Emergency escape

As the early spacecraft were developed from military missiles, they had a very nasty tendency to explode on or shortly after lift-off. Getting these vehicles safe enough to carry a crew – man-rating – was a priority, but to be on the safe side, additional escape methods were developed. All systems are tested many times to ensure their correct operation in the event of an emergency and though no crew would wish to experience launch escape systems in action, it is comforting knowing that there is an option to get out of a bad situation if necessary, assuming you have time to do anything about it, of course.

The Soviet Vostok one-man craft employed an ejector seat, which would be used in the event of a launch failure or operationally for pre-landing ejection and parachute descent. In contrast, the Voskhod was the most dangerous of all spacecraft. Adapted from the basic Vostok one-man vehicle, it could carry two cosmonauts with spacesuits, or three without, but it didn’t have any room for ejection seats.

The US Mercury and Apollo spacecraft, and the Russian Soyuz spacecraft, utilised a rocket launch escape system during the final stages of the countdown and in the early stages of ascent. The Chinese Shenzhou has a similar rocket escape system to the Russian Soyuz. The Russians have experienced two launch aborts during the forty years of Soyuz operations. During the abort in 1975, the escape tower had been ejected and the crew had to rely on the ballistic abort and return separation sequence, enduring up to 20-G loads for a few seconds. Then in 1983, a Soyuz launch pad abort system was activated when a launch vehicle caught fire on the pad. It exploded seconds after the crew were boosted to safety by the escape tower.

The American Gemini spacecraft adopted ejector seats, which could be used prior to launch or during ascent if required. The first four Shuttle orbital test missions also had ejection seats fitted, but these were deactivated after the fourth and final test mission and removed after the fifth flight.

The Space Shuttle also has a series of abort modes available during the ascent phase, although, when asked whether they wanted to fly a test mission of these aborts, the astronauts declined, indicating that they would test them when they needed them.

In the event of a main engine failure prior to ignition of the twin Solid Rocket Boosters (SRBs), there are options to abort the launch and this has occurred on five occasions in the history of the Shuttle programme. The three official abort modes are Return to Launch Site (RTLS), Trans-Atlantic Abort (TAL) and Abort to Orbit (ATO).

RTLS occurs early in the flight if one or more engines are lost. This is the most risky, and many astronauts don’t believe it is survivable, as the stack has to turn around and fly back to the Kennedy Space Center. This would be a severe strain on the structural integrity of the vehicle. A TAL abort is a preferred option, with three prime locations in Europe, while an ATO is the only one to have actually occurred thus far. This was in 1985 during mission STS 51-F, when one engine shut down early during launch. The mission continued normally. It is obvious to all who fly the Shuttle, however, that a failure of an SRB (which occurred on the STS 51-L launch in January 1986) is non-survivable. There are other “contingency” aborts which are not “official” but are nonetheless trained for. The orbiter could shed its External Tank (ET) and conceivably land at Bermuda or other east coast sites in the USA, but this, too, would provide a real challenge for the flight crew – and quite a spectacle for the locals.

As the Shuttle launch pads were adapted from the older Apollo Saturn V launch pad, some of the facilities are still available to the crew on the pad in the event of an emergency situation. Should an emergency occur before launch, such as fire after a launch pad abort, the crew would evacuate the Shuttle and use “baskets” on slide wires to descend to the ground, then go through tunnels into an underground bunker. There is also the option of using an armoured personnel carrier to vacate the pad as quickly as possible. Any countdown demonstration test during training on the pad ends with this emergency drill, although it does not include the actual slide wire ride. During the Apollo era, and due to the height of the tower, the crew could have used a slide tube system leading to an underground protected bunker, if they had time to get there!

For resident crews on the International Space Station (ISS), and previously on the Soviet Salyut and Mir stations, an emergency return vehicle has always been

available – the Soyuz. There is always one attached to the station and when crews become larger as more of the station is built, there will be two attached. NASA has been planning and designing its own Crew Rescue Vehicle but it is unlikely that this will ever be built. The Soyuz is perfectly adequate for the job. It is probable, however, that if NASA build a Crew Exploration Vehicle for the Vision for Space Exploration pro­gramme, one or two of these will be docked to the ISS.