The Science of Navigation

ANCIENT NAVIGATION Mankind’s earliest navigational experiences are lost in the shadows of the past. But history does record a number of instances in which ancient mariners observed the locations of the sun, the moon, and the stars to help direct their vessels across vast, uncharted seas. Bronze age Minoan seamen, for instance, followed torturous trade […]
ANCIENT NAVIGATION Mankind’s earliest navigational experiences are lost in the shadows of the past. But history does record a number of instances in which ancient mariners observed the locations of the sun, the moon, and the stars to help direct their vessels across vast, uncharted seas. Bronze age Minoan seamen, for instance, followed torturous trade routes to Egypt and Crete, and even before the birth of Christ, the Phoenicians brought many shiploads of tin from Cornwall. Twelve hundred years later, the Vikings were probably making infrequent journeys across the Atlantic to settlements in Greenland and North America. How did these courageous navigators find their way across such enormous distances in an era when integrating accelerometers and handheld receivers were not yet available in the commercial marketplace? Herodotus tells us that the Phoenicians used the Pole Star to guide their ships along dangerous journeys, and Homer explains how the wise goddess instructed Odysseus to “keep the Great Bear on his left hand” during his return from Calypso’s Island. CELESTIAL NAVIGATION Eventually, the magnetic compass reduced mankind’s reliance on celestial navigation. One of the earliest references to compass navigation was made in 1188, when Englishmen Alexander Neckam published a colorful description of an early version consisting of “a needle placed upon a dart which sailors used to steer when the Bear is hidden by clouds.” Eighty years later the Dominican friar Vincent of Beauvais explained how daring seamen, whose boats were deeply shrouded in fog, would “magnetize the needle with a lodestone and place it through a straw floating in water.” He then went on to note that “when the needle comes to rest it is pointing at the Pole Star.” The sextant, which was developed and refined over several centuries, made Polaris and its celestial neighbors considerably more useful to navigators on the high seas. When the sky was clear, this simple device–which employs adjustable mirrors to measure the elevation angles of stellar objects with great precision– could be used to nail down the latitude of the ship so that ancient navigators could maintain an accurate east-west heading. However, early sextants were largely useless for determining longitude because reliable methods for measuring time aboard ship were not yet available. The latitude of a ship equals the elevation of the Pole Star above the local horizon, but its longitude depends on angular measurements and the precise time. The earth spins on its axis 15 degrees every hour, consequently, a one second timing error translates into a longitudinal error of 0.004 degrees–about 0.25 nautical miles at the equator. The best 17th-century clocks were capable of keeping time to an accuracy of one or two seconds over an interval of several days, when they were sitting on dry land. But, when they were placed aboard ship and subjected to wave pounding, salt spray, and unpredictable variations in temperature, pressure, and humidity, they either stopped running entirely or else were too unreliable to permit accurate navigation. To the maritime nations of 17th century Europe, the determination of longitude was no mere theoretical curiosity. Sailing ships by the dozens were sent to the bottom by serious navigational errors. As a result of these devastating disasters caused by inaccurate navigation, a special act of Parliament established the British Board of Longitude, a study group composed of the finest scientists living in the British Isles. They were ordered to devise a practical scheme for determining both latitude and longitude of English ships sailing on long journeys. After heated debate, the Board offered a prize of 20,000 British pounds to anyone who could devise a method for fixing a ship’s longitude within 30 nautical miles after a transoceanic voyage lasting six weeks. One proposal advanced by contemporary astronomers would have required that navigators take precise sightings of the moons of Jupiter as they were eclipsed by the planet. If practical trials had demonstrated the workability of this novel approach, ephemeras tables would have been furnished to the captain of every flagship or perhaps every ship in the British fleet. The basic theory was entirely sound, but, unfortunately, no one was able to devise a workable means for making the necessary observations under the rugged conditions existing at sea. THE MARINE CHRONOMETER However, in 1761, after 47 years of painstaking labor, a barely educated British cabinet maker named John Harrison successfully claimed the 20,000 British pound prize, which in today’s purchasing power would amount to about $1 million. Harrison solution centered around his development of a new shipboard timepiece, the marine chronometer, which was amazingly accurate for its day. On a rocking, rolling ship in nearly any kind of weather, it gained or lost, on average, only about one second per day. Thus, under just about the worst conditions imaginable, Harrison’s device was nearly twice as accurate as the finest landbased clocks developed up to that time. During World War II, ground-based radionavigation systems came into widespread