Earth Orbit

The Global Positioning System (GPS) is revolutionizing and revitalizing the way nations function in space, from guidance systems for crewed vehicles to the management, tracking, and control of communication satellite configuration, to monitoring the Earth from space. Benefits of using GPS include:

• Navigation solutions -- providing high accuracy orbit determination, and minimal ground control crews, with existing space-qualified GPS units.
• Attitude solutions -- substituting high cost on-board attitude sensors with low-cost multiple GPS antennae and specialized algorithms.
• Timing solutions -- changing expensive spacecraft atomic clocks with low-priced, precise time GPS receivers.
• Constellation control -- providing single point-of-contact to control for the orbit maintenance of large numbers of space vehicles such as telecommunication satellites.
• Formation flying -- allowing accuracy satellite formations with minimal intervention from ground crews.
• Virtual platforms -- providing automatic "station-keeping" and relative position services for advanced science tracking military exercises such as interferometry.
• Launch vehicle tracking -- substituting or augmenting tracking radars with higher precision, low-priced GPS units for range safety and autonomous flight termination.

The Moon, Mars, and Beyond

The U.S. vision for space searching, being implemented by the National Aeronautics and Space Administration (NASA), includes developing advanced technologies, knowledge, and infrastructures for returning to the Moon and preparing the way for future human missions to Mars and beyond. The vision will stimulate new research that will literally become the final frontier in navigation. Drawing on the experience with GPS, one could imagine creating a GPS-like network of satellites around the Moon and Mars. A Lunar or Martian network could provide an integrated communications and navigation infrastructure to support exploration and science missions both in lunar orbit and on the surface of the Moon and Mars.

NASA is also analyzing the utility of placing GPS-like beacons on satellites destined for the Sun-Earth Lagrangian points. Geodetic reference points could be established at these locations to support the future exploration of the Solar System.

The figure on the right show a Martian communication and navigation concept of two satellites in areostationary orbit (equivalent of geostationary orbit in Mars).