Conjunction assessment of space objects in Low Earth Orbit (LEO) generally uses information collected by ground-based space surveillance sensors. These sensors track both the primary object (normally an active satellite) and the secondary object (typically space debris). The tracking data is used to update both objects’ orbits for collision risk assessment. The primary satellite’s involvement in this process is that of a satellite in jeopardy - the primary satellite does not usually contribute tracking data on the secondary as they are typically unequipped to do so. In this paper, an examination how an at-risk LEO primary satellite could obtain optical tracking data on a secondary object prior to the Time of Closest Approach (TCA) and assess its own collision risk without the need for additional ground-based space surveillance data is performed. This analysis was made possible by using in-situ optical measurements of space objects conjuncting with the Canadian NEOSSat Space Situational Awareness R&D microsatellite. By taking advantage of the near “constant-bearing, decreasing range” observing geometry formed during a LEO conjunction, NEOSSat can collect astrometric and photometric measurements of the secondary object in the time prior to TCA, or in the multiple half-orbits preceding TCA. This paper begins by describing the in-situ phenomenology of optically observed conjunctions in terms of the observing approach, geometry and detected astrometric and photometric characteristics. It was found that conjuncting objects are detectable to magnitude 16 and astrometric observations can be used for position covariances in the computation of probability of collision. Illustrative examples are provided. In orbits prior to TCA, in-track positioning error is improved by a factor of two or more by processing space-based observations on a filtered position estimate of the secondary. However, cross-track positioning knowledge is negligibly improved due to the inherent astrometric measurement precision of the NEOSSat sensor and the oblique observing geometry during conjunction observations. A short analysis of object detectability where star trackers could be used to perform similar observations finds that larger payload-sized objects would generally be detectable. However, smaller debris objects would require higher sensitivity from the star tracker if employed for optical conjunction derisk observations.

低地球轨道（LEO）中的空间物体的联合评估通常使用地面空间监视传感器收集的信息。这些传感器同时跟踪主要物体（通常是活动的卫星）和次要物体物体（通常是空间碎片）。跟踪数据用于更新两个物体的轨道，以进行碰撞风险评估。主要卫星参与此过程的过程是处于危险中的卫星-主要卫星通常不提供辅助数据的跟踪数据，因为通常它们没有装备。在本文中，研究了处于危险中的LEO主卫星如何在最接近进场时间（TCA）之前获取次要物体上的光学跟踪数据并评估自身的碰撞风险，而无需其他地面空间监视数据被执行。通过使用与加拿大NEOSSat空间态势感知R＆D微卫星相结合的空间物体的原位光学测量，可以进行此分析。通过利用近乎“恒定轴承”的优势，NEOSSat可以观察到在LEO结合过程中形成的几何形状，可以在TCA之前的时间内或在TCA之前的多个半轨道中收集次要物体的天文测量和光度测量。本文从观察方法，几何形状以及检测到的天文和光度学特征入手，描述了光学观察到的连接的原位现象。结果发现，相交物体的大小可检测到16级，天体观测值可用于碰撞概率计算中的位置协方差。提供了说明性示例。在TCA之前的轨道上，通过对次级物体的滤波位置估计进行基于空间的观测，可以将轨道内定位误差提高两倍或更多。然而，由于NEOSSat传感器固有的天文测量精度以及联合观测期间的倾斜观测几何形状，跨轨定位知识的提高可忽略不计。一项对物体可检测性的简短分析（其中可以使用星跟踪器执行类似的观察）发现，通常可以检测到更大的有效载荷大小的物体。但是，如果将较小的碎屑物用于光学结合面观测，则将需要来自恒星跟踪仪的更高灵敏度。一项对物体可检测性的简短分析（其中可以使用星跟踪器执行类似的观察）发现，通常可以检测到更大的有效载荷大小的物体。但是，如果将较小的碎屑物体用于光学结合面观测，则将需要来自恒星跟踪仪的更高灵敏度。一项对物体可检测性的简短分析（其中可以使用星跟踪器执行类似的观察）发现，通常可以检测到更大的有效载荷大小的物体。但是，如果将较小的碎屑物用于光学结合面观测，则将需要来自恒星跟踪仪的更高灵敏度。