Preparing the stack

The next step in the launch preparation process was for Buran to be mated with its launch vehicle (Energiya rocket 1L) for an experimental roll-out to pad 37. The 1L rocket had always been well ahead of Buran in its launch preparations. Assembly of the core stage in the Energiya assembly building had begun back in October 1986, shortly after work with the core stage for vehicle 6SL had been completed. In early 1988 (14 January-2 February) the 1L rocket had already spent about three weeks on pad 37 for a variety of tests, including firing tests of the hydrogen igniters and retraction tests of the various platforms connecting the launch towers with the rocket.

The Energiya 1L-Buran stack arrived on the pad in the third week of May (the roll-out date has been given both as 19 May and 23 May). Once again a multi­tude of tests were performed, although none of them involved actual fueling of the rocket or the orbiter. One goal of the pad tests was to see if various sources of electromagnetic radiation at Baykonur did not interfere with the operation of on­board systems. The main problems uncovered during the pad tests were with the interaction between the orbiter and rocket computers and with the ground software needed to analyse telemetry at the cosmodrome and in Mission Control.

Actually, the pad tests in May-June were only part of a broader series of exercises at the cosmodrome intended to simulate pre-launch and post-landing operations, including numerous off-nominal situations. Involved in the exercises were not only the launch and recovery teams, but also the LII pilots, who simulated automatic landings on board Tu-154LL aircraft, with the MiG-25-SOTN performing the role of escort aircraft as it would during Buran’s final descent. The exercises also offered the opportunity to test virtually the entire communication network for the mission, including tracking stations, Mission Control in Kaliningrad, and orbiting communications satellites. Ground crews rehearsed post-landing operations and were trained how to deal with a return-to-launch-site abort during ascent. For this purpose, the OK-MT Buran mock-up was transported to the Yubileynyy runway.

The Energiya-Buran stack returned to the assembly building after about 3-4 weeks of tests (the roll-back date has been given both as 10 June and 19 June). Apparently, the original plan was for the orbiter and rocket to undergo some additional tests and then return to the pad for launch in the summer of 1988. Internal planning documents show that in early 1988 the launch was scheduled for July [37]. However, program managers felt that several problems that had surfaced during testing over the preceding weeks needed to be dealt with and decided to remove Buran from the rocket and return it to its MIK OK processing facility.

The most serious problem had cropped up in April during test firings of an ODU propulsion module at the Primorskiy Branch of NPO Energiya near Leningrad. A valve used in the liquid-oxygen gasification system of the primary thrusters failed

to close when commanded to do so, a problem that could jeopardize the operation of the thrusters in flight. Because of this and other issues with the ODU, it was deemed necessary to remove Buran’s ODU module and partially disassemble it to carry out modification work. This also required changes to the flight software, which had already been adapted numerous times in the preceding months, a penalty the

Russians had to pay for flying Buran unmanned. In the end, Buran went into orbit with the 21st version of the flight software.

After repairs to the ODU and integrated electrical tests with the final version of the flight software, Buran was moved back to bay 4 of the Energiya assembly building on 29 August for reintegration with Energiya 1L. With that work complete, the stack was rolled over to the nearby MZK building on 13 September for a series of hazardous and other operations. These included various loading operations (kerosene for the Buran propulsion system, hydrazine fuel and nitrogen gas for the Auxiliary Power Units, ammonia for the thermal control system, air for the cabin repressurization system), installation of batteries aboard Buran, solid-fuel separation motors on the strap-on boosters, and pyrotechnics for the Buran/core stage separation system.

Finally, the large doors of the MZK were opened in the early hours of 10 October and four diesel locomotives began pulling the impressive 3,500-ton combination of Energiya, Buran, and transporter to launch pad 37. In an old tradition, coins imprinted with the roll-out date were placed on the rails before the assembly passed

by and collected afterwards as souvenirs. It took the assembly some 3.5 hours to inch its way to the launch pad. Then another three hours were required to place the stack into vertical position and another hour to connect the Blok-Ya launch adapter to the launch table. All was now ready for final launch preparations to begin [38].