GPS Block IIIA

GPS Block IIIA

Artist's impression of a GPS Block IIIA satellite in orbit
Manufacturer Lockheed Martin
Country of origin United States
Operator US Air Force
Applications Navigation satellite
Specifications
Bus A2100
Design life 15 years
Launch mass 3,880 kg (8,553 lb)[1]
Dry mass 2,269 kg (5,003 lb)[1]
Power 4480 W (end of life)[1]
Batteries Nickel–hydrogen battery[1]
Regime Semi-synchronous MEO
Production
Status Development
On order 4
Retired >
← 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.[2] The United States Air Force plans to purchase up to 32 GPS III satellites. GPS IIIA-1, the first satellite in the series, was projected to launch in 2014,[3] but significant delays[4][5] have pushed the launch to no earlier than 2017.[6]

Overview

The United States' Global Positioning System (GPS) reached Fully Operational Capability on July 17, 1995,[7] 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 was projected for 2014.[8] Raytheon was awarded the Next Generation GPS Operational Control System (OCX) contract on Feb 25, 2010.[9]

Development

Block IIIA satellites use Lockheed Martin's A2100 bus structure. They are manufactured by Orbital ATK from lightweight, high-strength composite materials.[10] Each satellite will carry 8 deployable JIB antennas designed and manufactured by Northrop Grumman Astro Aerospace[11]

The first GPS III satellite was originally scheduled for launch in 2014,[3] but the March 2014 GAO report expects that the first satellite will launch no sooner than April 2016.[4][5] The most significant issues causing delays appear to be with the navigation payload.[12]

The U.S. Air Force awarded Lockheed Martin a $238 million contract for production of the third and fourth satellites in January 2012.[13]

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.[14]

On April 27th, 2016, Space Exploration Technologies Corp., in Hawthorne, California was awarded an $82,700,000 firm-fixed-price contract for launch services to deliver a GPS III satellite to its intended orbit. This launch service contract will include launch vehicle production, mission integration, and launch operations for a GPS III mission. The locations of performance are Hawthorne, California; Cape Canaveral Air Force Station, Florida and McGregor, Texas. The work is expected to be completed by July 31, 2018.[15]

New navigation signals

Main article: GPS signals

Civilian L2 (L2C)

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 can be transmitted by all block IIR-M and later design satellites. The original plan stated that until the new OCX (Block 1) system is in place, the signal would consist of a default message ("Type 0") that does not provide full navigational data.[16] OCX Block 1 with the L2C navigation data is scheduled to enter service in February 2016,[17][18] but that date does not reflect the two year first satellite launch delay projected by the GAO.[4][5] Attempts are underway to try to decouple L2C availability from the OCX Block 1 schedule, starting with activation of the L2C signal in April 2014.[19][20][21]

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:

It is defined in IS-GPS-200.[22]

Military (M-code)

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. Like the other new GPS signals, M-code is dependent on OCX—specifically Block 2—which is scheduled to enter service in October 2016,[18][23] but that date does not reflect the two year first satellite launch delay expected by the GAO.[4][5] Other M-code characteristics are:

Safety of Life (L5)

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.[24] The L5 navigation data will not be transmitted until OCS Block 2 enters service,[16] though there is some speculation that it will be made available in Block 1.[18][23] Efforts are underway to accelerate the testing and availability of the L5 signal, beginning with the transmission of the L5 signal from all satellites capable of doing so starting April 28, 2014, and further adding capabilities in December 2014.[21][25]

WRC-2000 added space signal component to this aeronautical band so the aviation community can manage interference to L5 more effectively than L2. It is defined in IS-GPS-705.[26]

New Civilian L1 (L1C)

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.[27] However the full navigation data (like L5) is dependent on OCX Block 2 entering service.[16]

It is defined in IS-GPS-800.[28]

Block III satellite improvements

Increased signal power at the Earth's surface

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.[29]

Ground control segment improvements

The ground 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 Operational Control System[33] (OCX), is fully developed and functional.

The new capabilities provided by OCX will be the cornerstone for revolutionizing GPS’s mission capabilities, and enabling [34] 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%[4] 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.

On September 14, 2011,[35] 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.

Ground control segment: The GAO Perspective

While the USAF has consistently claimed that the OCX segment has always been on time and on budget, the GAO has consistently disagreed.[36][37] In March 2013 the GAO estimated that the OCX budget had increased 43% to a total cost estimate of $3.7 billion.[37][38] As of March 2013, the USAF was still claiming an April 2014 “available for launch” date for the OCX segment.[37][38] As of April 2014, OCX was far from complete and the GAO estimated OCX initial capability no sooner than October 2016.[39]

Satellites

As of January 2016, five satellites are currently planned for launch.

