Not being able to charge your phone because you have the wrong USB cable is one thing, but imagine showing up at a space station with the wrong docking system. To prevent that from happening in the future, NASA has unveiled its new universal docking ports for the International Space Station (ISS) and other spacecraft. Built by a consortium of international partners, a pair of the International Docking Adapters (IDA) are undergoing tests before delivery to the station. With the designation of IDA-2, they are an upgrade of two previous adaptors that were lost when the CRS-7 mission exploded shortly after liftoff.

Since even before the first satellite was sent into orbit, the problem of how to dock two spacecraft and link them together has vexed engineers. If you look at early science fiction and books about space flight, the usual scenario was that shuttles approaching a space station would be manhandled into the dock by astronauts using mooring lines like dockhands hauling in a ship to a pier.

Various designs have been tried since the first docking between a manned Gemini capsule and an unmanned Agena satellite was achieved during the Gemini 8 mission in 1966, but an obvious problem was that of compatibility. The Apollo docking mechanism, for example, worked very well, but it had a male/female construction, which fits together like a key into a lock. This meant that a Command Module could dock with a Lunar Module, but not another Command Module, nor a Lunar Module with a Lunar Module.

It was even worse when two completely different spacecraft from different countries were involved, as was shown in the 1969 thriller Marooned, where a Soviet cosmonaut tries to help an American space crew stranded in orbit and is reduced to making hand gestures because he hasn't any way to link the two craft together.

When the first US/Soviet mission took place in 1975, the US Apollo and Soviet Soyuz spacecraft carried the first universal docking device, which was a cumbersome thing like a pair of giant steel flowers. The American version sported a huge airlock, so the two crews could meet despite the differences in cabin pressure. This was because the US spacecraft used pure oxygen at reduced pressure while the Soviets used oxygen/nitrogen at sea level pressure.

For the next two decades, the adaptor problem was a low priority, but when Space Shuttles began to visit the Mir space station and serious work started on the ISS, a universal adaptor became a priority. To find a common solution, a multinational effort was set up to create a standard docking system that can be fitted to all future manned and cargo spacecraft. The latest result is the IDA-2, which is more sophisticated than the previous version lost on CRS-7, but still conforms to the International Docking System Standard.

The IDA-2 is built by Boeing with Russia's RSC-Energia making the primary structures. Its purpose is not only to allow for more flexible operations while reducing the number of docking ports needed on the ISS, it also makes possible future rescue operations to recover crews of stricken spacecraft in an emergency.

Measuring 42-in (106-cm) tall by 63-in (160-cm) wide with an overall diameter of 94 in (239 cm), the design of the ring-like IDA-2 is androgynous. That is, both the docking mechanisms of both craft are identical and can fit together at any angle of rotation, while a set of three metal petals slide the docking rings into final adjustment so that the latches line up and lock. In addition, both are made to the same specifications, so they fit together properly. The new design is suitable for automated docking and includes laser reflectors, a revised targeting system, and fittings that allow data and power to pass between the craft without opening the hatch.

The first two IDAs are will be delivered to the ISS during a future cargo supply mission by a SpaceX Dragon. Once on station, the adaptors will be removed from the Dragon using a robotic arm and positioned within 30 cm (12 in) of the Harmony module's Pressurized Mating Adapters (PMA), where astronauts will make the final attachment.

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