GPS TECHNIQUE
TERM PROJECT
GROUP 6
Zeren Şenyıldız-010090609
Özge Kazan-
Azize Uyar-010090610
Zehra KoçMohsen Feizabadi- 010100910
Mustafa Serkan IşıkAtabak Sadeghinaibin- 010080918
TOPIC:
FEATURES AND CLASSIFICATIONS OF ARTIFICIAL SATELLITES FOR GPS AND GNSS:
SIGNAL, LIFESPAN, ORBITS, AND DETAILS.
GLONASS
Future of
Satellites
GALLILEO
Satellite
Technologies
and GPS
Signal types
and
processing
COMPASS
Classification
of
positioning
satellites
WHAT IS A SATELLITE?
• A satellite is a moon, planet or machine that orbits a planet or star.
For example, Earth is a satellite because it orbits the sun. Likewise,
the moon is a satellite because it orbits Earth.
• Usually, the word "satellite" refers to a machine that is launched into
space and moves around Earth or another body in space.
• Earth and the moon are examples of natural satellites. Thousands of
artificial, or man-made, satellites orbit Earth.
• Some taken pictures of the planet that help meteorologists predict
weather and track hurricanes. Some taken pictures of other planets,
the sun, black holes, dark matter or faraway galaxies. These pictures
help scientists better understand the solar system and universe.
• Still other satellites are used mainly for communications, such as
beaming TV signals and phone calls around the world.
• A group of more than 20 satellites make up the Global
Positioning System, or GPS. If you have a GPS receiver, these
satellites can help figure out your exact location.
• Satellites vary in size. Some cube satellites are as small as 10 cm.
Some communication satellites are about 7 m long and have
solar panels that extend another 50 m.
• The largest artificial satellite is the International Space Station
(ISS). (This is a habitable space laboratory. At an altitude of 400
km, the ISS travels at a speed of 28 000 km/h and orbits the
Earth once every 92 minutes. Scientists inside the ISS are able to
perform many valuable experiments in a microgravity
environment.)
• The main part of this is as big as a large five-bedroom house,
but including solar panels, it is as large as a rugby field.
ARTIFICAL SATELLITES
•
An artificial satellite is an object that people have made and
launched into orbit using rockets.
•
There are currently over a thousand active satellites orbiting
the Earth. The size, altitude and design of a satellite depend
on its purpose.
Types of Satellite:
•
Navigation satellites: The GPS (global positioning system) is
made up of 24 satellites that orbit at an altitude of 20 000 km
above the surface of the Earth. The difference in time for
signals received from four satellites is used to calculate the
exact location of a GPS receiver on Earth.
•
Communication satellites: These are used for television, phone
or internet transmissions, for example, the Optus D1 satellite
is in a geostationary orbit above the equator and has a
coverage footprint to provide signals to all of Australia and
New Zealand.
•
Weather satellites: These are used to image clouds and
measure temperature and rainfall. Both geostationary and low
Earth orbits are used depending on the type of weather
satellite. Weather satellites are used to help with more
accurate weather forecasting.
•
Earth observation satellites: These are used to photograph and
image the Earth. Low Earth orbits are mainly used so that a
more detailed image can be produced.
•
Astronomical satellites: These are used to monitor and image
space. A satellite such as the Hubble Space Telescope orbits at
an altitude of 600 km and provides very sharp images of stars
and distant galaxies. Other space telescopes include Spitzer
and Chandra.
•
The first artificial satellite was the Soviet Sputnik 1
mission, launched in 1957.
•
Since then, dozens of countries have launched
satellites, with more than 3,000 currently operating
spacecraft going around the Earth.
•
There are estimated to be more than 8,000 pieces
of space junk; dead satellites or pieces of debris
going around the Earth as well.
WHAT IS GPS ?
•
The Global Positioning System (GPS) is a U.S. owned utility that
provides users with positioning, navigation, and timing services. This
system consists of three segments: the space segment, the control
segment, and the user segment. The U.S. Air Force develops,
maintains, and operates the space and control segments.
Space Segment:
•
The GPS space segment consists of a constellation of satellites
transmitting radio signals to users. The Air Force manages the
constellation to ensure the availability of at least 24 GPS satellites,
95% of the time.
•
For the past several years, the Air Force has been flying 31
operational GPS satellites, plus 3-4 decommissioned satellites
