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SOS VIA SPACE

Дата публикации: 14 сентября 2018
Автор: Yu. Atserov
Публикатор: Александр Павлович Шиманский
Рубрика: ВОПРОСЫ НАУКИ
Номер публикации: №1536954036 / Жалобы? Ошибка? Выделите проблемный текст и нажмите CTRL+ENTER!


Yu. Atserov, (c)

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by Yu. ATSEROV, Head of All-Union Association Morsvyazsputnik

The USSR launched its Cosmos-1447 satellite carrying equipment for exploring space and taking fixes of aircraft and ships in distress on March 24, 1983. This satellite is the second Soviet one in the COSPAR-SARSAT system. The third satellite is the US one that was orbited on March 28, 1983.

...Shipping is an international affair and safety at sea is ensured internationally The SOS distress signal is understood by all, and any ship nearby, regardless of the flag it flies, is obliged to hasten to the rescue of craft in distress.

The USSR was one of the sponsors of an international system of space communication with ships afloat, that would be capable likewise of protecting life and property and quickly spotting and saving ships and men in the event of shipwreck.

But why space satellites? Because from times immemorial navigation has been based on two cardinal points. Firstly, the navigator must know where the ship he steers is and, secondly, he must be able to have the necessary information quickly relayed to and from him. Whereas even towards the middle of this present century an error of but 15-20 miles out in astronomically defining a ship's position was thought a fine achievement, today one must be a hundred times more accurate with but an error of 0.01-0.2 miles out accepted. Whereas before brief radio messages to distances of no more than 100 miles away from the shore were considered ample, today we want communication to be worldwide and the transmission and reception of large volumes of information by telegraph, telephone, phototelegraphy and other means to be as fast as up to 56 kilobits a second.

Bearings out at sea are taken either by computations based on a ship's speed and course or by phasal or pulse-phasal radionavigation systems. Yet neither are satisfactory in the light of modern requirements. The first is inadequate because of the extensive margin of error which increases with the passage of time; the second is inadequate because of the limited range of operation or the variable velocity with which electromagnetic waves propagate in various sectors of the ocean. Present-day navigational complexes employ one or several systems to obtain accurate bearings with one or the other periodically correcting. Hence, even the use of sophisticated radioelectronic instrumentation is inadequate to ensure foolproof navigation. Along with colleagues in other countries Soviet scientists have concentrated on exploring venues for making use of satellites for shipping at sea. The related research was coordinated by the Intergovernmental Marine Organization (IMO) of the UN system.

In 1966 IMO became operational. Soviet scientists and specialists drafted the technical, economic, administrative, and legal aspects of an international system of satellite communication with vessels at sea. Preference was given to satellites injected into a stationary orbit. Calculations showed that a parabolic aerial mirror with a diameter of but 1.2 m across would be adequate even for installation on relatively small ships of between 1,000 and 3,000 tons. Geostationary satellites at an altitude of up to 36,000 km in the equatorial place were selected to arrange for a ship- communication system.

Unfortunately, business competition between Western Europe and the USA to grab the profits netted from satellite manufacture caused delay Only in 1972 a team of experts on

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marine satellites eventually met within the IMO framework. In 1975 drafts of a convention and operational agreement for an international system of marine satellite communication called INMARSAT were drawn up. The two documents were to become valid should the convention be ratified by governments of countries whose total contributions would account for 95 percent of the overall investment required. On July 16, 1979, the governments of fifteen countries ratified the convention thus providing a total of 96.24 percent of the needed investment. Currently 37 countries are involved in INMARSAT.

Authorized by the USSR, Ukrainian and Byelorussian governments, the V/O Morsvyazsputnik signed the INMARSAT operational agreement and represents the Soviet Union in this organization. On February 1, 1982, INMARSAT initiated the system's commercial exploitation.

The technical backing was provided by the decision that the world administrative radio communication conference had taken allotting to shipping services two frequency bands of 7.5 MHz, one for satellite-to-ship transmission in the 1.5 GHz band and the other for ship-to-satellite transmission in the 1.6 GHz range.

In the three years till 1979, when the INMARSAT convention went into force, the Soviet specialists on the preparatory committee, proceeding from tentative technical solutions for the overall configuration and its individual elements, proposed having the system linked to special-purpose satellites whose relay transmitters would handle exclusively communication with ships at sea within the allotted frequencies. Taken into consideration were the extensive requirements of shipping services as concerned telephone and telegraph communication with ships at sea and also such radiotelegraph information as weather news navigational announcements, etc. Special heed was paid to ensuring safe shipping, the transmission of distress signals and the relaying of information essential to find and save ships and life at sea.

