The Propellant Feed System Analytical Tool (PFSAT) predicts heat leak based on insulation type, installation technique, line supports, penetrations, and instrumentation. It also determines the optimum orifice diameter for an optional thermodynamic vent system (TVS) to counteract heat leak into the feed line, and ensures that the temperature constraints at the end of the feed line are met. PFSAT was developed primarily using Fortran 90 code because of its computational speed and its ability to access directly real fluid property subroutines in the Reference Fluid Thermodynamic and Transport Prop erties (REFPROP) database developed by NIST.

A Microsoft Excel front end user interface was implemented to provide convenient portability of PFSAT among a wide variety of potential users, and for its ability to use a user-friendly graphical user interface (GUI) developed in Visual Basic for Applications (VBA). The focus of PFSAT is on-orbit reaction control systems and orbital maneuvering systems, but it may be used to predict heat leak into ground-based transfer lines as well. PFSAT can be used for rapid, initial design of cryogenic propellant distribution lines and thermodynamic vent systems.

Once validated, PFSAT will support concept trades for a variety of cryogenic fluid transfer systems on spacecraft, including planetary landers, transfer vehicles, and propellant depots, as well as surface-based transfer systems. This analytical tool is in the form of a Microsoft Excel workbook. The default worksheet when the workbook is opened contains two buttons that are assigned VBA macros to obtain inputs from the user through a series of VBA input forms, and initiate the solver, respectively. The solver macro sets up the discretized thermal circuit to be solved, and uses compiled dynamic link libraries (DLLs) to access the Fortran 90 code that executes the thermal analysis. Throughout the solution sequence, fluid properties are obtained from the REFPROP database at each element for each iteration to ensure that accurate real fluid properties are used to find the solution.

The analytical tool obtains inputs from the user through the VBA input forms. The user initiates the solver by clicking a button on the main Excel worksheet. Once the solver converges, the results are populated onto three worksheets. Six graphs are generated for the user to examine. All results are reported in English and SI units. Initial testing shows that the tool produces outputs consistent with baseline test data from the JSC Cryogenic Feed System Testbed.

This work was done by Brian Lusby, Bruno Miranda, and Jacob Collins of Johnson Space Center. For more information, contact the JSC Technology Transfer Office at (281) 483-3809. MSC-25181-1

NASA Tech Briefs Magazine

This article first appeared in the April, 2016 issue of NASA Tech Briefs Magazine.

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