Miniaturized Control Moment Gyro
Agency / Branch:
DOD / USAF
Honeybee Robotics Spacecraft Mechanisms Corporation proposes to develop a miniaturized control moment gyro for attitude control of small agile spacecraft. In Phase 1, we will specifically focus on demonstrating feasibility of developing the miniature CMG mechanism. The Phase 1 technical objectives are: 1. Derivation of a set of requirements for conceptual design and breadboarding. 2. Identification, down-selection, and refining of promising concepts for the system's component technologies, through modeling, simulation, and documented design trades. 3. Completion of a preliminary design of one single-gimbal CMG, which both addresses the miniaturization of a variable-speed momentum wheel actuator and verifies the requirements of the gimbal actuator. Mission planners envision agile spacecraft slew rates on the order of 5 degrees/second. This is roughly an order of magnitude higher than the current state of the art for small spacecraft. Therefore, the primary requirements are: 1. Maximize torque output to actuator mass (and volume) ratio to enable high slew rate capability a. This should also be traded against control complexity b. This should also be traded against pointing accuracy (low jitter) 2. Flexible and scalable design a. Able to compensate for uncertainty in spacecraft inertial properties b. Able to adjust on fly to avoid problematic structural resonance regimes BENEFIT: Along with the aerospace industry at large, the Missile Defense Agency and Air Force Research Lab have demonstrated an increasing need for smaller, more agile satellites. Programs like the Ballistic Missile Defense System, SBSS and Responsive Space require high-precision Earth observation, space-monitoring, and tracking spacecraft with demanding requirements placed upon the satellite's Attitude Orientation and Control System (AOCS). Future missions may require satellites to perform more difficult tasks; including satellite inspection, distributed platforms, self-assembling constellations, tracking of space debris and satellite docking. In addition to increased agility demands, there is also a trend towards smaller satellites across the industry. With the growing number of applications and burgeoning small satellite market, there is a need for miniaturized, flight-qualified attitude control systems capable of cost effectively meeting these challenges. There exists a market niche for agile attitude control systems for small satellites. Traditionally, small satellites have used reaction wheels for their attitude control system. Momentum wheels are good for precision pointing of miniature spacecraft. However, if they are sized to allow for agile maneuvers requiring rapid slew rates of 1-10 deg/sec, they will exceed the mass and power budget for miniature spacecraft. Control Moment Gyroscopes (CMGs) are capable of generating output torques an order of magnitude higher than reaction wheels of comparable mass. This is because a CMG is able to store a large amount of angular momentum that can then be converted to torque by changing the flywheel's orientation with respect to the spacecraft body frame via a gimbal axis - the output torque is limited by the amount of stored fly wheel angular momentum and the gimbal rate. By contrast, the torque output of a reaction wheel is limited by the maximum torque of the momentum wheel's motor - to obtain more torque a larger, more massive motor must be employed. Because CMGs are more mass-efficient (Nm/kg), they have found continued use in large satellites and spacecraft. If miniaturized this efficiency gain may be leveraged by small platform satellites resulting in increased agility and greater payload margins. This technology is now possible for smaller spacecraft with advances in components, materials, lubricants and controls and vibration suppression; even down to the nanosat level. The significance of this opportunity within the Department of Defense is highlighted by the recent successes of the MDA with respect to the Ballistic Missile Defense System Space Tracking and Surveillance System (STSS). The first two satellites are scheduled for launch in early 2009 with full deployment of this system requiring a constellation of small satellites. The first two satellites, meant for demonstration, rely on a payload with wide field of view and/or or tracking sensors on a gimballed platform. The ability to rapidly slew the entire spacecraft would provide added flexibility in mission and payload design. There is a clear military market need for advanced spacecraft dynamics and controls in miniaturized hardware packages for agile responsive spacecraft. A CMG capability for small satellites will need to be implemented with quick turn-around for meeting the goals of Operationally Responsive Space, wherein spacecraft will eventually need to be integrated and launched within a week. A modular package of CMGs which could be utilized for a variety of mission scenarios. Such a package would be assembled and integrated in a "plug-and-play" fashion, reducing the need for extensive analysis and testing.
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