("residuals") that can be reactivated if needed.
Control Segment:
•
The GPS control segment consists of a global
network of ground facilities that track the GPS
satellites, monitor their transmissions, perform
analyses, and send commands and data to the
constellation.
•
The current operational control segment includes a
master control station, an alternate master control
station, 12 command and control antennas, and 16
monitoring sites.
Gps Applications : Agriculture,Environment, Marine, Public safety & Disaster relief, Rail, Recreation,
Roads & Highways, Space, Surveying & Mapping, Timing..
GLONASS
GLObalnaya NAvigatsionnaya Sputnikovaya Sistema
GLONASS
GLONASS is a space-based satellite navigation system operated by the Russian
Aerospace Defence Forces. It is designed to provide instantaneous, high precision
location and speed information to users throughout most of the world. Deployed in
nearly circular orbits at an altitude of 19,100 km by Proton boosters. GLONASS
positional accuracies (95% confidence) are claimed to be 100 m on the surface of the
Earth, 150 m in altitude, and 15 cm/s in velocity. GLONASS is a dual-use system.
A fully operational constellation with global coverage consists of 24 satellites, while 18
satellites are necessary for covering the territory of Russia. To get a position fix the
receiver must be in the range of at least four satellites.
DEPLOYMENT OF THE GLONASS CONSTELLATION
Beginning on 12 October 1982, numerous rocket launches added satellites to the system
until the constellation was completed in 1995. When completed, the GLONASS
constellation was designed to provide 100 meters accuracy with its "standard precision"
C/A signals, which are deliberately degraded, and 10-20 meter accuracy with its P
"high-precision" signals, originally available exclusively to the military. This brought the
precision of GLONASS on-par with the American GPS system, which
had achieved full operational capability а year earlier.
After the full complement was achieved in December
1995, there were no further launches until
December 1999, because of financially
difficult period.
Программа развертывания орбитальной группировки ГЛОНАСС
30
numder of operational satellites in the constellation
27
24
24
20
21
18
18
15
13
12
9
8
8
8
9
9
10
13
14
14
24
24
24
24
24
24
20
18
15
11
6
6
3
0
2001
Блок 30
01. 12. 01
2002
Блок 31
25. 12. 02
2003
Блок 32
10. 12. 03
2004
Блок 33
26. 12. 03
2006
2005
Блок 34
25. 12. 03
GLONASS deployment milestones:
18 satellites in constellation – 2007
24 satellites in constellation – 2009
Блок 35
2007
Блок 36
Блок 37
Блок 38
2010
2009
2008
Блок 39
Блок 40
Блок 41
Блок К1
2011
Блок К3
Глонасс-К (ЛИ)
2012
Блок К3
At the end of 2004, the head of the Federal Space Agency, FKA, called the separation
between military and civilian frequencies in the GLONASS system, "awkward" and
promised to provide the access to the high-precision navigation data to all users.
GLONASS signal is free (available in latitude, longitude and altitude).
Over the three decades of development, the satellite designs have gone through
numerous improvements, and can be divided into three generations:
- The original GLONASS (since 1982),
- GLONASS-M (since 2003) and
- GLONASS-K (since 2011).
GLONASS (URAGAN)
The GLONASS (also called Uragan) satellite features a three-axis stabilization
system, which points it in nadir during the operational flight. Two solar arrays
provide power supply. Onboard cesium clocks provide time accuracy to 1,000
nanoseconds. The first generation GLONASS satellites were 7.8 m tall, had a
width of 7.2 m, measured across their solar panels, and a mass of 1,260 kg.
(Scale model of the Uragan
satellite.)
GLONASS-M
Glonass-M were developed beginning in 1990 and first
launched in 2003, launches of GLONASS-M satellites were expected to continue until 2012. The
GLONASS-M version of
the satellite featured improved antennas, extended lifetime
and the introduction of a separate transmission frequency dedicated to civilian users, known as L2.
The satellite also sported an increased clock stability, more accurate solar array orientation and
better maneuverability. It had a slightly larger mass than the baseline GLONASS, standing at
1,415 kg,
but it had double the original's lifetime,
decreasing the required replacement rate
by 50%. The new satellite also had better
accuracy and ability to broadcast two extra
civilian signals.
GLONASS-K
The first GLONASS-K satellite was successfully launched on 26 February 2011. The
GLONASS-K version featured lighter, standardized unpressurized bus. It has an
operational lifetime of 10 years, compared to the 7-year lifetime of the second
