Jump to content

GPS Block III: Difference between revisions

From Wikipedia, the free encyclopedia
Browse history interactively
← Previous editNext edit →
Content deleted Content added
VisualWikitext
m →‎Satellites: updated link
Rescuing 2 sources and tagging 0 as dead. #IABot (v1.5.5)
Line 175: Line 175:


*NASA has requested that Block III satellites carry laser [[Retroreflector|retro-reflectors]].<ref>{{cite web |url=http://ilrs.gsfc.nasa.gov/docs/retromtg_060406.pdf |title=ILRS Meeting on Retroreflector Arrays}}</ref> 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).<ref>{{cite web |url=http://ilrs.gsfc.nasa.gov/docs/retromtg_060406_slides.pdf |title=Slides from ILRS Meeting on Retroreflector Arrays |date=April 2006}}</ref>
*NASA has requested that Block III satellites carry laser [[Retroreflector|retro-reflectors]].<ref>{{cite web |url=http://ilrs.gsfc.nasa.gov/docs/retromtg_060406.pdf |title=ILRS Meeting on Retroreflector Arrays}}</ref> 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).<ref>{{cite web |url=http://ilrs.gsfc.nasa.gov/docs/retromtg_060406_slides.pdf |title=Slides from ILRS Meeting on Retroreflector Arrays |date=April 2006}}</ref>
*The [[USAF]] is working with [[NASA]] to add a [[Cospas-Sarsat|DASS]] payload to the second increment of GPS III satellites as part of the [[MEOSAR]] system.<ref name=autogenerated1>[http://searchandrescue.gsfc.nasa.gov/dass/index.html NASA Search and Rescue Mission Office : Distress Alerting Satellite System (DASS)]</ref>
*The [[USAF]] is working with [[NASA]] to add a [[Cospas-Sarsat|DASS]] payload to the second increment of GPS III satellites as part of the [[MEOSAR]] system.<ref name=autogenerated1>[http://searchandrescue.gsfc.nasa.gov/dass/index.html NASA Search and Rescue Mission Office : Distress Alerting Satellite System (DASS)] {{webarchive|url=https://web.archive.org/web/20160304072004/http://searchandrescue.gsfc.nasa.gov/dass/index.html |date=2016-03-04 }}</ref>


== Control Segment ==
== Control Segment ==
Line 182: Line 182:


=== Next-Generation Operational Control Segment (OCX) ===
=== Next-Generation Operational Control Segment (OCX) ===
In 2010, the United States Air Force announced plans to develop a modern control segment, 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<ref>{{cite web |url=http://www.losangeles.af.mil/library/factsheets/factsheet.asp?id=18676 |title= GPS ADVANCED CONTROL SEGMENT(OCX)}}</ref> (OCX), is fully developed and functional.
In 2010, the United States Air Force announced plans to develop a modern control segment, 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<ref>{{cite web |url=http://www.losangeles.af.mil/library/factsheets/factsheet.asp?id=18676 |title=GPS ADVANCED CONTROL SEGMENT(OCX) |deadurl=yes |archiveurl=https://web.archive.org/web/20120503181621/http://www.losangeles.af.mil/library/factsheets/factsheet.asp?id=18676 |archivedate=2012-05-03 |df= }}</ref> (OCX), is fully developed and functional.


OCX features are being delivered to the United States Air Force in three separate phases, known as "blocks."<ref name="gps_control">{{cite web |url=http://www.gps.gov/systems/gps/control/ |title=GPS Control Segment |work=GPS.gov |accessdate=December 25, 2016}}</ref> The OCX blocks are numbered zero through two. With each block delivered, OCX gains additional functionality.
OCX features are being delivered to the United States Air Force in three separate phases, known as "blocks."<ref name="gps_control">{{cite web |url=http://www.gps.gov/systems/gps/control/ |title=GPS Control Segment |work=GPS.gov |accessdate=December 25, 2016}}</ref> The OCX blocks are numbered zero through two. With each block delivered, OCX gains additional functionality.

