Space Shuttle Atlantis to fly! [Archive]

OVERTALK

10th Sep 2003, 18:26

There's some doubt however as to whether the FIX will be in.

Extract from Air Safety Week dated 08 Sep 03

Above all, in the aftermath of an accident, the potential for a repeat is perhaps best minimized when both sides of a problem are addressed - cause and effect. In the aftermath of the 1996 fuel tank explosion that destroyed TWA Flight 800, a major hunt for ignition sources was launched (cause). More belatedly, it was recognized that inerting was necessary to nullify the vapors for full protection against explosions (effect).

In the case of the Shuttle's vulnerable RCC leading edge tiles, the CAIB has addressed cause (external tank foam shedding), while breach (effect) remains a vulnerability. The CAIB said more RCC spares should be in hand, swapping them out on the basis of postflight condition, age, tap-tests, tactile tests, and so forth. And, to be sure, the external tank's propensity to shed foam needs to be fixed. But the failure-proofing of the RCC leading edge tiles was relegated to a desirable future "fix." Although not suggested in the CAIB report, the RCC tiles might be failure-proofed from impacts during the ascent phase, and from zinc erosion from flakes landing on the Orbiter from exposed primer paint on the launch pad during the pre-launch weeks spent in the open. One source suggested a protective "glove" or fillet on the RCC tiles, covering at a minimum the vulnerable inboard leading edge areas (where the fatal damage occurred on RCC tile 8, located right where the angle of sweepback changes). Because max Q (the aerodynamic force during ascent) is relatively low, hitting just over Mach 2, a glove on the RCC tiles would protect the brittle leading-edge RCC from the locus of impact and foam penetrating the tile as easily as was demonstrated during the CAIB's impact testing. The glove could be designed to ablate away during the heat of re-entry, providing further protection. Even a leading edge coating of one inch of Silastic might be sufficient to protect the Shuttle's leading edge during ascent - from the pointy trauma of impact.. That "sacrificial" coating would soon burn away under the temperatures of re-entry - but if thin two-strand wires were embedded beneath that Silastic layer atop, beneath and along the leading edge - and could still carry their currents to the wing-tip and back once in orbit, chances are that no RCC tiles would have sustained any significant damage.

The overarching theme of cause and effect emerges from the Shuttle investigation. Culture contributed to a dilution of proactive safety (cause #1). Foam shedding was tolerated, with resulting damage to the Shuttle's "flight critical" thermal protective system (cause #2, among others). Columbia's loss with all hands was the effect.

LINK ONE (http://www.iasa.com.au/folders/Safety_Issues/RiskManagement/sacrificialgloves.html)

LINK TWO (http://www.iasa.com.au/folders/Safety_Issues/RiskManagement/sacrificialgloves-1.html)

LINK THREE (http://www.iasa.com.au/folders/Safety_Issues/RiskManagement/sacrificial-0.html)