generation GLONASS-M. It will transmit more navigation signals to improve the system's
accuracy.
GLONASS-K2
A revised version of GLONASS-K satellite, known as GLONASS-K2 was originally promised as
early as 2013, however by 2012, it was not expected to enter service until 2015.
Group launch by
SOYUZ
GLONASS MODERNİZATİON
INTERACTION WITH AMERICAN GPS
Russia discussed various issues related to the development and use of GLONASS
in parallel with American GPS and European Galileo systems. According to the
head of Federal Space Agency, in December 2004 Russia and the US discussed
the ways of preventing the use of satellite navigation systems by terrorists.
GPS = GLONASS ?
The fundamental difference between the GLONASS and GPS navigators are the signal
itself and its structure.
- GPS system uses code-division channeling. GLONASS uses frequency-division
channeling.
- The structure of the signal also differs.
- Also the satellites motion is described using fundamentally different mathematical
models. In GLONASS differential model of motion is used. And GPS uses a model based
on osculating elements.
- GLONASS time and GPS time are not the same. (Leap seconds are an issue)
- GLONASS uses a different geocentric datum. (PZ-90)
PARTICIPATION IN EUROPE'S GALILEO NETWORK
Russia also was in talks with the European Space Agency on the possible cooperation on the
Galileo navigation network. Details beyond the possibility of launching Galileo satellites
onboard Soyuz rockets were not specified.
Cooperation with China
Number of contacts between Russian and Chinese space officials included discussions of the
GLONASS network. According to the Russian media, China considered the development of its
own satellite navigation system, which could involve purchases of the Russian technology.
GLONASS GROUND CONTROL
The ground control segment of GLONASS is almost entirely located within former Soviet
Union territory, except for a station in Brasilia, Brazil. The Ground Control Center and
Time Standards is located in Moscow and the telemetry and tracking stations are in Saint
Petersburg, Ternopol, Eniseisk, and Komsomolsk-na-Amure.
GALILEO
The Galileo programme is Europe's initiative for a state-of-the-art global satellite
navigation system, providing a highly accurate, guaranteed global positioning service
under civilian control. The system is intended primarily for civilian use, unlike the more
military-oriented systems of the United States (GPS), Russia (GLONASS), and China
(Beidou-1/2, COMPASS).The fully deployed system will consist of 30 satellites and the
associated ground infrastructure. Galileo will be inter-operable with GPS and
GLONASS, the two other global satellite navigation systems.
The first two operational Galileo
satellites were launched from Europe's
Spaceport in French Guiana in October
2011. Once the In-Orbit Validation (IOV)
phase has been completed, the remaining
satellites will be placed in orbit at regular
intervals to reach Full Operational
Capability.
• The complete Galileo constellation will comprise satellites spread evenly
around three orbital planes inclined at an angle of 56 degrees to the
equator. Each satellite will take about 14 hours to orbit the Earth. One
satellite in each plane will be a spare, on stand-by should any operational
satellite fail.
•
The Galileo IOV satellite
Mass
Size with solar wings stowed
Size with solar wings deployed
Design life
Available power
•
about 700 kg
3.02 x 1.58 x 1.59m
2.74 x 14.5 x 1.59 m
more than 12 years
1420 W (sunlight) / 1355 W (eclipse)
Orbit
Altitude
Inclination
23 222 km
56°
Three initial services will be provided from 2014 onwards:
• The Open Service: Galileo open and free of user charge signal,
• The Public Regulated Service: a special Galileo navigation service using encrypted
signals set up for better management of critical transport and emergency services,
better law enforcement, improved border control and safer peace missions,
• The Search And Rescue Service, contribution of Europe to COSPAS-SARSAT, an
international satellite-based search and rescue distress alert detection system.
Another services will be tested as of 2014 and provided as the system reaches full
operational capability with the 30 satellites:
• The Commercial Service that gives access to two additional encrypted signals.
Research is under way into future
improvements such as expanded
augmentation coverage, including how best
to support increased navigation in the Arctic
region as ice cover recedes, even more
precise atomic clocks, and inter-satellite links
to reduce Galileo’s dependence on its
ground segment for clock correction.
COMPASS
