This is the fourth episode of National Geographic's Extreme Universe series, and despite its title it splits its attention between two extremes: the deep ocean and outer space. Oceanographers and astronautics specialists appear on camera to explain what each environment does to the technology and people sent into it. Deep-sea submersibles built to withstand crushing pressure sit alongside space telescopes built to survive vacuum and radiation, and the episode uses both as case studies in engineering under extreme conditions. Interview subjects describe the physical dangers of deep dives and the hazards of working in space, treating the two as parallel problems in survival rather than separate subjects. The episode's argument is that pushing into either frontier, ocean floor or orbit, demands the same kind of specialized hardware and the same tolerance for risk, even though the environments could not be more different.