Safety considerations in a piloted spacecraft must take into account the possibility of an emergency at any stage of the flight, starting with the pre-launch countdown and ending with the vessel's return to Earth. Following the Challenger disaster in 1986, the crew compartment was found in the Atlantic Ocean. It appeared that at least some crewmembers survived the initial explosion and were alive before the impact with the water. But the seven astronauts had no way to escape, and their cloth uniforms offered no protection or survival capabilities. The National Aeronautics and Space Administration (NASA) proceeded to implement changes to the crew module and the astronauts' uniforms, making emergency evacuation and survival more likely during specific periods in the shuttle's mission.
In the event of an emergency on the launch pad, the astronauts can evacuate the shuttle up to 30 seconds before launch. The shuttle launch gantry is equipped with seven 1,200-foot-long sliding wires, each attached to a basket similar to those used for hot-air ballooning. Each basket can carry up to three people. The baskets descend steeply and rapidly down the wires to the ground, where the crew will proceed to a special bunker designed to shield them from a possible explosion on the launch pad.
Should the shuttle come in for a landing, but cannot reach a runway, the crew can evacuate while the orbiter is in the air. The side hatch on the shuttle can be discarded. A pole is then lowered from the hatch opening, and crewmembers can hook themselves to the pole. The astronauts will slide down the pole past the left wing, and slide off the pole into a freefall. The special suits worn by astronauts during launches and landings contain parachutes that will allow the crew to return safely to Earth.
The side hatch on the shuttle is similar in principle to the explosive hatches used on the Mercury spacecraft, starting with Gus Grissom's Liberty Bell. Mild explosives sever the hinges on the hatch, just the way the Mercury hatches worked. Hatch thrusters propel the hatch on the shuttle away from the main shuttle body.
When the shuttle is on the ground, an emergency evacuation can be achieved through the side hatch opening using an inflatable slide. A secondary emergency opening is through one of the overhead windows on the flight deck. Once that window has been opened, the astronauts climb special steps up to the opening and lower themselves to the ground over the side of the shuttle.
The current escape systems described above are considered inadequate in many scenarios involving catastrophic engine failure or a Challenger-like explosion. NASA has been studying additional emergency escape systems for the space shuttle. Among the options being considered are ejection seats and a detachable crew compartment with its own separation rockets. These systems are not new to human spacecraft. Ejection seats were used on the Gemini spacecraft, and on many Soviet spacecraft, as well as the first four shuttle missions. The Mercury and Apollo space vehicles were equipped with a launch escape tower—a tower bearing a rocket that could carry the crew capsule away from a burning launch pad or a fiery booster during launch, similar to the proposed detachable crew module for the shuttle.
Any upgrades to the safety systems will require major and expensive changes to the current space shuttle design. The space shuttle is scheduled to operate at least until 2012, and probably longer. Independent safety experts consider safety upgrades past due, given the planned life span of the shuttle program.
see also Apollo (volume 3); Challenger (volume 3); Emergencies (volume 3); Space Shuttle (volume 3).
Adi R. Ferrara
Swenson, Loyd S. Jr., James M. Grimwood, and Charles C. Alexander. This New Ocean: A History of Project Mercury. (NASA History Series SP 4201) Washington, DC: National Aeronautics and Space Administration, 1989.
Halvorson, Todd. "NASA Studies Advanced Shuttle Crew Escape Systems." Space.com. <http://www.space.com/news/spaceshuttles/shuttle_escape_systems_010410-1.html>.
EVA See Space Walks (Volume 3).