49th International Conference on Environmental System ICES-2019-26 7-11 July 2019, Boston, Massachusetts
Commercial EVA Space Suit System Development
Theodore C. Southern1 and Nikolay A. Moiseev2 Final Frontier Design, Brooklyn, NY 11205, USA
Final Frontier Design (FFD) is in development of an Extra Vehicular Activity (EVA) Space Suit System. The philosophy is to develop a simple, light weight, low cost EVA system with no return-to-Earth life cycle. FFD’s EVA suit has a rear entry hatch, with a soft upper torso and soft adjustable limb joints. A complete pressure garment and outer garment enclosure prototype has been patterned and fabricated, defining baseline sizing, interfaces and bearings, the ventilation system, the geometry of the torso and helmet, and materials configurations. A unique liquid cooling garment (LCG) has been developed and fabricated for use with the suit, using fabric panels with specialized flat water channels that can increase surface area and efficiency of the heat exchange. The prototype LCG and enclosure is intended to be used as a test bed for system interfaces and for training development. Additionally, a breadboard, closed-loop personal life support system (PLSS) has been designed and fabricated utilizing commercial off the shelf (COTS) components wherever possible. The PLSS includes an oxygen rebreather loop that removes heat, humidity, and CO2 from the breathing gas, and a water cooling system for the LCG. The PLSS has been tested using a human respiration analog. With the LCG, Enclosure and the PLSS subsystems, FFD aims to create a commercially focused, complete EVA system. A test program utilizing a space station breadboard and EVA tools is in development.
Nomenclature btu = British Thermal Unit COTS = Commercial Off the Shelf ES 3 = EVA Space Suit Enclosure EMU = Extravehicular Mobility Unit EVA = Extra Vehicular Activity FFD = Final Frontier Design FMEA = Failure Mode and Effects Analysis IVA = Intra Vehicular Activity LCG = Liquid Cooling Garment LEO = Low Earth Orbit PLSS = Personal Life Support System psi = pounds per square inch SBIR = Small Business Innovation Research SCFM = Standard Cubic Feet per Minute STD = NASA Technical Standard TRL = Technical Readiness Level
1 President, Final Frontier Design 2 Lead Designer, Final Frontier Design 1 International Conference on Environmental Systems
49th International Conference on Environmental System ICES-2019-26 7-11 July 2019, Boston, Massachusetts
I. Introduction Final Frontier Design (FFD) is proceeding through development, prototyping, and testing of their Extra Vehicular Activity (EVA) Space Suit System (ES3) for the microgravity environment. The goal of the ES3 is to create a simple, safe, relatively low cost, and complete system for tethered EVA on commercial space stations in Low Earth Orbit (LEO). The complete system includes the Liquid Cooling Garment (LCG), the enclosure (pressure garment, outer garments, helmet assembly, the bearings, interfaces, helmet, soft upper torso, and backpack enclosure), and the Personal Life Support System (PLSS). Related but undeveloped systems include the airlock, ground and flight support equipment, handrails, tethers and tools. The targeted weight of the ES3 is approximately 200 pounds, based on the current prototype. The ES3 is intended to be a ‘disposable’ system, with no re-entry or ground reservicing requirements, and a limited lifespan of 20x 6-hour EVAs, at a +5 psi operating pressure. Redundancy is built in throughout the ES3, with a goal of dual fault tolerance throughout the system. FFD’s goal is to meet or address the complete NASA Procedural Requirements 8705.2C, “Human-Rating Requirements for Space Systems”. Multiple supporting NASA standards (STD), including STD 6016 “Materials and Processes Requirements for Spacecraft” and STD 3001-B Human-Systems, are used as guidance. Some specific requirements for the system have been outlined in FFD’s prior ICES paper on the EVA prototype.1 The ES3 has undergone meaningful development in the last two years, including: ● the construction of a prototype full pressure suit enclosure, including pressure 3 garment, rear entry hatch, and outer Figure 1. The ES Subsystems. garment, ● bearing revisions and prototyping, ● development and fabrication of a unique low-profile LCG, and ● development and testing of the PLSS rebreather and water-cooling loop. The ES3 prototype consists of components with a Technical Readiness Levels (TRL) of 3-4. The softgoods arms, gloves, torso, hips, legs, and boots are the result of multi-year development efforts and qualify as TRL 4, with initial lab testing having taken place and significant materials and processes defined; the hatch, life support system, and bearings are TRL 3, having had their critical function established.
