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At least 217 records · Page 12

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NASA NTRS2008

A Freezable Heat Exchanger for Space Suit Radiator Systems

During an ExtraVehicular Activity (EVA), both the heat generated by the astronaut s metabolism and that produced by the Portable Life Support System (PLSS) must be rejected to space. The heat sources include the heat of adsorption of metabolic CO2, the heat of condensation of water, the heat removed from the body by the liquid cooling garment and the load from the electrical components. Although the sublimator hardware to reject this load weighs only 1.58 kg (3.48 lbm), an additional 3.6 kg (8 lbm) of water are loaded into the unit, most of which is sublimated and lost to space, thus becoming the single largest expendable during an eight-hour EVA. Using a radiator to reject heat from the astronaut during an EVA can reduce the amount of expendable water consumed in the sublimator. Radiators have no moving parts and are thus highly reliable. Past freezable radiators have been too heavy, but the weight can be greatly reduced by placing a small and freeze tolerant heat exchanger between the astronaut and radiator, instead of making the very large radiator freeze tolerant. Therefore, the key technological innovation to improve space suit radiator performance was the development of a lightweight and freezable heat exchanger that accommodates the variable heat load generated by the astronaut. Herein, we present the heat transfer performance of a newly designed heat exchanger that endured several freeze / thaw cycles without any apparent damage. The heat exchanger was also able to continuously turn down or turn up the heat rejection to follow the variable load.

Nabity, James A.↗

NASA NTRS2008

Feasibility of Suited 10-km Ambulation "Walkback" on the Moon

This viewgraph presentation reviews a study that examined the feasibility of having astronauts walk about 10 kilometers to the base in the event of a breakdown of the lunar rover. This was done in part to examine the possibility of having a single rover on the lunar exploration missions. Other objectives of the study are to: (1) Understand specific biomedical and human performance limitations of the suit compared to matched shirt-sleeve controls; (2) Collect metabolic and ground-reaction force data to develop an EVA simulator for use on future prebr eathe protocol verification tests (3) Provide data to estimate consum ables usage for input to suit and portable life support system (PLSS) design (4) Assess the cardiovascular and resistance exercise associa ted with partialgravity EVA for planning appropriate exploration exer cise countermeasures

Norcross, Jason↗

NASA NTRS2007

Space Suit Radiator Performance in Lunar and Mars Environments

During an ExtraVehicular Activity (EVA), both the heat generated by the astronaut's metabolism and that produced by the Portable Life Support System (PLSS) must be rejected to space. The heat sources include the heat of adsorption of metabolic CO2, the heat of condensation of water, the heat removed from the body by the liquid cooling garment and the load from the electrical components. Although the sublimator hardware to reject this load weighs only 3.48 lbs, an additional eight pounds of water are loaded into the unit of which about six to eight are sublimated and lost; this is the single largest expendable during an eight-hour EVA. Using a radiator to reject heat from the Astronaut during an EVA, we can significantly reduce the amount of expendable water consumed by the sublimator. Last year we reported on the design and initial operational assessment tests of our novel radiator designated the Radiator And Freeze Tolerant heat eXchanger (RAFT-X). Herein, we report on tests conducted in the NASA Johnson Space Center Chamber E Thermal Vacuum Test Facility. Up to 800 Btu/h of heat were rejected in lunar and Mars environments with temperatures as cold as 150 F. Tilting the radiator did not cause an observable loss in performance. The RAFT-X endured freeze/thaw cycles and in fact, the heat exchanger was completely frozen three times without any apparent damage to the unit. We were also able to operate the heat exchanger in a partially frozen configuration to throttle the heat rejection rate from 530 Btu/h at low water flow rate down to 300 Btu/h. Finally, the deliberate loss of a single loop heat pipe only degraded the heat rejection performance by about 2 to 5%.

