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Foundation ::
Spacecraft Design and Space Missions ::
MOLFLUX
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MOLFLUX
Molecular Flux Program
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SOURCE CODE AVAILABLE
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MOLFLUX (MOLecular FLUX Program) is a versatile program that can be used to predict the following spacecraft conditions:
- molecular flux to surfaces and surface molecular deposition,
- molecular density and molecular column densities in surrounding space, and
- molecular return flux to surfaces caused by molecular collisions both with the ambient atmosphere and from self-scattering
This includes the capability to predict the ambient gas density build-up in front of surfaces exposed to ram conditions by specifying the ambient flux rates for all species impinging on the surfaces, modifying these rates for chemical surface reactions, and applying these rates to the surfaces as emission rates. The user has the option to modify spacecraft configurations and sources of contamination and to choose which critical surfaces to examine.
MOLFLUX is a free molecular flow model with perturbations to account for "near-free" flow, and therefore appears to be adequate to deal with most space-related applications. This includes the mass flow in thruster plumes, with the exception of a small plume volume of viscous and transition flow close to the nozzles. The transport function for all species can include a small perturbation (due to molecular collisions) from the free molecular flow case, and allow for back-scattering return flux and flux attenuation calculations. The perturbation to the basic model is based on a numerical integration of the Bhatnagar, Gross, Krook (BGK) model approximation of the Boltzmann kinetic equation for a mixture of gases. As a result, MOLFLUX is a program of reasonable size and accuracy with maximum flexibility. Because a computational model is only as good as the input data used, the capability to introduce input data as well as to evaluate output data is left very general and adaptable to the needs of the user.
Modeling contamination generally requires addressing the following:
- the geometry of the space structure,
- the emission processes from all contamination sources,
- the transport of emitted contaminates, and
- the induced effects of the contaminants upon critical surfaces and scientific observation objectives.
The first three of these are handled analytically in MOLFLUX. Once contamination levels have been established, other computer programs and analytical techniques can be used to determine the induced effects.
In general, the input of a new configuration involves developing the necessary geometric relationships and mass transport factors for the particular configuration being analyzed. The most efficient approach is to use a thermal radiation program for generating new mass transport factor input data for MOLFLUX. Configurations can be geometrically synthesized with TRASYS using basic geometrical surfaces and shapes (cones, cylinders, spheres, etc.). The level of detail employed is selected to assure accurate surface shadowing and to establish adequate surface resolution for compatibility with the different vehicle surface materials and available thermal profile data. It is not necessary to run TRASYS to use MOLFLUX if the mass transport factor data have been pre-calculated and are available as permanent input data files. These input files need to be regenerated only when new configurations are to be evaluated or existing configurations are to be modified.
MOLFLUX carries the NASA case numbers MSC-22565 and MSC-22566. It was originally released as part of the COSMIC collection.
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