Version 1.4 of the Launch Vehicle Loads Analysis for Preliminary Design (VLOADS 1.4) computer program calculates in-flight launch-vehicle structural loads (that is, spacecraft-launching rockets) for preliminary design. The program can also be used to calculate structural loads in upper stages and planetary-transfer spacecraft.

VLOADS compiles and analyzes launch-vehicle information such as aerodynamic coefficients, mass properties, data on propellants, and engine thrusts, to calculate distributed shear loads, bending moments, axial forces, and vehicle line loads as functions of X station (position along the longitudinal axis of the vehicle). If the launch vehicle includes boosters or wings, then VLOADS also computes interface loads.

An attractive feature of VLOADS is that its source code is in Visual Basic for Applications and has been integrated into an easy-to-use Microsoft Excel user interface. VLOADS uses the individual worksheets in its Excel workbook as input and output data files, in a manner similar to the way in which traditional FORTRAN and BASIC programs have used text files as input and output files. Because VLOADS has been integrated into an Excel workbook, it is much easier for the user to edit the input data, run the program, and view the results.

The major strength of VLOADS is that it enables rapid analysis of structural loads in launch vehicles during the preliminary-design phase of development. Thus, VLOADS offers an alternative to the time-consuming and expensive chore of developing finite-element models for detailed analysis of loads. In preliminary design, much remains unknown about the details of the configuration to which the launch vehicle will mature.

It becomes necessary to make some simplifying assumptions to initiate the process by which loads can be calculated for preliminary design and analysis of structures. VLOADS implements a two-degree-of-freedom mathematical model for calculating the distribution of axial force, shear force, and bending moment along the length of the vehicle. The model essentially treats the launch vehicle as a rigid beam; vibrations are not considered. The method of sections is employed to determine the shear, moment, and axial load. Rotational acceleration in the pitch plane is assumed equal to zero, so that the sum of pitching moments equals zero.

VLOADS was developed as a Visual Basic macro in a Microsoft Excel 5.0/95 workbook program on a Power Macintosh computer. VLOADS has also been implemented on a '486-class personal computer using version 7.0a of Microsoft Excel for Windows 95, and on a '586-class personal computer running Windows NT 4.0. The standard distribution medium for VLOADS is one 3.5-in. (8.89-cm), 1.44MB, MS-DOS-format diskette. VLOADS was developed in 1996. The program is copyrighted work with all copyright vested in NASA.

This program was written by Paul L. Luz and Jerry B. Graham of Marshall Space Flight Center. No further documentation is available. MFS-27332

NASA Tech Briefs Magazine

This article first appeared in the August, 1999 issue of NASA Tech Briefs Magazine.

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