Orbit Determination for Long-term Prediction of Solar Power Sail Demonstrator IKAROS By ShoTaniguchi1), Takafumi Ohnishi1), Osamu Mori 2), Hideki Kato2), Hiroshi Takeuchi2), Atsushi Tomiki2), Yuya Mimasu2), Naoko Ogawa2), Jun Matsumoto2), Taichi ITO2), Tsutomu Ichikawa2), MakotoYoshikawa2), Shota Kikuchi3) , and Yosuke Kawabata3) 1) Technical computing solutions unit, science solutions div, Fujitsu Limited, Tokyo, Japan 2) Institute of Space and Astronautical Science, JAXA, Sagamihara, Japan 3) Department of Aeronautics and Astronautics, The University of Tokyo, Tokyo, Japan (Received April 24st, 2017) The world’s first solar sail IKAROS (Interplanetary Kite-craft Accelerated by Radiation of the Sun) was launched along with the Venus Climate Orbiter Akatsuki in May 2010. IKAROS was full successful of missions that have been planned for first half year. After the Venus flyby in Dec 2010, it was carried out an extended mission. IKAROS has succeeded many additional engineering and scientific missions. We are obtained many orbit determination skill1) in nominal and extended phase. However, the IKAROS was almost run out the fuel in Dec 2011, so attitude and spin rate was out of control .As a result, lost communication with the ground station due to the power shortage on December 24, 2011. After this operation IKAROS began to repeat the hibernation of the 10-month period by substantially fixed attitude in inertial coordinate while maintaining the spin rate between 5rpm and 6rpm without fuel. End of a hibernation, it is necessary to difficult orbit determination and 10 months or more of the long-term trajectory prediction for antenna tracking at USUDA deep space tracking station. In order to perform the orbit determination of long-term arc, an optical model2) of the solar sail back surface was constructed. Also we constructed attitude motion model3) to predict attitude of spin axis motion due to solar radiation pressure (SRP) torque. After Dec 2011, we couldn’t get normal range data, only obtained range rate data which using FFT analysis4) at offline data from open loop receiver. Also azimuth and elevation data when we observed IKAROS at beacon mode were obtained. In a very difficult situation, we study to estimate the uncertainty orbit determination error. And we try to considered search operation using USUDA deep space tracking station and Yamaguchi University tracking station for VLBI. In this paper, we present orbit and attitude determination using few year long-term data and how to search a large area for antenna tracking to find out IKAROS. Key Words: Orbit determination, IKAROS, Long-Term prediction, Attitude motion 1. Introduction rate between 5rpm and 6rpm without fuel. After wake up from hibernation, it is necessary to difficult orbit determination for The IKAROS (Interplanetary Kite-craft Accelerated by 10 months or more the long-term trajectory prediction. In Radiation Of the Sun) was launched along with the Venus order to perform the orbit determination of long-term arc to Climate Orbiter Akatsuki in May 2010. Fig. 1.1 shows construct an optical model of the solar sail back surface. And IKAROS’s mission sequence. IKAROS was successful we study to estimate the uncertainty orbit determination error. missions that have been planned for first half year. In this For the long-term prediction we have to study attitude phase, we were able to operate a stable orbit determination. motion and spin rate motion dynamics. Attitude motion is And we acquired the skills to consider polarization bias and to strongly related to spin rate, especially at low spin rate. eliminate spin modulation. These were required for orbit Recently we have find out signs that the spin rate is changing determination of the spin solar sail. in deceleration in the telemetry data at 2014 and 2015. After the Venus flyby in Dec 2010, it was carried out at extended mission that IKAROS had achieved a variety of 2. Overview of IKAROS results. One of the results was necessary to correspond to changes in spin rate in orbit determination arc at low spin rate. IKAROS is constructed to maintain the shape of a huge IKAROS was performed a reverse spin operation in order to 14 m x 14m square by spinning, and the square of the solve the problem of spin rate uncontrolled by the fuel quadrilateral have a mass attached. Spin rate and attitude are depletion in Oct 2011. After this operation IKAROS began to controlled through the tether by thruster of the main body in repeat the hibernation of the 10-month period by substantially the center. An outline of IKAROS is shown in Fig 2.1. fixed attitude in inertial coordinate while maintaining the spin 1 Reverse spin operation Inertial motion st Hibernation mode 1 Hibernation Fitr （2012/9/6） flyby Venus (2010/12/8) 2nd Hibernation Fitr （2013/6/20） Extra success (after flyby) 3rd Hibernation Fitr （2014/5/22） 4th Hibernation Fitr Full success （2015/4/16） (in six months) Demonstration of th 5 Hibernation Fiter guidance,navigation and （2016/1～2) plan） Minimum success control by solar sail. 6th Hibernation Fiter (in several weeks) Earth Flyby Demonstration of After Earth Flyby photon propulsion by （2016/11～12 plan） (2016/11～2017/8) solar sail. Power generation by thin film solar cells Launch (2010/5/21) Membrane deployment Fig. 1.1 Mission sequence Fig 3.1 Mission sequence. The world's深宇宙初のソーラ・セイル宇宙機 first solar sail spacecraft in the deep space. ☆展開した衛星の断面積は ☆The cross-sectional area of 183.93mexpanded 2spacecraft約14m× is14m の183.93m正方形2 The shape is square about 14m ×14m ☆衛星本体は直径☆Cylindrical spacecraft1.6m× 高 さbody0.8m isの円筒形、全部の重さ diameter 1.6m × height 0.8m,the total weight は310kg X band low gain is about 310kg antenna 1(XLGA1) Fig. 2.1 Overview of IKAROS Fig. 2.2 XLGA1 antenna position As a characteristic of IKAROS, rotational torque called the hibernation, it was necessary that a long-term prediction wind turbine effect occurred due to unbalance of solar orbital trajectory more than 10 months which considering the radiation pressure caused by unevenness of the large film. solar radiation pressure. Since this torque worked in the direction of gradually For that purpose, we are constructing an attitude dynamics decreasing the spin, nominal operation phase from launch to model 3) to predict attitude in the future, making it possible to Venus swing-by had to spin up by thruster periodically. create a future trajectory over several years. It was possible to maintain spin rate without consuming fuel due to changing direction of spin rate and rotational 3. Orbit determination for nominal phase torque by solar radiation pressure after reverse spin operation carried out. In the nominal phase, it was necessary to remove the spin The attitude of IKAROS is determined by the earth angle rate modulation and perform orbit determination. There was a using the amplitude of Doppler modulation by spin and the polarization bias due to the spin rate and it was necessary to sun angle by the sun sensor. The spin rate was known by consider it in the orbit determination. telemetry. Therefore, the earth angle is obtained using the The equation of Doppler bias due to polarization is shown amplitude magnitude. Fig 2.2 show position of X band Low in (1). Gain Antenna (XLGA). XLGA is located about 715 mm away 1 1 from the spin axis. This location makes Doppler modulation 푓푏푖푎푠 = 퐶 ( + ) 휔 (1) 푓푇 푓푅 and the Earth angle changes amplitude magnitude. The acceleration due to solar radiation pressure is about 100 m / sec in a half year. In search operation after wake up from 2 Table 3.1 shows the definition of variables. The estimated value of the solar radiation model was Table 3.1 Doppler bias due to polarization gradually changing in nominal phase. Fig. 3.2 shows the trend C: Speed of light(m/sec) of estimation value of solar radiation presser model. fT: transmit frequency(Hz) Solar radiation光学パラメータ推定値の推移 model estimation result fR: Receive frequency(Hz) GReflection（鏡面） coefficient D（Diffusion拡散） coefficient T（Transmittance透過） coefficient ω: Spin rate(round/sec) 参考EstimateGのみ推定Ref only 線形Linear(G（Ref鏡面）) 多項式2nd order(G（Ref鏡面）. ) 線形Linear(D（Dif拡散）. ) 多項式2nd order(D（Dif拡散）. ) 線形Linear(参考EstGのみ推定Ref only) fbias: Doppler bias due to polarization(m/sec) 1.5E+00 The solar radiation pressure model used is shown in Table 1.0E+00 3.2. A huge thin film of solar sail is thought to emit absorbed sunlight with almost no time delay. Therefore, a model 5.0E-01 considering the thermal radiation was needed. Fig 3.2 shows a 0.0E+00 Invisible Invisible period Invisible Invisible period conceptual view of the model considering the thermal 不 不 不 Invisible period 可 可 可 radiation. -5.0E-01 視 視 視 期 期 期 間 間 間 -1.0E+00 Sun 20106月1/06日/01 82010月31/08日/31 112010月30/11日/30 32011月1/日03/01 52011月31/05日/31 Γ Spin axis Fig. 3.2 The trend of estimation value of solar radiation Unit Vector Ｄ θ presser model. A（absorption） Unbalanced component of radiation Back side A×（Back F-Face F） The red line and the blue line are the trends when both Face side （２Γ COS(θ ）＋２／３ D）×COS(θ ） specular reflection and diffuse reflection parameters are （２Γ COS(θ ）＋２／３ D）×SIN(θ ） １－Γ －Ｔ＝Ａ＋Ｄ estimated at the same time. The purple line is the trend when Adsorption of diffusion Adsorption of absorption only reflection parameters estimated. The invisible period are 2/3 A（F2-F1)×SIN(θ ） Unbalanced component of radiation the earth angle became about 80 degrees or more. So in this ２Γ COS(θ ）＋２／３ D Specular reflection and diffuse reflection period, telemetry’s link became quite difficult.