Space Suit Portable Life Support System 2.0 Unmanned Vacuum Environment Testing

Home , Constellation Space Suit, Vacuum chamber

47th International Conference on Environmental Systems ICES-2017-105 16-20 July 2017, Charleston, South Carolina

Carly Meginnis,1 Ian Anchondo,2 Marlon Cox3, and David Westheimer4 NASA Johnson Space Center, Houston, TX, 77058

and

Matthew Vogel 5 HX5, LLC., Houston, TX, 77058

For the first time in more than 30 years, an advanced space suit Portable Life Support System (PLSS) design was operated inside a vacuum chamber representative of the flight operating environment. The test article, PLSS 2.0, was the second system-level integrated prototype of the advanced PLSS design, following the PLSS 1.0 Breadboard that was developed and tested throughout 2011. Whereas PLSS 1.0 included five technology development components with the balance of the system simulated using commercial off-the- shelf items, PLSS 2.0 featured first generation or later prototypes for all components, less instrumentation, tubing, and fittings. Developed throughout 2012, PLSS 2.0 was the first attempt to package the system into a flight representative volume. PLSS 2.0 testing included an extensive functional evaluation known as Pre-Installation Acceptance testing, Human-in- the-Loop testing in which the PLSS 2.0 prototype was integrated via umbilicals to a manned prototype space suit for 19 2-hour simulated extravehicular activities (EVAs), and unmanned vacuum environment testing. Unmanned vacuum environment testing took place from 1/9/15-7/9/15 with PLSS 2.0 located inside a vacuum chamber. Test sequences included performance mapping of several components, carbon dioxide removal evaluations at simulated intravehicular activity conditions, a regulator pressure schedule assessment, and culminated with 25 simulated EVAs. During the unmanned vacuum environment test series, PLSS 2.0 accumulated 393 hours of integrated testing, including 291 hours of operation in a vacuum environment and 199 hours of simulated EVA time. The PLSS prototype performed nominally throughout the test series, with two notable exceptions including a pump failure and a Spacesuit Water Membrane Evaporator leak, for which post-test failure investigations were performed. In addition to generating an extensive database of PLSS 2.0 performance data, achievements included requirements and operational concepts verification, as well as demonstration of vehicular interfaces, consumables sizing and recharge, and water quality control.

Nomenclature °F = degrees Fahrenheit acfm = actual cubic feet per minute AEMU = Advanced Extravehicular Mobility Unit

1 PLSS Development Engineer, Space Suit and Crew Survival Systems Branch, 2101 NASA Parkway, Houston, TX 77058. 2 PLSS Development Engineer, Space Suit and Crew Survival Systems Branch, 2101 NASA Parkway, Houston, TX 77058. 3 PLSS Development Engineer, Space Suit and Crew Survival Systems Branch, 2101 NASA Parkway, Houston, TX 77058. 4 PLSS Development Engineer, Space Suit and Crew Survival Systems Branch, 2101 NASA Parkway, Houston, TX 77058. 5 Thermal Analyst, Thermal Analysis and Electronics Design, 2224 Bay Area Boulevard, Houston, TX 77058. AFSA = Auxiliary Feedwater Supply Assembly AgF = silver fluoride ATCL = Auxiliary Thermal Control Loop BPV = Back Pressure Valve Btu = British thermal unit CO2 = carbon dioxide COTS = commercial off-the-shelf DACS = Data Acquisition and Control System DAQ = Data Acquisition System DP = differential pressure EMU = Extravehicular Mobility Unit EVA = extravehicular activity FSA = Feedwater Supply Assembly GN2 = Gaseous nitrogen H2O = water HCT = half cycle time hr = hour HITL = Human-in-the-Loop HMS = human metabolic simulator in = inch ISS = International Space Station IVA = intravehicular activity JSC = Johnson Space Center krpm = kilo revolutions per minute lb = pound lbm = pound mass LCVG = Liquid Cooling and Ventilation Garment min = minute mm Hg = millimeters of Mercury MSPV = Multiposition Suit Purge Valve NH3 = ammonia ops con = operational concept OVL = Oxygen Ventilation Loop PCO2 = partial pressure CO2 PEEK = poly-ether-ether-ketone PIA = Pre-Installation Acceptance PLSS = Portable Life Support System POL = Primary Oxygen Loop POR = Primary Oxygen Regulator POV = Primary Oxygen Vessel psia = pounds per square inch absolute psig = pounds per square inch gauge PT = pressure transducer RCA = Rapid Cycle Amine rpm = revolutions per minute SI = suit inlet SO = suit outlet SOL = Secondary Oxygen Loop SOR = Secondary Oxgyen Regulator SOV = Secondary Oxygen Vessel SSA = Space Suit Assembly SSAS = Space Suit Assembly Simulator SWME = Spacesuit Water Membrane Evaporator TCL = Thermal Control Loop TCV = Thermal Control Valve W = Watts

2 International Conference on Environmental Systems

I. Introduction n advanced space suit Portable Life Support System (PLSS) development effort has been underway for several Ayears at NASA’s Johnson Space Center (JSC) with the ultimate goal of producing a design that leverages historical lessons learned from the Space Shuttle/International Space Station (ISS) Extravehicular Mobility Unit (EMU) and technological advancements to generate a less complex design that is more robust and reliable, uses less consumables, and provides more operational flexibility and system capabilities than the current state-of-the-art. To this end, an iterative development approach was utilized in which component and system-level designs were built and tested to mature technologies, requirements, and interfaces for an exploration PLSS capable of supporting missions in low-Earth orbit, microgravity near-Earth destinations, the lunar surface, cislunar space, or the surface of Mars. The advanced PLSS development effort began with a schematic/technologies study in 2005 and progressed through component feasibility testing, system architecture design, and requirements development. The first system- level test, PLSS 1.0, followed in 2011 and accumulated more than 400 hours of integrated testing. PLSS 1.0 (Breadboard) incorporated five technology development prototypes – Primary Oxygen Regulator (POR) and Secondary Oxygen Regulator (SOR), Ventilation Loop Fan, Rapid Cycle Amine (RCA) swingbed, and Spacesuit Water Membrane Evaporator (SWME) – with the balance of the pneumo-hydraulic schematic simulated using commercial off-the-shelf (COTS) equipment.1 System performance and other lessons learned from this testing engendered improved component and system-level designs.2,3 With design and development starting in late 2011 through early 2013,4-6 PLSS 2.0 was conceived as the second system-level integrated advanced PLSS test article, containing second or third generation prototype components for the five technology development items included in PLSS 1.0 and first generation prototypes for the remaining components. Instrumentation, tubing, and most fittings were COTS items. PLSS 2.0 was packaged into a volume and outer mold line representative of the 2012 Suitport concept, but as this was the first proof-of-concept, non flight- like packaging attempt, the focus did not include weight optimization or environments such as launch vibration or radiation. PLSS 2.0 was developed to characterize system performance in several test configurations and orientations, evaluate operational concepts, and simulate failures. Further, the effort sought to mature controller algorithms as well as design requirements and specifications. Testing began with the Pre-Installation Acceptance (PIA) test series, which lasted from March 2013 until March 2014 and comprised 27 individual test sequences designed to functionally evaluate component performance as installed in the integrated system.7,8 The second PLSS 2.0 test series was Human-in-the-Loop (HITL) testing, which occurred from October through December 2014. For this test series, 19 manned 2-hour simulated extravehicular activity (EVA) test points were completed in which the test subject walked in the pressurized Mark III space suit prototype on a treadmill to achieve a desired metabolic rate profile. The PLSS 2.0 assembly, operated in an ambient pressure and temperature environment with vacuum access as required for nominal functionality, provided suit pressure regulation, carbon dioxide (CO2) and water (H2O) vapor removal, and test subject cooling during simulated nominal and contingency modes.9-11 After the completion of HITL testing, unmanned PLSS 2.0 testing resumed in January 2015 to demonstrate PLSS 2.0 performance in a vacuum environment as well as complete several follow-on evaluations in the ambient laboratory environment. PLSS 2.0 vacuum environment testing was performed at JSC from January through July 2015. The majority of this test series was completed with the PLSS 2.0 assembly operating in a vacuum environment, although several test sequences were conducted at ambient pressure. The test series included numerous independent tests and culminated with 25 simulated EVAs. This report presents a selection of results and findings from the PLSS 2.0 unmanned vacuum environment test series.

