A sensitivity study of the effectiveness of active debris removal in LEO
Introduction
Recent numerical simulations on the evolution of orbital debris population in low-Earth orbit (LEO, 200–2000 km altitude) indicate that the population has reached a point where the environment is unstable and population growth is inevitable [1], [2]. The main conclusion from the two studies is that even if no further space launches were conducted, the Earth satellite population would remain relatively constant for only the next 50 years or so. Beyond that, the debris population would begin to increase noticeably due to the production of collisional debris. In reality, the satellite population growth in LEO will undoubtedly be worse than the studies indicate, since spacecraft and their orbital stages will continue to be launched into space and unexpected major breakups may continue to occur. Postmission disposal of vehicles, such as limiting postmission orbital lifetimes to less than 25 years, can certainly slow down the population growth [3], [4], [5]. However, this mitigation measure will be insufficient to prevent further growth of the Earth satellite population. To better preserve the near-Earth environment for future space activities, other alternatives must be considered.
Concepts for removing large debris from LEO have been proposed for more than 25 years. Early ideas for using the U.S. Space Shuttle, either directly or in conjunction with an orbital transfer vehicle, were found unattractive due to safety, availability, cost, and policy issues. Numerous independent robotic concepts, ranging from classical space-based garbage scows to momentum and electrodynamic tethers, drag augmentation devices, solar and magnetic sails, and other exotic techniques, have also been considered. However, reviews by panels of international experts have repeatedly failed to identify a single plan which is both technically feasible in the near-term and economically viable.
Nonetheless, in late 2006 the International Academy of Astronautics (IAA) initiated a new study to determine if a nexus of technology, cost, and policy might lead to an achievable means of remediating the near-Earth space environment in the foreseeable future. Although the IAA study will not be completed until late 2008 or 2009, the purpose of the present paper is to describe the potential effectiveness of debris removal operations under various scenarios. These results, in turn, could influence the development of efficient debris removal techniques.
This paper summarizes a sensitivity study of the effectiveness of active debris removal (ADR). A non-mitigation scenario where the historical LEO population was simulated, then projected 200 years into the future, was adopted as the benchmark scenario. A simple selection criterion based on collision probability and mass of each 10 cm and larger object was developed. Numerical simulations of three ADR scenarios with different removal rates were carried out and compared with the benchmark population. The results demonstrated that, with a reasonable selection criterion, active debris removal could be a very effective way to limit the growth of future debris population.
Section snippets
Model description
The tool used in the study is the NASA orbital debris evolutionary model LEGEND (a LEO-to-GEO Environment Debris model). It is a high fidelity, three-dimensional, physical model. LEGEND is capable of simulating the historical and future debris environment from LEO to the geosynchronous orbit (GEO) regions [6], [7]. The focus of this study was the LEO environment. Each test scenario presented included 100 Monte Carlo simulations with a projection period of 200 years. Future launch traffic was
Active debris removal case study
Four test scenarios were selected for this case study. The first one was a non-mitigation (“business-as-usual”) scenario. The other three scenarios assumed ADR was implemented in the year 2020, with annual debris removal rates of 5, 10, and 20 objects, respectively (these three scenarios are referred to as 2020/5, 2020/10, and 2020/20 throughout the rest of the paper). Each scenario was carried out with a 200-year projection period and 100 Monte Carlo runs.
Fig. 1 shows the effective numbers of
Discussion
The test cases described in the previous section represented the first step to evaluate the effectiveness of ADR. The scenarios were designed to demonstrate and quantify, in a relative way, how ADR could reduce the growth of the future LEO debris population. The assumptions made in the simulations were reasonable, but certainly not perfect. The non-mitigation scenario was selected as a benchmark for comparison. Since mitigation measures (such as limiting postmission orbital lifetimes of
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