Kazufumi Fukuda
(Tohoku University, Japan)

The 50-kg micro satellite RISING-2 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. The attitude control system of the RISING-2 and its sensors and actuators are under development by the Tohoku University. The attitude control system realizes 3-axis stabilization for the observation by means of star sensors, gyro sensors, sun attitude sensors and reaction wheels. Accurate attitude control capability with less than 0.1 deg direction errors is required to realize this observation. The results of the simulation which based on component specifications and also includes noise data of the components show that the pointing error is less than 0.1 deg in most time. At the time of writing, the development of the Breadboard Model and Engineering Model has been completed. We will have completed the development of the Flight Model in spring 2011. We will improve the internal program and the control row through the tests using actual components, for example, Static or Dynamic Closed Loop Test. This paper summarizes the attitude control system of the RISING-2 and some evaluation tests.

Takayuki Hosonuma
(University of Tokyo, Japan)

Pico-satellite for Remote-sensing and Innovative Space Missions (PRISM) is an 8.5 kg remote sensing satellite, which has been launched with GOSAT by H-IIA rocket in January 23rd 2009. The objective of the mission is to obtain 30 m resolution earth images using an extended boom optical system. In this research, the outline of PRISM bus system and in-orbit performance, specifically attitude determination and control system will be presented. In order to obtain high resolution images, PRISM attitude should be stabilized to 0.7 degree/sec, which is difficult to achieve using only passive attitude control system. To meet attitude requirements, gyro sensors, sun sensors, magnetometers, and MTQ are attached to the satellite. In the satellite operation, the attitude was stabilized using Bdot and Cross Product control method to a 0.1 deg/s accuracy successfully. After stabilizing satellite attitude, 30m resolution images was obtained using NAC successfully. The research presents how to achieve the requirement and in-orbit performance of the ADCS.

Osamu Mori
(JAXA, Japan)

The Japan Aerospace Exploration Agency (JAXA) makes the world's first solar power sail craft demonstration of photon propulsion and thin film solar power generation during its interplanetary cruise by IKAROS. It deploys and spans a membrane of 20m in diameter using the spin centrifugal force of four tip masses. It also deploys thin film solar cells on the membrane. This deployment method can be realized with simpler and lighter mechanisms than conventional mast or boom types as it does not require rigid structural elements. The sail spacecraft controls the orientation and spin rate of the membrane by the gas jet thrusters mounted on the main body in time-to-time to demonstrate photon acceleration in accordance with the guidance strategy. This paper presents the attitude control dynamics of spinning solar power sail. First, the multi-particle model and the finite element method model, considering the devices on the membrane, are proposed. Second, they are modified by comparison with these simulation results and flight data. Next the modes of vibration of angular velocity during the attitude control are analyzed by these models in order to understand the flexible motion of spinning solar power sail.

Yuta Komiya
(Tokyo Institute of Technology, Japan)

This paper describes attitude analysis for the initial operation of 50kg-class technology demonstration small satellite "TSUBAME" being under developed by Laboratory for Space Systems (LSS). TSUBAME achieves sun-pointing stabilization in its initial operation with actuators of three magnetic torquers (MTQs) within the time constraint due to limited electric power before deploying solar panels. The proposed strategy for the management of MTQs takes advantage of spinning stabilization. The method can be divided in three phases. After the separation from the launch vehicle, the initial rotation is detumbled. Then the satellite spins up about its Z axis under a spinning operation mode. When achieving at a certain spin rate, the spinning direction is adjusted to let the solar panel towards the sun with eliminating undesirable nutation torque. To design a magnetic attitude control method to achieve robust sun-acquisition, the sensitive analysis to determine the appropriate transition conditions among these three phases was done based on numerical simulation. The electric power balance was also examined to verify the satellite can survive during the initial operation. Finally the simulation results using the determined condition with various initial conditions are presented showing that proposed method is feasible.

Tao Meng
(Zhejiang University, China)

TSUBAME, an agile nano-satellite developed by the Laboratory of Space Systems at Tokyo Institute of Technology, has many advanced missions for scientific demonstration. This paper focuses on the landmark tracking mission for Earth observation using micro control moment gyros (CMGs). The CMG is one of the best candidates for agile satellites due to its torque amplification capability. However, its inherent problems such as nonlinear coupling motion, singular gimbal states make it complicated for practical use. Moreover, the control system cannot be treated as linear system under large angle maneuver. Due to the fact that there exists no separation principle of nonlinear control system, it is critical to design a combined observer-controller for attitude control of agile satellite. In this paper, a guidance law is derived firstly through the geometric analysis as a reference trajectory. Then, a nonlinear observer based sliding mode controller is proposed to guarantee the globally stable asymptotic convergence to the desired attitude profile. Numerical simulations are carried out to demonstrate the performance of the proposed strategy.