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GMAT System Overview

Matthew Wilkins, Schafer Corporation

Moriba Jah, AFRL Maui

Steve Hughes, NASA Goddard

Darrel Conway, Thinking Systems Inc.

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What is GMAT?

• The General Mission Analysis Tool (GMAT) is a space trajectory optimization and

mission analysis system developed by NASA, AFRL ASTRIA, and private industry

in the spirit of the NASA Vision

• GMAT contains new technology and is a test-bed for future technology

development.

• To satisfy NASA’s mandate and maximize technology transfer, GMAT is an open

source software system licensed under the NASA Open Source Agreement

• GMAT is written to run on Windows, Linux and Macintosh platforms, using the

wxWidgets cross platform UI Framework

• GMAT can be built using either commercial development tools or the GNU

Compiler Collection (gcc)

• The system is implemented in C++ using an Object Oriented methodology

• Extensive documentation is available

– architectural design

– mathematical models and algorithms

– testing procedures

– system interfaces

– GMAT tutorials

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GMAT Mission and Vision

• Put simply, the goal of the GMAT project is to:

– Develop new space trajectory optimization and mission design

technology

– To work inclusively with ordinary people, universities, businesses,

and other government organizations

– To share that technology in an open and unhindered way

• GMAT is a free and open source software system:

– Free for anyone to use in development of new mission concepts

– Free to improve current missions

– Freely available in source code form for enhancement or further

technology development

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Motivation Behind GMAT

• Reduce cost of mission design technology development by

amortizing over a large portion of the space community

• GMAT would serve as a platform to develop, test, verify, and

transfer new technologies

• Provide a software architecture and design paradigm that more

efficiently accommodates new and changing operational and

mission requirements

• Provide a platform for transitioning new technology from the

research environment to the operational environment

• Provides a system in which mathematical models, architecture,

and design are open for inspection by all users and are held to a

rigorous validation and verification protocol

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GMAT Mission Tree

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GMAT User Interfaces

% -------------------------------------------

% Configure Resources

% -------------------------------------------

Create Spacecraft sat1

sat1 .SMA = 10000.0

sat1 .ECC = 0.25

sat1 .INC = 78.5

sat1 . RAAN = 45

Create ForceModel fm

fm. PrimaryBodies = { Earth }

fm. PointMasses = {Luna , Sun}

Create Propagator prop

prop .FM = fm

Create XYPlot posvel

posvel . IndVar = sat1 .X

posvel .Add = sat1 .VX

posvel .Add = sat1 .VY

posvel .Add = sat1 .VZ

% -------------------------------------------

% The Mission Control Sequence

% -------------------------------------------

While sat1 . ElapsedDays < 7

Propagate prop ( sat1 )

EndWhile

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Design Criteria

• User Extensibility

– Provide a tool that allows users to try new components and models without

rebuilding the tool from scratch.

• Formation Modeling

– Provide a tool that can treat collections of resident space objects as single

entities making the modeling of formations and constellations more streamlined

• Parallel Processing Capabilities

– Provide a tool that will enable the parallelization of tasks across multiple

processors, either within a single computing node or across a network of

computers.

• MATLAB Accessibility

– Provide a tool that allows users to develop new algorithms and prototype code

within MATLAB that can be easily integrated into the exisiting framework

• Open Source Availability

– This redistribution requirement drives the selection of external libraries and

packages used by GMAT

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Design Approach

• Modularity

– Designed to be implemented as a “divide and conquer” approach that uses simple components that combine to

satisfy the needs of the system

– Modularity keeps the individual components simple and simplifies the addition of new components

– Each category of resources has a well defined set of interfaces and all new components are derivatives of the

core functionality

• Loose Coupling

– The modularity of the components in GMAT are implemented to facilitate “plug and play” capability for the

components that allows them to be combined easily using a set of common interfaces

– Components built in the system have simple interfaces to be able to communicate with MATLAB and with one

another

– Dependencies and circular dependencies between components are minimized

• Late Binding

– GMAT is designed to support running of multiple instances of a mission simultaneously in order to satisfy

parallel processing requirements

– This capability is built into the system by separating the configuration of the components used in the mission

from the objects used during execution

– Configured objects are copied into the running area (i.e. the Sandbox) and then connected together to execute

the mission

• Generic Access

– GMAT components share a common base class that enforces a set of access methods that are used to serialize

the components facilitating both file level read and write access to the components and simplifying

communications with MATLAB and other external tools

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Key Elements of the GMAT Engine

• Moderator

– Singleton (only one allowed to exist)

– Controls the program flow in the Engine

• Factory Manager

– Singleton

– Responsible for the creation of objects and the Mission Control Sequence commands used in the flight

dynamics model

• Configuration Manager

– Singleton

– Stores and Retrieves user objects created by the Factory Manager

• Publisher

– Singleton

– Passes data generated during a run to the Subscribers that present these data to the users.

• Sandbox

– Multiple copies allowed

– The component that manages initialization and execution of the Mission Control Sequence when a

mission is run.

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GMAT Subsystem Interactions

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Sample Lissajous Trajectory

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Sample Lunar Transfer

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Sample Mars B-plane Targeting

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GMAT OD System Level View

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High Fidelity Modeling in GMAT

• All integration performed in the Earth’s Mean Equator and

Equinox of J2000 coordinate system

• Variety of integrators

• Variety of central bodies (Earth, Moon, Mars, etc)

• Non-spherical gravity fields (Earth Tide Models coming soon)

• Variety of atmospheric density models (e.g. Jacchia 77,

NRLMSISE-00, Russian GOST)

• High high fidelity visualization

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GMAT Participation and Collaboration

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GMAT Project Status

• Software currently is mature and thoroughly tested

• Currently in beta release

• Full release anticipated September 2009

• Has been used for operational missions but solutions were

independently verified with current operational software

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