The Ultraviolet Spectrograph Assembly The The Ultraviolet Spectrograph Assembly (USA) consists of a near Wadsworth spectrograph covering the extreme and far ultraviolet spectrum of 80 to 170 nm. A scanning mirror sweeps the spectrograph s field of view across the Earth's limb to obtain vertical profiles of the ionospheric and neutral atmospheric airglow radiances. The primary scan mode extends from 10 degrees to 27 degrees below the satellite horizon (with the capability to go from 10 degrees to 40 degrees in an alternate scan mode), forming vertical images of the Earth's atmosphere from approximately 50 km to 750 km. The scan is performed in the orbital plane of the satellite, looking either forward or aft (into the velocity or antivelocity direction). The USA generates a single event for each photon detected, consisting of wavelength and pulse height information. This information is transferred to the SSULI Control Electronics (SCE) for cataloging. If the USA is unable to accurately measure the photon event, an atypical code is substituted for the wavelength data.

	The Scan Mirror Assembly The Scan Mirror Assembly (SMA) provides a mounting interface to the Ultraviolet Spectrograph Assembly (USA) and allows the mirror to be scanned through the instrument's field of view. The scan mirror is the first element in the optical path. It is made of solid SiC and reflects incident light through the instrument field of view.

The Collimator The collimator is the second element in the optical path. It collimates the light reflected from the scan mirror entering the Ultraviolet Spectrograph Assembly housing by mechanically constraining the instrument's field of view.

The Grating The grating is the third element in the optical path. The grating focuses light from the field of view onto the detector and disperses the light into a spectrum ranging from 800 nm to 1700 nm.

The Detector The detector is the final element in the optical path. The detector is an imaging microchannel plate detector with a wedge and strip anode that characterizes photon events.

SSULI Control Electronics The SSULI Control Electronics (SCE) incorporates all electronic subsystems required to operate the Ultraviolet Spectrograph Assembly (USA), including housekeeping, mission data collection, and spacecraft interfaces. The SCE provides the command and mission data interface functions between the DMSP satellite's Operational Line scan System, the Signal Interface Unit, and SSULI. Instrument health data (such as temperatures and power supply voltages) are provided via spacecraft equipment status telemetry channels. The SCE controls SSULI subsystem operation and collects, formats, and compresses (USA) mission data. The SCE receives primary and redundant power from the spacecraft and distributes the switched primary power to the DC power converters that supply the appropriate voltages to the SSULI subsystems.

High Voltage Power Supply The High Voltage Power Supply (HVPS) receives 13.5 V DC power from the SSULI Control Electronics (SCE) and provides regulated DC power ranging between 3000 VDC and 5000 VDC to the Ultraviolet Spectrograph Assembly (USA) detector. Two redundant supplies are used, one providing primary power, the other backup power. Each HVPS is enclosed in a single container and is functionally identical and interchangeable with the other.

SSULI Harness Assembly The SSULI harness assembly provides the electrical interface between the USA, HVPS, and SCE.

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