The System: GLONASS Fumbles Forward

May 1, 2014  - By 0 Comments
GLONASS PLOT from the Roscosmos GLONASS Information-Analytical Centre, showing the 12-hour outage, with full service eventually restored on April 2.

GLONASS PLOT from the Roscosmos GLONASS Information-Analytical Centre, showing the 12-hour outage, with full service eventually restored on April 2.

Two April Disruptions Furnish Fodder for Multi-GNSS Receivers and Alternative PNT

In an unprecedented total disruption of a fully operational GNSS constellation, all satellites in the Russian GLONASS broadcast corrupt information for 11 hours, from just past midnight until noon Russian time (UTC+4) on April 2 (or 5 p.m. on April 1 to 4  a.m. April 2, U.S. Eastern time). This rendered the system completely unusable to all worldwide GLONASS receivers. Full service was subsequently restored.

“Bad ephemerides were uploaded to satellites. Those bad ephemerides became active at 1:00 a.m. Moscow time,” reported one knowledgeable source. GLONASS navigation messages contain, as they do for every GNSS in orbit, ephemeris data used to calculate the position of each satellite in orbit, and information about the time and status of the entire satellite constellation (almanac); user receivers on the ground processed this data to compute their precise position.

The GLONASS fix could not take effect until each satellite in turn could be reset, during its pass over control stations in Russian territory, in the Northern Hemisphere, thus taking nearly 12 hours.

During the outage, CEO Neil Vancans of Altus Positioning Systems reported “We are currently experiencing calls from customers all over the world who are experiencing GLONASS ‘outages’ and we have advised customers to switch GLONASS tracking off on our receivers.”

Such a — possibly human, possibly computer-generated — error could conceivably occur with GPS, Galileo, or BeiDou. “Another reason to have backups,” mused Richard Langley of the University of New Brunswick. “And not just other GNSS.”

Trouble Chronolog. The constellation suffered a second failure two weeks later. On April 14, eight GLONASS satellites were simultaneously set unhealthy for about half an hour, meaning that most GLONASS or multi-constellation receivers would have ignored those satellites in positioning computations. In addition, one other satellite in the fleet was out of commission undergoing maintenance. This might have left too few healthy satellites to compute GLONASS-only receiver positions in some locations.

The two blackouts followed two other high-profile disasters: the destruction-upon-launch of three new GLONASS satellites in July 2013, and the Pacific drowning-upon-launch of three satellites in December 2010.

Internal Dialog. The semi-official Russian news daily Izvestia (“Truth”) reported that the loss of service was inconsequential for Russian users. Loose translation courtesy of Google:

“Temporary GLONASS failure has not led to tangible consequences for consumers of services because chip manufacturing exclusively with GLONASS for the mass market is practically nil: there are chips that work only with the GPS signals, and there are those that see both GPS and GLONASS.”

In other words, there are practically no mass-market devices, even in Russia, that use exclusively GLONASS.

“In any case, the failure of the entire system for a long period is a serious blow to the image of GLONASS, especially in a situation where Russia has made efforts to promote domestic navigation system to external markets. Plus in 2012, the Russian government officially promised to maintain the characteristics of the international community GLONASS at the proper level for 15 years.”

Industry View, Multi-GNSS. During the first outage, chip company Broadcom was conicidentally conducting multi-constellation receiver tests in Asia. Frank van Diggelen, the company’s chief GNSS scientist, stated, “We have definitive data to show how a multi-constellation receiver survives such an outage. Test data coincident with the GLONASS ephemeris disruption show how a GPS/GLONASS/QZSS/BeiDou receiver survives the complete disruption of one of the constellations.”

A Broadcom 47531receiver tracking GPS/GLONASS/QZSS/BeiDou signals simultaneously and using logic to analyze redundant measurements to check the validity of all measurements successfully identified and removed the bad GLONASS ephemeris, maintaining position continuity and accuracy. Another receiver under test at the same time, tracking only GPS and GLONASS, wandered significantly in its position reports.

Industry View, Back Up PNT. Calling it an “unprecedented and deeply worrying total disruption…[that] shook the industry,” Locata Corporation reiterated its call for redundant terrestrial systems to back up GNSS in the wake of the outage.

Nunzio Gambale, Locata CEO, said “We have been telling the industry for years that you cannot have a critically important capability like GPS without also having a backup! What is Plan B if the satellite systems fail? What replaces the space signal when there is a problem? This event should terrify every nation, government, and company that depends on navigation satellites for their business or, in some cases, their very lives.”