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49th International Conference on Environmental System ICES-2019-26 7-11 July 2019, Boston, Massachusetts
II. Methods and Development
ES3 development, fabrication, and validation is broken into specific subsystems the LCG, the Enclosure, and the PLSS.
A. Liquid Cooling Garment (LCG)
FFD’s LCG is the result of a multi-year effort to create a more efficient and lower profile alternative to the standard tubing-based LCG of today. Traditional tube based LCGs have only a line point-of-contact with the body, because the tubing is circular in cross section. For this reason they are required to flow over nearly the entire body to effectively remove heat from an Figure 2. Comparison of LCG tubing cross sections. active individual. A lower profile garment was Polyester sheet reinforcement in green. desired that did not restrict mobility, did not add bulk to the limbs, and allowed more airflow-based evaporation over the body.8 With this goal in mind, FFD has developed a unique, welded-fabric cooling garment that utilizes thin, polyester sheets bonded to water tight nylon fabric. The polyester sheets maintain a flat shape while pressurized, resulting in flat channels rather than circular tubes. The resulting panels of channels allow complex water flow patterns with very high surface area contact with the body, because of the flat channel geometry (Figure 2). Multiple component level panels have been fabricated and tested for structure, flow, durability, leakage, and flexibility. The prototype panels were qualified at high pressures above +40 psid. The FFD LCG includes panels on the front and back of the torso and on the thighs; optional thin mesh sleeves and legs allow for EVA padding integration, or can be removed for an even less bulky garment. The water panels include cut voids to allow for water evaporation from the undergarment. The system can be used in a primary-redundant configuration, with the torso serving as a primary cooling garment and the thigh sections serving as a secondary backup. A closure running vertically on the torso allows entry to the garment. Ventilation tubing of the ES3 will be integrated directly into the pressure garment of the suit rather than on the LCG, eliminating the need for a separate tubing system, disconnect, or manifold on the body. FFD is currently developing a unique high-flexibility vent tube for this purpose.
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Figure 3. LCG Torso Panel, flow path (left) and in prototype testing (right).
B. Enclosure FFD’s EVA enclosure includes the pressure garment and outer garment, as well as all related hard systems including the helmet, bearings, hatch, and interfaces. The pressure garment leverages the significant work done through both NASA SBIRs, and internally with development of FFD’s Intra Vehicular Activity (IVA) space suit over the last 9 years. The EVA pressure garment utilizes similar materials, fabrication techniques, patterning, and sizing elements as our IVA pressure garment, particularly along the arms and legs. A pressure garment prototype has been fabricated, without redundant bladder or restraint systems. The pressure garment includes a hip-leg-boot assembly, arm assembly, gloves, and the soft upper torso. Prior NASA SBIR awards for elbow/shoulder assemblies, outer garments, and gloves are leveraged here. (Figure 4)
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Figure 4. ES3 Enclosure Prototype.
While the pressure garment prototype utilizes a single layer pressure garment similar to our IVA suit, FFD has developed a design that enables a redundant pressure garment in two layers. During nominal operations the outer layer of the pressure garment is pressurized, with pressure passing through a tiny orifice from the inner layer. If the outer layer is punctured, the inner layer can then hold pressure for a controlled and extended period of time. While the Russian Orlan EVA space suit has pressure garment Figure 5. ES3 Pressure Garment Elbow Assembly. redundancy, United States space suits traditionally do not. This adds an important fault tolerance in the overall system. FFD considers that a bladder failure has criticality 1 in a Failure Mode and Effects Analysis (FMEA), meaning loss of life for the astronaut. FFD has also patterned and fabricated a prototype outer garment for their EVA suit, following mobility joints and interfaces of the pressure garment. While natural nomex was used for the prototype of Thermal Micrometeoroid Protection Garment (TMG), FFD is considering Orthofabric, Vectran, or a blend of Nomex and Kevlar for the outer layer; the thermal barrier will include 5-7 layers of aluminized mylar film with mesh spacers; the liner and micrometeoroid layer will be joined, and consist of a single layer of urethane coated Kevlar. Albedo is an important consideration for the outer layer of the suit, as well as thermal range, UV stability, chemical resistance, flame retardancy, puncture and tear resistance, and vacuum suitability.