• The BNSS (BeiDou Navigation Satellite System) is a Chinese satellite navigation system. It consists of two
separate satellite constellations – a limited test system that has been operating since 2000, and a full-scale
global navigation system that is currently under construction.
• The first BeiDou system, officially called the BeiDou Satellite Navigation Experimental System and also
known as BeiDou-1,
•
consists of three satellites and offers limited coverage and applications. It has been offering navigation
services, mainly for customers in China and neighboring regions, since 2000.
• The second generation of the system, officially called the BeiDou Satellite Navigation System (BDS) and also
known as COMPASS or BeiDou-2, will be a global satellite navigation system and is under construction as of
January 2013.
• Consisting of 35 satellites, it became operational in China in December 2011, with 10 satellites in use, and
began offering services to customers in the Asia-Pacific region in December 2012. For future, it is planned to
begin serving global customers upon its completion in 2020.
DESCRIPTION
• BeiDou-2 (formerly known as COMPASS) is not an extension to the older BeiDou-1, but rather
supersedes it outright. The new system will be a constellation of:
35 satellites
which include 5 geostationary orbit satellites for backward compatibility with BeiDou-1
30 non-geostationary satellites (27 in medium earth orbit and 3 in inclined geosynchronous
orbit), that will offer complete coverage of the globe.
ACCURACY
•
There are two levels of service provided:
a free service to civilians : has a 10-meter location-tracking accuracy, synchronizes clocks
with an accuracy of 10 nanoseconds, and measures speeds to within 0.2 m/s.
licensed service to the Chinese government and military: has a location accuracy of 10
centimetres can be used for communication, and will supply information about the system status
to the user. To date, the military service has been granted only to the People's Liberation Army
and to the Military of Pakistan
AIMS
• The ranging signals are based on the CDMA principle and have complex structure typical of
Galileo or modernized GPS.
Similar to the other GNSS, there will be two levels of positioning service: open and
restricted (military). The public service shall be available globally to general users.
When all the currently planned GNSS systems are deployed, the users will benefit
from the use of a total constellation of 75+ satellites, which will significantly improve
all the aspects of positioning, especially availability of the signals in so-called urban
canyons.
The general designer of Compass navigation system is Sun Jiadong, who is also the
general designer of its predecessor, the original Beidou navigation system.
•
List of satellites (as of December 2012)[edit]
•
Date
•
Launcher
Satellite
Orbit
Usable
System
10/31/2000
LM-3A
BeiDou-1A
GEO 59°E
No
•
12/21/2000
LM-3A
BeiDou-1B
GEO 80°E
No
•
5/25/2003 LM-3A
BeiDou-1C
GEO 110.5°E
No
•
2/3/2007
BeiDou-1D
Supersync orbit
No
•
4/14/2007 LM-3A
Compass-M1
MEO ~21,500 km
Testing only
•
4/15/2009 LM-3C
Compass-G2
?
No
•
1/17/2010 LM-3C
Compass-G1
GEO 144.5°E
Yes
•
6/2/2010
LM-3C
Compass-G3[55] GEO 84°E
Yes
•
8/1/2010
LM-3A
Compass-IGSO1 118°E incl 55°
Yes
•
11/1/2010 LM-3C
Compass-G4
GEO 160°E
Yes
•
12/18/2010
LM-3A
Compass-IGSO2
118°E incl 55°
Yes
•
04/10/2011
LM-3A
Compass-IGSO3
118°E incl 55°
Yes
•
07/26/2011
LM-3A
Compass-IGSO4
95°E incl 55°
Yes
•
12/02/2011
LM-3A
Compass-IGSO5 95°E incl 55°
Yes
•
02/24/2012
LM-3C
Compass-G5
59°E
Yes
•
04/29/2012
LM-3B
Compass-M3
MEO incl 55°
Yes
•
04/29/2012
LM-3B
Compass-M4
MEO incl 55°
Yes
•
09/18/2012
LM-3B
Compass-M5
MEO incl 55°
Yes
•
09/18/2012
LM-3B
Compass-M6
MEO incl 55°
Yes
•
10/25/2012
LM-3C
Compass-G6[48] 80°E
LM-3A
Yes
BeiDou-1
BeiDou-2 (Compass)
COMPASS-M1 – DETAILED INFORMATION
• Compass-M1 is an experimental satellite launched for signal testing and validation and for the frequency filing on 14 April
2007. The role of Compass-M1 for Compass is similar to the role of the GIOVE satellites for the Galileo system. The orbit of
Compass-M1 is nearly circular, has an altitude of 21,150 km and an inclination of 55.5 degrees.
• Compass-M1 transmits in 3 bands: E2, E5B, and E6. In each frequency band two coherent sub-signals have been detected
with a phase shift of 90 degrees (in quadrature). These signal components are further referred to as "I" and "Q". The "I"
components have shorter codes and are likely to be intended for the open service. The "Q" components have much longer
codes, are more interference resistive, and are probably intended for the restricted service.
• The investigation of the transmitted signals started immediately after the launch of Compass -M1 on 14 April 2007. Soon