II. An Overview of the Portable Life Support System 2.0 Test System The design and configuration of the PLSS 2.0 test article is documented in other publications8,10; however, the test system was modified for each test series to achieve the particular set of objectives. The PLSS 2.0 test system was composed of hardware and instrumentation to support testing operations, including: a simulated vehicle thermal loop; simulated vehicle high pressure gas recharge system; human metabolic simulator (HMS); Space Suit Assembly (SSA) Simulator (SSAS); and vacuum system consisting of Vacuum Chamber C, a vacuum pump and liquid nitrogen coldtrap to increase pumping capacity, and various vacuum access lines to enable PLSS operation in different simulated configurations (EVA, intravehicular activity (IVA), airlock, Suitport, etc.).12 The PLSS prototype was installed inside Vacuum Chamber C for the duration of PLSS 2.0 vacuum environment testing. A block diagram of the PLSS 2.0 test system is shown in Figure 1. Figure 2 shows PLSS 2.0 installed in the vacuum chamber. Figure 3 shows the test-specific test system infrastructure.

3 International Conference on Environmental Systems

Figure 1. PLSS 2.0 test system block diagram.

Figure 2. PLSS 2.0 assembly installed in Vacuum Chamber C. Figure 3. SSAS, HMS, and Vacuum Chamber C.

The high-pressure gas supply and thermal loop conditioning/resupply systems were designed to simulate the functions and interfaces of a vehicle to facilitate pre-and post-EVA operational concepts (ops cons) evaluations. Current advanced PLSS ops cons involve using vehicle systems to provide thermal conditioning during pre- and post-EVA umbilical operations, and using either a vacuum access umbilical or small vacuum pump to desorb CO2 and H2O from the RCA during these operational phases. The test system also provides the capabilities to recharge the Primary Oxygen Vessel (POV) and Secondary Oxygen Vessel (SOV) with high-pressure (3000 psig) gaseous nitrogen (GN2), and the Primary Feedwater Supply Assembly (FSA) and Auxiliary Feedwater Supply Assembly (AFSA) with water. The SSAS served as the suit volume and was connected to the PLSS via extended lengths of tubing that passed through the vacuum chamber wall. The fluid lines between the PLSS and SSAS contained additional instrumentation to enable further evaluation of PLSS 2.0 performance, including flow meters, CO2 sensors, relative humidity sensors, pressure transducers, and temperature sensors (Figure 4). An instrumented manikin inside the SSAS produced the simulated metabolic heat load and transferred heat to the PLSS via an EMU Liquid Cooling and Ventilation Garment (LCVG) that included additional lengths of tubing woven through the torso region to enable

4 International Conference on Environmental Systems independent operation of the Auxiliary Thermal Control Loop (ATCL). A COTS Bronkhorst system installed on top of the SSAS enabled the injection of CO2 and H2O into the SSAS volume to represent the metabolically generated products of respiration and perspiration.

Figure 4. PLSS 2.0 Test System – instrumentation between PLSS and SSAS.

The PLSS 2.0 test system Data Acquisition and Control System (DAQ/DACS) was responsible for recording measurements from the PLSS 2.0 prototype as well as the test system. In addition, it sent signals per PLSS test operators or the DACS to PLSS 2.0 hardware controller to command POR and SOR delta-pressure setpoints, RCA bed switching, Oxygen Ventilation Loop (OVL) fan speed, Thermal Control Loop (TCL) pump speed, TCL Thermal Control Valve (TCV) position, and SWME back-pressure valve setpoint. The PLSS 2.0 DACS did not perform detailed component commanding such as motor commutation.

III. Testing Operations and Results PLSS 2.0 vacuum environment testing commenced on January 9, 2015, and continued through July 9, 2015. During this test series, PLSS 2.0 achieved 393 hours of integrated testing, including 291 hours of operation in a vacuum environment and 199 hours of simulated EVA time (Table 1). PLSS 2.0 vacuum environment testing comprised numerous independent test series culminating in the simulation of 25 EVAs, a major objective of the advanced PLSS development effort and the test series that accounted for more than 50% of vacuum and total test time. Other test series that involved operating all or part of the PLSS 2.0 included component performance mapping tests (SWME, RCA, FSA, AFSA), operational scenario simulations (airlock, Suitport, and EVA abort ops con evaluations), and stand-alone tests devised to answer a particular question (Pressure Schedule Regulation Test, RCA IVA Vacuum Access Evaluation). The following subsections detail the methodology used and test results from a selection of the test series.

5 International Conference on Environmental Systems

A. 25 Extravehicular Activity Test Series Table 1. Operational Test Time The intention of the 25 EVA test series Time was to demonstrate PLSS 2.0 performance (hrs:mins) through the completion of simulated EVAs Total PLSS 2.0 Operational Time 393:55 using the airlock ops con for pre-and post- Test Time, PLSS at Vacuum 291:34 EVA operations with Vacuum Chamber C Test Time, PLSS at Ambient Pressure 52:27 serving as the representative airlock volume. EVA Time (25 EVA Test Series) 199:39 After the vacuum chamber was pumped down Pre- & Post-EVA Time (25 EVA Test Series) 49:54 to sufficiently low pressure (approximately 50 millitorr), the duration of the EVA was carried out with PLSS 2.0 fully exposed to the vacuum environment. It was determined that 25 EVAs would be conducted to replicate the Space Shuttle/ISS EMU PLSS certification testing. For each simulated EVA, the nominal suit pressure, OVL flow rate, and metabolic rate profile were varied in accordance with Table 2, which shows the EVA sequence number, the date on which the test point was conducted, the duration of the simulated EVA, and the test parameters that defined the conditions for each EVA test point. Figure 5 illustrates six transient metabolic rate profiles that were used throughout the 25 EVA test series; the seventh metabolic profile simulated a constant 1200 Btu/hr for the entire EVA. Table 2. 25 EVA Test Series Test Point Definition Metabolic Rate Profile 1200 Btu/hr Btu/hr 1200 PLSS Standard PLSS Chamber End Front Loaded Aft End Loaded Max Transient PLSS 1.0 Correlation EVA #2 EVA #7 EVA #8 EVA #9 EVA #10 EVA #11 EVA #12 4/29/15 4/30/15 5/6/15 5/7/15 5/13/15 5/18/15 4.5 3/30/15 9:57 8:00 8:00 8:01 8:01 7:59 7:05 T3 T3 T3 T3 T3 T3 4.3 T1 EVA #1 EVA #14 EVA #23 EVA #24 EVA #21 EVA #25 EVA #22 3/26/15 6/3/15 6/18/15 6/22/15 6/16/15 6/23/15 6/17/15 6 6:16 8:38 8:00 7:50 8:00 8:32 7:00 T1 T3, A T3 T3 T3 T3, A T3

