Emergency escape rocket: the ultimate lifeboat for spacecraft

For decades, rockets have remained the fastest and most dangerous mode of transportation created by humans. Not surprisingly, engineers went to great lengths to develop "insurance policies" in case something goes wrong during a wild ride beyond the Earth atmosphere. As it turned out, the most practical way of escaping from a failing rocket would be to use yet another dedicated rocket! Such method was used onboard several generations of spacecraft, including American Mercury, Apollo and Russian Soyuz. The latter system had actually got a chance to prove itself in real life emergency situation...

Previous chapter: Soyuz spacecraft

The Emergency Escape System, SAS, fires on Sept. 26, 1983, saving lives of two cosmonauts aboard the Soyuz-T spacecraft as its launcher explodes below.

Development history

In 1961, Department 11 of OKB-1 started preliminary design of the emergency escape system for the future Soyuz spacecraft. During previous work on the Vostok manned capsules, as well as later on the Voskhod, engineers accepted the fact that a major malfunction during initial phases of the launch would make a rescue of the crew either unlikely or completely impossible. However, the original goal of the Soyuz project called for the development of ways and means of rescue during the full length of a ride to orbit.

The most challenging failure scenario, which ultimately determined the design of the emergency escape system, was the explosion of the rocket booster right on the launch pad. In such situation, ejection seats could not guarantee either a safe distance of escape from the exploding rocket, or reliable protection from its falling debris.

In 1962, Korolev's engineers studied the problem in cooperation with a team from Flight Research Institute, LII, led by N. S. Stroev. The work showed that the most efficient rescue would be achieved by pulling the crew capsule from the rocket with the help of dedicated solid propellant rockets and then landing the capsule as in any nominal mission. A prototype of such system was tested at the Flight Research Institute, LII, lab led by Guy I. Severin. The tests validated the concept.

Developers concluded that the escape with the help of a rocket would be necessary only during the flight in the lower denser layers of the Earth atmosphere, when the loss of control over the rocket would likely lead to its disintegration and explosion. At the same time, available statistics showed that beyond Earth atmosphere, the likelihood of rocket explosion was minimal, therefore a nominal separation of the reentry capsule with a following landing was adopted as a primary escape method.

During 1963, engineers at Department 3 and 11 of OKB-1 with support from Department 15 led by K. D. Bushuev and S.S. Kryukov developed structural design of the "Jettisonable Emergency Escape Head Section" known by its Russian abbreviation as OGB SAS. This work was also coordinated with the branch of OKB-1 in the city of Kuibyshev (now Samara), which at the time took over all development and production of the R-7-based launch vehicles.

Developers conducted an analysis of possible emergency flight scenarios in order to determine necessary capabilities of the escape system and its flight profiles. In addition, engineers had to adjust the design of the main parachute system, so it could be used in the aftermath of the flight on the emergency rocket. All specifications for the emergency escape system and its effects on parachute and landing systems were formulated in 1963.

Rocket failure diagnostic

An upper composite configuration during the Dec. 14, 1966, attempt to launch the Soyuz 7K-OK No. 1 vehicle. Copyright © 2016 Anatoly Zak

In order to trigger the emergency escape system, the Soyuz spacecraft needed a reliable diagnostic system, which would detect every conceivable failure onboard the launch vehicle. At the time, years of experience with the Vostok spacecraft and its rocket gave engineers a good idea what could possibly go wrong during launch. In 1964, K. D. Bushuev held a meeting with leading minds at OKB-1, including B. Chertok, S. Kryukov, E. Shabarov, S. Okhapkin and V. Timchenko, which finalized a list of likely failures. It included:

Loss of control (detected by gyroscope sensors)

Premature separation of booster stages (Stage I)

Loss of pressure in the combustion chambers

Lack of velocity

Loss of thrust (detected by appearance of weightlessness onboard)

Necessary systems capable of identifying such problems were added to the design of the launch vehicle intended to carry Soyuz. In the meantime, the spacecraft itself received a special sensor of weightlessness, which if detected earlier then expected in the nominal flight, could also trigger an emergency escape rocket.

Last but not least, "the failure" command could be issued from the ground via radio waves. (52) At Site 23, some 30 kilometers from the main launch site of Russian manned missions, the Kvant ground control station is used to transmit signals of the Command Radio Link of the Emergency Escape System, KRL SAS, which has ability to activate the escape rocket. Also at the same location, a KTNA antenna provides a backup capability for KRL SAS. (244)

(Ironically, it was the method used during a real life use of escape rockets in 1983)

In 1965, developers of the escape system stumbled upon a new serious problem. As it turned out, collision-free separation of the entire payload fairing from the service module of the Soyuz (which remained on the rocket) was practically impossible. After a series of brainstorming sessions, engineers split the payload fairing into top and bottom sections. In the emergency, the top section would fly away with the escape rocket and the crew compartments, while bottom section, surrounding the service module, would remain on the rocket.

To increase the aerodynamic stability of the shortened escape vehicle, it was equipped with four folding stabilizers.

Sergei Korolev, head of OKB-1 personally approved the design of the system and it became standard for each and every manned Soyuz spacecraft. (52)

Technical specifications of the emergency escape system (original version):

Escape altitude (in case of failure on the launch pad) No less than 850 meters Range of escape (in case of failure on the launch pad) No less than 110 meters G-loads on the crew (in case of failure on the launch pad) No more than 10 G-loads on the crew (in case of failure at T+400 seconds in flight) Up to 21 Maximum thrust of the escape system 76 tonnes Total mass of the escape module 7,635 kilogramms

Flight testing

During 1966 and 1967, the escape rocket flew two test missions, lifting the escape module from the ground. In one of the launches, excessive acoustic loads of the firing escape motors, blew out sections of coverings between top structural beams of the fairing. To fix the problem, the top section of the fairing received a layer of thermal protection.

