Return Maneuver

A Return Maneuver (MV) enabled Buran to return to its launch site runway in case of a single-engine failure on the strap-ons or the core stage early in the launch. The “negative return” point would have been reached between T + 2m05s-2m10s in the event of a strap-on failure and between T + 3m00s-3m10s if a core stage engine shut down.

If an RD-170 engine in one of the four strap-ons failed, the engine of the diametrically opposed booster would also shut down to make sure that the rocket did not deviate from its trajectory. Subsequently, all the remaining liquid oxygen in both strap-ons would have been dumped overboard to minimize the amount of dead weight carried up by the rocket and also to ensure that conditions at separation were close to the ones originally planned. The LOX could be released via a 600 mm diameter drainage channel, which exited the lower end of the LOX tank, situated some 15.5m above the engines. Kerosene, which comprised only one-third of the overall propellant mass in each booster, would not have been dumped overboard to prevent the formation of an explosive mix.

The return profile would have been very similar to that of a Return to Launch Site (RTLS) abort during Space Shuttle launches. The vehicle would have continued to fly downrange to expend excess propellant and would have performed a pitch- around maneuver to orient the stack to a heads-up attitude pointing towards the launch site. The core stage would then be separated, allowing Buran to glide to a landing on its cosmodrome runway. In order to improve Buran’s weight and center of gravity for the glide phase and landing, excess propellant for the ODU propulsion system was to be expended by simultaneously firing the two DOM engines and dumping liquid and gaseous oxygen overboard.