Mark A. Sturza, Viasat, Inc.; Mark D. Dankberg, Viasat, Inc.; William N. Blount, Viasat, Inc.
Keywords: Sustainable Space, Debris, Holistic, Modeling, Policy, Collision Risk
Abstract:
In 2018, the United States (US) Federal Communications Commission (FCC) proposed a rulemaking on Orbital Debris Mitigation (ODM) which plainly addresses risks in the New Space Age posed by debris objects in low-Earth orbit (LEO). That rulemaking notes that LEO is a finite resource and rivalrous (a zero-sum game), yet available to all, incentivizing a tragedy of the commons, and risking global loss of access to space for decades or even centuries.
At the start of 2022, there were around 6,000 satellites in LEO, with an approximate aggregate mass of 2,200 metric tons and cross-sectional area of 37,000 square meters. In 2021 alone, the International Telecommunication Union (ITU) received filings for more than 1 million additional LEO satellites. Even if only a fraction satellites are deployed, the result will be more than an order of magnitude increase in number of satellites, aggregate mass, and aggregate cross-sectional area in LEO.
Once satellites are in orbit, they are at risk of being fragmented by collisions with debris. The accumulation of debris in Earths orbits is one of the most pressing threats to the safety and sustainability of space exploitation. The main cost and risk of collisions with debris is the generation of further debris, ultimately leading to the so-called Kessler syndrome of cascading, self-generating collisions. This ecological tipping point may render certain orbits unusable. The potentially significant growth of lethal trackable (LT) and lethal non-trackable (LNT) debris has prompted rough estimates of when regions of LEO space may become unusable in the absence of new interventions.
So far, attempts to slow debris growth have consisted of ad hoc, heuristic, guidance for new missions. Examples include minimizing intentional debris creation, improving tracking precision, incentivizing maneuverability, and improving post mission disposal reliability and timeframes. While helpful, these mitigations only address individual missions or constellations, and do not address interactions among all systems and debris contributing to debris propagation. Moreover, it is unknown which, if any, of these types of guidance are most likely to result in a reduction of debris growth.
Even though LEO space is large, it is still finite and cannot support an unlimited number of satellite systems, even if each system individually complies with best practices. There are no comprehensive models or metrics considering all forms of debris propagation, extrapolating those effects into the future, and comparing effectiveness of candidate heuristic mitigations. We propose such a methodology, and metric, using a comprehensive multi-dimensional state vector and extrapolating that state vector into the future. It models debris population evolution due to interactions of maneuverable and non-maneuverable objects given key physical characteristics, such as, orbits, mass, cross sectional area, and area to mass ratios for trackable objects such as satellites, rocket bodies, and LT debris, as well as estimated equivalent distributions for LNT debris.
The goal is to facilitate: 1) quantitatively measuring absolute and relative effectiveness of candidate regulations and policies governing space access and operations, and remediations such as various debris removal strategies, 2) reframing the problem to consider interactions among all missions and constellations, instead of merely addressing each one individually and based on historical debris flux models, and 3) fostering identification of quantitative system design characteristics that slow, halt, or reverse acceleration towards a point in time when access to space is intolerably impaired or lost.
The metric is used to estimate the carrying capacity, the sustainable satellite population distribution in LEO. The proposed approach better estimates future debris propagation because it encompasses both existing debris, and the likelihood that non-debris objects become debris within a given time horizon. The performances of mitigations, such as Space Surveillance and Tracking (SST), Space Situational Awareness (SSA), and Space Traffic Management (STM) are accounted for in the metric computation. This methodology enables comparing holistic global contributions to debris propagation as a function of specific system characteristics and deducing the incremental impact of individual systems and characteristics on LEO carrying capacity.
Date of Conference: September 27-20, 2022
Track: Space Debris