Osamu Takahara

The Solar Optical Telescope onboard the Solar-B

The solar optical telescope onboard the Solar-B is aimed to perform a high precision polarization measurements of the solar spectral lines in visible wavelengths to obtain, for the first time, continuous sets of high spatial resolution (~0.2arcsec) and high accuracy vector-magnetic-field map of the sun for studying the mechanisms driving the fascinating activity phenomena occurring in the solar atmosphere. The optical telescope assembly (OTA) is a diffraction limited, aplanatic Gregorian telescope with an aperture of Φ500mm. With a collimating lens unit and an active folding mirror, the OTA provides a pointing-stabilized parallel beam to the focal plane package (FPP) with a field of view of about 360x200arcsec. In this paper we identify the key technical issues of OTA for achieving the mission goal and describe the basic concepts in its optical, mechanical and thermal designs. The strategy to verify the in-orbit performance of the telescope is also discussed.

Systematic Approach to Achieve Fine Pointing Requirement of SOLAR-B

Abstract The systematic approach adopted in SOLAR-B in order to achieve its fine pointing requirement is presented. The approach consists of : (1)unique pointing requirement analysis in frequency domain that provides a framework of satellite system design, (2)pointing performance analysis including attitude control, telescope pointing control, spacecraft dynamics, structural dynamics and telescope optics, (3)careful disturbance management both in frequency and time domain based on specially devised control parameters, and (4)elaborate tests such as microvibration transmissibility test using the structural model of the spacecraft with real and simulated disturbance sources and very sensitive inertial sensors.

Evaluation of developing inertial stabilization unit

Micro vibrations generated from some internal disturbance sources such as a reaction wheel degrades the pointing stability of an observation satellite. To suppress the pointing error, we have been developing an inertial stabilization unit. A prototype mechanism is designed based on concepts that it has non-contact actuators and sensors, and rotational leaf springs are applied to support a stabilized platform in order to meet two requirements which are precise drive and tolerance for launch load. Two kind of inertial sensors are installed on the platform to measure the attitude directly. Each of these two inertial sensors covers low or high bandwidth signal respectively. These signals will be able to be combined as one wideband signal to stabilize the platform in inertial space. In this paper, the developing prototype mechanism and control equipment are described and the basic evaluation results are reported. Less than 0.3urad as a drive precision and more than 100Hz as a local sensor control bandwidth are verified. The development of the system has not completely finished yet, but the basic performance is certified to meet the design specification. From now on, we continue to develop the unit. These future results can be applied to inter-satellite laser communication system.

Spacecraft with Very High Pointing Stability: Experiences and Lessons Learned

Abstract Technical issues associated with spacecraft with very high pointing stability requirement for short to medium term (typically, sub-micro radians for 1-100 seconds) are reviewed. Specifically, microvibration and pointing jitter, that are induced by various internal disturbance sources, is a major issue for this class of satellite. The experiences and lessons learned through the development of several satellites are presented. In particular, some basic concepts on attitude and pointing, new evaluation techniques of pointing stability, influence of high frequency microvibration on pointing and attitude, and dynamic interface between payload and bus are described in this context.