An energetic electron collimator for the measurement of loss cone fluxes in the Earth's radiation belts is presented.
This design addresses the problem of measuring low intensity fluxes in the presence of a large omni-directional
background flux. This disc loaded collimator comprises stainless steel baffles and tungsten vanes. Electron
rejection is accomplished via baffle spacing with baffles placed more closely deep within the collimator. The
collimator was fabricated. Its response was validated at the Goddard Spaceflight Center's Radiation Effects
Facility. The baffled design shows an angular cutoff of three orders of magnitude at the geometric cutoff angle
for electron energies less than 150 keV.
The Teledyne microdosimeter is a novel miniature dosimeter that has become recently available to satellite
manufacturers and programs to provide awareness of the total radiation dose received by the satellite and its associated
subsystems. A characterization of the response of the dosimeter to protons of energies from 30 - 200 MeV as a function
of angle, energy and dose rate is presented in this paper. In addition, the response of the dosimeter to a simulated Solar
proton event with several different levels of shielding has been measured. These results show that the dosimeter
response is relatively uniform over a wide range of conditions for protons. Monte Carlo modeling of the dosimeter for
isotropic particle fluxes (both electrons and protons) has also been accomplished. It is shown that a simplified model is
appropriate in determining the response of the dosimeter when using it to design low cost, simple instruments for space
weather and situational awareness applications.
The High Sensitivity Telescope (HST) is a sensor comprising part of the Loss Cone Imager (LCI) on the DSX mission. The primary objective of the HST is to observe fluxes of energetic electrons as small as 100 <i>e</i> cm<sup>-2</sup>sr<sup>-1</sup>s<sup>-1</sup> within the Earth's atmospheric loss cone. This is accomplished via a geometrical factor of 0.1 cm<sup>2</sup>sr combined with a collimator limiting the field of view to a 7 degree half-cone angle. The sensors are shielded to in order to reduce the background to levels permitting the detection of the stated flux. The HST will be looking for changes in this flux caused by events precipitating electrons into the atmosphere. Of primary interest are electrons
with energies between 20 and 500 keV. The HST utilizes two fully depleted solid state detectors and three analog measurement chains. The primary detector is 1500 um thick and uses two measurement chains. A faster measurement chain for counting events at rates of 300k/sec and a slower measurement chain for measuring the
energy deposited by an event more accurately. The secondary detector is 1000 um thick and is used to detect events that completely penetrate the primary detector. The analog electronics are built from discreet amplifiers. Events on the faster primary chain are sorted into 5 energy bins. Events from the slow chain are digitized to 8-bits of resolution.
A mechanical housing design is developed to ensure the survival of electronics and optimize the performance of solid
state detectors orbiting through the Van Allen radiation belts. This design is part of the Loss Cone Imager on board the
AFRL's DSX satellite and consists of three mechanically separate units: Fixed Sensor Head; High Sensitivity Telescope;
and Central Electronics Unit. These units need to withstand the vibrations and shocks associated with launch as well as
provide shielding to highly energetic radiation and micrometeorite impacts. To obtain optimal performance from the
detectors and high reliability from the electronics thermal restrictions are incorporated into the mechanical designs.
The Loss Cone Imager (LCI) will sample the energetic-particle pitch-angle distributions relative to the local geomagnetic field vector in the magnetosphere as a part of the Demonstration and Science Experiment (DSX) satellite. A description of the LCI electrical interfaces and data flow will be presented. The pitch angle and energy of energetic particles are recorded by the FSH (Fixed Sensor Head) and HST (High Sensitivity Telescope) sensor electronics using
solid state detectors. Energetic particle data must be extracted from the FSH and HST by the DPU (Data Processing Unit) and stored in a format that is practical for ground data analysis. The DPU must generate a data packet that is sent to the experiment computer containing science and housekeeping data, as well as receive ground and time commands from the experiment computer. The commands are used to configure the sensor electronics and change the data
acquisition periods of the science data. The instrument works in conjunction with the WIPER (Wave-Induced Precipitation of Electron Radiation) VLF (Very Low Frequency) transmitter on the DSX satellite to view the effects of VLF waves injected in the Earth's magnetic field on the precipitation of electrons into the Loss Cone. The system is designed to operate autonomously with the changing state of the transmitter to provide more appropriate data for examining the effects of the VLF transmitter.
The loss cone imager (LCI) on the demonstration science experiments mission (DSX) of the Air Force Research Laboratory (AFRL) was designed to measure the effect of waves on non-relativistic electrons in the slot of the radiation belts. The LCI comprises two instruments: a narrow ~7° acceptance-cone electron detector (HST) to measure the low-intensity electron flux in the local loss cone, and a three-pin-hole multi-pixel sensor, the fixed sensor head (FSH), measuring the electron intensity in a 180° x 10° continuous swath containing the HST look-direction at 45°. The design history of the LCI is briefly outlined; the relevant mechanical and signal processing parameters reviewed; and the differential response functions, including the normal data-number (DN) to engineering-unit (EU) conversion of raw data, required to generate the physics (model dependent) parameters discussed.
The Loss Cone Imager (LCI) instrument is part of the US Air Force Demonstration and Science Experiments (DSX) satellite and is comprised of three components: the Fixed Sensor Head (FSH), the High Sensitivity Telescope (HST), and the Central Electronics Unit (CEU). The emphasis of this paper is on the FSH, which is comprised of three Si solid state detectors (SSD) each comprised of six pixels capable of measuring incident particle energies (~ 30 keV - 500 keV) and their respective pitch angles. The FSH is mounted onto the exterior of the DSX Payload Module and covers a 180° by
10° view of the sky. Each pixel has a 10° by 10° field of view. Due to a small geometric factor, the FSH is able to operate
in the high particle flux areas of the Earth's magnetosphere. The Readout Electronics for Nuclear Application 3 (RENA3) chip, developed by NOVA R&D, contains 36 analog channels used for detection of nuclear events. Each of the 18 Si pixels is connected to a corresponding RENA3 channel for event detection and analog energy readout. The output of the chip is digitized and the digital value of each event, along with its corresponding RENA channel, is recorded by the Data Processing Unit housed in the CEU.