The design and implementation of a high sensitivity telescope for in situ measurements of energetic particles in the Earth's radiation belts

This work describes the design and implementation of a high-sensitivity telescope (HST) for in situ detection and energy analysis of energetic charged particles in the Earth's radiation belts from a near-equatorial orbit that will range over geocentric distances from ≈ 2--3.5 Earth radii as part of the US Air Force's Demonstrations and Science eXperiment (DSX) mission. The HST employs a two element silicon solid state detector telescope that has a geometrical factor of 0.1 cm2 sr with a 14° field-of-view centered on the on-orbit local magnetic field vector to detect ≈ 100 particles s-1 cm-2 sr-1 in the geomagnetic bounce loss cone. The pointing direction of the HST is guaranteed by the active attitude control subsystem of the spacecraft. A novel implementation of a knife-edged baffled collimator design restricts the field-of-view and provides a sharp cutoff (≈ 103) in the angular response to all particle species with energies from ≈ 40--800 keV. The HST detectors are shielded with 5g cm-2 of aluminum followed by 3.1 g cm-2 of tungsten in all non-look directions to reduce the background fluxes incident on the detectors through the orbit (>107 particles cm -2 s-1 for electrons and protons individually) to levels that will allow the detection of the target flux in the loss cone. The HST has been extensively characterized on the ground and is capable of analyzing the energies of particles over the range of 25--850 keV with an energy resolution of 3.7keV and a noise FWHM of 15keV. The calibration has been established using 241Am and 133Ba X-ray sources and verified using additional beta- and X-ray sources and the electron beams produced by the 2 MeV Van de Graaff accelerator at the NASA Goddard Spaceflight Center's Radiation Effects Facility. The instrument's calibration has been shown to vary by less than 2% over the operational temperature range of --20 to +35°C. Electromagnetic interference testing has proven that the HST is unaffected by strong VLF fields of peak amplitude 1.5 kV.