Paul, Heather↗

NASA NTRS2008

Fan Performance Testing and Oxygen Compatibility Assessment Results for Future Space Suit Life Support Systems

An advanced portable life support system (PLSS) for the space suit will require a small, robust, and energy-efficient system to transport the ventilation gas through the space suit for lunar Extravehicular Activity (EVA) operations. A trade study identified and compared ventilation transport technologies in commercial, military, and space applications to determine which technologies could be adapted for EVA use. Based on the trade study results, five commercially available, 24volt fans were selected for performance testing at various pressures and flow rates. Measured fan parameters included fan delta-pressures, input voltages, input electrical currents, and in some cases motor windings electrical voltages and currents. In addition, a follow-on trade study was performed to identify oxygen compatibility issues and assess their impact on fan design. This paper outlines the results of the fan performance characterization testing, as well as the results from the oxygen compatibility assessment.

Jennings, Mallory A.↗

NASA NTRS2008

Heat Exchanger/Humidifier Trade Study and Conceptual Design for the Constellation Space Suit Portable Life Support System Ventilation Subsystem

As development of the Constellation Space Suit Element progresses, designing the most effective and efficient life support systems is critical. The baseline schematic analysis for the Portable Life Support System (PLSS) indicates that the ventilation loop will need some method of heat exchange and humidification prior to entering the helmet. A trade study was initiated to identify the challenges associated with conditioning the spacesuit breathing gas stream for temperature and water vapor control, to survey technological literature and resources on heat exchanger and humidifiers to provide solutions to the problems of conditioning the spacesuit breathing gas stream, and to propose potential candidate technologies to perform the heat exchanger and humidifier functions. This paper summarizes the results of this trade study and also describes the conceptual designs that NASA developed to address these issues.

Paul, Heather L.↗

NASA NTRS2009

Evaluation of Carbon Dioxide Sensors for the Constellation Space Suit Life Support System for Surface Exploration

This paper presents the findings of the trade study to evaluate carbon dioxide (CO2) sensing technologies for the Constellation (Cx) space suit life support system for surface exploration. The trade study found that nondispersive infrared absorption (NDIR) is the most appropriate high Technology Readiness Level (TRL) technology for the CO2 sensor for the Cx space suit. The maturity of the technology is high, as it is the basis for the CO2 sensor in the Extravehicular Mobility Unit (EMU). The study further determined that while there is a range of commercial sensors available, the Cx CO2 sensor should be a new design. Specifically, there are light sources (e.g., infrared light emitting diodes) and detectors (e.g., cooled detectors) that are not in typical commercial sensors due to cost. These advanced technology components offer significant advantages in performance (weight, volume, power, accuracy) to be implemented in the new sensor. The exact sensor design (light source, transmitting optics, path length, receiving optics and detector) will be specific for the Cx space suit and will be determined by the performance requirements of the Cx space suit. The paper further identifies specifications for some of the critical performance parameters as well as discussing the engineering aspects of implementing the sensor into the Portable Life Support System (PLSS). The paper then presents testing results from three CO2 sensors with respect to issues important to Extravehicular Activity (EVA) applications; stability, humidity dependence and low pressure compatibility. The three sensors include two NDIR sensors, one commercial and one custom-developed by NASA (for a different purpose), and one commercial electrochemical sensor. The results show that both NDIR sensors have excellent stability, no dependence on ambient humidity (when the ambient temperature is above the dew point) and operate in low pressure conditions and after being exposed to a full vacuum. The commercial electrochemical sensor was not suitable for the Cx space suit for surface exploration. Finally, the paper identifies a number of techniques currently under development that offer significant advantages for EVA applications. These include miniaturized, room temperature, solid electrolyte systems and advanced optical detectors.

