Description of the BDD-IIR: Electron and proton sensors on the GPS

Abstract

The Burst Detector Dosimeter (Block) IIR (BDD-IIR) is a multipurpose silicon detector system that is scheduled to fly on two of the first 12 spacecraft of the Global Positioning System (GPS) Block 2 Replenishment series as an alternative to the Burst Detector X-ray (BDX) instrument. This instrument measures energetic-particle fluxes impinging on the GPS space vehicle (SV), primarily energetic electrons trapped in the Earth`s radiation belt, but also solar energetic particles and galactic cosmic rays. Absorbers located in front of eight separate silicon sensors determine energy thresholds for measuring incident particle fluxes, and the magnitude of energy loss in each sensor provides an imperfect but very good separation between ions and electrons over a wide range of energies. For each of two sensors, a conical collimator with a very small opening is used for low-energy particles. For four sensors, five small holes in a thick shield limits the flux on each sensor to manageable levels. For two sensors, solid domes are used to measure high-energy electrons and protons. These eight sensors provide eight channels that determine the electron energy spectrum from 77 keV to > 5 MeV and eight channels determine the proton spectrum from 1.3 to > 54 MeV. The radiation dose rate and total dose for a wide range of equivalent shielding thicknesses is inferred directly from the measured electron energy spectrum. Accumulations times are usually 240 s but can also be 24, 120, or 4,608 s. This report describes the BDD-IIR`s important mechanical and electronic features, its system tests and calibrations, the commands that can be sent to it, and the data that it returns.