GPS Block
IIIA

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GPS Block IIIA

Artist's impression of a GPS Block IIIA satellite in
orbit

General information

Manufacturer

Lockheed
Martin

Country of origin

United States

Bus

A2100

Applications

Navigation
satellite

Orbit regimes

Semi-synchronous
MEO

Operator

US Air
Force

Lifetime

15 years

Production

Status

Development

On order

4

← GPS Block
IIF

GPS Block IIIA, or GPS III is the next generation of GPS satellites which will
be used to keep the Navstar Global Positioning
System operational. Lockheed Martin is the
contractor for the design, development and production of the GPS III Non-Flight
Satellite Testbed (GNST) and the first eight GPS III satellites.[1]
The United States Air
Force plans to purchase up to 32 GPS III satellites. GPS IIIA-1, the first
satellite in the series, is projected to launch in 2014.[2]

Contents

1 Overview

2 Development

3 New navigation signals

3.1 Civilian L2
(L2C)

3.2 Military
(M-code)

3.3 Safety of Life
(L5)

3.4 New Civilian L1
(L1C)

4 Block III satellite
improvements

5 Ground control segment
improvements

6 See also

7 References

8 External
links

Overview[edit]

The United States' Global Positioning
System (GPS) reached Fully Operational Capability on July 17, 1995,[3]
completing its original design goals. However, additional advances in technology
and new demands on the existing system led to the effort to modernize the GPS
system. Announcements from the Vice President and the White House in 1998
initiated these changes. In 2000, the U.S. Congress authorized the effort,
referred to as GPS III.

The project involves new ground stations and new satellites, with additional
navigation signals for both civilian and military users, and aims to improve the
accuracy and availability for all users.

Lockheed Martin was
awarded the GPS III Space Segment contract on May 15, 2008. The first launch is
projected for 2014.[4]
Raytheon was
awarded the Next Generation GPS Operational Control System (OCX) contract on Feb
25, 2010.[5]

Development[edit]

Block IIIA satellites use Lockheed Martin's A2100 bus structure. They are
manufactured by Alliant Techsystems
from lightweight, high-strength composite materials.[6]

The first and second GPS III satellites are on schedule for launch in 2014
and 2015.[2]

The U.S. Air Force awarded Lockheed Martin a $238 million contract for
production of the third and fourth satellites in January 2012.[7]

Future Block III variants are planned to incorporate additional capabilities.
They include Distress
Alerting Satellite System (DASS) capabilities for search and rescue, as well
as satellite crosslinks for rapid command and reduced age of data.[8]

New navigation
signals[edit]

Main article: GPS signals

It has been suggested that
portions of this article be moved into
GPS
signals#Modernization and additional GPS signals. (Discuss)

This article duplicates, in
whole or part, the scope of other article(s) or
section(s), specifically, GPS
signals#Modernization and additional GPS signals. Please discuss this
issue on the talk page and conform with Wikipedia's
Manual of Style by replacing the section with a link and a summary of
the repeated material, or by spinning off the repeated text into an
article in its own right. (December
2013)

Civilian L2
(L2C)[edit]

One of the first announcements was the addition of a new civilian-use signal
to be transmitted on a frequency other than the L1 frequency used for the
existing GPS Coarse
Acquisition (C/A) signal. Ultimately, this became known as the L2C signal
because it is broadcast on the L2 frequency (1227.6 MHz). It is transmitted
by all block IIR-M and later design satellites, but until the new OCX (Block 1)
system is in place, the signal consists of a default message ("Type 0") that
does not provide full navigational data.[9]
OCX Block 1 with the L2C navigation data is scheduled to enter service in
February 2016.[10][11]

The L2C signal is tasked with providing improved accuracy of navigation,
providing an easy-to-track signal, and acting as a redundant signal in case of
localized interference.

The immediate effect of having two civilian frequencies being transmitted
from one satellite is the ability to directly measure, and therefore remove, the
ionospheric delay error for that satellite. Without such a measurement, a GPS
receiver must use a generic model or receive ionospheric corrections from
another source (such as a Satellite
Based Augmentation System). Advances in technology for both the GPS
satellites and the GPS receivers have made ionospheric delay the largest source
of error in the C/A signal. A receiver capable of performing this measurement is
referred to as a dual frequency receiver. The technical characteristics of it
are:

L2C contains two distinct PRN sequences:

CM (for Civilian Moderate length code) is 10,230 bits in length,
repeating every 20 milliseconds.

