NOMINAL FLIGHT SCENARIOS

The single mission flown by Buran on 15 November 1988 was not a standard flight. It was flown without a crew on board and with the sole intention of testing the launch and re-entry procedures. No major on-orbit tasks were scheduled and Buran flew without many of the systems that would have been required for a multi-day manned mission. What will be described here are the standard launch and landing procedures and standard on-orbit operations for operational missions with a crew on board. Details of actually planned missions will be given in Chapter 8.

Launch

The launch began with the ignition of the core stage’s four RD-0120 engines at T — 9.9 seconds, followed at T — 3.7 seconds by the ignition of the strap-on rockets’ RD-170 engines. The interval was required to allow the core stage engines to slowly build up thrust and thereby ease the acoustic loads on the orbiter. If an anomaly was detected by the rocket’s flight control system, all engines could be shut down at any moment prior to T — zero.

As the stack cleared the tower, it performed a pitch and roll maneuver to place it in the proper attitude for the remainder of the ascent. About half a minute into the flight the core stage and strap-on engines were throttled back to minimize aero­dynamic pressures and longitudinal loads on the vehicle. After passing through the densest layers of the atmosphere, all engines were throttled back up to nominal thrust, although the Blok-A RD-170 engines were soon again throttled down in preparation for shutdown. The four strap-on boosters shut down in pairs with an interval of 0.15 seconds and were jettisoned about two seconds later at T + 2m26s. They continued to fly in pairs, separating from one another somewhat later to come down some 425 km downrange. As mentioned earlier, the strap-ons could land on parachutes for recovery but were not configured as such on the two Energiya launches that were flown.

Moving on downrange, the core stage again began throttling down its four liquid oxygen/liquid hydrogen engines less than a minute before shutdown, which occurred at T + 7m47s. The engines were shut down in pairs with an interval of 0.2 seconds. Fifteen seconds later the orbiter separated from the core stage and safely maneuvered itself away with gentle burns of its primary thrusters. The core stage then continued on a ballistic trajectory to burn up over the Pacific Ocean. Not having required orbital velocity yet, Buran then needed two burns of one of its DOM engines about 11 and 40 minutes into the flight to place itself into an initial orbit. The required burn duration was calculated by the on-board computers on the basis of the launch vehicle’s performance. The maximum acceleration forces for the crew during launch would not have exceeded 3g.

The crew had no active role to play during the launch phase and merely had to monitor the operation of on-board systems on their cockpit displays. The orbiter’s computers automatically controlled the operation of the life support, thermal con­trol, power, and monitoring systems as well as that of the hydraulic systems and Auxiliary Power Units, which might be needed in a launch abort to perform an emergency landing. They also opened and closed the vehicle’s vent doors at the required moments [28].