UVOT bright source safing system

The Swift mission requires that the Swift UV optical telescope (UVOT) have the autonomous functionality to protect itself against the potentially damaging effects of observing bright sources. This capability had to be added to an existing heritage camera design, which was used for the Optical Monitor telescope (OM) on ESA's XMM-Newton spacecraft. The solution used a two part mechanism employing data from a catalogue of known bright sources, and a real-time system for monitoring the raw pixel data from the camera and automatically reducing the detector gain when a signal above a programmed threshold is seen. This discussion will describe the resulting Field Programmable Gate Array (FPGA) based implementation that sits alongside the heritage camera and processing electronics and can be programmed and monitored by the UVOT instrument controller.