Revision as of 17:44, 9 October 2017

GPS Block IIIA
Artist's impression of a GPS Block IIIA satellite in orbit
ManufacturerLockheed Martin
Country of originUnited States
OperatorUS Air Force
ApplicationsNavigation satellite
Specifications
BusA2100
Launch mass3,880 kg (8,553 lb)[1]
Dry mass2,269 kg (5,003 lb)[1]
Power4480 W (end of life)[1]
BatteriesNickel–hydrogen battery[1]
RegimeSemi-synchronous MEO
Design life15 years
Production
StatusDevelopment
On order10
Built1
Maiden launchSpring 2018 (planned)[2]
← 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.[3] 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,[4] but significant delays[5] have pushed the initial launch to the spring of 2018.[2]

Overview

The United States' Global Positioning System (GPS) reached Fully Operational Capability on July 17, 1995,[6] 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,[7] due to multiple delays, the date has slipped to spring 2018.[2] Raytheon was awarded the Next Generation GPS Operational Control System (OCX) contract on Feb 25, 2010.[8]

Development

Block IIIA satellites use Lockheed Martin's A2100 bus structure. The propellant and pressurant tanks are manufactured by Orbital ATK from lightweight, high-strength composite materials.[9] Each satellite will carry 8 deployable JIB antennas designed and manufactured by Northrop Grumman Astro Aerospace[10]

The first GPS III satellite was originally scheduled for launch in 2014,[4] but in December 2016 the Director of the U.S. Air Force's Global Positioning Systems Directorate announced the first satellite will launch in the spring of 2018.[2] In March 2017, the US General Accounting Office stated "Technical issues with both the GPS III satellite and the OCX Block 0 launch control and checkout system have combined to place the planned March 2018 launch date for the first GPS III satellite at risk."[11] The delays have been caused by a number of factors, primarily due to issues found in the navigation payload.[5][12]

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.[13]

On April 27, 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.[14]

On September 21, 2016, the U.S. Air Force exercised a $395 million contract option with Lockheed for the ninth and tenth Block IIIA space vehicles, expected to be available for launch by 2022.[15]

Space Vehicles 11+

On May 5, 2016, the U.S. Air Force awarded three Phase One Production Readiness Feasibility Assessment contracts for GPS III Space Vehicles (SV's) 11+, one each to Boeing Network and Space Systems, Lockheed Martin Space Systems Company, and Northrop Grumman Aerospace Systems.[16] The Phase 1 contracts are part of the U.S. Air Force's competitive bid effort for a follow-on firm-fixed price production contract to build up to 22 GPS III satellites, starting with Space Vehicle 11.[17] According to the Pentagon's Chief Financial Officer, procurement funds for Space Vehicles 11+ has been pushed out to Fiscal Year 2018 (FY18) budget.[18]

On April 19, 2017, the US Air Force Space Command announced the start of the second phase of its two-phase acquisition strategy by publishing a special notice for an "Industry Day" for companies planning on bidding for the contract to manufacture GPS III vehicles 11+.[19] During the event, the Air Force will share its acquisition strategy it plans on using to evaluate proposals and solicit feedback from potential bidders. The Air Force is expected to publish the formal Request For Proposals (RFP) for SV 11+ production later in 2017 and the winning bid will be announced in late 2018. The RFP will be for a firm-fixed price (FFP) contract to start delivering spacecraft in 2025.[20]

In July 2017, the Deputy Director of the U.S. Air Force GPS Directorate stated the acquisition strategy is to award the manufacturing contracts for all 22 satellites (SV 11 through 32) to the same contractor.[21]

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 contains no navigational data.[22] OCX Block 1 with the L2C navigation data was scheduled to enter service in February 2016,[23][24] but has been delayed until 2022 or later.[25]

As a result of OCX delays, the L2C signal was decoupled from the OCX deployment schedule. All satellites capable of transmitting the L2C signal (all GPS satellites launched since 2005[22]) began broadcasting pre-operational civil navigation (CNAV) messages in April 2014, and in December 2014 the Air Force started transmitting CNAV uploads on a daily basis.[22][26] The L2C signal will be considered fully operational after it is being broadcast by at least 24 space vehicles, currently projected to happen in 2018.[27] As of April 18, 2017, L2C was being broadcast from 19 satellites.[22]

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 CL 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.[28]

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, for receivers inside the spot beam, the GPS satellite will appear to be two GPS satellites occupying the same position.

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,[24][29] but that date does not reflect the two year first satellite launch delay expected by the GAO.[30][31] Other M-code characteristics are:

  • Satellites will transmit two distinct signals from two antennas: one for whole Earth coverage, one in a spot beam.
  • Binary offset carrier modulation
  • 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)

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.

