Kazufumi Fukuda

Attitude control system of micro satellite RISING-2

This paper summarizes the attitude control system of the 50-kg micro satellite RISING-2, which is now under development by the Tohoku University and Hokkaido University. The main mission of the RISING-2 is Earth surface observations with 5-m resolution using a Cassegrain telescope with 10-cm diameter and 1-m focal length. Accurate attitude control capability with less than 0.1 deg direction errors and less than 0.02 deg/s angular velocity errors is required to realize this observation. In addition, because of the larger power consumption of the science units than expected, actuators must be operated with sufficiently low power. The attitude control system realizes 3-axis stabilization for the observation by means of star sensors, gyro sensors, sun attitude sensors and reaction wheels. In this paper the attitude control law of the RISING-2 is analyzed to keep the power of reaction wheels under the limit. This simulation is based on component specifications and also includes noise data of the components which are under development. The simulation results show that the pointing error is less than 0.1 deg in most time with the RISING-2 attitude control system.

Satellite system integration based on Space Plug and Play Avionics

Professor Shinichi Nakasuka of University of Tokyo is now leading a small satellite development activity within the scope of a Japanese FIRST (Funding Program for World-Leading Innovative R&D on Science and Technology) program. In this program several 50 kg class microsatellites are going to be developed and launched by the end of Japanese fiscal year of 2013, including one scientific microsatellite under international cooperation. Tohoku University has been assigned as the project leader of this international scientific microsatellite named as RISESAT (Rapid International Scientific Experiment Satellite), and is developing the bus system as well as organizing scientific payload instruments from all over the world. This satellite shall demonstrate the performance of its bus system which is supposed to be offered as a common bus system for international scientific missions in the future. In order to accommodate a wide variety of payload instruments and to provide them flexible and comfortable integration environment, Space Plug and Play Avionics (SPA) standard is applied for the electrical interface between the payload instruments and the satellite bus system. The development of RISESAT flight model will be completed by the March 2013. This paper summarizes the system design of the satellite based on the SPA technology.

Ground test of attitude control system for micro satellite RISING-2

This paper summarizes the attitude control system and evaluation system of the 50kg class micro satellite RISING-2, which has developed by Hokkaido University and Tohoku University from 2010. In 2011, the flight models of each component were completed and now the software of RISING-2 is adjusted in order to put into an orbit in 2013. The missions of RISING-2 are observation of the earth surface, cumulonimbus clouds and planets with a telescope, measurement of the earth surface and ocean temperature distribution using a bolometer array and photography of sprite luminescence phenomenon using thunder observation camera and fish eye camera. To accomplish these scientific missions, the attitude control system needs to satisfy the requirements of observation equipments. This satellite attitude is controlled by the 3-axis reaction wheels in order to point to an arbitrary target direction. Especially, in the case of bolometer array observation, the target direction needs to be changed from deep space direction to the Earth-Center or the earth surface direction. We tried this observation sequence using the static closed loop test system which is constructed by the pre-flight model. Then, the test results illustrate that the attitude control system satisfy the requirements.

Static closed loop test system for attitude control system of micro satellite RISING-2

50-kg class micro satellite RISING-2 is now under development by Tohoku University and Hokkaido University. The development is at Flight Model phase. The main mission of the RISING-2 is Earth surface observations with 5-m resolution using a Cassegrain telescope with 10-cm diameter and 1-m focal length. Accurate attitude control capability with less than 0.1 deg direction errors and less than 0.02 deg/s angular velocity errors is required to realize this observation. The attitude control system realizes 3-axis stabilization for the observation by means of star sensors, gyro sensors, sun attitude sensors and reaction wheels. In this paper the static closed loop test system for the attitude control system of the RISING-2 is described. This test system is the simulation including the hardware of the attitude control system of the RISING-2. The results of the tests show that the pointing error is very larger than the results of software simulation.

Satellite-to-ground optical communication system on Low Earth Orbit micro-satellite RISESAT

Within the scope of a Japanese FIRST (Funding Program for World-Leading Innovative R&D on Science and Technology) program led by Professor Nakasuka of University of Tokyo, Tohoku University is developing a 50kg-class international scientific microsatellite named RISESAT. In addition to various scientific instruments, RISESAT is also equipped with a laser communication terminal VSOTA, developed by Japanese National Institute of Information and Communications Technology (NICT). Tohoku University and NICT are now developing the engineering model of the satellite and undertaking its ground tests. VSOTA has two different wavelengths of laser outputs in 980 nm and 1540nm. The collimators for these are fixed with the satellite structure pointing toward the Earth direction. RISESAT aims to control the direction of the laser beams being precisely pointed toward the NICTs optical ground station with a pointing accuracy of better than 0.4 deg (3σ) during the fly-by. RISESAT can send actual scientific data obtained by payload instruments through this optical communication link. This will be the world first demonstration of microsatellite-to-ground optical downlink. This will bring innovation to misrosatellites system engineering, utilization, and communication network. This paper describes the detailed specification, system design strategy, and real-life implementation of laser communication system on the micro-satellite RISESAT.

