Haruhiko Shimoji

Suppression of sun interference in the star sensor baffling stray light by total internal reflection

We have developed a star sensor as an experimental device onboard the SERVIS-1 satellite launched in October 2003. The in-orbit data have verified its fundamental performance. One of the advantages of our star sensor is that the baffle has a small length of 120 mm instead of 182 mm in the conventional two-stage baffle design. The key concepts for light shielding are total internal reflection phenomena inside a nearly half sphere (NHS) lens and scattering light control by gloss black paint. However, undesirable background noise by the sun outside of the field of view (FOV) was observed in the corner of the FOV in the orbital experiment. Ray trace simulations revealed that slight scattering light on the specular baffle wall entered the NHS lens and reached the corner of the image sensor through the multi-reflection path inside the lens. It was found that the stray light path can be shielded effectively if the diameter of the aperture under the NHS lens was reduced. We redesigned the baffle and evaluated the light shielding ability with our sun interference test facility on the ground, and confirmed that the stray light was reduced below the acceptable level. As a result, the light shielding technique which we have proposed was proved to be effective for a small-size baffle. The redesigned star sensor is planned to be installed as a main attitude sensor for the SERVIS-2 satellite scheduled to be launched in February 2008.

Solar-light shielding using a near-hemispherical lens for a star sensor

We have developed a light-shielding technique for a star sensor that can shorten the baffle length. We achieved a baffle length of 120 mm, two-thirds that of a conventional two-stage baffle. The key idea is that the first lens of the imaging optics is designed as a near-hemispherical (NHS) lens that can work as an angle filter; high-incidence-angle rays are not permitted to be transmitted but low-incidence-angle rays from stars can be. A star sensor system with the new light-shielding technique onboard the SERVIS-1 satellite was launched in October 2003 as an experimental device. Though the in-orbit data verified its fundamental performance in capturing star images, undesirable solar background noise was observed in two corners of the field of view. Ray-trace simulations revealed that slight scattered light on the specular baffle surface entered the NHS lens and reached the corners of the image sensor through a multireflection path inside the lens. We redesigned the baffle and confirmed that stray light was reduced below maximum acceptable levels in a ground test. The star sensor with redesigned baffles is planned to be installed as the main attitude sensor for the SERVIS-2 satellite to be launched in 2008 or later.

Control system of electrostatic levitation furnace

Abstract The electrostatic levitation furnace (ELF) is one of the experimental facilities for materials science research planned to be embarked on the International Space Station. The most significant feature of the ELF is that it creates a free-drifting space inside the furnace chamber by controlling the experimental materials not to collide against the chamber wall. The purposes of this paper are to introduce the control system of the ELF and to show the results of a flight test on a small sounding rocket, called TR-IA. By adopting high-speed position detectors and a field programmable gate array (FPGA) technique, rapid calculation of materials position up to 1000 Hz realized. The maximum control input (voltage) and the control cycle were chosen as 3 kV and 100 Hz , respectively. The flight data show that complete melting/solidification of the material ( 0.5 g BiFeO 3 ) was accomplished. Though the materials motion was fully controlled during the experiment, unexpected shaking occurred at high temperature due to a sudden drop of electrostatic charge. This phenomenon is understood as the most important issue to be solved.

Simulation System for a Space Robot using 6 Axis SERVOS

Abstract We aim to develop the space robot with a manipulator which is operated to catch and handle a target, in zero gravity environment. In this case, the behavior of the robot main body caused by the reaction force exerted by the manipulator motion has to be taken into consideration, in order to control the manipulator correctly. To solve this problem, we have constructed the ground simulation system combining numerical simulation and servo mechanisms. On this system, dynamics of the space robot and the target is solved based on the momentum conservation law, and the relative motion between them is realized. Using this simulation system, we can develop space robots efficiently.

Spacecraft Attitude and Body Rate Estimation with Four Star Sensor Heads: Concepts and Ground and On-Orbit Verification Results

Abstract We have developed a star sensor system with four heads as a prototype of a future small and low-priced satellite attitude controller. To reduce size and cost of the controller, we integrate attitude sensors into star sensors with medium resolution and medium sensitivity and adopt Commercial Off-The-Shelf (COTS) electrical parts for key parts such as CPU and CCD. Newly developed computer architecture is introduced for high reliability with COTS parts under the harsh space environment. In this paper, we will focus on the new star identification algorithm dedicated for the proposed four-head star sensor system and evaluate it with ground test and on-orbit check-out data.