1. Military Use of GPS

2. Overview
Navigation Mission
GPS Segments
FBCB2
Summary

3. - Worldwide Navigation Mission - Any weather - 24 Hours/day
Provide precise position, velocity, and time to users:
- Worldwide
- Any weather
- 24 Hours/day

4. System Segments
Space
Segment
User Segment
Control Segment

5. Space Segment Block IIA - 7 1/2 year design life
Block IIR - 10 year design life
Launched by Delta II from Cape Canaveral

6. Space Segment 24 satellites in constellation
6 orbital planes, 4 satellites in each plane
55 degree orbit inclination
Semisynchronous orbit
12 hour period
12,500 statute miles (10,900 nm) altitude
Constellation maximizes 3-D coverage
Ensures at least four satellites are visible to user anywhere in the world (usually 6-7 visible)

7. Space Segment (Constellation Phasing)
The GPS constellation is designed to provide 24 hour coverage with graceful degradation.

8. Monitor Stations & Ground Antennas
Cape
Canaveral
Colorado
Springs
Kwajalein
Hawaii
Diego
Garcia
Ascension
Island
5 Ground Antennas
Receive/send TT&C
Update NAV message and atomic clocks
5 Monitor Stations
Collect measurements from GPS satellites in view

9. The User Segment
Authorized Users: Military personnel, military systems, designated allies, and other authorized users
Non-Authorized Users: Civilians and commercial firms around the world. Civilian and commercial users of GPS greatly outnumber those of the military, and the system is transitioning to allow Non-Authorized users greater accuracy.

10. GPS Services Standard Positioning Service (SPS)
PLGR
Standard Positioning Service (SPS)
Intended for Non-Authorized Users
Provides decreased location and timing accuracy
Horizontal position within 100m or better (95%)
Timing accuracy within 340ns of UTC (95%)
Actual error based on current DoD Policy
Corrupts navigation signal by two methods
Epsilon: changes the satellites position
Dither: changes the satellites time
Precise Positioning Service (PPS)
Intended for Authorized (military) users
Provides very precise location and time accuracy
3-D position within 16m Spherical Error Probability (50%)
Timing accuracy within 100ns of UTC
PPS is controlled by special crytographic keys
TRIMPACK 46

11. Military GPS Receivers
Small Lightweight GPS Receiver (“Slugger”)
Most Models SPS
Used during Desert Storm
Precise Lightweight GPS Receiver (“Plugger”)
Standard Handheld Unit
PPS Capable
Miniature Airborne GPS Receiver
Standard Aircraft Unit
SLGR
MAGR
PLGR

12. Force XXI Battle Command Brigade and Below (FBCB2) Overview
Description:
Forms the principal Digital Command and Control System for the Army at Brigade and Below
Consists of hardware and software integrated into the various platforms at brigade and below, as well as appropriate Division and Corps slices necessary to support brigade operations
Interconnects platforms through a communications infrastructure called the Tactical Internet consisting of existing EPLRS and SINCGARS Radio nets to pass Situation Awareness data and conduct Command and Control
2179 FBCB2 Systems
Fielded to 4th for FDD

13. ONE PLATFORM’S WORTH OF FBCB2
DIGITAL COMPONENTS SUPPORTING SITUATIONAL AWARENESS
AND COMMAND AND CONTROL
PLGR GPS
GPS feeds directly into the FBCB2 computer thus giving precise locations to the user at all times. Because the GPS is completely integrated, the user can actively navigate off of the computer screen map. The GPS also provides a precise location for the user’s icon - generated by the FBCB2 hardware/software.
Hardware/Software
The FBCB2 hardware and software combine to provide the user with an integrated GIS system. The system allows users to manipulate map data, satellite photography, and digital elevation models. It also incorporates message capability. A key element of FBCB2 is Situational Awareness (SA). The software generates icons depicting actual units, vehicles, or soldiers deployed in the field.
EPLRS VHSIC
SINCGARS SIP/INC
Radios (Single Channel Ground Airborne Radio System and the Enhanced Position Location Radio System) interlink multiple FBCB2s to form a larger network. This associated radio network enables the SA to be transmitted and shared between platforms and command posts.

14. Common Message Functions (Create/Edit/Send/Manage)
Pull down menus allow the user to send various reports or build graphical overlays. When a report is sent, such as a Contact Report, the software automatically updates all other computers in the network with an enemy icon . Similarly, a commander can build a set of graphics depicting unit boundaries, friendly unit locations, known enemy locations, etc and quickly distribute this overlay around the battlefield.
Sending a message automatically updates all other FBCB2s in the network.

15. Combat Messages Spot Report
This sample report provides details pertaining to an enemy unit. Once again, information is automatically shared with all others.
Enemy location can be quickly entered by clicking the mouse cursor on the computer map where it is located.

16. Advantages and Disadvantages of GPS
Limitations
Advantages
All-weather
Day and night
Worldwide direct downlink
Passive
Common grid
Restricted access
Survivable
Provides 3-D position and velocity
Dependent on ground stations
Jammable signal
Line of Sight from GPS satellites
GPS is there when you need it, in all types of weather, 24 hours a day.
It is worldwide; the signal is sent directly from the satellite.
Because the system is completely passive, the unit receiving the global broadcast does not radiate and, therefore, is not susceptible to detection.
Each receiver set can be set to apply many different datums or grids (a datum or grid is a map type).
Sometimes 2 different map types will have slightly different coordinates.
By using GPS to specify the correct datum or grid, those minor “coordinate differences” can be resolved.
A GPS receiver can be used to translate coordinates from one datum or grid to another.
It also will coordinate time for all units involved in an operation, allowing coordinated attacks.
Because access is restricted, only those individuals or units with access can use it.
The GPS constellation is planned for graceful degradation even if the ground segments are taken out.
Graceful degradation means that if for any reason the constellation cannot be commanded, the navigation accuracy will worsen slowly over the course of time - it will not be lost immediately.
A Block II vehicle will degrade over 14 days.
A Block IIA vehicle will degrade over 67 days.
Provides the best position and velocity information available.

17. Summary GPS offers many advantages for navigation
The GPS system consists of a Space Segment, a Ground Segment, and a User Segment
Selective Availability ensures Authorized users can receive a highly accurate GPS signal while Non-Authorized users (potential adversaries) can be given a degraded signal
The most common military GPS receiver is the PLGR, but many other receivers exist as well.
GPS is evolving from a standalone capability into an integrated system called FBCB2.
FBCB2 integrates GPS and a militarized GIS program to give commanders and soldiers increased situational awareness
The three missions of GPS
Navigation -- provides precise position, velocity, and time to users.
Time transfer -- allows user to calculate time.
NUDET Detection -- provides worldwide NUDET detection surveillance.
Navigation Theory.
C/A Code
Code repeats itself every millisecond (1 MHz bit rate).
Easy to acquire, assists in acquiring P-Code.
Less complex, but no protection measures.
Normally only transmitted on L1.
P-Code.
Code repeats itself every week (10 MHz bit rate).
Difficult to acquire w/o handover from C/A Code.
Can be encrypted to create a Y-Code.
Normally transmitted on both L1 and L2.
Y-Code.
Encrypted P-Code used in the event of GPS satellite spoofing.
Available to authorized users.
Standard Positioning Service (SPS).
Horizontal position within 100m or better (95%).
Timing accuracy within 340ns of UTC (95%).
Actual error based on current DoD policy.
Cannot decrypt Y-Code or remove SA error.
Usually only on one frequency, C/A Code based.