The magnetic/extendible boom docking aid is an improved mechanism that enables two spacecraft to capture and structurally mate with each other without inducing the large (and frequently excessive) loads encountered in docking by use of prior docking mechanisms. The capability afforded by this mechanism should prove invaluable when applied to the International Space Station. This mechanism is relatively simple to construct, easily integrable into pre-existing docking hardware, and highly reliable.

Figure 1. The Boom Is Extended by unrolling a flattened tube from a motorized drum. The boom is flexible in torsion and bending, stiff in tension, and back-driven in compression. The electromagnet on the tip of the boom attracts a target plate on the mating spacecraft.
The magnetic/extendible boom docking aid (see Figure 1) includes an assembly that contains a powered extendible boom with an electromagnet attached to the end; this assembly is mounted on one of two spacecraft that are to dock with each other. A target plate is affixed to the other spacecraft in the mating position. There can be as many points of contact and corresponding magnetic/extendible boom docking aids as are needed to effect safe and efficient docking. When the two spacecraft have moved into docking approach position, the booms are extended and the electromagnets are switched on. The spacecraft are made to approach each other very slowly until the electromagnets make contact with, and become magnetically attached to, the target plates (see Figure 2). The spacecraft are slowly drawn together by withdrawing the booms until docking-mechanism latches are actuated. Mating is considered to have been achieved once the latches have been fully actuated.

Figure 2. Mating Parts of Two Spacecraft approach each other very slowly until the electromagnets on the extendible booms of one spacecraft magnetically attract the target plates of the other spacecraft. Then the booms are retracted slowly to complete docking.
Heretofore, two large spacecraft have been docked by causing the spacecraft to approach each other at a speed sufficient to activate capture latches — a procedure that results in large docking loads and is made more difficult because of the speed. The basic design and mode of operation of the magnetic/extendible boom eliminates the need to rely on speed of approach to activate capture latches, thereby making it possible to reduce approach speed and thus docking loads substantially.

Magnetic/extendible boom docking aids could be used on space-station modules and on proposed lunar transfer spacecraft. They could also be used in the construction and operation of underwater habitat modules. Ultimately, they may even be useful in robotic operation of submersible vessels used to drill for oil. However, the commercial market may be limited because most land-based processes and equipment can withstand the high contact loads of conventional docking.

This work was done by William C. Schneider, Kornel Nagy, and John P. McManamen of Johnson Space Center. For further information, contact the Johnson Space Center Commercial Technology Office at (281) 483-0474.

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