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Technical Paper

Spacecraft Radiator Freeze Protection Using a Regenerative Heat Exchanger with Bypass Setpoint Temperature Control

Spacecraft that must operate in cold environments at reduced heat load are at risk of radiator freezing. For a vehicle that lands at the Lunar South Pole, the design thermal environment is 215 K, but the radiator working fluid must also be kept from freezing during the 0 K sink of transit. A radiator bypass flow setpoint control design such as those used on the Space Shuttle Orbiter and ISS would require more than 30% of the design heat load to avoid radiator freezing during transit - even with a very low freezing point working fluid. By changing the traditional active thermal control system (ATCS) architecture to include a regenerating heat exchanger inboard of the radiator and using a regenerator bypass flow control valve to maintain system setpoint, the required minimum system heat load can be reduced by more than half. This gives the spacecraft much more flexibility in design and operation. The present work describes the regenerator bypass ATCS setpoint control methodology.
Technical Paper

Air Quality Standards for Space Vehicles and Habitats

NASA has unique requirements for the development and application of air quality standards for human space flight. Such standards must take into account the continuous nature of exposures, the possibility of increased susceptibility of crewmembers to the adverse effects of air pollutants because of the stresses of space flight, and the recognition that rescue options may be severely limited in remote habitats. NASA has worked with the National Research Council Committee on Toxicology (NRCCOT) since the early 1990s to set and document appropriate standards. The process has evolved through 2 rounds. The first was to set standards for the space station era, and the second was to set standards for longer stays in space and update the original space station standards. The update was to be driven by new toxicological data and by new methods of risk assessment for predicting safe levels from available data. The last phase of this effort has been completed.
Journal Article

A Comparison of the Apollo and Early Orion Environmental Control, Life Support and Active Thermal Control System's Driving Requirements and System Mass

The Orion Crew and Service Modules are often compared to the Apollo Command and Service Modules due to their similarity in basic mission objective: both were dedicated to getting a crew to lunar orbit and safely returning them to Earth. Both spacecraft rely on the environmental control, life support and active thermal control systems (ECLS/ATCS) for the basic functions of providing and maintaining a breathable atmosphere, supplying adequate amount of potable water and maintaining the crew and avionics equipment within certified thermal limits. This assessment will evaluate the driving requirements for both programs and highlight similarities and differences. Further, a short comparison of the two system architectures will be examined including a side by side assessment of some selected system's hardware mass.
Technical Paper

The Headache of Carbon Dioxide Exposures

Carbon dioxide (CO2), a natural product of human metabolism, accumulates quickly in sealed environments when humans are present, and can induce headaches, among other symptoms. Major resources are expended to control CO2 levels to concentrations that are tolerable to the crews of spacecraft and submersible craft. It is not practical to control CO2 levels to those found in the ambient environment on earth. As NASA looks ahead to long-duration missions conducted far from earth, difficult issues arise related to the management and effects of human exposure to CO2. One is the problem of “pockets” of CO2 in the habitat caused by excess generation of the gas in one location without a mechanism to purge the area with fresh air. This results in the crew rebreathing CO2 from their exhaled breath, exposing them to a much higher concentration of CO2 than whole-module measurements would suggest. Another issue is the potential increased sensitivity to CO2 in microgravity.
Technical Paper

Validation of the Volatile Organic Analyzer (VOA) Aboard the International Space Station

The Volatile organic analyzer (VOA) has been operated on the International Space Station (ISS) throughout 2002, but only periodically due to software interface problems. This instrument provides near real-time data on the concentration of target volatile organic contaminants in the spacecraft atmosphere. During 2002, a plan to validate the VOA operation on orbit was implemented using an operational scheme to circumvent the software issues. This plan encompassed simultaneous VOA sample runs and collection of archival air samples in grab sample containers (GSC). Agreement between the results from GSC and VOA samples is needed to validate the VOA for operational use. This paper will present the VOA validation data acquired through November 2002.
Technical Paper

Immobilized Antimicrobials for the Enhanced Control of Microbial Contamination

The active control of problematic microbial populations aboard spacecraft, and within future lunar and planetary habitats is a fundamental Advanced Life Support (ALS) requirement to ensure the long-term protection of crewmembers from infectious disease, and to shield materials and equipment from biofouling and biodegradation. The development of effective antimicrobial coatings and materials is an important first step towards achieving this goal and was the focus of our research. A variety of materials were coated with antibacterial and antifungal agents using covalent linkages. Substrates included both granular media and materials of construction. Granular media may be employed to reduce the number of viable microorganisms within flowing aqueous streams, to inhibit the colonization and formation of biofilms within piping, tubing and instrumentation, and to amplify the biocidal activity of low aqueous iodine concentrations.
Technical Paper

