May 2005 
Volume 04, Issue 1 
Integrated Defense Systems

Exactly positioned

Boeing plays big role in GPS's present, future


Exactly positionedIt all began on Feb. 22, 1978, when an Atlas F rocket launch placed the Pathfinder GPS (Global Positioning System) Navstar Block I satellite in orbit. Since then the GPS program has evolved; today, its capabilities have far exceeded anyone's expectations.

Boeing has played a major role in the development and operation of the GPS constellation and is working on the next generation of GPS.

Originally intended for military navigation and precise timing use, GPS has become routine on commercial airliners, cruise ships and cars. It's used by hikers, and it even monitors the earth's fault lines.

For the military user, ongoing operations in Afghanistan and Iraq have shown the value of precision strike. GPS-guided Joint Direct Attack Munitions, built by Boeing, have forever altered tactical strike techniques with unprecedented accuracy that greatly reduces collateral damage. A single tactical aircraft can now attack multiple programmed targets in one pass, resulting in less exposure to aircrews and a higher probability of mission success.

The Boeing GPS legacy dates back to 1974 with an initial U.S. Air Force contract award for the Pathfinder and initial Block I satellites. With subsequent upgrades, the satellites gradually evolved into the Block II and IIA. The Air Force declared the system operational on Dec. 9, 1993.

The GPS constellation, defined

The GPS (Global Positioning System) constellation is made of a minimum of 24 satellites operating in six near-circular orbits at 55 degrees inclination from the equatorial plane. At a mid-earth orbit altitude of approximately 11,000 nautical miles (20,400 kilometers), the satellites orbit the earth every 12 hours, compared to about 90 minutes for low-earth orbit. This provides a slower transit speed, and positions at least four satellites above the horizon for almost any observer's location at any given moment.

Each GPS satellite transmits an accurate position and time signal, on low-power L-band, that a receiving unit can use to determine its location to within a few feet (longitude, latitude and altitude), velocity to a fraction of a mile per hour, and the precise time to one-millionth of a second.

The U.S. Air Force's 50th Space Wing's 2nd Space Operations Squadron at Schriever Air Force Base, Colo., is responsible for precise controlling and monitoring of the GPS constellation around the clock. Among the control segment tasks is the process of individually contacting all 29 satellites every 24 hours to upload the latest navigational messages for the users.

In all, Boeing built 40 Block I, II and IIA satellites at its Seal Beach, Calif., facility (then part of Rockwell International), completing the last one in 1993. Of that group, 17 are still operational and are part of the 29 satellites in the GPS constellation. All 17 have far exceeded their 7.5-year design life.

"As we make significant progress toward the launch of the IIF spacecraft and integrate it with the improved GPS ground system, we leverage our 'legacy knowledge' and experience to meet the Block II modernization needs," said John Fuller, vice president, Air Force Space Systems.

Boeing is currently under contract with the Air Force Space and Missile Systems Center to build six Block IIF satellites. In January, Boeing was awarded two contract options to initiate production of Space Vehicles (SV) 07 through 09, and to procure long-lead hardware for production of an additional three satellites, SV-10 through 12. Actual assembly, integration and test on the first SV is under way at the Boeing Satellite Development Center in El Segundo, Calif.

Designed for flexibility and growth, the IIF satellites will provide new capabilities, including improved accuracy, anti-jam capabilities, increased service life, new signals for civilian users, and secure operational military codes for the warfighter. Currently Boeing Delta II rockets are launching Lockheed Martin Block IIR satellites to replenish the constellation. This series will be followed by the first Boeing IIF launch in 2007.

Next-generation GPS III

In January 2004, Boeing was one of two competing industry teams awarded a next-generation GPS III Phase A study. Under the contract agreement, the Boeing GPS III global team will perform a 24-month Systems Requirement Review Phase A study to assess mission needs and requirements, and evaluate innovative architecture recommendations.

"With GPS III we are charting a course to help the Air Force define the way the military operates over the next 30 years," said Mike Rizzo, director of Navigation Systems for Air Force Space Systems.


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