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	Director, Operational Test & Evaluation
	FY98 Annual Report

SYSTEM DESCRIPTION & CONTRIBUTION TO JOINT VISION 2010

The NAVSTAR Global Positioning System (GPS) is a 24-satellite constellation that provides highly accurate, real-time, all-weather, passive, common-reference grid position and time information to military and civilian users worldwide. GPS enables the military forces to precisely determine their position, velocity and time to: (1) enhance command and control and coordinate battle tactics and support; (2) engage in strategic and tactical warfare; (3) maneuver efficiently on the battlefield; (4) provide accurate and timely fire support; and (5) facilitate combat service support operations. In addition, knowledge of exact position and time is essential for reconnaissance and intelligence missions. GPS provides the precision, velocity, and time element of information superiority, and it serves as the cornerstone of the warfighter's ability to execute the Joint Vision 2010 concept of precision engagement.

GPS is an Air Force-managed Joint Service program and comprises three segments: space, control, and user equipment. The space segment consists of 24 satellites in semi-synchronous orbits around the earth. The original Block I satellites were replaced with Block II/IIA satellites. Currently, Block II/IIA satellites are being replaced with Block IIR as the II/IIA satellites fail on-orbit. The control segment consists of a master control station, four ground antennas, a pre-launch capability station, and five geographically dispersed monitoring stations. The control segment monitors satellite downlink signals and uploads corrections to diminish errors broadcast to users. The user segment consists of numerous forms of GPS receivers that use satellite downlink signals to determine position, velocity, and precise time. These receivers are hosted on a multitude of platforms and are classified into three general categories: high-dynamic sets (5+ channels); medium-dynamic sets (2 channels); and low-dynamic sets (usually single channel). The 5-channel sets are used primarily by the Air Force and Navy on aircraft, ships, and submarines. The 2-channel sets are used mainly by the Army in heliborne configurations. The single-channel sets are generally used in hand-held applications.

DoD approved the NAVSTAR GPS program in December 1973. Full-scale development began in June 1979. By 1985, the Joint Program Office had launched ten Block I satellites and developed the associated ground-control system software to support system test and checkout. The first production satellite launched successfully in February 1989. The Block I satellites were followed by 27 Block II/IIA satellites launches. IOC, which included the control segment, was declared on December 8, 1993.

The first Block IIR satellite was destroyed during launch when its Delta rocket exploded just after lift-off on January 17, 1997. The first successful launch of a Block IIR satellite was July 22, 1997, from Cape Canaveral Air Force Station, FL. The GPS IIR satellites provide the same functionality as earlier satellites, with added capabilities requiring less man-in-the-loop monitoring for on-orbit operations. There are 19 additional Block IIR launches planned. Block IIF satellites are under development, with the first IIF satellite launch planned for 2002, and are planned as functional equivalents to the current GPS IIR satellites to sustain the GPS constellation through 2010.

GPS user equipment development began in June 1979 with receiver testing (using Block I satellites) in a variety of land, sea, and air vehicles. Since then, numerous versions of single-, 2-, and 5-channel receivers have undergone development and fielding. GPS user equipment achieved full-rate production approval in January 1992. Full operational capability was declared in November 1995 after completion of Phase III IOT&E.

Space and control segment testing occurred in three phases. The Phase I IOT&E was conducted from 1989 to1990; Phase II IOT&E from 1990 to 1992; and Phase III from 1992 to 1994. Each test phase was successful and led progressively to an approved final operational capability, with a complete 24-satellite configuration. The Block IIA satellite constellation and ground system completed all operational test activities in prior years and are fully operational. There was no OT of these satellites or their control function during FY98.

The GPS TEMP was scheduled to be updated by February 1998, to cover test activities for GPS IIR and IIF satellites. However, it has not been completed or forwarded to DOT&E for final OSD review. This is a continuing item of concern for DOT&E, and has been raised as an indication of potentially significant problems during recent program reviews.

An OA originally scheduled to begin in January 1997, was delayed because of the launch failure of the first Block IIR satellite. The OA was conducted from July 23-28, 1998, after successful launch of the first IIR satellite. Although the IIR satellite met all navigation and timing requirements, a significant problem with the improved cross-link system of the GPS IIR satellite was uncovered. During the OA by AFOTEC, it was discovered that spurious radio frequency interference/noise was being sensed by the new cross-link system of the GPS IIR satellite. All GPS IIR launches were postponed until the problem was identified and a solution found. The next IIR launch is planned for 2QFY99, and a full evaluation of the solution is planned prior to any follow-on GPS IIR launches. Final OT&E for the GPS IIR satellites requires a minimum of five GPS IIR satellites on-orbit to fully test all features of the improved GPS IIR cross-link, and is planned for February-November 2000.

It is premature to report a final determination of the effectiveness and suitability of the Block IIR satellites. However, the successfully launched Block IIR satellite is performing it's navigation mission without any reported problems. The excessive in-band noise interference found during OT renders the GPS IIR satellites unable to perform required cross-ink functions. The basis for the cross-link problem is an inadequate understanding of the "real" on-orbit environment and the amount of radio interference "noise" from earthly sources. While there were pre-launch interference issues, all indications prior to launch of the first GPS IIR satellite suggested that "on-orbit" noise strength would not cause problems. The Air Force has a proposed a solution that is still undergoing final testing, and appears adequate to solve the cross-link problem.

The Block IIR initial operational test and assessment of the Block IIR portion of the GPS constellation is scheduled for 2000. This is based on a projected launch rate of four satellites per year and implementation of full functionality, including the auto-navigation capability, with a fully functional GPS IIR cross-link. Based on the history of the GPS program, the results of the OA, and the efforts to correct the interference problem, DOT&E believes that the Program Office is progressing toward fielding an effective and suitable system.

The follow-on Block IIF satellites are currently in production and scheduled for first launch in 2002. An OA of the space and control segment will take place with the first successful launch of a Block IIF satellite. An IOT&E of a partial constellation (minimum of 5-6 satellites) will occur in the 2003-2004 time frame.

Successful ground testing of flight hardware requires thorough Hardware-in-the-Loop testing under the proper set of conditions to assure valid results. While the core GPS functions-navigation and timing-are performing adequately, the enhanced capabilities of GPS IIR satellites require a fully functional cross-link. The initial setbacks for the GPS IIR cross-link indicate that there are still significant holes in our understanding of the space environment. Prior to implementing similar improvements to the GPS IIF satellites as part of GPS Modernization, DoD should ensure that each initiative is clearly understood, and that the potential impacts of the space environment are understood as well.