Decompression sickness is a significant risk to both current and future astronauts and currently significant time is lost in preparation for extra-vehicular activity on the ISS [including airlock utilisation for nitrogen-washout and pure oxygen cycle ergometer pre-breathe]. In the event of sudden decompression [such as micro meteor strike] astronauts in the ISS could seal off a section of the ISS or retire to the Soyuez. Theoretically, if this was not an option [or not a possibility such as aboard a smaller space-craft on an ECM] astronauts would be at significant risk of decompression sickness and subsequent morbidity/mortality if they just donned their EVA suits. [Suits at 100% O2 and 4.3psi].

I have been reading the information on both the Dragon and Orion module. The Dragon states an 'internal pressurised atmosphere' and the Orion module states 'pressurised' and then clearly shows Nitrogen storage which could only be for atmospherics. In my opinion this suggests both are using an Earth-equivalent atmosphere [21% O2, 79% N2, at 14.7psi or roughly sea-level pressure]. This is the same as the ISS and reduces risk of fire [such as the 100% oxygen atmosphere of Apollo 1].

My question is as follows; Given the time lost in EVA / future surface activity preparation with the current atmospherics, would a change in internal atmosphere not significantly reduce this 'lost time'. If so would it not also be of great benefit in reducing risk during sudden decompression [in the event of emergency egress/EVA suit use] or even in an extra-vehicular emergency requiring immediate, unplanned EVA [such as an injured astronaut on EVA]. I have found one example of work using an atmosphere tri-mix [Helium] to reduce this risk, but little other work. Does anyone else have any knowledge on this subject?

Please note I know that there are some 'zero-prebreathe' suits in development such as the Mark III and Z-series. I am more interested in the possible changes/research in atmospherics or environmentals, or the prevention of decompression sickness for current spacecraft, if any is ongoing at all now that these suits are in development.

TLDR: Is anyone researching or developing new ways to prevent decompression sickness for astronauts other than the new 'zero-prebreathe' suits currently in development?

Many thanks for any responses and I hope this makes sense!

Links below:

Helium Tri-mix discussion: https://astronautics.usc.edu/assets/003/70954.pdf

Orion Capsule Datasheet: https://www.nasa.gov/pdf/306407main_orion_crew%20_expl_vehicle.pdf


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