Perhaps he's referring to ballistics. Rocket science generally refers to designing the rockets, which to this day sometimes blow up, lose engines, spiral off course, and suffer various other catastrophes.
There is no debate as to the science behind the failures of Colombia and Challenger, but there is a lot of debate about what human factors led up to those failures and what to do about them, which rather strengthens his point.
They might blow up, but they always land.
>Recently, my husband pointed me to the work of a well-known sociologist, Duncan Watts, earlier at Yahoo! Research, who explains why people exhibit such behavior. Here is my favorite part of his TED talk