Research Summaries

Back Optimal Back-Torque Steering for Extending CMG Capability

Fiscal Year 2016
Division Graduate School of Engineering & Applied Science
Department Mechanical & Aerospace Engineering
Investigator(s) Karpenko, Mark
Sponsor Department of Defense Space (DoD)
Summary Recent work at the Naval Postgraduate School has shown that many satellite imaging systems have physical capabilities that go un-tapped due to simplifications made in heritage algorithms. Because of this, the status quo for increasing the agility of CMG spacecraft is to use larger CMGs. The objective of this project is to develop new concepts for increasing the agility of CMG attitude control systems without relying on larger hardware. Our previous work has focused on designing maneuvers that leverage desirable properties of the inertia tensor: rotations are favored about axes where the torque-to-inertia ratios are largest. However, CMG systems have additional dynamics that were not considered before. In particular, we have recently learned that CMG back-torque can overwhelm gimbal drive motors and cause a loss of attitude control unless the spacecraft angular momentum vector is properly steered. Conventional algorithms address this issue by considering the worst-case effect to derive limits on maneuver rates. The true capability of CMG systems is much larger but to utilize their full capacity, it is necessary to design maneuvers to properly steer the back-torque magnitude in order to avoid back-driving the CMGs. Using techniques developed at NPS, it is possible to embed the necessary back-torque management directly into new attitude guidance trajectories for agile slews. The proposed approach therefore seeks to develop new nonlinear slewing algorithms that maximize the capabilities of a CMG attitude control system within the limits imposed by the governing physics, which are larger than heritage limits arrived at by conventional back of the envelope computations. As a result, spacecraft agility can be enhanced without an increase in SWaP. Life expectancy of the CMGs will be considered as an operational constraint on the maneuver design problem.
Keywords attitude control control moment gyroscopes
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Data Publications, theses (not shown) and data repositories will be added to the portal record when information is available in FAIRS and brought back to the portal