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The Radio Aurora Explorer (RAX) is an NSF sponsored nanosatellite being designed, built, and tested by students at the University of Michigan; it is currently scheduled for launch in 2010. The spacecraft utilizes a passive magnetic attitude control system consisting of a permanent magnet aligned with the axis of symmetry of the nanosatellite, and two magnetic hysteresis rods, each aligned along the other two principal axes of the nanosatellite; these hysteresis rods provide energy dissipation necessary to achieve alignment of the axis of the symmetry with the Earth's magnetic field. This paper presents an analytical model for the passive magnetically controlled attitude dynamics of the RAX nanosatellite, along with numerical simulations to assess the properties of the attitude dynamics.

A number of components and payload systems installed in satellites are found to be exposed to various disturbance sources, such as the reaction wheel assembly, the control moment gyro, coolers, and others. Low damping in space causes continuous microvibration that degrades the performance of various payload systems; this is customarily called jitter problem in spacecraft community. Various isolation systems have been developed to improve the performance of the optical payloads under the microvibration environments. During the spacecraft development process, an experimental validation of jitter effects (either controlled or not) on the performance of optical payloads using all the flight model components is not often conducted due to the scheduling issue or the product assurance activities. The disturbance characteristics of a prototype or an engineering model of the disturbance source such as reaction wheel assembly are significantly different from their flight model counterparts. Therefore, in order to facilitate jitter test as well as the performance evaluations of an isolator during the satellite development process, this article proposes a microvibration emulator that generates the real disturbance spectrums of flight models. The development procedure for the reaction wheel assembly emulator is described. Prototype single-axis and three-axis microvibration emulators are demonstrated, and the performances are evaluated by means of disturbance characteristics similar to those of the reaction wheel assembly.

Testing for time-related behaviors of PLC software is important and should be performed carefully. We propose a structural testing technique on Function Block Diagram(FBD) networks including timer function blocks. In order to test FBD networks including timer function blocks, we generate templates for timer function blocks and transform a unit FBD into a flowgraph using the proposed templates. We apply existing testing techniques to the generated flowgraph and describe how the characteristics of timer function blocks are reflected in the testing process. By the proposed method, FBD networks including timer function blocks can be tested thoroughly without the intermediate code which was essential in the previous FBD testing. To demonstrate the effectiveness of the proposed method, we use a trip logic of bistable processor of digital plant protection systems which is being developed in Korea.