CL (for Civilian Long length code) is 767,250 bits, repeating every
1,500 milliseconds (i.e.,
every 1.5 s).

Each signal is transmitted at 511,500 bits per second (bit/s); however, they are multiplexed to form a
1,023,000 bit/s signal.

CM is modulated with a 25 bit/s
navigation message with forward error
correction, whereas contains no additional modulated data).

The long, non-data CL sequence provides for approximately 24 dB greater
correlation protection (~250 times stronger) than L1 C/A.

L2C signal characteristics provide 2.7 dB greater data recovery and 0.7 dB
greater carrier tracking than L1 C/A

The L2C signals' transmission power is 2.3 dB weaker than the L1 C/A
signal.

In a single frequency application, L2C has 65% more ionospheric error than
L1.

It is defined in IS-GPS-200.[12]

Military
(M-code)[edit]

A major component of the modernization process, a new military signal called
M-code was designed to further improve the anti-jamming and secure access of the
military GPS signals. The M-code is transmitted in the same L1 and L2
frequencies already in use by the previous military code, the P(Y) code. The new
signal is shaped to place most of its energy at the edges (away from the
existing P(Y) and C/A carriers).

Unlike the P(Y) code, the M-code is designed to be autonomous, meaning that
users can calculate their positions using only the M-code signal. P(Y) code
receivers must typically first lock onto the C/A code and then transfer to lock
onto the P(Y)-code.

In a major departure from previous GPS designs, the M-code is intended to be
broadcast from a high-gain directional antenna,
in addition to a wide angle (full Earth) antenna. The directional antenna's
signal, termed a spot beam, is intended to be aimed at a specific region
(i.e., several hundred kilometers in diameter) and increase the local signal
strength by 20 dB (10× voltage field strength, 100× power). A side effect of
having two antennas is that the GPS satellite will appear to be two GPS
satellites occupying the same position to those inside the spot beam.

While the full-Earth M-code signal is available on the Block IIR-M
satellites, the spot beam antennas will not be available until the Block III
satellites are deployed, tentatively in 2014. Like the other new GPS signals,
M-code is dependent OCX—specifically Block 2—which is schedule to enter service
in October 2016.[13][11]

Other M-code characteristics are:

Satellites will transmit two distinct signals from two antennas: one for
whole Earth coverage, one in a spot beam.

Modulation is binary offset
carrier

Occupies 24 MHz of bandwidth

It uses a new MNAV navigational message, which is packetized instead of
framed, allowing for flexible data payloads

There are four effective data channels; different data can be sent on each
frequency and on each antenna.

It can include FEC and error detection

The spot beam is ~20 dB more powerful than the whole Earth coverage
beam

M-code signal at Earth's surface: –158 dBW for whole Earth antenna, –138
dBW for spot beam antennas.

Safety of Life
(L5)[edit]

Safety of Life is a civilian-use signal, broadcast on the L5 frequency
(1176.45 MHz). In 2009, a WAAS satellite sent the initial L5 signal test
transmissions. SVN-62, the first GPS block IIF
satellite, continuously broadcast the L5 signal starting on June 28, 2010.
However, like the L2C signal, the L5 broadcast will not include a data message
until OCX comes online.[14]
The L5 navigation data will not be transmitted until OCS Block 2 enters
service,[9]
though there is some speculation that it will be made available in Block 1.[13][11]

Improves signal structure for enhanced performance

Higher transmission power than L1 or L2C signal (~3dB, or twice as
powerful)

Wider bandwidth, yielding a 10-times processing gain

Longer spreading codes (10 times longer than used on the C/A code)

Located in the Aeronautical
Radionavigation Services band, a frequency band that is available world
wide.

WRC-2000 added space signal component to this aeronautical band so aviation
community can manage interference to L5 more effectively than L2

It is defined in IS-GPS-705.[15]

New Civilian L1
(L1C)[edit]

L1C is a civilian-use signal, to be broadcast on the same L1 frequency
(1575.42 MHz) that contains the C/A signal used by all current GPS users.
The L1C will be available with first Block III launch, scheduled for 2014,[16]
however the full navigation data (like L5) is dependent on OCX Block 2 entering
service.[9]

Implementation will provide C/A code to ensure backward compatibility

Assured of 1.5 dB increase in minimum C/A code power to mitigate any noise
floor increase

Non-data signal component contains a pilot carrier to improve
tracking

Enables greater civil interoperability with Galileo
L1

It is defined in IS-GPS-800.[17]

Block III
satellite improvements[edit]

Increased signal power at the Earth's surface

M-code: –158 dBW / –138 dBW.

