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TERSat Massachusetts Institute of Technology Eric Peters, Danilo Roascio, Leonard Tampkins, Kezi Cheng July 1st, 2012 1 Mission Overview Satellite Goals: - Demonstrate wave-particle interaction within the inner Van Allen belts - Transmit VLF waves at LEO altitude - Demonstrate science behind potential radiation remediation technique SHOT II Goal: - Use VLF wave transmitter to demonstrate ability to transmit signal to a receiver on the ground Stanford VLF group image Mini-demo Connection: - Demonstrates payload concept of operations, tests prototype VLF receiver parts 2 SHOT Design Overview 3 Mechanical Results • Box intact • Thermal isolation between requirements • Battery performed nominally (i.e., Tbatt > -10 °C) • PA didn’t exceed nominal temperature (i.e., Theatsink < 140 °C) • Cover slightly open • Several screws didn’t hold components during landing 4 Mechanical Results Box intact with cover slightly opened Components broke free of restraints during landing 5 VLF transmitter results – COIL • Goal: reception from ground of a VLF (17.319 kHz) signal generated by payload • Problems experienced: • Lots of VLF noise at launch site • Self oscillation of LNA amplifier • No properly keyed signal received at transmission frequency • Filtering of nearby signals doesn’t show expected keying pattern • Correlation may reveal something within noise, but in any case the transmission will not be as efficient as expected! 6 VLF transmitter results – PLATES • Goal: measure on-board the VLF (34.638 kHz) current transferred to plates in correlation with environment • Data loggers recorded a drop in the plates voltage ? CURRENT INCREASE? Baloon telemetry 7 VLF TX – Reasons for Voltage Drop? • What this could’ve meant: • Increase in current/radiation efficiency at high altitudes • What this probably means: • The plates (outside the box, T < -56 °C) cooled through copper cables and circuits to the op-amp input, and somehow influenced it • Temperatures of 1 MΩ resistor is unlikely to be involved, the transition to/from higher voltage drop is too sudden • More investigation needed to confirm this theory! 8 Lessons Learned and Future Work • Better securing of components inside box in future SHOT launches (only for functionality after recovery, no problems in flight) • VLF transmission with “infinitesimally short” antenna is HARD! • Focus more on reception equipment for VLF communication: • wideband receiver is not optimal in high noise conditions • tuned amplifier may help reject noise and stabilize operation • Anything outside the box is cold. This will involve additional precautions on the connections. But can we exploit for our goals the low temperature of the high altitude environment? • More research needed! 9 Thank you! Questions? Comments? 10