and
N.J.C. Packham
Lockheed Engineering & Sciences Company, 2400 NASA Road 1, Houston, Texas 77058, U.S.A.
Future NASA missions to explore the solar system will be long-duration missions, requiring human life support systems which must operate with very high reliability over long periods of time. Such systems must be highly regenerative, requiring minimum resupply, to enable the crews to be largely self-sufficient. These regenerative life support systems will use a combination of higher plants, microorganisms, and physicochemical processes to recycle air and water, produce food, and process wastes. A key step in the development of these systems is establishment of a human-rated test facility specifically tailored to evaluation of closed, regenerative life supports systems -- one in which long-duration, large-scale testing involving human test crews can be performed. Construction of such a facility, the Advanced Life Support Program's (ALS) Human-Rated Test Facility (HRTF), has begun at NASA's Johnson Space Center, and definition of systems and development of initial outfitting concepts for the facility are underway. This paper will provide an overview of the HRTF project plan, an explanation of baseline configurations, and descriptive illustrations of facility outfitting concepts.
Regenerative life support systems, based on a combination of biological and physicochemical components, may be used on future missions in low-Earth orbit, in transit to other planetary bodies, and on lunar and planetary surfaces. A regenerative life support system incorporates biological components in the synthesis, purification and regeneration of basic life support commodities. Interactions of plants and microbial species with the environment are complex, dynamic, and currently less understood than physicochemical processes. Physicochemical processes are not used to provide food; however, plants have a long history of doing this very efficiently. Higher plants in life support systems will be utilized in food production, CO2 uptake, and O2 release and, in concert with microbial systems, will support water purification.
A regenerative life support system will provide numerous advantages to the human space program, including reduced launch mass over the life of a long-duration mission, fewer and less time-critical logistic revisits, and an enhanced crew environment (i.e., fresh food and the psychological benefits of growing plants).
NASA's ALS Program has included the development of a breadboard facility, which is a non-human-rated test facility for crop production in a closed, ground-based system. The evolution of the ALS program at JSC is shown conceptually in Figure 1. Other regenerative life support functions, such as waste management, atmosphere control, and food processing are being pursued independently.
Fig. 1. Advanced life support system program evolution
The program has reached the point where the next logical step in development is the design and construction of the human-rated, ground-based regenerative life support system test facility necessary to conduct full-scale, integrated, long-duration demonstrations and evaluations of the regenerative life support system concept. At the Johnson Space Center (JSC), project planning activities, system requirements definition, and basic facility construction have already begun with respect to such a facility. The compilation of these ongoing efforts is referred to as the ALS Program's Human-Rated Test Facility (HRTF) Project.
Comprehensive testing of a human-rated regenerative life support system on Earth is critical for the development of such a system for extraterrestrial use. The overarching objective of the HRTF Project is to acquire the information and operational experience necessary to define performance and design requirements for advanced, regenerative life support systems which will be utilized by future flight systems. Extended-duration testing of a full-scale, integrated, regenerative life support system performed in the HRTF under closed, controlled conditions with human test subjects will meet this objective.
A primary facility objective is to support the physical integration of regenerative physicochemical and biological life support subsystems to create fully functional air revitalization, water recovery, biomass (food) production, solid waste processing/resource recovery, and thermal management systems. The ability to accommodate long-duration, closed-loop testing of these integrated systems within a large-scale control volume is another key HRTF objective. Also important is supporting the evaluation of integrated control strategies and data acquisition approaches for the various subsystems comprising the complex system.
The ability to accommodate testing pertinent to disciplines other than advanced life support is an additional benefit and thus a secondary objective of the HRTF. Human factors play a significant role in HRTF design with respect to maintaining test crew productivity and ensuring their overall comfort, which are factors vital to the success of long-duration tests. Cooperation between the advanced life support and human factors disciplines throughout all phases of HRTF development will help ensure test crew efficiency and well-being and will offer a unique, firsthand insight into human engineering concerns with respect to planetary habitat design. Medical disciplines as human physiology, psychology, and sociology, will also benefit from cooperative efforts in support of HRTF human testing.
To accomplish the above project objectives, the HRTF must be capable of supporting crew size and test duration scenarios representative of future extraterrestrial missions. Further, to provide a basis from which a set of system requirements can be derived, a reference mission scenario must be established for the HRTF. Through definition of such a mission scenario a tangible set of generic system operating parameters can be created, to which all elements of the HRTF can then be designed. The HRTF reference mission timeline (Figure 2) provides a simple yet reasonably representative set of system and facility operating guidelines, including mission duration, crew size, crew changeout schedule, and anticipated off-nominal operating conditions.
