How it WorksOTIS 4 is a general-purpose software program used for trajectory performance studies. Users can simulate a wide variety of vehicles defined by user inputs. The program uses trajectory simulation and optimization to predict how a vehicle will perform and to determine how best to fly a given vehicle.
OTIS 4 provides two general modes of operation: explicit trajectory integration, and optimization using either explicit or implicit integration. A calculator that recognizes commonly used mathematical functions, operators, and precedence rules enables the user to compute new quantities needed to resolve a specific trajectory problem. An innovative method for constructing constraints between phases of a simulation greatly expands the range of problems that OTIS 4 can solve and eliminates a major source of user error by creating a mathematically correct implementation of transphase constraints.
The measure between true physical behavior and the simulation is called a “defect.” OTIS 4 contains a unique method of taking this measurement, called a “quadrature defect” that has proved to be very stable and offer excellent convergence properties. This method has reduced defect values to nearly zero, attaining a very credible and accurate solution to an optimal control problem.
Why it is BetterOTIS 4 provides the latest mathematical techniques for solving trajectory optimization problems and is easy to learn and master. Earlier versions of OTIS proved far less userfriendly and were grounded in only one form of implicit integration. Now, OTIS 4 provides the capability to perform a broad spectrum of applications in one unified package. It uses state-of-the-art solution methods for optimizing trajectories and vehicle design parameters.
Users input commands via metastrings, a set of keywords that concisely convey specific but common information or actions. Metastrings are highly intuitive to the trajectory and mission analyst and specify functions pertinent to the simulation.
OTIS 4 offers many discrete, direct solution methods in one unified package is one of the best-tested and competent versions of trajectory optimization software that NASA has produced. Its use throughout the aerospace community, in both preliminary design efforts and detailed analyses, demonstrates its superior ability as a reliable, accurate, and robust trajectory analysis tool.
OTIS 4 can easily be used for non-aerospace applications. The program is distributed with software that automates its execution. It can run on any computer that has a Fortran 95 compiler, including Windows, Unix/Linus, or Macintosh OS X.
OTIS 4 is available for download from the NASA GRC Software Repository after completion of a Software Usage Agreement.
For more information on the OTIS 4 software and on obtaining OTIS 4, go to: The OTIS 4 Web site
For best performance, OTIS 4 relies on the non-linear optimization program SNOPT. NASA does not distribute the source code to SNOPT with OTIS 4. Users must purchase their own copy of SNOPT from Standford Business Software Inc. (http://www.sbsi-sol-optimize.com)
