Integrating Life Science, Engineering & Operations Research to Optimize Human Safety and Performance in Planetary Exploration

Transcription

1 Integrating Life Science, Engineering & Operations Research to Optimize Human Safety and Performance in Planetary Exploration Mike Gernhardt August 20, 2009

2 The Challenge of Moving Past Apollo Apollo was a remarkable human achievement, however fewer than 20 total program EVAs Both surface crew performed EVA, but a maximum of 3 EVAs per mission Up to 2000 EVAs (8 hrs/eva) without LER, up to 10,000 EVAs (shorter duration) with LER Limited mobility, dexterity, center of gravity and other features of the suit required significant crew compensation to accomplish the objectives. It would not be feasible to perform the Constellation EVAs using Apollo vintage designs The vision is to develop an EVA system that is low overhead and results in close to (or better than) 1g shirt sleeve performance i.e. A suit that is a pleasure to work in, one that you would want to go out and explore in on your day off Lunar EVA will be very different from Earth orbit EVA a significant change in design and operational philosophies will be required to optimize suited human performance in lunar gravity Unlike Shuttle & ISS, all CxP crewmembers must be able to perform EVA and suits must be built to accommodate and optimize performance for all crew Page 2

3 Biomedical & Technological Challenges of EVA Decompression (denitrogenation required to work in low pressure suit (4.3 psi)) *separate proposed risk* Thermoregulation (-120 o C to o C) Nutrition (200 kcal/hr requirement) Hydration (1 liter/eva) Waste Management Radiation Micrometeoroids and Orbital Debris Suit Trauma Mobility/Dexterity: current pressurized suits reduce mobility and dexterity Visibility Page 3

4 Human & EVA System Relationships HRP/EPSP: Provides medical expertise on what the human requires Biomechanics Human Factors EVA System: Working with HRP, determines what the system shall provide for the human Recommendations for: Optimal Suit Weight, Mass, Pressure, CG and Kinematics Suit Trauma/Injury Prevention Thermal & Metabolic Space Medicine Sensorimotor Radiation Protection DCS Protection Nutrition Bone & Muscle Exercise Physiology Suit Trauma Countermeasures Contingency Reponses (Walkback, Suit Leak, Degrade Cooling) Consumables, Usage & Management Biomedical Sensors and algorithms Validated Prebreathe Protocols Nutrition & Hydration Systems Waste Management System Exercise Countermeasure of EVA Page 4

5 Challenges for EVA on the Moon Dealing with risk and consequences of a significant Solar Particle Event (SPE) Long duration missions with three 8hr EVAs per person per week Apollo suits were used no more than 3 times Individual crewmembers might perform up to 76 EVAs in a 6-month mission Suit-induced trauma currently occurs with even minimal EVA time With Apollo style un-pressurized rover (UPR), exploration range is limited by EVA sortie time and 10 km walkback constraint Science/geology community input that optimal scientific return within this range could be accomplished within ~ 30 days of EVA Two UPRs could extend exploration range up to km (crew-day limited) Apollo highlighted the importance of dust control for future long duration missions Increased Decompression Sickness (DCS) risk and prebreathe requirements associated with 8 psi 32% O 2 cabin pressure versus Apollo with 5 psi 100% O 2 The high frequency EVA associated with the projected lunar architectures will require significant increases in EVA work efficiency (EVA time/prep time) Page 5

6 The Wall of EVA The Wall ISS Construction Gemini Apollo/Skylab Pre-Challenger Shuttle Shuttle Page 6

7 The Mountain of EVA 5000 The Mountain EVA Hours Available Lunar EVA Hours (LAT-2 Option 2) based on Three 8 hour EVAs per week using Unpressurized Rovers Need to extend range well beyond 10 km 1500 Gemini The Wall Apollo/Skylab Pre-Challenger Shuttle Shuttle ISS Construction (projected) Year Page 7

8 Systems Engineering Approach to Optimizing Human Safety & Performance in Planetary Exploration Contributing Factors in RMAT Page 8

