Design and Analysis of an Interplanetary SmallSat

Mayer, Ian A.; Lodge-McIntire, Gracie A.; Levi, Elijah B.; Kirejczyk, Matthew J.; LaGrasse, Bradley J.; Edwards, Smith T.; Zollinger, Peter J.

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Design and Analysis of an Interplanetary SmallSat

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This project presents the design and analysis of a 150kg small interplanetary spacecraft. This spacecraft is inserted into a near-GEO orbit and transfers to an elliptical orbit around asteroid 7 Iris. At Iris, this spacecraft will gather color photographs, spectral data, and topographic data using onboard sensors. Also, the spacecraft will record plasma activity along its trajectory using a plasma spectrometer. A novel iodine-fueled electric propulsion system is presented and a low-thrust trajectory to an observation orbit at Iris is determined. Fuel volume reduction of 40% is achieved compared to traditional xenon systems with minimal impact on performance, allowing the spacecraft to remain within the rideshare constraints. Power needs were satisfied using a combination of batteries, a solar array, and an EPS board. Simulations using sun-tracking were performed in STK allowing for accurate models of the generated, stored, and consumed power throughout the mission. Using these models, a solar array with an end-of-life power generation capability of 375W was achieved. A radio, antenna, and on-board computer were chosen to allow the spacecraft to communicate via the Deep Space Network ground stations. The data transfer rate was modeled by the Shannon-Hartley capacity theorem, and access windows were determined using Systems Toolkit. The attitude determination and control system uses star trackers and sun sensors to determine the orientation of the spacecraft throughout the mission. Multiple numerical simulations were performed in MATLAB to prove that the chosen Sputnix reaction wheel system can perform all analyzed maneuvers and be routinely desaturated using 16 Marotta microthrusters. Environmental factors including thermal, radiation, vibration, and debris were considered, and constraints were provided to each subsystem. Environmental simulations demonstrated the need for thermal control and radiation shielding in the form of MLI blankets. The spacecraft’s thermal properties during different phases of flight were analyzed using a simplified CAD model important into COMSOL Multiphysics software. Thermal control systems were sized through iterative simulation testing to rely on minimal heating power by thermally isolating components, retaining waste heat. The design and construction of a thermal vacuum chamber test cell to simulate the thermal environment of space is also presented. A preliminary test was performed to measure temperatures experienced by a sample inside the chamber at rough vacuum under the heating of four 250-Watt heat bulbs. Temperature data for heat-up and cool-down cycles were collected and compared to thermal simulations done in COMSOL Multiphysics. Experimental temperatures were found to be approximately 20°C higher than simulated. The difference between the measured and thermal simulation temperatures could be due to several factors, including imperfect vacuum conditions during testing, a lack of active cooling of the shroud, and additional heat sources such as reflected radiation from the tank wall.

This report represents the work of one or more WPI undergraduate students submitted to the faculty as evidence of completion of a degree requirement. WPI routinely publishes these reports on its website without editorial or peer review.

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