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Ambient Scattering from Ring-Symmetric Spacecraft Exhaust Plume.

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Contractor rept. Jan-Mar 87,

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We present a first-collision model for the evaluation of return flux from the exhaust plume of a ring-symmeric HFDF laser in LEO, generated by an incident flux of ambient molecules traveling at orbital speed. The steady plume is bounded by a pair of lip-centered rarefaction fans, and unless spacecraft attitude enables incident air molecules to reach the plume through the cavition through the cavitation regions that extend beyond these fans, the spacecraft is shielded from ambient scattering by its own plume. Assuming hard-speres collisions, the first-collision model is given by a simple closed-form expression that can be regarded as a source term for scattered exhaust molecules. This source term is integrated numerically throughout the fan, yielding the flux arriving at some surface target point. Quantitatively, it is shown that for a typical HFDF laser exhaust the contamination level generated by ambient scattering is not significant. It is found that the maximum return flux of HFDF constitutes about 2 of the incident ambient flux this ratio will be nearly constant for LEO altitudes. The value of this flux ratio is shown to be dependent on the molecular collision model it may change upon replacing the hard-speres approximation by a more realistic collision model. A possible modification of spacecraft charging by the exhaustwas examined, including production of HF- and DF-. The only significant effect seemed to be shadowing of the downstream half of the spacecraft at oblique orbital attitudes. Keywords Spacecraft contamination, Exhaust plume, Ambient scattering, First collision.

Subject Categories:

  • Fluid Mechanics
  • Combustion and Ignition
  • Astronautics

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