EVA #3 EVA #16 EVA #17 EVA #18 EVA #19 3/31/15 6/8/15 6/9/15 6/10/15 6/11/15 4.5 8:01 7:49 8:02 8:10 8:03 T2 T3, A T3 T3 T3 6.2 EVA #4 4/1/15 6 8:08 Suit Pressure (psia) Pressure Suit

VL Flow Rate (acfm) T3 EVA #5 EVA #13 EVA #15 EVA #20 4/2/15 5/21/15 6/5/15 6/12/15 4.5 8:02 8:00 8:00 8:00 T3 T3 T3 T3 8.2 EVA #6 4/23/15 6 8:05 T3 T1: Consumables Termination, defined as depletion of primary gas and water supplies (transition to SOV and TCL pump cavitation) T2: Limiting Consumable Termination, defined as reaching POV ullage (250 psig) or FSA ullage (PT-432A is 1.5 psi < PT-2027) T3: Full Metabolic Profile Duration or Limiting Consumable Termination, defined as adverse effects due to full depletion of consumable (i.e.: transition to SOR or loss of TCL flow/cooling) A: EVA Abort Simulation after reaching EVA termination criteria

6 International Conference on Environmental Systems

Figure 5. Transient metabolic rate profiles.

Altogether, the 25 EVA simulation tests accumulated 199 hours and 39 minutes of EVA time and an additional 49 hours and 54 minutes of pre- and post-EVA test time. The duration of simulated EVAs ranged from 6:16 to 9:57 and averaged 7.99 hours. Test data indicated nominal PLSS 2.0 performance throughout most EVA simulation testing. The PLSS 2.0 maintained suit pressure and appropriately managed simulated crew heat, CO2, and H2O for metabolic rates ranging from 80-878 W (273-2999 Btu/hr). The following subsections detail pre-EVA operations illustrated by EVA 14 test results to show airlock operational concepts, PLSS 2.0 EVA functionality as illustrated by EVA 25 test results, a summary of test results from PLSS 2.0 Chamber C 25 EVA testing, and a list of anomalies that occurred during the testing.

1. Pre-EVA Test Operations as Illustrated by EVA 14 Test Results Demonstration of flight-like operational concepts was an important objective of the 25 EVA testing. Simulated pre-EVA airlock operations prepared the PLSS for EVA and also transitioned the environment from a 14.7 psia IVA environment to an EVA space vacuum environment. Simulating airlock operations required considerable simultaneous activity involving the PLSS 2.0 assembly and PLSS 2.0 test system with the latter acting as the host vehicle. Once testing shifted into EVA mode, test operations were simpler and consisted primarily of simulating crew metabolic loading.

7 International Conference on Environmental Systems

Figure 6 is the first of three figures to illustrate typical pre-EVA operations by highlighting POV/SOV and GN2 supply high pressures (PT-112, -215, -602, scaled right), POR outlet pressure (suit pressure delta, DP-114), suit absolute pressure (PT-2027), Chamber C pressure (PT-116, “Airlock”), RCA vacuum port pressure (PT-1001), POR/SOR stepper motor counts, and RCA bed A indicator (GX-380E). Whereas most highlighted steps follow current ISS EMU pre-EVA protocol, pre-EVA steps unique to the PLSS 2.0 include the TCL FSA charging and RCA ammonia desorb process. The EVA start time for test data analysis purposes was defined to be when the airlock pressure reached vacuum levels and is practically equivalent to the current ISS EVA start time delineation of the switch to battery power – a step that occurs right before SCU disconnect with the ISS airlock at vacuum. Finally, it should be emphasized that POR and SOR stepper motors are typically not adjusted once they are set to flight positions during pre-EVA operations.

Figure 6. EVA 14 pre-EVA airlock operations overview highlighting primary and secondary oxygen loop and test system pressure measurements.

Figure 7 presents OVL and HMS pre-EVA operations by plotting fan speed, OVL volumetric flow rate, RCA bed A indicator (GX-380E_SW), and the HMS CO2 and H2O injection rates. The metabolic gas consumption/suit leakage (MGC/SL) is also plotted as is the suit absolute pressure (PT-2027) and purge flow valve indicator (SOV- 866) for reference. PLSS 2.0 OVL pre-EVA ops are relatively simple and consist of starting the RCA ammonia (NH3) desorb process, powering the fan and setting it to its proper speed, and changing RCA control mode from the

8 International Conference on Environmental Systems

NH3 desorb timed mode to CO2 partial pressure mode. In the case of EVA 14, the fan speed was set to 65 krpm (green dotted line scaled right) to produce a minimum 6 acfm OVL flow rate. Finally, PLSS 2.0 Test System pre- EVA operations related to the OVL consisted of simulating crew breathing and suit leakage of which initiation of CO2/H2O injection and MGC/SL flow are noted.

Figure 7. EVA 14 Pre-EVA airlock operations overview highlighting OVL and crew metabolic gas test system operations.

TCL pre-EVA operations started after PLSS power up with charging the FSA, a multistep process mostly captured by the TCL pump inlet absolute pressure (see PT-432 in Figure 8). The next steps were to set the pump to a pre- determined speed to achieve 200 lb/hr flow and then open the SWME Back Pressure Valve (BPV). This latter step was required for degassing the LCVG and to allow the SWME vapor volume to vent during airlock depress. Easy to see in Figure 8 is the crew cooling provided by the simulated vehicle cooling loop as illustrated by the drop in water temperatures immediately after pump powering. Initial SWME heat rejection started 08:13 test time and is characterized by the sudden decline of the SWME outlet temperature. The start of SWME heat rejection coincided with the end of the airlock depress, which is marked by the sudden drop of the Chamber C pressure (PChamber-C, PT- 116) from approximately 0.4 psia to 0 psia. Finally, automatic control of the SWME outlet temperature to 50°F was set during pre-EVA operations, but did not become active until the SCU was disconnected about 2 minutes after airlock depress completion at 08:15 test time.

9 International Conference on Environmental Systems

Figure 8. EVA 14 pre-EVA airlock operations overview highlighting TCL operations.

2. An Overview of PLSS 2.0 EVA Functionality as Illustrated by EVA 25 Test Results Conducting the EVA phase for most PLSS 2.0 Chamber C testing EVA test points proved relatively straightforward because the PLSS 2.0 was mostly operating autonomously and test personnel were primarily concerned with properly simulating crew metabolic loading. EVA 25 was selected to provide an overview of PLSS 2.0 EVA time performance, partly because test operations went as well as one would expect after building expertise through the previous 24 EVA test points. In addition, EVA 25 was selected because its metabolic rate profile was a maximum transient one, thus presenting a very dynamic metabolic load profile, and it was one of three EVA test points ending with an EVA abort simulation. Primary Oxygen Loop (POL) and Secondary Oxygen Loop (SOL) performance during EVA 25 is summarized in Figure 9 by plotting the tank pressure, tank temperature, and regulator interstage pressure for each Oxygen Loop. The POR outlet pressure (Pd,POR), serving as a proxy for the SOR outlet pressure and scaled by a factor of 10 for plotting purposes, is also plotted in Figure 9, along with the MGC/SL outflow. Several notable POL/SOL results stand out, starting with the period prior to and including activation of POL flow that is marked by “A”. Until just before 09:00 test time, the POR outlet pressure remained above its 4.3 psid setpoint, thus resulting in a locked up