As a result of schedule delays to the GPS III control segment, the L5 signal was decoupled from the OCX deployment schedule. All satellites capable of transmitting the L5 signal (all GPS satellites launched since May 2010[32]) began broadcasting pre-operational civil navigation (CNAV) messages in April 2014, and in December 2014 the Air Force started transmitting CNAV uploads on a daily basis.[33] The L5 signal will be considered fully operational once at least 24 space vehicles are broadcasting the signal, currently projected to happen in 2024.[32] As of April 18, 2017, L5 was being broadcast from 12 satellites.[32]

  • Improves signal structure for enhanced performance
  • Higher transmission power than L1 or L2C signal (~3 dB, 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 worldwide.

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.[34]

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.

L1C broadcasting will start when GPS III Control Segment (OCX) Block 1 becomes operational, currently scheduled for 2022.[25][2] The L1C signal will reach full operational status when being broadcast from at least 24 GPS Block III satellites, currently projected for the late 2020s.[35]

  • 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.[36]

Block III satellite improvements

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.[37]

  • NASA has requested that Block III satellites carry laser retro-reflectors.[38] 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).[39]
  • 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.[40]

Control Segment

The GPS Operational Control Segment (OCS),[41] consisting of a worldwide network of satellite operations centers, ground antennas and monitoring stations, provides Command and Control (C2) capabilities for GPS Block II satellites. The latest update to the GPS OCS, Commercial Off-The-Shelf Upgrade #2 (CUP2), was completed on December 1, 2016.[42]

Next-Generation Operational Control Segment (OCX)

In 2010, the United States Air Force announced plans to develop a modern control segment, 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[43] (OCX), is fully developed and functional.

OCX features are being delivered to the United States Air Force in three separate phases, known as "blocks."[44] The OCX blocks are numbered zero through two. With each block delivered, OCX gains additional functionality.

In June 2016, the U.S. Air Force formally notified Congress the OCX program's projected program costs had risen above $4.25 billion, thus exceeding baseline cost estimates of $3.4 billion by 25%, also known as a critical Nunn-McCurdy breach. Factors leading to the breach include "inadequate systems engineering at program inception", and "the complexity of cybersecurity requirements on OCX."[45] In October 2016, the Department of Defense formally certified the program, a necessary step to allow development to continue after a critical breach.[46]

The US GAO believes the delivery date for OCX Block 0 will not be delivered until 2018, stating in a report "The contractor’s performance over the past year suggests a 2-year extended schedule approved in 2015 is insufficient. ... According to Air Force officials, the 2-year extension will likely be extended by an additional 6 months."[47]

OCX Block 0 (Launch and Checkout System)

OCX Block 0 provides the minimum subset of full OCX capabilities necessary to support launch and early on-orbit spacecraft bus checkout on GPS III space vehicles.[2]

As of April 2017, OCX Block 0 has completed its factory qualification and is scheduled for final delivery by October 2017.[48] OCX Block 0 has been deployed at Schriever Air Force Base, outside Colorado Springs, Colorado, and is currently undergoing site acceptance testing.[48]

OCX Block 1 (Civilian GPS III features)

OCX Block 1 is an upgrade to OCX Block 0, at which time the OCX system achieves Initial Operating Capability (IOC). Once Block 1 is deployed, OCX will for the first time be able to command and control both Block II and Block III GPS satellites, as well support the ability to begin broadcasting the civilian L1C signal.[2]

As of April 2017, OCX Block 1 development was underway.[48] Block 1 is scheduled for delivery to the United States Air Force in late 2020, and is projected to achieve Ready To Operate (RTO) status in the first quarter of 2022.[25][49]

In November 2016, the GAO reported that OCX Block 1 has become the primary cause for delay in activating the GPS III PNT mission.[50]

OCX Block 2 (Military GPS III features, Civilian Signal Monitoring)

OCX Block 2 upgrades OCX with the advanced M-code features for military users and the ability to monitor performance of the civilian signals.[44] In March 2017, the contractor rephased its OCX delivery schedule so that Block 2 will now be delivered to the Air Force concurrently with Block 1.[49] In July 2017, an additional nine months delay to the schedule was announced. According to the July 2017 program schedule, OCX will be delivered to the Air Force in April 2022.[51]

Contingency Operations

GPS III Contingency Operations ("COps") is an update to the GPS Operational Control Segment, allowing OCS to provide Block IIF Position, Navigation, and Timing (PNT) features from GPS III satellites.[2] The Contingency Operations effort enables GPS III satellites to participate in the GPS constellation, albeit in a limited fashion, without having to wait until OCX Block 1 becomes operational (currently scheduled for 2022).