Dietrich, Daniel L.↗

NASA NTRS2009

Heat Exchanger/Humidifier Trade Study and Conceptual Design for the Constellation Space Suit Portable Life Support System Ventilation Subsystem

Paul, Heather L.↗

NASA NTRS2009

Fan Performance Testing and Oxygen Compatibility Assessment Results for Future Space Suit Life Support Systems

An advanced portable life support system (PLSS) for the space suit will require a small, robust, and energyefficient system to transport the ventilation gas through the space suit for lunar Extravehicular Activity (EVA) operations. A trade study identified and compared ventilation transport technologies in commercial, military, and space applications to determine which technologies could be adapted for EVA use. Based on the trade study results, five commercially available, 24-volt fans were selected for performance testing at various pressures and flow rates. Measured fan parameters included fan delta-pressures, input voltages, input electrical currents, and in some cases motor windings electrical voltages and currents. In addition, a follow-on trade study was performed to identify oxygen compatibility issues and assess their impact on fan design. This paper outlines the results of the fan performance characterization testing, as well as the results from the oxygen compatibility assessment.

Paul, Heather L.↗

NASA NTRS2009

The Effect of Center of Gravity and Anthropometrics on Human Performance in Simulated Lunar and Mars Gravity

Drawing from the experiences of the Apollo missions, it is evident that the off nominal center of gravity (CG) induced by the portable life support system (PLSS) had significant impact on the locomotion stability of the crew. This in turn is believed to have been a major contributor to the high numbers of falls and high metabolic rates experienced by the crew, and thus significantly hampered the crew s performance. With this in mind, the EVA Physiology, Systems and Performance (EPSP) group at the NASA Johnson Space Center (JSC) has been conducting tests to assess how spacesuit CG location impacts human performance in simulated lunar and Mars gravity. The results acquired to date show correlations between CG location and performance. However, noticeable variations in the performance data have been observed across subjects for fixed CG configurations. Consequently, it was hypothesized that this variability may be attributed to the anthropometrics of the different test subjects. It was further hypothesized that trunk-to-height ratio (THR) may be directly correlated to performance in reduced gravity; i.e. subjects with increased THR may have increased performance. To test this hypothesis, lunar and Mars gravity test data acquired over three years during NASA Neural Buoyancy Lab (NBL) tests and NASA Extreme Environment Missions Operation (NEEMO) missions were analyzed against THR, height, trunk length, and subject body mass/weight. The results of the study supported the hypothesis relating THR and performance, while the other three anthropometric parameters did not provide consistent correlations with performance. This in turn suggests that human performance in reduced gravity may be more dependent on anthropometric proportions than on body segment lengths and mass/weight.

Mulugeta, Lealem↗

NASA NTRS2009

Hollow Fiber Space Suit Water Membrane Evaporator Development for Lunar Missions

The Space Suit Water Membrane Evaporator (SWME) is the baseline heat rejection technology selected for development for the Constellation lunar suit. The Hollow Fiber (HoFi) SWME is being considered for service in the Constellation Space Suit Element (CSSE) Portable Life Support Subsystem (PLSS) to provide cooling to the thermal loop through water evaporation to the vacuum of space. Previous work described the test methodology and planning to compare the test performance of three commercially available hollow fiber materials as alternatives to the sheet membrane prototype for SWME: 1) porous hydrophobic polypropylene, 2) porous hydrophobic polysulfone, and 3) ion exchange through nonporous hydrophilic modified Nafion. Contamination tests were performed to probe for sensitivities of the candidate SWME elements to organics and non-volative inorganics expected to be found in the target feedwater source, i.e., potable water provided by the vehicle. The resulting presence of precipitate in the coolant water could plug pores and tube channels and affect the SWME performance. From this prior work, a commercial porous hydrophobic hollow fiber was selected to satisfy both the sensitivity question and the need to provide 800 W of heat rejection. This paper describes the trade studies, the design methodology, and the hollow fiber test data used to design a full

Bue, Grant C.↗

NASA NTRS2009

Results of the Particulate Contamination Control Trade Study for Space Suit Life Support Development

As the United States plans to return astronauts to the moon and eventually to Mars, designing the most effective, efficient, and robust space suit life support system that will operate successfully in these dusty environments is vital. There is some knowledge of the contaminants and level of infiltration expected from the Lunar and Mars dust, however risk mitigation strategies and filtration designs to prevent contamination within the space suit life support system are still undefined. A trade study was initiated to identify and address these concerns, and to develop new requirements for the Constellation Space Suit Element (CSSE) Portable Life Support System (PLSS). This trade study investigates historical methods of particulate contamination control in space suits and vehicles, and evaluated the possibility of using commercial technologies for this application. In addition, the trade study examined potential filtration designs. This paper summarizes the results of this trade study.