use when military commanders in the European theater needed to vector their bombers toward specific targets deep in enemy territory. Both Allied and Axis researchers soon learned that ground-based transmitters could provide reasonably accurate navigation within a limited coverage regime. In the intervening years America and various other countries have operated a number of ground-based radionavigation systems. Many of them – Decca, Omega, Loran – have been extremely successful. But in recent years, American and former Soviet scientists have been moving their navigation transmitters upward from the surface of the earth into outer space. There must be some compelling reason for installing navigation transmitters aboard orbiting satellites. After all, it costs something like $100 million to construct a navigation satellite and another $100 million to launch it into space. Moreover, at least a half-dozen orbiting satellites are needed for a practical spaceborne radionavigation system. WHAT IS NAVIGATION? Navigation can be defined as the means by which a craft is given guidance to travel from one known location to another. Thus, when we navigate, we not only determine where we are, we also determine how to go from where we are to where we want to be. 1. Piloting 2. Dead reckoning 3. Celestial navigation 4. Inertial navigation 5. Electronic or radionavigation Piloting, which consists of fixing the craft’s position with respect to familiar landmarks, is the simplest and most ancient method of navigation. In the 1920s bush pilots often employed piloting to navigate from one small town to another. Such a pilot would fly along the railroad tracks out across the prairie, swooping over isolated farmhouses along the way. Upon arrival at a village or town, the pilot would search for a water tower with the town’s name printed in bold letters to make sure the intended destination have not been overshot. Dead reckoning is a method for determining position by extrapolating a series of velocity increments. In 1927 Charles Lindbergh used dead reckoning when he flew his beloved Spirit Of St. Louis on a 33-hour journey from Long Island to Le Bourget Field outside Paris. Incidentally, Lindberg hated the name. The original name was “dead reckoning” (deduced reckoning), but newspapers of the day could never resist calling it “dead reckoning” to remind their readers of the many pilots who had lost their lives attempting to find their way across the North Atlantic. Celestial navigation is a method of computing position from precisely timed sightings of the celestial bodies, including the stars and the planets. Primitive celestial navigation techniques date back thousands of years, but celestial navigation flourished anew when cabinetmaker John Harrison constructed surprisingly accurate clocks for use in conjunction with sextant sightings aboard British ships sailing on the high seas. The uncertainty in a celestial navigation measurement builds up at a rate of a quarter of a nautical mile for every second timing error. This cumulative error arises from the fact that the earth rotates to displace the stars along the celestial sphere. Inertial navigation is a method of determining a craft’s position by using integrating accelerometers mounted on gyroscopically stabilized platforms. Years ago navigators aboard the Polaris submarine employed inertial navigation systems when they successfully sailed under the polar ice caps. Electronic or radionavigation is a method of determining craft’s position by measuring the travel time of an electromagnetic wave as it moves from transmitter to receiver. The position uncertainty in a radionavigation system amounts to at least one foot for every billionth of a second timing error. This error arises from the fact that an electromagnetic wave travels at a rate of 186,000 miles per second or one foot in one billionth of a second ACTIVE AND PASSIVE RADIONAVIGATION According to the Federal Radionavigation Plan published by the United States government, approximately 100 different types of domestic radionavigation systems are currently being used. All of them broadcast electromagnetic waves, but the techniques they employ to fix the user’s position are many and varied. Yet, despite its apparent complexity, radionavigation can be broken into two major classifications: 1. Active radio navigation 2. Passive radio navigation. A typical active radionavigation system is sketched in Figure 1. Notice that the navigation receiver fixes its position by transmitting a series of precisely timed pulses to a distant transmitter, which immediately rebroadcast them on a different frequency. The slant range from the craft to the distant transmitter is established by multiplying half of the two-way signal travel time by the speed of light. In a passive radionavigation system (see Figure 1), a distant transmitter sends out a series of precisely timed pulses. The navigation receiver picks up the pulses, measures their signal travel time, and then multiplies by the speed of light to get the slant range to that transmitter. A third navigational approach is called bent pipe navigation. In a bent-pipe navigation system a transmitter attached to a buoy or a drifting balloon broadcasts a series of timed pulses up to an orbiting satellite. When the satellite picks up each timed pulse, it immediately rebroadcasts it on a different frequency. A distant processing station picks up the timed pulses and then uses computerprocessing techniques to determine the approximate location of the buoy or balloon.
