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Precise Threedimensional Positioning of Spacecrafts by Multifrequency VLBI and Doppler Measurementys
https://ir.soken.ac.jp/records/407
https://ir.soken.ac.jp/records/40775f9556173f44434ac3d00376f89e9a1
名前 / ファイル  ライセンス  アクション 

要旨・審査要旨 / Abstract, Screening Result (338.5 kB)


本文 (3.9 MB)

Item type  学位論文 / Thesis or Dissertation(1)  

公開日  20100222  
タイトル  
タイトル  Precise Threedimensional Positioning of Spacecrafts by Multifrequency VLBI and Doppler Measurementys  
タイトル  
タイトル  Precise Threedimensional Positioning of Spacecrafts by Multifrequency VLBI and Doppler Measurementys  
言語  en  
言語  
言語  eng  
資源タイプ  
資源タイプ識別子  http://purl.org/coar/resource_type/c_46ec  
資源タイプ  thesis  
著者名 
河野, 裕介
× 河野, 裕介 

フリガナ 
コウノ, ユウスケ
× コウノ, ユウスケ 

著者 
KONO, Yusuke
× KONO, Yusuke 

学位授与機関  
学位授与機関名  総合研究大学院大学  
学位名  
学位名  博士（理学）  
学位記番号  
内容記述タイプ  Other  
内容記述  総研大甲第586号  
研究科  
値  数物科学研究科  
専攻  
値  09 天文科学専攻  
学位授与年月日  
学位授与年月日  20020322  
学位授与年度  
値  2001  
要旨  
内容記述タイプ  Other  
内容記述  The study on orbital motion and the interior structure of the Moon and planets is one of the methods to approach for the revolution as a dynamical system and the origin of the solar system. It is a powerful method to measure the gravity fields obtained by the orbital motion of a spacecraft in order to estimate the inner layer and the density structure of the Moon and the planets. Orbits or positions of a lunar or planetary spacecraft have mainly been determined by range and Doppler measurements. These measurements provide only onedimensional information about the position along the line of sight. On the other hand, differential VLBI (Verv Long Baseline Interferometry) has the sensitivity of positioning in direction perpendicular to the line of sight, so that combining both range and Doppler measurements with differential VLBI enables us to measure threedimensional position of a spacecraft. The research in this thesis is to develop a new threedimensional positioning technique to determine the position and the motion of a spacecraft and to estimate the gravity fields and interior of the Moon or planets. In order to attain this purpose, a new differential VLBI, "Multifrequency VLBI" is proposed, and the developments of its system and software for the estimation of phase delay are described. In addition to the VLBI method, effects caused by an antenna phase pattern and a spin on Doppler measurements are also described, and the correction method of this effect is proposed to improve the Doppler measurement accuracy. VLBI methods have been used for positioning of spacecrafts since 1960's. In these methods, carrier waves were transmitted from a spacecraft because of saving its transmitting power and obtaining hish SNR. Unfortunately, the phase delay of a carrier wave, however, has cycle ambiguities, therefore only phase delay rate has been mainly used so far. If plural carrier waves at different frequencies are transmitted from a spacecraft, the group delay among the plural carrier waves enables us to resolve the cycle ambiguity of the phase delay. There is one example which used two carrier waves. 6.5MHz apart transmitted from the spacecraft of the Venus. A group delay between the two frequencies was successfully determined without the ambiguity, in other words, bandwidth synthesis of only two frequencies was first conducted in this experiment. The accuracy of positioning reached 10 km for about 1 AU distance. In addition, the ionospheric effect could not be corrected because the two carrier waves were in the same frequency band. We propose a new VLBI method, "Multifrequency VLBI". The system transmits three frequency signals in Sband and one signal in Xband. These frequencies are set to resolve the cycle ambiguity from a lot of group delays and to correct the ionospheric effect. In this system, the phase delay of RF signals at S and Xband can be estimated, so that the accuracy of positioning can be drastically improved by a factor of 1300 (8.4GHz/6.5 MHz). In order to realize this VLBI method, we developed a ground VLBI system, software to estimate phase delays and an irnterface with the software of gravity fields and orbits estimation. This software has the distinctive features as follows. It can estimate the current frequency from the predicted orbital motion and calculates the phase delay from the phase difference at the frequency. This performance allows us to utilize the oscillator for general use, such as a crystal oscillator, as a frequency reference onboard a spacecraft. We carried out VLBI experiments of NASA's spacecraft, Lunar Prospector (LP), as a preliminary test of the whole system. Unfortunately, LP transmitted only one frequency signal, so that we could not correct the phase variations with period longer than several tens seconds due to the ionosphere, troposphere, discrepancy of the lunar gravity model and so on. As a result of this experiment, residual phases from predicted ones are within ±2π, and the Root MeanSquare (RMS) of the residual for the period of several seconds is about 4 degrees. The RMS residual for the several seconds, however, means that we can determine the position of LP within the accuracy of 1.5m around the Moon if we can correct the variations with long period by using the Multifrequency VLBI. In the study of the Doppler measurements, we pointed out seven error sources that are the ionosphere, the troposphere, spin of the spacecraft, a phase pattern of an antenna, attitude of spacecraft, instability of a transponder and instability of a frequency standard. In particular, the effects caused by spin of a spacecraft and phase pattern of an antenna have not been discussed so far. We pointed out that the spin and the phase pattern of the antenna considerably affect the Doppler measurements and these effects must be removed from observed Doppler frequency data for a precise gravity determination. For this research, we analyzed a Doppler data of spin stabilized satellite, "Nozomi" and detected their effects of the spin and the phase pattern of the antenna for the first time. Furthermore, we developed a new method to remove this effect, and confirmed the validity of the method by applying the method to Doppler data of "Nozomi" All the Multifrequency VLBI and corrected Doppler frequency data can be combined as observables in the orbit and the lunar gravity estimation software of "GEODYNII", and analyzed for threedimensional positioning of a spacecraft. Because the VLBI system uses narrow bandwidth signals and the amount of the data is much less than those in conventional one, the system has a potential of real time VLBI through the INTERNET. This means that the system can be widely used in real time positioning of various spacecrafts, for instance a module landing on the Moon and the "Nozomi" in a transfer orbit to the Mars. 

所蔵  
値  有  
フォーマット  
内容記述タイプ  Other  
内容記述  application/pdf  
著者版フラグ  
出版タイプ  AM  
出版タイプResource  http://purl.org/coar/version/c_ab4af688f83e57aa 