Accession Number : ADA183076

Title :   Ambient Scattering from Ring-Symmetric Spacecraft Exhaust Plume.

Descriptive Note : Contractor rept. Jan-Mar 87,

Corporate Author : FALCOVITZ (JOSEPH) HAIFA (ISRAEL)

Personal Author(s) : Falcovitz,Joseph

PDF Url : ADA183076

Report Date : Apr 1987

Pagination or Media Count : 66

Abstract : We present a first-collision model for the evaluation of return flux from the exhaust plume of a ring-symmeric HF/DF 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 HF/DF laser exhaust the contamination level generated by ambient scattering is not significant. It is found that the maximum return flux of HF+DF 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 exhaust/was 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.

Descriptors :   *EXHAUST PLUMES, *AIR, MOLECULES, SCATTERING, COLLISIONS, MODELS, FLUX(RATE), RATIOS, CAVITATION, CONTAMINATION, EXHAUST GASES, HYDROGEN FLUORIDE LASERS, ORBITS, SATELLITE ATTITUDE, LOW ALTITUDE, EARTH ORBITS, RAREFACTION, HYDROGEN FLUORIDE, COMPUTER PROGRAMS, MOLECULAR PROPERTIES, MOLECULAR STRUCTURE, SPACECRAFT, ELECTRIC CHARGE, PLUMES, STEADY STATE, VELOCITY, ATTITUDE(INCLINATION), SURFACE TARGETS

Subject Categories : Fluid Mechanics
      Combustion and Ignition
      Astronautics

Distribution Statement : APPROVED FOR PUBLIC RELEASE