The Southwest Ultraviolet Imaging System (SWUIS) is an innovative telescope/charge-coupled device (CCD) camera system that operates from inside the shuttle cabin. SWUIS is used to image planets and other solar system bodies in order to explore their atmospheres and surfaces in the ultraviolet (UV) region of the spectrum, which astronomers value for its diagnostic power.

SWUIS will fly its second space shuttle mission on STS-93. This mission will focus on obtaining UV imagery of an array of planetary and astrophysical targets. The specific objectives of SWUIS during this flight are to (i) obtain the mid-UV albedo (reflected light) from Mercury for the first time and search for spatial variations across the planet; (ii) record mid-UV dynamic movies of the upper atmospheres of Venus and Jupiter; (iii) establish the morphological appearance and phase curve of the moon in the mid-UV for the first time; (iv) search for vulcanoids, a putative population of small, asteroid-like bodies residing interior to Mercury's orbit; and (v) obtain mid-UV dynamic movies of the airglow along the Earth's limb (in camera science mode [CSM]).

SWUIS is stored in the orbiter middeck lockers during launch and entry and is assembled for on-orbit operations. Video data from the SWUIS intensified charge-coupled device (ICCD) camera are recorded on the camcorder and also downlinked to the SWUIS ground personnel located in the JSC Payload Operations Control Center (POCC)

SWUIS presently has two hardware configurations for space shuttle
missions: (1) telescope science mode (TSM) and (2) camera science mode. TSM uses a telescope for high-spatial resolution imaging of faint object targets such as planets, comets, and space debris. CSM
uses a wide-field camera lens for imaging bright targets that occupy larger swaths of the sky such as aurora and lightning sprites. Both TSM and CSM hardware are sensitive to UV, visible (VIS), and infrared (IR) wavelengths.

The SWUIS TSM hardware is composed of three major elements: the telescope, the ICCD camera, and the electronics that provides power and control of the ICCD camera. In addition to these major components, SWUIS uses a custom-built mounting bracket that couples the telescope to the space shuttle side-hatch window for UV observations; a telescope optical coupling assembly (TOCA) that physically and optically couples the ICCD camera to the telescope and which can hold up to three imaging filters in the optical path; a filter caddy that holds the filters and lenses used in the TOCA; and associated power and data cables. The data from the ICCD camera are an analog video signal that is recorded on-board the shuttle with a portable camcorder and which can be downlinked from the shuttle to the ground for real-time assessment.

The telescope, built by Questar Corporation, is a custom 7-inch-diameter (18 cm) Maksutov-Cassegrain design ruggedized for space flight use. It incorporates a UV transmissive front-end corrector lens made of magnesium fluoride, and mirror optical coatings composed of aluminum overcoated with magnesium fluoride for enhanced sensitivity at UV/VIS/IR wavelengths (200-1000 nm). The telescope incorporates a small 6x30 mm finder telescope that allows the shuttle mission specialist to make fine pointing adjustments to the telescope during target acquisition. The telescope is hard mounted to the side-hatch window in the shuttle mid-deck area via a custom two-axis mounting bracket with manual slow motion controls for fine-pointing. A light shield made of Pyrell foam is placed between the window and the telescope to block unwanted cabin light from entering the telescope. The telescope and mounting bracket weigh approximately 30 lb.

A variety of ruggedized ICCD cameras, built by Xybion Inc., which are sensitive to UV, VIS, and near-IR (NIR) wavelengths, can fly as part of the SWUIS hardware complement. The wavelength sensitivity of each ICCD camera is determined by the type of photocathode material used in the camera's design. The UV/VIS version uses a Generation II photocathode with a sensitivity in the 180-820 nm wavelength range. A second VIS version uses an extended blue Generation III photocathode with high sensitivity between 450 and 910 nm. The NIR version has high sensitivity between 600 and 1000 nm. The output of the ICCD camera is a standard RS-170 video signal at an interlaced frame rate of 60 Hz with 370 lines of horizontal resolution. The camera weighs 2.75 lb. and draws about 5 watts.

The TOCA is a mechanical interface between the telescope and the ICCD
camera. It is designed to hold both imaging filters and lenses. The
effective focal length of the SWUIS TSM system can be varied between 105 and 257 cm for a FOV range between 0.3 and 0.6 deg (full cone). The power interface box (PIB) provides power conditioning from the shuttle orbiter's video interface unit to the ICCD camera. The PIB also has manual adjustment controls of the ICCD camera's internal sensitivity (gain) and video output signal. The video output signal is buffered by the PIB to allow multiple data paths to camcorders, monitors, and to the shuttle's video downlink system. During shuttle missions, SWUIS data are recorded on board with a portable camcorder and can also be sent to the ground via satellite link.

SWUIS TSM mode provides astronomers and planetary scientists with a small but highly capable space telescope. Although far less sensitive than the Hubble Space Telescope, SWUIS has its own advantages. These include a far wider FOV and the capability to study objects that are much closer to the sun, such as the inner planets and comets.

The SWUIS CSM configuration is very similar to the TSM mode except the ICCD camera is used with a UV transmissive wide-field lens, instead of the main telescope. A mini-TOCA is used to hold filter combinations. The CSM can be mounted to any of the shuttle windows including the side-hatch window and the nine flight deck windows, using a Bogan bracket camera mount. The wide-field lens assembly provides a FOV of approximately 12.5 deg (full cone).