Aug 172007
 

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I just hope they’re right.


NASA advises the extent of underbelly ceramic heat shield damage to Endeavour as follows:

Two heat-shield tiles on the shuttle’s belly were damaged when a chunk of foam debris, possibly including ice, slammed into the orbiter 58 seconds after launch last Wednesday. The impact gouged out an irregular pit crossing the boundary between two tiles, measuring roughly two inches by three inches across and nearly penetrating the full 1.12-inch thickness of the tile. A small, 1-inch by 0.2-inch gash at the bottom of the pit exposed an underlying support pad just above the shuttle’s aluminum skin.

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The metal skin of the orbiter is exposed, however NASA believes any heat soak which eventuates as a result of re-entry will be dissipated through the framework of the wing sub-section immediately beneath the exposed area, due to an adjacent large support member. In other words, the airframe of the orbiter wing will act as a heat sink. I realise that there’s a lot more science involved than simply saying, “she’ll be right”, and that NASA knows what fallout will eventuate from adverse public opinion if they allow another Columbia episode to occur, but everytime a shuttle goes up it suffers some level of heatshield damage no matter how many precautions and equipment changes are made. It’s the nature of the process and the vehicle employed. In fact, it’s been recorded that prior to Columbia’s demise in February 2003, damage inspections of the shuttle fleet following return from orbit routinely revealed heatshield damage of the type now showing on Endeavour’s underside. Some evidence exists that in many cases, entire tiles were missing. That’s not to say that just because a vessel comes back in one piece that any damage it suffered on the way up was, and will probably always be inconsequential. The loss of Columbia proved that assumption wrong in the most dramatic manner possible, and that damage was known about well and truly before re-entry.
NASA believe they’ve made the right punt. A punt it most surely must be given that Endeavour and its damaged underbelly are at least 340 kms distant at moment and while engineers can look at the damage through cameras and laser photography, they won’t know for certain that it’s not terminal damage until 03:00am Thursday 23 August, Australian Eastern Standard Time. Undoubtedly there are valid reasons for not attempting a repair, the least of which is probably the danger of space-walking under the shuttle. No tethers, no hand holds. Just an astronaut strapped into the foot restraints of either the station’s or shuttle’s Canadarm. Not an experience I’d like to indulge in, but if it meant the difference between knowing I’d come back alive and hoping so, I’d be out there in a flash.
Let’s hope NASA have made the right call, for a whole bunch of good reasons.