West Europe, US propose rival satellite navigation systems

Western Europe is proposing an all-civilian system of satellite navigation that would rival United States plans for a similar network under the auspices of the Department of Defense.

According to the 11-nation European Space Agency, which is based in Paris, the civilian system would better suit the needs of users such as ships and aircraft. This is because the satellites would be less complex and thus less expensive than those in the military network.

And the European spacecraft would be run by a civilian agency that is committed to providing a service. Under current plans for the US satellites, they would be switched off or their frequencies altered in times of international emergency or war.

The US plans are much further ahead than those of the Europeans. But there is still a lot of controversy over exactly how the American system, called Navstar, will be implemented.

In both systems, a set of satellites encircles the world at an altitude of some 20,000 kilometers (12,500 miles). The West Europeans want 24 space vehicles; the US is counting on 18.

The European system is estimated to cost about $2.5 billion; the US network, more than twice that much.

The vehicles relay signals from earth stations to small computerized terminals on ships, aircraft, or land vehicles. The terminals receive ''fixes'' from several spacecraft simultaneously and can work out exactly where they are.

The information would pinpoint position to an accuracy of 100 meters in three dimensions. A satellite system would represent an advance on current methods of navigation, which are inaccurate or do not give continuous coverage.

The Department of Defense already has six experimental Navstar vehicles in orbit. A prototype satellite navigation system called Transit provides an intermittent service.

Last May the Department of Defense ordered 28 more ''operational'' satellites from Rockwell. They will cost $1.21 billion and are to be put into orbit by the space shuttle in the next few years. Running costs and earth stations will push the total cost of Navstar above $5 billion.

Eighteen of the 28 satellites will work all the time, leaving the rest as orbiting ''spares.'' The Pentagon plans to offer a full service by 1988.

Under the current plan the system is primarily for military use. For example, data from the spacecraft would guide nuclear missiles to targets with an accuracy of centimeters. Navstar would also help submarine commanders or ordinary soldiers with receiving terminals in their backpacks to know where they are.

But the Department of Defense says the spacecraft could also be used by civilians. For an annual fee of $370, they would receive the code with which signals from the spacecraft are encrypted. A separate code would reserve more detailed navigation information for military use.

There are moves in Congress to orient the Navstar system more toward the needs of civilians. One proposal would revoke the annual license fee on the grounds that the navigation service should be a free national resource.

The Federal Aviation Administration is talking to the Defense Department about how airliners could use the network.

A decision on the pricing policy is expected during the next year.

By contrast, the European system would be financed by government agencies and would be free to users.

The European agency is still considering the technology for its system and monitoring the views of possible users. The satellites themselves are not likely to enter orbit until 1988.

Calin Rosetti, the official in charge of the European project, said the ESA has started discussions with the US Department of Defense, together with agencies in Japan and the Soviet Union, on the subject of coordinating plans for satellite navigation. The talks could lay the basis for a joint international system for the 1990s.

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