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in space navigation, a series of consecutive maneuvers by which one spacecraft is brought into close proximity to another. The aim of approach may be inspection, mooring, or assembly in orbit. Inspection, for example, entails the examination of a spacecraft at close range in order to determine the necessity of repairs. Mooring involves the temporary linking of two spacecraft with a flexible line.
Approach may be accomplished in two ways. In one technique only the final distance separating the two spacecraft is critical, and the closing speed at the moment of closest approach is not a factor. In the second technique the closing speed up to the moment of closest approach should be very low, ideally zero. This second technique requires larger expenditures of fuel than the first.
Approach requires that the two spacecraft be equipped with radio communications systems, computers, rocket engines, and navigation control systems. The active spacecraft carries out the search, maneuvering, and approach missions, while the second one is passive.
The first approach of two spacecraft with crew participation was carried out by the American spacecraft Gemini 6 and Gemini 7 in 1965. The first approach of three spacecraft with crew participation was carried out by the Soviet spacecraft Soyuz 6, Soyuz 7, and Soyuz 8 in 1969.