EMERGENCY SITUATIONS Launch and landing emergencies

The Energiya-Buran launch profile offered more rescue options for the crew than that of the Space Shuttle, mainly because of the use of liquid-fuel rather than solid – fuel boosters. Whereas a Solid Rocket Booster (SRB) failure will almost always result in the loss of vehicle and crew (as tragically demonstrated by the Challenger disaster), an engine failure on one of Energiya’s four strap-ons would not necessarily have had catastrophic results. Buran cosmonauts had the following escape options.

Pad emergency escape system

In case of an emergency on the launch pad the crew could egress Buran and flee to an underground bunker using the pad emergency escape system. Unlike the slidewire baskets used on the Space Shuttle launch pads, the cosmonauts were to glide down a giant chute and subsequently seek shelter in bunkers under the launch pad (see Chapter 4).

Ejection seats

For its manned test flights Buran was to be equipped with ejection seats, allowing the crew members to escape through two overhead hatches in case of an emergency on the pad, in the early stages of launch and the final phases of landing. Ejection seats were also flown on the four two-man test flights of the US Space Shuttle Columbia, but were disabled for Columbia’s first operational mission (STS-5, which carried two mission specialists on the flight deck) and eventually removed altogether. The Russians were planning both two-man and four-man test flights and the intention was to have ejection seats for all cosmonauts irrespective of crew size. With a crew of four, the two non-pilots would have been seated in the front part of the mid-deck and could have been ejected via two hatches mounted in between the forward reaction control system and the six forward cockpit windows. In that configuration the front equipment bay in the mid-deck would have been moved to the rear. The ejection seats would have been removed for flights carrying more than four cosmonauts.

Buran’s ejection seats (called K-36RB or K-36M11F35) belonged to the family of K-36 seats of the Zvezda organization that are standard equipment on Soviet high-performance combat aircraft. More than 10,000 K-36 seats had been produced by the early 1990s and several hundred real ejections had been made with very high survival rates.

The K-36 seats are based on a modular design to which systems are added or deleted depending on the specific aircraft on which they are installed. The modifica­tions for Buran were needed not so much for the landing phase, but mainly to pull the cosmonauts away to a safe distance from the rocket in case of a pad or launch accident. For that purpose they were equipped with a small solid-fuel rocket that would have been needed only for ejection during launch and on the pad (after retraction of the crew access arm). In the latter scenario the K-36RB would have been able to reach an altitude of 300 m in order to clear the 145 m high rotating service structure which would have been in its path. The pilot was supposed to come down 500 m from the pad in a matter of just 10 seconds.

Another feature unique to the K-36RB was an under-seat stabilization system with drag parachutes that would be used up to an altitude of about 1 km. The system’s two booms were separated along with the solid-fuel rocket at a point near the upper portion of the seat’s trajectory. This was installed in addition to a standard two-boom upper stabilization system with end-mounted parachutes.

The cut-off altitude and speed for the use of the K-36RB during launch would have been 30-35 km and Mach 3.0-3.5, respectively (compared with 24 km and Mach 2.7 for the Shuttle seats), which roughly equates to T + 100 seconds in a normal

K-36RB ejection seat and Strizh pressure suit (B. Vis).

launch profile. That limit was determined by the ability of the Strizh pressure suits to protect the pilot from the thermal stresses experienced in an ejection. The Strizh suits were covered with special heat-resistant material to protect the pilot against heating caused by the high aerodynamic loads during ejection. The K-36RB could also be used during landing, from the moment speed was reduced to Mach 3.0-2.5 all the way to wheels stop. The seats were also installed on the BTS-002 atmospheric test model (as they were on Enterprise for the Approach and Landing Tests). The ejection seats could be activated by the crew, by on-board automatic devices, or by a command from the ground.

Also unique to the K-36RB was a computer linked to Buran’s computers that ensured that the seat was configured for one of five ejection modes corresponding to

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Ejection seats fired from a mock-up of Buran’s cockpit (B. Vis files).

the orbiter’s launch or landing phase. Mode 1 was for ejection on the launch pad, mode 2 for ejection during initial ascent, mode 3 for high-Mach/high-altitude ejections, mode 4 for the landing approach, and mode 5 for the final approach, touchdown, and roll-out.

The K-36RB was tested in at least three ways with mannequins clad in Strizh pressure suits. In one method the seat was installed in a ground-based mock-up of Buran’s cockpit and in another in the aft cockpit of a converted two-seater MiG – 25RU training aircraft (serial number 0101). A rather original way was found of testing the ejection seats and associated escape suits at much higher velocities and altitudes. An experimental version of the seats called K-36M-ESO was carried as a piggyback payload on five unmanned Soyuz rockets carrying Progress resupply ships between September 1988 and May 1990 (Progress 38, 39, 40,41, and 42). The ejection seats were fitted inside the rocket-powered tower atop the launch vehicle and ejected at altitudes between 35 and 40 km and speeds between Mach 3.2 and 4.1.

Emergency Separation

Emergency Separation (Russian acronym EO) would have been activated if a serious launch vehicle problem had forced shutdown of all engines above the altitude where the ejection seats could be used. In that scenario, Buran could have swiftly separated from the core stage using four small solid-fuel motors in its nose section and subse­quently attempted to stabilize itself to perform a manual emergency landing on a runway downrange after having dumped excess propellant from the ODU engine system. In case no emergency runway was available, the crew could still have used their ejection seats once Buran was stabilized and had reached a safe altitude.

NASA studied a similar escape option for the Shuttle called “Fast Separation” that would have allowed the Orbiter to separate from the External Tank in approxi­mately three seconds in case of an SRB failure. However, analysis showed that if this is attempted while the SRBs are thrusting, the Orbiter would “hang up” on its aft attach points and pitch violently, probably resulting in the destruction of the vehicle. Similarly, the Russians concluded that Emergency Separation would be hard to achieve without Buran hitting the core stage, especially when the stack experienced high aerodynamic pressures in the early stages of the launch, virtually all the way to separation of the strap-on boosters. Moreover, safely landing the vehicle in such a scenario would have required a very elaborate and costly network of emergency runways all the way downrange.