Andrea D’Ambrosio, Massachusetts Institute of Technology; Miles Lifson, Massachusetts Institute of Technology; Daniel Jang, Massachusetts Institute of Technology; Celina Pasiecznik, Massachusetts Institute of Technology; Richard Linares, Massachusetts Institute of Technology
Keywords: Space Sustainability, Evolutionary Modeling, Orbital Capacity, Constellations, Low Earth Orbit
Abstract:
The increasing number of satellites planned for launch into LEO over the next few years has major potential impacts for the sustainability of the space environment. This paper seeks to address and estimate this orbital capacity, through a two phase approach. First, large constellations are modeled and, where possible, deconflicted to ensure orbital separation. Second, the estimated trends for the LEO orbital population are estimated via a multi-species multi-shells evolutionary source-sink model.
In the first phase, large constellations are modeled for potential altitude overlaps. ITU filings, as well as detailed public technical disclosures, are collated to craft an estimate for future LEO constellation demand. In particular, this set of constellations is evaluated for potential overlaps in orbital altitude based on various assumptions including the stated altitude ranges as proposed in the regulatory filings, ranges based on uncontrolled eccentricity vectors and resulting osculating variation about the constellations given nominal altitude, and ranges based on orbits with frozen eccentricity vectors and minor adjustments to nominal altitude to preserve orbital separation where feasible.
In the second phase, the long-term impact of this analysis on the LEO orbital capacity is studied by means of a source sink evolutionary model, where results from slotting and intrinsic capacity analysis are included. This is a multi-species multi-shells model, where the LEO region is divided into many orbital altitude shells and different objects categories are considered in each shell, such as active slotted satellites, unslotted satellites, derelict satellites, and debris. Fragmentation events and interactions among the species, such as collisions, are included in the model and several fluxes of incoming and outgoing objects are evaluated for each shell. For example, the atmospheric drag flux is taken into account since it causes the satellites to decay and acts as the only natural sink in the model.
The proposed source-sink model is employed to perform long-term simulations to evaluate potential future trends in LEO due to proposed mega constellations and fragmentation events, and the impact of enforcing orbital separation between shells. A preliminary estimation is provided for overall LEO orbital capacity, while fulfilling constraints related to a sustainable use of the space environment, computed in terms of growth of the space debris population, as well as the intrinsic orbital capacity, which estimates the maximum number of slotted satellites that can fit into an orbital altitude shell and the number of shells per altitude bin. To do so, an optimization approach, based on metaheuristic algorithms such as the Particle Swarm Optimization, is used with the launch rate of active satellites being the optimization variables. Thus, the propagation of the source-sink model is carried out within the optimization procedure to study the evolution of the space environment over a time span of about 200 years. The cost function is then computed considering the maximization of the number of satellites that can fit in LEO and the penalty terms due to the constraints. The obtained solution for LEO overall capacity is then compared and tested against the future capacity demands.
Moreover, some sensitivity analyses are performed varying the probability of success of the post-mission disposal and the collision avoidance efficacy coefficient. The benefits of slotting satellites are assessed.
Date of Conference: September 27-20, 2022
Track: Space Debris