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Soyuz launch escape system

The Soyuz launch escape system has the acronym САС, SAS (Система Аварийного Спасения, Sistema Avariynogo Spaseniya) and is activated should anything go wrong on the launch pad, or on the ride into orbit. It is attached to the shroud covering the Soyuz spaceship during launch. The main events that would trigger the system during launch are loss of control, premature booster stage separation, loss of pressure in the combustion chambers, lack of velocity and loss of thrust.

The system can also be triggered from the ground by remote radio control (КРЛ, Командная Радиолиния, Komandnaya Radioliniya – Command Radio-Line). The command is sent from the Kvant ground control station at Site 23, 30 kilometers away from the Soyuz launch site.

The SAS is activated and ready from 15 minutes before launch to 157 seconds from launch. On activation, three floating struts on the payload fairing fixate to the lower structural ring of the Soyuz Descent Module to transfer loads from the payload fairing. The main escape motors fire for 2-6 seconds, taking with them the top two sections of the Soyuz spaceship (Habitation and Descent Modules; the Instrumentation Module remains with the rest of the rocket). The rockets can lift the SAS to a height of 1-1.5 kilometers from the ground. The Descent Module is then disconnected from the fairing, a separation motor fires and the Descent Module falls out of the bottom of the fairing, deploys its parachute and lands in the normal manner.

This extract from Mir Hardware Heritage describes the only time the SAS has been used, so far:

  • Pad Abort September 26, 1983
  • Vladimir Titov, Gennadi Strekalov
  • Crew code name: Okean

Refer to figure 1-29. Shortly before liftoff, fuel spilled around the base of the Soyuz launch vehicle and caught fire. Launch control activated the escape system, but the control cables had already burned. The crew could not activate or control the escape system, but 20 sec later, ground control was able to activate the escape system by radio command. By this time the booster was engulfed in flames. Explosive bolts fired to separate the descent module from the service module and the upper launch shroud from the lower. Then the escape system motor fired, dragging the orbital module and descent module, encased within the upper shroud, free of the booster at 14 to 17 g’s of acceleration. Acceleration lasted 5 sec. Seconds after the escape system activated, the booster exploded, destroying the launch complex (which was, incidentally, the one used to launch Sputnik 1 and Vostok 1). Four paddle-shaped stabilizers on the outside of the shroud opened. The descent module separated from the orbital module at an altitude of 650 m, and dropped free of the shroud. It discarded its heat shield, exposing the solid-fuelled land landing rockets, and deployed a fast-opening emergency parachute. Landing occurred about 4 km from the launch pad. The aborted mission is often called Soyuz T-10a in the West. This was the last failed attempt to date to reach a space station to date.

Soyuz abort sequence

An account from Leaving Earth by Robert Zimmerman:

It was not to be. Ninety seconds before blast-off, with Titov and Strekalov waiting at the top of their fully-fueled Soyuz rocket, a fuel valve at the base of the rocket malfunctioned, opening and spilling fuel uncontrollably onto the launchpad. A fire broke out and flames engulfed the rocket with its 180 tons of very flammable fuel. At that moment, the automatic launch-escape system should had kicked in, executing the following steps: First, explosive bolts fire, flinging the Soyuz T capsule free of the three-stage rocket. One second later, solid-fuel engines in a tower attached to the top of the capsule ignite, lifting the Soyuz T orbital module and descent module away and clear. Five seconds after that, more explosive bolts fire to separate the manned descent module from everything else. Its parachutes then release and its retro-rockets fire, slowing the capsule enough for a safe landing.

The automatic launch-escape system did not kick in, however. The fire had burned the system’s wiring, preventing it from being activated automatically. Feeling strange vibrations and seeing black smoke and yellow flames outside their window, Titov and Strekalov tried to fire the launch-escape system manually, only to get no response. To fire the escape system manually from mission control required each of two different operators, located in two separate rooms, to press separate buttons at the same time. With flames rising from the launchpad and the entire rocket already leaning 20 degrees to the side, controllers scrambled madly to get the system to free.

