Exospheric conditions, to a height of 3500 km, derived from satellite accelerations in 1964

Lifetimes for low-energy protons in the outer radiation zone

“…A more realistic temperature at the base of the exosphere near solar minimum is probably •800øK [cf. Keating and Prior, 1967;Fea, 1966], which would be reflected in lower concentrations predicted by the above model exosphere and, by invoking a linear interpolation of Johnson's [1961] results, position the concentration profile for ballistic orbits only in good agreement with our present results (see Figure 6). The calculated concentration profile for atomic hydrogen with both ballistic and captive elliptical .orbits differs, even with this lower temperature, significantly when compared with our present results.…”

“…Table I Table 1) demonstrates that Coulomb scattering is not a c.ompetitive loss mechanism. Similarly the relative ineffectiveness of ionization may be evaluated by comparison of the measured ionization cross sections for protons incident upon hydr.ogen atoms (p q-H-• 2p q-e) or 1.5 X 10 -•and 5 X 10 -= em '• at 40 and 7 key, respectively, with the corresponding experimental values for the cross sections for charge exchange in this collision (p + H • H + p) of 3.0 X 10 -• and 1.2 X 10 -•* em • at the above energies, respectively [Fire et al, 1960]. Hence, since the loss of incident proton kinetic energy is only of the order of the ionization potential of atomic hydrogen per ionizing collision, loss of proton kinetic energy by ionization of at<)mie hydrogen over the above energy range is a relatively unimportant loss mechanism within the outer radiation zone at altitudes •>1000 km.…”

“…Finally, we have calculated the chargeexchange lifetimes for low-energy pr.otons mirroring at the magnetic equator as functions of magnetic shell parameter L and proton energy, utilizing our present observations of proton lifetimes and the measured charge-exchange crosssections for protons incident upon atomic hydrogen [Fire et al, 1960;Allison, 1958], and have summarized these lifetimes in Figure 7. Charge-exchange lifetimes for mirror latitudes A,,,,, 'x' at a specified L value but not at the magnetic equator can be adequately approximated with the cos 6 X• • dependence invoked by Liemohn [1961], as discussed in the previous section.…”

“…Current knowledge of the concentrations, constitution, and temperature of the terrestrial exosphere is incomplete and largely inferred from rocket observations of scattered and absorbed solar Lyman-a emissions [cf. Kupperian et al, 1958Kupperian et al, , 1959Purcell and Tousey, 1960;Morton and Purcell, 1962]; air drag experiments conducted with balloon satellites have provided concentration determinations up to altitudes of 3500 km [Fea, 1966]. Our calculations of the atomic hydrogen concentrations as derived from in situ observations of charge-exchange lifetimes for protons over a large range of mirror-point altitudes require only that atomic hydrogen, not helium or oxygen, is the principal neutral exospheric constituent over the altitude range 8000-25,000 km.…”