Buran’s ISS legacy

Despite the fact that the Soviet orbiters had long been mothballed by the time ISS construction began, one piece of Buran technology does play a vital role in station

operations. This is the Androgynous Peripheral Docking System (APDS—Russian acronym APAS), a Russian-built docking mechanism that allows Space Shuttles to dock with the US-built Pressurized Mating Adapters (PMAs) on the ISS “node” modules. Built at RKK Energiya under the leadership of Vladimir Syromyatnikov, the first APAS (APAS-75) was developed back in the 1970s for the Apollo-Soyuz Test Project. A modified version (APAS-89) appeared in the 1980s to enable Soviet orbiters to dock with the axial APAS docking port of Mir’s Kristall module. In the end, Buran never flew to Mir and the Kristall APAS docking port was used only once by Soyuz TM-16 in 1993.

In July 1992 NASA initiated the development of the Orbiter Docking System (ODS) to support Shuttle flights to Mir. Mounted in the forward end of the payload bay, the ODS consists of an external airlock, a supporting truss structure, and an APAS docking port. While the first two elements were built by Rockwell, the APAS was manufactured by RKK Energiya. Although Energiya’s internal designator for the Shuttle APAS is APAS-95, it is essentially the same as Buran’s APAS-89. While the ODS was slightly modified for Shuttle missions to ISS, APAS remained unchanged. There was even a suggestion to launch Buran to Mir to test the docking system prior to the beginning of the Shuttle-Mir flights [31].

The APAS consists of a three-petal androgynous capture ring mounted on six interconnected, ball screw shock absorbers that arrest the relative motion of the two vehicles and prevent them from colliding. The APAS-89 differs from APAS-75 in several key respects. It is much more compact (although the inner egress tunnel diameter is more or less the same), has twelve structural latches rather than eight, the guide ring and its extend/retract mechanism are packaged inside rather than outside the egress tunnel, and the three guide petals are pointed inboard rather than outboard [32].

Russian plans to sell their entire Buran Docking Module to NASA fell through, but its design did serve as the basis for the construction of the Russian Pirs airlock module, docked to ISS in September 2001. This retains the central part of the adapter’s spherical section (2.55 m in diameter). Mounted to its aft end is a small section of the Buran airlock’s cylindrical tunnel (without the extendable part) and attached to the front end is the forward part of a Soyuz-TM/Progress-M orbital module. The design was more complex than that of the Docking Module of Mir (316GK), which did not have to be used as an airlock and was merely an extension to the Kristall module to facilitate Shuttle dockings [33].