From the Editors
Public appreciation of satellite-based navigation—as embodied in the Global Positioning System—has risen dramatically since the 1991 Gulf War and even more so during Operation Enduring Freedom. Yet the history of this revolutionary system extends back more than 40 years. Many organizations—including The Aerospace Corporation—helped define its earliest goals and capabilities by evaluating, integrating, and reconciling a host of competing ideas.
Like the Internet, GPS was originally intended for military applications, but it now boasts more civilian than military users. A major challenge, then, will be to keep GPS reliable enough for civilian use yet secure enough for critical defense needs. Indeed, the increase in civil and commercial applications has made protection against disruption more vital than ever before. Continued commercial development—not to mention government sponsorship—depends on keeping the system affordable, predictable, and responsive to user needs.
Aerospace played a central role in the evolution of the GPS architecture and continues to help guide its future course. For example, Aerospace models are used to optimize the constellation, determining the best configuration for a given set of user needs. Research into atomic standards, differential techniques, and augmentation schemes helped increase overall ranging accuracy. Studies of antijamming and hybrid navigational receivers have enhanced GPS support to military missions. Studies of signal propagation and frequency allocations have helped military and commercial developers share the system responsibly. Even ancillary work in GPS-supported orbit determination has produced tangible benefits for satellite operators.
A full account of The Aerospace Corporation's involvement in satellite-based navigation is beyond the scope of this single issue of Crosslink. Nonetheless, we hope this edition will serve as a useful introduction to the company's wide-ranging work in this field.
