Methods as old as navigation itself combine with 21st century technologies to provide guidance, navigation and control for the International Space Station.
The ISS finds its way in the dark of space by using two independent, hardware and software-based tools: Russia's Motion Control System and the US's Guidance, Navigation and Control system.
The two systems continuously exchange data for redundancy and comparison tests. They are complementary except for propulsion, which is provided by the Russians. The Russian system is also generally responsible for Guidance, which constitutes telling the ISS which route to follow from point A to point B.
The Navigation portion of the U.S. Guidance, Navigation and Control system primarily relies on Global Positioning System (commercially known as GPS) data to determine ISS position, velocity and attitude. Russia's GPS counterpart, the Global Navigational Satellite System (GLONASS), provides data to Russia's Motion Control System.
Attitude data is also drawn from two sets of three U.S. ring laser gyros called "rate gyro assemblies." These use variations in laser light beam lengths to sense attitude change and the rate at which it is occurring. The data they produce is used to supplement GPS data.
In addition to the hi-tech approach, Russia's system determines the ISS's attitude by tracking the stars and the sun, and by gauging the horizon -- time tested navigation techniques that will still be in use when humans first land on Mars.
To learn more about these topics, please refer to the Guidance, Navigation and Control (PDF) and the Control Moment Gyroscope (PDF) overviews.
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