See also

References

  1. 1 2 3 4 "GPS III fact sheet" (PDF). LockheedMartin. Retrieved 6 May 2016.
  2. ↑ "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
  3. 1 2 "U.S. Air Force Awards Lockheed Martin GPS III Flight Operations Contract" (Press release) Lockheed Martin 2012-05-31
  4. 1 2 3 4 5 "Future GPS: The USA’s GPS-III Programs". Defense Industry Daily. May 14, 2014. Retrieved May 17, 2014.
  5. 1 2 3 4 "Defense Acquisitions: Assessments of Selected Weapon Programs". Report Number GAO-13-294SP. U.S. Government Accountability Office.
  6. ↑ "Launch of First GPS 3 Satellite Now Not Expected Until 2017". SpaceNews. Retrieved February 2015.
  7. ↑ U.S. Coast Guard Navigation Center. "GPS FAQ". U.S. Department of Homeland Security.
  8. ↑ "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.
  9. ↑ "Raytheon Wins Next-Gen GPS Award". Aviation Week. The McGraw-Hill Companies, Inc. 2010-05-01.
  10. ↑ "Lockheed Orders GPS 3A Satellite Buses from ATK"
  11. ↑ "Northrop Grumman's Astro Aerospace Delivers Antennas For Next-Generation GPS III Satellites 3 through 6"
  12. ↑ http://economictimes.indiatimes.com/news/international/world-news/us-air-force-not-happy-with-delays-on-lockheed-gps-satellite/articleshow/35465485.cms
  13. ↑ http://www.lockheedmartin.com/us/news/press-releases/2012/january/0112_ss_gps.html
  14. ↑ http://www.gps.gov/systems/gps/space/
  15. ↑ http://www.defense.gov/News/Contracts/Contract-View/Article/744434
  16. 1 2 3 "New Civil Signals: Second Civil Signal". National Coordination Office for Space-Based Positioning, Navigation, and Timing. 2013-02-06. Retrieved 2013-11-21.
  17. ↑ "Control Segment: Next Generation Operational Control System". National Coordination Office for Space-Based Positioning, Navigation, and Timing. 2013-09-26. Retrieved 2013-11-21.
  18. 1 2 3 Kolibaba, Ray (2012-11-14). "GPS OCX Program Status" (PDF). Stanford 2012 PNT Challenges and Opportunities Symposium. Retrieved 2013-11-21.
  19. ↑ Don Jewell (January 9, 2013). "2C or not 2C: An Important Signal Question". GPS World.
  20. ↑ "Air Force Directs Early Civil Navigation (CNAV) Message-Populated L2C and L5 Signals". GPS World. December 17, 2013.
  21. 1 2 "DOD Announces Start of Civil Navigation Message Broadcasting". GPS World. April 29, 2014.
  22. ↑ "Interface Specification IS-GPS-200, Revision E" (PDF). Coast Guard Navigation Center. 2010-06-08.
  23. 1 2 Divis, Dee Ann (January–February 2013). "More Than Money Worries: OCX and the New Civil Signals". Inside GNSS. Retrieved 2013-11-21.
  24. ↑ "New Civil Signals: Third Civil Signal". National Coordination Office for Space-Based Positioning, Navigation, and Timing. 2013-02-06. Retrieved 2013-11-21.
  25. ↑ "NR-209-14: DOD Announces Start of Civil Navigation Message Broadcasting". US Department of Defense. April 25, 2014.
  26. ↑ "Interface Specification IS-GPS-705, Revision A" (PDF). Coast Guard Navigation Center. 2010-06-08.
  27. ↑ "Block III GPS Upgrade for Satellites to be Tested in Colorado by Lockheed Martin". TMCnet. 2011-12-13.
  28. ↑ "Interface Specification IS-GPS-800, Revision D" (PDF). National Coordination Office for Space-Based Positioning, Navigation, and Timing. 2013-09-24.
  29. ↑ Lazar, Steven (Summer 2002). "Modernization and the Move to GPS III" (PDF). Crosslink 3 (2): 42–46.
  30. ↑ "ILRS Meeting on Retroreflector Arrays" (PDF).
  31. ↑ "Slides from ILRS Meeting on Retroreflector Arrays" (PDF). April 2006.
  32. ↑ NASA Search and Rescue Mission Office : Distress Alerting Satellite System (DASS)
  33. ↑ "GPS ADVANCED CONTROL SEGMENT(OCX)".
  34. ↑ "GPS III Operational Control Segment (OCX)". GlobalSecurity.org.
  35. ↑ "GPS Completes Next Generation Operational Control System PDR". Air Force Space Command News Service. 2011-09-14.
  36. ↑ http://www.insidegnss.com/node/3054
  37. 1 2 3 http://gpsworld.com/next-gen-gps-ground-control-system-in-question/
  38. 1 2 http://www.gao.gov/products/GAO-13-294SP
  39. ↑ http://www.gao.gov/assets/660/653431.txt

External links

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