L1 and L2: –157 dBW for the C/A code signal and –160 dBW for the P(Y) code
signal.

L5 will be –154 dBW.

Researchers from The Aerospace
Corporation confirmed that the most efficient means to generate the
high-power M-code signal would entail a departure from full-Earth coverage,
characteristic of all the user downlink signals up until that point. Instead, a
high-gain antenna would be used to produce a directional spot beam several
hundred kilometers in diameter. Originally, this proposal was considered as a
retrofit to the planned Block IIF satellites. Upon closer inspection, program
managers realized that the addition of a large deployable antenna, combined with
the changes that would be needed in the operational control segment, presented
too great a challenge for the existing system design.[18]

NASA has requested that Block III satellites carry laser retro-reflectors.[19]
This allows tracking the orbits of the satellites independent of the radio
signals, which allows satellite clock errors to be disentangled from ephemeris
errors. This, a standard feature of GLONASS, will be included in
the Galileo
positioning system, and was included as an experiment on two older GPS
satellites (satellites 35 and 36).[20]

The USAF is working with NASA to add a DASS payload to the
second increment of GPS III satellites as part of the MEOSAR system.[21]

Ground
control segment improvements[edit]

The control segment determines the orbital position of satellites and
transmits information to satellites in space to keep the GPS system operational
and performing within specification. The Operation Control Segment (OCS)
currently serves as the control segment of record. It provides the operational
capability that supports global GPS users and keeps the GPS system operational
and performing within specification. OCS successfully replaced the legacy
1970’s-era mainframe computer at Schriever Air Force Base in September 2007.
After installation, the system helped enable upgrades and provide a foundation
for a new security architecture.

In 2010, the United States Air Force announced plans to develop a modern
control segment, which would act as a critical part of the GPS modernization
initiative. OCS will continue to serve as the ground control system of record
until the new system, Next Generation GPS Operation Control System[22]
(OCX), is fully developed and functional.

The new capabilities provided by OCX will be the cornerstone for
revolutionizing GPS’s mission capabilities, and enabling [23]
Air Force Space Command to greatly enhance GPS operational services to US combat
forces, civil partners and myriad domestic and international users.

The GPS OCX program also will reduce cost, schedule and technical risk. It is
designed to provide 50% [24]
sustainment cost savings through efficient software architecture and
Performance-Based Logistics. In addition, GPS OCX expected to cost millions less
than the cost to upgrade OCS while providing four times the capability.

The GPS OCX program represents a critical part of GPS modernization and
provides significant information assurance improvements over the current GPS OCS
program.

OCX will have the ability to control and manage GPS legacy satellites as
well as the next generation of GPS III satellites, while enabling the full
array of military signals.

Built on a flexible architecture that can rapidly adapt to the changing
needs of today’s and future GPS users allowing immediate access to GPS data
and constellations status through secure, accurate and reliable
information.

Empowers the warfighter with more secure, actionable and predictive
information to enhance situational awareness.

Enables new modernized signals (L1C, L2C, and L5) and has M-code
capability, which the legacy system is unable to do.

Provides significant information assurance improvements over the current
program including detecting and preventing cyber attacks, while isolating,
containing and operating during such attacks.

Supports higher volume near real-time command and control
capability.

On September 14, 2011,[25]
the U.S. Air Force announced the completion of GPS OCX preliminary design review
and confirmed that the OCX program is ready for the next phase of development.
The GPS OCX program has achieved major milestones and is on track to support the
GPS IIIA launch in May 2014.

See also[edit]

GPS
signals

GPS satellite

List of GPS
satellite launches

References[edit]

^
"U.S. Air Force Awards Lockheed Martin Contracts to Begin Work on
Next Set of GPS III Satellites" (Press release) Lockheed Martin
2013-02-25

^ a
b
"U.S. Air Force Awards Lockheed Martin GPS III Flight Operations
Contract" (Press release) Lockheed Martin 2012-05-31

^
U.S. Coast Guard
Navigation Center. "GPS FAQ".
U.S. Department of Homeland Security.

