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The balloon-borne very long baseline interferometry (VLBI) experiment is a technical feasibility study for performing radio interferometry in the stratosphere. The flight model has been developed. A balloon-borne VLBI station will be launched to establish interferometric fringes with ground-based VLBI stations distributed over the Japanese islands at an observing frequency of approximately 20 GHz as the first step. This paper describes the system design and development of a series of observing instruments and bus systems. In addition to the advantages of avoiding the atmospheric effects of absorption and fluctuation in high frequency radio observation, the mobility of a station can improve the sampling coverage ("uv-coverage") by increasing the number of baselines by the number of ground-based counterparts for each observation day. This benefit cannot be obtained with conventional arrays that solely comprise ground-based stations. The balloon-borne VLBI can contribute to a future progress of research fields such as black holes by direct imaging.

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A fold process of a deployable space membrane with retraction mechanisms is examined to reduce wrinkles and to improve the fold precision of the membrane retracted repeatedly. The properties of the fold process are investigated experimentally with experimental retraction mechanisms which wrap and fold the membrane with tensile forces and rotation of the center hub. To reduce wrinkles, and to improve the fold precision, hinge mechanisms which are stiffened elements attached on the membrane are proposed. To examine the effects of the hinge mechanisms, fold patterns, and configuration of the center hub on the properties of the fold process, the retraction experiments are performed. The experimental results indicate that the distribution of the tensile forces and the hinge mechanisms mainly determine the fold process. Introducing the mixed spiral fold which consists of Z-folds and spiral folds, the membrane is successfully folded with fewer wrinkles and higher precision than the rotationally skew fold.