after in June 2007, engineers at CNES reported the spectrum and structure of the signals. A month later, researchers from
Stanford University reported the complete decoding of the “I” signals components. The knowledge of the codes allowed a
group of engineers at Septentrio to build the COMPASS receiver and report tracking and multipath characteristics of the “I”
signals on E2 and E5B.
• Characteristics of the "I" signals on E2 and E5B are generally similar to the civilian codes of GPS (L1-CA and L2C), but
Compass signals have somewhat greater power. The notation of Compass signals used in this page follows the naming of the
frequency bands and agrees with the notation used in the American literature on the subject, but the notation used by the
Chinese seems to be different and is quoted in the first row of the table.
FOR FUTURE
• According to the authorities." The system became operational in the China
region that same month. The global navigation system should be finished
by 2020.As of December 2012, 16 satellites for BeiDou-2 have been
launched, 14 of them are in service.
CLASSIFICATION OF ARTIFICIAL AND GPS SATELLITE ORBITS
1.Centric classifications
•
Galactocentric orbit is an orbit about the center of a galaxy. The Sun follows this
type of orbit about the galactic center of the Milky Way.
•
Heliocentric orbit is an orbit around the Sun. In our Solar System,
all planets, comets, and asteroids are in such orbits.
•
Geocentric orbit is an orbit around the planet Earth, such as that of the Moon or
of artificial satellites.
•
Areocentric orbit is an orbit around the planet Mars, such as that of its
moons or artificial satellites.
•
Lunar orbit is an orbit around the Earth’s moon.
2. Altitude classifications for geocentric orbits
•
Low Earth orbit (LEO): Geocentric orbits with altitudes up to 2,000.
•
Medium Earth orbit (MEO): Geocentric orbits ranging in altitude from 2,000 km
to just below geosynchronous, matching the Earth's sidereal rotation period orbit at
35,786 kilometres. Also known as an intermediate circular orbit. These are most
commonly at 20,200 kilometres or 20,650 kilometres with an orbital period of 12
hours and are used by the Global Positioning System. Other satellites in Medium
Earth Orbit include GLONASS (with an altitude of 19,100 kilometres) and
GALILEO (with an altitude of 23,222 kilometres) constellations.
Geosynchronous orbit is an orbit around the Earth with an orbital period of
one sidereal day (23 hours 56 minutes and 4 seconds)
2. Altitude classifications for geocentric orbits
• Medium Earth orbit (MEO)
• High Earth orbit: Geocentric orbits above the
altitude of geosynchronous orbit 35,786.
3. Inclination classifications
•
Inclined orbit is an orbit whose inclination in
reference to the equatorial plane is not 0.
 Polar
orbit: An orbit that passes above or nearly
above both poles of the planet on each revolution.
Therefore it has an inclination of (or very close to)
90 degrees.
 Polar
Sun-synchronous orbit: A nearly polar
orbit that passes the equator at the same local solar
time on every pass.
3. Inclination classifications
•
Non-inclined orbit: An orbit whose inclination is equal to zero with respect to
some plane of reference.
Ecliptic orbit is a non-inclined orbit with respect to the ecliptic.
Equatorial orbit is a non-inclined orbit with respect to the equator.
•
Near equatorial orbit: An orbit whose inclination with respect to the equatorial
plane is nearly zero.
4. Eccentricity classifications
There are two types of orbits:
•
Closed (periodic) orbits: Circular and elliptical orbits
•
Open (escape) orbits: Parabolic and hyperbolic orbits.
Circular orbit: An orbit that has an eccentricity of 0 and whose path traces
a circle.
Elliptic orbit: An orbit with an eccentricity greater than 0 and less than 1 whose
orbit traces the path of an ellipse.
The orbits of GPS are nearly circular, with a typical eccentricity of less than 1.
5. Synchronicity classifications
•
Geostationary orbit (GEO): A circular geosynchronous
orbit with an inclination of zero. To an observer on the
ground this satellite appears as a fixed point in the sky.
All geostationary orbits must be geosynchronous, but not
all geosynchronous orbits are geostationary.
It is 35,786 kilometres above the Earth's equator and
following the direction of the Earth's rotation. An object
in such an orbit has an orbital period equal to the Earth's
rotational period (one sidereal day), and thus appears
motionless, at a fixed position in the sky, to ground
observers. Communications and weather satellites are
often given geostationary orbits.
GPS SIGNALS