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FFD has further developed our bearing designs for the EVA suit system, with the fabrication of blanks for the wrist, elbow, and shoulder bearings. Restraint line anchor points have been designed into the bearing outer races, to simplify the overall assembly and reduce part count.
Figure 6. ES3 Arm Bearing Blanks. Including scye bearing (left), arm bearing (middle, showing restraint line anchor points) and wrist bearing (right).
A prototype rear entry hatch has been fabricated and integrated with the pressure garment for evaluation. The hatch utilizes extruded aluminum channel with customized fittings channel for assembly, and measures 15” wide and 25” tall. The hatch allows FFD to simply and cheaply evaluate sizing parameters, hinge and latch options, and methods to enable self donning and closure of the hatch. While limited in pressurization capabilities, the hatch represents a useful placeholder to better define sizes and geometries of the soft upper torso. Production of a full- fledged enclosure design is planned for late 2019.
C. Personal Life Support System (PLSS) Through the support of a 2018 NASA Small Business Innovation Research (SBIR) award, FFD has developed a breadboard, limited-use PLSS for an EVA space suit, including a rebreather or gas loop, a sublimator system, and a cooling water loop. The gas loop includes a low power blower, CO2 scrubber cartridge, heat exchanger, multiple filters, water separator, sponge water collector, gas cylinders, and regulators, to effectively pressurize a suit and scrub human respiration up to approximately 1600 btu, with a flow rate of 6 scfm, for at least 6 hours. The breadboard PLSS includes 2 digital pressure transducers, and an analog flow gauge; a portable CO2, temperature, and humidity is placed in the suit simulator. The cooling loop includes a water pump, filter, supply tank, heat exchanger, and cooling bypass, all of which are generally only appropriate for ground-based operations.
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Figure 7. Mechanical Schematic of the PLSS.
FFD’s primary goal for the PLSS research was to identify and utilize appropriate commercial off the shelf (COTS) items. Reducing the complexity and custom parts in the PLSS can minimize risk and cost for NASA and FFD. COTS items generally are mass produced and well understood, and benefit in pricing from mass production.
Some components, including the CO2 scrubber, cylinders, and high-pressure regulators, have flown to the stratosphere in human life support operation, giving them a high TRL. Other items in the gas loop can be considered TRL 4-5, while the cooling water loop is intended for only ground support operations currently. The pressurization goal of the gas loop is between 4.3 psi and 8 psi. For the gas loop rebreather, we focused on systems and components that are compatible with pure oxygen operations. There are many examples of pure oxygen rebreather systems used on Earth, including for firefighters, mine safety, SCUBA, and even high-altitude aircraft flight. While we are designing for use with pure oxygen in operations, we are currently only using breathing air with a ~20% oxygen partial pressure.
