Proposed Schematics for an Advanced Development Lunar Portable Life Support System Bruce Conger' Hamilton Siindstrand, Houston, Texas 77058 Cinda Chullen2 NASA, 2102 NASA Parkway, Houston, Texas 77058 Bruce Barnes Jacobs Engineering, Houston, Texas 77058 and Greg Leavitt4 Wyle Integrated Science and Engineering Group, Houston, Texas 77058 The latest development of the NASA space suit is an integrated assembly made up of primarily a Pressure Garment System (PGS) and a Portable Life Support System (PLSS). The PLSS is further composed of an oxygen (Oz) subsystem, a ventilation subsystem, and a thermal subsystem. This paper baselines a detailed schematic of the PLSS to provide a basis for current and future PLSS development efforts. Both context diagrams and detailed schematics describe the hardware components and overall functions for all three of the PLSS subsystems. The various modes of operations for the PLSS are also presented. A comparison of the proposed PLSS to the Apollo and Shuttle PLSS designs is presented, highlighting several anticipated improvements over the historical PLSS architectures. Nomenclature Bht = British thermal twit CM = crew member COz = carbon dioxide DCM = Display and Controls Module DCS = decompression sickness ECLSS = Environmental Control and Life Support System EMU = Extravehicular Mobility Unit EVA = extravehicular activity GSE = ground support equipment HZO = water ISS = International Space Station IVA = Intravehicular Activity JSC = Johnson Space Center Ibm = pounds mass LCVG = liquid cooling and ventilation garment LiOH = lithium hydroxide Metox = metal oxide micro-g = microgravity NASA = National Aeronautics and Space Administration ' Project Manager, Thermal and Environmental Analysis, 2224 Bay Area Blvd. ; Houston, Texas 77058/JE-5EA. 2 Project Engineer, Space Suit and Crew Survival Systems Branch, 2102 NASA Parkway, Houston, Texas/ECS. 3 Thennal Engineer, Thermal and Environmental Analysis, 2224 Bay Area Blvd., Houston, Texas 77058/JE-5EA. 4 Systems Engineer, System Engineering, 1 300 Hercules Drive, Houston, Texas 77058/FH-W5. American Institute of Aeronautics and Astronautics Oz = oxygen Pa = Pascal PCAI = Power, Conununication, Avionics, and Informatics PGS = Pressure Garment System PLSS = Portable Life Support System psi = pounds per square inch differential Asia = pounds per square inch absolute psid = pounds per square inch differential RCA = Rapid Cycle Amine SOP = secondary oxygen pack SWME = Spacesuit Water Membrane Evaporator TCV = Temperature Control Valve TD = Thermal DesktopTM W = Watts I. Introduction HE space-suited astronaut is the ultimate symbol of human exploration.' The space suit provides for distinct Tprotection of a single crew member (CM) working and operating in challen ging extravehicular activity (EVA) environments. The space suit is often referred to as a "mini or one-person spacecraft" because of this EVA distinction. One of the most complex aspects of this distinct EVA protection is the life support function of the space suit. Due to the need to be mobile during EVA and self-contained, the space suit must provide a unique approach to the CM's overall life support. This paper focuses on the future exploration life support system architecture for the EVA-unique portable aspects associated with the Portable Life Support System (PLSS). The effort to select the baseline PLSS architecture for future exploration activities was completed and documented in 2007.2 This paper identifies additional details for the baseline schematic. In particular, details the fluid lines of the baseline schematic are provided in a manner that identifies useful PLSS functions in various operational scenarios, while attempting to minimize complexity. This baseline schematic was reviewed by the National Aeronautics and Space Adnunistration (NASA), Johnson Space Center (JSC) PLSS development team. It underwent updates resulting from various evaluations. This schematic design is not intended to be a final design, but is intended to be a theoretically workable, but unproven, layout for use as the basis for furore efforts. The information in this paper was based on design and analysis cycles and technology development work completed through September 2009. Overall, the detailed schematic with component numbers and descriptions are documented in 20083 and 20094. PLSS fitnctions