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Today, NASA Human Space Flight lost the Space Shuttle "Columbia" over North Central Texas while on approach for a landing at Kennedy Space Center in Florida. Apparently, the thermal shield consisting of ceramic tiles failed and in consequence, the hull disintegrated. All seven crew, including the first Israeli and the first Indian astronauts ever, will be pronounced dead. This happend just days after the 17th anniversary of the "Challenger" explosion (mission 51-L).

A space flight includes two critial phases. The first, after lift-off. Rockets and boosters accelerate the ship from zero to about 8000 meters per second, with a critical moment when traversing Mach 1. During that phase, "Challenger" was lost. The second, when re-entering the earth atmosphere. Then, using braking rockets negative acceleration in the magnitude of serveral g is applied to slow down the vehicle from said 8000 meters per second to about 83 meters per second (300 kilometers per hour) touchdown speed. This happens about 20 minutes before landing.

During that phase, due to the extreme forces air resistance causes the nose and the wing tips to heat up to more than 2500 degrees Celsius. Flames build up and cover the entire front of the vehicle. Ceramic tiles designed to withstand temperatures of more than 3000 degrees Celsius are applied to the outer structure and the wings to protect the ship from damages. Under normal conditions, several tiles crack or fall off, and after each mission, the heat shield receives maintenance.

As "Columbia" was the oldest Space Shuttle, it can be assumed that fatigue combined with a shield damage discovered on launch 16 days ago but considered minimal led to a failure of the thermal shield. In this case, the heat can work on the structure, weaken it until a hole builds. Latest when the hole reaches the pressurized cabin, the hull breaks up and the ship falls to pieces. This might take no longer than 10 to 30 seconds in total. The resulting unprotected pieces start to anneal and while travelling to earth surface, a part of the matter dies down. This mechanism is sometimes used to discard thermally unprotected and unmanned space vehicles like satellites. In such a controlled crash, satellites normally die down entirely before reaching earth surface.

Update

Failure of the thermal shield of course is only one possible cause, likely and easy to assume. Other possible causes include aerodynamic effects caused by rolling at a wrong angle (descend is without power, and "piloting the shuttle on reentry as like trying to fly a brick with wings") and the left wing separating from the hull as at ascent, this wing was struck by debris from the external tank insulation, another damage considered minimal. Data analysis will unveil what mostly likely has happened, and until then, of course, media will demonstrate once more how scientifically unbiased most of their staff is. Links via IT+W.