What caused the crash of the space shuttle challenger?

Answer 1

It is a misconception that the Challenger exploded, or that it was destroyed by the explosion of the fuel in the External Fuel Tank. That's not true. Challenger was destroyed by Aerodynamic Breakup, which is what happens to an aircraft traveling at supersonic speeds that is suddenly thrown out of its flight profile. The resulting G-Forces on the aircraft are too strong for the aircraft to endure, and it breaks up in flight.

Another false conception is that the Astronauts all died when the orbiter broke up - that's also not the case. Astonauts are secured by harness in their seats in full environmental suits upon liftoff. The crew cabin is reinforced to withstand impacts and other stresses, and is designed to detach during a catastrophic failure. Several of the Astronauts survived the breakup, but died upon impact when it crashed into the ocean. We know this because several oxygen bottles used by them were almost completely depleted, and there was evidence that at least one had attempted to help another.

Although this wasn't determined until after the investigation took place, the reason that many believe it exploded is that the rapid burn rate of the ruptured fuel from the EFT made it appear that it had exploded in mid-air.

The official cause of the accident is the failure of starboard (right side) SRB O-Ring, leading to solid fuel propellant leakage at the SRB joint. The propellant burned through the lower SRB strut, causing it to separate, rotate and detach from the External Fuel Tank (EFT). This action broke open the tank, releasing liquid Hydrogen and Oxygen from the tank. Ignited by the SRB's exhaust flames, the fuel rapidly burned and propelled the Orbiter out of an aerodynamic flight profile at over Mach 3. This led to aerodynamic breakup of the Orbiter.

Solid Rocket Boosters are the 2 white rockets outside the external tank which help propel the shuttle into orbit. The EFT is the orange external tank the shuttle attaches to - it contains liquid Hydrogen and liquid Oxygen in separate tanks, and acts as a huge "gas tank" for the shuttle's main engines.

The solid fuel propellant in the SRB's are set into different sections and separated by huge O-rings, flexible band seals that allow the SRB to flex in flight. The temperature that week was extremely cold for Florida, with ice having to be knocked off of the launch pad areas. Being of a rubber material, the O-rings were extremely susceptible to the cold, and became stiff, losing their flexible properties. When the Challenger lifted off, since the seals could not function properly to prevent propellant gases from leaking, they ignited and burned through the lower attachment strut, leading to catastrophic failure.

The real tragedy is that it could have been prevented. Engineers from Morton-Thiokol, the makers of the SRB, warned NASA administrators of a possible O-ring failure, but since there was no actual test evidence that it could happen, and because of the pressures of getting the shuttle into orbit, NASA did not heed the warning and authorized the launch anyway. The rest is history.

There is a video DVD on the Challenger Accident which is the official NASA report on the accident. It's available on NASA themed DVD at Best Buy and similar stores. Although it's technical in its presentation, I first saw it as part of my orientation into NASA QA procedures 17 years ago. I worked on Manned Flight and other NASA programs for 9 years, retiring in '99 before the Columbia accident. It could have been prevented as well, but many factors led to the NASA culture that let it happen then.