^
"U.S. Air Force Awards Lockheed Martin Team $1.4 Billion Contract
To Build GPS III Space System" (Press release). Lockheed Martin.
2008-05-15.

^
"Raytheon Wins Next-Gen GPS Award". Aviation Week. The
McGraw-Hill Companies, Inc. 2010-05-01.

^
"Lockheed Orders GPS 3A Satellite Buses from ATK"

^
http://www.lockheedmartin.com/us/news/press-releases/2012/january/0112_ss_gps.html

^
http://www.gps.gov/systems/gps/space/

^ a
b
c
"New Civil Signals: Second Civil Signal". National
Coordination Office for Space-Based Positioning, Navigation, and Timing.
2013-02-06. Retrieved
2013-11-21.

^
"Control
Segment: Next Generation Operational Control System". National
Coordination Office for Space-Based Positioning, Navigation, and Timing.
2013-09-26. Retrieved
2013-11-21.

^ a
b
c
Kolibaba, Ray
(2012-11-14). "GPS OCX Program Status". Stanford 2012 PNT Challenges and
Opportunities Symposium. Retrieved
2013-11-21.

^
"Interface Specification IS-GPS-200, Revision E" (PDF). Coast
Guard Navigation Center. 2010-06-08.

^ a
b
Divis, Dee Ann
(January–February 2013). "More Than Money
Worries: OCX and the New Civil Signals". Inside GNSS. Retrieved 2013-11-21.

^
"New Civil Signals: Third Civil Signal". National
Coordination Office for Space-Based Positioning, Navigation, and Timing.
2013-02-06. Retrieved
2013-11-21.

^
"Interface Specification IS-GPS-705, Revision A" (PDF). Coast
Guard Navigation Center. 2010-06-08.

^
"Block III GPS Upgrade for Satellites to be Tested in Colorado by
Lockheed Martin". TMCnet. 2011-12-13.

^
"Interface Specification IS-GPS-800, Revision A" (PDF). Coast
Guard Navigation Center. 2010-06-08.

^
Lazar, Steven
(Summer 2002). "Modernization and the Move to GPS III". Crosslink
3 (2): 42–46.

^
"ILRS
Meeting on Retroreflector Arrays".

^
"Slides from ILRS Meeting on Retroreflector Arrays". April
2006.

^
NASA
Search and Rescue Mission Office : Distress Alerting Satellite System
(DASS)

^
"GPS ADVANCED CONTROL SEGMENT(OCX)".

^
"GPS III Operational Control Segment (OCX)".
GlobalSecurity.org.

^
"The USA’s GPS-III Satellites". Defense Industry Daily.
2011-10-13.

^
"GPS Completes Next Generation Operational Control System
PDR". Air Force Space Command News Service. 2011-09-14.

External links[edit]

Cheung, Wai; Stansell, Tom; Fontana, Richard D.
(2001-09-01). "The Modernized L2 Civil Signal". GPS
World.

Barker, Capt. Brian C.; Betz,, John W.; Clark,
John E.; Correia, Jeffrey T.; Gillis, James T.; Lazar, Steven; Rehborn, Lt.
Kaysi A.; Straton, III,, John R. "Overview of the GPS M Code Signal".

"Getting to M". GPS World. 2005-04-01.

"GPS
III / GPS Block III". GlobalSecurity.org. 2008-04-17.

"GPS III Operational Control Segment (OCX)".
GlobalSecurity.org. 2008-04-17.

Perton, Marc (2006-01-25). "Government turns up volume on GPS". Engadget. AOL
Inc.

Ballenger, Col. Allan (2006-09-26). "GPS Program Update" (PDF). Space and Missile Systems
Center.

Wilt, Lt. Col. John (2001-09-10). "GPS Modernization" (PPT).

Office of Space Commercialization. "GPS
Modernization". U.S. Department of Commerce.

v

t

e

NAVSTAR
Global Positioning System satellites

Block I

1

2

3

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8

9

10

11

Block II

1

2

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5

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7

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9

Block IIA

1

2

3

4

5

6

7

8

9

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16

17

18

19

Block IIR

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

Block
IIRM

1

2

3

4

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8

Block IIF

1

2

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5

6

7

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Block
IIIA

1

2

3

4

5

6

7

8

List of
GPS satellites

Retrieved from "http://en.wikipedia.org/w/index.php?title=GPS_Block_IIIA&oldid=591500944"

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