Abstract: Mars One Surface Habitat ECLSS Conceptual Design Assessment

Transcription

1 Abstract: Mars One Surface Habitat ECLSS Conceptual Design Assessment Paragon was contacted by Mars One and awarded a contract to develop a conceptual design of the Surface Habitat Environmental Control and Life Support System (ECLSS). The Habitat ECLSS performs the following functions: Maintain a safe and comfortable atmosphere within the pressurized elements of the habitat. This includes keeping the air at the right pressure and free of contaminants such as carbon dioxide and trace contaminants (think ammonia released in sweat by the crew during exercise and methane produced during the digestion of food). The oxygen level, air temperature, and humidity are also maintained for safety and comfort. Finally, monitoring of oxygen, carbon dioxide, humidity, air pressure, and combustion products (i.e. fire detection) is continuously performed to provide control of these parameters and to signify if a problem is developing. Receive wastewater from other vehicle systems (humidity condensed out of the air, recovered water from wet waste, and water recovered from Martian ice) and purify it for human consumption, bathing, and electrolysis into oxygen (for breathing) and hydrogen. Recover additional water from wet waste produced by the crew. Sources of wet waste include urine, waste food, and even fecal matter. Collect, transport, and reject heat from the crew and equipment in the habitat to the external Martian environment. Utilize in-situ resource utilization (ISRU) processes to recover argon and nitrogen gas from the Martian atmosphere (to maintain atmospheric pressure in the habitat) and liquid water from ice bound in Martian regolith or soil (for crew consumption and oxygen generation). It is important to note that there are many other important functions that are not part of the ECLSS but are performed by other Habitat systems that are essential to maintaining a safe and comfortable environment for the crew. These include atmospheric leak detection and repair, as well as crew systems functions such as clothing, personal items, entertainment, galley and food, hygiene, lavatory, exercise, medical, lighting, fire suppression, and radiation protection. In addition, other Habitat systems provide electrical power and ISRU systems associated with collecting and transporting water-laden Martian regolith to the Habitat. The work started with Mars One providing Paragon with their preliminary thoughts and estimates regarding what they thought the ECLSS would consist of and how big it would be. It is important to note that this input from Mars One was not binding in other words their input was not considered to be hard targets that the conceptual design had to meet.

2 Before launching into the conceptual design, Paragon started by identifying major drivers (we call them system-level design drivers) that we believe will significantly affect the design and operation of the Surface Habitat ECLSS. A few of the top system-level design drives include: ISRU Mastering living off the land is the single greatest driver to the short and long-term success of the Mars One mission. Maturing and deploying robust and reliable ISRU systems to extract argon, nitrogen, and water from the Martian environment must be achieved for the program to be viable. This can be achieved by including leading industrial experts and corporations in the fields of surface mining (for gathering water-laden Martian regolith or soil) and gas separation (for extracting nitrogen and argon from the Martian atmosphere) on the Mars One team and coupling their expertise with that of the established aerospace community. No New Materials, Physical Processes, or Technologies The fundamental materials, physical processes, and technologies exists to implement the Surface Habitat ECLSS required to embark on this grand initiative. In order to prevent spiraling development costs and schedule delays, the program must resist the temptation to continually develop better solutions. From a programmatic perspective, this is a huge driver as it is anticipated that the program cannot tolerate significant cost overruns or schedule delays. Delivered Mass and Volume Constraints on the allowable mass and volume delivered to the Martian surface must be minimized to the greatest extent practical. During the initial years when the Surface Habitat operates as an outpost, it is essential that the transportation system established between Earth and Mars allows for the requisite delivery of consumables and goods that cannot be produced in situ. This implies that Mars One must identify and implement costeffective transportation services between the Earth and Mars to meet the required frequency and quantity of hardware that must be delivered to the surface. No Initial Reliance on Plant Growth for Life Support It is understood that from the very first mission, the crew will incorporate plant growth to improve quality of life. However the Surface Habitat ECLSS utilizes a strictly physiochemical architecture to provide all required functionality. Initially, the integration of low levels of plant growth will have minimal impact to the design and operation of the physiochemical-based ECLSS. However, as Mars One intends to introduce aspects of bioregenerative life support (i.e. growing plant for food, to revitalize the atmosphere, and purify waste water) as soon as possible, more work beyond the scope of this initial effort will be required to ensure the continuous and uninterrupted operation of the physiochemical ECLSS no matter what the state of development is for the bioregenerative life support. Gravity The presence of an appreciable gravitational field on Mars allows for gravitational phase separation of solids, liquids, and gasses to be implemented to simply daily routine operation. Whether this is collecting metabolic waste from the crew or separating condensed water from the atmosphere gravitational phase separation greatly simplifies this critical function as compared to microgravity. In-situ Manufacturing The fraction of spares and consumables will continue to increase Earth resupply cargo up until the point that in situ manufacturing is made possible by building up a Mars manufacturing capability. As the Mars One goal is to steadily build from a permanently staffed outpost to a permanent and largely self-sufficient settlement, it is understood that Page 2 of 7

