For a quarter of a century, GPS (Global Positioning System) and other GNSS (Global Navigation Satellite Systems) have steadfastly provided excellent time and positioning information to mariners of vessels great and small, across oceans and ponds, in all seasons and in all weathers. We are now seeing a second generation of boaters and seafarers who have never known a world without chart plotters and AIS, many of whom have never once plotted even their GPS position on a paper chart.
Mostly this confidence in our electronics is well founded. Many of us have successfully crossed thousands of miles of waterways using this technology as our primary means of navigation. However, we are now reaching a better understanding of just how vulnerable this system can be, and the possible necessity of navigating with GPS-independent means of determining position, course, and speed while underway. Some of these vulnerabilities have been known and understood since the first GPS/Navstar satellites were launched in 1978, while other vulnerabilities are just now coming to light.
It should be remembered that when GPS/Navstar was first envisioned and created, it was never intended for U.S. civilian and commercial users, let alone foreign nations, to have access to (or even knowledge of) this system.
In autumn of 1983, a number of unrelated (or accidentally related) incidents very nearly turned the Cold War into the other kind. If you have never heard of the joint NATO exercise called “Able Archer 83,” it is likely because everything relating to that was classified until three years ago. It’s beyond the scope of this article—but worthy of an internet search—at a time when you don’t actually need to sleep afterward. The gist of it is that throughout most of 1983, the United States and NATO were engaged in a series of progressively escalating military exercises that Soviet intelligence communities mistook for prelude to an actual nuclear war.
Into this tense environment, on September 1, 1983, was thrown a civilian commercial airliner, Korean Airlines Flight 007, on its final leg from Anchorage to Seoul, South Korea. After a series of navigational errors, the Boeing 747 strayed north of its intended track, and crossed over the restricted Soviet airspace of the Kamchatka Peninsula and then Sakhalin Island. At 18:26 UTC, a Soviet Sukhoi Su-15 interceptor jet shot down KAL-007, killing all 269 passengers and crew on board.
In direct response to this tragedy, president Ronald Reagan ordered that GPS signals and technology, once online and fully operational, be made freely available to all civilian users and all nations, with varying degrees of accuracy.
Selective Ability was developed in order for the U.S. government to degrade GPS regionally during times of conflict. The most extreme use of this to date was during the 1999 Kargil War between India and Pakistan, when both nations were allegedly denied access to U.S. GPS signals. This inspired India to develop their own satellite navigation system, IRNSS. Other nations have also developed independent GNSS systems, such as the Russian GLONASS, the Chinese BeiDou (also called COMPASS), and Europe’s Galileo. Some higher-end GNSS receivers can accept signals from several or all of these, providing some internal level of redundancy, but deliberate degradation of signal by the operating nation will always be a possibility.
GPS signals can also be degraded on small and large scales by radio interference from telecommunication satellites and land stations, and also by deliberate jamming. Even when directly overhead, satellites are never closer to the user than 20,000 km, and the transmitters are broadcasting at only about 500 watts, so the receiving power is less than (usually considerably less than) three watts at the receiver. Any L-band radio broadcast with twice the received signal strength will override the GPS signal. This may be accidental and innocent, or it may be quite deliberate. Small GPS jammers may be purchased (illegally in most places!) for under $100. Most of these off-the-shelf jammers have a very limited transmission range, but can often be easily modified.
AIS spoofing is even easier, and requires no special equipment other than a laptop computer, access to the internet, and a motive. AIS is a wonderful tool, but I would never, ever trust it as my only means of collision avoidance.
On July 23, 2012, earth’s orbit was intersected by a solar coronal mass ejection (CME) of monstrous proportions. If it had happened nine days earlier it would have hit earth dead-on, and would have caused massive electrical and electronic outages and disruptions on earth as well as in earth’s orbit. Cost estimates for such an event range between $2- and $3,000,000,000,000 dollars (that’s trillions), and we would still be cleaning up the mess that would have happened in the aftermath.
Our GPS and other GNSS satellites orbit in the “safe zone” between the inner and outer Van Allen radiation belts. This provides them protection from the belts themselves, but significantly diminishes the protection the belts afford us on earth from such solar storms. It is fair to assume that in the event of a solar storm of this magnitude, enough of the GPS satellites would be put out of commission to seriously degrade or even eliminate GPS availability on earth. Even much smaller solar storms could significantly degrade GPS outputs as they are received on earth.
NASA predicts that the probability of the earth being hit square-on by a CME of this magnitude over the next decade is a seemingly incredible 12%.
All of these threats to satellite navigation have been known and understood for some time. However, other than ground-based jamming and spoofing, no one had given serious consideration to the GPS satellites being directly vulnerable to hostile action. The reasoning for this was simple (and reasonable). Whereas the Low Earth Orbiting (LEO) communications, weather, and other satellites were indeed vulnerable to attack from basically any government or organization which could get a ballistic missile into space, GPS satellites were simply in too high an orbit to be reached by an aggressor—we cannot even reach them ourselves. Another issue we have with GPS satellites is that once they are on station, no nation on earth presently has the technology to send a human being up to repair them. Launching GPS satellites is a little like tossing a frisbee up onto a very high roof; you can get it up there, but you’re never going to get it down again.
Then, in 2013 and 2014, in addition to their other anti-satellite assets, China and Russia each demonstrated capabilities for their own satellites to intercept and destroy GPS satellites in Medium Earth Orbit (about 20,000 km up; for comparison the International Space Station orbits at 400 kilometers) as well as geosynchronous communications satellites at 36,000 km.
In unrelated news, as of 2015 the United States Air Force, Navy, Coast Guard, Federal Aviation Administration and the BSA have all taken a renewed and marked interest in celestial, terrestrial, and other forms of conventional navigation. As of September 2015, for example, the USCG-licensing exams for commercial mariners for Near Coastal (out to 200 nautical miles offshore) deck licenses now require celestial navigation, which until now was only required for vessels on trans-oceanic voyages.
If the Navy, Coast Guard, and Merchant Marine are now requiring their people to be proficient in satellite-independent navigation, then recreational mariners need to be as well.
However, many of the older classic texts on navigation—because they were written in a time before GPS—presume the routine carriage of equipment that not only do many of us not own, we may never have actually seen before. Not only have I never seen a stadimeter (an optical rangefinder) or alidade (turning board) on a cruising powerboat, I have never seen them on container ships or tankers.
Our challenge then is to be able to navigate, safely and routinely, without input from GPS satellites using the equipment we have (or should have) onboard a typical cruising powerboat. To this end, in this column we will be discussing ancient techniques, modern technologies, and practical applications of inland, coastal ,and ocean navigation. For many of the articles, we will presume that your vessel has a radar, a depth sounder, a chart plotter of some sort, and paper charts as a back up. To this we may add a few inexpensive tools which realistically should be onboard anyway, but often are not.
Vessels have navigated safely across oceans without GPS for millennia, but in the past two decades many of us have become complacent and dependent on that technology, to the point that many vessels (both recreational and commercial) would not set sail without it. It is time to remember that GPS is simply one very useful tool in our navigation toolbox, but we have many others as well.
And at the end of the day, whatever our tools, and whatever our resources, we still have to get the boat home.