AETHER Data Modeling Solicitation 2025-09-30.pdf

Extravehicular Activity Pre-breathe Protocol Modeling for Exploration Missions

Specific Focus Area The focus of this effort is to produce a model that allows for the accurate prediction of Spaceflight Decompression Sickness (DCS) risk based upon evidence from studies from operational data sources. Using retrospective and prospective data, the goal is for the model to be used as an operationally-feasible, mission-relevant DCS risk prediction tool for lunar and Mars exploration.

Request For Information Questions:

The information obtained will be used by NASA for planning and acquisition strategy development. NASA will use the information obtained as a result of this RFI. Comments are sought to help refine the following research areas:

1. Publicly available DCS datasets

2. Modeling approach

3. Physiologic / demographic parameters and impact to modeling approach.

4. Statistical approach and level of confidence based on available datasets.

5. Including animal data in the model.

Specifications The model must predict the risk of both Type I and Type II DCS in nominal and off-nominal conditions and may include but is not limited to factors such as: variations in cabin and suit pressures, sex, cardiorespiratory fitness, body composition, hydration status, diet, ambulation, temperature and intermittent and continuous pre-breathe durations.

Model must be validated according to NASA's Standard for Models and Simulations (NASA- STD-7009) (NASA-STD-7009B-Final-3-5-2024.pdf) or equivalent.

Modeling teams will develop a model within 6-month period based upon a representative training dataset provided by NASA.

NASA will hold a comparable dataset for the purposes of model validation, that will occur within a 2-month period. Proposers will receive an additional 2-months to revise and submit the revised model based on feedback from the NASA review before final deliverable submission.

Teams also may supplement with publicly available or other datasets appropriate to this spaceflight DCS risk.

NASA will assess the prediction accuracy with a different but comparable test dataset.

Prediction accuracy and precision will be assessed in a masked manner by NASA statistical and modeling experts. The incorporation of other applicable datasets and results from ongoing data collection will be addressed in follow-on solicitations.

Required Deliverables The investigator team shall provide:

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1) The modeling tool in a compiled/executable or other directly operable form as well as all raw source code, spreadsheets, analysis and configuration files needed to update, alter, and recompile the tool into a directly operable form with supporting documentation.

2) Final reports detailing the methods, results (with the appropriate statistical analysis), and discussion of the findings. The report also should include:

a. User guide for running the model

b. Description of any synthetic datasets used, rationale for approach on synthetic datasets and how those synthetic datasets were tested

c. A “lessons learned” section

d. Recommendations to further mitigate DCS risk to an acceptable level

3) A publication plan as well as copies (PDF) of peer-reviewed publications, if appropriate

4) Two demonstrations of the model to NASA. The first following the 6-month period of model development and a second after incorporation of feedback from NASA.

NASA resources:

NASA will provide the modeling teams with:

- A set of data to develop their model

- NASA subject matter experts in decompression sickness will be available to respond to questions from the research teams, and content from these answers will be distributed to all participating available to all teams through distributed documentation.

Specifics on what data are available (parameters) Retrospective data from NASA will include subject demographics (age, height, weight, body mass index, cardiorespiratory fitness [peak oxygen consumption], the details of the decompression stress (e,g., ambient breathing gas composition, starting and final ambient barometric pressure) and pre-breathe protocol (breathing gas composition, duration, decompression rate, resting or exercise), metabolic load during pre-breathe when exercise was performed, DCS status (none, Type I, Type II; time of symptoms reported), venous gas emboli maximum Spencer grade, posture before, during, and after pre-breathe, and metabolic rate during simulated EVA following pre-breathe. NASA will provide data from ~1500 trials but hold a comparable dataset for validation of the proposed model.

Optional dataset While not mandatory, below is one of the publicly available datasets that can be incorporated into the model:

CBDN Public Site at https://biodyn.istdayton.com/CBDN/Login/

The Altitude/Decompression Sickness module has an icon of the Altitude Chambers (click on). The 3 main sections are

1. ADRAC Model (decompression sickness prediction)

2. DCS Research Records (records used to establish and validate the model)

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3. Literature database for altitude exposure and DCS

