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

(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 radio positioning/navigation (POS/NAV) system that provides extremely accurate, three dimensional, common grid position, velocity and time of day information to users anywhere on or near the earth.  The system uses a constellation of 24 satellites which provides navigation data to both military and civilian users worldwide. The system provides reliable and accurate passive worldwide positioning, navigation, and timing information in all weather conditions, in real time, using a common grid reference system.  

(U)  The BLOCK IIF satellites are the third series of operational satellites being developed.

(U) The Block IIF Program incorporates current and leading edge technology to sustain the GPS utility for military and commercial use. The IIF contract allows the Air Force to purchase 33 satellites.  The Block IIF system allows affordable technology insertion and block upgrades, while  emphasizing compatibility and  interoperability with the current space vehicles, ground control system, and user equipment.   The system will interface with the new GPS Operational Control System (OCS) architecture currently under  development, and with the Air Force Satellite Control Network (AFSCN).

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 mile) 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 a10.23 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)  The Block IIF Program incorporates current and leading edge technology to sustain the GPS utility for military and commercial use. 

(U)  The Block IIF system allows affordable technology insertion and block upgrades, while emphasizing compatibility and interoperability with the current space vehicles, ground control system, and user equipment. The system will interface with the new GPS Operational Control System (OCS) architecture currently under development, and with the Air Force Satellite Control Network (AFSCN).

(U)  The Air Force will use the Evolved Expendable Launch Vehicle (EELV) as the booster to place these satellites in orbit.

(U)  The requirement to maintain a worldwide navigation service provided by a 24 satellite constellation for military and civilian users drives the Block IIF program. 

(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.

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) Programmed.
	(U) IOC: 10/2001 (1QFY2002).
		(U)  Contract Award - 3QFY96
(U)  System Design Review - 4QFY96
(U)  Preliminary Design Review - 2QFY97
(U)  Final Design - 1QFY98
(U)  First Delivery - 3QFY01
(U)  First Launch - 1QFY02
	(U) FOC: 04/2003 (3QFY2003).

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, Space-Based Warning

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)
18 May 1998

(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).)