Due to commercial considerations the INMARSAT system comprises not only such special-purpose satellites of the MARISET and MARECS type but also multipurpose satellites of the INTELSAT-Vtype with relay transmitters operating at a frequency band of 1.5 and 1.6 GHz.

The INMARSAT system provides ships, drilling rigs, and other devices at sea with services ensuring communication by telegraph, telex, telephone and phototelegraphy, transmitting at speeds of 2.5 kilobits and 56 kilobits per second. The most popular type of communication with transports and freighters is telex as it enables a ship's officers to relay to consignor, consignee shipowner, harbor master and other subscribers worldwide all necessary information automatically. As the experience amassed in operating satellite- linked stations aboard freighters and cargo vessels has shown, cruising times have been essentially cut by faster administrative decision and the quicker selection of optimum routes with an eye to weather forecasts. Experts say a damage from shipwreck and other accidents has thus been reduced by an annual 10 percent. It has also been estimated that for a 20,000-ton cargo vessel, satellite communications spell an annual savings of between 35,000 and 45,000 rubles. For other types of ships as, for instance, fishing, and research vessels or drilling and oil rigs, telephoning and telegraph may prove better. In other words, this means that in the foreseeable future all at sea will have efficient technical means for dependable worldwide automatic communication.

But as research never stops, both Soviet and other experts are currently tackling the technical aspects for INMARSAT'S second- generation satellites, which are to be injected into orbit in 1987- 1988 to be operative till 1995.

Under Acad. V. Kotelnikov, Vice-President of the USSR Academy of Sciences, a team of Soviet scientists, proceeding from the data acquired in tracking the first Soviet Sputnik, proposed the Doppler technique for determining orbital parameters. Investigations have demonstrated that by tracking one satellite loop alone one may determine orbital components with adequate accuracy. A solution was likewise found for what may be termed as reverse objective; thus, it was demonstrated that on the basis of orbital parameter information it is possible to take an object's bearings by measuring the Doppler frequency shift or during satellite flight within the object's zone of visibility Moreover, this was easier to work out as it was enough to conduct measurements not for the entire loop but merely for a restricted sector of it.

Orbited on March 31, 1978, was Cosmos-1000 for taking fixes of transport and fishing ships carrying equipment working on the Doppler principle.

Shipboard equipment for satellite navigation operates on frequencies of 150 and 400 MHz and is comprised of aerial, receiver, satellite signal decoder, frequency standard, electronic computer, and display and printout. After initial data have been fed in, the entire process is automatic with bearings computed according to course and speed. Results are no more than 0.1-0.3 miles out, which is quite satisfactory for navigation even in narrow straits let alone on the high seas. True, low-orbit satellite navigation systems are not devoid of drawbacks. Thus, it is impossible to get a fix at every time of the day with, for instance, equatorial discrete-ness in the case of six satellites amounting to about eighty minutes; furthermore, measurements occupy a relatively long time interval of anywhere from 6 to 16 minutes.

Besides satellite navigation systems, ships carry other electrically operated radionavigation instruments such as a gyro-compass for steering, a depth sounder, which beeps whenever the ship is in dangerously shallow waters, a log for measuring speed relative to water and bed, a radio-direction finder, which actually is not used for navigation but for defining the direction of any object signaling distress, the aforementioned radar station, which is excellent for avoiding collision and coping with navigational objectives, the receiving indication screen of a radionavigation system operating in close and long range and which in combination with satellite navigation system corrects the indications of one system on the basis of data coming from the other-which all means that the ship carries a complex ensuring reliable and highly accurate navigation.

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Another example of the use of space technology at sea, one of vital and humane significance, is represented by what the USSR, USA, Canada, and France are doing in their common effort to use low-orbit satellites for obtaining fixes of ships and aircraft in distress.

The three groups drew up a protocol to cooperate in the experimental use of satellites for searching and saving ships and aircraft in distress. This document was signed on March 18, 1977. Shortly afterwards the French national center for space research joined in.