Supplementary Operational and DCS Information

Given that extravehicular activity (EVA) suit operations are conducted in a reduced pressure environment relative to the vehicle or habitat, there is a risk of DCS during EVA in weightlessness and partial gravity during planned exploration missions. For many years, pre-breathe protocols with 100% oxygen (O2) have been performed prior to EVA by Space Shuttle and International Space Station astronauts to reduced DCS risk and are supported by the resources that may be readily re-supplied from the ground. Resources, including crew time, will be constrained during lunar stays and missions to Mars, and astronauts will be expected to perform multiple EVAs within a mission. Efficacious DCS risk mitigation activities could decrease consumable use and crew time while maintaining or reducing risk and maximizing EVA performance, thus extending the availability of resources, protecting reserves for contingency scenarios, and elevating the potential to achieve mission objectives. Manipulating vehicle or habitat and suit environments (e.g., breathing gas composition, pressure) can impact the requirements for DCS risk mitigation, and many of these environments are not yet defined, particularly for commercial providers.

Prebreathe has been performed for EVAs in weightlessness, but the Apollo missions used a 100% O2 vehicle atmosphere and therefore did not require prebreathe in the partial gravity environment on the lunar surface. Ambulation and increased physical workload during planetary EVAs will increase DCS risk compared with operations in microgravity, meaning that existing DCS risk mitigation protocols used on ISS likely are not applicable for planetary EVA (1).

Given the limited conditions in which DCS risk mitigation strategies have been studied and the limited experience of EVAs in partial gravity, current models of DCS risk are severely limited in their ability to accurately inform exploration DCS risk mitigation protocols which can substantially affect the design and operation of vehicles, habitats, EVA suits, and launch entry and abort (LEA) suits.

Background The goal of NASA’s approach for EVA DCS risk mitigation for current and future missions is to avoid Type II (serious) DCS and to limit the incidence of Type I DCS to within acceptable limits (NASA-STD-3001, V2 6008) or lower. The acceptable incidence of Type I DCS for a particular mission will be determined primarily based on the consequences of losing one or more EVAs due to Type I DCS. Mitigation of DCS risk typically involves trading impacts to vehicle atmospheres, spacesuit pressures (affecting crewmember dexterity and fatigue), crew time (i.e., prebreathe duration), crew hypoxia (NASA does not accept less 2.46 psia PIO2), and operational complexity (e.g., prebreathe masks, campout protocols).

In the Apollo program, NASA dictated the conditions in the vehicles and suits, using 100% O2 to eliminate DCS risk and crew time requirements for prebreathe prior to EVA at the expense of increased flammability risk. NASA does not anticipate operating at vehicle atmospheres exceeding 34% O2 due to flammability and O2 toxicity concerns, and atmospheres involving inert gases other than N2 have not traded favorably due to vehicle mass and complexity impacts

80JSC025DCS Page 3 of 5 09/30/2025 https://humanresearchroadmap.nasa.gov/Evidence/reports/Evidence%20Report%20Hypoxia%20and%20DCS_FINAL_1-8-2024.pdf https://humanresearchroadmap.nasa.gov/Evidence/reports/Evidence%20Report%20Hypoxia%20and%20DCS_FINAL_1-8-2024.pdf https://standards.nasa.gov/system/files/tmp/NASA-STD-3001%20Vol%202%20Rev%20E_1.pdf?check_logged_in=1 for life support systems. The trade space is complicated by the broad array of launch, transit, and orbiting vehicles, pressurized rovers, habitats, LEA suits, and EVA suits that will enable the Moon-to-Mars architecture, with many elements being provided by international and commercial partners and the potential for a variety of potential atmospheres and operating pressures.

The majority of data used in the construction of current DCS models resulted from studies in which the baseline condition that simulated the cabin or vehicle environment was similar to Earth’s sea level condition (~21% oxygen, 14.7 psia) and a common reduced pressure condition simulating the EVA suit environment (~95% oxygen, 4.3 psia); however, NASA and their international and commercial partners may choose to utilize different environments to reduce or manage DCS risk while maximizing suit mobility and controlling for flammability concerns and other hazards. Given the conditions that have been tested previously were targeted for specific purposes, decisions regarding the acceptability of cabin, habitat, rover, and suit environments that might be proposed by commercial providers and international partners are dependent upon improved modeling with a larger, more robust data set encompassing the range of environmental conditions in which an astronaut might be expected to live and work.