Just 10 seconds after the flames first appeared, controllers miraculously managed to somehow do this, activating the escape system and throwing Titov, Strekalov and the Soyuz T capsule more than 3000 feet into the air. For five seconds the emergency engines fired, subjecting the two men to forces exceeding 15 g’s. Then the engines cut off, the descent module separated, and its parachutes unfolded.

At that moment, the entire rocket and launchpad exploded. The blast was so intense that the capsule, three miles away, was thrown sideways, and launchpad workers in underground bunkers felt the pressure wave.

Strekalov and Titov landed safely, their capsule hitting the ground with a hard bump that shook both men up but did them no damage. Rescuers quickly pulled them from the capsule, then gave them a glass of vodka to calm their nerves as everyone watched the nearby launchpad crumble in flames and clouds of smoke. It took 20 hours to put the fires out.

Soyuz abort parameters
Breakout altitude in the event of launch failure 850 meters
Breakout distance in the event of launch failure 110 m
G-load on humans
  • during EDS operations, no more than: 10 g
  • in emergency 400 seconds into the mission: 21 (K = 0)
Initial mass of separating nose section, not more than 7635 kg
Total EDS thruster burns 123 TF-S
Maximum EDS thruster propulsion unit thrust 76 TF

SoyCOM: 3.20. Система Аварийного Спасения (САС) (Launch Escape System)

CAC system purpose and composition

The CAC System is designed for bringing the crew modules away from the failed Launch Vehicle and providing conditions for guarantied operation of the landing aids while at the launch site and in the orbit injection phase.

The system is fully automatic. In case of the Launch Vehicle failure the “АВАРИЯ НОСИТЕЛЯ” ( Launch Vehicle Failure) red light illuminates (ТСЭ-3) and also the Central Light goes ON and the intermittent audio signal sounds.

Having received these signals the crew reports to the Launch Control and prepares to withstand the accelerations associated with the launch escape procedures.

General CAC System design is shown in Fig.1.

The CAC System consists of:

Двигательная Установка САС (ДУ САС) (CAC Propulsion System)

The ДУ САС is an active aid which enables the spacecraft rescued part to escape in case of the Launch Vehicle failure both at the launch site and in the orbit injection phase.

The ДУ САС consists of:

The ЦРД engine is designed for the spacecraft crew module (БО-СА) escape from the failed Launch Vehicle and climb up to the altitude necessary for the parachute system operation in case of emergency at the launch site or in launch vicinity conditions.

The УРД thrusters are designed for executing the preset spacecraft crew module escape trajectory in case of emergency at the launch site or in the vicinity of the launch site.

The РДР thrusters are designed for executing the evasive trajectory of the CAC System after its nominal jettison in the spacecraft orbit injection phase. The РДР thrusters are also used to take the Cap+БО cluster away from the CA at the climb portion of the spacecraft rescued part launch escape trajectory.

Apart from the ДУ САС Propulsion System the following thrusters are located on the Aerodynamic Cap:

The РДГ thrusters are designed for raising the climb altitude of the spacecraft rescued part in case of emergency in launch vicinity conditions and also for taking the rescued part away in the orbit injection phase after the ЦРД nominal jettison and prior to the Cap jettison.

The ДСС thrusters are designed for taking the Cap sections away from the spacecraft during its nominal jettison procedure in the orbit injection phase.

Crew Module Aerodynamic Cap

The Crew Module Aerodynamic Cap is the structural base for the escaping crew modules.

CAC System Automatic Equipment

The CAC Automatic Equipment is designed for joint operation with the spacecraft and the Launch Vehicle systems in generating signals and executing commands for the crew module escape from the failed Launch Vehicle in case of emergency at the launch site or in the orbit injection flight phase.