described within this paper include the operational scenarios: charging operations, nominal operations, and contingency operations. The focus is the fluid-related components within the PLSS. Electronic and power devices are mentioned, including an emphasis on major interfaces of electronic equipment with the fluid systems. Additionally, a comparison of the baseline PLSS to the Apollo and the current Space Shuttle/International Space Station (ISS) EVA PLSS to support mission options is provided. II. System Requirements and Assumptions The EVA System consists of three internal elements that interface: suit element. vehicle interface, and tools & equipment. These elements are necessary to protect crewvmembers and allow them to work effectively in the pressure and thermal environments that exceed the human capability during all crewed mission phases. The space suit contains three systems: the PLSS, the Pressure Garment System (PGS), and the Power, Communications, Avionics, and Informatics (PCAI) system. The space suit is necessary to support extravehicular planetary exploration on the Moon and Mars. The space suit functions include: • Maintain pressure on the CM • Deliver breathing gas to the CM • Maintain core body temperature of the CM • Provide the mobility to perform required tasks • Provide communications to and from the CMs • Provide CM biomedical data American Institute of Aeronautics and Astronautics Protect the CM during launch, entry and abort Protect the CM from the environment during EVA Provide CM waste management The PLSS is envisioned to be worn as a backpack to the PGS, a multi-layered space suit Linder development, which together constitutes the EVA capability along with the associated PCAI and the ground support equipment (GSE). Figure 1; represents a simplified rendition of the baseline PLSS functions for explanatory purposes. ` The PLSS consists of the 0 subsystem, the ventilation subsystem, and the thermal control subsystem. The PLSS houses 2 PCAI system components that provide connnunications, avionics, and the information systems. However, the focus of this paper is on the fluid subsystems. The 0 subsystem provides 0, to the CM for breathing through the 2 ventilation subsystem. The ventilation subsystem receives the CM expired components of 0 , CO , and H O and 2 2 2 processes them through a regenerable scrubber where the CO and H O are vented to vacuum. This regenerable 2 2 aspect of the scrubber allows it to be reused resulting in consumable savings over historical designs. The thermal subsystem provides cool water to the suit for CM thermal comfort and receives warm H O back to the subsystem for 2 conditioning. Water that is evaporated from the cooling loop is resupplied by H O storage within the suit. Overall, 2 these subsystems work in unison to provide an active PLSS for the CM engaged in an EVA. 02 (Replenishing) 'A/ 02 2 Ventilation ! CO2, H O (vapor) 02, CO2, H2O - ------------ - cool H20: Thermal H2O (vapor) warm H2O Vacuum (Replenishing) H2OLife —s upport fu nctions only no electronics or communications represented Figure 1. Simplified PLSS Functions. The 02, ventilation, and thermal subsystems work together to provide oxygen, thermal control, humidity control, carbon dioxide (CO2) control and, trace contaminant control. Environmental control and life support systems (ECLSSs) are being designed to keep a CM alive within the confines of the crewed habitat. Although the fundamental principles of an ECLSS are the same as the PLSS, the PLSS is a smaller, more compact, and a uniquely different life support system necessitating unique requirements and assumptions. The PLSS specifically supports the following activities: • Preparing for an EVA • Perfonning an EVA • Perfonning post-EVA processing • Supplying storage between EVAs • Perfonning scheduled maintenance American Institute of Aeronautics and Astronautics This paper focuses on the functions performed by the PLSS enabling an EVA. The primary function of the PLSS is to provide critical life support capabilities for the CM. The PLSS specifically provides the following critical life support functions for the CM: • Oxygen (02) • Thennal control • Humidity control • Carbon Dioxide (CO2) control • Trace contaminant control Requirements for the PLSS for longer microgravity use, lunar applications or even Mars missions indicate longer