Each satellite transmits a regular GPS
signal that is carried by radio waves in
the microwave part of the
electromagnetic spectrum

GPS satellite transmits data on two
frequencies, L1 (1575.42 Mhz) and L2
(1227.60 MHz)

L5 is the third civilian GPS signal,
designed to meet demanding
requirements for safety-of-life
transportation and other highperformance applications.
WHAT DOES THE
SIGNAL CONSIST OF?

Digital Informations: Two pseudorandom
noise (PRN) codes, along with satellite
ephemerides (Broadcast Ephemerides),
ionospheric modeling coefficients, status
information, system time, and satellite clock
corrections

First pseudorandom noise (PRN) code is the
Course-Acquisition (C/A) code.

Second pseudorandom noise code is the
Precise Code, or P code
COARSE-ACQUISITION (C/A) CODE

The C/A code is the base for all civil GPS receivers

modulated onto the L1 carrier

Selective Availability (SA) -intentional degradation of public GPS signals implemented for national security
reasons.
EFFECT OF SELECTIVE
AVAILABILITY
The data indicates a circular error of only
2.8 meters and a spherical error of 4.6
meters during the first few hours of SA-free
operation
COURTESY OF GPS SUPPORT
CENTER, AIR FORCE SPACE
COMMAND
EFFECT OF SELECTIVE AVAILABILITY
NOAA NATIONAL GEODETIC SURVEY
PRECISE CODE

The P- and Y-code are the base for the
precise (military) position determination

The P code is ten times as fast, which means
it can determine the pseudorange ten times
more accurately

Carried by both L1 and L2 codes

Since January 31, 1994 the AS-system is
operating continuously and the P-code is
only transmitted as Y-code

