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 SegmentsSpaceSegmentUser SegmentControl Segment
5 Space Segment Block IIA - 7 1/2 year design life Block IIR - 10 year design lifeLaunched by Delta II from Cape Canaveral
6 Space Segment 24 satellites in constellation 6 orbital planes, 4 satellites in each plane55 degree orbit inclinationSemisynchronous orbit12 hour period12,500 statute miles (10,900 nm) altitudeConstellation maximizes 3-D coverageEnsures 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 CapeCanaveralColoradoSpringsKwajaleinHawaiiDiegoGarciaAscensionIsland5 Ground AntennasReceive/send TT&CUpdate NAV message and atomic clocks5 Monitor StationsCollect measurements from GPS satellites in view
9 The User SegmentAuthorized Users: Military personnel, military systems, designated allies, and other authorized usersNon-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) PLGRStandard Positioning Service (SPS)Intended for Non-Authorized UsersProvides decreased location and timing accuracyHorizontal position within 100m or better (95%)Timing accuracy within 340ns of UTC (95%)Actual error based on current DoD PolicyCorrupts navigation signal by two methodsEpsilon: changes the satellites positionDither: changes the satellites timePrecise Positioning Service (PPS)Intended for Authorized (military) usersProvides very precise location and time accuracy3-D position within 16m Spherical Error Probability (50%)Timing accuracy within 100ns of UTCPPS is controlled by special crytographic keysTRIMPACK46
11 Military GPS Receivers Small Lightweight GPS Receiver (“Slugger”)Most Models SPSUsed during Desert StormPrecise Lightweight GPS Receiver (“Plugger”)Standard Handheld UnitPPS CapableMiniature Airborne GPS ReceiverStandard Aircraft UnitSLGRMAGRPLGR
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 BelowConsists 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 operationsInterconnects 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 Control2179 FBCB2 SystemsFielded to 4th for FDD
13 ONE PLATFORM’S WORTH OF FBCB2 DIGITAL COMPONENTS SUPPORTING SITUATIONAL AWARENESSAND COMMAND AND CONTROLPLGR GPSGPS 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/SoftwareThe 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 VHSICSINCGARS SIP/INCRadios (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 LimitationsAdvantagesAll-weatherDay and nightWorldwide direct downlinkPassiveCommon gridRestricted accessSurvivableProvides 3-D position and velocityDependent on ground stationsJammable signalLine of Sight from GPS satellitesGPS 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 SegmentSelective Availability ensures Authorized users can receive a highly accurate GPS signal while Non-Authorized users (potential adversaries) can be given a degraded signalThe 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 awarenessThe three missions of GPSNavigation -- 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 CodeCode 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.