Rocket science can be broadly described as the science and technology of space research. Few would argue that this particular area of human activity is not a complex one and that rocket scientists are, in all probability, highly skilled and knowledgeable people.
In colloquial British English you will often hear the expression 'It's not rocket science'. This means that the process or activity being described is very simple and the expression is often used in a situation where the speaker is frustrated or annoyed by another person's inability to perform a simple task. For example, 'Come on! Changing a light-bulb isn't exactly rocket science' or 'You don't have to be a rocket scientist to assemble flat-pack furniture!'
One question remains. What do rocket scientists themselves say in such situations?