CAC system operational procedure

The CAC System total operational period is subdivided into six portions:

  1. From the moment of the “Взведение САС” (CAC arming) command for configuring the CAC System for operation up to the “КП” (контакт подъема – Lift-Off Contact).
  2. From the “КП” up to 20 seconds of flight elapsed time.
  3. From the FET 20 s up to the ДУ САС jettison programmed time.
  4. From the ДУ САС programmed jettison up to the Cap (ГО) jettison.
  5. From the ГО programmed jettison up to the “ПО” (предварительное отделение – preliminary separation) command.
  6. From the “ПО” command up to the Launch Vehicle 3rd stage Propulsion System Shut Off command. First Portion Procedure

In this CAC System operational period portion the emergency signal can be issued only by the Launch Director via the КРЛ system from the Launch Control vault.

On receiving the “Авария” (Emergency) signal the following commands are issued:

In 1.8 s after the “Авария” signal is issued the УРД thrusters are fired under the program control which depends on the wind direction and the location of the launch facilities.

In 4 s after the “Авария” the РДГ thrusters are fired.

At the escape trajectory peak the САС Automatic Equipment issues commands:

After the ВСК jettison the a РДР thruster is fired and carries the Cap+БО cluster away from the СА so as to prevent their collision. At the preset time moment the parachute system is put to operation and follows a reduced time program.

Second Portion Procedure

This portion features low flight altitudes. So the failed Launch Vehicle Propulsion System is not cut off to carry the Launch Vehicle away from the launch facilities as far as possible. The parachute system operates under the control of reduced time programs.

Third Portion Procedure

When the “Авария” signal arrives the following commands are issued:

  1. The Launch Vehicle Propulsion System emergency ignition;
  2. Execution of all the commands according to the First portion program of the CAC operation with exceptions:
    • only the first ЦРД chamber is ignited (the altitude clearance is sufficient for the КСП complex operation;
    • the РДГ is not fired (altitude sufficient for the КСП operation);
    • only one УРД thruster is burnt, the one located in plane II.

At the preset moment the КСП Complex is put to operation.

Fourth Portion Procedure

This portion’s peculiar feature consists in using the РДГ thrusters as active aid for the crew module escape. On the “Авария” signal the spacecraft is separated at the СА-ПАО interface and two РДГ thrusters are ignited. In 0,32 s after the “Авария” command the second РДГ thruster group is ignited to take the crew modules away from the failed Launch Vehicle trajectory. According to the preset program the CAC automatic equipment issues commands for the ВСК jettison and for the СА/БО separation.

At the preset moment the КСП Complex is put to operation following the nominal time program.

Fifth Portion Procedure

There are no active aids used in this portion for the crew module evasive maneuver away from the failed Launch Vehicle. So the nominal spacecraft separation aids are employed. On the “Авария” signal the САС automatic equipment issues commands for the Launch Vehicle Propulsion System emergency cut off and for the spacecraft crew module nominal separation. The КСП operation follows the nominal time program.

Sixth Portion Procedure

It is this portion’s peculiarity, that in case of emergency separation the spacecraft injection to off-nominal orbits is possible. So based on the long duration (>30 min) crew life support requirement for the offnominal orbit flight the crew rescue is executed within the integrated spacecraft. On the “Авария” signal the CAC automatic equipment translate command for the spacecraft nominal separation from the Launch Vehicle 3rd stage. The separation is accomplished followed by the spacecraft descent. The integrated spacecraft separation is executed nominally at the atmosphere reentry. The spacecraft landing aids operate on the nominal program.

Fig. 1. CAC System Diagram:

  1. Stabilizer.
  2. I-III, II-IV – Stabilization Planes.
  3. View A:
    • БГ – Balance Weight;
    • УРД – Attitude Control Thrusters;
    • РДР – Separation Thrusters;
    • ДУ САС – CAC Propulsion System;
    • ЦРД – Central Rocket Engine;
    • ГО – Aerodynamic Cap;
    • ДСС – Section Jettison Thrusters;
    • ВО – Upper Support;
    • РДГ – Cap Thrusters;
    • БО – Habitable (Crew Resting) Module;
    • СА – Descent Module;
    • НО – Lower Support;
    • ВСК – Cosmonaut Visual System.