Navigation

Navigation - from Latin navigare (to guide a ship), Sanskrit navgathi - is the "art of steering" on water (see nautical science), on land and in the air. Its aim is to steer the vehicle or aircraft safely to the desired destination. Steering is preceded by two geometric tasks: determining the current position (location) and finding the best route to the destination.

With the beginning of space flight, the tasks of navigation were generalized to near-Earth space, which required, among other things, the transition from two-dimensional methods (2D, including flight altitude 2½D) to three-dimensional methods. The acceleration of aviation has furthermore led to the development of integrated systems, such as Flight Management Systems.

Navigation in its most general sense includes other aspects, such as the sense of balance and spatial awareness. It can then be defined as finding one's way in a topographical space in order to reach a desired location. For similar reasons, finding one 's way with computer programs on the Internet has also been called navigation. Thus, Netscape Navigator is the name of the leading web browser in the mid-1990s for Microsoft's 16-bit operating systems and Apple's Mac OS.

For some time now, the term has also been used for orientation on the Internet or in a homepage.

Basics

The activity of navigating consists of three parts:

1. Determine geographic position by locating using various methods,
2. Calculate the optimal path to the destination and
3. Guiding the vehicle to this goal, i.e. above all maintaining the optimum course, possibly taking drift into account.

Subtasks 2 and 3 require the ability to maintain traffic even under difficult conditions (e.g. in fog, danger of ice or thunderstorms) and to exclude any possibility of collision with other vehicles. Navigation therefore also includes the technology and science of being able to re-optimise the route en route in addition to locating it, as well as quickly detecting changes in the attitude and altitude of aircraft and adjusting course/speed accordingly.

The basis of any navigation is visual navigation (spatial awareness and visual control) and coupling (path calculated from the course), but today supplemented by methods of radio or satellite navigation. The latter allows even with cheap handheld devices under 100 € an accurate location determination to about 10-20 meters.

Until about the year 2000, however, dead reckoning was the most important method - calculating or estimating the distance travelled by means of course and speed (or, in the case of larger aircraft and rockets, also by means of acceleration). The longer the distance or the more complicated the route, the more this navigation (which is usually unconscious in the case of pedestrians or car drivers) must be supplemented by position measurements en route. Because even with good compasses etc., the coupling accuracy is limited to 1-3 percent of the distance covered at best, but can also deviate by 10 percent from the assumed ("gissten") course due to crosswinds and ocean currents.

Basic methods

Most navigation methods originate from nautical science, i.e. the determination of the location and control of ships. The classical aids of localization are of a geometric nature (angle measurement and direction measurement) as well as the determination of intrinsic speed and distances. They have been used for centuries in the following method groups:

• visual navigation: finding your way around the coast by memory and simple coastal or nautical charts ("portolanes")
• terrestrial navigation: the determination of the location near the coast on the basis of landmarks (prominent points on land) and occasional lighthouses. Sounding (determining the depth of the fairway) is also part of this. Today, these proven methods are supplemented by densely marked harbour entrances, various navigation marks and radio beacons.
• Dead reckoning: the continuous determination of position from course and speed. The course can be determined with the sun, celestial bodies and (since the Middle Ages) with the compass, the speed by estimation or with the railing log. To this day, the entry in the log book is supplemented by graphically adding up the distance travelled on the nautical chart. The position determined in this way is known as the "gisster" or dead reckoning and is - depending on the weather - accurate to a few percent (see also Etmal).
• If possible, wind drift is taken into account when coupling; modern aids such as course computers (for wind triangle, radio beacon, etc.) and Doppler radar increase the accuracy to about 0.5% of the distance, and inertial navigation again.
• Astronomical navigation: the determination of location by measuring the angle of elevation to the sun, navigation stars or planets. It complements the three above methods on long distances. The achievable accuracy with Jacob's staff is about 20 km, with modern sextants 1-2 km.
• These methods, which had been tried and tested for centuries, were joined for the first time by radio navigation in 1899 and satellite navigation in 1964 (see next but one chapter).
• Polynesian navigation, which has largely been lost, was based on star path and zenith star navigation, among other things. Together with the observation of waves, wind, animals and clouds, the Polynesians were thus able to find their way even to distant, flat atolls.

Long-range navigation

Long-range navigation (LRN) is the term used in nautics and aviation (long-range flight) to describe the procedures for determining location and controlling vehicles over distances of several 100 km.

