I work on autonomous submarines that image the seafloor, and let me tell you it is very hard to engineer deep ocean systems. Just operationally, testing things in rolling waves is a brutal job. Arguably at parity with space as an engineering design environment.
I forget who said it, but there's a quote about how _of course_ we know more about space than the bottom of the ocean - in space we only have to deal with one atmosphere.
I (briefly) worked as a test engineer on a similar kind of contract. To meet the UX requirements for the system we were building, it had to be reliably operable in sea state 7+. The customer wanted touch screen interfaces. I exited that project when they were looking for volunteers to go spend time offshore in the Gulf of Alaska in bad weather, because that was the test environment they could find that met the requirements. Insanity.