AS-anti spoofing-encryption of P codes into
Y codes
NAVIGATION MESSAGE
 low frequency signal added to the L1 codes
that gives information about the satellite's
orbits, their clock corrections and other system
status(Basically Almanac data and Ephemeris
data)
 Ephemeris data is data that tells the GPS
receiver where each GPS satellite should be at
any time throughout the day
 Complexity may sometimes be an advantage/
GPS receivers know the PRN codes for each
satellite and so can not only decode the signal
but distinguish between different satellites
GPS SIGNAL ERROR
 Ionosphere and troposphere delays
 Multipat
 Receiver clock errors
 Orbital errors
 Satellite geometry/shading
SATELLITE
GEOMETRY/SHADING
When the satellites are all in the same part of the sky, readings will be less accurate.
GPS Modernization
It is the policy of the United States to maintain U.S. leadership in the service,
provision, and use of satellite navigation systems. The U.S. government has
additional policy goals to meet growing demands by improving the performance
of GPS services, and to remain competitive with international satellite navigation
systems.
The GPS modernization program is an ongoing, multibillion-dollar effort to
upgrade the GPS space and control segments with new features to improve GPS
performance. These features include new civilian and military signals.




New Civil Signals
Future Satellite Generations
Control Segment Modernization
Program Schedule
 New Civil Signals (L2C,L5,L1C)
A major focus of the GPS modernization program is the addition of new navigation
signals to the satellite constellation.
The government is in the process of fielding three new signals designed for civilian
use: L2C, L5, and L1C. The legacy civil signal, called L1 C/A or C/A at L1, will
continue broadcasting in the future, for a total of four civil GPS signals.
The new civil signals are phasing in incrementally as the Air Force launches new
GPS satellites to replace older ones. Most of the new signals will be of limited use
until they are broadcast from 18 to 24 satellites.
Second Civil Signal (L2C): designed specifically to meet commercial needs.
Third Civil Signal (L5): designed to meet demanding requirements for safety-oflife transportation and other high-performance applications.
Fourth Civil Signal (L1C): designed to enable interoperability between GPS and
international satellite navigation systems.
 Current and Future Satellite Generations
The GPS constellation is a mix of new and legacy satellites.
 GPS Block IIA: It is an upgraded version of the GPS Block II satellites
launched in 1989-1990. The "II" refers to the second generation of GPS
satellites, although Block II was actually the first series of operational GPS
satellites. The "A" stands for advanced.
 GPS Block IIR: The IIR series were produced to replace the II/IIA series as
the II/IIA satellites. The "R" in Block IIR stands for replenishment.
 GPS Block IIR(M): The IIR(M) series of satellites are an upgraded version
of the IIR series. The "M" in IIR(M) stands for modernized, referring to the
new civil and military GPS signals added with this generation of spacecraft.
 GPS Block IIF: The IIF series expand on the capabilities of the IIR(M) series
with the addition of a third civil signal. The "F" in IIF stands for follow-on.
Compared to previous generations, GPS IIF satellites have a longer life
expectancy and a higher accuracy requirement.
 Current and Future Satellite Generations
 GPS Block III: the GPS III series is the newest block of GPS satellites. It will
provide more powerful signals in addition to enhanced signal reliability,
accuracy, and integrity. As of April 2013, GPS III Satellite Vehicles (SVs) 03-08
are in the Production and Deployment Phase. Future versions will feature
increased capabilities to meet demands of military and civilian users alike.
 Control Segment Modernization
As part of the GPS modernization program, the Air Force has continuously
upgraded the GPS control segment over the past few years and will keep doing so
in the years to come. It includs the Architecture Evolution Plan (AEP) and the
Next Generation Operational Control System (OCX).
The schedule for the parallel space and control segment upgrades
REFERENCES:
• http://en.wikipedia.org/wiki/satellite
• http://www.sciencelearn.org.nz/Contexts/Satellites/Science-Ideas-and-Concepts/Artificial-satellites
• http://www.nasa.gov/audience/forstudents/5-8/features/what-is-a-satellite-58.html#.UqoABPRdXw• http://www.gps.gov/
• http://www.csr.utexas.edu UNIVERSITY OF TEXAS
• Croucher, Phil. Professional Helicopter Pilot Studies. 2007
• http://www.oxts.com/glossary/coarse-acquisition/
• http://ec.europa.eu/enterprise/policies/satnav/galileo/
• http://www.gsa.europa.eu/galileo/programme
• http://en.wikipedia.org/wiki/galileo_%28satellite_navigation
• http://www.esa.int/our_activities/navigation/the_future_-_galileo/galileo_satellites