0The average depth of the ocean is about 4km. Some deep-sea vessels are capable of reaching this depth.
The deepest point in the Ocean is the Mariana Trench at about 11km. This depth was also reached by several vessels (James Cameron visited the Mariana trench using Deepsea Challenger and made a movie about it).
Deep sea exploration is not as popular with the general public as space achievements, so they don’t get as much funding.
The difficulties are not the same:
In space, you need a considerable thrust to clear earth atmosphere and get into orbit, while reaching the bottom of the ocean requires weight and patience.
The pressure difference between in and out : space: 1 atmosphere (of course), Mariana Trench: 1100 atm. A deep sea vessel needs to be 1100 times stronger than a spacecraft to support a crew. Extravehicular activity is impossible at that depth. The suit would have to weight several tons (so it would be a vehicle)
Rocket launches are often paid for by private companies, that derive revenue from operating satellites. When oil companies realised they could extract oil by drilling the deep seabed, they built oil rigs like deep water horizon (and made a mess). I’m afraid if the seabed gets extensively explored one day, it will mean something valuable was found, and it will, therefore, be exploited and destroyed in a few decades, like anything humanity touches.
