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Conceptual Design and Analysis of Rockets and Their Missions
Latest Available Version:  1702

ZOOM First WindowZOOM is a windows-compatible computer program that determines the quasi-optimum trajectory and rocket configuration for a mission objective and constraints defined by the user. The program is very useful for conceptual design and analysis studies. ZOOM has been tested with Windows XP, 7, 8.1, and 10 operating systems and works with keyboard/mouse and touch-screen interfaces.

ZOOM incorporates many of the algorithms and procedures developed and refined over decades beginning in the 1970's. The optimization engine uses the Simplex algorithm of Linear Programming in an innovative way that has proven robust and effective in solving a wide variety of rocket trajectory optimization problems. These include long-range, low-altitude intercepts of re-entry vehicles, deliveries of large payloads from the earth's surface into various earth orbits including geostationary orbits, deliveries of payloads from an airborne platform to low earth orbit, rendezvous with orbiting satellites in sun-synchronous and other earth orbits, re-entry of the Space Shuttle, descent from lunar orbit to the moon's surface, and a variety of other problems.

Falcon 9R Mission

Two of the sample missions provided with the program simulate the delivery of payload by Space-X's Falcon 9R rocket to low earth orbit and the return of the rocket's first stage to the launch site. The payload delivery mission is of mission type "Inject Into Conic", and the first-stage return is of mission type "Achieve Specified State"

ZOOM's Capabilities

ZOOM is probably unsurpassed in the wide variety of in-flight and end-point constraints that can be imposed on the trajectory solution. These include constraints on initial mass, aerodynamic normal acceleration, axial acceleration, dynamic pressure, aerodynamic heating rate, propellant loading, and rocket-motor thrust. The intercept of a target spacecraft or re-entry vehicle can be an impact or rendezvous. A wide selection of mission objectives is available. These include minimizing the rocket's initial mass, maximizing payload, minimizing flight time, minimizing aerodynamic heating, maximizing altitude, maximizing ground range, and maximizing or minimizing final speed.

Scope of the Program Code

The ZOOM program is written in the FORTRAN 95 language. The source code is contained in 67 text files (with .f95 file extension) and consists of the main program, 155 subroutines, 286 function routines, and 7 modules. These program units contain 28,709 FORTRAN statements, 7209 blank lines, and 6393 comments (most of which are on the same line with a FORTRAN statement). Counting blank lines and statement continuation lines there are a total of 38,541 lines (records) in the source code.

With Windows 8.1 and 10 operating systems, an apparently random and relatively rare "Stopped Working" error has been seen to occur, at least in the early versions of these two operating systems. This error does not occur with Windows XP or 7 operating systems. The cause of the error has not been determined. In virtually all problem cases the error has occurred while ZOOM solutions are being examined and has not interrupted the solution process.


Comprehensive information about ZOOM can be obtained from the  ZOOM User Manual

A free copy of the latest ZOOM version can be downloaded from:   ZOOM  (Version 1702)

When the download is complete, the ZIP file can be unzipped to reveal the ZOOM Folder.  The "Read Me" file in the folder explains how to execute the program.

Any user of ZOOM is entitled to a reasonable amount of free technical assistance by contacting the developer, David Williams, at Any comments that can improve ZOOM are welcomed.

ZOOM is being offered free of charge in order to facilitate the conceptual design and analysis of rockets and their missions. Anyone who is inclined to express their appreciation is encouraged to donate to a worthy charity. Of special worthiness to the developer of ZOOM are children's hospitals. Three notable such hospitals are:

Children's of Alabama hospital in Birmingham, Alabama,
St. Jude Children's Hospital in Memphis, Tennessee, and
Cincinnati Children's Hospital in Cincinnati, Ohio.