Fig. 2. HRTF reference mission timeline
The scenario dictates that the HRTF accommodate crews of four persons on a normal basis, and accommodate up to eight persons for short-duration (48 hour) crew changeout activities. Testing will be comprised of two distinct phases:
The durations of these two test phases are sixty days and one year, respectively. The HRTF systems will be designed to support smooth transitioning between these two test phases and will support investigations relating to the evolution of the regenerative life support system from a predominantly physicochemically-based system to one which is predominantly biologically-based. Additionally, to investigate the full range of system performance characteristics, off-nominal conditions will be imposed on the test scenario such as reduction of crew metabolic loading during extended duration extravehicular activities.
With respect to providing life support to the crews throughout the extended tests, the HRTF will be required to perform the following functions: air revitalization, water recovery, biomass (food) production, solid waste processing/resource recovery, and thermal management. To accomplish these basic functions, the HRTF will also require adequate control and monitoring provisions and adequate information and data analysis capabilities to support ongoing test activities and post-test reporting.
As a NASA-JSC facility, the HRTF will additionally be required to abide by established design and operational guidelines within which the system requirements described above will be satisfied. The facility must meet general safety, reliability, quality assurance, and maintainability requirements as previously established both by NASA and JSC. The facility must meet established medical and health maintenance requirements to ensure the well-being of the crew and test support personnel during all phases of test operations. The facility must also meet established human factors requirements applicable to crew habitation during their extended periods of confinement.
The reference facility configuration (Figure 3) depicts five major functionally distinct chambers joined by an interconnecting transfer tunnel and accessed via an airlock. Also shown are "scars" which permit the expansion of the overall facility by the addition of an additional two chambers to support potential future program needs. The five major chambers, each measuring 4.6 m in diameter and 11.3 m in length, have identical basic interior structures consisting of two decks, support beams, and stairway and ladder accesses (Figure 4). Each chamber has dual entry/egress hatches: a normal-use hatch at the forward end of the chamber, and an emergency access hatch at the aft end. Figure 5 shows two of the five chambers installed in the facility.
Fig. 3. HRTF conceptual reference configuration
Fig. 4. HRTF chamber interior structure
The HRTF project will be comprised of three distinct segments which will follow parallel design, development, integration, and testing paths:
This partitioning of the project relates directly back to the overarching objective of the HRTF. The multichamber facility, including the five major chambers, airlock, interconnecting transfer tunnel, internal and external utilities, test data acquisition provisions, and external supporting facilities, provides the basic structure in which to conduct closed, controlled life support testing on a large scale. The life support provisions support integrated testing of biological and physicochemical life support systems--a major thrust of the ALS Program--in the areas of air revitalization, water recovery, food production, solid waste processing, and thermal management. And the crew accommodations provide a comfortable, productive environment for the test crews during the long-duration missions.
Fig. 5. Two of the five HRTF chambers installed in the facility
Following are further descriptions of the elements comprising the three HRTF project segments as well as the test subject crew. These three segments, combined with the crew, will comprise the integrated, functioning regenerative life support system.
Multichamber Facility: The multichamber facility, including the five major chambers, airlock, interconnecting transfer tunnel, internal and external utilities, test data acquisition provisions, and external supporting facilities, provides the basic structure in which to conduct closed, controlled life support testing on a large scale.
Basic chamber complex. The basic chamber complex is an interconnected multichamber facility which provides atmospheric isolation of the chamber internal atmosphere from the ambient environment. This complex is comprised of the chamber cylinders, the interconnecting transfer tunnel, tunnel adapter sections, decking, hatches, penetration plates, and support cradles.
Chamber internal utilities. The internal utilities of the basic chamber complex provide distribution of essential utilities (e.g., power, data, communications, fluid distribution, ventilation, thermal control) from the internal chamber systems to each other and--via penetration plates--to and from the external chamber utilities.
Chamber external utilities. The basic chamber complex external utilities provide distribution of the utilities to and from the chamber internal utilities via penetration plates and provide distribution of specific externally located utilities (e.g., power, control and data acquisition, fluid sampling, thermal control) to facilities which are external to the chamber complex.
Data acquisition. The data acquisition system for the overall multichamber facility consists of equipment and capabilities necessary for acquisition, recording, display and storage of all certified HRTF test data. Other data collected strictly for engineering information and evaluation may be collected by the HRTF's life support systems integrated control equipment.
