GPS

Global Positioning System(GPS)
An easy to use
technology for everyone
SATELLITE COMMUNICATION

2
CONTENTS
 Introduction to GPS
 Preface to Satellite
 Important features of Satellite
 Launching a Satellite
 Orbits
 Latitude & Longitude
 History of GPS
 Basic principle
 Working
 Segments of GPS
 Advantages
 Applications.
 Bibliography

What is GPS ?
A very precise positioning system
• Satellite Based Navigation System
 Constellation of 24 satellites.
 Developed and maintained by the US
Department of Defense (DOD).
 To determine location,time & speed.

A Preface to SATELLITE
 Example- Sputnik 1 :
• the first satellite-launched by Soviet Union in 1957.
• is an artificial satellite which revolved around the Earth in an elliptical
orbit in Low Earth Orbit(LEO).
• used to broadcast radio signals.
 Example-Moon :
• Is a natural satellite that revolves around the earth in Lunar orbit.
 an object which revolves around
another reference large body placed
in an orbit into space.

Some imp. features of Satellite
 Weight can vary from 1 kg. to a few thousands of kg.
 Can operate at temp. ranges from -150°C to 150°C.
 It requires fuel(like Hydrazine-N2H4 or N2O4) to run various
stages and functions performed in satellite :-
 For alligning a satellite to point to a specific location.
 For maintaining satellite to remain in its orbit.
 Amount of fuel contained also determines the lifespan of satellite.
 It also requires power to run its electronic equipments obtained
from solar panels or backup batteries.
 A minimal fuel is left so as to degrade the satellite to become
space debris or deteriorated.

Launching a satellite
 The first stage of the launch vehicle contains
the rockets and fuel that are needed to lift the
satellite.
• As satellite is lifted,first stage falls.
 The second stage contains smaller rockets that
ignite after the first stage is finished.
• Used to send satellite to the space and burst
up in earth’s atmosphere.
 Launched with the help of rockets which go under different
stages to make the satellite suspended to its orbit.
♦ The upper stage is enclosed in a metal shield, called “fairing”.
• The satellite separates from the upper stage & moves to “transfer orbit”.
♦ Once the satellite reaches its desired orbital height,it unfurls its solar
panels and communication antennas.

 Launched by ISRO On 4th April 2014 from the Satish Dhawan
Space Center,about 50 miles north of Chennai.
 Weighed 1,432 kg at an altitude of 20,610 km. Geosynchronous
orbit.
 Designed for a 10-year lifetime.
 Five more Indian navigation spacecraft are scheduled for launch by
mid-2015.

Orbits
 An orbit is the
gravitationally curved path
of an object around a point
in space.
 Orbits of planets are
typically elliptical.
Types of ORBITS -:
 LEO
 MEO
 GEO/GSO
 HEO

LEO(LOWER EARTH ORBIT)
 Closest to earth.
 Extends upto an altitude of 160-2000 Km.
 Orbiting period is 90 min.
 Orbital speed is about 28,000-30,000 Km./h
 Have less lifespan-approx. 5 yrs.
 Advantages-
 Access to visit Hubble Space Telescope & International Space Station.
 Only way to go up and do experiments,testing & repairing of satellites.
 High resolution pictures.
 Ozone layer & other atmospheric disturbances monitoring.
 Disadvantages-
 Atmospheric Drag.
 Less Dwell Time.

 Extends upto an altitude of 2000-35,786 Km.(optimum
value-20,000 km.)
 Orbiting period is12 hrs.
 Orbital speed is about 18,000Km./h
 Have an average lifespan-approx. 10 yrs.
 GPS satellites mostly orbits in MEO.
 Advantages-
♦ Used for navigation, communication and space
environment science.
♦ Signal time delay is less.
MEO(MEDIUM EARTH ORBIT)

 Geosynchronous means orbiting its path in synchronization with
Earth.
 Also includes GSO(Geostationary Earth orbit).
 Extends upto an altitude of 35,786 Km and above.
 Orbiting period is 24 hrs.
 Orbital speed is about 14,000Km./h
 Have a good lifespan-approx. 15-18 yrs.
 Advantages -:
 Weather and TV Broadcasting.
 Natural Calamities alert and warning.
 Disadvantages -:
 Introduces large time delays in broadcasting.
GEO(GEOSYNCHRONOUS EARTH ORBIT)

 Extends upto an altitude of 50,000 km. to some
lakhs of km.
 Above this orbit is the-’graveyard Orbit’.
 Orbiting period is some days.
 Orbital speed is about 3,000-5000 Km/h
Example :-
 Moon-have an altitude of 3,85,000 km.
 Orbital speed is 3,600 km/h and takes 25 days
to complete its orbit around the Earth.
HEO(HIGH EARTH ORBIT)

LATITUDE AND LONGITUDE
Latitude - is the angular distance, in degrees,
minutes, and seconds of a point north or south
of the Equator. Lines of latitude are often
referred to as parallels.
Longitude - is the angular distance, in degrees,
minutes, and seconds, of a point east or west of
the Prime (Greenwich) Meridian. Lines of
longitude are often referred to as meridians.
Altitude - is the distance of an object
measured w.r.t ground or sea level usually in
vertical direction.