GNSS navigation and timing functions underpin the world’s banking systems, stock exchanges, digital TV and Internet, cell-phone networks, and, in some cases, the national electricity supply, Locata pointed out. GPS, in particular, plays a crucial role in transportation, shipping, and logistics, serving as the enabling technology for critical functions like air traffic control. Reliability is therefore not just important; it is essential across all applications.

“We ignore the possibility of these ‘Black Swan’ events at our own peril,” added Chris Rizos of the University of New South Wales.

eLoran Authorization in Progress

Russia’s April 1 GLONASS blackout occurred, ironically, only hours after the U.S. House of Representatives passed legislation to preserve infrastructure that could support a backup system for GPS that could be used for critical infrastructure and applications in the event of a similar disaster occurring in the United States.

The 2014 Coast Guard Authorization Act requires the Department of Homeland Security (DHS) to halt dismantling and disposal of infrastructure that could be used for a terrestrial system during times and in places where GPS is not available.

DHS had announced in 2008 that it would build such a backup system, but it never did so, and actually began dismantling, destroying, and divesting itself of Loran equipment and properties. The equipment, facilities, and sites could be used to implement a new generation eLoran system for GPS backup, among other applications. Despite strong recommendations to the contrary by its own panel of experts, the Obama administration, DHS, and the Coast Guard moved in 2009 to kill the Loran program.

Watchdogs. Congress has lately become more visibly concerned about the vulnerability of the nation’s space systems. The 2014 National Defense Authorization Act tasked the administration with reporting on how it was going to provide necessary national security capabilities when space systems were disrupted. More recently, Congressmen Duncan Hunter (Republican, California), chair of the House Coast Guard and Marine Transportation Subcommittee, held a hearing at which he expressed his concern that the nation has no backup for GPS. He also expressed his frustration with the Department of Homeland Security, reporting that “They said they need to do a study about their study.”

Congressman John Garamendi (Democrat, California), commented “GPS will go down one day. The question is, is there a backup?”

The legislation passed by the House authorizes DHS to partner with public or private entities to build a system that would not only back up GPS, but also work indoors, underground and underwater — all characteristics of long-wave Loran technology.

Resilient PNT. Dana Goward, president of the Resilient Navigation and Timing Foundation, said such a project would be relatively inexpensive. “If the existing equipment and infrastructure are preserved and reused, the system could be restored and put into operation for less than half the cost to dispose of it.”

“It isn’t an issue of money,” Goward continued. “It is a question of the government taking this problem seriously and acting on it.”

The foundation has as offered to partner with the government to build the system.

“Our government has known about this issue for a long time,” Goward said. “At least since 2001. And there has been a standing presidential direction to obtain backup capability since 2004. But for some reason, it hasn’t yet happened.”

The government’s official website about GPS (www.gps.gov) has recently updated its page on eLoran and Loran-C with a tracking log for Coast Guard and Maritime Transportation Act of 2014, which now goes to the Senate.

IRNSS’s Second of Seven

India’s Space Research Organisation launched a navigation satellite on April 4. IRNSS-1B is the second of seven that will comprise the first-generation Indian Regional Navigation Satellite System (IRNSS). It joins IRNSS-1A, already in orbit.

IRNSS will consist of three geostationary satellites and two pairs in inclined geosynchronous orbits. Each IRNSS satellite uses a rubidium-based atomic clock to keep time, transmitting signals on L and S-band frequencies at 1176.45 and 2492.028 megahertz respectively.

Lag in Recent GPS IIF’s Health Status

By Richard Langley

The GPS Block IIF satellite, IIF-5 or SVN64 (PRN30), launched on February 21, had not as of press time been set healthy. Typically, GPS satellites are checked out and made operational within about a month after launch.

The delay is due to an extended navigation test being performed by the GPS master control station. A navigation upload for SVN64 was performed in March with ephemeris and clock data as usual streching weeks in advance. However, unlike with operational satellites, no further updated uploads have been performed. The aging ephermis and clock data gradually becomes less and less accurate as time goes by, but should degrade gracefully.

Some observers will have noticed that the received navigation data from SNV64 changes infrequently. Currently, the navigation data changes once per day with an epoch of 13:00 GPS Time, unlike every two hours with operational satellites. And the data fit interval is 26 hours, compared to four hours.

The test is scheduled to run until mid-May.

 

GPS World staff

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