mission durations than Apollo with fewer opportunities for resupplying resources. Therefore, a reduction in consumables will be necessary for each EVA. A new approach was needed for the PLSS to help reduce the overall consumables for longer microgravity use, lunar and Mars mission requirements significantly. Also, to maximize flight crew productivity towards achieving exploration objectives, the required crew time for EVA preparation and maintenance activities needed to be shorter than the Space Shuttle and International Space Station (ISS) EVA times. When the Apollo astronauts were interviewed in the 1990's to help define EVA system requirements for future missions, they agreed that appropriately automating the PLSS had advanta ges, but they wanted to maintain a "keep it simple" approach. They concluded that "All subsystem designs should be based on fundamental principles of simplicity and reliability. Given a trade-off, simplicity and reliability are to be preferred over added functionality.-6 The following is a list of assumptions and requirements based on the initial PLSS architecture and the baselined system requirements as of September 2009. 7 The PLSS shall: • Function in Lunar thermal environments, hot and cold extremes • Function in orbital and transit (micro-g) environments • Support EVA durations of 8 hours with an average metabolic rate of 300 W (--1,000 Btu/hour) per CM • Maintain nominal suit pressure at 4.3 psid for EVA and 0.9 psid for Intravehicular Activity (IVA) • Provide redundant life support for 30 minutes after a single component failure excluding catastrophic gas depressurization • Provide life support services for two CM's using a single functional PLSS and buddy umbilical for 90 minutes to support a 10 kin walk-back emergency of a life critical component failure • Support vacuum removable capability where a second suited CM assists the first suited CM (with life support functions provided by an umbilical) in detaching the PLSS from the suit in vacuum environments while suited • Operate with vehicle or rover configurations that supply low-pressure 02 as well as configurations that supply high-pressure 02 with vacuum access for subsystem operations III. Overall Schematic The functional diagram of the baseline PLSS is shown in Fig. 2. Gaseous 02 storage (shown in orange and pink) provides the makeup 02 to the ventilation loop (shown in green). A fan provides momentum to circulate the ventilation flow, which is first routed to the helmet and then into the suit. It is then picked up in the arm and leg areas of the suit by the liquid cooling and ventilation garment (LCVG). The LCVG is a relatively tight fitting garment that has water tubes sewn into it in order to cool the CM. The LCVG also includes ventilation ducting that picks up ventilation gases that have flowed over the body and returns the ventilation gases to the PLSS. The ventilation gases are then routed to the Rapid Cycle Amine (RCA) unit where CO, and humidity are removed. The thermal subsystem comprises the blue components in the diagram. The pump routes cooling H 2O from the suit to the Spacesuit Water Membrane Evaporator (SWME), which is the cooling unit that removes metabolic heat and electronic heat from the PLSS and the PGS. The cooling H2O is routed to a temperature control valve that the CM adjusts, to control the amount of cool water entering the LCVG to maintain thermal comfort. The H2O then exits the suit and returns to the pump. Water stored in the feedwater tanks replaces the H 2O that evaporates from the SWME in the H2O loop. The detailed baseline PLSS schematic contains additional minor components and flow paths and is shown in fig. 3. American Institute of Aeronautics and Astronautics Secondary OZ rechai ge pigtail ........ .. .,.. _ .... .... High piessure OZ from Umbilical ^I O secondaiy02 O I^^I umbilical pigtail ^ Q Q Presaire Gamaern ^ r ^ r SunsysremlPGS) - Primary0n Secondary 0• ChuOm2 &id ity ?y ............................... _......... _. Secaoen^dearr^yo Hir^o VTheenrtimlaatilon to ambient 0 ® Feedwater _^_ Pari emsaerry^HaO bi ^.. H2O fr om b.