DCS testing protocols are developed to provide a well-defined set of conditions from which data can be extracted for models, but performance of DCS risk mitigation activities in an operational context may not be as tightly controlled or possible. For example, breaks in prebreathe protocol execution have occurred but the consequence of these and the potential mediation strategies are not well understood (2, 3). Additionally, DCS modeling to date has focused on predicting risk in a single exposure, but in the current lunar and Mars mission architecture astronauts may be expected to perform multiple EVAs in a relatively short period of time (up to 24 hours per week per astronaut which would be enabled by multiple EVAs, potentially on back-to-back days with 24 hours separating start times) though the effect of cumulative exposures is not well characterized. Further, prebreathe activities have predominantly been used for studying or conducting EVAs in weightlessness, but astronauts will perform ambulatory EVAs in partial gravity during exploration missions (1). Exercise during prebreathe is one approach that has been used to accelerate denitrogenation (4) but other methods (e.g., pharmaceuticals) have not been fully examined. Importantly, current models are based largely upon sample of male subjects and thus may not be representative of the astronaut population (5, 6).

Additionally, planning for exploration missions beyond low Earth orbit must consider contingency scenarios in the event of unplanned depressurization of the vehicle’s cabin, the habitat, or the EVA suit. In the event of cabin or habitat depressurization, the pressure and duration for which the life support system must “feed the leak” to allow astronauts to don LEA spacesuits, as well as the pressure of those suits, are of critical importance. Suit pressure must also mitigate DCS risk to an acceptable level, and possibly contribute to hyperbaric DCS treatment, but it may also be necessary to transiently decrease suit pressure to improve mobility while performing certain EVA tasks to recover from the depressurization.

A summary of the current evidence for these risks, and a reference list, is available at https://humanresearchroadmap.nasa.gov/evidence/. The content relevant for this solicitation can be found under the Risk of Injury and Compromised Performance Due to EVA Operations.

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The Evidence Reports can be found at:

RISK OF REDUCED CREW HEALTH AND PERFORMANCE DUE TO

DECOMPRESSION SICKNESS AND HYPOXIA

RISK OF INJURY AND COMPROMISED PERFORMANCE DUE TO EVA OPERATIONS

Additionally, the Office of the Chief Medical Officer released a technical brief relevant to this topic:

Decompression Sickness (DCS) Risk Mitigation OCHMO-TB-037 Rev C

Relevant historical work in this research area was summarized in a NASA technical report:

Preventing Decompression Sickness Over Three Decades of Extravehicular Activity

Prior modeling work at NASA is summarized in a NASA technical report:

Probability of Decompression Sickness and Venous Gas Emboli from 49 NASA Hypobaric Chamber Tests with Reference to Exploration Atmosphere

REFERENCES

1. Conkin J, Pollock NW, Natoli MJ, Martina SD, Wessel JH, Gernhardt ML. Venous Gas

Emboli and Ambulation at 4.3 psia. Aerosp Med Hum Perform 88: 370–376, 2017. doi:

10.3357/AMHP.4733.2017.

2. Conkin J. Decompression sickness after air break in prebreathe described with a survival model. Aviat Space Environ Med 82: 589–598, 2011. doi: 10.3357/asem.3020.2011.

3. Conkin J, Abercromby AFJ, Dervay JP, Feiveson AH, Gernhardt ML, Norcross JR, Ploutz-Snyder R, Wessel JH. Hypobaric Decompression Sickness Treatment Model.

Aerosp Med Hum Perform 86: 508–517, 2015. doi: 10.3357/AMHP.4178.2015.

4. Foster PP, Pollock NW, Conkin J, Dervay JP, Caillot N, Chhikara RS, Vann RD, Butler BD, Gernhardt ML. Protective mechanisms in hypobaric decompression. Aviat Space Environ Med 84: 212–225, 2013. doi: 10.3357/asem.3314.2013.

5. Platts SH, Bairey Merz CN, Barr Y, Fu Q, Gulati M, Hughson R, Levine BD, Mehran R, Stachenfeld N, Wenger NK. Effects of Sex and Gender on Adaptation to Space:

Cardiovascular Alterations. J Womens Health (Larchmt) 23: 950–955, 2014. doi:

10.1089/jwh.2014.4912.

6. Strock N, Rivas E, Goebel KM. The Effects of Space Flight and Microgravity Exposure on Female Astronaut Health and Performance. In: 2023 IEEE Aerospace Conference. 2023 IEEE Aerospace Conference, p. 01–12.

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Extravehicular Activity Pre-breathe Protocol Modeling for Exploration Missions