Most radionavigation systems determine the user’s position by measuring the signal travel time of an electromagnetic wave as it travels from one location to another. In active radionavigation the timed signal originates on the craft doing the navigating. In passive radionavigation it originates on a distant transmitter.

The USS Virginia – America’s Newest Nuclear Sub

By Captain Ray Wellborn, Instructor, Applied Technology Institute On July 4, 2004, the U.S. Navy commissioned the lead ship in a new class of nuclear-powered attack sub-marine: USS VIRGINIA (SSN 774). The new submarine warship is 377 feet in length, 34 feet in the beam, has a draft of 30.5 feet at the designer’s waterline […]
By Captain Ray Wellborn, Instructor, Applied Technology Institute On July 4, 2004, the U.S. Navy commissioned the lead ship in a new class of nuclear-powered attack sub-marine: USS VIRGINIA (SSN 774). The new submarine warship is 377 feet in length, 34 feet in the beam, has a draft of 30.5 feet at the designer’s waterline and displaces 7,800 dead weight tons submerged. She can accommodate a ship’s company of 134 including 14 officers. VIRGINIA’s length-to-breadth ratio of 11.09 is com-parable to an 11.01 for LOS ANGELES-Class submarines with a 33-foot beam, and is somewhat more than SEAWOLF’s 8.4 with a 42-foot beam, but a little less than Ohio’s 13.3, also with a 42-foot beam. Officially, the U.S. Nary will neither confirm nor deny any U.S. submarine’s speed to be greater than 20 knots, nor any test-depth to be greater than 400 feet. According to open liter- attire, however, VIRGINIA is powered by a S9G pressurized water reactor, made by General Electric, which will not require re-coring for the life of the ship./ Her propulsion plant is rated to produce 40,000 shaft horsepower for a single shaft, and sustain a maximum rated submerged speed of 34 knots. The wall-thickness and diameter of VIRGINIA’s inner pressure hull of cold- rolled, high-yield strength steel, with scrupulously designed hull-penetrations and conscientious seam-welds, allows submarine design engineers to impose a safe-diving test-depth of 1,600 feet. Furthermore, this innovative design reduces the number of needed hull-penetrations with eight non-hull penetrating antennae packages. To meet yet another top-level requirement VIRGINIA is fitted with SEAWOLF-level acoustic quietness for stealth, as well as acoustic tile cladding for active acoustic signal absorption. For additional tasking, VIRGINIA is fitted with an integral nine-man lockout chamber for use with the Advanced SEAL (sea, air and land) Delivery System (ASDS), which essentially is a mini-submarine capable of dry-delivery of a SEAL team. Moreover, the internal torpedo magazine space arrangement can be adapted to provide 2,400 cubic feet of space for up to 40 SEAL team members arid their equipment. And, VIRGINIA is capable of carrying and operating advanced unmanned underwater vehicles, wake-homing detection equipment and a deployable active hi-static sonar source. VIRGINIA is an extremely capable submarine and, in the hands of a well- trained, experienced ship’s company skilled in the operational arts of submarine warfare, has an incisive ability for both deep-ocean and shallow- water operations of all kinds, including antisubmarine warfare. So, for comparison to early strivings for more precise navigation on the open sea, consider the most sophisticated state-of-the art computer-data processors, which precisely calculate the output of an absolutely ingenious arrangement of gyros and accelerometers as they sense the slightest nano-scale movement. This ever-so-precise, self-contained navigational system is fitfully named SINS, the Ship’s Inertial Navigation System. In the modem era, the encapsulated inner workings of SINS can be held in the palm of your hands. But, at the top of the list, are the technological advancements resident in the Common Submarine Radio Room (CSRR) in that a U.S. submarine can be in constant communication with the submarine operating authority while submerged at sea anywhere in the oceans of the world For perspective and historical comparison of technological advances, note that the first nationally authorized submarine warship was not officially commissioned until 1900, while the first trans-Atlantic radio-telegraph was not operational until 1901. VIRGINIA’s modern CSRR for entering the 21st century is for a worldwide battle space. A modernized ship self-defense system will replace the advanced combat direction system in VIRGINIA-Class upgrades. All the software programs for the command-control system module in VIRGINIA are compatible with the Joint Military Command Information System. The Global Command-Control System (GCCS) is a