Supporting external facilities. Located externally to the HRTF chambers will be facilities which provide support to the operations and testing conducted in the HRTF. For example, these facilities include an external control center from which the HRTF testing activities will be coordinated and from which all official communications with the crew will be performed. This control center will provide supplemental control functions to those controls resident within the test facility and operated by the crew. Additionally, these external facilities include analytical laboratories which will provide chemical and microbiological sample analysis support during ongoing HRTF testing activities. Medical support facilities, too, will be required outside the HRTF for monitoring of crew health during the planned long-duration tests.
The life support provisions accommodate integrated testing of biological and physicochemical life support systems--the thrust of the ALS Program--in the areas of air revitalization, water recovery, food production, solid waste processing, and thermal management.
Air revitalization system. The HRTF air revitalization system (ARS) will maintain the sealed chamber complex atmospheric parameters within prescribed limits to ensure crew health and safety. The subsystem functions of the ARS include CO2 removal, CO2 reduction, O2 generation, trace contaminant removal, makeup gas storage, and unrecovered waste gas storage. During the first stage of the reference mission, the physicochemical elements of the ARS will solely and independently provide for all air revitalization functions. During the second stage of the mission in which the biomass production chambers are activated, these physicochemical elements will provide decreasing amounts of life support as the higher plants provide increasing levels of air revitalization. During metabolic step changes, such as those present during a 48 hour crew changeout, the physicochemical elements will automatically activate to compensate for the additional metabolic load.
Water Recovery System. The water recovery system (WRS) will process and supply water used by the crew for drinking, food preparation, and hygiene activities and used by the higher plants in the biomass production chambers. The WRS subsystem functions consist of waste hygiene water collection, waste hygiene water processing, urine collection, urine processing, potable water production, water quality monitoring, makeup water storage, and unrecovered wastewater storage. The WRS is not intended to be comprised solely of physicochemical elements, though only the physicochemical elements will be active during the first stage of the reference mission. Rather, it will be designed to incorporate the most efficient blend of physicochemical water recovery subsystems, higher plants, and microbial bioreactors.
Biomass (food) production system. The biomass production system (BPS) provides for the growth of higher plants for the purpose of supplying food to the HRTF crew. The BPS also encompasses equipment necessary for the seeding, harvesting, processing, and storage of basic foodstuffs prior to final preparation in the galley. Though it is expected that the BPS will not supply the entirety of the crew's nutritional and varietal needs, it will nonetheless be designed to provide the majority of the caloric and nutritional requirements for the crew.
Solids (waste) processing system. The solids processing systems (SPS) provides for the processing of solid wastes, including feces, inedible biomass, and uneaten food, for recovery of useful products. The SPS may use a combination of physicochemical and biological approaches to achieve effective resource recovery. The SPS also provides stabilization and storage of those solid wastes from which no useful products can be economically reclaimed.
Thermal control system. The HRTF thermal control system (TCS) provides for the acquisition of waste heat, its subsequent transport out of the chamber internal volume, and its ultimate rejection to the external environment. Both metabolic and equipment heat loads will be handled by the TCS.
Integrated systems control. Providing supervisory control and safing functions for the HRTF and coordinating the simultaneously occurring activities of the above five life support systems, the HRTF integrated systems control provisions will be comprised of state-of-the-art computer controllers with standardized data input/output devices for all systems and subsystems. Additionally, the integrated systems control provisions will include sophisticated graphical display software to aid the crew in determining HRTF systems health status, to analyze performance of the various subsystems, and to perform system troubleshooting conveniently and efficiently.
Crew accommodations. The crew accommodations provide a comfortable, productive environment for the test crews while occupying the HRTF during the planned long-duration missions. Additionally, several crew accommodation items provide essential interfaces between the crew and the life support systems, most notably the accommodations in the hygiene area.
General accommodations. General accommodations required for the crew during testing include internal chamber lighting provisions, audio and audio-visual means of communications within the chamber complex and with the outside world, storage of all kinds for crew equipment and supplies, and a trash management system. Also included within this category are crew safety provisions (e.g., fire extinguishers) and crew medical provisions, including first aid kits, medical monitoring devices, and medical sampling equipment.
Personal accommodations. The test subject crew will require certain personal accommodations during the confinement of the long duration tests, particularly a private area for each crewmember equipped with comfortable, acoustically isolated sleeping provisions. Temporary sleeping provisions offering limited isolation and privacy will also be required to support the 48 hour crew changeout periods. Personal accouterments for the crew include clothing items and a sufficient supply of hygiene items, such as soap, deodorant, washtowels, toothbrushes and toothpaste, shaving supplies, hair grooming supplies, and contact lens care supplies. Items such as soap and toothpaste which are rinsed down drains after use must be tested and approved prior to human testing to verify their compatibility with the water recovery system.
