I like MatLab, but for me (biologist) it's a very intricate language to learn, and AFAIK not easy to use in multiple platforms where you don't have the framework installed. And "expensive" too (as Mathematica).
But as a rocket scientist, he says there is a lot of software ready-made for him to use, which even included graphics/animation, analysis of realtime data feeds, and limited finite-element analysis of the rocket's structure. Also, his boss had a good software budget at the time.