History of GPS
Ivan A. Getting Roger L. Easton Bradford Parkinson
 GPS was initially created for the United States Air Force by the Raytheon Company.
In 1967, the U.S. Navy launched TRANSIT, the first satellite navigational system,
which was used to help guide the Navy’s submarines-missiles.
1974, the first atomic clocks were put into orbit.
By 1978, the U.S. military had launched the first four GPS satellites.
Until 1983, GPS technology was available for U.S. military use only.
 In 1983,due to a tragedy with Korean Air Lines Flight 007 accident, President
Ronald Reagan (U.S)issued a directive that when GPS technology was operational, it
would be free and available to the world.
On Feb. 14, 1989, the first modern satellite,” USA-35” was launched.
By July 17, 1995, the global positioning system was complete.

Principle of GPS
 TRILATERATION :-
Process to determine your position on a map knowing the
precise distance from three different landmarks using a pair of
compasses. Where the three circles centered on each of the
landmarks overlap,gives you,your location.
In GPS, the calculations are carried out in three-
dimensions with an imaginary set of 3D compasses so that
your location is where three spheres of radius given by the
distance to each of three satellites overlap.
4 satellites gives accuracy.

How GPS Works ………
Uses measurements from 4+ satellites
Distance = travel time x speed of light
Source:Trimble

 Each satellite knows its
position and its distance
from the center of the earth.
 Each satellite constantly
broadcasts this information.
 With this information and
the calculated distance, the
receiver calculates its
position.
 Just knowing the distance
to one satellite doesn’t
provide enough
information.

 When the receiver
knows its distance from
only one satellite, its
location could be
anywhere on the earth’s
surface that is an equal
distance from the
satellite.
 Represented by the
circle in the illustration.
 The receiver must have
additional information.

With signals from two
satellites, the receiver can
narrow down its location to
just two points on the earths
surface.
Where the two circles
intersect.

 Knowing its distance
from three satellites, the
receiver can determine its
location because there is
only two possible
combinations and one of
them is out in space.
 In this example, the
receiver is located at b.
 The more satellite that are
used, the greater the
potential accuracy of the
position location.

Segments of GPS
1. Space Segment
A constellation of 24 satellites
2. Control Segment
A network of earth-based facilities
Source:Trimble
1. Users Segment
Ground, Sky and Marine.

1.Space Segment
 The current GPS configuration consists of
a constellation of 24 satellites(with 6
spares)in high orbits around the Earth.
 Extends at an altitude of about 20,000 km.
 Has an orbital speed of about 14,000 km/hr
& orbital period is roughly 12 hrs.
 The orbits are designed so that there are
always 6 satellites in view,from most
places on the earth.
♦ Powered by solar cells, the satellites continuously
orient themselves to point their solar panels toward
the sun and their antenna toward the earth.

2.Control Segment
 The CS consists of 3 entities:
Master Control Station
Monitor Stations
Ground Antennas
1. Master Control Station
• The master control station, located at Falcon Air Force Base in
Colorado Springs, Colorado, is responsible for overall management of
the remote monitoring and transmission sites.
• Provide commands and control of the GPS constellation.
• It generates and uploads navigation messages and ensures the health
and accuracy of the satellite constellation.
• It receives navigation information from the monitor stations, utilizes
this information to compute the precise locations of the GPS satellites in
space, and then uploads this data to the satellites.

2. Monitor Stations
 Monitor stations track the GPS satellites as they pass overhead and
channel their observations back to the master control station.
 Monitor stations collect atmospheric data, range/carrier
measurements, and navigation signals.
 The sites utilize sophisticated GPS receivers and are operated by
the MCS.
 There are 16 monitoring stations located throughout the world,
including six from the Air Force and 10 from the National
Geospatial-Intelligence Agency (NGA).
3. Ground Antennas
 Ground antennas monitor and track the satellites from horizon to
horizon.
 They also transmit correction information to individual satellites.

3.User Segment
 GPS receivers are generally composed of an antenna, tuned to
the frequencies transmitted by the satellites.
 They can also include a display for showing location and
speed information to the user.
 A receiver is often described by its number of channels this
signifies how many satellites it can monitor simultaneously.
 Some Common Receiver’s are -:

MAP for location of Control Stations

Advantages of GPS
Free of cost
Easy to use
Reliable to much extent
Unlimited Users Capacity
Operates in all Weather conditions
Complete coverage of Globe
Updated regularly
Compact-Mobile phones/Watches
Full time access
Determination of exact location,distance & speed.
Gives you inf. About Latitude & Longitude.
Allows to search for nearby Ammenities.
Determination of traffic,weather conditions.
Keep track of your friend’s or target’s location.

Applications of GPS
 ROAD APPLICATIONS
 Used to determine location,speed,traffic and distance to destination.
 Used to search nearby Ammenities like malls,restaurants,theatres etc.
 Sources include-Mobiles,Laptos,GPS mount for automobiles.
 SPACE APPLICATIONS
 Weather monitoring, Launch Vehicle tracking, Disaster Alerts,Space Shuttle nav.
 Keep track of other space elements like space debris,asteroids,etc.
 RAIL APPLICATIONS
 To maintain smooth flow of traffic.
 Prevent collisions by precise knowledge of other trains locations.
 MILITARY: GPS systems are installed with fighters, bombers, tankers, helicopters,
ships, submarines, tanks, jeeps and soldiers to combat various attacks.
 AVIATION APPLICATIONS: GPS provides position determination for all phases
of flight from departure, en route, and arrival, to airport surface navigation.
 AGRICULTURE: farm planning, field mapping, soil sampling, tractor guidance,
crop scouting, variable rate applications, and yield mapping.

Bibliography
 www.wikipedia.org
 www.youtube.com
 www.astronomy.ohio-state.edu
 www.mio.com
 www.cfa.harvard.edu
 www.gpspassion.com
 www.lockheedmartin.co.in
 http://gps.about.com/

GPS

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