Structure of High Precision Large Deployable Reflector for Space VLBI

[Abstract] To achieve scientific improvements from VSOP(HALCA) mission, operated until 2005, to expected VSOP-2(ASTRO-G) mission, the satellite design incorporates the engineering characteristics of a large-scale deployable antenna of offset Cassegrain type with observation bands of 8, 22, and 43GHz. The antenna subsystem requires the target surface accuracy of 0.4mm-rms on the main reflector of about 10m in diameter. An off-axis paraboloid reflector is composed of seven deployable modular antennas, and each of the modules employs a new idea of radial-rib/hoop-cable reflector construction to stretch knitted metal fabric surface and to satisfy the required surface accuracy for millimeter-wave observation. Deployment mechanism employs the most of the deployable truss technology developed for JAXA's ETS-VIII satellite. Some prototype models of one module have been made to investigate the surface accuracy. In addition, the antenna will have a gimbal adjuster mechanism for the main reflector, and a gimbals and focus adjustment mechanism for the sub-reflector in order to optimize the antenna gain after deployment in orbit.