Challenger

One of his last contributions was the work he did on solving why the Challenger mission ended in a fiery explosion mid-flight not long after take off in 1986. Feynman asked about everything there was to know about shuttles and the equipment that was used in conjunction with them, and finally discovered what he believed was the problem, the O-rings. The O-rings that the solid rocket booster joints used did not expand properly when the temperature was less than freezing temperature (32 degrees F). He tested his theory with ice water and found that he was correct, and even demonstrated the failure on television the day after he found he was right. Gaps caused by an unexpanded O-ring let gas leak out, which then ignited - destroying the shuttle and its crew. This was even confirmed by the picture shown above where you can see the ignited gas leak that caused the explosion as shown by the arrow.