Ryu Funase

Generalized Attitude Model for Spinning Solar Sail Spacecraft

An attitude model for a general spinning solar sail spacecraft under the influence of solar radiation pressure is presented. This model, called “Generalized Spinning Sail Model”, can be applied to realistic sails with nonflat surfaces that have nonuniform optical properties. The unique behaviors predicted by the generalized spinning sail model are verified by actual operation of the Japanese spinning solar sail spacecraft IKAROS. It is shown how imperfections in the sail surface affect the attitude motion of spinning sails, and a compact mathematical model that can precisely reproduce the spin-averaged motion of the spinning sails is derived. The stability conditions and a reduced model that preserves the key characteristics of the generalized spinning sail model are also derived to reveal the unique properties of the attitude behavior of spinning sails.

High-performance image acquisition & processing unit fabricated using COTS technologies

It is becoming imperative to have visual capabilities for space activities. There are increasing opportunities to use visual images coupled with image processing technologies for spacecraft sensing and control. To fill this need, we have developed a small, low-cost, high-performance image acquisition and processing unit (HP-IMAP), which uses commercial off-the-shelf technologies. In 2010, the HP-IMAP was launched to monitor a deployable structure. Herein, we describe the HP-IMAP and discuss its qualification tests.

REMOTE SENSING BY UNIVERSITY OF TOKYO’S PICO-SATELLITE PROJECT “PRISM”

This paper presents our design concept and some technological topics in our ongoing project, “PRISM” which stands for “Pico-satellite for Remote-sensing and Innovative Space Missions”. Nakasuka laboratory in University of Tokyo has been designing and developing this pico-satellite since 2002. Its main mission is remote sensing. Basically, we aim to obtain Earth images with as high resolution as about 30 meters by its compact spacecraft bus, which is a 17cm*17cm*25cm and will be weigh less than 5kg. PRISM has a refracting optical system using one group of lenses, unlike most of the Earth Observation satellites. A main reason why we adopted this kind of optics is the possibility of downsizing the whole optics with extensible tube framework for telescope. Moreover, we’ve been dedicated to design and development of many components in every subsystem. The fundamentals of its bus technologies are on the basis of the experience in our previous project, “CubeSat XI” [sai] [1], which was launched in 2003 and has been operative for more than 16 months. We are now developing PRISM engineering model with a hope to launch its flight model between 2005 and 2006.

Modeling of Spinning Solar Sail by Multi Particle Model and Its Application to Attitude Control System

In this paper, the attitude motion and attitude control strategy of spinning solar sail are discussed. As the spinning type solar sail does not have any rigid structure to support its membrane, the impulsive torque by the RCS can introduce oscillatory motion of the membrane. Thus, an “oscillation free” attitude controller is needed, which takes into account the flexibility of the membrane and avoid unnecessary oscillatory motion. First, the dynamics model and numerical model were introduced, and the validity of these models and dominant out-of-plane membrane vibration mode is examined by membrane vibration experiment and comparison between both models. Then, based on the analysis of the dynamics of torque-free motion, it was shown that a spinning solar sail has three oscillation modes of nutation, one of which is equal to the spinning rate of the spacecraft. The dominancy of each nutation mode was analytically and numerically discussed. Then, we discussed the spin axis maneuver control using conventional RCS. It was analytically shown that continual impulsive torque synchronizing the spin rate can excite nutation velocity and that a controller is needed to damp the nutation while controlling the spin axis at the same time. The authors proposed new controller named Flex-RLC and improved one. Their effectiveness was verified by numerical simulations using precise multi-particle numerical model which can express higher order oscillatory motion of the flexible membrane, and it was found that the proposed method can control the attitude of spinning solar sail while drastically reduces the nutation velocity compared with conventional control logic. So, it can be said that the proposed method is promising fast and stable controller for spinning solar sail.© 2009 ASME

TARGET ATTITUDE MOTION ESTIMATION AND TRACKING EXPERIMENT ON MICRO-SATELLITE "MICRO-LABSAT"