Common area accommodations. Within the HRTF, areas will be dedicated for common access by the crew for non-work related activities which are nonetheless crucial for the crew's well-being. Included in this category are a galley for meal preparation and a corresponding dining area. The galley will be equipped to prepare all foods planned to be consumed by the crew during the tests--both stored food items and those which are grown in the biomass production chambers. Food processing wastes and uneaten food will be temporarily stored in the vicinity of the galley for eventual recycling via the solids processing system. Another designated common area will house the crew exercise equipment, which will help to keep the crewmembers in good physical shape within the confines of the facility and which will likely interface with the medical monitoring equipment to provide medical data required to be obtained at high metabolic rates. An efficient, effective hygiene area will be required not only to provide the crew with toilet, shower, hand wash, and oral hygiene facilities, but also to serve as an interface point with the HRTF water recovery system to collect various wastewaters. Laundry accommodations, too, will be located in a common access area and will interface with the water recovery system. Incorporated in the laundry area will be centrally-located storage provisions for equipment and supplies to support general housekeeping activities within the chamber complex.
Work area accommodations. Since one of the goals of the HRTF is to minimize the crew time required to support a fully regenerative life support system, the resulting crew time saved can be put to productive use. Thus, an efficient work area, complete with workstations, computer facilities, and telephone and data fax communications will be required. Crewmembers can then devote a significant portion of their workday to the same type of work they would perform in any standard office environment. Other, more specialized work areas include a laboratory workstation and a maintenance work area. The laboratory workstation will be outfitted with basic sample analysis equipment used by the crew to assess overall life support system performance and condition. It will also provide sample preparation capabilities for those samples designated to be analyzed externally in the supporting laboratories. In the maintenance work area will be located a general duty workbench as well as storage of tools, equipment, spares, and materials to support all maintenance activities scheduled to be performed during test and to support likely equipment failure scenarios.
Participants of the HRTF tests will be chosen via standard JSC test subject selection processes and will receive adequate training to allow them to perform daily duties without outside assistance and to perform maintenance and troubleshooting activities with appropriate external guidance. A total of six test subject crews (i.e., 24 subjects) will be required over the course of the fourteen-month reference mission. It is anticipated that crew makeup will consist of both sexes. Because of the extended durations of the crew shifts, trained backup test crewmembers will likely be required to allow replacement of on-duty crewmembers who may need to leave the HRTF facility for emergency reasons or other unforeseen events.
In order to aid in the definition of requirements specific to the interactions among the project segments and among their systems, a system-to-system interface matrix will be developed for the HRTF. A primary objective of developing this matrix is to identify complex interfaces which could be simplified by redefinition of specific responsibilities of the numerous elements of the project. As full decomposition of the project into increasingly smaller elements progresses, each system and subsystem will become better defined, aiding in the establishment and refinement of required interfaces.
In support of defining lower-level requirements for the HRTF, a set of system sizing models will be developed for each of its systems and subsystems. These sizing models will be developed using basic process modeling software applications. Additionally, models will be developed to assess the dynamics within systems and among systems of the HRTF.
The anticipated results of development and testing of the HRTF are that NASA will for the first time have demonstrated long-duration operation of a full-scale, integrated biological and physicochemical regenerative life support system and that the database will then exist to lend confidence to those future mission planning and development activities which support further and more ambitious human presence in low-Earth orbit, in transit to other planetary bodies, and on lunar and planetary surfaces.
Over the next several years, HRTF systems modeling, design, and development activities as well as major facility construction activities will steadily progress, resulting in what is intended to be the state-of-the-art facility for conducting integrated biological and physicochemical life support systems testing with human participation. After the extended duration reference mission testing is successfully performed, it is anticipated that the HRTF will be capable of being reconfigured to support additional test mission scenarios, including scenarios which call for replacement or upgrade of the subsystem technologies of the HRTF life support systems. Other anticipated future testing activities may examine the impacts on the life support systems of recharging and servicing space suit portable life support systems and the impacts of losing airlock atmosphere during extra-habitat activities. Different surface module geometries also may be evaluated by attaching newly configured chambers to the HRTF's scarred ports on the interconnecting transfer tunnel or by replacing existing chambers outright. Finally, the entire facility may be required to be modified to support future NASA programs which baseline reduced cabin pressures. These modifications would include reworking the chamber complex pressure shells and adding facilities for pumpdown and reduced pressure maintenance, as well as providing additional safety systems to the facility.
In summary, it is anticipated that the HRTF Project will provide essential data in the near term on integrated biological and physicochemical life support system performance at a reasonable scale and will be an adaptable project over the long run to support the evolving needs of NASA in the area of advanced life support.