Small-Body Postrendezvous Characterization via Slow Hyperbolic Flybys
Small-Body Postrendezvous Characterization via Slow Hyperbolic Flybys
复制标题
通过慢速双曲线飞越进行小天体交会后表征
DOI：
10.2514/1.53722
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发表时间：
2011
影响因子：
2.6
通讯作者：
D. Scheeres
中科院分区：
文献类型：
--
作者：
Yu Takahashi;D. Scheeres
DOI：10.2514/1.53722航天器到达小天体时最关键的任务是确定该天体的重力场强度。这项研究提出并通过一系列的缓慢飞越模拟这种初始特征，并分析如何快速的重力场可以估计和精度，它可以确定。本文提出了两个分析问题，这两个问题与该表征过程的设计有关，并可用于评估是否需要激光雷达测量。提出了一种新的操作过程，称为V测距，它可以消除激光雷达在初始表征阶段的需要。在此之后，重力场的表征是通过围绕三个小行星：丝川，Didymos和爱神星，代表了两个数量级的大小差异进行协方差分析。I.引言随着航天器交会任务的开展，人们对研究小天体系统（如小行星和彗星）的兴趣日益浓厚。到达小天体后，航天器最重要的任务之一是表征天体的环境，以确定天体的重力参数和重力场。这是航天器在接近物体时扰动的主要来源，缺乏对重力场的了解可能会推迟主要科学使命的开始。因此，以尽可能快的方式对身体进行初步表征并且对航天器的风险最小是有意义的。重力参数和重力场fabody的估计通常使用最小二乘滤波器，最常见的是批量平方根信息滤波器（SRIF），因为它的数值稳定性（1-3），假设与真实动态的偏差可以近似在航天器建模的非线性动态的线性范围内（4）。除重力项外，滤波器中的其他常用估计参数是航天器状态、物体自旋状态和导航机动。估计的参数可以是与时间相关的（如航天器位置和速度），也可以是与时间无关的（即，全球），如在更高程度和更高阶的重力场。正如后面将要说明的那样，提出了一种通过一系列相对较低的飞越来完成这种初步估算任务的方法。我们探讨了使用这种方法可能发生的表征水平，以及这种方法是否可以消除对某些使命类型的专用轨道阶段的需要。本课题采用解析和数值方法进行研究。为了明确起见，我们假设目标天体是一颗近地小行星，关于它的大小、形状、自旋状态和日心轨道的更多细节将在后面给出。本文由分析部分和数值部分组成，这两部分都将讨论小天体引力环境的估计。这里给出的结果结合了联合收割机以前的两篇会议论文（5，6）。论文的第一部分（分析）分析了在只有光学观测的双曲线飞越中执行精确方法来打破尺度不变性的有效性。这项分析的目的是确定携带激光或雷达测距仪以感知到小行星的距离的必要性，并将其替换为称为V测距的概念。Alonso等人（7）也讨论了一个类似的概念，即使用基于光学的导航来估计飞行和Valaseketal背景下的相对位置和姿态。（8）自主空中加油的应用。在此之后，我们provideV测距，这是一种新的方法来分析估计的重力参数确定的精度的基础上的几何形状和时间的航天器轨道周围的小行星的推导。具体地说，我们推导出解析表达式的小天体重力场和航天器的相对轨迹使用多普勒跟踪和光学导航的不确定性。传统的方法是利用入站和出站双曲线速度V1的大小相等并由双曲线转向角θ分开的特性来推导的。该方法将b1（撞击半径）、V1和双曲线速度Vflyby的变化作为函数。我们新的分析估计是基于飞越轨迹的测量飞行时间来推导出Δ的表达式。将这两个解析表达式与本文第二部分讨论的全最小二乘协方差进行比较，以确定实际控制全估计的效应。
DOI: 10.2514/1.53722 The most crucial task for a spacecraft upon arriving at a small body is to determine the strength of the body's gravity field. This research proposes and models this initial characterization via a series of slow flybys and analyzes how rapidly the gravity field can be estimated and the precision to which it can be determined. Two analytical issues areaddressedinthispaperthatarepertinenttothedesignofthischaracterizationprocessandcanbeusedtoevaluate whether thereis aneed for lidarmeasurements. A new operational procedure calledV rangingis proposed, which can eliminate the need for lidar during the initial characterization phase. Following this, the characterization of the gravity field is addressed by performing a covariance analysis around three asteroids: Itokawa, Didymos, and Eros, representing a two-order-of-magnitude difference in size. I. Introduction T HEREisanincreasinginterestinstudyingsmall-bodysystems, such as asteroids and comets, with spacecraft rendezvous missions. On arrival to a small body, one of the most important tasks is for the spacecraft to characterize the body's environment to determine the gravitational parameterand the gravity field of the body. This is the major source of spacecraft perturbation when in proximity to the body, and lack of knowledge of thegravity field can delay the start of the main scientific mission. Thus, it is of interest to carry out this initial characterization of the body in as rapid amanner as is feasible and with minimum risk to the spacecraft. Estimation of thegravitationalparameterandgravitational fieldofabodygenerally uses a least-squares filter, most commonly a batch square-root infor- mation filter (SRIF) due to its numerical stability (1-3), assuming that the deviation from the true dynamics can be approximated within the linear range of the modeled nonlinear dynamics of the spacecraft (4). In addition to the gravity terms, other commonly estimated parameters in the filter are the spacecraft state, body's spin state, and navigationV maneuvers. The estimated parameters can be time-dependent as in spacecraft position and velocity, or time- independent (i.e., global) as in the higher-degree and higher-order gravity field. As will be shown later, a method for carrying out this initial estimation task throughaseriesof relativelyslow flybys ofthe body is proposed. We probe the level of characterization that can occur using this approach, and whether such an approach could eliminate the need for a dedicated orbital phase for some mission types. This topic is studied using both analytic and numerical methods. For definiteness, we assume that the target body is a near- Earth asteroid, with additional details on its size, shape, spin state, and heliocentric orbit given later. This paper consists of an analytical section and a numerical section, bothof whichwill discussthe estimation ofthesmall body's gravitational environment. The results presented here combine two previous conference papers (5,6). The first (analytical) part of the paperanalyzestheeffectivenessofperformingaprecisemaneuverto break the scale invariance in a hyperbolic flyby with optical-only observations. The goal of this analysis is to characterize the need for carrying a laser or radar ranging instrument to sense distance to the asteroid, and replaces this with a concept calledV ranging. A similar concept using optical-based navigation is also discussed by Alonso et al. (7) to estimate the relative position and attitude in the contextofformation flyingandValaseketal.(8)fortheapplicationof autonomous air refueling. Following this, we provideV ranging, which is a derivation of a new method to analytically estimate the precision of the gravitational parameter determination based on the geometry and time of the spacecraft trajectory around an asteroid. Specifically, wederiveanalytical expressionsfor the uncertainty of a small-body gravity field and spacecraft relative trajectory using Doppler tracking and optical navigation. The conventional method derivesby leveraging the property that the inbound and outbound hyperbolicvelocitiesV1 areequalinmagnitudeandseparatedbythe hyperbolic turn angle� . This method rendersas a function ofb1 (impact radius),V1, and change in hyperbolic velocityVflyby. Our new analytical estimate is based on the measured time of flight of a flyby trajectory to derive an expression for� . These two analytical expressionsforarecomparedwiththefullleast-squarescovariance discussedinthesecondpartofthispaperinordertodeterminewhich effect actually controls the full estimation.