The Center for Land Use Interpretation Newsletter

Global Positioning Pivots Around Colorado Springs


633 Schriever stands out all alone in the prairie east of town. CLUI photo

LESS CELEBRATED THAN CHEYENNE MOUNTAIN, it's Colorado Springs Cold War cousin, Schriever Air Force Base’s role may be even more significant in the enveloping electronic world. Among a host of space warfare and satellite functions at the base, Schriever is the control center for the global positioning system, the only system of its kind in the world, and a system that is increasingly vital to military and civilian infrastructure. GPS operates using the speed of light rate of electronic signals to determine the relative distance between objects. To do so it couples the most precise clocks in the world to a global network of satellites whose position is precisely monitored and measured.

For the centuries before the space age, military superiority was largely determined at sea. The invention of longitude as a ship-based navigation system, using accurate portable clocks on board ships and calculating distances relative to known celestial entities, revolutionized the ability for colonial scouts and imperial forces to discover, conquer, and control the world. The center for this global navigational system was Greenwich, England, at the seat of the ruling empire of the era. Global time, and global space (longitude) was calibrated from this point, and governed by the Royal Navy.

Due to this historic and critical foundation for timekeeping, the Navy has traditionally controlled time in the United States as well, based out of the Naval Observatory in Washington DC (which shares its grounds with the official Vice President’s residence). The nation’s “Master Clock,” regulated by the atomic decay of hydrogen, resides at the observatory, overseen by the Director of Time Service, and the Superintendent of the Naval Observatory, who is designated as the DOD Precise Time and Time Interval (PTTI) Manager.

In the past few decades however, the global systems of surveillance, communication, and navigation have steadily moved upwards, above the roiling seas, into space, borne by satellites. And in the USA, space is not the Navy’s realm, it is the Air Force’s. With the development of GPS, the Air Force finally captured some control of Time from the Navy, and now has an official atomic clock of its own, the “Alternate Master Clock.” While the calibration of the Alternate Master Clock is linked to the Navy’s Master Clock in Washington,* and its existence is often explained as being a redundant back-up of the Master Clock, it is, as official Coast Guard documents explain, “capable of independent performance” suggesting some degree of autonomy for the Air Force. And, it is located at Schriever, confirming its status as the Greenwich of the Space Age.

Since nearly all military bases in the USA have origins in or soon after WWII, Schriever, established from scratch as Falcon Air Force Station in 1983 (renamed Schriever in 1998), is quite possibly the newest major military base in the country. It was built on 3,800 acres in the rolling plains, several miles east of its parent, Petersen Air Force Base. Its original stated function was to be a back up satellite control facility for Onizuka Air Force Station, in Mountain View, California, where all DOD satellites were being controlled from at that time (from the famous “Blue Cube” building, visible next the highway, and surrounded by Lockheed’s main satellite manufacturing plant). By 1987, Schriever had control of most of the DODs satellites, including the Navstar System, the original Global Positioning Satellite network.

At all times there are at least 24 operational satellites in the GPS constellation (sometimes as many as 29), guaranteeing that at least three or four satellites are visible simultaneously from any place on earth. To control this continuously orbiting network, monitoring locations positioned around the globe (in Guam, Ascension Island, Diego Garcia, Hawaii, California, Colorado, Florida, Greenland, and the UK) send information to Schreiver’s Master Control Center. In addition to keeping track of the location of these satellites to a degree of precision measured in nanoseconds, some of these monitoring stations also upload adjusted time and location information from Schriever to the satellites. Additionally, each satellite has its own atomic clock, and all onboard clocks are centrally calibrated by the Alternate Master Clock at Schriever.

This global network of monitoring locations and earthstations, controlled by the Master Control Station at Schriever, operates instantaneously and continuously, and connects to all the satellites in the GPS constellation. As a result, each satellite knows exactly where it is at any given moment, and beams this information back to earth as a continuous stream of radio waves. These radio waves are picked up by GPS receivers the world over, whether they are on aircraft carriers, or in the hands of hikers with Garmins from Walmart. With a minimum of three separate satellite location/time streams, the GPS device does a little math to triangulate its own location relative to those “fixed” points in space. As the receiver moves, its position relative to those points is continuously recalculated, and a three dimensional picture of its position, heading, speed and altitude is formed, another object moving through space. It is all relative to, and centered in, the time/space hub of Colorado Springs, Colorado. 

* The “calibration” of time, and a global agreement of what time it really is, is determined by machines and complex diplomatic international agreements and policies involving several different time types and standards of deviation (Coordinated Universal Time, International Atomic Time, etc.) Thousands of people the world over must be involved in “global time” vocations – an international temporal bureaucracy. The machines involved are generally what are called “atomic clocks,” as they use some form of atomic oscillation to regulate them. Both of the US’s Master Clocks, at the Naval Observatory and at Schriever, use devices known as hydrogen masers, caster-mounted file-cabinet sized appliances manufactured by the Symmetricom company in Beverly, Massachusetts.