^' '" Umbilical H2O to - `""" Umbilical (1) Pressure Sensor t® Pressuresensor(dual 'OrOifriifcicee Filter-non Fitting and Temperature Pressure Regulator! ^Filte _ @0R TeelmiepfVeraaltuyree Sensori7 ®04 P Pmrereassdsseuu)r+reelGo Rcaaeugl grueelaatdoor ut qFc TCeosnt tProolrletr ^^'to atFomi latembrb-iefileonnwtt ®TFFriilalttecerer Contaminantq SCuolntPtreonlVeatrlavteion HFaannd Va lve fFYieltmer-a mflohwien 0 CheokValve co Carbon Dioxide Sensor ElFlow Switch d<D Solenoid Valve I^ Hand Valve ® and Filltetoronnect10 Pump ® RCRUalves 'figure 2. Overall functional diagram. The PLSS consists of the Oz subsystem, ventilation subsystem, and thermal subsystem. 5 American Institute of Aeronautics and Astronautics Portable Life Support System (PLSS) -- ----- Pressure Garment System (PGS) KEEP- a ygen X P Multiple Subsystem - P Connector; ----R- -------------- - - E - - I^^ Pigta Al . ^. P P _*T410 -- -- ---- ----.---.-.__.-----.-.-_----.- - - - - - -MRCAUnit (T CO2 Ventilation Subsystem ii i B SWME i T =; a P s i ^ --- b COLORLEGEND C b m Primary 02 m C — Secondary02 P ow 1 LCVG Ventilation P Thermal Feedwater Feedwater i P j a PGSBoundary Thermal Control _ _ i i Subsystem Sensor ^ Pressure sensor (dual r Orifice E Filter-nonflow ^j Temperature a Pressure Regulator] Filter ture Sensor mode)+ local readout F Test Port to ambient Fitting Control Valve Hand Valve F lrve FPPrreessssuurree GReaguiuglea tor lqo Controtller etFoi latmerb-fileonwt rTrace Contaminant E] PCahses ctkhVroaulvgeh qx QCuloicsked D wishceonnnect Fan nt Motor cot Carbon Dioxide Sensor 0 Flow Switch a-0 SolenoidValve HoHand Valve RCAValves Mated Valve ^D Pump Figure 3. System Level Baseline PLSS Schematic. This schematic shows the majority of the PLSS components with the exception of fittings and some of the filters. 6 American Institute of Aeronautics and Astronautics IV. Oxygen Subsystem The 0, subsystem consists of the primary and secondary 02 storage tanks, along with the regulators that provide 0, to the space suit at the required pressures. The 0, tanks are refilled via the 0, recharge line, which connects to the umbilical with a quick disconnect and filter. The primary and secondary 02 tank designs allow them to store 0, at 3,000 psia nominally, when full. Single stage regulators (two for the primary and two for the secondary) function to condition the 0, down to usable suit pressure levels of 4.3 psid for primary operations and 3.6 psid for secondary operations. In general, the included filters protect components from potential debris in the fluid lines. All fluid lines that lead to the ambient environment include filters to prevent the lunar dust from entering these lines. This is also true for the ventilation subsystem and the thermal subsystem. The high level functional diagram for the O, subsystem is shown in Fig. 4. The O, subsystem interfaces with the recharge umbilical for 02 recharge of the storage tanks and provides 02 to the ventilation subsystem. The 02 subsystem stores the high-pressure 02 in primary and secondary storage tanks. The primary 02 tank nominally supplies the ventilation subsystem with regulated makeup 02 as needed. In the event of primary 02 system depletion or failure; the secondary system will supply the ventilation subsystem with regulated redundant 0 2. Pressure sensors in the 02 subsystem monitor both the primary and secondary 02 tank pressures as well as the regulated intermediate pressure downstream of the tanks. secondarY as .ecliargepf^i.dl vlv 16gh Puss urr . rrssni. Regnl.n..r Ha;rul.xw ^i— Law Prosswe f Low Prassmo ^r^.C]^ ^ 1 ReJU14101 10-1 RrgdLNOr SKandmy Dr ... ...0 ,.e umhllltal plgtall 1{^J' i...................................... VenNleHon Subsystem Figure 4. Oxygen subsystem functional diagram. The 02 subsystem is recharged via high pressure 02 delivered by the umbilical and provides regulated 02 to the ventilation subsystem. V. Ventilation Subsystem The controlled flow of 02 to and from the space suit within the ventilation subsystem is shown in Fig. 5. The vehicle or rover (both via umbilical flow) or a PLSS fan can provide flow momentum. In emergency purge mode, the CM opens one of the purge valves, as neither the fan nor the umbilical are assumed to function. The drop in suit pressure causes the secondary 02 subsystem regulators to crack and maintain suit pressure by providing flow to the helmet. During nominal EVA operations, the ventilation flow recycles through the ventilation loop with the Rapid Cycle Amine (RCA) providing CO2 and humidity removal functions. Without the RCA unit, the CO2 and humidity levels would build up rapidly to toxic levels. The