10 International Conference on Environmental Systems regulator with no flow demand for make-up gas. This locked up POR is illustrated by the constant POV pressure and low POR interstage pressure. Upon reaching 4.3 psid, POR begins to flow gas and control outlet pressure as illustrated by the dropping POV pressure and a step increase of the POR interstage pressure. A closer look at the latter measurement shows a sharp small decrease followed by a larger sharp increase to approximately 200 psia. This behavior resulted from the POR second stage opening first as the POR outlet pressure dropped below its setpoint lower deadband, causing a pronounced pressure drop in the POR interstage, mainly due to its very small volume. Subsequently, the POR interstage pressure dropped below its deadband, causing the POR first stage to open to meter high-pressure gas, thus bringing the POR interstage pressure up. While POL pressures behaved as expected and reflected nominal POR performance, the POV wall temperature dropping from 78 to 74°F during the initial no flow period proved surprising and stands out in contrast to the steady 78°F SOV temperature. Assuming these temperatures are accurate, it is expected that a complete explanation would require the combination of a high-fidelity thermal math model and an in-depth investigation of the test data. It is Figure 9. An overview of PLSS 2.0 POL/SOL performance during EVA 25 testing. believed an alternate explanation, such as instrumentation issues, has low probability given the POV and SOV temperatures at the test point end indicate nominal temperature measurements as the sudden temperature declines were expected due to gas expansion during the purge flow. After POR flow initiation, the POR interstage pressure exhibited frequent spikes at varying frequency. Although not shown, these spikes correspond to RCA bed cycling that cause small OVL pressure fluctuations to which the POR responded. References 9 and 10 contains analysis of this phenomenon that was done in support of PLSS 2.0 HITL testing. Also noted in Figure 9 by “B” are pronounced changes in the POV pressure slopes that reflect pronounced changes in the MGC/SL flow rates. Smaller changes in the pressure slopes can be seen at any point during the test where MGC/SL flow rates changed. Again, this is nominal behavior and reflects flight-like operations where the crew oxygen consumption, and thus demand for make-up oxygen, varies with the crew work rate (metabolic rate). The POV pressure behavior is of interest for many reasons. One reason has to do with plans to embed POV pressure and temperature measurements into the Advanced EMU (AEMU) PLSS Caution Warning and Control System oxygen flow rate calculations so that real-time approximations of crew metabolic rates can be produced. During the EVA 25 contingency purge simulation, POV/SOV pressures and temperatures declined sharply as shown in Figure 9 due to high flow demands and gas expansion effects (marked by “C”). The POR provided the initial purge flow gas until the POV was emptied. Upon a close look at Figure 9, it can be seen the POR outlet pressure experienced a small amount of droop during the purge with POR outlet pressures maintained by the POR at 4.17 psid, well within the 4.3±0.2 psid requirement. Subsequent SOR purge gas flow maintained SOR outlet pressure as indicated by the POR outlet pressures between 3.65 and 3.69 psid, well within the 3.7±0.2 psid requirements. Finally, the SOR interstage pressure followed the same pattern exhibited by the POR in which the initial demand for flow from the locked-up SOR caused the SOR interstage pressure to drop sharply followed by a

11 International Conference on Environmental Systems sharp increase to values higher than the lock-up pressure as the SOR first stage opened to supply high-pressure gas to the second stage. The overview of PLSS 2.0 OVL performance starts by reviewing OVL fan performance since it is key to transporting OVL gas around the loop and washing CO2 away from the crew oronasal area. For the EVA test series, an ISS EMU philosophy was emulated in which the fan was set to a speed that previous testing determined would provide a minimum desired flow rate. In the case of EVA 25, fan speed was 65 krpm (FN-323_Tach in Figure 10) for a target OVL flow rate of 6 acfm. Figure 10 plots OVL flow rates (FS-802) showing flow rates averaged around 6.5 acfm. However, the OVL flow rates plotted in Figure 10 are uncorrected for an instrumentation issue identified posttest and resulting in a zero flow offset. Actual flow rates that account for the zero flow offset were calculated posttest and averaged 5.8 acfm, 12% lower. OVL flow rates experienced downward spikes that are attributable to the RCA bed cycling that causes approximately 1- second-long closures of the OVL, a PLSS 2.0 characteristic that was detailed further in References 9 and 10. Figure 10 also illustrates cessation of fan and RCA operations at 16:30 test time for the contingency purge flow simulation. Suit inlet (SI) volumetric flow rates corrected for the zero flow offset averaged 1.9 acfm, a approximately 50% reduction compared to the real-time flow rate average of 3.9 acfm, but 12% above the current AEMU PLSS low flow purge Figure 10. OVL Fan Speed and Volumetric Flow Rate During EVA 25 specification of 1.2 acfm. Also critical to OVL performance is the ability of the RCA to remove CO2 from the gas stream such that the CO2 partial pressure (PCO2) at the SI meets requirements. Figure 11 plots instantaneous OVL PCO2 at the SI (CO2-2006) and suit outlet (SO) (CO2-2026) along with the HMS CO2 injection flow rate and three calculated values; running mean PCO2, half cycle time (HCT) mean PCO2, and OVL HCT mean CO2 acquisition gain for comparison to the HMS injection rate. The first two calculated values are a function of the SI PCO2 only while the OVL CO2 gain rate is a function of SI/SO PCO2, OVL flow rate, and SI/SO water vapor measurements. HCT mean values are the time- weighted averages of a variable over the period of each RCA half cycle and used to capture the dynamic transient trends while removing the instantaneous spikes inherent to RCA operations. The OVL CO2 gain rate is defined with respect to the SSAS and equals the rate at which the OVL acquires CO2 from the SSAS. This terminology was selected to serve the opposite of the RCA CO2 desorption rate, which mathematically equals OVL gain rate minus the amount of CO2 flowing overboard through the MGC/SL line and SO CO2 gas analyzer (CO2-2026). At cyclical steady state, the OVL CO2 inflow and outflows should equal on average resulting in a zero net.

12 International Conference on Environmental Systems

Figure 11. EVA 25 EVA time SI and SO CO2 measurements.

A review of the instantaneous SI PCO2 in Figure 11 shows the RCA was properly cycled at 3 mm Hg SI PCO2 during the vast majority of the EVA. However, the instantaneous SI PCO2 appears elevated above 3 mm Hg for significant periods of time during the periods corresponding to 3000 and 2500 Btu/hr metabolic rate simulations (09:15, 14:10, 14:20 test time), an observation further suggested by the sharp increase in the SI HCT mean PCO2. Another related observation is that the instantaneous SI PCO2 during these periods is indistinguishable, which suggests the RCA HCTs approached the default minimum 30 seconds. All of these cursory observations combined indicate the PLSS 2.0 commanded the RCA properly in response to challenging CO2 loads, but the RCA may have reach its limits. The running mean PCO2 peaked at 2 mm Hg early in the EVA, but then remained less than 2 mm Hg for the remainder of the nominal EVA and finished at 1.84 mm Hg. As expected, it declined further during the contingency purge flow simulation due to the stoppage of OVL flow circulation and all SI gas supply coming from the Oxygen Loops, which is free of CO2. HCT mean PCO2 ranged from a low of 1.1 mm Hg at the 340 Btu/hr metabolic rate period end (11:00 test time) to 2.5 mm Hg during the first 3000 Btu/hr. HCT mean PCO2 during the two 1600 Btu/hr periods (09:25, 14:30 test times) of 2.1 mm Hg, plus or minus small variations, confirm the selection of 3 mm Hg as the RCA bed cycling PCO2 value. In response to agency-wide discussion regarding acceptable crew CO2 levels, the AEMU PLSS project decided upon a 3 mm Hg PCO2 RCA bed cycling value for PLSS 1.0 integrated testing to 2 produce a time-weighted average SI PCO2 of 2.2 mm Hg for a metabolic rate of 1600 Btu/hr. Crew health is a function of actual inspired CO2, which is impractical to measure in-flight with current technologies. PLSS requirements currently dictate inspired PCO2 limits to which verification will be computed analytically and by test given a selected suit and helmet inlet manifold configuration coupled to the selected flow rate. While much work pertaining to inspired CO2 remains, future assessments will most likely include an evaluation of instantaneous, running mean, and HCT mean CO2 partial pressures at the SI and oronasal area. OVL water vapor measurements of SI/SO relative humidity and dry bulb temperature were converted to dewpoint temperatures (Figure 12). Instantaneous SI dewpoint temperatures ranged from -18°F to 38°F during the EVA time phase of the test point. HCT mean SI dewpoint temperatures ranged from 2°F to 16°F, remaining well below the current AEMU PLSS specification of 20°F to 45°F. The OVL water vapor gain rates in Figure 12 are also defined with respect to the SSAS, meaning the OVL water vapor gain rate equals the rate at which the OVL acquires water vapor as the OVL flows through the SSAS. Water vapor gain rates trended with the HMS water vapor injections, but varied above and below depending on HMS water vapor injection rates. For almost the first 2 hours of the EVA simulation, the OVL gain rate was less than the HMS water vapor injection flow rates. Other periods

