A new GPS civilian signal is now available for use. The new signal is stronger, more accurate, more resilient to interference events, and interoperable with European Galileo system.
On Jan. 13 at 21:29 Finnish time, the first GPS III satellite (SVN74) was marked healthy after extensive operational testing in orbit. The satellite broadcasts PRN04 identification codes. It also transmits a new GPS civilian signal, known as L1C, different than the legacy L1 C/A signal used nowadays.
10 times longer
The two signals are transmitted at the same frequency, but L1C codes are 10 times longer than L1 C/A. This makes the signal more robust to interference when multiple satellites are tracked on the same frequency band.
“Marking a satellite health means receivers can use this satellite in their positioning, navigation and timing applications,” said Octavian Andrei, senior research scientist at the Finnish Geospatial Research Institute (FGI). “L1C is the 4th GPS signal for the civilian use.” The Finnish Geospatial Research Institute is a part of the National Land Survey of Finland.
The other three civilian signals of GPS are L2C, L5 and L1 C/A.
Interoperable with the European GNSS signalL1C signal is transmitted on L1-band at 1575.42 MHz. It is meant to replace the legacy C/A signal in the future. L1C allows for the first time GPS compatibility and full interoperability with signals from other satellite systems, such as E1 signal from the European Galileo.
The interoperability with Galileo is further enhanced by transmission of the inter-system timing biases; that is, the GPS-Galileo Time Offset. All these improvements will bring further benefits and developments to the GNSS market and civilian users in general.
Ionosphere no problem with dual-frequency
Andrei said the new signals means “Exciting times ahead for the civilian users and applications that demand precise satellite positioning and navigation. Most of the effects due to the ionosphere layers of the atmosphere are removed by combining signals from two frequency bands sufficiently apart from each other. This is the case with L1 and L2 or L1 and L5. All these civilian signals are stronger and more robust than ever before,” he explained.
The satellite signals are affected by errors while travelling through the atmosphere. The main errors are due to the ionosphere, which is a dispersive medium and frequency dependent. The latter proves to be actually a significant benefit for the precise applications.
The new signal (L1C, marked with blue) is 3-5 dBHz stronger and more robust than the legacy L1 C/A signal (marked with orange). (Image: Octavian Andrei)
More than 99 % of the ionosphere effect is removed by forming special linear combination of signals observed on two different frequencies. This is the main reason why high-precision is achieved with dual-frequency receivers.
FinnRef network ready for new satellites and signals
“Two GPS III satellites have been launched until now and two more are expected to be launched during 2020. With signals from four satellites, we will also be able to estimate L1C-only positions,” Andrei said.
The first GPS III satellite SVN74, nicknamed Vespucci, was launched on Dec. 23, 2018. The second satellite SVN75, nicknamed Magellan, was launched on Aug.22, 2019. The third and the fourth satellite are planned to be launched in March and July during 2020. The first L1C testing signals were recorded at the FinnRef station in Metsähovi on April 5, 2019.
FinnRef national network includes state-of-the-art multi-constellation tracking stations distributed around Finland. These stations are capable of tracking multiple satellite signals on multiple L-band frequencies from almost 120 GNSS satellites, including the European Union’s Galileo, US GPS, Russian GLONASS, and Chinese BeiDou constellation.
Using new signals often requires updates to station equipment, usually meaning firmware updates on the receiver software. After the new firmware enabling L1C tracking is properly tested, the receivers will be updated and then whole FinnRef will start tracking GPS L1C.
When managed by a new ground control system, GPS III satellites will offer triple the accuracy and eight times the anti-jamming capabilities of the satellites currently comprising the U.S. Air Force’s GPS constellation. Users military and civilian will reap ample benefits.
Everything changed for space-based positioning, navigation and timing around the world on Dec. 23, 2018. Or maybe it didn’t. The innovations heralded by the launch of the first GPS III satellite will take years more to occur. We tabulate here the advances that Generation Three will bring over GPS-to-date, and review the timeline for their actual arrival.
While these new capabilities exist — in concept — in space, they can’t be leveraged on the ground (or in the air, or at sea) until a sufficient number of additional GPS III satellites have joined the constellation, and until a new ground control system comes online. This will occur — perhaps — in 2023. At that time the satellites’ talents will be unleashed.
“As more GPS III satellites join the constellation, it will bring better service at a lower cost to a technology that is now fully woven into the fabric of any modern civilization,” stated Lt. Gen. John Thompson, commander of the U.S. Air Force’s Space and Missile Systems Center and the Air Force’s program executive officer for space.
The many GPS III upgrades should make the service more reliable and accurate for civilians, more secure against those who want to jam military users, and more cyber-secure for everyone.
TALKIN’ ‘BOUT OUR GENERATION
GPS constellations have grown through six major iterations since 1978. The sixth, GPS IIF, rose during the years 2010 to 2016. Those 12 satellites are all designed to last 12 years. Some of their notable features include the ability to receive software uploads, better jamming resistance and increased accuracy.
