/ 2000, 20,000, and 100,000.
The Goddard High Resolution Spectrograph (GHRS) is one of five scientific
instruments that currently share the focal plane of the Hubble Space Telescope
(HST). Its purpose is to obtain ultraviolet spectra of astronomical objects in
the 1150 - 3200 Å range at spectral resolutions of / 2000, 20,000, and 100,000.
It has two square entrance apertures: the large science aperture (LSA) is 2".0 on a side (1".74 post-COSTAR) and the small science aperture (SSA) is 0".25 on a side (0".22 post-COSTAR).
Two photon-counting 512-diode Digicons serve as the detectors. Side 1 uses a CsI photocathode with a LiF faceplate to provide higher sensitivity at the shortest wavelengths (and the only low-resolution capability), and Side 2 uses a CsTe/MgF2 combination to cover the entire wavelength range of the GHRS. The GHRS acquires spectra in either an accumulation or rapid-readout mode.
Routine GHRS observations were possible by September, 1990, a few months after
the discovery of spherical aberration in the HST optics. Side 1 observations
were suspended in August, 1991, due to problems with a low-voltage power
supply, and resumed after the first servicing mission fixed these problems in
December, 1993. The installation of the Corrective Optics Space Telescope
Axial Replacement (COSTAR) on HST at this time allowed the GHRS to fully
recover its designed sensitivity and resolution, except for reduced
sensitivity in the far UV (
< 1200 Å) due to the COSTAR mirrors.