13 International Conference on Environmental Systems where OVL gain rates less than injection rates occurred when the injection rates were greater than 75 g/hr. This difference suggests the formation of condensate with the cold water flowing through the LCVG is one likely cause. In contrast, OVL water vapor gain rates were consistently greater than the water vapor injection rates when the injection rates were 50 g/hr or less. This difference indicates the evaporation of condensate.

Figure 12. EVA 25 EVA time SI and SO water vapor measurements with OVL water vapor gain rates calculated per corrected OVL flow rates. The SWME outlet temperature and BPV step count in Figure 13 succinctly provides a summary of the PLSS 2.0 TCL performance during EVA 25 EVA time. With the exception of three sudden changes in SWME heat loading, the PLSS 2.0 TCL control algorithm maintained the SWME outlet water temperature to its 50°F target within the AEMU PLSS specification of ±2°F. Even in those instances where the SWME outlet temperature exceeded the specification ±2°F variance, temperatures were brought into tolerance very quickly by large BPV adjustments. A key factor in the successful temperature control was the SWME outlet temperature control band of ±0.18°F. Much of the time the controller only needed to make minor BPV adjustments to maintain temperatures within the target band. Finally, the steep SWME outlet temperature increase at 16:30 test time coincided with the cessation of nominal EVA operations and start of the simulated EVA abort contingency. The SWME BPV was closed at this point, thus resulting in the measured temperature rise, and the ATCL was activated (not shown).

14 International Conference on Environmental Systems

Figure 13. TCL SWME outlet temperature and BPV step count during EVA 25 testing.

3. Summary of Test Results from the PLSS 2.0 Chamber C 25 EVA Testing Detailed test results were presented in previous sections to illustrate nominal pre-EVA and EVA operations using two representative test points. For the sake of brevity, results cannot be presented for all 25 test points. Review of the test data produced the following summaries of PLSS 2.0 performance throughout the 25 EVA testing:  Nominal POR/SOR performance in the 20 EVA test points in which the POR was set to 4.3 and 6.2 psid. In the 6.2 psid test points, the POR controlled tightly about an average of 6.34 psid. This offset is considered a non-issue and expected to be resolved by a simple adjustment of the setpoint protocol. The initial two 8.2 psid EVA test points exhibited some POR outlet pressure control instability that was resolved by an adjustment to the POR motor step algorithm. The 8.2 psid control instability was due to a POR internal design issue that was independently identified by the POR manufacturer through its own testing. Design modifications eliminating this issue have already been developed and incorporated into follow-on units. The subsequent 8.2 psid test points exhibited nominal POR performance.  Nominal fan performance with respect to fan speed control, flow rate consistency, average electrical current draw, and stator temperatures.  Nominal RCA performance throughout the entire 25 EVA test series. The few instances in which SI CO2 partial pressures increased significantly above the 3 mm Hg bed switch value were caused by test operator errors that resulted in very high CO2 injection rates or Test System issues including data acquisition system communication faults or inadvertent vacuum system shutdown. The unplanned high CO2 injection rates demonstrated quick recoveries by the RCA and also successful contingency default minimum 30-second timed mode RCA control. SI water vapor levels were consistently low with inlet dewpoint temperatures averaging roughly between 0 and 15°F.  Nominal SWME heat rejection performance for the first five EVA test points, a slightly degraded performance up to EVA 9, significantly degraded high heat load SWME performance in EVA 15, and then loss of SWME control early in EVA 16. The degraded EVA 15 heat rejection and subsequent loss of control in EVA 16 was caused by a leak in the SWME. The remainder of EVA 16 focused on regaining SWME control, which was achieved. TCL test operations were refined in the subsequent two EVA test points to minimize the impact of the SWME leak, thus resulting in nominal SWME outlet temperature control and helping the AEMU PLSS team continue the 25 EVA test series until completion. Results were presented from the final EVA test point, EVA 25, to illustrate that, in spite of the leak, the SWME controlled outlet temperatures to 50±0.2°F as heat loads varied between 550 to 1750 Btu/hr.

15 International Conference on Environmental Systems

 An OVL CO2 mass balance analysis demonstrated excellent agreement between the CO2 injection rate, a measured value, and the calculated OVL CO2 gain rate after applying posttest corrected OVL flow rates. The OVL CO2 gain rate is the rate at which the OVL gas stream acquires CO2 from the space suit (SSAS). Differences between the two ranged up to 7%.  The OVL water vapor mass balance analysis demonstrated good agreement on an accumulated basis and strong OVL water vapor gain rates dependency upon OVL flow rates and LCVG water temperatures. Comparing instantaneous OVL water vapor gain rates to injection rates indicated periods of condensate formation and evaporation with the LCVG being the water vapor sink and source. This water vapor interaction with the LCVG was also noted in PLSS 2.0 HITL testing.

