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34.1 GHRS History

Critical events in the operational history of the GHRS include:

  1. The GHRS was launched inside HST in April 1990.
  2. The Side 1 low-voltage power supply (LVPS) had repeated problems in the summer of 1991, eliminating access to both low- and high-dispersion modes in the far-UV (G140L and Ech-A). Prior to this loss, Ech-A was the most-requested GHRS grating, but deconvolution techniques allowed G160M observations to approach Ech-A resolution. Hence some of this science was done with Side 2 during Cycles 2 and 3.
  3. The LVPS problem was fixed during the first servicing mission, restoring important capabilities and leading to greater GHRS usage.
  4. The failure of the SC1 calibration lamp eliminated redundancy for wavelength calibration. Fortunately, the specifications for lamps were very conservative and SC2 had ample lifetime to meet observer needs.
  5. Acquisitions during the early years had to specify BRIGHT and FAINT limits, leading to failed acquisitions and wasted telescope time. Implementation of BRIGHT=RETURN eliminated this problem. Also, BRIGHT=RETURN used 32 bits, preventing register overflow.
  6. Corrective Optics Space Telescope Axial Replacement (COSTAR), installed during the first servicing mission of December 1993, changed the net throughput of the large science aperture (LSA) by very little (two extra reflections offset the better PSF), but the contrast of the PSF changed enormously, resulting in reliable fluxes. Small science aperture (SSA) throughput improved too, by about a factor of two.
  7. Before COSTAR, HST's spherical aberration was sometimes a "feature" for acquisitions in the sense that the algorithm could find the wings of the PSF even when centering was poor.
  8. A catastrophic failure occurred one week before the second servicing mission, resulting in the complete shutdown of the GHRS. The most important loss was some special observations that were to be made with the COSTAR mirrors withdrawn to try to determine the origin of far-UV sensitivity losses.


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