The F-layer depletion resulting from the orbit circularization maneuver at LEO apogee is more severe, but relatively short-lived. The F2 peak electron density is reduced to one third of its normal value over a region approximately 1000 by 2000 km for a period of about 4 h. The hole would be longer-lasting if the orbital maneuver occurred at night. The computed rate of production of hydrogen atoms reaching the upper thermosphere (above 3000-km altitude) amounts to 1.3 xlO31 per HLLV launch for the first 30-h period. This might be sufficient to double thermospheric H-atom concentrations after six launches.
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