Chosen for the system were low-orbit satellites flying at an altitude of between 800 and 1,000 km up and with near-polar orbital inclination, and the two frequencies of 121.5 MHz and 406.1 M Hz for radio beacons. At such altitudes the satellite can receive signals from a circular area of up to 27,000 km 2 by sea or land, provided the diameter is about 6,000 km and the angle of ground visibility is 7 0 .

Set up are ground receiving stations operating on a frequency of 1,544.5 MHz to receive satellite information, which after preliminary processing is relayed to a computer center. On the basis of satellite ephemeredes, that is of the orbital trajectory in three dimensions, the bearings of the distress radio beacon are ascertained. The information is immediately relayed to the nearest search-and-rescue center of the country receiving the information, which either takes action itself by dispatching the necessary rescue means to the spot or relays the information to a similar center in the country to which the ship or plane in distress belongs or that is responsible for search and rescue operations in a definite sector of the ocean.

A fix on the radio beacon from the distressed craft is obtained by processing signals on the basis of the Doppler frequency shift factor and synchronizing results. To elucidate such data with needed accuracy the satellite must be about 8-12 minutes within the zone of visibility. The fix obtained on the 121.5 frequency, which is allotted to aircraft is no more than 10-15 km out, while on the 406.1 MHz frequency, which the international regulations for radio communications have specially assigned to satellite SOS beacons, the fix is no more than 2-3 km out. However, should the shipwreck have occurred on the high seas or should the plane have crashed in a mountainous area additional information is necessary to enable the rescue team reach the spot sooner. In such cases it is more convenient for the aircraft rescue service to employ a signal on the 121.5 M Hz frequency, as rescue planes and helicopters in all countries are equipped with direction finders operating on that frequency.

Between 1977 and 1982, working in line with a coordinated program, specialists of the four countries concerned drafted scientific and technical projects for organizing a rescue system. They have also come up with the equipment that satellites and ships and aircraft should carry and have also devised a distress radio beacon as the initial element. The project is known as COSPAR-SARSAT, a combination of Russian and English acronyms meaning "search and rescue by satellite".

Already established and in operation by now are information receiving stations in Moscow, Toulouse, Ottawa, and Saint Louis and work on such stations in Arkhangelsk, San Francisco, Kodiak in Alaska, and Tromse in Norway is nearing completion. The network of these stations will be expanded; more specifically, another one is to be built in Vladivostok in the USSR. Considering this country's vast expanse it may be necessary to have one more station in Western Siberia. A system of four constantly orbiting satellites and a sufficiently dense network of receiving stations will ensure the reliable reception of SOS signals and fixing within a time interval of several to sixty minutes in equatorial areas, where the satellites are furthest apart.

The system underwent technical trials immediately after Cosmos-1383 was orbited. They showed that fixes were obtained with an error of no more than 10-15 km out on the 121.5 MHz frequency and of no more than 3 km out on the 406.1 MHz frequency, provided the SOS beacons were on land. Also studied was possible static on the second frequency and especially the possibility of false signals. Adverse in this respect were Europe, North Africa and the Middle East centering on the Red Sea, Australia and Indonesia centering on Perth, and Central America centering on Panama.

The system demonstrated its merits from the very outset. First saved, especially thanks to the Soviet Cosmos-1383 satellite, were three Canadians.

The system also did good service for ships in distress at sea. Thus, on October 10, 1982 the trimaran Gonzo capsized in the Atlantic 300 miles off US shores. The information the US Coastal Guard received from Cosmos-1383 made for a speedy rescue operation, which thus saved the lives of two Americans and one Englishman.

In line with a program agreed by the four countries involved, a demonstration of the system for purposes of appraisal was initiated on January 31, 1983 after the features of the joint system had been recorded, its effectiveness in multinational search and rescue operation had been elucidated, and operational recommendations had been drafted. After Cosmos-1383, another Soviet satellite of the same order, Cosmos-1447, was orbited.

To sum up: space technology is being expeditiously applied for shipping. Already some 40,000 ships around the world are outfitted with space navigation equipment while upwards of 1,600 vessels are linked to the INMARSAT international satellite communication system. Now on the agenda is the need to equip ships with SOS beacons that would be connected through low-orbit satellites.

When the entire system is fully operational and four satellites will be travelling on circum-Polar orbits, in the vicinity of the North and South Poles, every place on the globe will be within range at every hour of day or night. This will naturally greatly raise the level of safety for travel by both air and sea and will make for the better worldwide organization of rescue operations for ships and aircraft in distress.

Опубликовано 14 сентября 2018 года




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