The SPEAR Instrument and On-Orbit Performance

The SPEAR (or "FIMS") instrumentation has been used to conduct the first large-scale spectral mapping of diffuse cosmic far-ultraviolet (FUV; 900-1750 Å) emission, including important diagnostics of interstellar hot (10 4 -10 6 K) and photoionized plasmas, H 2 , and dust-scattered starlight. The instrumentation's performance has allowed for the unprecedented detection of astrophysical diffuse FUV emission lines. A spectral resolution of λ/Δλ ~ 550 and an imaging resolution of 5' is achieved on-orbit in the Short (900-1150 Å) and Long (1350-1750 Å) bandpass channels within their respective 4 0 × 4 6 and 7 4 × 4 3 fields of view. We describe the SPEAR imaging spectrographs, their performance, and the nature and handling of their data.