGS 1, 2, and 3: F583W, F5ND, F550W, PUPIL FGS 1 and 3: F605W; FGS 2 only: F650W	SCANS, STEP-SIZE, ACQ-DIST

 

The sections on the following pages provide further details of the entries to be made on the Visit and Exposure Specifications when a particular FGS Mode/Configuration is chosen.