Exploring the Cosmos Starts Here: Simulate with GMAT

The ability to simulate and analyze satellite or spacecraft missions before they ever leave the ground is one of the most powerful tools in modern aerospace engineering. Among the most accessible and capable tools for this purpose is NASA’s GMAT — the General Mission Analysis Tool.

Developed by NASA’s Goddard Space Flight Center, GMAT is a free and open-source platform for designing and simulating space missions. It has been used in real-world missions such as LCROSS (Lunar Crater Observation and Sensing Satellite) and the Lunar Reconnaissance Orbiter.

This article offers a high-level overview of what GMAT can do, followed by a hands-on walkthrough of a simple satellite orbit simulation. The aim is to introduce the software's utility in a way that is accessible even to those without prior experience.

What is GMAT?

GMAT is a space mission analysis and trajectory optimization tool. It allows users to simulate spacecraft motion under a variety of physical forces including gravity, atmospheric drag, and solar radiation. Its most widely used feature is the Orbit Simulator Tool, which models orbital dynamics and provides visual and data-driven insights into mission behavior.

The software includes both a graphical interface for quick configuration and a powerful scripting language for more complex simulations. It is suitable for educational, research, and operational use.

Key Capabilities of the Orbit Simulator Tool

• Design and simulate spacecraft orbits around Earth, the Moon, or interplanetary bodies.

• Model real-world forces such as atmospheric drag, solar pressure, and multi-body gravitational effects.

• Visualize satellite orbits in 2D and 3D views.

• Define ground stations and analyze ground tracks and revisit times.

• Plan orbital maneuvers and evaluate propulsion needs.

• Generate detailed reports on spacecraft state and mission events.

Real-World Application Example

Let’s consider a common scenario in satellite mission design: deploying a satellite into low Earth orbit (LEO) for Earth observation. This mission requires precise planning to determine the satellite’s altitude, inclination, and ground coverage.

Problem Statement

You are developing a 700 km altitude Earth observation satellite and need to simulate its orbit, calculate the revisit time, and evaluate its Earth coverage.

How GMAT Can Help

Using GMAT, you can define the satellite’s orbital parameters, simulate its motion for 24 hours, visualize its orbit and ground track, and generate data to understand how frequently it passes over different regions.

Below is a simplified visual representation of a 700 km circular orbit around Earth:

This circular orbit, commonly used in remote sensing, provides near-polar coverage when configured with an inclination around 98 degrees, making it suitable for global observation.

Step-by-Step Tutorial: Simulating a Low Earth Orbit Satellite

1. Install GMAT

Download GMAT from https://software.nasa.gov/software/GSC-17177-1 and install it on your system.

2. Create a New Mission

Open GMAT and start a new mission. You’ll work within the Mission Tree workspace.

3. Add and Configure the Satellite

• Add a new spacecraft named LEOSat.

• Set the orbit to:

  • Semi-major axis: 7071 km (6371 km Earth radius + 700 km altitude)

  • Eccentricity: 0 (for a circular orbit)

  • Inclination: 98 degrees

  • Other values (RAAN, Argument of Periapsis, True Anomaly): leave at 0 or defaults

4. Set Up the Mission Sequence

• Add a Propagate command to simulate the satellite motion.

• Set the propagation duration to one day (ElapsedDays = 1).

• Add OrbitView to visualize the orbit.

• Add a Report command to log state vectors (position, velocity, time).

5. Run the Simulation

Click “Run” to execute the simulation. You’ll see:

• The satellite orbiting Earth in the OrbitView window.

• A log file with data such as position, velocity, altitude, and time.

6. Add Ground Track Visualization (Optional)

To visualize the satellite’s movement over Earth’s surface:

• Add a GroundTrackPlot.

• Assign the satellite and Earth as the primary bodies.

• Run the simulation again to see ground coverage.

What You Can Learn from This Simulation

• How different orbital parameters affect satellite motion and Earth coverage.

• How frequently the satellite revisits the same location.

• How to visualize and extract mission-critical data using GMAT tools.

Final Thoughts

GMAT’s Orbit Simulator Tool is more than just a visualizer—it's a mission design environment. It empowers users to test concepts, evaluate performance, and troubleshoot before a single piece of hardware is launched. From students exploring orbital mechanics to professionals working on mission design, GMAT offers a bridge between theory and real-world application.