On a NASDA’s microsatellite named “μ-LABSAT,” which was launched by H-IIA on December 14, 2002 (Fig.1), Communications Research Laboratory (CRL), National Aerospace Laboratory (NAL) and University of Tokyo (UT) have been jointly performing several orbital experiments as technology demonstration towards the future orbital servicing missions. In University of Tokyo’s experiment which was held on May 14, 2003, the micro-satellite released a small object named “target,” and its rotational motion was estimated by the images captured continually using a camera developed by CRL. Then satellite attitude control was performed by visual feedbacks of the target image position on the camera frame so that the target image may come to a certain point on the camera frame. This is a pre-experiment of so-called LOS (Line Of Sight) control, which will be indispensable during rendezvous and docking to the satellite to be serviced. In this paper, the objectives and procedure of these experiments, and the results will be described. 54th International Astronautical Congress of the International Astronautical Federation, the International Academy of Astronautics, and the International Institute of Space Law 29 September 3 October 2003, Bremen, Germany IAC-03-A.P.06 Copyright

Thermal-IR imaging of a near-Earth asteroid

The Japan Aerospace Exploration Agency/Institute of Space and Astronautical Science Hayabusa2 mission (see Figure 1) is due to be launched in 2014 with the aim of returning a sample from the C-type (rich in carbon) near-Earth asteroid 1999JU3, which is thought to contain organic or hydrated materials.1 A thermal emission map of the asteroid’s surface can be derived from regional variations in measurements of thermal inertia. These measurements provide information about the physical properties of the surface (i.e., whether sand, pebble, or boulder-sized materials are present) and will be used to identify a suitable landing site. Hayabusa2 is a follow-up to the Hayabusa probe that performed the first round trip, with sample return, to an asteroid in 2010. The Hayabusa2 spacecraft design builds on the heritage of Hayabusa, but includes several refinements. Although the primary goal of the mission is to return a sample of the asteroid, remote sensing of the body is also an important aspect. The physical properties and composition of the uppermost layer of the asteroid will be investigated in an active impact experiment where the small carry-on impactor instrument will form a crater (a few to several meters in diameter) and excavate parts of the subsurface. The crater and surrounding ejecta will be studied with an optimized set of remote sensing instruments that include multi-band telescopic and wide-angle imagers, a laser ranger (lidar), a near-IR spectrometer (to detect an absorption band at 3 m characteristic of water ice or hydrated minerals), and a thermal-IR imager (TIR). With these sensors, the mid-IR thermal emission and surface temperature profiles of the asteroid will be acquired, as well as their temporal variation with the asteroid’s rotation. Our TIR instrument is based on the design of the longwavelength IR imager that was built for the Venus climate mission Akatsuki.2, 3 It has been adapted to meet the Hayabusa2 Figure 1. An artist’s impression of the Hayabusa2 probe’s encounter with a near-Earth asteroid. ( c Akihiro Ikeshita.)

Design Criteria of Spinning Solar Sail Surface Based on Attitude Dynamics

This paper describes design criteria for sail surface quality derived from requirements about attitude dynamics of spinning solar sail spacecraft. The method has been developed by an experience of the Japanese interplanetary solar sail mission IKAROS. The authors derived, in their previous work, a combination of a generalized spinning attitude model and a finite element model-based sail deformation analysis method to directly relate the sail surface wrinkling and the attitude disturbance via solar radiation pressure effect. Based on this work, this paper attempts to derive design criteria for the sail surface quality, which is useful for the mission analysis and the quality control in sail production. Specifically, this paper provides an acceptable deformation level as a function of scale length for given attitude stability requirements against the solar radiation pressure disturbance, which is then compared and verified by the post-flight analysis of IKAROS.

Prospective 3-Axis Attitude Control using Solar Radiation Pressure

Abstract Developing higher level 3-axis attitude control mechanics is desired in recent satellite attitude control systems, so that we propose an innovative 3-axis attitude control for recent and future satellites by using Re ectivity Control Device, RCD, which is capable of changing its re ectance according to applied voltage. This paper shows some examples of the high accuracy and stability 3-axis attitude control method using RCD, and indicates usefulness of this method with the 3-axis attitude control simulation including the torques generated by solar radiation pressure.