FOR SOLAR SAIL DEMONSTRATOR IKAROS CONSIDERING. ATTITUDE DYNAMICS .... formed (The black line shows the attitude sequence). After launch, the ...
AAS 10-231
ESTIMATION OF SOLAR RADIATION PRESSURE PARAMETERS FOR SOLAR SAIL DEMONSTRATOR IKAROS CONSIDERING ATTITUDE DYNAMICS Yuya Mimasu, * Jozef C. van der Ha, † Tomohiro Yamaguchi, ‡ Ryu Funase, § Yuichi Tsuda, ** Osamu Mori** and Jun’ichiro Kawaguchi†† Japan Aerospace Exploration Agency (JAXA) has developed the small demonstration solar sail spacecraft IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun), which will be launched in mid 2010. The main objective of this spacecraft is to deploy the 20m class sail membrane, and demonstrate the acceleration of a spacecraft by the solar radiation pressure (SRP) by means of that sail. It is important to model the SRP force adequately for the objective of navigation, especially for interplanetary spacecraft. In order to improve the model of the SRP torque induced by the sail membrane, the IKAROS project team plans to estimate the SRP torque parameters in orbit. In this paper, we present the approach to obtain the parameters needed for constructing the photon torque model through the analysis of the attitude dynamics.
INTRODUCTION The propulsion technique using the Solar Radiation Pressure (SRP) force is called ‘solar sailing’. In this technique, no propellant is needed to produce the thrust force. This possibility has motivated people to research this field and it is expected to widely expand the space exploration field1. Although much research on solar sail spacecraft has been done all over the world, so far there has been no actual flight of a solar sailing spacecraft in space history. Nevertheless, the Japan Aerospace Exploration Agency (JAXA) succeeded in the deployment of a membrane in the space with the S-310-34 experiment in 20042. At present, JAXA plans to launch the world’s first demonstration solar-power sailcraft named IKAROS (Interplanetary Kitecraft Accelerated by Radiation Of the Sun). This spacecraft will demonstrate several technologies, for example, photon propulsion, thin film solar power generation system, and the deployment of the sail membrane during its interplanetary cruise.
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Graduate Student, Dept. of Aeronautics and Astronautics, Kyushu University, Nishi-ku, Fukuoka 819-0395, Japan. Professor, Dept. of Aeronautics and Astronautics, Kyushu University, Nishi-ku, Fukuoka 819-0395, Japan. ‡ Graduate Student, Dept. of Space and Astronautical Science, The Graduate University for Advanced Studies, Sagamihara, Kanagawa 229-8510, Japan. § Engineer, Japan Aerospace Exploration Agency, Sagamihara, Kanagawa, 229-8510, Japan. ** Assistant Professor, Japan Aerospace Exploration Agency, Sagamihara, Kanagawa, 229-8510, Japan. †† Professor, Japan Aerospace Exploration Agency, Sagamihara, Kanagawa, 229-8510, Japan. †
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IKAROS will be the very first actual solar sail flying an interplanetary voyage. The spacecraft aims at the technical demonstration to generate the acceleration induced by the Solar Radiation Pressure (SRP). IKAROS deploys and spans a 20-meter class membrane by taking advantage of the spin’s centrifugal force. The spacecraft weighs approximately 315kg and will be launched together with JAXA’s Venus Climate Orbiter, PLANET-C in mid 2010. Both spacecraft are boosted by the JAXA’s H-IIA launch vehicle directly onto the transfer trajectory bound for Venus. This demonstrator attempts further to deploy thin-film solar cells on the sail membrane in order to evaluate the performance of its thermal control and radiation resistance performance in orbit. The spacecraft controls its attitude orientation in real-time in order to demonstrate the capability of controlling the photon acceleration in accordance with the imposed guidance strategy. One of the most significant tasks to achieve this solar-sail mission is to estimate the force and torque induced by the SRP in order to establish the precise SRP model in support of its navigation objectives. The estimation and modeling of the SRP force for this spacecraft from the viewpoint of orbit dynamics has already been studied3. In addition to this force model, the IKAROS project aims to establish the SRP torque model of IKAROS as well. The estimated torque parameters have a few common parameters with the force model (such as the parameters to express the shape of the sail membrane). Therefore, the study of SRP torque model in-orbit has may be able to contribute to the establishment of a more precise force model.
Figure 1. Solar Sail Spacecrafts JAXA developed and plans to launch.
OUTLINE OF IKAROS Devices on Sail Membrane The solar sail demonstration spacecraft IKAROS developed in JAXA has a square sail membrane shown in Figure 2. The sail membrane of IKAROS consist of 7.5 [m] Polyimide evaporated 80 [nm] aluminum. A polyimide has the high thermal, mechanical and chemical resistance properties and the mass is very small. It is not an exaggeration to say that this material enables the actual manufacturing of the solar sail. By receiving the sunlight on the aluminum side of the membrane, the thrust force is generated by its high reflectivity in the IKAROS case. There are various devices placed on the sail membrane. The main devices are the Flexible Solar Array (FSA) 4, and the Reflectivity Control Device (RCD) 5. The FSA is a thin power generator by using the incident sunlight. If a large power generation system could be constructed based on FSA, it may be possible to carry a high-power electric propulsion system on the spacecraft. The purpose of the RCD is to control the spacecraft attitude. This device is mounted on the edge
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of the sail membrane (as shown in Fig. 2), and it can generate a torque by actively changing the optical properties. This device is mainly made of liquid crystal, and it can modify the ratio of reflectivity between specular and diffuse by applying a different voltage. Therefore, the induced effective solar radiation force is different on each element’s surface. In this study, however, the optical properties are assumed to be represented by the membrane itself. Flexible Solar Array
Reaction Control Devices Power OFF
Power ON
Figure 2. Layout of Devices on Membrane of IKAROS.
Attitude Sequence In the IKAROS mission, not only the deployment of the sail membrane, but also the guidance capability of the solar sail is planned to be demonstrated. The most demanding of all attitude requirements come from the radio communication constraints as shown in Figure 3. When the Earth aspect angle is within 0 - 60 [deg] or 120 - 180 [deg], IKAROS can communicate with the ground station by using one of the Low Gain Antennas (LGA1 or LGA2). In addition to this constraint with respect to the Earth angle, the Sun aspect angle must be less than 45 [deg] due to the power supply. Figure 3 shows how the Sun acquisition and Sun-pointing control of the spin-axis are performed (The black line shows the attitude sequence). After launch, the spin axis of IKAROS is controlled to reorient from 0 [deg] to 45 [deg] from the Sun during the first 30 days. Subsequently, it maintains the Sun angle at 45 [deg] until 100 days. From 100 days to 130 days, IKAROS cannot communicate with the ground station due to the RF interference of the membrane. Afterwards, the spin axis is again reoriented to the 45 [deg] Sun angle as at the end of the nominal mission phase at 100 days.
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