The developers had to begin a major review of the SAS operations on Dec. 14, 1966, following an accidental triggering of the emergency rockets on the launch pad, which led to three fatalities and a major damage to the facility. It appears that in the wake of this accident, engineers considered the activation of the SAS rockets after the ignition of the first stage, even if the liftoff had been aborted and the rocket had remained on the pad. (774)

Modifications for Soyuz T

As early as 1968, OKB-1 started developing a new version of the emergency escape system, which would eventually become part of upgrades of the Soyuz T spacecraft. Department 241 led by V. A. Timchenko at OKB-1 was responsible for the escape system and landing systems. Beginning in 1974, a special laboratory 179, led by V. A. Ovsyannikov took over the responsibility.

The new version of the escape system promised higher reliability, and it could fly higher and farther thanks to the new solid-rocket motor developed by Iskra plant in the city of Perm. The new escape rocket also allowed Soyuz to use the main parachute during landing, instead of a less reliable backup parachute.

To guarantee a safe landing of the reentry capsule far away from the launch site, the new system could take into account wind characteristics, while selecting an optimal escape trajectory.

To provide an escape during a short period after jettisoning of the emergency escape rocket, but before the separation of the payload fairing, which previously had no immediate escape scenario, two pairs of solid motors were placed on the fairing. In turn, this upgrade allowed to drop the main escape rocket 123 seconds after the launch, instead of previous 160 seconds, thus compensating for added mass of the new escape system.

Another major improvement included an addition of a second tier solid motor above the original one. In case of a fire on the launch pad it would activate to increase the altitude of escape, while in case of trouble at high altitude, where the escape module has less stability, it would play a role of a stabilizing mass.

Flight control systems for the escape rocket were also updated to accommodate new escape scenarios and improve its general reliability. (52)

Testing again

In a new round of flight testing, traditional firing of the escape rocket, imitating escape from the ground was made more complex. It was designed to replicate the failure of the rocket after separation of the main escape rocket, known as Flight Phase 1A. For this purpose, a test vehicle was equipped with two engines, which played a role of a rocket booster. They lifted the craft to the altitude of 2.5 kilometers, where after separation of the head section, Phase 1A escape scenario was rehearsed.

Flight tests validated the new design, which remained unchanged on all future modifications of the Soyuz spacecraft. (52)

In real life, the system proved itself, when it saved lives of two cosmonauts during fire and explosion of the launch vehicle on the launch pad in 1983.

Modifications for Soyuz TM

The Iskra plant re-designed escape rocket one more time to contribute into weight-saving efforts during the development of the Soyuz TM version of the spacecraft. It entered service after the launch of the Mir space station. Two core engines -- central and add-on engine -- were replaced with a single one-chamber engine. Both chambers would burn along the same profile but using a unified nozzle. The redesign significantly cut the weight of the escape rocket. The main diameter of escape rocket was also reduced, further improving aerodynamic qualities of the entire escape module and reducing the mass of the balancing weight.

The nominal separation time of the escape rocket was further advanced to 115th second after the launch (52) (to 114th second according to another source 243). That change freed more weight for payload and enabled to combine drop zones for the escape rocket and boosters of the first stage in the same area downrange from Baikonur. Total weight savings from the redesign of the escape rocket and its flight profile reached around 60 kilograms.

Emergency flight profiles

The top section of the Soyuz spacecraft design for escape in case of the emergency was known as OGB SAS. It included:

reentry capsule

habitation module

payload fairing

solid-propellant escape rocket (with the thrust of 785 kH on the original system 2)

The escape motor would be installed on top of the payload fairing.

Prior to launch, the emergency escape tower would be calibrated relative to the vehicle's center of gravity. In case, the main rocket would deviate from its standard attitude, the flight trajectory of the escape module could be adjusted accordingly with the help of its own gyroscopes and dedicated solid-propellant thrusters.

The emergency escape system is activated 15 minutes before launch and, from that point it could be used all the way until 157th second in flight, on the original Soyuz spacecraft. The escape rocket would then separates, followed by the separation of the payload fairing at T+161 seconds in flight. (52)

During a normal flight, three "floating" struts on the payload fairing would simply "follow" the structure of the spacecraft inside it. However, in case of emergency they would be instantly fixated to the lower structural ring of the reentry vehicle, thus transferring all loads from the payload fairing, during the escape flight.

The main escape motors would then fire for 2-6 seconds (2), pulling away the top section of the vehicle, including habitation module and the reentry capsule with the crew from the rest of the rocket. The instrument module of the Soyuz would remain with the rocket.

The escape rocket would accelerate up to 50-150 meters per second, and, in the case of emergency on the ground would lift the capsule to the altitude of 1-1.5 kilometers, which would be enough for normal landing under a parachute. (2)

After the OGB SAS stack reached a safe distance from the failing rocket, the reentry capsule would be disconnected from the fairing and a separation motor would fire, allowing the capsule with the crew to slide away from the bottom of the payload fairing, like a bullet from a rifle. A normal landing under a parachute would follow. The same solid motor would be used during a nominal flight to separate the emergency escape tower from the rocket.