multi-service information management system for maritime users that displays and disseminates data through an extensive array of common interfaces. GCCS is also a multi-service information management system for maritime users that can display and disseminate data through an extensive array of common interfaces. GCCS is also a multi-sensor data-fusion system for command analyses and decision- making. Thus, in the main, it is utilized for overall force coordination The ocean surveillance information system receives, processes, displays and disseminates joint-service information regarding fixed and mobile targets on land and at sea. The innovative design of the upgraded Automated Digital Network System (ADNS) encompasses all radio frequency circuits for routing and switching both strategic and tactical command control communication computer information (C41) with an internet-like transmission control protocol. In doing so, ADNS links battle group units with each other and with the digital information system network. The ADNS now has 224 ship-based units, and four shore-based sites. Network operation centers are linked to three naval computer and telecommunication area master stations, plus one in the Persian Gulf at Bahrain. The Global Broadcast Service is the follow-on for U.S. Navy ultra-high- frequency radio communication via satellite. By 2009, the advanced wide- band system will be the communication upgrade for all U.S. submarines and surface ships, and there is a version planned for U.S. aircraft installation that is under study, Virginia’s combat system suite satisfies a top-level requirement to counter multiple threats with a mission-essential-need statement that details a very effective set of acoustic sensors. The suite features two reel-able towed, linear sonar arrays, the TB-l6 and the thin-line TB-29. Just inside the thin-skinned acoustic window in the bow section of the outer hull is a very sophisticated, state-of-the-art active-passive spherical sonar array, the AN/BQQ-5E. In addition, there are wide-aperture flank-mounted passive sonar arrays; a keel and fin-mounted high sonic frequency active sonar for under-the-ice ranging and maneuvering, and for mine detection and avoidance; a medium sonic frequency active sonar for target ranging; a sonar sensor for intercept of active-ranging signals from an attacking torpedo; and, a self- noise acoustic monitoring system. Moreover, all acoustic systems have advanced signal processors and, where appropriate, algorithms are programmed for beam forming. The Electronic System Measures suite features the AN/BRD-7F radio direction finder; the electronic signal monitors, AN/WLR-lH and AN/WLR-8(V2/6); the AN/WSQ-5 and AN/BLD-1 radio frequency intercept periscope-mounted devices; and the AN/WLQ-4(V1), AN/WLR-l0 and AN/BLQ-l0 radar warning devices. The AN/BPS-15A and BPS-16 are I and J-band navigational piloting radars, respectively, with each having separate wave-guides—one mounted inside a retractable mast and the other mounted inside a periscope. Virginia has four 21-inch-diameter internally loaded torpedo tubes with storage cradles for a combination of an additional 22 torpedoes, missiles, mines, and 20-foot-long, 21-inch diameter Autonomous Underwater Vehicles. In the free-flooding area between the outer and inner hulls, just aft of the bow-mounted AN/BQQ-5E spherical sonar array is Virginia’s Vertical Launch System, comprised of twelve externally loaded 21-inch diameter launch tubes for Tomahawk, the Sea-Launched-Cruise-Missile (SLCM). Shallow water is an anathema for submariners because submarines on the surface are exceptionally vulnerable. Thus, it is said that the best place to sink a submarine is while it is in port. Does that mean that Virginia cannot operate effectively in shallow water?Absolutely not! Another disconcerting imprecation to submariners is hearing the high-pitch “pings— active sonar accompanied by the shrill of cavitations from small, high-speed screws, which are the distinctive sounds of an acoustic torpedo running to ruin your entire day. French author Jules Verne (1825-1905) entertained readers with exciting tales of undersea adventure featuring his fictional submarine Nautilus in his book 20,000 Leagues Under The Sea. Notably, USS Nautilus (SSN 571) logged much more than 20,000 leagues under the sea—like, 80,000 nautical mile before her first re-coring, and Virginia will log over 125,000 leagues of submerged steaming in her service life– without refueling. The nuclear-powered submarine is a far-ranging, very effective, versatile warship for the 21st century—and, the projection of national power by ASDS and SLCMs from international waters only requires unilateral action by the National Command Authority.