GPS III, the seventh generation, will launch nine more satellites to join SV01 already in space. GPS III SV02 is scheduled to launch in July of this year, SV03 in late 2019, and SV04 in 2020. The final III payload should rise in 2023. From that point on, the follow-on era of GPS IIIF takes over.
How Long, How Long? “Projections for how long the current constellation will [continue to] be fully capable have increased by nearly two years to June 2021, affording some buffer to offset any additional satellite delays,” reported the Government Accounting Office at the end of 2017. This provided some schedule buffer for launching the first GPS III satellite, but it did not reduce the desire to launch as soon as the booster rocket became available.
The new birds will introduce new capabilities to meet higher demands of both military and civilian users: once filled out, the GPS III constellation will bring three times better accuracy and up to eight times improved anti-jamming capabilities. Spacecraft life requirement will extend to 15 years, 25 percent longer than the latest GPS satellites and twice the original design life of the oldest satellites on orbit today.
The new L1C civil signal broadcast by GPS III is an interoperable signal with other international global navigation satellite systems, like Galileo, improving connectivity for civilian users.
GPS III will eventually actualize full M-code capability — carried aboard the IIR-Ms and IIFs but not yet completely implemented — in support of warfighter operations. GPS III M-code capability exceeds that of GPS IIR-M and GPS IIF.
GPS III will complete the deployment of the L2C civil signal and the L5 safety-of-life signal capabilities that began with \GPS IIR-M and GPS IIF satellites.
Finally, GPS III will enact improved integrity: the ability of the satellite to detect and issue alerts on its own reduced accuracy, should that phenomenon ever occur.
Military Signal Power Up. Encrypted M-code signals will be up to eight times more powerful than currently. This makes them more reliable. but also enables the sats to overcome efforts to jam their signals.
Other signals also offer increased signal power at the Earth’s surface. L1 and L2: −158.5 dBW for aC/A code signal and −161.5 dBW for the P(Y) code signal. L5 will be −154 dBW.
Family Features. The most recent generations of the GPS constellation. IIR, IIR-M and III were produced by Lockheed Martin, while IIF was built by Boeing. One GPS IIA satellite is still in operation, at 25 years young (design life was 7.5 years). All satellites carry Harris Corporation payloads. (Graphic sourced from: Lockheed Martin and Boeing Co.)
L SIGNALS
L2C, the second open GPS signal, after L1 C/A, has been available from every new GPS satellite since the first IIR-M launch in 2005. L5, the third open GPS signal, became available with the first IIF launch in 2010. Now L1C, the fourth open GPS signal, joins the band, broadcasting from every new GPS satellite, starting with the recent GPS III launch (see First Light).
The first GPS III satellite is in checkout and testing that could last up to 18 months before it enters service. “After its Dec. 23 launch, GPS III SV01 successfully completed its orbit raising and deployment of all of its antennas and solar arrays. On Jan. 8, the satellite’s navigation payload began broadcasting navigation signals,” said Johnathon Caldwell, Lockheed Martin vice president for navigation systems. “On-orbit testing continues, but the navigation payload’s capabilities have exceeded expectations and the satellite is operating completely healthy.”
Testing, Testing. Using the Air Force’s Back-to-Basics program, which involved early prototyping and simulations, Lockheed Martin developed GPS III with an approach that involved rigorous quality-build certificates, component testing and system-level testing. The comprehensive requirements verification and validation process ensured more than 30,000 requirements were achieved. The system functional qualification includes the performance verification in multiple environmental tests, including the acoustic, thermal vacuum (TVAC) and electromagnetic spectrum.
“We consider thermal vacuum the gold standard for testing any satellite before it goes into operations,” Col. Steve Whitney, director, GPS Directorate, wrote in GPS World in December. “It really is putting the craft through the paces. When it goes through the testing, the satellite is on. It is working. It is exposing it to the heat and the cold and the zero pressure while the satellite is functional. The entire thermal vac testing from start to end is about 70 days. Test like you fly. From the time it launches and deployment sequence, we test it like it is real. Minus the shaking, the satellite thinks it is getting launched. Meanwhile, our people are looking at the data and its health. TVAC is a huge milestone for a satellite to go through and come out no issues.”
To date, more than 90 percent of parts and materials for all 10 GPS III satellites have been received from more than 250 aerospace companies in 29 states.
BRAIN OF THE BUNCH
THE FIRST GPS III satellite was fully assembled and entered into SV single-line flow when Lockheed Martin technicians integrated its system module, propulsion core and antenna deck. (Photo: Lockheed Martin)
Harris Corporation is a subcontractor to Lockheed Martin for development and production of GPS III Mission Data Units (MDUs) and transmitters for the GPS space section. Six have been delivered.
The Harris MDU, together with the Atomic Frequency Standards and the L-band transmitter equipment, make up the Navigation Payload Element. The MDU performs the primary mission of the GPS satellite: generation of the navigation signals and data on a continuous basis. The MDU controls the generation of the precise timing signals used for navigation signals while distributing the timing signals to other satellite components.
