Atmosphere of Venus water and subsequent rise of the levels of other greenhouse gases. Despite the harsh conditions on the surface, the atmospheric pressure and temperature at about 50 km to 65 km above the surface of the planet is nearly the same as that of the Earth, making its upper atmosphere the most Earth-like area in the Solar System, even more so than the surface of Mars. Due to the similarity in pressure and temperature and the fact that breathable air (21% oxygen, 78% nitrogen) is a lifting gas on Venus in the same way that helium is a lifting gas on
S-80-class submarine weapons and sensors, which their government decided not to fund. DCNI then proposed a cheaper option called the S-90B, an S-70 "Agosta"-class submarine with limited improvements which was again rejected by the French but which was exported to Pakistan. Meanwhile, Spain faced the same problem in replacing their "Daphné"s, known as the "Delfín" class in Spanish service, as part of Plan ALTAMAR. Bazán (later Izar, and then Navantia) started on a new design but when it started to look like the S-80, it was agreed to collaborate in a joint venture based on the French S-80. This joint design was