Space Telescope Science Institute
Call for Proposals and HST Primer
help@stsci.edu
Table of Contents Previous Next Print


Hubble Space Telescope Primer for Cycle 22 > Chapter 2: System Overview > 2.1 Telescope Design and Field of View

2.1 Telescope Design and Field of View
The design and layout of HST are shown schematically in Figure 2.1. The telescope is powered by two solar arrays that are oriented towards the sun. Nickel-hydrogen batteries power the telescope during orbital night. Two high-gain antennae provide communications with the ground via the Tracking and Data Relay Satellite System (TDRSS). Power, control, and communication functions are carried out by the Support Systems Module (SSM) that encircles the primary mirror.
Scientific instruments (SIs) are mounted in bays behind the primary mirror. WFC3 occupies one of the four radial bays; it has a 45 pick-off mirror that allows it to receive the on-axis beam as shown in Figure 2.2. There are three Fine Guidance Sensors (FGSs), each in the other radial bays, that receive light that is 10 to 14 arcseconds off-axis in the telescope’s field of view. At least two FGSs are required to guide the telescope, therefore, it’s possible to conduct astrometric observations with the third FGS. The remaining SIs are mounted in the axial bays and receive images several arcminutes off-axis.
The coordinate system used for HST’s focal plane is fixed to the telescope; it consists of three orthogonal axes: U1, U2 and U3. As shown in Figure 2.1, U1 lies along the optical axis, U2 is parallel to the solar array rotation axis, and U3 is perpendicular to the solar array axis. (Note: Some HST documentation uses the alternative V1, V2, V3 coordinate system for which V1=U1, V2= –U2 and V3= –U3.)
Figure 2.1: The Hubble Space Telescope Configuration after Servicing Mission 4 in 2009
Major components are labeled, and a diagram in the lower left shows the U1,U2, and U3 spacecraft axes.
Figure 2.2: HST Field of View
Aperture locations for science instruments and FGSs are shown in the (U2,U3) focal plane, as it would appear projected onto the sky. The scale is in arcseconds.
Table 2.1 lists the rough effective locations of the SI apertures in the (U2,U3) coordinate system. Precise values, available in the HST Instrument Handbooks (see Section 1.3), depend on subtleties in aperture definitions and operational modes.
Table 2.1: Nominal Effective Relative Aperture Locations

Hubble Space Telescope Primer for Cycle 22 > Chapter 2: System Overview > 2.1 Telescope Design and Field of View

Table of Contents Previous Next Print