The special methods of long-range navigation have today - due to the predominance of GNSS satellite methods such as GPS and GLONASS - receded into the background, but are still necessary for redundantly secured navigation independent of GPS. Until about 1995, it could be said in nautical science that long-range navigation was always required when terrestrial navigation (in the wider visual range of a coast or islands) was no longer sufficient and the destination had to be approached more precisely than about 50 km.

Astronavigation

Astronavigation by means of time and angle measurements to the sun and bright stars is the classic method that has been part of the experience of all navigators since the voyages of discovery by the Polynesians and other seafaring peoples - and is still part of training today. Until about 1970, it was the basis of long-distance navigation in the entire southern hemisphere, but was also used in northern countries for about 10-20% of all location determinations. Since the 1970s, it has been increasingly displaced by radio and satellite methods in the south as well (see below), but is still necessary today for small ships and for emergencies (power failure, etc.).

Radio navigation

Important in radio navigation are

• LORAN (LOng RAnge Navigation) should be mentioned (in addition to the older LORAN-A (medium waves), especially LORAN-C (a hyperbolic method based on time-of-flight measurement with long waves)). Although it often suffers from poor coverage in remote regions, it has become significant again in the last decade due to technical modernization and signal processing. The Federal Radionavigation Plan 1994 and the EU had already considered phasing out LORAN, but its importance as a backup in curved flight and in case of GPS or Galileo failures was recognized in time.
• Between about 1975 and 1995 there was also the world-wide OMEGA system, which, because of the use of longitudinal waves, managed with only 8 transmitting stations, the operation of which, however, became too expensive despite international cooperation, or was rendered superfluous by the advent of GPS.
• Other - more regional - methods such as the Russian Alpha (a LORAN equivalent), the British Decca, the post-World War II NavaRho and others.

Satellite navigation

• From about 1960, the US Navy's transit NNSS system (5-6 polar orbiting navigation satellites), which was released for all civilian uses in 1963/1964 and remained available until the late 1990s,
• and, since about 1990, the Global Positioning System (GPS) of the US Department of Defense. Its simple version (CA code), which has been in civilian use since its beginnings, is sufficient for 99% of long-range positioning tasks. The number of satellites (20,200 km high) increased over time from 5-10 to about 30 and provides worldwide coverage with 5-8 simultaneously measurable satellites (4 are necessary).
• Furthermore, the GLONASS (Russian/English GLObal NAvigation Satellite System), which was developed by the Soviet Union and is similar to GPS.
• and, from 2012-2015, the European Galileo system, which will significantly improve the GPS methodology and make it even more widely usable.

Special procedures

Last but not least, special methods such as meteorological navigation, magnetics, polar navigation or depth measurement (echo sounder, etc.) should be mentioned for special tasks on long distances. In antiquity and in the early days of the great "Age of Discovery" (14th-16th centuries), the method of lunar parallaxes and observation of natural phenomena such as bird flight, drifting grasses, dead wood, seaweed, etc. were also important. Also useful for finding the way across the Atlantic or Pacific were approximately known ocean currents or wind systems (trade winds!).

Today's navigation methods

In addition to the 3 classic methods (see above), others were added over time. Today, one generally distinguishes 7 groups of methods and, as the eighth, their optimal combination:

• Terrestrial navigation involves determining position near the coast using landmarks (prominent points on land), radio beacons and other navigation marks.
• Visual navigation is based on the comparison of the map and the terrain (coastal shape, capes, coastal places).
• Astronomical navigation locates the position by measuring the direction and altitude of celestial bodies (sun, planets or fixed stars).
• Dead reckoning is the continuous determination of position from heading and speed. The position determined in this way is called the dead reckoning or gybed (assumed) position. By calculating or directly observing the drift, the lateral displacement caused by the wind is taken into account; Doppler radar and inertial navigation increase the accuracy from a few percent to about 0.2 percent of the distance covered.
• Radio navigation uses transmitting stations whose radio signals produce geometric locations for one's own position (straight lines, circles and hyperbolas).
• Inertial navigation allows autonomous navigation by using accelerometers and gyroscopes.
• Satellite navigation (see also GPS, GLONASS and Galileo) uses signals from 4-6 simultaneously visible satellites, from whose transit times to the location of a receiver its position can be calculated.
• Integrated navigation or hybrid navigation combines several of these methods and weights them according to their quality. The position optimally calculated in this way allows statements to be made about their accuracy and reliability ("integrity").

A U.S. Air Force soldier goes through a checklist for controlling GPS satellites in a satellite control room at Schriever Air Force Base in Colorado, U.S.