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related debris during spacecraft deployment, however, may be more difficult to avoid. One example is dispensers for multiple spacecraft (e.g., the forward payload adapter on the Titan III and the SPELDA device used with the Ariane launch vehicle). Methods for retaining or deorbiting such items have not yet been developed, but development of such methods does not seem to be an inherently intractable problem.
Reducing the amount of mission-related debris created during the course of crewed space activities will have little effect on the overall debris hazard to space operations. Since human activities in space currently take place at low altitudes, the debris they release (mostly from intentional refuse dumping and extravehicular activities) experiences rapid orbital decay and does not contribute to the long-term debris population. Although there are a number of possible methods to further reduce the hazard to space operations from such debris (e.g., bringing the refuse back to Earth during scheduled crew rotations or attaching a drag augmentation device to speed its orbital decay), implementing such methods will not reduce the overall long-term debris hazard. However, since this debris contributes to the short-term hazard in an area containing valuable spacecraft, the use of low-cost methods of debris reduction (if such methods are available) appears to be worthwhile.
Curtaining the release of exhaust products of solid rocket motors will also do little to reduce the debris hazard to space operations. As discussed in Chapter 3, solid rocket firings produce a vast number of very small (<10-micron) debris, but their orbital lifetimes are fairly short due to the strong effect of perturbing forces such as solar radiation pressure; less than 5% will remain in orbit after a year. In addition (as described in Chapter 4), the surface degradation these particles can cause is not a major hazard to functional spacecraft.
The only methods of meaningfully reducing this population would be either to restrict solid rocket motor firings in orbit or to alter the composition of solid rocket motor fuel. Because either action would impose cost increases or performance reductions on many space activities, and the lifetime of these exhaust particles and the potential damage that they can cause to functional spacecraft are so small, it seems clear that neither step is yet warranted at present. It is not yet clear, though, whether anything should be done to limit the population of 1-cm and larger pieces of slag (discussed in Chapter 1) that are also believed to be ejected during solid rocket burns. Whereas the larger size and longer orbital lifetimes of these particles may make them a greater hazard to spacecraft than the small aluminum oxide particles, too little is currently known about them (in particular, how many are typically produced in a solid rocket motor firing) to determine if there is any need to search for ways to prevent their creation.