9 Suit Design Parameters: Risks to Crew Health Suit-Induced Trauma Comprehensive review of musculoskeletal injuries/minor trauma sustained throughout U.S. space program (Scheuring et al., 2009) 219 in-flight injuries, of which 50 were from wearing EVA suit Incidence rate of 0.26 injuries per EVA (3 injuries per week based on LAT2 model) Nine of the 219 in-flight injuries were sustained by Apollo astronauts who were performing lunar surface EVAs. One wrist laceration from the suit wrist ring while working with drilling equipment One account of wrist soreness due to the suit sleeve rubbing repeatedly One shoulder injury while attempting to complete multiple surface activities on a tight mission timeline. During Apollo Medical Operations Project summit, Apollo astronauts were adamant that the glove flexibility, dexterity, and fit be improved. (Scheuring et al., 2007) 86 astronaut-subjects evaluated during 770 suited NBL test sessions. Symptoms reported in 352, or 45.7%, of the sessions. Of these injuries, 47% involved hands; 21% shoulders; 11% feet; 6% each involved arms, legs, and neck; and 3% involved the trunk Strauss S. (2004) Extravehicular mobility unit training suit symptom study report. TP NASA Lyndon B. Johnson Space Center, Houston. Scheuring RA, Jones JA, Polk JD, Gillis DB, Schmid JF, Duncan JM, Davis JR. (2007) The Apollo Medical Operations Project: recommendations to improve crew health and performance for future exploration missions and lunar surface operations. TM NASA Johnson Space Center, Houston. Scheuring RA, Mathers CH, Jones JA, Wear ML, Djojonegoro BM. (2009) Aviat. Space Environ. Med., 80(2): Page 9

10 Human Performance Testing Series Objectives & Measurements Objectives Identify the relative contributions of weight, pressure, and suit kinematics to the overall metabolic cost of the MKIII suit in its POGO configuration in lunar gravity Human Performance Measurements Collected: Metabolic Rate CO 2 and humidity produced Body heat production & storage Human kinematics (range of motion, cycles) Gait parameters Subjective measurements of perceived exertion, comfort, and Ground Reaction Forces (from surface contact) *NEEMO and C-9 environments did not allow measurement of oxygen consumption To quantify the effects of varied gravity, varied mass, varied pressure, varied cg, and suit kinematic constraints on human performance To develop predictive models of metabolic rate, subjective assessments, and suit kinematics based on measurable suit, task, and subject parameters Page 10

11 Initiating the Suit Human Performance Test Program Energy -velocity tests vs. gravity level - Earth, Lunar and Mars Transition speeds 10 Km walk back Metabolic Costs Ground reaction forces and time series motion analysis Skin and core temperatures, EKG, Cooper Harper, RPE Primary Objective: Collect biomedical and human performance data and produce a crew consensus regarding the feasibility of performing a suited lunar 10 km Walk back. Products: Understanding of biomedical & performance limitations of the suit compared to weight matched unsuited controls Data to estimate consumables usage for input to suit and portable life support system (PLSS) design Metabolic & ground reaction force data to allow development of an EVA simulator to be used on future prebreathe protocol verification tests Assessments of cardiovascular & resistance exercise associated with partial gravity EVA to be used in planning appropriate Exploration countermeasures. Page 11

12 45 40 Earth, unsuited ( ) VO 2 (ml/min/kg) Metabolic Cost Moon, suited ( ) Inertial Mass Kinematics Pressure Weight Factors Total Metabolic Cost of Suit Initial Metabolic Data Lunar Gravity Moon, unsuited ( ) 5 Moon, unsuited / weighted ( ) Speed (mph) 400 Transport Cost (ml/kg/km) Moon, unsuited weighted Transport Cost Moon, suited Earth, unsuited Moon, unsuited Speed (mph) Page 12

13 Exploration Task Metabolic Cost Varied Weight VO2 - ml/kg rock (Shoveling) Rock Transfer Shoveling 60 Busy Board Total O2 - l/task (Busy Board & Rock Transfer) g Equivalent Suit Weight (kg) Page 13