CO, sensor monitors concentrations of CO2 in the ventilation loop at the suit inlet and outlet. This sensor provides information for warning the CM when high levels of CO, exist. It can also provide metabolic information. Humidity levels must be controlled in the ventilation loop to provide comfort to the CM and to prevent fogging in the helmet. The RCA is very efficient at removing humidity. It is expected that humidity levels exiting the RCA American Institute of Aeronautics and Astronautics will be too dry for CM comfort. To mitigate this issue, the current design shows a humidity controller integrated with heat exchanger; as a liquid to gas membrane unit that transfers H 2O vapor from the H2O loop to the dry ventilation stream at the exit of the RCA. Figure 5, shows the high level functional diagram for the ventilation subsystem. The ventilation subsystem interfaces with the thermal subsystem by receiving cooling water that circulates through the heat exchanger and interfaces with the 42 subsystem by receiving 02 to replenish the ventilation loop. The function of the ventilation subsystem is to circulate cool breathing 02 to the PGS. The ventilation subsystem circulates OZ through the ventilation loop by using a fan. A heat exchanger that uses cool water from the thermal subsystem cools the 02 before it enters the PGS. A CO2 sensor is used to measure the levels of CO2 entering and exiting the PGS and data obtained from the CO, sensor may be used to calculate the metabolic rate. Two additional sensors measure the pressure and temperature of the 02 in the ventilation loop entering the PGS. The return flow from the PGS is scrubbed by the RCA. The RCA removes CO, and humidity from the ventilation loop and vents these constituents to vacuum. OxygeIn iun auty Cool w<uei t Waiin water of second.uy tanks Q'® m Rt Al.U^ COZ & humidity nEal CO2 Pressure Garment to atnhienlg 3 Subsystem (PGS) Ct Figure 5. Ventilation subsystem functional diagram. The ventilation subsystem provides conditioned breathing gas to the PGS for CM consumption. The Oz subsystem provides makeup oxygen to the ventilation subsystem while the thermal subsystem provides cooing water for ventilation loop gas cooling. VI. Thermal Subsystem Thermal comfort for the CM and temperature control of the PLSS equipment is provided by the thermal subsystem. The CM controls the amount of cooling or heating provided by the thermal subsystem by adjusting the thermal control valve. Cooling H2O flows via the pump to the LCVG to provide the majority of a CM's cooling requirements (some sensible and evaporative cooling is provided by ventilation flow within the suit). 8 A Spacesuit Water Membrane Evaporator (SWME) removes heat from the thermal subsystem's water loop by evaporating water through a membrane. The evaporated water is vented to the vacuum environment. Feedwater tanks provide water to replenish the thermal subsystem as water evaporates within the SWME. The high level functional diagram for the thermal subsystem is shown in Fig. 6. The thermal subsystem interfaces with the ventilation subsystem to provide cooling water to the heat exchanger and interfaces with the PGS to provide cooling water to the CM. The function of the thermal subsystem is to provide cooling to the CM and electronic components. The thermal subsystem circulates H2O through the H2O loop by using a pump. The SWME cools the H2O loop by using a control valve to evaporate a regulated amount of H2O to ambient. The cooling water circulates through the heat exchanger for ventilation loop cooling and circulates through the electronics cold plate for electronics cooling. A heater provides additional heating to the H 2O loop, if needed, before returning to the PGS. Four pressure sensors and two temperature sensors monitor the pressure and temperature of the H 2O loop. Two feedwater reservoirs located in the PGS provide makeup H 2O to the H2O loop. The primary feedwater reservoir nominally supplies the H2O loop with makeup H2O as needed. In the event of primary feedwater reservoir depletion or failure, the secondary system will supply the H2O loop with redundant H2O. American Institute of Aeronautics and Astronautics Ventilation Subsyste m Pressure Garment Subsystem (PGS) Wean w,de^ ..ul wace^ 0 i ^ 9^1 a o H Ambiem Figure 6. Thermal subsystem functional diagram. The thermal subsystem conditions the thermal loop to provide cooling to the CM. Feedwater tanks that are located in the PGS provide makeup water to the thermal subsystem. The tanks are recharged with water from the umbilical. The thermal subsystem provides cooing water to the ventilation subsystem for ventilation loop gas cooling. VII. PLSS Modes of Operation The PLSS has 6 primary modes of operations for lunar applications. L Nominal EVA -In the nominal EVA Mode, the PLSS performs autonomously to provide CM life support functions. The PLSS will rely on a low-pressure ambient environment for the SWME and RCA technologies to function. 