GHRS Instrument Science Report 072 "A Review of the Utility of SPYBALs" Lisa E. Sherbert and Stephen J. Hulbert Oct 1995 Abstract Many times users want to know how long they can observe without a spectrum Y-balance (SPYBAL) in an effort to limit the motion of the carrousel during an observation. This report discusses the rationale for SPYBALS in terms of the drift of the spectrum across the photocathode with time, taking into account the tilt of the spectrum across the diode array. The results of our investigation reconfirm that the default schedule of SPYBALs should be used to keep the spectrum properly centered on the diode array.