The gas rebreather loop pulls air from the suit enclosure and filters and scrubs the air for CO2 using a Lithium or Sodium Hydroxide canister (the scrubber material can vary depending on the application). The canister will be changed out after every sortie or use; in addition, the water collector sponge must be dried after each use. A small form factor blower capable of operation in vacuum pulls the air through the system at a variable rate, with a target flow rate of 6 SCFM. The gas is then sent through the heat exchanger for cooling, and consequently through a coalescing filter and water separator. Finally, the pressure is topped off with a pressurized air tank, utilizing two separate regulators- a high pressure first stage regulator (~2500 psi to ~200 psi) and a variable low pressure second stage regulator (~200 psi to ~4.3-8 psi) In addition to the gas loop rebreather and water cooling loop, the development of the PLSS included detailed work on the heat exchanger, power and control, and a human respiration analog In addition, Earth based rebreather systems generally have minimal issue rejecting heat from the system and the human, through convection to the environment. A space based PLSS must reject metabolic and electronic 7 International Conference on Environmental Systems
49th International Conference on Environmental System ICES-2019-26 7-11 July 2019, Boston, Massachusetts heat to a vacuum, and therefore generally requires a liquid cooling garment, cooling water loop, sublimator plate or other advanced cooling system, heat sinks, and a high-power water pump to reject heat. FFD designed a heat exchanger, with a sublimation cooling method. The gas loop and cooling water loop heat exchanger channels share a wall with the sublimator chamber, which has a porous plate partially exposed to vacuum where sublimation theoretically occurs. (Figure 8, porous plate not shown) The sublimation chamber is fed water from a feedwater tank under slight pressure, which contains the water in a softgoods bladder. The porous plate freezes over upon the feedwater exposure to vacuum, and the metal walls allow heat transfer from the heat exchanger to the cold plate. The sublimation of water, from solid to gas, results in a cooling effect on the plate, which is transferred to the water-cooling loop. This method of cooling has been used for EVA PLSS systems since the 60’. For the Russian Orlan EVA system, water lost to vacuum over a 6-8 hours EVA at 2000 btu/hour is estimated between 2-3 liters. FFD’s heat exchanger is a 3D printed assembly, designed to maximize surface area while minimizing pressure drop. The design takes advantage of unique internal geometries that 3D printing allow. The heat exchanger is integrated with the sublimator plate, effectively rejecting heat from the system. We have defined and printed the initial configuration of the heat exchanger and sublimator. The baseline configuration for the heat exchanger and sublimator plate includes inlets and outlets for the breathing gas loop and water cooling loop; the larger barbs are for the breathing gas, while the smaller internal barbs are for the water cooling loop. Two smaller inlets on the bottom are for the feedwater system for the sublimator, which has redundant sides, top and bottom. (Figure 8) A large rectangular internal volume is for the sublimator assembly includes the internal metal foam, the vacuum facing porous plate Figure 8. PLSS Heat Exchanger / Sublimator Plate Frame and a protective mesh grid, on both top and bottom. FFD recognizes that NASA has focused on water permeable membranes and other evaporator configurations for EVA heat rejection recently. For this and other reasons FFD is less focused on sublimator development moving forward. The power distribution, control and display, software, and microcontroller subsystems will require development and integration in a future system configuration. Phase I of the SBIR utilized COTS sensor systems and manual control of the pump, fan, and diverters. No wireless telemetry, remote control systems, or customized astronaut control units were physically developed in Phase I. Variable DC power supplies were used to power the fan and water pump, and adjusted manually to control flow levels as required. Pressure was measured using an Arduino microcontroller and multiple transducers in the ventilation system, both upstream and downstream of the pump, to measure pressure drop of the system. Water cooling loop temperature was measured using a log and simple readout display system. Power parameters were defined and a preferred output of sensors (0-5 VDC) has been outlined. A space suit simulator and human respiration analog was developed for testing of the system, to simulate the pressurized and enclosed environment of the suit, while adding CO2, metabolic heat, and humidity to the system.
A 0.5 cubic meter enclosed pressure chamber served as the space suit simulator. A regulated CO2 tank introduced a measured flow of pure CO2 into the chamber, while 2 portable humidifiers introduced approximately 50 ml per hour, to simulate vigorous human activity. A heat pad introduced 1000+ btu (305 watts) of heat to the chamber. Pass throughs were cut into the chamber for air ventilation in and out, and water cooling in and out. The heating pad was 8 International Conference on Environmental Systems
49th International Conference on Environmental System ICES-2019-26 7-11 July 2019, Boston, Massachusetts placed over the outside of a large diameter aluminum pipe, to act as a simulated “liquid cooling garment” and human.
