Global Positioning System (gps)

Global Positioning System (GPS)

Introduction

AIM To acquaint the student officers about GPS working, its different parts, orbital characteristics of satellite constellation and its uses in daily life.

Sequence • • • • • • • • • •

History and Development Working of GPS Parts of GPS GPS Caps Satellite Orbital Characteristics GPS Mapping Uses of GPS Application of GPS in Pakistan Recommendations Conclusion

History and Development •Formerly known as NAVSTAR •Initiated in 1973 •Maint by U.S. Department of Defence •Broad Usage •Useful for classical navigational applications.

GPS Working •Time difference to locate object •Time broadcast by satellite •Need of an atomic clock •Measurement from fourth satellite •Latitude,longitude,altitude & time.

GPS Working

Parts of GPS System (The Space segment) • • • • • •

Incl satellites launched from Florida Altitude 17500 km A period of 12 hrs Inclination towards Earth is 55 degrees Powered by solar cells Each satellite has 4 atomic clocks.

The Space Segment (NAVSTAR)

NAVSTAR (cont)

• • • • • •

Min 5 satellites always in view worldwide L1 band freq(1575.42 MHz) L2 band freq(1227.6 MHz) L1 carries P-code and C/A code L2 carries only P-code Encrypted P-code is called the Y-code.

NAVSTAR (cont) • Block I satellites for sys testing • Block II satellites were Ist functional satellites having cesium clocks ✔Radiation Hardened Electronics ✔Detecting errors & sending out of svc msgs ✔Operate for 3.5 days between uploads

• • •

Block IIA operate for 180 days Block IIR can generate own nav info The satellite identification scheme.

GLONASS • • • • • • • •

24 satellites, 8 in each orbit Operate in circular 19100 km Inclination angle is of 64.8 degrees Have a period of 11hr-15min L1 band freq(1609 MHz) L2 band freq(1251 MHz) Its signal carry both P-code & C/A code P-code is encrypted & C/A aval to all users.

The Control Segment

The Control Segment (cont)

The User Segment • • • • •

User and the GPS reciever Calculates posn based on GPS signal Features and cost dependent on functions Interface with memory cards Mil application incl: ✔Tgt designation,close air support,RV detection

• Civ uses incl: ✔Surveying,en-route nav,tracking sys,precision farming,in-car nav,in space shuttles etc

• Can serve unlimited number of users.

GPS Capibilities • Precise positioning service(PPS) ✔22 meter Horizontal accuracy ✔27.7 meter vertical accuracy ✔200 nanosecond time accuracy

• Standard positioning service(SPS) ✔100 meter horizontal accuracy ✔156 meter vertical accuracy ✔340 nanoseconds time accuracy

Orbital characteristics (The NAVSTAR contellation)

Orbital characteristics (The NAVSTAR contellation) • Block I satellites ✔Built by Rockwell International ✔Operate for 3.5 days between uploads

• Attitude controlled by: ✔Magnetic coils ✔Thrusters(high momentum above 109 min)

• Master control station is info when this occurs.

Block I satellites (cont) • Nuc detonation sensors ✔Eqpt carried from SV8 satellites ✔Previously fulfilled by VELA satellite sys ✔More satellites in NAVSTAR sys as compared to VELA sys

• Instruments carried are: ✔X-ray sensors ✔Background sensor ✔Bhang meters ✔Radio wave detectors.

Block I satellites (cont) • X-ray flash for less than 1 microsecond • Measured by several satellites to determine the loc of nuc exploision • Background detectors provide accurate record of X-ray environment around Earth

Block II satellites • • • •

Built by General Electric Astrospace Life span is of 7.5 years Req min interaction with gr stas Periodic uploads causes no disruption to svc • Its antenna provide greater gain than the antenna of block I satellite.

Block IIA satellites • Almost identical to Block II satellite with one exception • Cont to transmit same nav msg for 180 days without gr sta uploads • Orbits of satellites will change

Block IIR satellites

• Autonomous navigation • Can create their own nav msgs without upload from the gr • Sys accuracy is thus extended over a longer period.

GPS Mapping • Msg consists of time tagged data bits • A data bit frame consists of 1500 bits divided into five 300 bit sub-frames • A data frame is transmitted every 30 secs • Each frame consists of five sub-frames • Three 6 sec sub-frames contain orbital and clock data • Entire set of 25 frames(125 sub-frames) msg is sent over 12.5 min period • Old data can be used for 4 hrs.

GPS Mapping (cont)

Uses of GPS • Intelligent transportation sys

Uses of GPS (cont) • • • • • • •

Traffic control Traveler information sys Vehicle control Meteorological Use Surveying Life saving technology Commercial use

Mil uses of GPS •Attk coordination •Marine nav •Aircraft nav •Land nav •Missile guidance •Air defence •Intelligence •En radar location •Mine location etc.

Application of GPS in Pakistan (Mil usage) •Personal gadget of a soldier •Pakistan Navy is using it for marine nav •PAF is using it for aircraft nav •Corps of Engineers is using it for surveying of sites for dams and bridges •Due to non-auth of PPS, it can’t be utilized for missile guidance sys.

Application of GPS in Pakistan (Civ usage) • GPS has not gained enough popularity in civil life • Lack of awareness • Need of the hour.

Conclusion

Recommendations • The cars should be equipped with GPS reciever and a city map in the computer which should be updated for busy roads by an Earth sta situated in the city to avoid traffic jams • People going to northern areas should use handheld GPS to find their route • GPS to be used to measure atmospheric changes to predict abnormalities in the weather.

Questions?