B. Pressure Schedule Regulation Test The Pressure Schedule Regulation Test, conducted on 2/11/15 and 2/12/15, involved varying the nested pressure set-points of the POR and SOR to characterize the regulators’ performances at the system level. This test was performed to evaluate the possibility of reducing the nominal suit pressure regulation band. For reference, while the Space Shuttle/ISS EMU primary regulator controls suit pressure to 4.3 psia and the secondary regulator controls to 3.7 psia, during the Apollo era the primary regulator was set to control to 3.85 +/-0.15 psia while the Oxygen Purge System regulator controlled to 3.7 +/-0.3 psia.13 In the Apollo application, an actuator was used to engage the Oxygen Purge System, unlike the normally-on nested regulator scheme employed by both the Space Shuttle/ISS EMU and the AEMU. This testing was conducted to demonstrate the feasibility of reducing the set-point of both the POR and the SOR without eliciting flow from the SOL during nominal operations. For this evaluation, the POR was set to 3.8 psia while the SOR was set to 3.5 psid. It should also be noted that whereas the PLSS 2.0 OVL was operated at subambient pressure, the PLSS was exposed to ambient lab pressure (i.e., Vacuum Chamber C was not drawn down to vacuum). For each test point, metabolic products (heat, CO2, and water vapor) and suit leakage were set to simulate conditions during a nominal EVA. Because RCA cycling and/or contingency operation of the Multiposition Suit Purge Valve (MSPV) could cause OVL pressure perturbations or regulator droop, respectively, these functions were assessed at the reduced POR/SOR pressure schedule. Each of the following tests were repeated five times, with PLSS 2.0 exposed to the ambient laboratory environment; however, the RCA ambient reference line plumbed to a vacuum source to enable subambient OVL operation:  1-hour steady-state OVL operations with fan on and RCA cycling  Deplete POV while demonstrating purge using the MSPV low flow setting  Deplete SOV while demonstrating purge using the MSPV high flow setting Because all five trials yielded similar results, select datasets will be used to illustrate key findings. Figure 14 plots the POR and SOR outlet pressures (DP-114 and DP-214, scaled left), inlet pressures (PT-112 and PT-215, scaled right), and interstage pressures (PT-115 and PT-216, scaled right) from the steady-state portion of the third trial. POR and SOR outlet pressure measurements show the OVL pressure response to RCA cycling with both simultaneously experiencing pressure fluctuations on the order of 0.02 psi every 2 minutes while the differential pressure measurements ranged from 3.74 to 3.70 psid. The POR inlet pressure (PT-112) decreased throughout the test as expected going from 1245 to 367 psia as make-up gas was provided for the OVL gas that flowed to the vacuum system via simulated suit leakage/metabolic gas consumption and RCA cycling.

16 International Conference on Environmental Systems

The SOR inlet pressure (PT-215) in Figure 14 experienced a slight decrease from 1211 psia to 1201 psia. Recharge was completed immediately prior to testing and time was not provided for the tanks to reach thermal equilibrium, thus hand calculations were performed to determine if the pressure reduction was due to intermittent SOR activation or tank cooling. During the test, the tank temperature Figure 14. Pressure schedule regulation test trial III steady-state evaluation. decreased from 79.8°F to 74.7°F. Given the tank internal volume of 200 in3 and assuming no leakage, it can be shown using the ideal gas law that the mass of the GN2 in the tank stayed relatively constant at 0.680 ± .001 lbm during the 1-hour steady-state evaluation. These data suggest that intermittent SOR activations were unlikely. The data in Figure 14 also show that the SOR interstage pressure (PT-216) steadily decreased from 166 psia to 140 psia at approximately test time 14:09, then subsequently increased to 141 ± 1 psia where it stayed for the remainder of the test. This behavior is most likely explained by the interstage gas cooling and thus decreasing in pressure until the pressure fell below the first-stage regulation point, at which point the first stage regulator opened to maintain the set point pressure. Additional data from the low and high flow purge evaluations (not shown) demonstrated nominal performance of the POR and SOR without any evidence of inadvertent SOR activation due to RCA cycling. Regulator set points were shown to be repeatable, and the possibility of the reduced pressure schedule remains promising.

C. Spacesuit Water Membrane Evaporator Mapping Two days of testing were performed in February 2015 to map the PLSS 2.0 SWME performance and provide a baseline for comparison during and after the extensive PLSS 2.0 Chamber C testing, as well as to characterize the SWME performance to inform future SWME designs, refine advanced PLSS requirements, and verify analytical PLSS models. Test points varied water flow rate (100, 150, and 200 lb/hr), BPV position (10%, 25%, and 50%, and 100% open), and heat input via a COTS chiller cart to maintain a desired SWME outlet water temperature (45°F, 50°F, 55°F, and 60°F). Test results from the SWME performance mapping testing are summarized in Figure 15 and show the fully open BPV SWME rejected from 733 to 962 W. All test points, except the two noted in the Figure 15 legend, targeted 200±4 lb/hr water flow, the nominal PLSS flow rate. Actual flow rates ranged from 203 to 208 lb/hr. Heat rejection at the SWME design point of 200 lb/hr, 50°F outlet temperature, and fully open BPV was 918 and 912 W during the initial and repeat test, respectively. They were performed at the beginning of the first day and end of the second day. This 915 W average equals 3122 Btu/hr.

17 International Conference on Environmental Systems

Figure 15. PLSS 2.0 Chamber C testing SWME performance mapping test heat rejections.

Of all of the permutations, the design point of 200 lbm/hr inlet flow, 50°F outlet temperature, and 100% open BPV is of key interest with initial and repeat testing at these conditions yielding 912 and 918 W SWME heat rejections. Relative to the beginning of life design requirement of 900 W, this performance is considered excellent since the SWME was about 2 years old at the time of testing and had already been used in the PLSS 2.0 PIA and HITL testing. As expected, SWME heat rejections increased with increasing outlet temperatures and increasing BPV opening. The SWME heat rejection also increased as expected with decreasing inlet mass flow for fixed outlet temperatures.

D. Rapid Cycle Amine Mapping The RCA swingbed mapping test series was devised to characterize the performance of RCA 2.0 as installed in PLSS 2.0 while the PLSS was operating in a vacuum environment. To enable pre-EVA RCA desorb as well as Suitport operations for other test series, the test system was designed such that the RCA vacuum port (1-in inner diameter) was connected to a series of tubing and fittings (primarily 1.5-in and 2-in inner diameter components) that passed through the wall of Vacuum Chamber C and to the PLSS Lab Vacuum System coldtrap. The test system configuration was designed to prevent the RCA vacuum access umbilical from significantly impacting vacuum conductance. RCA mapping was carried out over 6 days in February 2015. A total of 27 test points were completed that varied RCA mode (CO2 or Timed), bed switching trigger (2, 3, or 4 mm Hg CO2, or 2 or 4 minutes), simulated metabolic rate (400, 1000, 1600, 2400, or 3000 Btu/hr) and OVL flow rate (4.5 or 6 acfm). Figure 16 summarizes the RCA baseline dataset by plotting mean SI PCO2 and average HCTs versus nominally simulated metabolic rates, as well as RCA bed switch PCO2 values. Test results demonstrate expected RCA trends in that mean PCO2 increased with increasing metabolic rates while HCTs inversely decreased. Similarly, SI PCO2 and corresponding HCT increased as the PCO2 at which the RCA bed was switched increased from 2 to 4 mm Hg.

18 International Conference on Environmental Systems

The 3 mm Hg RCA bed switch data are highlighted in Figure 16 with trend lines because RCA PCO2 control per SI PCO2 of 3 mm Hg has been the nominal AEMU PLSS control mode since PLSS 1.0 testing, whereas switching the RCA bed at constant HCTs is planned for contingency operations. Originally, the 3 mm Hg RCA bed switch value was selected to yield a SI mean PCO2 of 2.2 mm Hg at 1600 Btu/hr metabolic rate. The RCA used in PLSS 2.0, referred to as RCA 2.0, has more amine sorbent, which resulted in a 2.0 mm Hg mean SI PCO2 at the simulated 1600 Btu/hr metabolic rate. Figure 16. RCA mapping test baseline test results for the 2, 3, and 4 mm Hg Interpolating the 3 mm Hg RCA bed switch PCO2 values. dataset at 1200 Btu/hr yields a mean SI PCO2 of 1.7-1.8 mm Hg and HCT of approximately 5 minutes and provides a baseline to compare EVA time mean values from the 25 EVA test series of which each test point was operated at 3 mm Hg SI RCA control and designed to simulate an EVA mean metabolic rate of 1200 Btu/hr. Finally, it is interesting to note the SI mean PCO2 at 3000 Btu/hr was in line with the other data points, but the corresponding HCT was the RCA default 30- second minimum. The HCT trend line was calculated using data from 400 to 2400 Btu/hr and then extrapolated to 3000 Btu/hr to highlight RCA operations at 3000 Btu/hr metabolic rate, where the RCA would have cycled at approximately 18 seconds per the extrapolation to achieve the test mean PCO2. RCA performance with respect to its constant HCT control mode (timed mode) is always of interest since this mode is the default mode during some contingency operations such as SI gas sensor failure. The question of what the default HCT will ultimately be is answered in part by RCA performance mapping test results, as plotted in Figure 17. Upon determining the contingency mean metabolic rate and SI PCO2 requirements, PLSS engineers will be able to select an appropriate HCT. Finally, comparing timed mode test results in Figure 17 to select RCA PCO2 control mode test results in Figure 16 verifies consistent RCA performance. For example, the 1600 Btu/hr, 2-minute HCT mean SI PCO2 of 1.9 mm Hg compares very well with the 3 mm Hg RCA bed switch, 1600 Btu/hr test results of 2.0 mm Hg mean SI PCO2 and 2.36-minute HCT average. The slightly higher HCT in the RCA PCO2 mode test point yielded a commensurate increase in mean SI PCO2. Figure 17. SI mean PCO2 from RCA mapping testing RCA timed mode test points.

