The NASAN computer program can perform detailed analyses of molecular column density and molecular deposition on and around such complex space structures as the International Space Station (ISS). Contamination from both point sources (e.g., thrusters and vents) and diffuse sources (e.g., reflected plumes or outgassing of materials) can be analyzed. NASAN has been used to perform the assessments reported in the ISS incremental-design-review documents.
NASAN consists of several interactive tools (subroutines) that are linked together into a single, modular computer program that takes advantage of common program elements, which include manipulation of geometric models and plotting of results of computations. The central program components are designed to be easily expandable to perform additional analyses.
NASAN includes ray-tracing subroutines that are efficient means for calculating surface shadowing within the various program application modules. A variety of mathematical models of plumes can be easily called from the application modules. Two of these plume models calculate surface view factors, as needed, so that contamination calculations can proceed efficiently.
Because geometric models with as many as 25,000 surfaces can be analyzed, the fidelity achievable by use of NASAN is greater than that achievable with software developed previously for the same purpose. The modular structure of NASAN, along with a high degree of portability, makes it possible to perform contamination calculations on a much wider variety of computer platforms than was previously possible. Considerable time is saved over prior software of this type by use of NASPLT, which is a plotting subroutine within NASAN: this is because results of contamination calculations can be plotted from within the same subprograms that perform the calculations.
Another module of NASAN is CDPLT, which is a unique software tool for calculating and displaying the molecular column density around a spacecraft. This module has enabled the completion of numerous column-density calculations that, previously, could not be attempted.
Yet another module, FIRJET, models a surface plume and enables quick calculation of direct-flux molecular deposition onto a geometric model that has easily reorientable surfaces. The surface-source-plume model has enabled the analysis of more outgassing sources and model configurations than were previously possible.
The program is operational on several UNIX platforms, and some ray-tracing calculations can be performed in parallel on computers that include multiple processors. A simple, interactive user interface enables quick, interactive calculations, and facilitates setup for longer batch calculations. The contamination analyses performed by use of NASAN are helping to make possible the ISS design and verification activities to proceed on schedule. NASAN is also a powerful means for more detailed assessments of the local environments around specific payloads.
This program was written by Charles Lynn Hakes, Rose T. Rodriguez, Doug Warrington, and Eleazar Rios of Lockheed Martin for Johnson Space Center. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Software category. MSC-22963