Within the domain of Space Situational Awareness (SSA), tracklet association is a critical step for accurate orbit determination. Conventional approaches typically assume perfectly calibrated observations, thereby neglecting the interdependence between tracklet association and spatial calibration. For space-based optical sensors, spatial deviations induced by spacecraft attitude errors further exacerbate this challenge. Incorrect associations lead to inaccurate calibration, and vice versa, forming a vicious cycle that degrades orbit tracking accuracy and undermines SSA reliability. To overcome these challenges, this paper proposes a joint tracklet association and spatial calibration approach for space-based optical observations. By integrating both processes into a unified optimization framework with iterative feedback, the proposed method enables accurate association and calibration simultaneously. Simulation results verify its effectiveness and demonstrate its potential to enhance the accuracy, robustness, and safety of space object tracking.

The rapid development of Low Earth Orbit (LEO) mega constellations has significantly contributed to several aspects of human scientific progress, such as communication, navigation, and remote sensing. However, unrestrained deployment of constellations has also strained orbital resources and increased spacecraft congestion in LEO, which seriously affects the safety of in-orbit operations of many space assets. For the long-term and sustainable development of space activities in LEO regions, space environment stability must be maintained using more rational surveillance and governance mechanisms. This review contributes to the research gap and facilitates the development of LEO mega constellations. First, the current development of typical LEO mega constellations is reviewed, followed by the analysis of the impact of LEO mega constellations in terms of astronomical observation, spacecraft safety in orbit, and space environment evolution. Then, two main solutions to conduct the challenges raised by LEO mage constellations are elaborated: one is to ensure the safety operation of spacecraft using space surveillance infrastructures and space situational awareness technologies, and the other is to accelerate the deorbit of constellation satellites at the end of life based on postmission disposal and active removal methods. Finally, the future development and potential research directions of LEO mega constellations are prospected.

This paper presents a tool for the numerical propagation of high-fidelity astrodynamics, called PHiFA. The coupled orbit-attitude dynamics for space objects are modeled by considering various types of perturbative forces and torques. Two methods have been implemented to calculate the surface forces: the area matrix method and the beam method. The beam method is more precise as it discretizes the source media (e.g., sunlight and aerodynamic wind) and the surface of the target into multiple rays and finite elements, respectively, and then accumulates the effect of each hit. The PHiFA tool was tested and validated using a 3U CubeSat model and the defunct European environment satellite (Envisat) model.