LEGEND – a three-dimensional LEO-to-GEO debris evolutionary model

doi:10.1016/j.asr.2003.02.027

Advances in Space Research

Volume 34, Issue 5, 2004, Pages 981-986

https://doi.org/10.1016/j.asr.2003.02.027 Get rights and content

Abstract

A new orbital debris evolutionary model is being developed by the NASA Orbital Debris Program Office at Johnson Space Center. LEGEND, a LEO-to-GEO Environment Debris model, is capable of reproducing the historical debris environment as well as performing future debris environment projection. The model covers the near Earth space between 200 and 40,000 km altitude and outputs debris distributions in one-dimensional (altitude), two-dimensional (altitude, latitude), and three-dimensional (altitude, latitude, longitude) formats. LEGEND is a three-year (2001–2003) project. The historical part of the model has been completed and the future projection part is being developed/tested. The model utilizes a recently updated historical satellite launch database, two efficient and accurate propagators, and a new NASA satellite breakup model. This paper summarizes the justifications for building a full-scale three-dimensional debris evolutionary model, the overall model structure, and several key components of the model. Preliminary model predictions of debris distributions in the Low Earth Orbit (LEO), Medium Earth Orbit (MEO), and Geosynchronous Earth Orbit (GEO) regions are presented.

Introduction

To continue to improve our understanding of the orbital debris environment, the NASA Orbital Debris Program Office has initiated an effort to develop a new debris evolutionary model to replace EVOLVE. The first generation of the EVOLVE model was written in 1986 (Reynolds, 1991). Over the years, several major upgrades have been developed and implemented into the main and supporting models, including Reynolds and Eichler (1995), Reynolds et al. (1998), and Krisko et al. (2000). EVOLVE is a one-dimensional model describing the Low Earth Orbit (LEO) debris environment between 200 and 2000 km altitude. For more than a decade it has been a leading model providing critical insights into the orbital debris environment. It was also the tool supporting the development and publication of NASA Safety Standard 1740.14 in 1995 (Reynolds, 2001).

The motivations to build a new model to replace EVOLVE are twofold. First, a one-dimensional description and treatment in altitude of the debris environment is not adequate to address all issues. The spatial density of debris at the same altitude can vary significantly as a function of latitude. In addition, populations such as objects in Geosynchronous Earth Orbit (GEO) and recent breakup fragments from parent objects in Sun-synchronous orbits all have strong longitudinal dependence. To describe the orbital debris environment adequately and to properly analyze its future behavior (such as collisions), a three-dimensional model is needed. Second, as the debris populations continue to grow, there is a need to build a full-scale debris model describing the near-Earth environment from LEO to MEO, and to GEO and above. In addition, the dated program structure of EVOLVE and the patches added to the model over the last 15 years make it highly inefficient to upgrade. It is simply a better approach to build a modern code from scratch.

LEGEND, a LEO-to-GEO Environment Debris model, is a full-scale three-dimensional debris evolutionary model. It covers the near-Earth space between 200 and 40,000 km altitude, including LEO (200–2000 km altitude), Medium Earth Orbit (MEO, 2000–34,000 km altitude), GEO (34,000–38,000 km altitude), and super GEO (38,000 km and above) regions. The model is capable of providing debris characteristics (size distribution, spatial density distribution, velocity distribution, flux, etc.) as functions of time, altitude, longitude, and latitude. LEGEND includes a historical simulation component (1957–2001) and a future projection component. The historical part of the model is described in this paper.

The main function of the LEGEND historical component is to reproduce the debris environment between 1957 and 2001. The model utilizes a recently updated historical satellite launch database (DBS-database), two efficient state-of-the-art propagators (PROP3D, GEOPROP), and a new NASA satellite breakup model. The overall program structure and the input and output options are optimized to allow reasonable execution time and manageable file storage space. The program is capable of providing multi-dimensional descriptions of the debris environment. Additional analysis modules are also developed to visualize the outputs and to enable easy comparisons with existing ground-based debris observations. The main program is written in FORTRAN 90 with additional analysis tools written in IDL.

Section snippets

Legend structure and supporting models

The top-level LEGEND model structure is outlined in Fig. 1. The logic is very similar to other debris evolutionary models, such as EVOLVE (Krisko et al., 2000), IDES (Walker et al., 1996), and SDM (Rossi et al., 1998). Source mechanisms (satellite launches and breakups) add objects to the environment while sink mechanisms (decay and deorbit) remove objects from the environment. Major perturbations that affect the orbital evolution of debris objects are included in the program. The two

Model outputs

LEGEND outputs debris distributions in 1D (altitude), 2D (altitude, latitude), and 3D (altitude, latitude, longitude) formats at a given time or as functions of time. The orbital element arrays maintained by the program are processed in several modules analyzing debris characteristics in multi-dimensions. In general, the altitude–latitude 2D distributions are sufficient for debris environment definition and characterization. The exceptions are GEO objects or recent breakup fragments in near

Summary

The historical component of LEGEND has been completed. Comparisons in 1D, 2D and 3D with the SSN catalog and MAX radar data indicate that overall the model-predicted debris environment for objects greater than 10 cm, between 1957 and 2001, agrees with the data (see also Liou et al., 2001). The next step in the LEGEND development is to validate the breakup model for fragments smaller than 10 cm (down to 1 mm). The NaK and SRM modules are also needed to complete the environment description for

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LEGEND – a three-dimensional LEO-to-GEO debris evolutionary model

Abstract

Introduction

Section snippets

Legend structure and supporting models

Model outputs

Summary

Adv. Space Res.

Adv. Space Res.

Planet. Space Sci.

Luni-solar perturbations of the orbit of an Earth satellite

Geophys. J. R. Astron. Soc.

Satellite Orbits in an Atmosphere