GNSS Advances, Despite Setbacks

 - September 2, 2013, 12:45 AM
Several satellites in Europe’s satnav constellation, Galileo, are already in place, with the full complement of 30 set for launch by 2019.

After several years of anticipation, the planned earth-girdling network of five global navigation satellite system (GNSS) constellations is taking tangible form in space. Two of them–America’s GPS and Russia’s Glonass–are already fully operational. Glonass reached that goal in 2009, joining the pioneering GPS, which achieved that status in the 1980s. The other three: Europe’s Galileo, China’s Compass and India’s regional navigation satellite system (IRNSS), have each begun launches of their own GPS-like constellations, with their expected completion dates forecast in the 2018 to 2022 period.

Each constellation, consisting of up to 36 individual satellites, transmits signals at slightly different, non-interfering UHF frequencies in the dedicated satellite radio band, although each will have one frequency that will be common to all five constellations, to support future satellite and constellation interoperability. All provide basic navigation positioning data (generally with an accuracy of better than 10 meters), and each also offers, or will offer, accuracy augmentation–similar to the FAA’s Waas–down to better than three meters, as well as additional channels providing encrypted or other data for unique military or commercial use in their region of the world.

GPS was, of course, a U.S. initiative in the Cold War with Russia, and Glonass was Russia’s response. With the end of the Cold War, the U.S. continued to develop GPS, while Glonass slowly fell behind. However, virtually every other nation was quick to adopt GPS, including Russia eventually.

So why are other nations now building their own GPS-like systems, at a cost of billions of dollars? First, nations began to realize that they were becoming more and more dependent on the U.S.-controlled GPS to run their essential services, such as communications, defense, transportation, utilities and so on, while living in a world of possibly changing political alliances.

Second, satnav technology has become a huge, but still primarily U.S.-owned and -controlled, industry that produces vast amounts of wealth. For Western Europe, Russia, China and India, the political and industrial benefits of owning and controlling their own satellite constellations became irresistible. Already, Russia has decreed that within its borders, only Glonass, or Glonass integrated with GPS, will be permitted in Russian-registered aircraft, ships, ground vehicles and other applications after January 2018. It seems highly probable that China and India will eventually announce similar mandates. Smartphone sales alone in those three countries could carry a value in the billions of dollars. And, evidently to reassure future foreign investors, Russia quickly demonstrated its ability to recover from major setbacks when it lost its large Proton-M booster rocket and three Glonass satellites after a failed launch in July, by announcing that two replacement satellites would be launched in September and October. In earlier times, Russia had never provided such a level of support.

U.S. in Catch-up Mode

Meanwhile, GPS finds itself in catch-up mode, since the new foreign constellations are expected to offer several commercial fee-bearing features, such as performance guarantees, enhanced navigation and search-and-rescue support. However, the DOD’s next-generation GPS III, whose first satellite launch is planned for 2015, will remain strongly military oriented while, as today, allowing only limited civil access. With more powerful signals, GPS III will provide better jamming resistance and improved accuracy, although it is still unclear whether that will be available to civil users. GPS III will also be significantly more expensive than its non-military equivalents.

In fact, there is growing interest within the DOD in finding a future system that could replace GPS, especially to avoid its vulnerability to both unintentional and deliberate jamming and spoofing, which is said to have already limited some military operations. Ideally, such a system would not rely on any external signals and, recently, the Defense Advanced Research Projects Agency (Darpa) sought bidders for a “Chip-Scaled Combinatorial Atomic Navigator,” a small, advanced atomic/inertial navigator. Prototype tests reportedly indicate excellent position accuracy, but serious drift rates over periods longer than 20 minutes.

On the other hand, those following developments in the wake of the San Francisco Asiana Boeing 777 crash have pointed out the interesting fact that while the Runway 22L ILS glideslope was off at the time of the accident, the runway did have a Waas LPV procedure with a 213 feet decision altitude which, assuming GPS/Waas was installed in the aircraft and its data fed to the FMS, could conceivably have been used to provide substitute centerline and glideslope guidance from many miles out to support a stabilized approach to finals.

Indeed, and in retrospect, the current availability of LPV approach procedures at SFO–and at LAX, SNA and many other “fully equipped” airline airports–is a Waas safety benefit that some of us may not have fully appreciated, thinking that LPV was aimed primarily at providing better guidance for general aviation at smaller fields. Should we now be asking the FAA to provide LPV procedures at all large airports as well?

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The FAA does provide LPV at major airports, including, as the article says, on the accident runway at SFO. The issue is that Boeing, for various wrong-headed reasons (they probably saw it competing with their RNP program that required special approvals and generated revenue), steadfastly refused to implement WAAS avionics in their aircraft. Many airlines asked them about WAAS and each was told they were the only one asking and would have to bear all the development costs. WAAS LPV minima match CAT I ILS, require no airport infrastructure, allow seamless RNAV transitions to approach, support variable glide path angles and do not require protected areas near runways that can reduce airport capacity. WAAS also provides rock-solid lateral and vertical guidance right down to the surface, with none of the scalloping found with some ILS installations.

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