This MDU is 70 percent digital. The next to come, aboard GPS IIIF satellites, will be fully digital.
When asked about the advantages of an all-digital payload, Harris Corporation’s Jason Hendrix, PNT program director, told GPS World in April 2018, “The advantages and the 30 percent difference are the timekeeping system portion. We’re moving from manual, analog timing to digital to deliver to the Air Force more flexibility. It’s a nice option to have to be able to reprogram in orbit and maybe enhance capabilities desired in the future.”
LIVING BETTER, LIVING LONGER
Greater mission longevity is one of the key improvements GPS III delivers over those currently in service. Space Vehicles 1–10 have a planned mission life of 15 years, 25 percent longer than their predecessors. That begs the question, “How long should a satellite live in space, with technology innovation occurring almost annually?”
Advanced payload technology provides a partial answer. Lockheed Martin and Harris point to new payload capabilities with built-in flexibility to adapt satellites in orbit to technology advances, as well as changes in missions. According to Harris, the fully digital navigation payload will provide the ability to change and upgrade the satellites incrementally over mission life.
In late 2017, Lockheed announced a partnership with NEC Corporation to introduce artificial intelligence for computer learning in orbit. The company touted significant advances in processors and a move toward next-generation antennas, arrays and transmitters to drive more satellite flexibility, capability and resilience.
FROM THE GROUND UP
GPS IIIF’s M-Code can be broadcast from a high-gain directional antenna in a concentrated, high-powered spot beam, in addition to a wide-angle, full-Earth antenna. (Artist rendering: Lockheed Martin)
GPS III’s military upgrades require new ground control stations, a replacement effort called OCX that has suffered repeated delays and cost increases, due to the complexity of the programming and requirements modifications. The new jamming-resistant military signal will not be available until the new, highly complex ground control system is available, and that is not expected until 2022 or 2023. Delay and cost considerations were driven in part by full implementation of all Department of Defense 8500.2 “Defense in Depth” information assurance standards without waivers, giving it the highest level of cybersecurity protections of any DoD space system.
Deliverables for GPS OCX are divided into three blocks. Block 0 delivery took place in fall 2017, enabling it to support the December launch. Block 1 delivery will take place in 2021, providing full operational capability to control both legacy and modernized satellites and signals. Block 2, delivered concurrently with Block 1, adds operational control of L1C and modernized M-code.
In 2018, wrote Col. Whitney of the GPS Directorate, “We have actively utilized the [Block 0] system in a variety of exercises, training events, compatibility tests and launch readiness events. We also completed a comprehensive security review of the system to demonstrate our readiness to start operations. The system is ready to go. We continue to work the development of the OCX Block 1 system and are wrapping up the initial coding of the system early in 2019, leading into our integration and test campaign.”
Given delays in OCX, “the Directorate is actively working two major upgrades to bridge the gap,” Whitney continued. “The first is GPS III Contingency Operations (COps) modification which will allow the 2nd Space Operations Squadron (2SOPS) to command and control the GPS III family of vehicles in a mission state matching today’s legacy signals for all users world-wide. The second modification is M-code early use (MCUE), which enables 2 SOPS to operationalize the Modernized GPS military (M-code) navigation signals for the warfighter.”
Before December’s launch, OCX underwent rigorous cybersecurity vulnerability assessments that tested the system’s ability to defend against both internal and external cyber threats. GPS OCX prevented the broadcast of corrupt navigation and timing data in all tests, bolstering the program’s readiness for GPS III.
“We’ve built a layered defense and implemented all information assurance requirements for the program into this system,” said Dave Wajsgras, president of Raytheon Intelligence, Information and Services. “The cyber threat will always change, so we’ve built OCX to evolve and to make sure it’s always operating at this level of protection.”
The new Harris navigation payload offers a smooth transition to use of OCX. The payload for the first 10 GPS III satellites has been verified for OCX compatibility so the same OCX commands will seamlessly port to the Harris fully digital design, minimizing integration risks and associated costs.
According the the GAO, “Full M-code capability —which includes both the ability to broadcast a signal via satellites and a ground system and user equipment to receive the signal — will take at least a decade once the services are able to deploy military GPS user equipment (MGUE) receivers in sufficient numbers.” The April 2019 issue of GPS World will review M-code implementation across U.S. DoD platforms.
THE FUTURE’S NOT OVER YET
In spring 2018, Lockheed Martin submitted a proposal for the GPS III Follow On (GPS IIIF) program, which will add enhanced capabilities to the satellites. New hardware — a high-gain directional antenna — aims signals in a spot beam at a limited area, but blasts the signal at high power for strategic use by the military.
Inter-Satellite Links. Block IIIF satellites will carry laser retro-reflectors to enable orbit tracking independently of the satellites’ radio signals, which in turn will allow satellite clock errors to be disentangled from ephemeris errors. A standard feature of GLONASS, this is included in the Galileo positioning system, and was flown as an experiment on two older GPS satellites, 35 and 36.
In September 2018, the Air Force selected Lockheed Martin to build up to 22 additional satellites under the GPS IIIF program.