Figure 9. Human Respiration Analog Suit Simulator. Left, showing the pressure pot, right, showing internal humidifiers, heating system, and CO2 sensor.
III. Results
A. Liquid Cooling Garment The total surface area of FFD’s LCG, including the chest and thigh panels, is 285 in2 or 0.185m2. This is a relatively large surface area that rivals a full body LCG, with panels only in limited areas on the torso and thighs. The entire garment holds approximately 1.3 pounds of water under pressure, and was tested without failure to an internal pressure of over 40 psi. The garment has been worn by multiple test subjects and good body-panel surface contact was noted on both the thighs and the chest. Mobility is minimally affected by the garment, which is primarily stretch- mesh based, with critical cooling panels located at non-mobility areas on the torso and thighs. Because the channels are relatively large in cross section and there are multiple manifolds, the pressure drop over the garment is minimal. FFD is considering the necessity of a single smaller size.
B. Enclosure FFD’s EVA prototype is capable of pressurization to approximately +1 psid, with a goal to make a preliminary evaluation of the system. We have limited the pressure differential to +1 psi because of the preliminary nature of the hatch, Figure 10. FFD’s visor rings, and bearing blanks. Our goal is to evaluate bearing inner diameter sizes LCG Prototype 9 International Conference on Environmental Systems
49th International Conference on Environmental System ICES-2019-26 7-11 July 2019, Boston, Massachusetts
Figure 11. Human trials of the ES3 Enclosure. and geometries, helmet visor and waist ring angles, arm and leg sizing and comfort, hatch sizing, interface systems, donning and doffing procedures, and systems level integration at low pressure. Multiple test subjects have donned the suit, and some basic sizing and comfort conclusions have been garnered from the trials. While the suit is appropriate for pressurized use, there are multiple elements in need of development for pressurized testing and conclusions. One critical data point occurred when a larger test subject became temporarily entrapped inside the prototype. A subject was able to enter the hatch with some difficulty, and successfully donned the ES3 prototype for a pressurized evaluation. Upon doffing the suit, it was found that the subject could not push upwards and outwards of the suit while contracting his back adequately to fit through the hatch width. Emergency procedures were followed and the soft upper torso was removed from the hatch to allow the subject to egress quickly and safely. A very useful conclusion is that it is more difficult to get out of a rear entry space suit than it is to get into it, and sometimes it is possible to don the suit and not be able to doff it. This was not our experience with our chest entry IVA suits. Beyond this, we have clearly defined sizing maximum dimensions for evaluation prior to entry in the suit. Future suit sizing for very large test subjects will flow size changes to the soft upper torso architecture.
C. Personal Life Support System The breadboard PLSS system used an analog respiration system and space suit chamber. Various respiration rates were mimicked using the analog system, with a goal to define the maximum btu parameters of the rebreather in particular.
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Figure 12. Breadboard PLSS System test configuration.
Respiration rates were guided by NASA’s prior life support respiration guidelines. Table 1 below defines the general levels of heat, CO2, and water vapor for various metabolic rates.
Table 1. BTU and Respiration Rates 4 Met Rate Master List
BTU Watts of Heat CO2 ml/m H2O ml /m 1000 293 0.774 1.38
1200 351 0.929 1.47 1600 468 1.238 1.48 2000 586 1.548 1.25 {sic}
CO2 was introduced to the test chamber using a variable flow gauge, from a large high pressure (1000 psi)
CO2 tank. CO2 flow rates were carefully monitored during testing to conform to the defined test parameters.
Measurements of CO2 inside the chamber were required to remain below 1%.
First testing was pegged at 1000 btu equivalent, or approximately 0.77 ml / min of CO2. Based on pressure
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compensated CO2 percentage readings of the ambient air inside the chamber, CO2 levels remained below 1% and generally between 0.5% and 0.75% for a total of 6 hours for a single cartridge. Figure 13 below shows a 2 hour section of this test, along with the test end.
