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.