Session
Technical Session VIII: Attitude Control Technologies
Abstract
This paper will address the authors' experience with the current SMEX (SMall EXplorer) ACS (Attitude Control System) hardware design. The authors have been responsible for the design, development, fabrication, and testing of all the in-house ACS hardware for the common design which will fly on the SWAS (Sub-Millimeter Wave Astronomy Satellite), TRACE (Transition Region and Coronal Explorer), and WIRE (Wide field InfraRed Explorer) satellites. These missions have very different ACS requirements which lead to different sensor complements on each mission; however, they are all low-cost, small scientific satellites which require three-axis fine attitude control. It will be shown how the common hardware design which was used has allowed a faster, better, and cheaper solution to the ACS requirements of these three missions. The standard hardware design includes an interface to a standard set of sensors, drivers for a standard set of actuators, and a hardware safehold mode controller (re-used from SAMPEX - Solar Anomalous and Magnetospheric Particle Explorer - an earlier SMEX mission). The standard sensor and actuator hardware also includes a three-axis inertial package (with a redundant gyro), four reaction wheel assemblies, and a magnetometer. The remaining ACS sensors and actuators are procured hardware. The in-house hardware includes a 8085 microprocessor to perform formatting for a MIL-STD-1553B interface with the main spacecraft computer (80386/80387), as well as an analog safehold which is not dependent upon either processor. Although the in-house hardware was configured with the intent to support simpler missions with a reduced hardware set, this capability has never been used. The paper will also discuss problems encountered in the process of developing and using this hardware. There were a series of difficulties encountered in the initial design and build (SWAS) which were corrected in the later builds; the authors will examine the sources of these problems. In addition, there were a series of initially unplanned requirements which developed for the later builds; the authors will discuss how these requirements were met by adaptation, rather than by redesign. This process led to a cheaper, more robust, and faster development of these later missions (TRACE and WIRE); which, otherwise would have followed the more traditional path to become essentially new designs with related expenses and risks. Finally, the authors will discuss how this experience has led to the planned development (currently underway) of the next generation 'SMEX-Lite' attitude control hardware design.
The SWAS, TRACE, and WIRE Attitude Control Hardware Design
This paper will address the authors' experience with the current SMEX (SMall EXplorer) ACS (Attitude Control System) hardware design. The authors have been responsible for the design, development, fabrication, and testing of all the in-house ACS hardware for the common design which will fly on the SWAS (Sub-Millimeter Wave Astronomy Satellite), TRACE (Transition Region and Coronal Explorer), and WIRE (Wide field InfraRed Explorer) satellites. These missions have very different ACS requirements which lead to different sensor complements on each mission; however, they are all low-cost, small scientific satellites which require three-axis fine attitude control. It will be shown how the common hardware design which was used has allowed a faster, better, and cheaper solution to the ACS requirements of these three missions. The standard hardware design includes an interface to a standard set of sensors, drivers for a standard set of actuators, and a hardware safehold mode controller (re-used from SAMPEX - Solar Anomalous and Magnetospheric Particle Explorer - an earlier SMEX mission). The standard sensor and actuator hardware also includes a three-axis inertial package (with a redundant gyro), four reaction wheel assemblies, and a magnetometer. The remaining ACS sensors and actuators are procured hardware. The in-house hardware includes a 8085 microprocessor to perform formatting for a MIL-STD-1553B interface with the main spacecraft computer (80386/80387), as well as an analog safehold which is not dependent upon either processor. Although the in-house hardware was configured with the intent to support simpler missions with a reduced hardware set, this capability has never been used. The paper will also discuss problems encountered in the process of developing and using this hardware. There were a series of difficulties encountered in the initial design and build (SWAS) which were corrected in the later builds; the authors will examine the sources of these problems. In addition, there were a series of initially unplanned requirements which developed for the later builds; the authors will discuss how these requirements were met by adaptation, rather than by redesign. This process led to a cheaper, more robust, and faster development of these later missions (TRACE and WIRE); which, otherwise would have followed the more traditional path to become essentially new designs with related expenses and risks. Finally, the authors will discuss how this experience has led to the planned development (currently underway) of the next generation 'SMEX-Lite' attitude control hardware design.
