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Feasibility Study of Two Candidate Reaction Wheel/thruster Hybrid Control Architecture Designs for the Cassini SpacecraftAs the first spacecraft to achieve orbit at Saturn in 2004, Cassini has collected science data throughout its four-year prime mission (2004-08), and has since been approved for a first and second extended mission through 2017. Cassini carries a set of three "fixed" reaction wheels and a backup reaction wheel (reaction wheel #4) is mounted on top of an articulable platform. If necessary, this platform could be articulated to orient the backup reaction wheel with the degraded wheel. The reaction wheels are used primarily for attitude control when precise and stable pointing of a science instrument such as the narrow angle camera is required. In 2001-02, reaction wheel #3 exhibited signs of bearing cage instability. As a result, reaction wheel #4 was articulated to align with reaction wheel #3. Beginning in July 2003, Cassini was controlled using wheel #1, #2, and #4. From their first use in the spring of 2000 until today, reaction wheels #1 and #2 have accumulated more than3.5 billions revolutions each. As such, in spite of very carefully management of the wheel spin rates by the mission operation team, there are some observed increases in the drag torque of the wheels' bearings. Hence, the mission operations team must prepare for the contingency scenario in which the reaction wheel #1 (in addition to wheel #3) had degraded. In this hypothetical fault scenario, the two remaining reaction wheels (#2 and #4) will not be able to provide precise and stable three-axis control of the spacecraft. In this study, we evaluate the feasibility of controlling Cassini using the two remaining reaction wheels and four thrusters to meet the science pointing requirements for two key science operational modes: the Optical Remote Sensing and Downlink, Fields, Particles, & Waves operation modes. The performance (e.g., pointing control error, pointing stability, hydrazine consumption rate, etc.) of the hybrid controllers in both operations scenarios will be compared with those achieved using an all-thruster controller design. Strength and weaknesses of the hybrid control architecture are assessed quantitatively.
Document ID
20140002052
Acquisition Source
Jet Propulsion Laboratory
Document Type
Conference Paper
External Source(s)
Authors
Macala, Glenn A.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Lee, Allan Y.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Wang, Eric K.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Date Acquired
March 19, 2014
Publication Date
August 13, 2012
Subject Category
Spacecraft Design, Testing And Performance
Meeting Information
Meeting: AIAA Guidance, Navigation, and Control Conference and Co-located Conferences
Location: Minneapolis, Mn
Country: United States
Start Date: August 13, 2012
End Date: August 16, 2012
Sponsors: American Inst. of Aeronautics and Astronautics
Distribution Limits
Public
Copyright
Other
Keywords
Cassini
attitude control
hybrid controller

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