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The new NASA orbital debris breakup model J.-C. Lioua, N. L. Johnson6, P. H. Kriskoa and P. D. Anz-Meador° aLockheed Martin Space Operations, Houston, TX77058, USA. bNASA Johnson Space Center, Houston, TX77058, USA. °Viking Science and Technology, Houston, TX77058, USA.

A new breakup model, including on-orbit explosions and collisions, has been developed and implemented in the NASA orbital debris dynamical model EVOLVE 4.0. It is based on more than twenty well-observed on-orbit explosions, one on-orbit collision, and several laboratory hypervelocity impact experiments. The revised size distributions of breakup fragments are quite different from the ones used previously. The new distributions are simpler and well supported by the data. The predicted 10 cm and greater debris populations between 1957 and 1999, based on simulations with the new breakup model, compare well with those derived from radar observations.

1. introduction

To model the past, current, and future space debris environment in low Earth orbit (LEO, defined as the region between 200 and 2000 km altitude), the Orbital Debris Program Office at the NASA Johnson Space Center has developed a numerical program, EVOLVE [1,2]. The first step in EVOLVE is to model historical launches and breakup events, including explosions and collisions. Breakup fragments are then propagated forward in time numerically with other intact objects. The gravitational force of Earth and its J2 perturbation, solar-lunar perturbations, and atmospheric drag are all included in the propagator. The intact object and debris populations since 1957 are calculated until the end of 1999. The spatial density or number of debris objects of a given size and greater, at a given altitude and at a given time, from EVOLVE can then be compared with radar, optical, or in situ debris measurements. Once the current debris environment is modeled properly, EVOLVE takes an assumed launch traffic and an assumed solar activity projection and uses a Monte Carlo approach to model future on-orbit explosions and collisions and predict the future LEO debris environment.

2. the breakup model

A key module in a dynamical orbital debris model, such as EVOLVE, is the breakup model. A breakup model includes the size distribution of collision or explosion fragments, the area-to-mass ratio of the fragments, and their relative velocity distribution with respect to the parent object. Explosion/collision rate and the fragment size distribution determine the production rate of debris particles while the area-to-mass ratio and the relative velocity distribution determine how they evolve and eventually decay. In this paper, we focus on the size distribution of the breakup fragments. These distributions are different for explosions and collisions, and are discussed separately below.

2.1. Explosion fragment size distribution

The previous EVOLVE breakup model assumes that two fragment size distributions are possible for explosions: high-intensity and low-intensity explosion size distributions [3]. A single event may produce fragments that follow both distributions (e.g., 10% of the fragments follow high-intensity explosion size distribution while the remaining 90% follow low-intensity explosion size distribution). The high-intensity explosion size distribution has the form:

where Nhi,cum is the number of fragments greater than diameter L (in meters), mtot is the total mass of fragments (in kg) which follow this size distribution, and a, b, and c are three positive constants. The low-intensity explosion size distribution has the general form of:

tow,cum where Niow,Cum is the number of fragments greater than diameter L (in meters); a and b are two positive constants that depend on the mass of the parent object.

A recent review of more than twenty well-observed on-orbit explosions, including spacecraft and rocket bodies, indicates that there is not sufficient evidence to support the above-described two types of explosions. Table 1 lists the seven regular rocket body explosions examined. The derived total masses of fragments of these events, based on radar observations, are all within 10% of the published dry masses of their parent objects.

Table 1

Explosion events used to derive the new fragment size distribution

Table 1

Explosion events used to derive the new fragment size distribution

Name

International

Debris

Event Date

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