14 Predicted Metabolic Rate Algorithm Preliminary linear regression model Uses the following combination of variables to predict normalized metabolic rates during locomotion in the MKIII EVA suit: MR = b0 + (b1 V locomotion W total ) + (b2 M body ) + (b3 (W total L leg )) + (b4 P suit ) where MR = metabolic rate expressed as normalized VO2 (ml kg-1 min-1) V locomotion = locomotion speed (km/h) W total = total weight of EVA suit plus astronaut (N) M body = body mass of unsuited astronaut (kg) L leg = leg length of astronaut (cm) 17.5 = suit pressure (kpa) P suit 308 kg R 2 = Predicted effect of suit weight on metabolic rate (operational concepts) 247 kg Model Predicted VO 2 (ml kg -1 min -1 ) R 2 = Root mean square error = 2.52 ml kg-1 min-1 (< 3.5 ml kg-1 min-1) VO 2 (ml kg -1 min -1 ) Intrasite Translation Site to Site Translation Walkback -1 ± 3.5 ml kg -1 min 186 kg 121 kg Baseline 63 kg Measured VO 2 (ml kg -1 min -1 ) Speed (km h -1 ) Page 14

15 Center of Gravity Studies Background: Center of Gravity (CG) is likely to be an important variable in astronaut performance during partial gravity EVA The Apollo lunar EVA experience revealed challenges with suit stability and control Likely a combination of mobility and center of gravity factors CG Studies conducted in several environments: NBL (2007) NEEMO (Missions 9-13) Pogo (Integrated Suit Test 3) C-9 Parabolic Aircraft Initial testing focused on 6 different CG locations that included the baseline PLSS design and the extremes of what was considered a realistic PLSS mass distribution After initial testing, PLSS packaging was refined resulting in two new configurations (fanny pack, flex pack). Additionally the Apollo PLSS, and a true 0,0 CG location were evaluated Page 15

16 Underwater CG Study Results 10.0 Modified Cooper-Harper Ratings for Varied CG Configuration Ambulation vs. Exploration Tasks Mo odified C-H Rating Average C-H (ambulation) Average C-H (exploration) Initial 6 CG configs Refined CG configs, plus Apollo Task Performance Adequate w/o hardware improvement Ideal Low Forward High Aft Baseline Flex. Backpack Ambulation Forward Ideal Low High Baseline Aft CG Configuration Rank Order (Best to Worst) Exploration Tasks Forward Ideal Low Baseline High Aft Incline Forward Ideal Low High Baseline Aft Flex. Fanny Pack Apollo 0,0,0 Decline Forward Ideal Low Baseline High Aft Page 16

17 C9 CG Comparison Modified CH & RPE Preliminary Data Subject Variability PHASE II DATA Subject ID Task CG RPE CH RPE CH RPE CH RPE CH RPE CH RPE CH Walking Backpack CTSD POGO Kneel/ Backpack Recover CTSD (down) POGO Kneel/ Backpack Recover (up) CTSD POGO Rock Pickup Backpack CTSD POGO Shoveling Backpack CTSD POGO CH variability across subjects C9 data at suit/rig mass of 400 lb; NEEMO/NBL at 195 lb Page 17

18 Earth Shirt-Sleeve Performance Index (ESSPI) Earth Shirt-sleeve Performance Index = MET RATE X MET RATE earth shirt-sleeved ESSPI is an index which relates metabolic rate for a given condition of interest to metabolic rate during the same task in the reference 1g shirtsleeved condition where x = condition being tested (1/6g suited, etc.)) Exploration Tasks Ambulation Page 18

19 10 km Walkback Summary Speed (mph) km Walkback Summary Data (averaged across entire 10 km unless noted) MEAN SD Avg walkback velocity (mph) Time to complete 10 km (min) Avg %VO2pk 50.8% 6.1% Avg met rate (BTU/hr) Time (min) Max. 15-min-avg met rate (BTU/hr) Total energy expenditure (kcal) RPE Cooper-Harper Water used for drinking (oz) ~24-32 N/A Planning / PLSS Sizing Data Walkback Apollo O 2 Usage 0.4 lbs/hr 0.15 lbs/hr BTU average 2374 BTU/hr 933 BTU/hr Cooling water 3.1 lbs/hr 0.98 lbs/hr Energy expenditure 599 kcal/hr 233 kcal/hr Page 19

20 Implications for Walkback Transport cost, Moon suited ( ) 3000 Transpo ort Cost (ml/kg/km) Heat Pr roduction (BTU/hr) 150 Heat Production ( ) Cooling Limit of Apollo & STS Suits Speed (mph) 1000 Faster speeds provide improved efficiency, but require higher metabolic cost and associated heat production Cooling is a limiting factor Page 20