The Portable Monitor for Measuring Combustion Products Aboard the International Space Station

The Toxicology Laboratory at Johnson Space Center (JSC) had provided the combustion products analyzer (CPA) since the early 1990s to monitor the spacecraft atmosphere in real time if a thermodegradation event occurred aboard the Shuttle. However, as the operation of the International Space Station (ISS) grew near, an improved CPA was sought that would include a carbon monoxide sensor that did not have a cross-sensitivity to hydrogen. The Compound Specific Analyzer-Combustion Products (CSA-CP) was developed for use on the International Space Station (ISS). The CSA-CP measures three hazardous gases, carbon monoxide, hydrogen cyanide, and hydrogen chloride, as well as oxygen. The levels of these compounds in the atmosphere following a thermodegradation event serve as markers to determine air quality. The first permanent ISS crew performed the CSA-CP checkout operations and collected baseline data shortly after arrival aboard the ISS in December 2000.
Technical Paper

The Volatile Organic Analyzer (VOA) Aboard the International Space Station

The Volatile Organic Analyzer (VOA) was launched to the International Space Station (ISS) aboard STS-105 in August 2001. This instrument has provided the first near real-time data on the concentrations of trace contaminants in a spacecraft atmosphere. The VOA data will be used to assess air quality on ISS in nominal and contingency situations. Until the VOA presence on ISS, archival samples that were analyzed weeks if not months after the flight were the only means to obtain spacecraft air quality data on volatile organic compounds (VOCs). Especially in contingency situations, real-time data is important to help direct crew response and measure the effectiveness of decontamination efforts. The development and certification of the VOA has been chronicled in past ICES papers. This paper will discuss the preparation of the VOA for ISS operations. Also, examples of VOA data acquired during flight will be presented to demonstrate the value of the instrument in assessing the ISS environment.
Technical Paper

Evaluation of a Portable Carbon Dioxide Monitor for Use Aboard the International Space Station

The crew of flight 2A.1 that manned the International Space Station (ISS) assembly mission (STS-96) in May 1999 experienced symptoms that they attributed to poor air quality while working in the ISS modules. Some of these symptoms suggested that an accumulation of carbon dioxide (CO2) in the work area could have contributed to temporary health impacts on the crew. Currently, a fixed-position CO2 monitor in the FGB is the only means of measuring this air contaminant aboard ISS. As a result of this incident, NASA directed the Toxicology Laboratory at Johnson Space Center (JSC) to deliver a portable CO2 monitor for the next ISS assembly mission (STS-101). The Toxicology Laboratory developed performance requirements for a CO2 monitor and surveyed available CO2 monitoring technologies. The selected portable CO2 monitor uses nondispersive infrared spectroscopy for detection. This paper describes this instrument, its operation, and presents the results from ground-based performance testing.
Technical Paper

A Second Generation Volatile Organic Analyzer for the International Space Station

Experiences during the Shuttle and NASA/Mir programs illustrated the need for a real-time volatile organic analyzer (VOA) to assess the impact of air quality disruptions on the International Space Station (ISS). Toward this end, a joint development by the Toxicology Laboratory at Johnson Space Center and Graseby Dynamics (Watford, UK) produced a 1st generation VOA that has been delivered and is ready for the first 5 years of ISS operation. Criteria for the selection of the 1st generation VOA included minimizing the size, weight, and power consumption while maintaining analytical performance. Consequently, a VOA system based upon gas chromatography/ion mobility spectrometry (GC/IMS) was selected in the mid-90’s. A smaller, less resource-intensive device than the 1st generation VOA will be needed as NASA looks beyond ISS operations. During the past three years, efforts to reduce the size of ion mobility spectrometers have been pursued.
Technical Paper

Toxicological Assessment of Sealed Spacecraft Modules

Spacecraft modules that are last purged with clean air several months before they are entered by humans on orbit require careful management. The crew must not be exposed to harmful concentrations of air pollutants when they first enter. The magnitude of the pollution the crew will encounter depends on the volume of the module, the length of time since the last clean-air purge or scrub, the inherent offgassing rate of the materials in the module, the interior temperature of the module while offgassing occurs, and the system leak rate. The time of the last module purge or scrub can be several months before crew entry, so it is essential that the offgassing rate within the module be measured over a suitable interval of time to estimate pollution levels with confidence. Air samples were taken from the STS-74 Russian Docking Module, the STS-79 Spacehab, and the ISS Node 1 prior to launch to predict pollution levels at crew first entry.
Technical Paper

