TRMM VIRS: a design for low radiation space environments

The Visual and Infrared Scanner (VIRS) is an instrument aboard the Tropical Rainfall Measuring Mission (TRMM) satellite. This instrument uses a paddle wheel mirror arrangement in conjunction with a Cassegrain telescope to obtain five bands of calibration and earth data. The acquisition, packetization, and transmission of the data is coordinated by one of two 1750 A-based processor boards. This processor and its associated flight software are also responsible for receiving commands, executing commands, and safing the instrument. The design of the VIRS processor hardware and flight software was driven by a number of the usual concerns over reliability and availability. However, one of the other major design drivers was the operating environment of the satellite. Since the VIRS is operating at an altitude of 350 kilometers, the environment is a fairly benign one with respect to radiation exposure. This paper describes the top-level operation and design of the VIRS instrument. The operation section summarizes the top-level operation of the instrument. The design section focuses on the hardware and software tradeoffs that were made with a low radiation environment in mind