2.2 INJECTANTS 2.2.1 H2O/H2 Injections The amounts and altitude profiles of injections are shown in Fig. 1 (see also Appendix B, Table B.2) and also in Tables 1, 3, and 4. To maximize the thrust per unit propellant from a rocket engine, many rocket engines are run fuel rich so that the effective molecular weight of the exhaust is relatively low. In the present case, approximately 30% of the hydrogen atoms in the exhaust are emitted as H2 rather than as H2O. 2.2.2 NO Production on Reentry (Park) Every object reentering the earth's atmosphere is slowed down by friction, and the kinetic energy lost by the reentering body goes to heat up air to rather high temperatures. The amount of air heated depends upon the projected area of the body, its speed, the reentry time, and the ambient air density. Temperatures in excess of 2000 K are achieved, and at these temperatures some nitric oxide is produced, and "freezes in" as the air cools. For an entry vehicle of the size, mass, and shape of the HLLV, the amount of nitric oxide expected to be produced is approximately 22% of the mass of the vehicle. The NO produced will be distributed between 55 and 100 km in altitude, the peak being around 70 km (Rakich, Bailey, and Park, 1975; Park, 1979, to be published). 2.2.3 Construction Debris (Whitten) During construction of the SPS satellites in space, there will certainly be some waste material or lost items. Even though a serious effort will be made to minimize any losses, yet, presumably, some of this material will reenter the earth's atmosphere. Small pieces will burn up on reentry, producing fine (micron or submicron sized) particles analogous to meteoritic dust, as well as a small amount of NO due to reentry heating. Large objects, such as Cosmos 954 or Skylab, may maintain their integrity during reentry, producing NO and a possible ground-level hazard. Other objects, such as large, light sheets of material with appropriate aerodynamic characteristics, could be expected to reach the earth's surface without ablation, giving rise to troublesome effects. The structural material for the satellites will be largely graphite composite (see RSR, 1978, p. 58ff), which will burn up on reentry, but there will be a certain amount of Al and Si/SiO? that will presumably form small oxide particles. Regarding the quantity of material involved, lacking other information, it will be assumed here that 1% of the total mass of a 5-GW system is lost each year. From RSR, 1978, p. 59, this loss gives a mass injection rate of (3-5) x 10^ kg/yr, perhaps half metal (Fe, Cu, etc.) and half stony (SiC^, A^O^). This quantity is small compared with the annual mass injection of meteoritic material, which is of the order of 4 x 10' kg/yr (see Park and Menees, 1978, p. 4033); thus the effect of such structural debris is probably negligible unless some exotic material such as teflon,
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