The United States Air Force awarded the 96 million dollar Contingency Operations contract in February 2016.[52] The GPS Contingency Operations program successfully completed its Critical Design Review (CDR) in November 2016.[53] Final delivery to the United States Air Force is projected to occur in spring 2019.[2]

Deployment Schedule

Date Deployment Space Vehicles Remarks
Command & Control In GPS Constellation
OCS OCX
October 2017[48] OCX Block 0 Block II Block III
(Launch and Checkout only)[2] 		Block II OCS and OCX operate in parallel
Spring 2019[2] Contingency Operations Block II
&
Block III
January 2023[25][49][51] OCX Block 1 & OCX Block 2 Block II & Block III OCS no longer used, L1C transmissions begin, full GPS III functionality achieved

Satellites

Main article: List of GPS satellites § Block IIIA (spacecraft 1-10)

As of September 2016, there are ten Block IIIA satellites on order. The first ten Block III Space Vehicles are scheduled for launch beginning in 2018, continuing through at least 2022.[2][54]

See also

References

  1. ^ a b c d "GPS III fact sheet" (PDF). LockheedMartin. Retrieved 6 May 2016.
  2. ^ a b c d e f g h i j k l Whitney, Steven (December 2, 2016). "Directions 2017: GPS navigates the future". GPS World. Retrieved December 25, 2016.
  3. ^ "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
  4. ^ a b "U.S. Air Force Awards Lockheed Martin GPS III Flight Operations Contract" (Press release) Lockheed Martin 2012-05-31
  5. ^ a b "GPS III satellite delivery slips because of capacitor". GPS World. September 15, 2016. Retrieved December 25, 2016.
  6. ^ U.S. Coast Guard Navigation Center. "GPS FAQ". U.S. Department of Homeland Security.
  7. ^ "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.
  8. ^ "Raytheon Wins Next-Gen GPS Award". Aviation Week. The McGraw-Hill Companies, Inc. 2010-05-01.
  9. ^ "Lockheed Orders GPS 3A Satellite Buses from ATK"
  10. ^ "Northrop Grumman's Astro Aerospace Delivers Antennas For Next-Generation GPS III Satellites 3 through 6"
  11. ^ ""Assessments of Selected Weapon Programs"" (PDF). US General Accounting Office. March 2017. Retrieved June 20, 2017.
  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.gps.gov/systems/gps/space/
  14. ^ http://www.defense.gov/News/Contracts/Contract-View/Article/744434
  15. ^ Gruss, Mike (September 21, 2016). "Lockheed Martin to build two more GPS 3 satellites for U.S. Air Force". Space News. Retrieved 2016-09-22.
  16. ^ "Air Force's Space and Missile Systems Center Awards Global Positioning System III Space Vehicles 11+ Phase 1 Production Readiness Feasibility Assessment Contracts"
  17. ^ "U.S. Air Force Releases Solicitation For Next GPS 3 Satellites - See more at: http://spacenews.com/u-s-air-force-releases-solicitation-for-next-gps-3-satellites/"
  18. ^ "GPS III Budget Slashed as Air Force Shifts Money to Fix Delayed OCX" Inside GNSS, 15 Feb 2016
  19. ^ Devis, Dee Ann (April 27, 2017). "Door Open to New Bidders as Air Force Moves Closer to GPS III Buy". InsideGNSS.com. Retrieved May 3, 2017.
  20. ^ "GPS III Follow-On Phase 2 Production Draft Request for Proposal and Industry Day Announcement". US Air Force Space Command, Space and Missile Systems Center. July 10, 2017. Retrieved July 14, 2017.
  21. ^ Divis, Dee Ann (July 17, 2017). "GPS Official: Expect One Follow-on GPS III Contractor, Tech Insertion Points". InsideGNSS.com. Gibbons Media & Research LLC. Retrieved August 15, 2017.
  22. ^ a b c d "New Civil Signals: Second Civil Signal". National Coordination Office for Space-Based Positioning, Navigation, and Timing. 2016-09-23. Retrieved 2017-04-20.
  23. ^ "Control Segment: Next Generation Operational Control System". National Coordination Office for Space-Based Positioning, Navigation, and Timing. 2013-09-26. Retrieved 2013-11-21.
  24. ^ a b Kolibaba, Ray (2012-11-14). "GPS OCX Program Status" (PDF). Stanford 2012 PNT Challenges and Opportunities Symposium. Retrieved 2017-05-02.
