Part 6: Shuttle Dynamic Rotating Forces Need Not Have Been Lethal
Advanced Crew Escape Suit
Columbia’s left wing was struck by a piece of insulating foam that fell off the external tank during ascent. On descent, hot gases entered the cracked leading edge, destroying the hydraulic lines, which powered the control surfaces (rudder, elevons, and ailerons). Columbia then entered a “highly oscillatory slow (30 to 40 degrees per second) flat spin,” according to a simulation performed by the Spacecraft Crew Survival Integrated Investigation Team (SCSIIT). This spinning became worse as the orbiter broke up. According to the Columbia Crew Survival Investigation Report, these rotational loads would have been lethal to the unconscious crewmembers for two reasons.
First, the shoulder belts did not retract and lock, which left the astronauts’ upper bodies unrestrained. The inertial reel used with the shoulder belts had been designed for military helicopters. Some time after the design for Shuttle seats was completed, but prior to the Columbia flight, Department of Defense investigators had concluded that this particular inertial reel (when used in helicopters) was, “deficient in design and proven to be unreliable in survivable crash conditions.” It is very difficult to understand why this component had not been replaced in the Shuttles. As a result of the crew survival investigation, the reels were replaced with a newer model after the accident.
Second, the ACES helmet does not support an astronaut’s head. In case of unconsciousness or sudden impact, the head could continue to move violently enough to fracture the skull (as in several fatal motor racing accidents). The report recommended that future astronaut suits incorporate a device similar to that used in racing, e.g. the Head and Neck Support (HANS) device.
The layout of the controls with the Shuttle requires astronauts to lean forward to reach some of them. Shoulder belts that allow this, yet still lock when required to protect against injury, are required. Astronauts may also need to turn their heads to see all instruments and controls. A HANS device might interfere with this. The new Orion capsule has been designed so that all tasks can be performed without leaning forward, so it has no inertial reels.
Conscious crewmembers could have braced themselves against the rotational loads and would have survived them. However, they may not have been able to make it to the escape hatch. This is a limitation of the current system (as opposed to an ejection seat).