Cognata, Thomas J.↗

NASA NTRS2008

Regenerative Blower for EVA Suit Ventilation Fan

Portable life support systems in future space suits will include a ventilation subsystem driven by a dedicated fan. This ventilation fan must meet challenging requirements for pressure rise, flow rate, efficiency, size, safety, and reliability. This paper describes research and development that showed the feasibility of a regenerative blower that is uniquely suited to meet these requirements. We proved feasibility through component tests, blower tests, and design analysis. Based on the requirements for the Constellation Space Suit ventilation fan, we designed the critical elements of the blower. We measured the effects of key design parameters on blower performance using separate effects tests, and used the results of these tests to design a regenerative blower that will meet the ventilation fan requirements. We assembled a proof-of-concept blower and measured its performance at low pressures that simulate a PLSS environment. We obtained head/flow performance curves over a range of operating speeds, identified the maximum efficiency point for the blower, and used these results to specify the design and operating conditions for the ventilation fan. We designed a compact motor that can drive the blower under all anticipated operating requirements and operate with high efficiency during normal operation. We identified materials for the blower that will enhance safety for operation in a lunar environment. We produced a solid model that illustrates the final design. The proof-of-concept blower produced the flow rate and pressure rise needed for the CSSS ventilation subsystem while running at 5400 rpm and consuming only 9 W of electric power and using a non-optimized, commercial motor and controller and inefficient bearings. Scaling the test results to a complete design shows that a lightweight, compact, reliable, and low power blower can meet the performance requirements for future PLSSs.

Paul, Heather↗

NASA NTRS2010

Biosensors for EVA: Improved Instrumentation for Ground-based Studies

During lunar excursions in the EVA suit, real-time measurement of metabolic rate is required to manage consumables and guide activities to ensure safe return to the base. Metabolic rate, or oxygen consumption (VO2), is normally measured from pulmonary parameters but cannot be determined with standard techniques in the oxygen-rich environment of a spacesuit. Our group has developed novel near infrared spectroscopic (NIRS) methods to calculate muscle oxygen saturation (SmO 2), hematocrit, and pH, and we recently demonstrated that we can use our NIRS sensor to measure VO 2 on the leg during cycling. Our NSBRI project has 4 objectives: (1) increase the accuracy of the metabolic rate calculation through improved prediction of stroke volume; (2) investigate the relative contributions of calf and thigh oxygen consumption to metabolic rate calculation for walking and running; (3) demonstrate that the NIRS-based noninvasive metabolic rate methodology is sensitive enough to detect decrement in VO 2 in a space analog; and (4) improve instrumentation to allow testing within a spacesuit. Over the past year we have made progress on all four objectives, but the most significant progress was made in improving the instrumentation. The NIRS system currently in use at JSC is based on fiber optics technology. Optical fiber bundles are used to deliver light from a light source in the monitor to the patient, and light reflected back from the patient s muscle to the monitor for spectroscopic analysis. The fiber optic cables are large and fragile, and there is no way to get them in and out of the test spacesuit used for ground-based studies. With complimentary funding from the US Army, we undertook a complete redesign of the sensor and control electronics to build a novel system small enough to be used within the spacesuit and portable enough to be used by a combat medic. In the new system the filament lamp used in the fiber optic system was replaced with a novel broadband near infrared LED light source. The compact grating spectrometer was replaced with a chip-scale spectrometer. With this new design, the sensor is 4 in 2 in 0.5 in, weighs 60 g, and no fiber optic cables are needed. The sensor, which contains the light source and the spectrometer, is adhered directly to the skin with medical grade adhesive. The sensor can be powered via the USB port of the laptop computer that controls the sensor operation. Alternatively, for studies in the spacesuit, the sensor can be powered by a small battery pack and operated by an ultra-portable hand-held computer. Both the handheld computer and battery pack will easily fit within the PLSS of the test spacesuit. System automation was significantly improved, to add features suggested by our colleagues in the Cardiovascular Laboratory and the NASA JSC Exercise Physiology and Countermeasures Project. The functionality and portability of this system were demonstrated in our UMass laboratory.

