SSUSI-Lite is an update of an existing sensor, SSUSI. The current generation of Defense Meteorological Satellite Program (DMSP) satellites (Block 5D3) includes a hyperspectral, cross-tracking imaging spectrograph known as the Special Sensor Ultraviolet Spectrographic Imager (SSUSI). SSUSI has been part of the DMSP program since 1990. SSUSI is designed to provide space weather information such as: auroral imagery, ionospheric electron density profiles, and neutral density composition changes. The sensors that are flying today (see http://ssusi.jhuapl.edu) were designed in 1990 - 1992. There have been some significant improvements in flight hardware since then. The SSUSI-Lite instrument is more capable than SSUSI yet consumes ½ the power and is ½ the mass. The total package count (and as a consequence, integration cost and difficulty) was reduced from 7 to 2. The scan mechanism was redesigned and tested and is a factor of 10 better. SSUSI-Lite can be flown as a hosted payload or a rideshare – it only needs about 10 watts and weighs under 10 kg. We will show results from tests of an interesting intensified position sensitive anode pulse counting detector system. We use this approach because the SSUSI sensor operates in the far ultraviolet – from about 110 to 180 nm or 0.11 to 0.18 microns.
SSUSI-Lite is a far-ultraviolet (115-180nm) hyperspectral imager for monitoring space weather. The SSUSI and GUVI sensors, its predecessors, have demonstrated their value as space weather monitors. SSUSI-Lite is a refresh of the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) design that has flown on the Defense Meteorological Satellite Program (DMSP) spacecraft F16 through F19. The refresh updates the 25-year-old design and insures that the next generation of SSUSI/GUVI sensors can be accommodated on any number of potential platforms. SSUSI-Lite maintains the same optical layout as SSUSI, includes updates to key functional elements, and reduces the sensor volume, mass, and power requirements. SSUSI-Lite contains an improved scanner design that results in precise mirror pointing and allows for variable scan profiles. The detector electronics have been redesigned to employ all digital pulse processing. The largest decrease in volume, mass, and power has been obtained by consolidating all control and power electronics into one data processing unit.
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 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 e cm-2sr-1s-1 within the Earth's atmospheric loss cone. This is accomplished via a geometrical factor of 0.1 cm2sr 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.