models simulate only the LEO environment, however; similar models with the capability to predict the effectiveness of debris reduction measures on the semisynchronous or GEO environment have not yet been developed.
Figures 8-7 and 8-8 show the result of one of these model simulations (Rex and Eichler, 1993). 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. Scenario 1 shows the predicted 2042 LEO population resulting from an immediate and complete cessation of all space launches. The model suggests that in this case, although the population of launched objects and explosion debris would decrease as a result of orbital decay, some collision debris and some debris from explosions of objects already in orbit would be generated, keeping the total population nearly constant over the 50 years of the simulation. Scenario 2 represents the other extreme, in which the linear growth of space activity drives the population of objects