Cis-Lunar Object Detection Using Earth-Orbiting Microsatellites

This paper presents a study on the detection of objects in the cis-lunar environment using Earth-orbiting microsatellites equipped with electro-optical sensors as observers located in low-Earth orbits (LEO) or geostationary orbits (GEO). Cis-lunar space domain awareness (SDA) is important for reasons that span from purely scientific interest to security and support of space programs. The rationale that motivates the interest in space-based space systems for surveillance and monitoring is what justifies the idea of carrying out cis-lunar object-detection duties using space-based observers on LEO and GEO, as the limitations that constraint on-Earth observers would not be relevant. Furthermore, orbits around the Earth are more accessible and manageable than more complex alternatives that might involve Lagrangian points of the Earth-Moon system. This work evaluates the ability of Earth-orbiting observers to detect targets in the cis-lunar environment. A series of assessments are performed. First, mission scenarios are generated using FreeFlyer by defining a set of observers and a target, enabling the assessments about the obstruction of the line of sight (LOS) and general geometrical constraints. Then, an assessment about the visible magnitude of the target is performed by relying on the well known Pogson formula, to introduce the dependency on the shape and the optical properties of the target, as well as to find the requirements in terms of ability to capture tan object brightness that a sensor has to meet. Then, the concept of exclusion angle is introduced in the study to allow an evaluation of the target brightness that account also for any technical constraint of the sensor. This way, also the importance of the presence of the Moon and the Earth luminosity is accounted for, which is crucial given the nature of the observers. The results allow to set a baseline for the requirements that must be met to complete in-space cis-lunar SDA tasks. Moreover, this study is to assess the effectiveness of LEO and GEO observers in supporting cis-lunar SSA activities.