Figure 13. CO2% test results @ 1000 btu
Next, higher CO2 levels were introduced, starting with 1200 and then 1600 btu, with levels of 0.92 ml/m and 1.28 ml/m respectively for CO2 introduction. (Figure 14) While the NaHO scrubber cartridges were able to keep up with the 1200 btu levels, with ambient concentrations below 1%, 1600 btu levels of CO2 were too much for the cartridges and even pressure compensated levels rose above 1%. FFD has defined a threshold of maximum exertion with these style cartridges at 1200 btu, and can validate the performance at 1000 btu for an extended 6 hour period. Further evaluations are desired to more clearly define the duration of maximum exertion upper limits. This 4 performance is roughly similar to the ISS EMU in CO2. 2000 btu was also evaluated, with CO2 levels further rising over an hour long period to above 2% briefly. Figure 15 shows the CO2 percentage with the gas introduced at 1200 btu equivalent (0.92 ml/m) for the first hour, and at 2000 btu equivalent (1.58 ml/m) the second hour. Given these results we can conclude that 2000 btu CO2 output human respiration levels are not safe with this system.
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Figure 14. CO2 % at 1200 btu (first hour) and 1600 btu (second hour)
Figure 15. CO2 % (1200 btu first hour, 2000 btu second hour)
For heat and humidity, the rates were not varied for testing. Heat was introduced at a steady 305 Watts or approximately 1000 btu for each test, through a heat pad covering an aluminum water tube. Water vapor was 13 International Conference on Environmental Systems
49th International Conference on Environmental System ICES-2019-26 7-11 July 2019, Boston, Massachusetts introduced through portable humidifiers at a fixed rate of 50 ml/m, which approximates the range of water vapor defined above. Heat exchange and heat rejection was a big challenge for our Phase I efforts. The sublimator system represents one of the most unique items of a space suit PLSS, and is impossible to source off-the-shelf. FFD spent a large proportion of the SBIR Phase I project attempting to configure a functional sublimator system, with limited success. While the parameters of the porous plate, feedwater pressure, and vacuum environment are well defined, we experienced a great deal of difficulty accounting for the introduction of water into the high vacuum environment. Required vacuum levels were not met, and heat exchange was not as efficient or effective as estimated or required. Initial research defined the vacuum environment required for the sublimation process of 10-2 torr or lower. This pressure was achieved with several different chamber configurations, however, the introduction of water through the feedwater system inevitably made the chamber pressure rise again to above 5 torr, minimizing the dual phase change advantage of sublimation and causing cooling only through evaporation to the vacuum. FFD invested in increasingly more powerful vacuum pumps and eventually configured a “nested vacuum chamber” consisting of an internal high vacuum chamber with an external lower vacuum chamber to offset leakage and water vapor from the internal tank. Despite the complexity of work involving sealed pass throughs, the nested chamber setup was not any more effective at achieving medium vacuum levels. While water loop cooling occurred when using the sublimator system, and remained lower and more consistent than more simple ice-bucket style cooling, it is clear that a much more powerful vacuum pump and chamber configuration is required to truly understand and optimize a functional sublimation system. The cooling witnessed in Phase I is attributed to simple evaporative cooling. Alternative cooling methods for ground based testing have been explored, including phase change frozen gels in a cold water bath. Some rebreathers use a phase change gel canister for their cooling loop, which was trialed in the ventilation system loop; there are other water cooling systems using gels as a COTS item. An electronic peltier plate system could also work for a ground based system. In addition, NASA is currently focused on incorporating a membrane evaporator for next generation suits, which could be integrated into this system. A detailed analysis of the heat loads and metabolic rates required for our potential use cases, including lab testing, NBL testing, IVA flight scenarios, along with the requirements defined for EVA, should be considered to better understand and down-select options. As described in detail above, sublimation was generally unsuccessful during Phase I, and for this reason heat was somewhat uncontrollable in testing, rising to above 110 F in some tests. However, the sublimation system, even operating with only evaporative cooling inside the ~5 Torr chamber, was able to plateau at about 80°F, while a simple ice water bath of the heat exchanger showed only linear temperature increase from 40° to 110° F. Humidity was also a major challenge in the system. Our first configuration utilized a centrifugal water separator canister, relying on gravity and flow to pull out trace water from the ventilation loop. The centrifugal separator was completely inadequate for the level of humidity introduced, partly because it did not drain to