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Solar Probe Plus: Epi-Hi and Epi-Lo Instruments
The Solar Probe Plus (SPP) mission, due launch in 2018, flies within ten solar radii of the Sun’s surface. SPP is designed to survey the birthplace of the solar wind and its embedded magnetic and electric fields, explore the origins of large-scale disturbances created during powerful explosions such as solar flares and coronal mass ejections (CMEs), and reveal how these conspire to accelerate solar energetic particles (SEPs).The Caltech Space Radiation Laboratory's two Energetic Particle Instruments on SPP measure lower (EPI-Lo) and higher (EPI-Hi) energy particles. EPI-Lo measures ions and ion composition from ∼20 keV/nucleon–15 MeV total energy and electrons from ∼25–1000 keV. EPI-Hi measures ions from ∼1–200 MeV/nucleon and electrons from ∼0.5–6 MeV.
As an intern, I was given systems level overview of the overall design, fabrication and calibration/testing of both Epi-hi and Epi-lo instruments. My engineering tasks primarily involved front end electronics assembly (minor) and its testing using silicon detector signal emulators, for the instruments final engineering model (before flight model). The signals (emulated) from the silicon detectors, stored in a hold capacitor, were processed using a PHASIC (Pulse Height Analysis System Integrated Circuit) . The PHASIC used Wilkinson rundown ADCs, which determined the pulse height by measuring the time interval required for discharging a hold capacitor using a constant current. These were controlled using routines/test programs that were written in FORTH.
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PHASIC Chip
My other tasks included , redesigning variable load boxes (and its fixture) that interface between the power modules and various different silicon detectors. For all detectors to function reliably, they require a known fixed bias voltage. Also the hold capacitor is then discharged using a fixed current w.r.t to a fixed load on the overall circuit. Now due to loss in overall power of spacecraft due to factors like degradation of solar panels over time or trajectory position that is farther away from sun, it may be required to reconfigure this bias voltage/current across multiple detectors (by a known ratio) and hold capacitors to compensate loss in satellite's power/voltage production. These load boxes therefore could be reconfigured to switch to modes where overall impedance of the circuit(s) of different detector types could be varied (reduced) in fixed ratios, and yet the detectors perform reliably, with a known response function. I reverse engineered these circuits and then helped redesign them using Altium (sent for fabrication to external vendor). I also rolled out the inventory parts/vendor database program for the project using Filemaker for the upcoming flight module fabrication, housekeeping and order management.
Variable Load Box
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