21 The New Lunar Architecture Drives Out The Need For A New Class Of EVA Surface Support Vehicles Page 21

22 Small Pressurized Rover Design Features (Slide 1 of 2) Radiator on Roof: allows refreezing of fusible heat sink water on extended sorties Suitports: allows suit donning and vehicle egress in < 10min with minimal gas loss Suit PLSS-based ECLSS: reduces mass, cost, volume and complexity of Pressurized Rovers ECLSS Aft Driving Station: enables crew to drive rover while EVA Ice-shielded Lock / Fusible Heat Sink: lock surrounded by 5.4 cm frozen water provides SPE protection. Same ice is used as a fusible heat sink, rejected heat energy by melting ice vs. evaporating water to vacuum. Work Package Interface: allows attachment of modular work packages e.g. winch, cable reel, backhoe, crane

23 Small Pressurized Rover Design Features (Slide 2 of 2) Two Pressurized Rovers: low mass, low volume design enables two pressurized vehicles, greatly extending contingency return (and thus exploration) range Exercise ergometer (inside): allows crew to exercise during translations Dome windows: provide visibility as good, or better than, EVA suit visibility Docking Hatch: allows pressurized crew transfer from Rover-to-Habitat, Rover-to-Ascent Module and/or Rover-to-Rover Modular Design: pressurized module is transported using Mobility Chassis. Pressurized module and chassis may be delivered on separate landers or pre-integrated on same lander. Cantilevered cockpit: Mobility Chassis does not obstruct visibility Pivoting Wheels: enables crabstyle driving for docking

24 Small Pressurized Rovers: Functional Requirements Power-up and Check-out including suit/plss power up and check-out: 1hr Mate/de-mate from Hab/Lander: 10mins and 0.03kg gas losses Nominal velocity: 10kph Driving naked-eye visibility should be comparable to walking in suit i.e. eyes at same level, similar Field-of-View Augmented by multi-spectral cameras/instruments Visual accessibility to geological targets comparable to EVA observations i.e. naked eyes 1m of targets Possibility of magnification optics providing superior capability than EVA observations Suit don and Egress/Egress 10mins 0.03kg gas losses per person 2 independent methods of ingress/egress Vehicle Mass (not incl. mobility chassis) 2400kg Habitable volume: ~10 m person EVA hours at 200km range on batteries and nominal consumable load Ability to augment power and consumables range and duration to achieve 1000km PLSS recharge time 30mins Crewmembers 20mins from ice-shielded lock SPE protection (incl. translation to Small Pressurized Rovers and ingress) Heat and humidity rejection provided by airflow through ice-shielded lock and condensing heat exchanger Page 24

25 Hypotheses 1. Performance achieved during 1-day exploration/mapping/geological traverses using the Small Pressurized Rover (SPR) will be equal to or greater the performance achieved during Unpressurized Rover (UPR) traverses, with less suit time. 2. Range achieved during 1-day exploration/mapping/geological traverses in the SPR will be greater than during 1-day UPR traverses. 3. Subjective assessment of contextual observations from inside an SPR will be equal to suited contextual observations. 4. Human interfaces to the SPR suit ports and alignment guides will be acceptable as assessed by human factors metrics. 5. The human factors and crew accommodations within the SPR will be acceptable to support a 3-day exploration/mapping/geological traverse. 6. Single-person EVA from the SPR exploiting the advantages of IVA and EVA crewmembers will result in performance equal to or greater than a twoperson EVA from the SPR or UPR, with less EVA suit time. Page 25

26 Study Design Two 2-person EVA crews One astronaut per crew One field geologist per crew Only one crew performed the 3-day SPR traverse Crew A Crew B UPR Traverse UPR1A SPR Traverse UPR1B 1-day SPR Traverse SPR1A UPR Traverse SPR1B 3-day SPR Traverse SPR3A For the purpose of UPR-SPR comparisons, practically significant differences in metrics were prospectively defined for the testing of study hypotheses 10% difference in time, range and productivity metrics Categorical difference in subjective human factors metrics Page 26

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31 UPR 1-day Traverse Timeline SPR 1-day Traverse Timeline Page 31

32 Performance Metric Page 32

33 Unique Performance Data Sheets created for each traverse based on predefined traverse objectives Value of Traverse Objectives pre-assigned by Science Team Data Quality scores assigned post-traverse by science team consensus Page 33