19 International Conference on Environmental Systems

E. Feedwater Supply Assembly /Auxiliary Feedwater Supply Assembly Charge, Discharge, and Ullage FSA and AFSA charge, discharge, and ullage testing intended to characterize the performance of the TCL and ATCL compliant water bladders that store the water supplies of 10 and 1 lbs of water, respectively, plus ullage. This testing involved both stand-alone tests on various days throughout the spring of 2015, as well as piggyback evaluations on other test sequences such as the 25 EVA test series. FSA recharge was performed at a variety of suit pressures (8, 6.2, and 4.3 psid referenced to both vacuum and ambient pressure), simulated vehicle water pressures (15, 8, 6, and 2 psig), with the TCV in LCVG or bypass position, and with the TCL pump on or off. FSA recharge profiles were generated at each of the test conditions to evaluate different recharge configurations and assess repeatability. Testing was also done to demonstrate the performance and repeatability of FSA/AFSA discharge and to evaluate the functionality and repeatability of the low water level alert pressure signal generated by compression of a compliant tube located inside the bladder. Throughout this testing, the FSA successfully achieved its primary objectives of storing and sourcing the cooling water for the TCL, as well as setting the TCL pressure based on suit pressurization. This test series successfully characterized FSA water recharge as a function of TCL absolute pressure change and rate of recharge (lb/hr) such that fill time and quantity could be predicted given suit pressure, water recharge pressure, and the configuration of the pump and TCV. FSA charge operations consisted of pressurizing the water supply to push water into the TCL. This measured mass of water was compared to the total SWME evaporated water mass calculated by integrating the SWME heat rejection over the EVA phase (Figure 18). On average, the comparisons were good with FSA charge and calculated SWME water evaporation averaging 9.55 lbm and 9.85 lbm, respectively. With respect to individual EVAs, the FSA charge water mass was within ± 15% of the calculated SWME evaporated water mass. In spite of executing a LCVG degassing procedure each EVA, it is believed the most probable cause of these per-EVA variations was entrained air entering via a faulty TCL quick disconnect and/or LCVG fittings within the SSAS. Pertaining to discharge testing, performance of the low-level alert signal proved to be inconsistent. The low-level alert mechanism generated a resistance that measurably impacted the TCL pressure as the FSA water quantity approached ullage; however, the signal was not repeatable.

Figure 18. FSA mass balance summary.

F. Portable Life Support System 2.0 Component Anomalies Throughout the course of PLSS 2.0 testing, several anomalous conditions were identified that impacted the performance of the PLSS 2.0 prototype. Unexpected hardware issues resulted in failure investigations and, in some cases, design changes. The following subsections will be limited to those anomalies that were unexpected and have the potential to impact subsequent advanced PLSS design considerations. Issues resulting from manufacturing errors or from obsolete component design features will not be addressed, nor will problems resulting from PLSS 2.0 test system hardware or software anomalies.

20 International Conference on Environmental Systems

1. RCA Bead Liberation In January 2015, during the test system reconfiguration and checkouts preceding PLSS 2.0 unmanned vacuum environment testing, a number of RCA amine coated beads (estimated to be 10s of beads) were found in the test system OVL line at the RCA outlet (Figure 19). Throughout the duration of the PLSS 2.0 unmanned vacuum environment testing, the OVL lines were occasionally inspected for evidence of additional RCA bead liberation, but no additional beads were observed. Additional investigation and inspection of RCA 2.0 required to determine the failure mode is anticipated when resources permit. The next generation design iteration, RCA 3.0, which was designed concurrently with PLSS 2.0 testing, incorporates a filter in the outlet header to prevent RCA beads liberated from the canister from migrating out of the RCA assembly. Figure 19. RCA bead liberation.

1. TCL Water Pump Failure On 3/3/15, the TCL water pump failed to spin up during nominal PLSS 2.0 startup. When commanded to a non- zero speed, the pump made intermittent noises as though it was periodically attempting to spin up, while the pump tachometer read a constant zero rpm. The pump was a positive displacement pump with brushless direct current motor and an integrated COTS motor controller. Despite troubleshooting efforts, functionality of the pump could not be recovered. Following completion of PLSS 2.0 testing, the failed water pump was removed from the PLSS assembly, disassembled, and inspected in support of the failure investigation. It was determined that the pump failure was most likely caused by contamination resulting from plating of biocidal silver within the roots of the gerotor. The silver contamination created interference between the gear and rotor generating repetitive, compressive stress that either created excessive torque on the motor or resulted in the fracture of the inner gerotor teeth that ultimately caused the pump to seize. As a result of the observed pump failure mode and effect, the advanced PLSS development team considered changing the material of the internal gear mechanism to help preclude contamination and its effects on the pump.

2. SWME Leak On 6/8/15, a significant water leak was identified within the SWME assembly during EVA simulation test #16, resulting in the release of liquid water from the TCL into the SWME housing. By the time the situation was identified early in the EVA, the SWME valve and stepper motor had experienced significant icing, shown in Figure 20, that prevented the SWME backpressure valve motor from moving the valve poppet and resulted in a loss of cooling control. The test point was continued to determine whether the SWME could regain control. It was hypothesized that when the SWME outlet temperature deviated beyond the set-point control band, the control algorithm would attempt to drive the stepper motor and the heat generated by the current to the motor windings could melt the ice on the backpressure valve. After 5 to 6 hours of Figure 20. SWME leak/freeze event. operation, most of the ice on the backpressure valve had been eliminated and conditions were present that required readjustment of the SWME valve position per the control algorithm. The stepper motor overcame the remaining ice on the valve assembly and began to move and control to the nominal SWME outlet temperature, although with an inaccurate step count due to significant stepper motor slippage while the valve was frozen. It is also worth noting that while the SWME backpressure valve was frozen and inoperable, cooling was maintained as a result of the partially open position in which the valve failed. Throughout the 5- to 6-hour duration before valve control was recovered, the SWME outlet water temperature increased from the nominal 50±0.1°F to approximately 56°. Because the SWME could not be further investigated or serviced without significant hardware and testing schedule impacts, it was resolved that the 25 EVA test series would be completed while managing the SWME leak. Following the completion of PLSS 2.0 testing, the SWME was removed from the PLSS assembly and a failure investigation was initiated. The investigation revealed a ruptured fiber in the SWME hollow-fiber bundle as well as apparent hydrophobicity degradation on the inlet end of the fiber bundle, both of which would have likely contributed to SWME leakage. The failure investigation also involved an

21 International Conference on Environmental Systems examination of the water quality throughout PLSS 2.0 testing to assess the effectiveness of biocide control using silver fluoride (AgF). Findings from the water quality assessment are documented in Ref. 14.