3 reliance on resupply must be drastically reduced as time progresses and the habitat increases in size and population. It will take significant time to build the infrastructure required to develop a manufacturing base, but this capability must be developed if a permanent settlement is to be achieved. As recorded in the course of human history, self-sufficiency is an essential characteristic of permanent and successful human settlements. Paragon also generated a preliminary list of driving requirements to define the functional, performance, and material storage requirements. This list of requirements was then refined in an iterative process as the conceptual design was developed. Ultimately, hundreds of value-added requirements must be rigorously established to so that a compliant surface Habitat ECLSS can be realized. A few of the driving requirements that have been identified so far are summarized below: Atmospheric Leak Rate Some nominal atmospheric leakage through the Habitat walls and internal-external interfaces such as the Habitat Airlock and ISRU interfaces is unavoidable. However, any leakage of argon, nitrogen, oxygen, and water vapor requires a commensurate increase in the ISRU processing rate since all of these life critical commodities are exclusively obtained from the Martian environment. Minimizing the planned nominal atmospheric leak rate will reduce the load on the ISRU systems and that in turn will have beneficial impacts with regards to reduced nominal wear and tear, electrical power consumption, required maintenance and refurbishment, etc. Gases and Water Storage Buffers Even with the inclusion of redundant life support functions, there will inevitably be planned and unplanned temporary shutdowns of life support systems and subsystems to think otherwise would be naive. Therefore, storage buffers of the primary life support commodities (argon, nitrogen, oxygen, and water) are essential to provide transient life support functionality. Given that any planned or unplanned maintenance or repair activity must be conducted by the crew with the resources at hand, the maximum practical time to recover the system and restore functionality gives critical margin to overcoming unexpected difficulties. With this in mind, increasing storage buffers of critical life support commodities should be given priority to the maximum extent practical. Electrical Power Availability Although it is not an ECLSS System, the Surface Habitat Electrical Power System is perhaps the most critical Habitat system following the Pressure Vessels that maintain the pressurized atmosphere. Without reliable and sufficient electrical power, the Habitat ECLSS cannot perform its critical functions. In addition, most systems run at peak efficiency when they are operated continuously (as opposed to going through daily startup and shut-down cycles). Therefore, minimization of fluctuations in electrical power availability due to day/night and seasonal cycles is generally considered beneficial. Pre-Crew Autonomous Operations With No Maintenance The surface Habitat, including the ECLSS, must operate autonomously for the first 2+ years. Although some essential robotic operations are expected (e.g. moving and placing landers, making fluid connections between landers and delivering water-laden regolith to the ECLSS ISRU system), there is currently no anticipated robotic-assisted maintenance or repair functionality. This implies that the ECLSS must complete its critical pre-crew arrival functions without the benefit of routine maintenance Page 3 of 7

