The standard ST-16 star tracker is mounted in a 2 mm thick aluminum chassis, designed to be as light as possible so that it can fit into a nanosatellite. But what if you can afford some extra mass, and want to go to a high radiation environment?
Introducing the -3 order code for the ST-16! This is the lot-screened ST-16 electronics (-1 order code) provided in a chassis with additional high-Z shielding material to stop solar flare protons and high altitude electrons. [The ST-16 electronics are naturally tolerant of trapped protons.]
A white paper detailing the expected survival lifetime in various orbits and interplanetary trajectories for the -1 and -3 build options, will be released in several weeks.