The diving experiments were provisionally concluded with a 40-day HELIOX saturation dive in 615 m.
Apart from the necessary readiness for the underwater training for astronauts and for the treatment of major decompression accidents, since 1991 the scientific work has focused on questions of air and space travel like isolation, altered gas mixtures, the development of space suits, EVA-related problems and activities in great height.
HelioxHeliox is a mixture of oxygen and helium; the percentage of oxygen may - depending on the manner of use - be above or below the normal value of 21 %. In diving, helium serves as a replacement for nitrogen, which is responsible for the narcotic effect (rapture of the depth) in great depth.
Helium is obtained as a "by-product" from natural gas sources and is - like nitrogen - an inert gas. Helium has a clearly smaller density (= 0,178 g/l) than air (= 1,2 g/l) and the speed of sound amounts to 1017 m/s at 300 K (air 347 m/s). With speech production, the oscillations of higher frequency that occur in the larynx and are emphasized by resonance in the nasopharyngeal cavity are preferred by helium. The resulting "duck voice" can be compensated only incompletely by the use of an unscrambler (electronic device for speech rectification).
On one hand, this entails a substantial complication of work because the personnel on deck may be unable to understand the diver correctly . On the other hand, the problems in vocal communication between the divers lead to social and psychological problems. Helium also has a strong cooling-down effect, as its heat conductivity is much higher (=0.143 W/mK) than that of air (=0.024 W/mK). For this reason, a habitable helium atmosphere has to be heated to approx. 32°C in spite of its lower thermal capacity in order to prevent loss of the diver's body heat.