Soller, B.↗

NASA NTRS2010

Lunar Dust-Tolerant Electrical Connector

An electrical connector was developed that is tolerant of the presence of lunar dust. Novel features of the connector include the use of a permeable membrane to act both as a dust barrier and as a wiper to limit the amount of dust that makes its way into the internal chamber of the connector. The development focused on the Constellation lunar extravehicular activity (EVA) spacesuit s portable life support system (PLSS) battery recharge connector; however, continued research is applying this technology to other lunar surface systems such as lunar rover subsystems and cryogenic fluid transfer connections for in-situ resource utilization (ISRU) applications. Lunar dust has been identified as a significant and present challenge in future exploration missions. In addition to posing contamination and health risks for human explorers, the interlocking, angular nature of lunar dust and its broad grain size distribution make it particularly harmful to mechanisms with which it may come into contact. All Apollo lunar missions experienced some degree of equipment failure because of dust, and it appears that dust accumulation on exposed material is unavoidable and difficult to reverse. Both human EVA and ISRU activities are on the mission horizon and are paramount to the establishment of a permanent human base on the Moon. Reusable and dust-tolerant connection mechanisms are a critical component for mission success. The need for dust-tolerant solutions is also seen in utility work and repair, mass transit applications, construction, mining, arctic and marine environments, diving (search and rescue), and various operations in deserts, where dust or sand clogging and coating different mechanisms and connections may render them difficult to operate or entirely inoperable.

Herman, Jason↗

NASA NTRS2010

Modeling Of Metabolic Heat Regenerated Temperature Swing Adsorption (MTSA) Subassembly For Prototype Design

This paper describes modeling methods for the three core components of a Metabolic heat regenerated Temperature Swing Adsorption (MTSA) subassembly: a sorbent bed, a sublimation (cooling) heat exchanger (SHX), and a condensing icing (warming) heat exchanger (CIHX). The primary function of the MTSA, removing carbon dioxide from a space suit Portable Life Support System (PLSS) ventilation loop, is performed via the sorbent bed. The CIHX is used to heat the sorbent bed for desorption and to remove moisture from the ventilation loop while the SHX is alternately employed to cool the sorbent bed via sublimation of a spray of water at low pressure to prepare the reconditioned bed for the next cycle. This paper describes subsystem heat a mass transfer modeling methodologies relevant to the description of the MTSA subassembly in Thermal Desktop and SINDA/FLUINT. Several areas of particular modeling interest are discussed. In the sorbent bed, capture of the translating carbon dioxide (CO2) front and associated local energy and mass balance in both adsorbing and desorbing modes is covered. The CIHX poses particular challenges for modeling in SINDA/FLUINT as accounting for solids states in fluid submodels are not a native capability. Methods for capturing phase change and latent heat of ice as well as the transport properties across a layer of low density accreted frost are developed. This extended modeling capacity is applicable to temperatures greater than 258 K. To extend applicability to the minimum device temperature of 235 K, a method for a mapped transformation of temperatures from below the limit temperatures to some value above is given along with descriptions for associated material property transformations and the resulting impacts to total heat and mass transfer. Similar considerations are given for the SHX along with functional relationships for areal sublimation rates as limited by flow mechanics in t1he outlet duct.

