An advanced docking system is undergoing development to enable softer, safer docking than was possible when using prior docking systems. This system is intended for original use in docking of visiting spacecraft and berthing the Crew Return Vehicle at the International Space Station (ISS). The system could also be adapted to a variety of other uses in outer space and on Earth, including mating submersible vehicles, assembling structures, and robotic berthing/handling of payloads and cargo.
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 present advanced docking system would eliminate 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.
The system would comprise an active subsystem on one spacecraft and a passive subsystem on another spacecraft with which the active subsystem will be docked. The passive subsystem would include an extensible ring containing magnetic striker plates and guide petals. The active subsystem would include mating guide petals and electromagnets containing limit switches and would be arranged to mate with the magnetic striker plates and guide petals of the passive assembly. The electromagnets would be carried on (but not rigidly attached to) a structural ring that would be instrumented with load sensors. The outputs of the sensors would be sent, along with position information, as feedback to an electronic control subsystem. The system would also include electromechanical actuators that would extend or retract the ring upon command by the control subsystem.
In preparation for docking, one spacecraft would move to a position near (but not touching) the other spacecraft, with the docking ports of the two spacecraft in approximate alignment. Then while one spacecraft maintained an approximately constant position relative to the other spacecraft, the actuators of the active subsystem would be made to extend the ring, gently pushing the guide petals and electromagnets toward the passive ring guide petals and magnetic striker plates: in effect, the active subsystem would reach out, comply, and grab the passive subsystem.
During this reaching out, the hardware and software of the feedback control subsystem would command the actuators to respond to sensed loads to correct for any misalignments between the docking ports, i.e., to comply. The reaching-out-and-alignment process would continue until the limit switches indicated soft capture - i.e., final petal alignment and magnetic capture of the magnetic striker plates. Once soft capture and alignment was complete, the ring would be retracted, then mechanical latches would be engaged to secure the docked spacecraft to each other.
The active subsystem ring, electromagnets, and petals would then be withdrawn, and the latches would continue to hold the spacecraft together. Later, the undocking could be effected by releasing the mechanical latches.
This work was done by James L. Lewis of Johnson Space Centerand Monty B. Carroll, Ray Morales, and Thang Le of Lockheed Martin.
This invention has been patented by NASA (U.S. Patent No. 6,354,540). Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to
the Patent Counsel
Johnson Space Center
Refer to MSC-22931.