IV. Conclusions PLSS 2.0 testing served to evaluate the performance of the advanced PLSS components and system-level designs; the unmanned vacuum environment testing extended this experience base to include the highest-fidelity environments test and ops cons evaluations to date. In addition to generating an extensive database of advanced PLSS 2.0 test performance including pressure, delta-pressure, temperature, water mass flow, gas volumetric flow, CO2 partial pressure, water vapor, relative humidity, motor parameters (speed, power, step count, etc.), and electrical measurements, a number of other achievements were realized through the PLSS 2.0 unmanned vacuum environment testing. Accomplishments include:

 Gained operational experience with PLSS component and system-level designs o Validation and update of component specifications and PLSS requirements o Improvement of component designs, hardware selection, and PLSS schematic  Tested some hardware to failure and simulated other failure conditions  Functionally evaluated ops cons at different suit pressure schedules and revised operational sequences based on system performance o Airlock operations (pre-EVA, depress, repress, and post-EVA) o EVA abort o Suitport operations  Evaluated controller algorithms  Demonstrated vehicular interfaces and consumable recharge methods, flow rates, and times o 3000 psi gas recharge o Primary and auxiliary feedwater recharge o 28V power o IVA vacuum access for RCA desorption  Demonstrated consumables sizing and run to depletion, including telemetry signatures  Evaluated and demonstrated the PLSS and associated vehicle simulation test system with varying levels of AgF as a biocide

Acknowledgments PLSS 2.0 development and testing was a complex and highly successful effort that could not have been achieved without significant contributions from many JSC Advanced PLSS team members, including: Bruce Barnes, Colin Campbell, Cinda Chullen, Bruce Conger, Kevin Ehlinger, Eric Falconi, Bill Lynch, Janice Makinen, Russell Ralston, Walt Vonau, and Gregg Weaver.

References 1Watts, C., Campbell, C., Vogel, M., and Conger, C., “Space Suit Portable Life Support System Test Bed (PLSS 1.0) Development and Testing,” AIAA 2012-3458, 42nd International Conference on Environmental Systems, American Institute of Aeronautics and Astronautics, July 2012. 2Vogel, M., “Portable Life Support System 1.0 Test Report,” ESCG‐4470‐12‐TEAN‐DOC‐0021, Engineering & Science Contract Group, March 2012. 3Swickrath, M., Watts, C., Anderson, M., Vogel, M., Colunga, A., McMillin, S., and Broerman, C., “Performance Characterization and Simulation of Amine-Based Vacuum Swing Sorption Units for Spacesuit Carbon Dioxide and Humidity Control,” AIAA-2012-3461, 42nd International Conference on Environmental Systems, AIAA, July 2012. 4Campbell, C., “Schematics and Behavioral Description for the Advanced EMU (AEMU) Portable Life Support System (PLSS),” CTSD-ADV-959 Rev NC, Crew and Thermal Systems Division, Engineering Directorate, NASA-JSC, April 2012. 5Campbell, C., “Advanced EMU Portable Life Support System (PLSS) and Shuttle/ISS EMU Schematics, a Comparison,” AIAA-2012-3411, 42nd International Conference on Environmental Systems, AIAA, July 2012. 6Campbell, C. “Shuttle/ISS EMU Failure History and the Impact on Advanced EMU Portable Life Support System (PLSS) Design,” ICES-2015-327, 45th International Conference on Environmental Systems, International Conference on Environmental Systems, Inc., July 2012. 7Vogel, M., Anchondo, I., Cox, M., and Westheimer, D., “Portable Life Support System 2.0 Pre-Installation Acceptance (PIA) Test Report,” EM-PEM-15-0001, Crew and Thermal Systems Division, Engineering Directorate, NASA-JSC, 2016.

22 International Conference on Environmental Systems

8Anchondo, I., Cox, M., Watts, C., Westheimer, D., and Vogel, M., “Space Suit Portable Life Support System (PLSS) 2.0 Pre-Installation Acceptance (PIA) Testing,” ICES-2016-86, 46th International Conference on Environmental Systems, International Conference on Environmental Systems, Inc., July 2016. 9Vogel, M. and Ross, A., “Integrated Portable Life Support System 2.0/Human-in-the-Loop (PLSS 2.0/HITL) Summary Test Report,” EM-PEM-15-0002, Crew and Thermal Systems Division, Engineering Directorate, NASA-JSC, May 2015. 10Watts, C., and Vogel, M. “Space Suit Portable Life Support System 2.0 Human-in-the-Loop Testing,” ICES-2016-87, 46th International Conference on Environmental Systems, International Conference on Environmental Systems, Inc., July 2016. 11Bue, G., Watts, C., Rhodes, R., Anchondo, I., Westheimer, D., Campbell, C., Vonau, W., Vogel, M., and Conger, B., “Experimentally Determined Heat Transfer Coefficients for Spacesuit Liquid Cooled Garments,” ICES-2015-330, 45th International Conference on Environmental Systems, International Conference on Environmental Systems, Inc., July 2015. 12Vogel, M., Anchondo, I., and Cox, M., “Integrated PLSS 2.0 Chamber C Testing Report,” EM-PEM-15-0007, Crew and Thermal Systems Division, Engineering Directorate, NASA-JSC, 2017. 13Gibson, J. L., “Apollo Operations Handbook Extravehicular Mobility Unit,” MSC-01372-1 Rev 5, Crew Systems Division, Manned Spacecraft Center, NASA, March 1971. 14Steele, J., Quinn, G., Campbell, C., Makinen, J., Watts, C., and Westheimer, D., “Advanced Space Suit PLSS 2.0 Cooling Loop Evaluation and PLSS 2.5 Recommendations,” ICES-2016-239, 46th International Conference on Environmental Systems, International Conference on Environmental Systems, Inc., July 2016. 15Rhodes, R., Bue, G., Meginnis, I., Hakam, M., and Radford, T., “Thermal Performance Testing of EMU and CSAFE Liquid Cooling Garments,” AIAA-2013-3396, 43rd International Conference on Environmental Systems, AIAA, July 2013. 16Bue, G., Makinen, J., Cox, M., Watts, C., Campbell, C., Vogel, M., Colunga, A., and Conger, B., “Long-Duration Testing on a Spacesuit Water Membrane Evaporator Prototype,” AIAA-2012-3459, 42nd International Conference on Environmental Systems, AIAA, July 2012. 17Mosher, M. and Campbell, C., “Design and Testing of a Variable Pressure Regulator for a Flexible Spacesuit Architecture,” AIAA-2010-6064, 41st International Conference on Environmental Systems, AIAA, July 2010. 18Paul, H., Jennings, M., and Waguespack, G., “Requirements and Sizing Investigation for Constellation Space Suit Portable Life Support System Trace Contaminant Control,” AIAA-2010-6065, 40th International Conference on Environmental Systems, AIAA, July 2010. 19Papale, W., Nalette, T. and Sweterlitsch, J., “Development Status of the Carbon Dioxide and Moisture Removal Amine Swing-Bed System (CAMRAS),” AIAA-2012-3411, 40th International Conference on Environmental Systems, AIAA, July 2009.

23 International Conference on Environmental Systems