Abstract NASA׳s plans for future human exploration missions utilize a new atmosphere of 56.5kPa (8.2psia), 34% O2, 66% N2 to enable rapid extravehicular activity (EVA) capability with minimal gas losses; however, existing EVA prebreathe protocols to mitigate risk of decompression sickness (DCS) are not applicable to the new exploration atmosphere. We provide preliminary analysis of a 15-min prebreathe protocol and examine the potential benefits of intermittent recompression (IR) and an abbreviated N2 purge on crew time and gas consumables usage. A probabilistic model of decompression stress based on an established biophysical model of DCS risk was developed, providing significant (p<0.0001) prediction and goodness-of-fit with 84 cases of DCS in 668 human altitude exposures including a variety of pressure profiles. DCS risk for a 15-min prebreathe protocol was then estimated under different exploration EVA scenarios. Estimated DCS risk for all EVA scenarios modeled using the 15-min prebreathe protocol ranged between 6.1% and 12.1%. Supersaturation in neurological tissues (5- and 10-min half-time compartments) is prevented and tissue tensions in faster half-time compartments (≤40min), where the majority of whole-body N2 is located, are reduced to about the levels (30.0 vs. 27.6kPa) achieved during a standard Shuttle prebreathe protocol. IR reduced estimated DCS risk from 9.7% to 7.9% (1.8% reduction) and from 8.4% to 6.1% (2.3% reduction) for the scenarios modeled; the penalty of N2 reuptake during IR may be outweighed by the benefit of decreased bubble size. Savings of 75% of purge gas and time (0.22kg gas and 6min of crew time per person per EVA) are achievable by abbreviating the EVA suit purge to 20% N2 vs. 5% N2 at the expense of an increase in estimated DCS risk from 9.7% to 12.1% (2.4% increase). A 15-min prebreathe protocol appears feasible using the new exploration atmosphere. IR between EVAs may enable reductions in suit purge and prebreathe requirements, decompression stress, and/or suit operating pressures. Ground trial validation is required before operational implementation.
Highlights Approaches for suit port based extravehicular activities (EVA) are presented. We estimate decompression sickness risk (PDCS) using a biophysical bubble model. Suit purges to 80% vs. 95% O2 save gas and time with minimal increase in PDCS. Multiple short EVAs with brief recompressions to cabin pressure may reduce PDCS. N2 reuptake penalty between EVAs outweighed by decreased bubble size benefit.
Modeling a 15-min extravehicular activity prebreathe protocol using NASA׳s exploration atmosphere (56.5kPa/34% O2)
Acta Astronautica ; 109 ; 76-87
2014-11-28
12 pages
Article (Journal)
Electronic Resource
English
British Library Conference Proceedings | 2013
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