(U) NAVSTAR Global Positioning System(GPS) Block IIA

(The effects of any budget/program decisions made since the information was collected during 1997-98 are NOT reflected in the National Security Space Road Map (NSSRM).)

Overview: (U)
(U)  NAVSTAR Global Positioning System (GPS) is a satellite-based positioning system using a constellation of 24 satellites which provides navigation data to both military and civilian users worldwide. The system will provide reliable and accurate passive worldwide positioning, navigation, and timing information in all weather conditions, in real time, using a common grid reference system.   The BLOCK II/IIA satellites, SVNs 13 through 40, are the second series of operational satellites developed by Rockwell International, (now Boeing North American, Inc.).

Description: (U)
(U)  The Space Segment is an earth-orbiting constellation of 24 NAVSTAR satellites in six planes. The nominal circular orbit has a  20,200 kilometer (10,900 nautical miles) altitude and the orbits are inclined at an angle of 55 degrees with a 12-hour period. The spacing of satellites in their orbital planes are arranged such that a minimum of four satellites will be in view everywhere on and near the surface of the earth at any time. Each NAVSTAR satellite is designed to broadcast a pair of L-band radio frequency (RF) signals, known as Link 1 (L1 = 1575.42 MHz) and Link 2 (L2 = 1227.6 MHz). The L1 signal carries a precision ranging code and coarse / acquisition code,  while L2 carries only the precise ranging code. The signals are broadcast using spread spectrum techniques, employing two different spreading functions: a 1.023 MHz coarse / acquisition (C/A) code on L1 only and a 10.23 MHz precision (P) code on both L1 and L2. The minimum signal power for the different signals at a GPS receiver are: L1 C/A = -160 dBW; L1 P = -163 dBW; and for L2 P = -166 dBW. Superimposed on these codes are low-rate navigation message data, including satellite clock and ephemeris parameters, satellite signal health data, and Coordinated Universal Time (UTC) synchronization information. 

(U)  Block II SVs were built by Rockwell International. The first of 28 Block II SVs, SV PRN number 14, was launched on 14 February 1989 from Cape Canaveral AFS, FL using a Delta II MLV and was set "healthy" in its broadcast 50 Hz navigation message for global use on 14 April 1989. The last Block IIA is forecast to be launched on 5 November 1997.

(U)  Significant Block II SV enhancements to the signal-in-space (SIS) interface were: 

 -- (U)  Radiation hardened electronics to prevent random memory upset events to improve SIS reliability and survivability. 
 -- (U)  Capacity to store 180 days worth of 50 Hz navigation message data, compared to only 3.5 days worth of storage in the Block I SVs, to guarantee SIS availability. 
 -- (U)  Full selective availability (SA) and anti-spoof (A-S) capabilities to provide for SIS security. 
 -- (U)  Automatic detection of certain error conditions and switching to non-standard PRN Code transmission or default navigation message data (alternating ones and zeros) to protect users from tracking a faulty SV and maximize SIS integrity. 

(U)  The GPS control or ground segment consists of five unmanned monitor stations located around the world (Hawaii; Kwajalein in the Pacific Ocean; Diego Garcia in the Indian Ocean; Ascension Island in the Atlantic Ocean; and Colorado Springs, Colorado); a master ground station at Schriever Air Force Base in Colorado Springs, Colorado; and four large ground antenna stations that broadcast signals to the satellites. The stations also track and monitor the GPS satellites.

(U)  On 5 November 1997, the 28th and final launch of a GPS Block IIA satellite was accomplished.  A Boeing Delta II booster launched the satellite from Cape Canaveral into a 10,993 X 100 nm transfer obit inclined 35 degrees.  The spacecraft's apogee kick motor later placed the satellite into its 11,000 nm operational orbit. 

User Impact: (U)
(U)  GPS provides an all-weather, global, protected (encrypted) navigation signal to all DoD users and allies.  The signal provides positioning accuracy's to about 7m 50 percentile spherical error probable and a timing signal for DoD communications and command and control systems to a precision of <100ns dual root mean square.  GPS receivers vary in capability and performance but are being integrated into many operational systems at costs under $3,000/platform

Programmatics: (U)
(U) Operational.
	(U) IOC: 10/1995 (1QFY1996).
	(U) FOC: 04/1998 (3QFY1998).
	(U) Termination: 01/2001 (2QFY2001).
		(U)  The 01/01/2001 termination date is an approximate date used to show the follow-on relationship between NAVSTAR GPS Block IIA and NAVSTAR GPS Block IIR.

Related Initiatives: (U)
(U) 3A Airborne Receiver, 3S Shipborne Receiver, Arnold Engineer Dev Cntr (AEDC), Combat Survivor Evader Locator, CRPA/AE-1, Defense Advanced GPS Receiver, Delta II, Eastern Range, Embedded GPS Inertial Nav. Sys., FRPA./AE-4, GAS-1 CRPA/AE, GPS Block IIR, GPS Receiver Applications Module, GPS VME Receiver Card (GVRC), Miniature Airborne GPS Rec. 2000, Miniaturized Airborne GPS Rec., Precision Lightweight GPS Rec.

Related Requirements: (U)
(U) None.

Related Categories: (U)
(U) Navigation, Satellite Operations, Space Systems

Road Map Placements: (U)
(U) Major DoD Space Programs, National Security Space Road Map, NAVIGATION.

Lead Office: (U)
(U) Air Force.

Date of Information: (U)
15 November 1997

(The effects of any budget/program decisions made since the information was collected during 1997-98 are NOT reflected in the National Security Space Road Map (NSSRM).)