34 Hypothesis 1: Performance achieved during 1-day exploration/ mapping/ geological traverses using the Small Pressurized Rover (SPR) will be equal to or greater the performance achieved during Unpressurized Rover (UPR) traverses, with less suit time. Data Collection: Performance and EVA Suit Time data collected during 2x 1-day UPR traverses and 2x 1-day SPR traverses [100% COMPLETE] Results: EVA Time Performance 61% less EVA Time 57% greater Performance HYPOTHESIS ACCEPTED Page 34

35 Hypothesis 1: Performance achieved during 1-day exploration/ mapping/ geological traverses using the Small Pressurized Rover (SPR) will be equal to or greater the Performance achieved during Unpressurized Rover (UPR) traverses, with less suit time. HYPOTHESIS ACCEPTED Comments: SPR performance per EVA hr = 3.4 to 6.1 x greater than UPR Mean: 4.7 x more productive per EVA hr than UPR Page 35

36 Hypothesis 3: Subjective assessment of contextual observations from inside an SPR will be equal to suited contextual observations. Data Collection: Four geologists were allowed up to 20 mins to make shirt-sleeve observations of an area of the BPLF. They were then allowed up to 20 mins to make observations from within the SPR and then rated the Geological Observation Quality (scale below) from inside the SPR and provided other subjective remarks. [100% COMPLETE] Page 36

37 Hypothesis 3: Subjective assessment of contextual observations from inside an SPR will be equal to suited contextual observations. Results: Average Geological Observation Quality inside SPR = 2.9 Shirt-sleeve Geological Observation Quality = 3.0 HYPOTHESIS ACCEPTED Comments: Results of this protocol suggest that for this terrain the quality of contextual observations from inside the SPR are approximately equal to unsuited contextual observations. Test Area

38 Suitport Egress

39 Hypothesis 4: Human interfaces to the SPR suit ports and alignment guides will be acceptable as assessed by human factors metrics. Data Collection: Suit port human factors data collected from four subjects during 5 days of SPR traverses [100% COMPLETE] Results: Suit port human factors data are currently being analyzed. Preliminary analysis of data (next slide), including data collected during JSC dry-runs, suggests that human factors of the suit ports and alignment guides are indeed acceptable. Issues have been identified with the latching mechanisms and potential solutions identified. HYPOTHESIS ACCEPTED

40 Suit Port Human Factors Unacceptable Borderline Acceptable Page 40 Interior vehicle volume for donning Interior vehicle volume for doffing Translation into suit port Translation out of suit port Doffing Donning Internal access Interior hand holds General IVA operations External access External hand holds General EVA operations Overall human factors Modifie d Cooper-Harper

41 Hypothesis 5: The human factors and crew accommodations within the SPR will be acceptable to support a 3-day exploration/ mapping/ geological traverse. 10 Fatigue: Pre- and Post- 1-day Traverses 9 8 Average Fatigu ue UPR SPR UPR SPR Pre-Flight Post-Flight Page 41

42 Hypothesis 5: The human factors and crew accommodations within the SPR will be acceptable to support a 3-day exploration/ mapping/ geological traverse. Results (cont.d): Fatigue Ratings during 3-day SPR Traverse 10 9 Subject 1 Subject Fatigue Pre Post Pre Post Pre Post Day 1 Day 2 Day 3 Page 42

43 Summary of SPR Test Performance 1-day Traverse Distance: 31% increase Productivity: 57% increase Productivity per EVA Hour: 470 % increase Boots Boots-on on-surface EVA Time: 23% increase Total EVA Time: 61% decrease Crew Fatigue: Statistically significant decrease Crew Discomfort: Statistically significant decrease Page 43

44 Reduced Decompression Stress (DCS) Suit Ports enable crew members to perform multiple short extravehicular activities (EVAs) at different locations in a single day versus a single 8-hr EVA Intermittent Recompressions (IR) during saturation decompression previously proposed as a method for decreasing decompression stress and time (Gernhardt,1988) Gas bubbles respond to changes in hydrostatic pressure on a time scale much faster than the tissues Cabin Pressure Recompression Suit Pressure Pressure (psia) EVA EVA IR has been shown to decrease decompression stress in humans and animals (Pilmanis et al. 2002, Møllerløkken et al. 2007) Time (hours) Page 44