Reduction in the Iodine Content of Shuttle Drinking Water: Lessons Learned

Iodine is the disinfectant used in U.S. spacecraft potable water systems. Recent long-term testing on human subjects has raised concerns about excessive iodine consumption. Efforts to reduce iodine consumption by Shuttle crews were initiated on STS-87, using hardware originally designed to deiodinate Shuttle water prior to transfer to the Mir Space Station. This hardware has several negative aspects when used for Shuttle galley operations, and efforts to develop a practical alternative were initiated under a compressed development schedule. The alternative Low Iodine Residual System (LIRS) was flown as a Detailed Test Objective on STS-95. On-orbit, the LIRS imparted an adverse taste to the water due to the presence of trialkylamines that had not been detected during development and certification testing. A post-flight investigation revealed that the trialkylamines were released during gamma sterilization of the LIRS resin materials.
Technical Paper

Thermal Performance of the Radiator Advanced Demonstrator

Space suits for advanced missions have baselined radiators as the primary means of heat rejection in order to minimize consumables and logistics requirements. While radiators have been used in the active thermal control system for spacecraft since Gemini, the use of radiators in spacesuits introduces many unique requirements. These include the ability to reduce the amount of heat rejection when overcooling or overheating of the crew member is a concern. Overcooling can occur with low metabolic rates, cold environments or a combination of the two, and overheating can occur with high metabolic rates in a warm environment. The main goal of the Radiator Advanced Demonstrator (RAD) program is to build and fly a radiator on the current Extravehicular Mobility Unit (EMU) in order to verify thermal performance capabilities in actual flight conditions. The RAD incorporates an aluminum plate separated from the primary water panel with a silicone gasket.
Technical Paper

Microbiological Analysis of Water in Space

One of the proposed methods for monitoring the microbial quality of the water supply aboard the International Space Station is membrane filtration. We adapted this method for space flight by using an off-the-shelf filter unit developed by Millipore. This sealed unit allows liquid to be filtered through a 0.45 μm cellulose acetate filter that sits atop an absorbent pad to which growth medium is added. We combined a tetrazolium dye with R2A medium to allow microbial colonies to be seen easily, and modified the medium to remain stable over 70 weeks at 25°C. This hardware was assembled and tested in the laboratory and during parabolic flight; a modified version was then flown on STS-66. After the STS-66 mission, a back-up plastic syringe and an all-metal syringe pump were added to the kit, and the hardware was used successfully to evaluate water quality aboard the Russian Mir space station.
Technical Paper

Space Station Radiation Dosimetry and Health Risk Assessment

Current dosimetric practices do not provide comprehensive classification of high-energy charged particle radiation, so that the ability to adequately project health risk to astronaut crews is limited. To address this shortcoming in dosimetry for Space Station missions, a new generation of active radiation monitors is being developed to supplement traditional dosimetry. One active monitor is a Tissue Equivalent Proportional Counter (TEPC) to measure the linear energy transfer (LET) spectrum of space radiation. Two versions of a second type of active monitor, the Charged Particle Directional Spectrometer (CPDS), will be deployed, one internal and one external to the Station. The CPDS consists of a stack of lithium-drifted silicon detectors used to classify the radiation by particle charge and energy. The comprehensive data set obtained by using the TEPC and the CPDS permits significant improvement in assessing crew radiation exposures.
Technical Paper

Regenerable Biocide Delivery Unit

The Microbial Check Valve (MCV) is used on the Space Shuttle to impart an iodine residual to the drinking water to maintain microbial control. Approximately twenty MCV locations have been identified in the Space Station Freedom design, each with a 90 day life. This translates to 2400 replacement units in 30 years of operation. An in situ regeneration concept has been demonstrated that will reduce this replacement requirement to less than 300 units based on data to date and potentially fewer as further regenerations are accomplished. A totally automated system will result in significant savings in crew time, resupply requirements and replacement costs. An additional feature of the device is the ability to provide a concentrated biocide source (200 mg/liter of I2) that can be used to superiodinate systems routinely or after a microbial upset. This program was accomplished under NASA Contract Number NAS9-18113.