2. Umbilical Modes — In the umbilical modes, the PLSS performs in conjunction with umbilical services. • No Recharge Mode - In the umbilical (no recharge mode), the umbilical provides O Z and cooling H2O to the CM, but neither the Oz tanks nor the feedwater tanks are refilled. • Recharge Mode - The umbilical with recharge mode accomplishes refilling the O Z and feedwater tanks during suited or unsuited conditions. Cooling water used to refill the feedwater tanks is provided by the umbilical, and the pump and the SWME are not functioning. 3. Decompression Sickness (DCS) Treatment Mode - The CM can select DCS Treatment Mode with two options, the EVA option and the umbilical option. The DCS Treatment Mode EVA option flow paths are nearly identical to the nominal EVA Mode. The DCS Treatment Mode umbilical option is nearly identical to the umbilical (no recharge mode). 4. Buddy Mode — This is a mode to cover the situation in which one CM's PLSS encounters a failure, such as a loss of power, during an EVA. The PLSS that did not encounter failure (functional PLSS) supplies the 02 and cooling H2O to the CM with the failed PLSS (disabled PLSS) through the Buddy umbilical. The Space Shuttle and ISS EMUs do not include a Buddy capability. The EVA CMs will travel much farther from the airlock during hear EVAs, as compared to ISS and Shuttle EVAs with less time to retreat back to the airlock in case of failure. This mode is economical (in terms of mass and volume) emergency PLSS system design for lunar and Mars EVA support.$ American Institute of Aeronautics and Astronautics 5. Secondary 02 Modes - The secondary 02 modes are autonomous emergency modes where the PLSS encounters a failure and cannot rely on the Buddy Mode for whatever reason. There are three options within the secondary 02 modes: the helmet purge option, the suit purge option, and the operational option. The secondary 02 modes assume that low-pressure and vacuum ambient conditions exist. 6. PLSS Removed Umbilical Mode - The current operational concept for returning from a lunar nussion includes the ability to doff the PLSS and leave it on the lunar surface before launching to return to earth. A possibility exists for the doffing procedure to take place at vacuum conditions. The PLSS schematic includes quick disconnects to allow for removal of the PLSS when the suited CM is relying on the umbilical for life support functions. The direction of the cooling H2O flow through the LCVG reverses, as compared to the LCVG flow in the modes discussed previously. This section describes the various modes of operation for the PLSS. For each mode, the overall schematic is displayed and active plumbing for that mode is highlighted. Descriptions of the functions of major components operating are presented as well as overall PLSS capabilities during each mode. A. Nominal EVA In the EVA Mode, the baseline PLSS perfornls autonomously to provide CM life support functions. The PLSS relies on a low-pressure ambient environment for the SWME and RCA technologies to function. Figure 7, shows the fluid lines that are active during the EVA Mode of operation. In the nominal EVA Mode, the primary 02 tank stores 02 at 3,000 psia and provides makeup 02 for replacing metabolically-consumed 02 and ullage 02 vented by the RCA unit. It also replaces the small amount of gas that nominally leaks from the suit or PLSS. The primary pressure regulator steps the 02 pressure down to the pressure required by the suit (4.3 psid) in nonunal EVA Mode. This regulator performs as a variable pressure regulator, an isolation valve, and a check valve at different times because of the various functions it provides in the different PLSS modes of operation. 10 American Institute of Aeronautics and Astronautics