The deployment of megaconstellations in low Earth orbit (LEO) poses significant collision risks with space debris. This paper focuses on analyzing the short-term and long-term collision probabilities of megaconstellations to assess their collision risk. Firstly, a short-term collision risk evolution model is developed to accurately address rendezvous collisions. Secondly, a long-term collision risk evolution model is established by considering space object density, space debris attenuation, space target disintegration, and the distribution of disintegration targets. Through simulations conducted on the Starlink Phase I constellation, the results demonstrate a 30–40% increase in short-term collision probability within the constellation shell, a 70.2% probability of at least one collision during the constellation’s lifetime, and a 25.3% increase in secondary collisions following a collision event. This study provides a reference and application for analyzing the orbital safety of LEO megaconstellations and for promoting the sustainable development and utilization of space resources.

With the increase in satellites in the medium Earth orbit (MEO) region, there should be a focus on orbit safety in the MEO region. A safe orbit disposal strategy is necessary to maintain the sustainability of the MEO region. This paper focuses on long-term evolution modeling, safety analysis of MEO objects, and different disposal techniques for end-of-life BDS-2 MEO satellites. On the one hand, a long-term numerical evolution model is established, and mean equinoctial elements are adopted to propagate a long-term orbit. Long-term evolution for the MEO region over 100 years is carried out, including the Galileo, BDS, GPS, and GLONASS constellations. The earliest orbit intersection time with other global navigation satellite system (GNSS) constellations is put forward. On the other hand, a dynamic model and an optimization model for disposal orbit are established, which minimize the eccentricity growth within 200 years and the fuel consumption for maneuvering to the disposal orbit. The bounds for the disposal region of BDS MEO satellites are also proposed, which consider the measurement and control error of BDS MEO satellites and the eccentricity bounds for end-of-life BDS MEO satellites. A genetic algorithm is adopted to optimize the orbital elements for end-of-life BDS MEO satellites. In addition, two disposal cases, namely, upraising and reducing the orbit, for end-of-life BDS MEO satellites are simulated. The long-term evolutions for the disposal of orbital elements within 200 years are implemented, and the fuel consumption is calculated. The results show that the current MEO region is relatively safe and that the eccentricity is the most important factor that influences the long-term evolution of safety analysis for BDS MEO disposal orbits. Upraising the orbit is safe for end-of-life BDS MEO satellites. This investigation provides the theoretical foundation for investigating the long-term evolutionary mechanisms of the MEO region and references disposal strategy analysis for decommissioned navigation satellites, and the spent upper stages for other GNSS constellations.

The LEO megaconstellations have thousands of satellites, which operate on similar orbital heights. Because of increasing space debris, the satellites accelerate the growth of the number of space objects, increase the threat to their own safety and sustainable utilization of the space environment. This paper focuses on short-term collision probability and long-term collision probability calculation model for collision risk of mega constellations. On the one hand, aiming at how to solve the problem quickly and accurately for rendezvous collisions, a short-term collision risk evolution calculation model of LEO mega-constellation is established. By investigating the space collision target screening methods of large-scale satellites against large-scale space debris, including apogee–perigee filtering, time window filtering, space discrete volume element filtering and relative position filtering, the filtered target trajectory is fitted by Lagrange interpolation method to obtain the motion state at the closest time. Then, the collision probability calculation method of Laplace transform is used to calculate the collision probability of the target at the closest time. On the other hand, the long-term collision risk evolution model of LEO Mega constellation is established. By simplifying the model of debris and collision, we explore the calculation method of space object density, space debris attenuation model, space target disintegration model and the distribution of disintegration targets are studied. According to the way of space debris’ generation and extinction to calculate the change of space density. The collision probability between the satellite and space debris and space debris are calculated by using the calculation method of collision probability of particle-in-a-box (PIB). Finally, through the simulation of Starlink phase I constellation, results show that after the deployment of the Starlink constellation, the probability of a short-term collision in the constellation shell increases by 30–40%, the probability of at least one collision in the constellation lifetime is 70.2%, and the probability of a secondary collision increases by 25.3% after a collision. This study provides a theoretical reference for analyzing the orbital safety of the LEO mega-constellation, and provides a reference for the safe operation of spacecraft on-orbit and the sustainable development and utilization of space resources.