| 摘要 | 空间碎片作为地球轨道上的无功能人造物体，其被动运动的特点使得人们难以得到其准确的轨道和姿态信息，从而增加了正常工作航天器的碰撞风险，特别是失效卫星、火箭末级这类大型空间碎片。目前主要根据地基观测来确定空间碎片的轨道,光度观测是地基观测空间目标的主要观测手段之一，利用空间目标的光度信息能够估计空间目标的相关特征信息。国内外针对目标光度数据使用各种方法来反演空间目标特性，包括极值点法、基于光变曲线周期的方法、非线性滤波法等。为了确定火箭末级的旋转状态，本文建立了关于火箭末级的光度模型并根据光度模型得到模型光变曲线，比对实测光变曲线和模型光变曲线确定火箭末级的旋转参数。本文以猎鹰九号火箭末级(NORAD ID:42968)作为研究对象，首先获取目标的轨道信息，选择在观测时段内过境的猎鹰九号火箭末级目标。本文利用云南天文台1.2米光学望远镜及配套控制系统获取猎鹰九号火箭末级的光度图像，再对获取到的目标图像进行平场本底处理、流量定标、异常点处理和斜距归一化等处理得到观测目标的视星等，并分析目标视星等随时间变化的归一化光变曲线。结合猎鹰九号的形状参数和轨道参数，根据目标的轨道确定测站-目标-太阳的几何关系，利用太阳辐射理论建立目标光度模型，目标简化为中空圆柱刚体，将目标的形状拆分为几个简单的几何体并单独计算这些几何体的光照有效面积。由目标惯性坐标系及本体坐标系之间的关系确定描述目标旋转状态的参数并针对这些参数进行分析。根据简化的火箭末级结构和旋转刚体的特性确定了火箭末级会绕最大转动惯量轴旋转，并确定了目标的最大转动惯量轴为圆柱体横向轴；基于相位离散最小化方法分析目标实测光变曲线的光变周期得到目标的旋转周期；使用最小二乘法分析模型光变曲线与实测光变曲线的关系，遍历参数来确定目标的旋转初相位和旋转轴指向。本文得到了42968目标三天观测时段内的旋转参数(旋转轴指向：赤经λ°，余纬θ°，旋转周期Ts)：2019年12月13日(32,64,249.5)、(212,116,249.5);2019年12月14日(34,83,247.4)、(254,156,247.4)；2019年12月15日(40,59,248.4)、(218,102,248.4),将得到的旋转参数代入到光度模型中与实测数据比对，比对结果表明二者的变化趋势吻合的很好。14日旋转参数与另外两天旋转参数存在显著差异，观测几何有明显不同应该是其主要原因，有待进一步分析。最后分析圆柱体有效面积随时间变化的趋势来解释目标的旋转过程。本文根据猎鹰九号火箭末级光度图像研究其旋转状态并确定了其旋转参数，为后续开展其他空间目标的姿态研究提供参考。 |
| 其他摘要 | Space debris is a kind of non-functional man-made object in earth orbit.The characteristic of it's passive movement makes it difficult to get it's accurate orbit and attitude information,thereby increasing the collision risk of normal working spacecrafts,especially for large space debris such as defunct satellites and rocket upper stages.At present, the approximate orbits of space debris is mainly determined based on ground-based observations.Photometric observation is one of the main methods of ground-based observation of space object,the photometric information of the space object can be used to estimate the space object's relevant characteristic informations.Various methods are used to estimate the characteristics of space object using its photometric data,including extreme point method,method based on light curve period and nonlinear filtering method etc.In order to determine the rotation state of the rocket upper stage,in this paper, the photometric model of the rocket upper stage is established and then the model light curve is calculated.The rotation parameters of the rocket upper stage are estimated by comparing the measured light curve with the model light curve. The Falcon 9 rocket upper stage is selected as the research object.First it is necessary to get the object's orbit informations,the Falcon 9 rocket upper stages that transited during the observation period are selected.The 1.2-meter optical telescope and supporting control system of the Yunnan Observatory is used to obtain photometric images of the Falcon 9 rocket upper stage.Then the acquired object image are processed including flat and bias processing、flux calibration、outlier handling and distance normalization,the normalized light curves are analyzed.Then 42968 object is selected as the research object according to the change trend of the light curve.The shape parameters and orbit parameters of the object are obtained by searching the relevant data of Falcon 9.The distance is calculated according to the object's orbit and the object's photometric model is established based on the geometric relationship of observation-object-sun and solar radiation theory.the object is simplified as a hollow cylindrical rigid body,the shape of the object is splited into a few simple geometries and the effective lighting areaof these geometries is calculated separately.According to the relationship between the object inertial coordinate system and the body coordinate system, the parameters is calculated to describe the target rotation state.According to the simplified structure of the rocket upper stage and the characteristics of the rotating rigid body, it is determined that the rocket upper stage should rotate around the axis of maximum inertia and the axis of maximum inertia of the object is the transverse axis of the cylinder.Using the phase dispersion minimization method, the period of the measured light curve is analyzed to obtain the rotation period of the object;using the least square method,the relationship between the model light curve and the measured light curve is analyzed,and the initial phase of rotation and the direction of the rotation axis is determined through traversing the parameters.The rotation parameters of the 42968 target during the three-day observation are obtained(direction of the rotation axis:right ascension:λ°,colatitude:θ°,rotation period:Ts)2019.12.13(32,64,249.5)、(212,116,249.5);2019.12.14(34,83,247.4)、(254,156,247.4)；2019.12.15(40,59,248.4)、(218,102,248.4).Substituting the obtained rotation parameters into the photometric model and comparing with the measured data,the results show that the trends of the two agree well.There is a significant difference between the rotation parameters in 20191214 and the rotation parameters of the other two days,obviously different observation geometry should be the main reason,and need further analysis.Finally, the trend of the effective area of the cylinder with time is analyzed to explain the rotation process of the object.In this paper, based on the photometric images of the Falcon 9 rocket upper stage, its rotation state is studied and its rotation parameters are determined,providing a reference for the follow-up attitude research of other space objects |
修改评论