U.S. Navy career Captain Ray Wellborn
Over a 30-year U.S. Navy career Captain Ray Wellborn served some 13 years in submarines. He graduated with a B.S. from the U.S. Naval Academy in 1959, a M.S. in Electrical Engineering from the Naval Postgraduate School in 1969, and a M.A. from the Naval War College in 1976. He was a senior lecturer for marine engineering at Texas A&M University Galveston from 1992 to 1996, and currently is a consultant for maritime affairs, and a once-a-year part-time instructor for the Applied Technology Institute’s three-day course titled “Introduction to Submarines—and, Their Combat Systems.  

Routing Ships on the High Seas

Researchers and technicians at Oceanroutes in Palo Alto, California, earn their daily bread using three different types of satellites for finding safe and efficient trajectories for large oceangoing vessels. Each optimum route takes into account real-time weather conditions, the physical characteristics of the ship, and the wishes of the ship’s master — who is given […]
Researchers and technicians at Oceanroutes in Palo Alto, California, earn their daily bread using three different types of satellites for finding safe and efficient trajectories for large oceangoing vessels. Each optimum route takes into account real-time weather conditions, the physical characteristics of the ship, and the wishes of the ship’s master — who is given an updated trajectory twice each day. The Navstar constellation provides accurate positioning information that is relayed from the ship to Palo Alto through INMARSAT satellites. Weather satellites from various countries furnish the necessary meteorological reports. Sitting in their comfortable offices in Palo Alto and in several other cities around the globe, Oceanroute’s engineers work with more than a thousand ships in a routine month. Each recommended route is custom designed for that particular ship “on that specific voyage, with the given cargo load, status of trim and draft, with the ship’s own distinctive speed and sea-handling characteristics.” The computer program emphasizes emerging weather, but it also takes into account currents, fog, choke points, navigational hazards, and sea ice in northern regions. Some cargoes, such as fruit and oil, are temperature-sensitive; others, such as automobiles and heavy machinery, may shift under heavy waves. Still others have time-critical deliveries. The Oceanroute’s program successfully takes these and numerous other factors into account whenever it makes its routing recommendations. The cost of the service for a typical voyage is $800, a fee that is repaid 30 to 40 times over by shortened travel times and more efficient maritime operations. In 43,000 crossings aided by Oceanroute’s computers, travel times have been reduced an average of four hours in the Atlantic and eight hours in the Pacific. Operating a large oceangoing vessel can cost as much as $1,000 per hour, so time savings alone can translate into enormous reductions in cost. Other expenses are also reduced. When Oceanroute’s services were not yet available, the cost of repairing weather-damaged ships ran from $32,000 to $53,000 in an average year. Today, for some companies, these costs have plummeted to only about $6,000. Cargo damage has also declined. One international auto dealer told a team of Oceanroute’s researchers that his cargo damage claims had dropped by over $500,000 per year.