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Completed TRL 2 (started at 1, targeting 2)
The proposed E-sail control system employs a novel decentralized controls algorithm wherein the satellite at the end of each tether controls its own station keeping to ensure proper configuration of the system as a whole is maintained while working coherently with the other satellites to perform system-level controls function, such as steering the sail to a different attitude. It will be developed by performing mission analysis for SPI and Interstellar Probe in order to determine the most stressing parts of these missions on the vehicle and control system, design the vehicle and control system architectures and select dispersed design parameter values, run attitude dynamics and control Monte Carlo simulations at checkpoints in orbit chosen from mission analysis, and analyze the results to assess sensitivities and feasibility of vehicle performance (KPPs of maximum slew rate and maximum SIA) and control system robustness (KPPs of gain margin and phase margin).
This technology and approach differ from previous efforts by the control algorithm used and the incorporation of high-fidelity models of driving vehicle dynamics phenomena (flexible body dynamics of the tethers, disturbance torques, etc.) and realistic environmental conditions (time- and space-dependent solar wind dynamic pressure, large and varying SIAs, etc.). Through this innovation and work plan, a conceptual design and math/software model of a control system for a highly-dynamic, multi-tether, spinning E-sail, as well as supporting analyses proving its feasibility for application to SPI and Interstellar Probe, will be delivered, raising the TRL to 3 with an analytical proof-of-concept. After this effort, the resulting control system will serve as the baseline design/model for breadboard ground testing (e.g. spin test on a Flat Floor) and, ultimately, a Technology Demonstration Mission.
High-value Heliophysics missions identified in the most recent Heliophysics decadal survey (2013), Solar Polar Imager (SPI) and Interstellar Probe, require advanced propulsion technology to be realized. Solar sails are envisioned in the decadal survey as the state-of-the-art propulsion technology for these missions, but the Electric Sail (E-sail) carries many of the same advantages that make solar sails ideal for these missions, being a propellantless propulsion system that provides practical access to and maintenance of unstable orbits. However, E-sail has the additional benefit of potentially enabling the target orbits for these missions to be reached in half the time, from 8 years to 4 for SPI and 20 years to 10 for Interstellar Probe. As the attitude of the E-sail (and solar sails) is crucial to controlling the thrust vector by slewing and achieving large sun incidence angles (SIAs), as required for rapid transit for the target missions, the control system proposed here is a key enabling technology for these applications of E-sail.
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