Low amounts released wouldn’t endanger anyone

Fragmentation It is estimated [Gafarov 1991] that the ASOs minimum mass which can cause full destruction of a spacecraft with an NRS, colliding at the most probable impact relative velocity 10 km/s is in the range of 1.65-33 kg. The corresponding mass for a fuel core would be in the range of 0.023-0.46 kg. According to the empirical dependence of the space object masses on their cross-section areas [Kessler and Cour-Palais 1978] the diameter of ASOs, causing full destruction of a spacecraft with a NRS, would be 23-85 cm; and that of a fuel core is 3.5-13 cm. The comparison of these results with actual parameters of ASOs in near-earth orbits suggests that possibility of ORM full destruction resulting from their collisions with other space objects is real. At present, there is no model of ORM fragmentation which can account for all possible characteristics of colliding objects and collision conditions. In this connection, the effect of fragmentation on lifetime was considered using an example of possible fragmentation of a spacecraft with a NPS into separate structural parts as it collides with an ASO. Design characteristics given in Table 2 correspond to an spacecraft of the "Kosmos-954" satellite type. In the analysis it was assumed that the aerodynamic drag coefficient is the same for all fragments, and that their lifetime is determined only by their mass ratios of M, to cross-section area, A. In Table 2 lifetimes, T I, are normalized to the lifetime of the most characteristic object: a NRS with an orbit transfer unit at the most unfavorable orientation-that is sideways to the incoming projectile (the angle of attack c = 90 ) . The lifetime of the NRS + OTU in these conditions amounts to 150 years. [[TABLE 2 OMITTED]] At Table 2 shows, the fragmentation analysis considered cases, ranging form complete spacecraft with NRS down to, separate fuel cores. The analysis showed that the orbital lifetime proved to be higher as the fragments become smaller in size. This effect is related to the fact that among these fragments the fuel core has the highest density. The orbit lifetime of fuel core fragments is shorter than that of the intact fuel core. Still it should be taken into account that the fragment radioactivity is lesser that activity of the whole fuel core. For example, the orbit lifetime of particle of 10 mm radius is about 150 years; that is approximately one third the orbit life of the fuel core. The radioactivity of such particle is only 10 -3 of the fuel core activity. The orbit lifetime of particles of 0.1 mm radius is only 1.5 years. But particles of such sizes originated from fuel cores of "Kosmos-954"-type satellite SNPSs constitute no danger for a man in approximately two weeks after reactor shut down. Thus, for the fragmentation model considered destruction of a spacecraft with a NRS does not involve an increase of radiation danger for the Earth population in spite of possible sharp reduction in orbital lifetime of fragments formed. It should not be noted, that the fragmentation model under consideration is characteristic for NRS designed and tested for aerodynamic dispersion during atmospheric reentry.