Orbital Debris A Technical Assessment (1995) / Chapter Skim
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8 THE FUTURE ORBITAL POPULATION AND THE EFFECTIVENESS OF DEBRIS REDUCTION MEASURES
8 THE FUTURE ORBITAL POPULATION AND THE EFFECTIVENESS OF DEBRIS REDUCTION MEASURES
Pages 157-174
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From page 157... ...
have decayed into the atmosphere and, at the peaks of the 11-year solar activity cycle, the overall losses of cataloged space objects have occasionally outnumbered the increases, resulting in an overall decline in the cataloged population. It is this balance between the creation of new debris and the orbital decay of existing debris that will determine the magnitude and distribution of the future debris population.
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From page 158... ...
can use a variable number of bins, but typically uses 15 mass and 36 altitude ranges. Although these models incorporate a variety of different assumptions, they generally carry out similar procedures to predict the future debris population.
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From page 159... ...
Predictions of the number and characteristics of space objects that will be added to various orbital regions as a result of future launches are also uncertain. The future launch rate, the size ranges of future spacecraft, and the distribution of orbits into which these spacecraft will be launched cannot be predicted in detail because they depend on such unpredictable factors as future mission requirements, technologies, economics, and global politics.
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From page 160... ...
Predictions of the Future Orbital Environment If the only additions to the future debris population were rocket bodies, nonfunctional spacecraft, mission-related debris, and the products of explosions and surface deterioration, the space object population would likely continue its roughly linear growth. Implementation of measures to reduce the number of explosions of spacecraft and rocket bodies, and to limit the amount of mission-related debris released as a result of spacecraft deployment and operations, might result in a slower rate of growth, just as changes in future launch patterns could result in a faster rate of growth.
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From page 161... ...
The exponential growth visible in predictions of the 1-cm debris population is only a symptom, not the cause, of collisional population growth. Though these models all show that an exponential rise in the orbital debris population will occur unless preventive measures are taken, the time frame over which this rise will occur cannot be determined precisely.
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From page 162... ...
500000 0 400000 300000 ^ 200000 Q 100000 o o 1 ' 1 ' 1 ~ , 1 /_/ / 990 2010 2030 year / 1 I . 1 , ~ 2050 2070 FIGURE 8-2 Different model simulation of the future LEO space object population (constant launch rate and explosion rate at current level, no mitigation measures)
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From page 163... ...
~_, ~ . ~ type and altitude region P(i-j,~)
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From page 164... ...
Figure 8-5 shows the effect of varying the mass distribution of collision fragments in a different simulation of the future environment; it is clear from the figure that this factor also introduces a large uncertainty into the predicted growth rate of the future debris population. Since models of the future debris population must incorporate both these uncertainties, as well as others, it is premature to suggest exactly when collisional growth will begin to occur; it may already be under way, or it may not begin for several decades.
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From page 165... ...
The addition of new objects to already crowded orbital regions will likely increase the collision probability for functional spacecraft in these regions, as well as the rate and magnitude of their future collisional population growth. LEO regions that have not reached a critical density may still be af 1 ,000,000 800,000 ~ 600,000 A In C' a)
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From page 166... ...
fected by collisions in those regions that have surpassed their critical density. For example, as can be seen from Figure 8-6, the debris population at altitudes below about 700 km is not likely to exceed the critical density; at these altitudes, atmospheric drag typically will remove collision fragments before they collide with another object.
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From page 167... ...
EFFECTIVENESS OF DEBRIS REDUCTION MEASURES There are two major types of methods to reduce the debris hazard in Earth orbit. One set of methods aims at limiting the number of potentially harmful objects in orbit, primarily by reducing the release of missionrelated debris and by preventing further explosions of spacecraft and rocket bodies.
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From page 168... ...
Figure 8-7 shows the predicted effect of various debris reduction methods on the LEO population of collision fragments and other types of debris in 2042, and Figure 8-8 shows how these measures are predicted to affect the total LEO debris population over time. In Figure 8-7, the first bar shows the estimated population of LEO objects larger than 1 cm in 1992, and the other bars show the predicted 2042 population of debris if various reduction methods are implemented.
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From page 169... ...
/ Removal of 3000 'old' P/L and RIB from 2010 2022 2032 2042 year FIGURE 8-8 Predicted effect of debris reduction measures over fifty years on space object population. SOURCE: Rex and Eichler, 1993.
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From page 170... ...
This model incorporates different initial assumptions than the previous model and examines the effect of a different set of potential debris reduction meth ods. The figures focus on the object flux in the 900-km-altitude regime, which (as discussed earlier)
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From page 171... ...
It is clear from this figure that orbital lifetime reduction measures can slow the rate at which the debris population increases and that the greater the reduction in orbital lifetime, the less will the debris environment grow. However, given all the uncertainties involved, the model does not suggest that any one particular chosen target lifetime is more cost-effective than another.
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From page 172... ...
may be required to prevent an eventual exponential rise in the debris population. FINDINGS Finding 1: If the only additions to the future debris population were rocket bodies, nonfunctional spacecraft, mission-related debris, and the products of explosions and surface deterioration, the space object population would probably continue its roughly linear growth.
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From page 173... ...
1992. Analytical model for orbital debris environment management.
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