Computers

The heart of Buran’s flight control system were two Soviet-built redundant computer sets known as the Central Computing System and the Peripheral Computing System, each consisting of four identical computers called “Biser-4” (“Beads”). The US Space Shuttle has a single redundant set of four computers and a fifth back-up computer using different software. Weighing 33.6 kg and using 270 watts of power, each Biser was made up of a central processing unit to provide the central computational capability and an input-output processor to transmit commands to vehicle systems and validate response data from those systems. The computers ran in sync with each other, with the computations of each computer being verified by the other. If one of the computers failed, it was voted out by the others. Each redundant set remained fully operational with two computers down. If a third one failed, there was still at least a 75 percent chance of maintaining the same capacity as a full set. Rather than using program synchronization as was the case with the Shuttle’s General Purpose Computers, the Biser computers were synchronized by a single quartz clock generator that emitted 4Mhz clock pulses to all eight computers at intervals of 32.8 milli­seconds. The generator had five redundant channels.

Each Biser-4 was equipped with 131,072 32-bit words in random-access memory and 16,384 in read-only memory. The software was divided into system software to operate the computers themselves and applications software to perform the functions required to fly and operate the vehicle. While the operations system software perma­nently resided in the computer, the applications software was too big to fit in the available computer memory space. Therefore, it was divided into several memory groups corresponding to specific flight phases and stored on a magnetic tape mass memory unit with a capacity of 819,200 32-bit words. In that way, applications software needed for a specific phase of the flight could be loaded into the computers’ random-access memory from the mass memory unit when needed. The unit stored two versions of each memory group.

The lead organization for the development of the on-board computers was NPO AP, headed until 1982 by Nikolay Pilyugin, who was subsequently replaced by Vladimir Lapygin. Originally, the software was also to be written at NPO AP, but software development ran into major problems in the early 1980s, which is why several other organizations became involved in 1983. Two new specific software languages known as “PROL-2’’ (used by the on-board computers) and “DIPOL” (used by ground computers during vehicle testing) as well as a software language enabling those two to interact (“FLOKS”) were devised for Buran under the leadership of Mikhail Shura-Bura at the Institute of Applied Mathematics [22].