45 Tissue Bubble Dynamics Model (TBDM)- Provides Significant Prediction and Fit of Diving and Altitude DCS Data Decompression stress index based on tissue bubble growth dynamics (Gernhardt, 1991) Diving: n = 6437 laboratory (430 DCS cases) Logistic Regression Analysis: p <0.01 Hosmer-Lemeshow Goodness of Fit = 0.77 Altitude: n = 345 (57 DCS, 143 VGE) Logistic Regression Analysis (DCS): p <0.01 Logistic Regression Analysis (VGE): p <0.01 Hosmer-Lemeshow Goodness of Fit (DCS): p = 0.35 Hosmer-Lemeshow Goodness of Fit (VGE): p = 0.55 r = Bubble Radius (cm) t = Time (sec) a = Gas Solubility ((ml gas)/(ml tissue)) D = Diffusion Coefficient (cm 2 /sec) h(r,t) = Bubble Film Thickness (cm) P a = Initial Ambient Pressure (dyne/cm 2 ) v = Ascent/Descent Rate (dyne/cm 2 cm 3 ) g = Surface Tension (dyne/cm) M = Tissue Modulus of Deformability (dyne/cm 2 cm 3 ) P Total = Total Inert Gas Tissue Tension (dyne/cm 2 ) P metabolic = Total Metabolic Gas Tissue Tension Gernhardt M.L. Development and Evaluation of a Decompression Stress Index Based on Tissue Bubble Dynamics. Ph.D dissertation, University of Pennsylvania, UMI # , Page 45

46 Reduced Decompression Stress 3 x 2hr EVA at 4.3 psi Bubble Growth Index (BGI) hr Continuous EVA 0.5hr between 2hr EVAs 1hr between 2hr EVAs 2hr between 2hr EVAs 3hr between 2hr EVAs Time (hours) Page 46

47 Lunar Ground Reaction Forces: Implications for Prebreath and Exercise Countermeasures Earth V ertical G ro u n d R eactio n F o rce (lb s) Unsuited weighted Suited Unsuited % D C S % CI 10/20 Arms (NS) Legs (p=0.0008) Speed (mph) /20 Ambulatory 3/21 1/21 Non-Amb. Duke, NASA micro-gravity simulation (non ambulation-3.5 hr prebreathe) Page 47

48 Background: Abbreviated Suit Purge Mass and Time Savings EVA suits are purged of N 2 prior to depressurization to achieve 95% 0.81lb O 2 Purge requires ~ 8 minutes and uses 0.65 lb gas per purge per suit In an airlock, most of this gas is reclaimed but with a suit port this gas is vented to vacuum Shortening the purge will expedite vehicle egress & save gas A 2 min purge saves ~0.48 lb gas and 6 minutes of crew time per person per egress compared with a standard 8 min purge Cumulative Gas and Crew Time Saved by Abbreviated Purge 0.16lb 0.32lb 0.65lb 6 month mission, 4 crew, 3 egresses /day, 6 days/week: 900 lb gas + tankage = 1800 lb (819 kg) Over 31 hours of crew time saved Page 48

49 Background: Abbreviated Suit Purge Decreased Off-Gassing Gradient An abbreviated purge saves gas and crew time, but decreases the tissue N 2 off-gassing gradient because suit O 2 reaches only 80% compared with 95% O 2 achieved during an 8 minute purge Approximate. Based on 1.5ft 3 floodable 8 PSI However, the benefit of 95% O 2 vs. 80% O 2 for denitrogenation is reduced when initial saturation pressure is 8 PSI, 32% O 2 (LER) vs PSI 21% O 2 (ISS) as there is a smaller change in off-gassing gradient Page 49

50 Alternate Configuration Pancake V-Node Cylindrical inflatable dome: Height: 5.2m Volume: 63m3 Diameter: 4.2m Flr area: 12m2 (129ft2) x2 Inflatable dome is same diameter as pressure vessel, so nodes with domes can be docked together Deployable lightweight metal decking and supports (assembled autonomously, or by crew after inflation) Minimal node contains ECLSS, core functions, plumbing, water wall shielding, etc. Pancake V-Node in Lunarbago mode Page 50