Agility Analysis of the James Webb Space Telescope
King, Jeffrey T.
Dennehy, Cornelius J.
Ross, I. Michael
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The agility of a rigid-body spacecraft can be expressed in terms of a geometric, three-dimensional, solid called the agilitoid. Originally developed as a means for explaining the concept of “hidden agility” made visible through the use of optimal control techniques, a modified agilitoid called an agility envelope is presented here that is compatible with conventional eigenaxis maneuvers. This paper demonstrates how the agility envelope can be applied to size an attitude control system (ACS) and/or assess the capability of an existing design. Analysis of the James Webb Space Telescope (JWST) ACS shows that the agility envelope accurately predicts the true capability of the ACS: a 90 deg maneuver can actually be completed 15% faster than the conventional back-of-the-envelope slew-sizing equations suggest. The utility of the agility envelope is further illustrated by showing how an alternative control allocation scheme can reduce the JWST torque and momentum requirements by 40%. The otherwise hidden agility can be recovered to enhance the slew performance of the JWST or allow the reaction wheel array to be reduced from six to five wheels, while meeting existing maneuver requirements. The agility envelope allows such design trades to be studied without the need to perform detailed simulations of the attitude control system.
The article of record as published may be found at http://dx.doi.org/10.2514/1.G003816
RightsThis publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.
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Karpenko, Mark; King, Jeffery T. (SAGE, 2018);Spacecraft agility is limited by the maximum torque that reaction wheels can provide. Therefore, a reaction wheel array is typically configured to maximize the inscribed sphere of the reaction wheel torque envelope. Agility ...
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King, Jeffery T.; Karpenko, Mark (American Astronomical Society, 2017);Rigid-body agility is limited by the maximum torque and orientation of the reaction wheels. Maximizing the inscribed sphere of the torque envelope can underestimate the true capability of the system because spacecraft ...