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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Androgynous Peripheral Attach System | 2/3 | https://en.wikipedia.org/wiki/Androgynous_Peripheral_Attach_System | reference | science, encyclopedia | 2026-05-05T12:35:20.650397+00:00 | kb-cron |
After the June meetings, Johnson had put Bill Creasy and his mechanical designers to work on the preliminary design of a docking mechanism. By the time the NASA delegation left for Moscow, Creasy's crew had designed and built a 1-meter double ring and cone docking system that had four guide fingers and attenuators on both rings, so either half could be active or passive during docking. The Structures and Mechanics Laboratory at MSC made 16-millimeter movies demonstrating this system in action, which Johnson took to Moscow in November, along with a booklet describing the system and a model of the capture latches. To Johnson's surprise, Vladimir Syromyatnikov had been working on a variation of NASA's ring and cone concept since the previous October. Instead of the four guide fingers in the American proposal, Syromyatnikov suggested three, and in lieu of hydraulic shock-absorbers, he proposed electromechanical attenuators. In essence, the Soviets had accepted the idea of using a set of intermeshing fingers to guide the two halves of the docking gear from the point of initial contact to capture. The concept of using shock absorbing attenuators on the active spacecraft's capture ring to buffer the impact of two spacecraft coming together was also acceptable. Both groups of engineers planned to retract the active half of the docking gear using an electrically powered winch to reel in a cable. Once retracted, structural or body latches would be engaged to lock the two ships together. Three basic issues had to be resolved — the number of guides, the type of attenuators, and the type of structural latches — before the design of a universal system could proceed. Johnson, Creasy, and the other engineers in the Spacecraft Design Division had wanted to use four guides because they believed that it provided the best geometry when using hydraulic attenuators. As Bill Creasy subsequently explained it, the most probable failure situation using hydraulic attenuators would be a leak that would cause one shock absorber to collapse on impact. A study of various combinations had led the MSC specialists to conclude that four guides and eight shock absorbers was the optimum design. Creasy pointed out too that the most likely trouble with an electromechanical system would be a freeze-up or binding of one of the pairs of attenuators. Thus, the Soviets had sought to minimize the number of pairs in their system for the same reason that the Americans had preferred a larger number to limit the probability of something going wrong. Since the United States had no significant engineering or hardware equity in its proposed design, and since the USSR had considerable equity in its proposed design, the Soviet design was selected as a baseline for the next phase of study. By the end of the November–December meeting, the two teams had signed a set of minutes outlining the basic concept for a universal androgynous docking system. The formal statement read, "The design concept includes a ring equipped with guides and capture latches that were located on movable rods which serve as attenuators and retracting actuators, and a docking ring on which are located peripheral mating capture latches with a docking seal." Basic information on shapes and dimensions of the guides were also included in the minutes. They were to be solid and not rodlike; as first proposed by the Soviets, and three in number. As long as the requirement for absorbing docking forces was met, each side was free to execute the actual attenuator design as it best saw fit. The Soviets planned to use an electromechanical approach designed for the Soyuz docking probe, and the Americans proposed to stick with hydraulic shock absorbers similar to those used on the Apollo probe. This proposal also called for developing docking gear that could be used in either an active or passive mode; when one ship's system was active, the other would be passive. Looking into the detailed design of the mechanism, the two sides had further agreed that the capture latches would follow the design developed at MSC and the structural latches and ring would follow the Soviet pattern. These paired sets of hooks had been successfully used on both Soyuz and Salyut. In addition, the group concurred on details regarding the alignment pins, spring thrusters (to assist in the separation of the spacecraft at undocking), and electrical connector locations. To evaluate the docking system concept and to ensure the establishment of compatibility at an early point in the development, the men planned to build a two-fifths-scale test model, the exact details of which would be decided at the next joint meeting. Upon his return to Houston, Caldwell Johnson prepared a memorandum to document some of the informal understandings reached in Moscow. He indicated that this reflected "upon the manner in which the two countries will conduct and coordinate the next phase of the engineering studies of those systems ... The understandings ... were reached more often than not outside of formal meetings, and so are not likely otherwise to be reported." For example, in the area of hatch diameter, he noted that "it became apparent from the beginning ... that a hatch diameter greater than about 800 mm could not be incorporated into the Salyut spacecraft without great difficulty," but MSC had "long since reconciled itself" to a test hatch diameter of less than 1 meter. Johnson went on to comment that "the capture ring assembly had variously been called ring and cone, double ring and cone, and ring and fingers. It was agreed henceforth to call the capture ring 'ring' and the fingers 'guides.'" Bill Creasy and several of his colleagues worked with Yevgeniy Gennadiyevich Bobrov at the drafting table to lay out these first Soviet-American engineering drawings. Larry Ratcliff drew the capture ring and guides on drafting paper, and Robert McElya supplied the details of the structural interface ring, while Bobrov prepared a similar drawing for the structural latches. T.O. Ross then took these drawings and conducted a dimensional analysis to be sure that all items were compatible. Agreement on technical specifications for the docking system cleared the way for NASA to begin discussions with Rockwell about building the docking system. In April 1972, the Soviets informed NASA that they had chosen to use a Soyuz spacecraft in place of a Salyut space station for cost and technical reasons. Final official approval of a joint docking mission came in Moscow on 24 May 1972. U.S. President Nixon and U.S.S.R. Premier Aleksey N. Kosygin signed the Agreement Concerning Cooperation in the Exploration and Use of Outer Space for Peaceful Purposes, including development of compatible spacecraft docking systems to improve safety of manned space flight and to make joint scientific experiments possible. The first flight to test the systems was to be in 1975, with modified Apollo and Soyuz spacecraft. Beyond this mission, future crewed spacecraft of the two nations were hoped to be able to dock with each other.