Hayabusa2 is the ongoing JAXA’s sample and return mission to the asteroid Ryugu. In late 2018, Ryugu was in superior solar conjunction with the Earth. It is the first time that a spacecraft experiences the blackouts in the communication link with the Earth while hovering around a small celestial body. In this article, the design of the nominal conjunction trajectory flown by the Hayabusa2’s spacecraft is presented. The requirements for the conjunction trajectory were (1) to guarantee a low fuel consumption, (2) to ensure the visibility of the asteroid by the spacecraft’s wide angle camera ( $60^{\circ }$ FoV), and (3) to increase the spacecraft altitude to a safety location ( $\sim109~\mbox{km}$ ) from the nominal BOX-A operation of 20 km (Home Position - HP). Finally, (4) to return at BOX-A after the conjunction phase. Given the mission constraints, the designed conjunction trajectory appears to have a fish-shape in the Hill coordinates therefore we renamed it as “ayu” (sweetfish in Japanese) trajectory. The optNEAR tool was developed for the guidance ( $\Delta V\mbox{s}$ planning) and navigation design of the Hayabusa2’s conjunction mission phase. A preliminary sensitivity analysis in the Hill reference frame proved that the ayu trajectory is a good candidate for the conjunction operation of hovering satellite. The solution in the Hill coordinates is refined in the full-body planetary dynamics (optNEAR Tool) before flight. The ayu conjunction trajectory requires (a) two deterministic $\Delta V\mbox{s}$ at the Conjunction Orbit Insertion (COI) point and at the Home-position Recovery Maneuver (HRM) point respectively. (b) Two stochastic $\Delta V\mbox{s}$ , known as Trajectory Correction Manoeuvres (TCMs), before and after the deep conjunction phase are also required. The constraint linear covariance analysis in the full-body dynamics is here derived and used for the preliminary guidance and navigation planning. The results of the covariance analysis were validated in a nonlinear sense with a Monte Carlo approach which proved the validity of the semi-analytic method for the stochastic $\Delta V\mbox{s}$ planning derived in this paper.

中文翻译：

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Hayabusa2 的卓越太阳能合相

Hayabusa2 是正在进行的 JAXA 样本和返回小行星 Ryugu 的任务。2018 年末，龙宫与地球处于优越的太阳合相。这是航天器第一次在一个小天体周围盘旋时，与地球的通信链路中断。在本文中，介绍了隼鸟2号飞船的名义会合轨迹设计。对交会轨迹的要求是（1）保证低燃料消耗，（2）保证航天器广角相机对小行星的可见度（$60^{\circ}$FoV），以及（3）增加从标称 BOX-A 操作 20 公里（原位 - HP）到安全位置（$\sim109~\mbox{km}$）的航天器高度。最后，（4）在合相阶段后返回 BOX-A。鉴于任务限制，设计的结合轨迹在希尔坐标中似乎具有鱼形，因此我们将其重命名为“ayu”（日语中的香鱼）轨迹。optNEAR 工具是为隼鸟 2 号连接任务阶段的指导（$\Delta V\mbox{s}$ 规划）和导航设计而开发的。Hill参考系中的初步敏感性分析证明ayu轨迹是悬停卫星会合操作的良好候选。希尔坐标中的解决方案在飞行前在全身行星动力学（optNEAR 工具）中进行了改进。ayu 会合轨迹需要 (a) 两个确定性的 $\Delta V\mbox{s}$ 分别位于连接轨道插入 (COI) 点和原位恢复机动 (HRM) 点。(b) 两个随机 $\Delta V\mbox{s}$ ，也需要在深度结合阶段之前和之后进行轨迹校正机动 (TCM)。这里推导出全身动力学中的约束线性协方差分析，用于初步制导和导航规划。协方差分析的结果用蒙特卡罗方法在非线性意义上进行了验证，证明了本文推导的随机$\Delta V\mbox{s}$规划的半解析方法的有效性。