National Aeronautics
and Space Administration

What is GPS?

The Global Positioning System (GPS) is a space-based radionavigation system, owned by the
U.S. Government and operated by the United States Air Force (USAF). It can pinpoint a three
dimensional position to meter-level accuracy and time to the 10-nanosecond level, worldwide
and 24/7. GPS is comprised of three different segments: the space segment, control segment
and user segment.

GPS has its origins in the Sputnik era when scientists were able to track the satellite with shifts in its
radio signal, known as the “Doppler Effect,” which became the foundational idea for modern GPS.
Today the GPS satellite constellation (the space segment) consists of over 30 operational satellites,
each equipped with redundant atomic clocks and tracked by a ground control network (the control
segment). Each satellite transmits its position and time at regular intervals and those signals are
SQ intercepted by GPS receivers (the user segment). The receiver is able to determine its position by
SS calculating how long it took for the signals to reach it.

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NASA's mission to pioneer the future in space exploration, scientific discovery and
aeronautics research necessitates the proactive development and implementation of a
number of GPS applications toenable greater spacecraft autonomy and more advanced
space science and Earth monitoring applications. To accomplish this, NASA works
alongside the USAF to continue improving GPS capabilities to support space operation
and science applications.



— GPS and NASA

Defining the “N” in Spacecraft Orbit and Trajectory Determination: Traditionally, space missions have determined their orbit by using commu-
nications channel tracking, in which a Flight Dynamics Facility uses positioning information from two-way communication

Space Communications signals between the spacecraft and a ground station or relay satellite to calculate the spacecraft’s orbit. Alternatively,
F . missions that choose to use GPS to determine their position track radionavigation signals from GPS satellites and process

and Navigation these signals on-board to determine position and time. This increases spacecraft autonomy, enables new methods of

spaceflight operations and reduces the burden on NASA's tracking stations.
The Policy and Strategic Communications Division

within the Space Communications and Navigation Science Applications: GPS is used as a remote sensing tool to support atmospheric and ionospheric sciences, geodesy
(SCaN) Program Office at NASA manages and and geodynamics — from monitoring sea levels and ice melt to measuring the Earth’s gravity field. SCaN and NASA's
protects NASA‘s GPS equities through policy Science Mission Directorate have partnered to improve the performance of the GPS constellation through policy advocacy
development and advocacy. SCaN protects legacy for modernization improvements via the GPS requirements process, the National Space-based Positioning, Navigation,
GPS application investments while enabling new, and Timing (PNT) Executive Committee and the National Space-based PNT Advisory Board.

improved techniques to be implemented by

missions. GPS Receiver Development: NASA has developed, and continues to improve, GPS flight and science receivers that are

already in use.

Benefits of GPS to Users in High Earth Orbit |= The Future of GPS To Learn More, Visit:

© Significantly improves real-time navigation performance from Worldwide government and commercial spacecraft launch https://www.nasa.gov/directorates/heo/
km-class to meter-class projections over the next two decades show that approximate- scan/communications/policy/

Supports quick trajectory maneuver recovery from 5-10 hours ly 60 percent of future missions will operate in low-Earth orbit

to minutes and 95 percent of missions will operate at or below geosyn.

Timing capabilities reduce a spacecraft's need for expensive chronous orbit. NASA will continue to protect current invest- Follow @NASASCaN

on-board clocks ments and improve upon existing capabilities by working

© Supports increased satellite autonomy, lowering mission alongside other U.S. Government agencies and pursuing

operations costs compatibility and interoperability with other Global Navigation

¢ Enables new and enhanced capabilities and better performance Satellite System (GNSS) constellations.

for users in high-Earth orbit and Cislunar space

nasa.gov