Design, fabrication, and implementation of an embedded flight computer in support of the ionospheric-thermospheric scanning photometer for ion-neutral studies CubeSat mission
Handley, Matthew Lee
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As society increasingly relies on space-based assets for everything from GPS-based directions and global communications to human-driven research on the ISS, our understanding of space weather becomes vital. Timely predictions of a solar storm's impact on the ionosphere are imperative to safing these assets before damaging storms hit, while minimizing downtime during lighter storms. The topside transition region (TTR) is a global boundary where the concentration of O+ significantly decreases due to charge exchange with H+ and He+ from the thermosphere, as well as protons and neutral atomic oxygen from the plasmasphere. When high-energy electrons in the ionosphere intercept O+ ions, they combine and release photons at 135.6-nm. The Ionospheric-Thermospheric Scanning Photometer for Ion-Neutral Studies (IT-SPINS) mission will provide 135.6-nm nightglow measurements from a 3U CubeSat equipped with a high-sensitivity UV photometer. The CubeSat will spin about orbit normal, sweeping its photometer field of view through the ionosphere. Ground-based post processing will yield 2D altitude/in-track images of O+ density, providing weighting parameters for models of the TTR. This low-earth orbit (LEO) small satellite mission is a collaboration between the John Hopkins University Applied Physics Laboratory, SRI International, and Montana State University (MSU). This research describes the design, fabrication, and implementation of the space flight computer (SFC) hardware and software responsible for handling all commands, telemetry, and scientific data required by this National Science Foundation (NSF) funded mission. The SFC design balances requirements derived from the mission objectives while leveraging heritage hardware and software from MSU's many successful CubeSat missions (HRBE, FIREBIRD, FIREBIRD-II) and payloads (EPISEM) [1-3]. This low-power (100 mW) embedded computer features dual 16- bit PIC microcontrollers running at 16 MHz with only 96 kB of RAM and runs the microC/OS-II real-time operating system (RTOS). The SFC also includes a TCXO-driven mission elapsed time clock with plus or minus 2 ppm temperatures stability, a 1 GB NAND flash for data storage, and interfaces to all other subsystems in the satellite. The SFC has passed all standalone testing. It is currently being integrated and tested with the entire IT-SPINS spacecraft and is planned to fly in late 2018.