Development of the tip-tilt mirror system for the solar XUV telescope

This paper describes the design and prelaunch performance of the tip-tilt mirror (TTM) system developed for the XUV Cassegrain telescope aboard the ISAS sounding rocket experiment. The spatial resolution of the telescope is about 5 arcsec, whereas the rocket pointing is only controlled to be within +/- 0.5 degree around the target without stability control. The TTM is utilized to stabilize the XUV image on the focal planes by tilting the secondary mirror with two-axes fixed-coil type actuators. The two position- sensitive detectors in the telescope optics and in the TTM mechanical structure from the normal and local closed-loop modes. The TTM has four grain modes with automatic transition among the modes. The low gain mode is used in the initial acquisition, and in case the TTM loses the tracking. The high gain mode is used in the normal tracking mode. This arrangement provides us with the wide initial acquisition angle with single TTM system as well as the high pointing accuracy once the tracking is established. The TTM has a launch-lock mechanism against the launch vibration of 16G. The closed-loop control with command and telemetry interface is done by the flight software against the launch vibration of 16G. The closed-loop control with command and telemetry interface is done by the flight software on the DSP processor. The use of the fast processor brings in the significant reduction in the weight and size of the control- electronics, more flexible control system, and shorter design and testing period.