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Instrumentation and Operations

Telescope: The telescope is a 38 cm Ritchey-Chretien telescope, with a system focal ratio of f/9, effective focal length of 342.9 cm, and field of view of 40 arcmin.

Image Motion Compensation: An Image Motion Compensation (IMC) system stabilized the UIT pointing at a finer level than possible with the Spacelab Image Pointing System (IPS) on the shuttle. Two gyros and a CCD startracker were used to sense motion. A servomechanism that controls small tilts of the UIT secondary mirror was then commanded to maintain stable pointing. Pointing problems affected about a third of the UIT images, evidenced by asymmetric stellar images.

Filters: Each camera had 6 filter settings. The A6 filter wheel slot was empty to accomodate tranmsmission grating mode observations.

Filter
Effective
Wavelength
(Å) 		Bandwidth
(Å) 		Number of
Observations
A1 2488 1147 172
A2 1892 412 51
A3 1964 173 4
A4 2205 244 32
A5 2558 456 74
A6 Grating 15
B1 1521 354 455
B2 1359 160 2
B3 1445 256 2
B4 1585 129 10
B5 1615 225 610
B6 1496 404 54

Transmission Grating: The grating was ruled at 75 lines mm-1 on a CaF2 substrate. The first order yields a linear dispersion of 840 Å, with a resolution of about 19 Å in the range 1400 - 3400 Å over a 35 arcmin field of view.

Cameras: Two detectors were used, each of which was a magnetically focused, two-stage image intensifer with phosphor output, coupled with fiber optics to 70mm film. The near-ultraviolet (NUV or "A") camera used a Cs2Te photocathode, while the far-ultraviolet (FUV or "B") camera camera used CsI. The NUV camera failed at launch during ASTRO-2 and was not used during that flight. Both provided long-wavelength cutoffs that made the instrument solar-blind.

Film: The images were recorded on Kodak IIa-O film. The specially designed film transports each held about 1200 frames. The film was advanced by stepper motors. Annotation devices projected the frame count, exposure time, 30-step grey scale, and fiducial marks on each frame.

Further information about the UIT instrument and operations may be found in Section 1. Introduction and UIT Overview of the 1997 PASP article describing the UIT mission, as well as the earlier 1992 ApJ article describing its design and performance.