altitudes (100 km and above) one would expect more rapid spreading, and in any case east-west dispersion is more rapid than north-south spreading because of the zonal winds associated with the rotation of the earth. 2.7 ENERGY AND MOMENTUM TRANSFER DUE TO ROCKET EXHAUST PLUMES (Forbes) The HLLV second stage has a mass flow of 6500 kg/sec, of which 6300 kg/sec is I^O and 200 kg/sec H2 (see Fig. 1). The heat of combustion of and ©2 is approximately 58 Kcal/mole, and thus the total rate of thermal energy production is 90 GW. At 95 km altitude the mean speed of the HLLV is 4 km/sec and the temperature is 200 K, so that the thermal energy in the exhaust is equal to the thermal energy of the air molecules contained in a cylinder of radius 6 km, which is approximately equal to one scale height. Thus for a distance of this order around the trajectory one would expect to find noticeable disturbances, with the possible production of shocks and gravity waves that would tend to propagate upwards with increasing amplitude as the density falls. In fact, during the ascent of Apollo 15, 16, and 17, signals were detected on a microbarograph on the ground from the plume in the 30-150 km altitude range (see Hilton et al. (1972), Henderson and Hilton (1974a,b, and Gardner and Rogers (1979), who analyzed the Concorde "hyperboom." Dissipation of energy in the rocket plume is expected to occur via both radiative cooling and the excitation of acoustic and/or gravity waves. Oscillations with periods on the order of minutes in the bottomside F-region ionization were observed 1000 km away from the launches of Apollo 14 and 15 (Arendt, 1971, 1972). Depending on the value of the Brunt-Vaisala frequency N, which is equal to about 1.9 x 10 sec at 110 km, the oscillations can be interpreted as acoustic wave modes if their frequency f > N/2ir, or as gravity wave modes if f < N/2tt. It is possible that these waves could act to cause Sporadic E in the vicinity of the rocket launch. By studying archived data and future launches of opportunity, the generation of wave disturbances in the ionosphere and related effects should be confirmed. The magnitude of the HLLV effect would of course be much greater, so some understanding of the physics involved would be necessary to extrapolate these results. 2.8 PHOTOCHEMICAL EFFECTS (Turco) SPS rocket injection of large quantities of H2O/H2 and NO into Domain A (the mesosphere and lower thermosphere) may cause important local and global scale effects, such as: (1) Enhanced airglow, particularly from vibrationally excited OH (infrared bands) produced by the reaction of H with On, and Ringlet oxygen atoms ( D at 630 nm and S at 557.7 nm) generated by OH^ and 0^ recombination with electrons. The increase in OH emission should roughly parallel the increase in total hydrogen in the upper mesosphere (~ 90 km). The intensity of singlet oxygen emission will depend on the fraction of injected H2O/H2 molecules that react with atomic ions in the thermosphere. Nitric oxide chemiluminesence, due to the reactions, NO + 0 and N0? + 0, may be prominent during rocket reentry.
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