On-orbit Estimation of Optical Property by Precomputed Tensor Method for High-fidelity SRP Model
On-orbit Estimation of Optical Property by Precomputed Tensor Method for High-fidelity SRP Model
复制标题
高保真SRP模型预计算张量法光学特性在轨估计
DOI：
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发表时间：
2016
期刊：
影响因子：
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通讯作者：
Nakasuka
中科院分区：
文献类型：
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作者：
S. Ikari;Kakeru Tokunaga;Takahiro Ito;T. Inamori;R. Funase;Shinichi;Nakasuka
太阳辐射压是航天器在地球高空或行星际轨道运行时所受到的主要干扰力和力矩。为了计算准确的SRP，最近的研究人员提出了高保真多面体建模方法[1]。该方法可以计算准确的SRP，包括其他表面投射在表面上的阴影的影响。由于这些精确方法的计算成本太高而不能用于实际的天体动力学分析，通常，预先计算某些太阳矢量的SRP力或力矩，并且将力或力矩的数据集存储为数据表或扩展为与作为近似的某个函数对应的系数。虽然该表或近似系数可以用于在短的计算时间内计算准确的SRP，但是该方法对于更实际的使用仍然存在几个问题。问题之一是，该方法不能用于估计每个表面的光学性质，这是SRP计算中最不确定的参数，因为建模方法不分离几何信息和光学性质。估计方法是修正包含不确定性的数值模型以适应在轨结果的关键技术。传统的方法可以通过修正近似系数来拟合在轨结果。然而，这些系数不适合于估计，因为它们没有任何约束（例如，系数的数量及其值的限制）。已经讨论了一些光学性质估计方法，但是这些方法集中于低保真度几何模型并且不考虑阴影效应[2]。为了构造一个能够估计光学性质的高保真SRP模型，作者提出了预计算张量方法[3]。所提出的方法预先计算和近似的能见度功能，而不是总SRP力或扭矩作用在航天器上的每个表面。可见性函数是单位球面上的二元函数，表示来自某个太阳向量的光线是否能到达曲面。可见度函数的近似系数被处理为张量，并且可以仅从几何信息获得的预先计算的张量被计算。利用预先计算的张量，可以将SRP力和力矩方程表示为张量形式的方程。该方法利用预先计算的张量，将几何信息和光学性质完全分离。因此，该方法可用于高保真SRP模型的光学性质估计。在这项研究中，所提出的方法被应用到一个实际的在轨航天器的分析验证的方法的效果。分析了作者开发并于2014年12月发射的50公斤级行星际微型航天器PROCYON的飞行数据。在PROCYON使命中，在轨道上测量了许多太阳矢量的SRP扭矩，用于SRP建模研究，并且测量的SRP扭矩用于验证和所提出的方法的光学性质估计。该方法的预计算张量是使用新开发的张量计算工具从PROCYON项目的真实的CAD数据中计算出来的。对PROCYON所用材料的光学性质进行了地面测量，并与估算值进行了比较。本文介绍了预计算张量的计算过程、光学性质的估算方法以及利用PROCYON卫星数据进行在轨估算的结果。将估算结果与地面实测值进行了比较，揭示了所提方法的有效性，并指出了进一步提高轨道扰动建模精度应注意的问题。
Solar Radiation Pressure (SRP) is a major disturbance force and torque for spacecraft in the high altitude earth or in the interplanetary orbits. In order to calculate accurate SRP, high-fidelity polyhedron modelling methods have been proposed by recent researchers [1]. The methods can calculate accurate SRP including effects of shadows on the surfaces casted by other surfaces. Since the calculation cost of these accurate methods is too high to be used in a practical astrodynamics analysis, usually, SRP forces or torques of certain sun vectors are precomputed, and the data set of the forces or torques is stored as a data table or is expanded to coefficients corresponding to a certain function as an approximation. Although the table or the approximated coefficients can be used to compute accurate SRP in a short computation time, the methods still have several issues for more practical usage. One of the issues is that the methods cannot be used to estimate optical properties of each surface which are most uncertain parameters in a SRP calculation, because the modelling methods do not separate geometrical information and optical properties. The estimation method is a key technology to correct numerical models including uncertainties to suit on-orbit results. The conventional methods can correct the approximated coefficients to fit on-orbit results. However, the coefficients are not suitable for the estimation because they do not have any constraints (e.g., the number of coefficients and the limitation of their value). Some optical property estimation methods have been discussed, but these methods focus on low-fidelity geometrical models and do not consider the shadow effect [2]. In order to construct a high-fidelity SRP model, which can estimate optical properties, authors have proposed the precomputed tensor method [3]. The proposed method precomputes and approximates the visibility functions of each surface instead of total SRP force or torque acting on spacecraft. The visibility function is a binary function on the unit sphere and represents whether a ray from a certain sun vector can reach to the surface or not. The approximated coefficients for the visibility functions are handled as tensors, and precomputed tensors which can be obtained from only geometrical information are calculated. The SRP force and torque equations can be expressed as tensor form equations by using the precomputed tensors. The proposed method completely separates the geometrical information and optical properties by using the precomputed tensors. Thus the method can be used for an optical property estimation of high-fidelity SRP models. In this study, the proposed method is applied to an actual on-orbit spacecraft analysis for verification of the effect of the method. Flight data of PROCYON, which is a 50-kg class interplanetary micro-spacecraft developed by authors and launched in Dec. 2014, is analysed. In the PROCYON mission, SRP torques at many sun vectors were measured on orbit for SRP modelling studies, and the measured SRP torques are used for verification and the optical property estimation of the proposed method. The precomputed tensors for the proposed method are calculated from the real CAD data of the PROCYON project by using the newly developed tensor calculation tool. The optical properties of material used in PROCYON are also measured on ground to compare with the estimated values. This paper introduces a process of the precomputed tensor calculation, a method for the optical property estimation, and the result of the on-orbit estimation by using the PROCYON data. The estimated results are compared with on-ground measured value, and the comparison reveals the effect of the proposed method and some issues for more accurate orbital disturbance modelling.
影响因子：
2.6
作者：
Rodriguez-Solano, C. J.;Hugentobler, U.;Steigenberger, P.
通讯作者：
Steigenberger, P.