a source collector, so water vapor quickly added up. After 2 hours of vapor introduced at 50 ml/m humidity levels regularly peaked at 98%. For this reason, desiccant dryer was introduced to the system, requiring an additional filter downstream to reduce risk of inhalation. While desiccant is not standard in US EVA systems because of the risk of inhalation, it can be safe for breathing systems and is utilized by supply companies such as Aircel and Deltech. Silica particles were used for their simplicity and ubiquity, though higher performance desiccants could be considered, such as Zeolite. Small volume desiccants of less than a couple of pounds were inadequate at removing water for any meaningful time, but a large volume canister measuring 24” long x 5” diameter was able to remove a great deal of water vapor, and keep the humidity in the system below 75% for 6 hours. However, the desiccant did leave a large amount of dust and grain in the filter downstream, reducing confidence that a single filter was adequate to eliminate inhalation risk. In addition, the large volume desiccant bowl and silica itself were by far the largest and heaviest parts of the PLSS. Finally, the desiccant is hard to handle, requiring careful transfer for baking off of water and risking contamination. Alternatives to desiccant were sought. 14 International Conference on Environmental Systems
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Ultimately the water separator architecture was explored again, this time with an active drain system in a coalescing filter to draw away and collect water vapor collected. To achieve a contained water draw-off from the separator, the drain outlet of the filter was connected to a hose barb, feeding to an inlet back upstream of the fan. The lower pressure upstream of the fan pulls out collected water droplets from the coalescer canister, and through an inline filter and sponge canister. The loss of flow is easily compensated by the fan, running at less than half of maximum voltage/amperage while achieving the target 6 SCFM delivery to the analog suit chamber. The sponge within the canister collects water effectively and the results are readily verifiable. A visible stream of water is removed from the separator, and past the sponge no water is visible. After testing with an introduction of 150 ml of water vapor over 3 hours, the sponges collected 120 ml of water, approximately. The water separation function works in 1G, and can be tilted to within approximately 20° of nadir without assistance. Future sponge inserts in the filter could improve the draining effective angle, and the system will likely work in microgravity.
Figure 16. Water drain line. Showing water flow, left, and Filter and drain line, right.
Modifications to the system, including increases to the volume of the sponge chamber, ease of interfacing with robust and low-profile hose connections, and a more robust closure indicate that a custom sponge canister is required to optimize this system. We were unable to validate this greatly improved water separation system in Phase I, and plan to continue the work as we develop the PLSS.
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Figure 17. Showing air temp (green), water temp (red/blue), and humidity % (yellow), for a test using a ice water bath for heat exchange and a low volume desiccant.
Figure 18. Showing air temp (green), water temp (red/blue), and humidity % (yellow), for the sublimator system at ~5 torr, and a large volume desiccant.
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IV. Conclusions / Next Steps Leveraging multiple and diverse contracts with in-house development funds and engineering time, FFD is beginning to assemble a complete EVA system. We have fabricated and performed fittings on our LCG and a complete space suit enclosure, and made tangible progress in defining an effective PLSS.
A. Liquid Cooling Garment While the current LCG pictured represents a major step in development, we have defined several changes to optimize the garment as we progress. This includes reducing the tubing diameters downstream of the quick disconnects, to minimize tubing bulk and stiffness. In addition, we are developing an inlet and outlet manifold to distribute water in a more compact interface. Our next garment prototype will not include sleeves to further minimize the garment bulk, and will feature a front torso zipper for easier self donning of the garment. Testing of the LCG to validate heat removal will take place using a heat vest and a water cooling loop sensor system, beginning in the spring of 2019.
B. Enclosure FFD’s first physical ES3 enclosure is a major step in visualizing our EVA system progress. Multiple elements of the prototype demand updating, with our first priority being the integration of functional, custom bearings in the arms. While all prior iterations included only bearing blanks, we have defined and are evaluating fabrication options for a full suite of wrist, arm, and shoulder bearings in the next enclosure. In addition, development in the hatch closures and life support interfaces are in work. Baseline interface elements for the chest control pack are in development, to allow user interface to control temperature, pressure, and communications.
