On February 1, 2003, the Space Shuttle Columbia re-entered Earth's atmosphere after an otherwise routine mission. When the Shuttle launched a few days earlier, a half-kilo piece of insulating foam on the external fuel tank had broken off during launch and slammed into the port wing at 900 kilometers per hour. No damage was seen on video taken from the ground, and NASA assumed nothing had happened.
However, what they couldn't see was that the piece of foam had punched a hole in the wing itself. When Columbia entered the atmosphere, gas at plasma temperatures entered the hole, ate through the support structure, and the wing essentially broke apart. The Shuttle destabilized and was lost, along with her crew.
The key events have been released by NASA before, but a new report has just been released talking specifically about the loss of the crew themselves. [Note: I couldn't find anything on the NASA site, so that link goes to WFTV in Orlando that has the report, plus video taken onboard Columbia moments before the Shuttle was lost.]
The executive summary gives five main fatal circumstances for the Columbia crew:
1) Depressurization of the crew module at or shortly after orbiter breakup.
The crew's suits were not configured for vacuum at the time of the disaster -- meaning they were not airtight. Had they been buttoned up, they would not have survived this anyway, but in the future, with more protection in place, a crew might live through such an event.
2) Exposure of unconscious or deceased crew members to a dynamic rotating load environment with a lack of upper body restraint and nonconformal helmets.
The crew cabin split off from the Orbiter and started to spin. The crew were strapped to their seats, but only with what is essentially a lap belt. Their torsos were whipped around, causing lethal trauma.
3) Separation of the crew from the crew module and the seat with associated forces, material interactions, and thermal consequences.
Basically, the crew module broke apart at 200,000 feet and was still moving at hypersonic velocities. Had the crew still been alive when this happened, this event alone would have killed them. Rapid deceleration, seat restraint injuries, pressure, and heat would have all been lethal.
4) Exposure to near vacuum, aerodynamic accelerations, and cold temperatures.
When the Shuttle broke up, it was so high that even the pressure suits worn by the astronauts would not have protected them from that environment.
5) Ground impact. This is self-evident.
So, what to do? In some cases, there are things NASA can do to prevent these five issues in the future. Better suits and more rigid protocols for them, automatic systems that detect an impending disaster and deploy safeguards (parachutes, for example), better dynamic control of the components to prevent them from lethal motion on descent: all of these may save the lives of astronauts in the future.
Of course, preventing the entire event from happening in the first place is the best remedy. Better foam application on the external tank would only have prevented this particular disaster. There are many, many other things that can spell doom for a machine that is by design meant to travel at high velocities in both air and a vacuum.
But better component design and a more thorough process during that design may prevent future astronauts from going through what those seven people did on that winter day in 2003. In many ways, a simple rocket-to-orbit is safer, since it's simpler to design and the aerodynamic loads on the returning capsule are simpler to engineer for; that's why Apollo used it, and that's why Constellation will as well.
As hard as it was to read the parts of the report I did, it must have been incredibly difficult for the NASA investigation team to write it and release. I'm glad they did, and I hope that NASA, and all spaceflight teams across the world, can learn from what happened. Space flight will go on, and there will be more accidents, more deaths. We owe it to the Columbia crew, and to those future explorers, to do the utmost best we can to ensure their safety while still learning how to make us a space-faring species.