NASA’s Glenn Research Center (Cleveland, OH) and Boeing employees have won the 2008 NASA Software of the Year Award for the development of a general-purpose program used to perform trajectory optimization and performance studies for a wide variety of vehicles including aircraft, rockets, satellites, and interplanetary vehicles. The Software of the Year Award recognizes developers of exceptional software created for or by NASA and owned by NASA.
The team developed Optimal Trajectories by Implicit Simulation, version 4 (OTIS4), which utilizes state-of-the-art numerical integration and optimization technologies to predict how a vehicle will perform or to determine how best to fly it. Data generated by the program allows a variety of studies to be accomplished including vehicle and sub-system design trades, guidance studies, error analyses, and mission planning.
With OTIS4, users can seamlessly generate optimal trajectories and parametric vehicle designs simultaneously. Flight paths can be generated with respect to any of the major bodies in the solar system. In addition, OTIS4 can be used to solve non-aerospace continuous time optimal control problems.
OTIS4 simulates the trajectory performance of a wide variety of vehicles. Primarily a point mass, three-degree-of-freedom (3DOF) simulation program, OTIS4 has options that allow six-degree-of-freedom (6DOF) simulations. The user inputs the vehicle models; there are no embedded, vehicle-specific aerodynamic or propulsion models. OTIS4 allows progressively more detailed simulations as the vehicle and mission design advance.
OTIS4 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 OTIS4 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.” OTIS4 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.
OTIS4 offers many discrete, direct solution methods in one unified package and 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.
The software recently was used to conduct a launch abort analysis of the Orion crew exploration vehicle. Its highly generalized modeling capabilities enable developers to generate more detailed simulation as the vehicle and mission design advance without abandoning the basic simulation framework. More realistic constraints can be added and design options easily traded off to obtain insight into the final design.
Other applications within the aerospace industry include development programs for personal air vehicles, subsonic aircraft, missiles, hypersonic systems, and extraterrestrial exploration. Non-aerospace applications include performance verification and validation activities, feasibility studies, advanced missile projects, and submersible marine vehicles.
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/Linux, or Macintosh OS X.
For more information on OTIS4, and to download the program, visit otis.grc.nasa.gov .