C. Personal Life Support System FFD has completed more than 30 hours of testing of their rebreather system along with a prototype sublimator system and water cooling loop. A human respiration analog system has been built and implemented to vary output, allowing an adjustable btu equivalent in heat, water vapor, and CO2 into the system. FFD has identified many COTS components appropriate for the system, and has defined upper limits of btu for the CO2 scrubber system. Trades have been identified and some components have been rejected and replaced. System performance at various btu equivalents have been carefully logged and recorded. Multiple configurations of the system have been defined, for orbital EVA, high altitude IVA, and ground based training. FFD intends to further develop their life support system, with a focus on the rebreather loop for ground and flight applications. Refined options for the rebreather, including advanced water removal, filter upgrades, and cooling strategies are key for our implementation of a fully functional system. While pure oxygen operations remain a long-term goal, short term the focus will be on oxygen safety protocol and analysis of materials for oxygen operations including an Oxygen Compatibility Assessment (OCA). Component testing for failure and life cycling will be focus, to better understand failure conditions. A subsystem level failure mode and effects analysis (FMEA) will be executed to better understand criticality of systems and refine the design to avoid risk.
D. Human Testing Finally, FFD is partnering with Integrated Spaceflight Services to perform umbilical-based testing of the ES3 in a lab environment. A 2-axis gravity offset system is being fabricated for use in a high bay, to mimic operations in either microgravity or reduced gravity. Various EVA tasks, including space station busy boards, interfaces, geology and field research, and airlock systems will be evaluated utilizing the ES3. It is a challenge to integrate all the systems within the EVA suit for a physical test, and we look forward to this work in the fall of 2019.
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49th International Conference on Environmental System ICES-2019-26 7-11 July 2019, Boston, Massachusetts
Acknowledgements A range of individuals from NASA and beyond deserve recognition for their support and encouragement of our EVA system development, including: Amy Ross, Richard Rhodes, and Raul Blanco of NASA’s Crew Systems, Bruce Conger of Jacobs Engineering and Shane McFarland of KBR-Wyle for their support of the LCG development, and Jesse Buffington as the technical point of contact for our life support system efforts. Finally we would like to thank our professional consultants Gary Harris and Miguel Iturmendi. Thank you!
References 1. Southern Theodore C., and Moiseev, Nikolay A. “Final Frontier Design’s EVA Suit Enclosure (ESSE)”, ICES-2017-230 47th International Conference on Environmental Systems (ICES), Charleston, South Carolina 2. Harris, Gary L. “The Origins and Technology of the Advanced Extravehicular Space Suit, volume 24.” AAS History Series, 2001. 3. NASA-IG-17-018 (A-16-014-00) “NASA’s Management and Development of Space Suits” 4. Chullen, C., Conger, B., McMillin, S., Vonau, W., Kanne, B., Korona, A., and Swickrath, M. “Results from Carbon Dioxide Washout Testing Using a Suited Manikin Test Apparatus with a Space Suit Ventilation Test Loop” International Conference on Environmental Systems, 2016-071 Vienna, Austriaz 5. Campbell, C., “Advanced EMU Portable Life Support System (PLSS) and Shuttle/ISS EMU Schematics, a Comparison,” AIAA-2012-3411, 42nd International Conference on Environmental Systems (ICES), San Diego, California, July 2012 6. Jones, Harry W., and Anderson, Grant, “Need for Cost Optimization of Space Life Support Systems,” ICES- 2017-83, 47th International Conference on Environmental Systems (ICES), Charleston, South Carolina, July 2017 7. Shero, James Philip, “Porous Plate Sublimator Analysis,” November 1969, Rice University 8. Conger, Bruce and Makinen, Janice, “High Performance Torso Cooling Garment”, ICES-2016-412, 46th International Conference on Environmental Systems (ICES), Vienna Austria
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