As traditional satellites successfully utilize extensible structures such as long magnetic booms or large antennae, the variety of space missions to be realized by nano-scale satellites would be greatly expanded if they employed such structures. Specifically for remote sensing applications, extensible structures are convenient for achieving long focal lengths required by the optics system. In our laboratory, a nano-scale remote sensing satellite “PRISM” has been developed with an expected launch date in the 2008 fiscal year. PRISM has an extensible boom with a telephoto lens at its tip, creating a refractive telescope, which on the orbit can acquire earth images with a resolution better than 30m. In this paper, we describe the design of the boom and present results from a micro-gravity experiment where the operation and system identification tests were performed.

Nano-satellite PRISM is being developed at the Intelligence Space System Lab at University of Tokyo. The objective of PRISM mission is to observe earth with 30m resolution. Thus, a novel design of fabricated optics system with the extendable boom structure is required to attain longer focal length. For the purpose of attitude control of PRISM, we need to understand dynamics of the deployable boom, and vibration experiment under micro-gravity was conducted during parabolic flight tests at Nagoya, Japan. Input and output datum of transverse motions of the boom structure under gravity and micro-gravity was measured, and using this datum we report identification of the extendable boom system.

Nano-JASMINE (Nano-Japan Astrometry Satellite Mission for INfrared Exploration), a nano-satellite currently underdevelopment at Intelligent Space System Laboratory (ISSL) Univ. of Tokyo in cooperation with National Astronomical Observatory of Japan (NAOJ). The mission is to measure the 3D positions of stars to an accuracy of 1.8 mas. In order to get accurate star position data, Nano-JASMINE should be stabilized to less than 740 mas/8.8s (equivalent to 4e-7rad/s) accuracy during observation. Currently there are not sensors available for a nano-satellite to get accurate attitude information as is required by the mission. This research consider the method to determine and control attitude to a high accuracy in Nano-JASMINE mission.

Nano-JASMINE is planned as a nano astrometry satellite at the ISSL lab, of the University of Tokyo in cooperation with the National Astronomical Observatory of Japan (NAOJ). This research presents the method for determining satellite stability and control from star images from the mission telescope. To estimate satellite attitude at a high accuracy, several eects such as star color, and star acquisition period should be considered. Based on simulation results, the paper concludes that the use of blurred star image data to determine the control attitude is a feasible method for use on the Nano-JASMINE mission.

The capabilities of a multi-tethered aerostat positioning system are investigated using experimental and simulation results. The system consists of a platform supported by a helium-filled aerostat and attached to three anchored ground tethers actuated using computer-controlled winches. The experimental system was designed to perform a proof-of-concept study of a novel large-scale radio telescope requiring a receiver to be positioned accurately at an altitude of up to 500 m. Results from a series of flight tests are presented with a comparison between the passive response of the system and the response using proportional, integral, and derivative (PID) controllers with a position feedback. The motion of the platform is smaller for all cases using the feedback control. To improve on the PID results, a dynamics model of the system is used to develop and simulate optimal and feedforward (FF) control strategies. The optimal linear quadratic Gaussian (LQG) controller offers a 50% improvement over the PID controller, and both the LQG and the PID feedback controllers were shown to benefit considerably from the addition of a FF control term that exploits the measurements of the system's main disturbance force

An aerial positioning system consisting of a helium-filled aerostat and three actuated tethers arranged in a tripod is studied. The original concept for the positioning system was introduced as part of a novel large-scale radio telescope. A one-third scale experimental system was developed to compare the dynamic response with the results given by a comprehensive nonlinear dynamics model developed previously. Flight tests were performed in the spring of 2005 that used position feedback and a PID controller to demonstrate the disturbance rejection capabilities of the system. In this paper, the test results are compared to simulation results of the nonlinear model and good agreement was observed. Open-loop frequency response of the experimental system was also compared to that of a linear dynamics model, which also provided a good match. With the dynamics model validated, it was used as a design tool to investigate how certain system parameters, such as the number of tethers, affect performance.

An aerial positioning system is proposed using a helium aerostat and a series of tethers attached to the ground. The system is intended to position the receiver for a large-scale radio telescope. An experimental tritethered system was developed to evaluate the behavior of the system and provide a basis for comparisons with a previously developed dynamics model. The dynamics model combines discretized lumped-mass tether models, an aerodynamic model of the aerostat and a turbulent wind model. Results from four test flights at different geometrical configurations are presented. The tritethered aerostat system exhibited impressive performance, as the payload motion was 2 orders of magnitude smaller than the aerostat motion. Validation of the dynamics model was achieved through a two-stage process. In the first step, the tether model was verified independently of the aerostat and wind models. Once the fidelity of the tether model was established, simulation results for the full dynamics model were compared to experimental results and the model proved to be effective for predicting the statistics of the motion of the system.

The Canadian design for the Square Kilometre Array radio telescope includes a large multi-tethered aerostat to support the telescope’s receiver. To validate this design concept, two parallel tracks have been undertaken: a numerical simulation of the multi-tethered aerostat system has been assembled, and a one-third scale prototype of the system has been constructed. This paper describes the experimental facility, presents results from initial tests of the uncontrolled system and compares these results to the predictions of the computer model of the system. Generally, the results compare very favourably. Using the simulation, we arrive at two important design philosophies to be used in the design of the full-scale system: (a) perturbations on the confluence point should be minimized, and (b) the system stiffness should be maximized to ensure minimum response to disturbances.

The National Research Council of Canada's Herzberg Institute has proposed a design for a new radio telescope known as the 'Large Adaptive Reflector' (LAR). The LAR telescope is comprised of a 200 m reflector and a receiver held aloft at an altitude of 500 m by a tethered aerostat. The position of the receiver is actively controlled by a series of tethers connected to winching systems on the ground. Computer simulations of the LAR positioning system have shown that the proposed design holds a great deal of promise. To add confidence to these results and give further assurance that the concept is practical, experimental validation is crucial. Therefore design and construction was undertaken of a one-third-scale model of the multi-tethered aerostat component of the LAR to further study the dynamics and control of this subsystem. The design process begins with an analytical study of the scaling process. All variables liable to affect the dynamics of the system were identified and dimensionless groups were formed by applying Buckingham's Pi Theorem. Once the desired physical characteristics of the scaled system had been identified, components were chosen to satisfy those characteristics. The key components to be selected included the aerostat, tethers, sensing instruments and winches. The design process for selecting these components is discussed and an overview of the construction of the system is given.