There is definitely a difference in meaning, maybe just in specialized fields like theology and economics. An Austrian school economist, or an Arianist in the

There is definitely a difference in meaning, maybe just in specialized fields like theology and economics. An Austrian school economist, or an Arianist in the early Christian church, would be called "heterodox" but probably not "unorthodox". It has the connotation of following a definite tradition that is not the main tradition in the field. "Unorthodox" means something more like "doing your own thing", so Steven Levitt (the Freakonomics guy) might be called an "unorthodox economist" because he studies unusual topics like drug dealers, but not a "heterodox economist" because he studies these strange topics using mainstream theories. I think "heterodox" fits reasonably well in this article, it suggests that these engineers are following a distinct tradition, not just "doing their own thing".