Development of small optical transmitter for microsatellites

In this paper the small optical transmitter for microsatellite which is now under development is described. In recent years, the amount of downlink data is increasing and the faster speed communication system has been required. Therefore the optical communication which can realize the high data rate transmission by far than conventional radio waves has been attracting attention. However the high precision pointing is required in optical communication. Although conventional optical communicators of large satellites have been achieving high pointing accuracy by mechanical gimbal and movable pointing mirror, this type optical communicator would occupy a high proportion of mass and power resources of microsatellites. Then the optical transmitter without mechanical gimbal which points to the target by the Attitude Control System (ACS) of the satellite was proposed. Optical communicator of this method can be very compact and can be mounted on microsatellites. However initial discovery by ground station communicator is difficult in this method. For this reason the adjustable beam spread angle type was adopted in desired optical transmitter. The beam divergence from this transmitter can be expanded and initial discovery will be easy. The status of development is test model. The behavior of received light was analyzed in simulation and receive gain of more than - 40 dBm.

Impacts of Space Plug-and-Play Technology on Micro- and Nano-satellites

Abstract The Space Robotics Laboratory of Tohoku University has been investigating application method of Space Plug-and-Play technology for microsatellites together with AAC Microtec AB. The first and second micro-satellites RISING-1/-2 are carrying technology demonstration payloads for this purpose, and the functionality of the former one has been already verified in space environment. Accordingly SPA technology was applied to the real-life international scientific mission on the third micro-satellite RISESAT. Payload instruments of RISESAT were converted into SPA compatible devices. The result of application illustrated that SPA allows modular, reusable, and rapid system design approach. A CubeSat mission based on SPA technology where AAC Microtec AB is involved also successfully demonstrated correct performance in space environment. SPA technology is revealing its attractive capabilities to micro- and nano-satellites.

Model-Based Environment for Verification and Integration of Micro-Satellites

Abstract The Space Robotics Laboratory of Tohoku University has been developing multiples of micro-satellites for years and has gathered experiences in their development, verification, integration, and operation. SRL has recently started development of model-based simulation, verification and integration environment to realize rapid and cost-effective development of reliable micro-satellites. The conceptual design and its functionality have been verified through the real-life micro-satellite project RISESAT, which is a 50kg class international scientific micro-satellite. The developed environment can be utilized in different configurations depending on requirements in each satellite development phase. This environment is designed to be modular and very flexible and can be utilized for other micro-satellites and possibly even much smaller space system projects in the future.

Lessons learned on structural design of 50kg micro-satellites based on three real-life micro-satellite projects

The Space Robotics Laboratory (SRL) of Tohoku University has developed three 50kg Micro-satellites. The first satellite “SPRITE-SAT” has been successfully launched into Earth orbit, and also been operated. The flight model of the second satellite “RISING-2” has been assembled and its software development is now finalized, being ready for the launch planned in next year. The third satellite “RISESAT” project is during the EM (Engineering Model) development phase at the time of writing. The launch is planned in the later half of 2013. The structural design of all these satellites is based on central pillar configuration, while continuous improvements have been made through the projects. The paper will discuss these aspects of structural design and evaluation summarizing the results of numerical analyses and mechanical tests conducted by the SRL during the past 5 years of micro-satellite development activities.

Radiation effect mitigation methods for electronic systems

Effects of space radiation on space systems have been considered as the main challenge in designing sustainable space systems, and investigations have been done about the mitigation methods against various types of radiation effects. On March 11, 2011, a massive earthquake and tsunami hit the eastern Japan, particularly Tohoku area. Since then, the Fukushima Daiichi Nuclear Power Station has been facing a crisis. To respond to this situation, Tohoku University conducted studies to redesign mobile robots for disaster response missions, and has realized the fact that there was no practical information available about the radiation effects on electronic devices to be installed on those mobile robots and the mitigation methods against them, which revealed the importance of establishing a knowledge-base about the way of designing radiation-tolerant or radiation-hard electronics systems even for terrestrial applications. Space Robotics Laboratory of Tohoku University has been conducting researches on space systems engineering and has gathered knowledge about the radiation effects on space systems electronics devices through its real-life microsatellite development and operation activities. Based on this background, this paper summarizes the general radiation effects on electronics devices and the cost-effective way of their mitigation methods, together with the application example of microsatellite systems developed by the Space Robotics Laboratory. This paper aims to contribute to establish such kind of knowledge-base together with a variety of aerospace and terrestrial engineering communities.