Hironori Ishikawa

Study on Ground Verification for Large Deployable Modular Structures

A quantitative assessment is provided of the difficulty of ground deployment tests and evaluates the validity of modularized deployment testing for large space structures. An index that well shows the difficulty of ground deployment tests is the ratio of gravity force to deployment force. The relationship between this index and the accuracy of deployment tests is calculated using an analysis model of the large deployable antenna reflectors onboard Engineering Test Satellite VIII (ETS-VIII). The index showed that a deployment structure whose diameter is more than 10 m has insufficient evaluation accuracy; thus the structure should be divided into modules. The index also showed that the single module of the large deployable antenna onboard ETS-VIII is of the appropriate size to evaluate deployment reliability. The influence of module connection on the deployment motion is also examined. The cross correlation between the changes in strain energy profile during deployment in a single module and those in combined modules is calculated to show how many modules should be connected and tested. The resistance force that arose due to the module connection is also calculated using the beam strain energy. It is clarified that ground deployment testing for four combined modules should be conducted in addition to the ground deployment testing for a single module when the deployment force margin is not large enough.

ANALYSIS AND TEST METHODS FOR LARGE DEPLOYABLE SPACE STRUCTURES

This paper describes deployment analysis, test methods and results for a large aperture modular mesh deployable antenna reflector. The reflector will be installed on the Engineering Test Satellite VIII, which will be launched in 2003. Two kinds of development models are considered in this paper. One is a full-scale, fourteen modules engineering model, the other is a half-scale, seven modules flight model for in-orbit experiments by ARIANE 5. Some important items to be considered for the design and evaluation of large deployable reflectors are described. Typical results gained with our analysis tool SPADE for large deployable space structures are discussed. They include redundant constraints, ground testing contingency mode, and mesh behavior. Essential items in the design and evaluation of LDR for ETS-VIII were considered. Resultant deployment characteristics obtained by deployment analysis are correlated to the results of ground deployment testing. Micro-gravity experiments in a jet-airplane were performed to eliminate the ambiguity discovered in a deployment analysis. We proposed a modularized test method for large deployable space structures. Limitation of the analysis are clarified.

A Study on the Accuracy of Deployment Testing for Large Deployable Structures

This paper examines the difficulty of ground deployment tests quantitatively. An index that well shows the difficulty of ground deployment test is the ratio of gravity torque to deployment torque. The relationship between this index and the accuracy of deployment test is developed. We perform deployment tests using a simple planar truss under micro gravity and gravity environments. Ground tests in which the index value of the truss is incremented several times are also performed. Comparing these test results, we find that the estimation error of the deployment force is 10%, even for the simplest structure whose difficult index value = 1. We introduce an empirical equation that sets a linear relationship between the difficulty index value and the evaluation accuracy. We can conclude that that it is infeasible to test the ground deployment of structures whose difficulty index value exceeds 1000. The difficulty index of the modularized large deployable reflectors for ETS-VIII is calculated. We find that the single module of the LDR was designed to be appropriate size to evaluate the deployment reliability, however, evaluation accuracy would be insufficient if ground deployment testing is performed only on more than seven combined modules.

A Feasibility Study on the Program Tracking of the Satellite Tracking Antenna Mounted on Train

We have proposed mobile multimedia satellite communication system designed to realize high-speed multimedia communications. This system uses a mobile network for the return link and the developed satellite-tracking antenna that receives high-speed satellite signals for the forward link. The satellite-tracking antenna, which consists of four planar antennas, measures the pointing error by the phase monopulse and has achieved the satellite-tracking control by the co-phasing combining and the mechanical drive. When the satellite-tracking antenna is applied to the car and the ship, it is necessary to decide the tracking drive angle constantly. When it is applied to the train, the satellite-tracking can be expected to be achieved by specifying the tracking drive angle in accordance with the distance because the train runs in the same route. This tracking method is called a program tracking in this paper. This paper describes the tracking drive angle and the error factor of the program tracking quantitatively. We concluded that it was possible to apply the program tracking to the train if operating rate of the system was 70% or less.