selected to provide 28 Block II (operational) Navstar GPS satellites.  Development of the

satellites continued throughout Phase II.

Phase II for the User Segment was divided into two parts.  In Phase IIA, starting in July 1979,

four contractors were selected to conduct performance analyses and preliminary design of UE.  In

Phase IIB, starting in 1982, two of the four contractors were selected to continue UE

development.  Phase IIB included design refinement, fabrication of prototypes, qualification

testing, and extensive field testing of the UE. The UE was tested at YPG and at sea.  Testing at

sea was conducted by Naval Ocean Systems Center located in San Diego, California.

1.6.4  Phase III   Production and Deployment (1986 to Present)

1.6.4.1  Space Segment (1986 to Present)

The Block II satellites were originally designed to be launched aboard the Space Transportation

System (Space Shuttle).  Following an accident with the Space Shuttle Challenger in 1986, the

Block II satellite to launch vehicle interface was modified to enable launch aboard the Delta II

booster.  The first Block II satellite was launched on 14 February 1989.  The combined

constellation of Block I and Block II satellites achieved worldwide two dimensional positioning

capability in June 1991.  Worldwide 3 D capability was achieved in 1993.  The Initial Operational

Capability (IOC) was declared on 8 December 1993.  A full 24 satellite constellation of Block II

satellites was achieved in April 1994.  The military Full Operational Capability is planned for

1995.  The remaining Block II satellites will be launched on demand.  Table 1 2 is a summary of

the Block II launch dates and status.

In June of 1989 a contract was awarded for 20 GPS replenishment satellites, designated Block

IIR.  The Block IIR satellites will have the capability to autonomously generate their own

navigation messages.  The Block IIR production schedule may allow a first launch as early as

August 1996.  In 1994, efforts were begun by the GPS JPO to procure additional Navstar

satellites to sustain the GPS satellite constellation past the year 2000.  These satellites are

designated Block IIF (Follow On).  The contract to provide the Block IIF satellites is planned for

November 1995.  The planned production schedule supports a first launch in the year 2001.

In 1994 the GPS JPO also began studies for an Augmented GPS (AGPS).  The AGPS concept is

to enhance the availability, accuracy and integrity of the GPS system using up to six geostationary

AGPS satellites.  The satellites would broadcast integrity information and range corrections for all

GPS satellites via GPS like ranging signals.

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