Bower, Chad E.↗

NASA NTRS2010

Testing and Results of Vacuum Swing Adsorption Units for Spacesuit Carbon Dioxide and Humidity Control

A principal concern for extravehicular activity (EVA) space suits is the capability to control carbon dioxide (CO2) and humidity (H2O) for the crewmember. The release of CO2 in a confined or unventilated area is dangerous for human health and leads to asphyxiation; therefore, CO2 and H2O become leading factors in the design and development of the spacesuit. An amine-based CO2 and H2O vapor sorbent for use in pressure-swing re-generable beds has been developed by Hamilton Sundstrand. The application of solid-amine materials with vacuum swing adsorption technology has shown the capacity to concurrently manage CO2 and H2O levels through a fully regenerative cycle eliminating mission constraints imposed with non-regenerative technologies. Two prototype solid amine-based systems, known as rapid cycle amine (RCA), were designed to continuously remove CO2 and H2O vapor from a flowing ventilation stream through the use of a two-bed amine based, vacuum-swing adsorption system. The Engineering and Science Contract Group (ESCG) RCA is the first RCA unit implementing radial flow paths, whereas the Hamilton Sundstrand RCA was designed with linear flow paths. Testing was performed in a sea-level pressure environment and a reduced-pressure environment with simulated human metabolic loads in a closed-loop configuration. This paper presents the experimental results of laboratory testing for a full-size and a sub-scale test article. The testing described here characterized and evaluated the performance of each RCA unit at the required Portable Life Support Subsystem (PLSS) operating conditions. The test points simulated a range of crewmember metabolic rates. The experimental results demonstrate the ability of each RCA unit to sufficiently remove CO2 and H2O from a closed loop ambient or subambient atmosphere.

McMillin, Summer↗

NASA NTRS2011

NEEMO 14: Evaluation of Human Performance for Rover, Cargo Lander, Crew Lander, and Exploration Tasks in Simulated Partial Gravity

The ultimate success of future human space exploration missions is dependent on the ability to perform extravehicular activity (EVA) tasks effectively, efficiently, and safely, whether those tasks represent a nominal mode of operation or a contingency capability. To optimize EVA systems for the best human performance, it is critical to study the effects of varying key factors such as suit center of gravity (CG), suit mass, and gravity level. During the 2-week NASA Extreme Environment Mission Operations (NEEMO) 14 mission, four crewmembers performed a series of EVA tasks under different simulated EVA suit configurations and used full-scale mockups of a Space Exploration Vehicle (SEV) rover and lander. NEEMO is an underwater spaceflight analog that allows a true mission-like operational environment and uses buoyancy effects and added weight to simulate different gravity levels. Quantitative and qualitative data collected during NEEMO 14, as well as from spacesuit tests in parabolic flight and with overhead suspension, are being used to directly inform ongoing hardware and operations concept development of the SEV, exploration EVA systems, and future EVA suits. OBJECTIVE: To compare human performance across different weight and CG configurations. METHODS: Four subjects were weighed out to simulate reduced gravity and wore either a specially designed rig to allow adjustment of CG or a PLSS mockup. Subjects completed tasks including level ambulation, incline/decline ambulation, standing from the kneeling and prone position, picking up objects, shoveling, ladder climbing, incapacitated crewmember handling, and small and large payload transfer. Subjective compensation, exertion, task acceptability, and duration data as well as photo and video were collected. RESULTS: There appear to be interactions between CG, weight, and task. CGs nearest the subject s natural CG are the most predictable in terms of acceptable performance across tasks. Future research should focus on understanding the interactions between CG, mass, and subject differences.

Chappell, Steven P.↗

NASA NTRS2011

Testing and Oxygen Assessment Results for a Next Generation Extravehicular Activity Portable Life Support System Fan

NASA is designing a next generation Extravehicular Activity (EVA) Portable Life Support System (PLSS) for use in future surface exploration endeavors. To meet the new requirements for ventilation flow at nominal and buddy modes, a fan has been developed and tested. This paper summarizes the results of the performance and life cycle testing efforts conducted at the NASA Johnson Space Center. Additionally, oxygen compatibility assessment results from an evaluation conducted at White Sands Test Facility (WSTF) are provided, and lessons learned and future recommendations are outlined.

Paul, Heather L.↗