  25. ^ a b c d "GAO: New GPS Ground System, Not GPS III Engineering, Primary Cause for Delays". Inside GNSS. November 30, 2016. Retrieved December 25, 2016.
  26. ^ Jewell, Don (August 12, 2015). "L2C and Next-Generation Smart PNT Receivers". GPS World. Retrieved December 28, 2016.
  27. ^ Cameron, Alan (July 22, 2015). "To L2C or Not to L2C? That Is the Operational Question". GPS World. Retrieved December 28, 2016.
  28. ^ "Interface Specification IS-GPS-200, Revision E" (PDF). Coast Guard Navigation Center. 2010-06-08.
  29. ^ Divis, Dee Ann (January–February 2013). "More Than Money Worries: OCX and the New Civil Signals". Inside GNSS. Retrieved 2013-11-21.
  30. ^ "Future GPS: The USA's GPS-III Programs". Defense Industry Daily. May 14, 2014. Retrieved May 17, 2014.
  31. ^ "Defense Acquisitions: Assessments of Selected Weapon Programs". Report Number GAO-13-294SP. U.S. Government Accountability Office.
  32. ^ a b c "Civil Signals - Third Civil Signal: L5". GPS.gov. September 23, 2016. Retrieved April 20, 2017.
  33. ^ "DOD Announces Start of Civil Navigation Message Broadcasting". U.S. Department of Defense. April 25, 2014. Retrieved December 28, 2016.
  34. ^ "Interface Specification IS-GPS-705, Revision A" (PDF). Coast Guard Navigation Center. 2010-06-08.
  35. ^ "Civil Signals - Fourth Civil Signal: L1C". GPS.gov. September 23, 2016. Retrieved December 28, 2016.
  36. ^ "Interface Specification IS-GPS-800, Revision D" (PDF). National Coordination Office for Space-Based Positioning, Navigation, and Timing. 2013-09-24.
  37. ^ Lazar, Steven (Summer 2002). "Modernization and the Move to GPS III" (PDF). Crosslink. 3 (2): 42–46.
  38. ^ "ILRS Meeting on Retroreflector Arrays" (PDF).
  39. ^ "Slides from ILRS Meeting on Retroreflector Arrays" (PDF). April 2006.
  40. ^ NASA Search and Rescue Mission Office : Distress Alerting Satellite System (DASS) Archived 2016-03-04 at the Wayback Machine
  41. ^ "GPS Operational Control Segment". U.S. Air Force. November 27, 2012. Retrieved December 25, 2016.
  42. ^ "GPS constellation has upgraded control system". Shephard Media. December 5, 2016. Retrieved December 25, 2016.
  43. ^ "GPS ADVANCED CONTROL SEGMENT(OCX)". Archived from the original on 2012-05-03. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  44. ^ a b "GPS Control Segment". GPS.gov. Retrieved December 25, 2016.
  45. ^ http://spacenews.com/air-force-declares-nunn-mccurdy-breach-on-gps-ground-system/
  46. ^ Insinna, Valerie (October 17, 2016). "Raytheon's OCX Offering Survives Nunn-McCurdy Breach". DefenseNews. Retrieved December 25, 2016.
  47. ^ Chaplain, Cristina (May 17, 2017). "DOD Continues to Face Challenges of Delayed Delivery of Critical Space Capabilities and Fragmented Leadership" (PDF). US General Accounting Office. Retrieved June 20, 2017.
  48. ^ a b c d Insinna, Valerie (April 6, 2017). "Amazon cloud, automation help resuscitate OCX program". DefenseNews.com. Retrieved April 11, 2017.
  49. ^ a b c Divis, Dee Ann (April 27, 2017). "OCX Passes Deep Dive Review; GAO Says Program Risk Remains High". InsideGNSS.com. Retrieved April 28, 2017.
  50. ^ Cite error: The named reference gps_ocx_primary delay was invoked but never defined (see the help page).
  51. ^ a b Divis, Dee Ann (July 31, 2017). "OCX Delayed Again as Development Jumps to $6 Billion". InsideGNSS.com. Gibbons Media & Research LLC. Retrieved August 15, 2017.
  52. ^ Seligman, Lara (March 3, 2016). "Weapons Tester Warns of Risk to Air Force's GPS Contingency Plan". Defense News. Retrieved December 25, 2016.
  53. ^ "Lockheed Martin and the U.S. Air Force Move Forward with Ground System Upgrade to Support Contingency GPS III Operations". Lockheed Martin. December 12, 2016. Retrieved April 11, 2017.
  54. ^ GPS III 9 and 10 procured, targeting 2022 launch GPS World. October 3, 2016
Retrieved from "https://en.wikipedia.org/w/index.php?title=GPS_Block_III&oldid=804540392"