4 or contingency repair. This in turn implies that the unit processes employed by the ECLSS must be sufficiently robust and/or include sufficient redundancy to operate as required. Particular attention must be applied to meeting this requirement. Sufficient redundancy (including using dissimilar redundancy) must be integrated into the final design. Once the initial set of system-level design drivers and requirements were established, Paragon developed the conceptual design of the Surface Habitat ECLSS. As mentioned previously, there was some iteration involved as requirements were updated to reflect initial system sizing results. The ECLSS functions are distributed across five primary systems as shown in Figure 1 and a top-level schematic is shown in Figure 2. Additional key attributes infused into the design of the Mars One Surface Habitat ECLSS include: Implement sparing and refurbishment at the lowest practical level to minimize the mass and volume of spare parts delivered to the surface. To the extent practical, maximally utilize common fittings, components, parts, and tools to minimize the quantity and type delivered for spares and to effect repairs post-crew arrival. To the maximum extent practical, utilize soft goods to contain and store gasses and water so that the volume of these reservoirs is minimized during transit to the Martian surface. Employ dissimilar redundancy to the maximum extent practical to circumvent in-family or common-cause failures. Package fixed systems, subsystems, assemblies, and components (including spares) so that they are optimized for access during post-crew arrival maintenance and repair Post-crew arrival, utilize automation to the minimum amount practical; alternatively, utilize crew time to the maximum amount practical to achieve required levels of reliability and performance. Automation will gradually be implemented as the surface systems are matured and knowledge is gained on where it is effective to do so. Implementing and requiring automation across the board to maintain life support functionality will drive development cost and schedule. Post-crew arrival, utilize crew intervention and action to directly contribute to an additional level of fault tolerance to loss of life (with reasonable time constraints defined). The Atmosphere Management System (AMS) and Water Management System (WMS) employ a number of technologies utilized aboard the U.S. segment on the International Space Station (ISS). It is noted that these technologies will be implemented in a significantly different manner. In almost all cases the exact ISS hardware and systems will not be utilized; rather it is application of the core technologies that will be implemented and optimized for the Mars One mission. The AMS scrubs carbon dioxide from the atmosphere using a mature process (pressure- and thermalswing molecular sieve) and rejects it to the external atmosphere. Oxygen is produced via water electrolysis a mature process used aboard submarines and the ISS that splits water into oxygen and hydrogen. The oxygen is utilized by the crew and the hydrogen is vented to the external environment. Later as the habitat matures, additional subsystems (such as a Sabatier Reactor) can be added to utilize the waste hydrogen and carbon dioxide to generate additional recovered water. Other AMS functions Page 4 of 7

5 such as trace contaminant control, air circulation and pressure control, post-fire atmospheric cleanup employ mature life support technologies to maintain healthy and comfortable atmosphere in the habitat. Habitat ECLSS Atmosphere Management System (AMS) Water Management System (WMS) Thermal Control System (TCS) In-Situ Resource Processing System (ISRPS) Wet Waste Processing System (WWPS) Pressure Control Water Storage Heat Collection Regolith Water Extraction Wet Waste Processing Air Revitalization Primary Water Processor Heat Transport N2/Ar Extraction Residual Wet Waste Storage Gas Storage Water Quality Monitor Heat Rejection Fire Detection and Atmosphere Recovery Insulation Air Quality Monitor Figure 1: The Mars One Habitat ECLSS Functional Breakdown. The Thermal Control System (TCS) includes both active components such as pumped liquid cooling loops and passive components such as insulation and surface coatings to control temperatures throughout the habitat. As a general rule everything works best within specific temperature ranges (especially humans). The purpose of the TCS is to keep everything within those comfort ranges by passive means if possible and active means as necessary. The Wet Waste Processing System (WWPS) serves to isolate human wet waste (principally urine, feces, food waste and hygiene waste) and recover water using a low-tech approach. Rather than introduce the significant complications of direct urine and fecal matter processing, this conceptual approach is one of Page 5 of 7

6 a passive drying system that will extract water from the human waste while maintaining isolation from other systems. This is accomplished by using a humidity exchange membrane. Dry habitat air blowing across one side of the membrane will pull humidity from the warm wet side, along with a very limited quantity of known contaminants. Heat input on the waste side drives the release of water vapor from the wet waste. The water vapor laden air is then returned to the AMS where trace contaminants are removed and water is condensed and transported to the WMS for further processing. The resultant residual wet waste (sludge) will be periodically removed by the crew and stored for eventual future use as a rich and valuable source of organic and inorganic compounds. The in-situ Resource Processing System (ISRPS) performs two primary functions. The first function is to extract water from externally supplied Martian regolith and/or water ice. This system relies on an external and Non-ECLSS Regolith Supply and Return System (RSRS) to supply water-ice laden regolith and to dispose of water depleted regolith. An ISRPS hopper is opened to the external environment and filled with regolith and then closed and pressurized for processing. In batches, the regolith is heated and pressurized to vaporize the water from the regolith. The water is then condensed in a purified--but non potable--form, and then transferred to the Water Management System for purification to potable water. The dried Martian regolith would then be removed from the hopper and returned to the external environment with the non-eclss RSRS and the next batch introduced. The cyclical process is then repeated. The second ISRPS function is to extract usable gasses from the Martian atmosphere for use by the Atmosphere Management System. Martian ambient atmosphere is filtered to remove particulates and compressed to multiple atmospheres and cooled to create liquid or solid carbon dioxide enabling the efficient separation of trace nitrogen (~2.7%) and argon (~1.6%) from the predominantly carbon dioxide (~95.3%) in the Martian atmosphere. The separated nitrogen/argon gas is then transferred to the Air Management System where any trace carbon dioxide or other contaminants (such as carbon monoxide) are removed via the existing life support subsystems. Page 6 of 7

7 Figure 2: The Mars One Surface Habitat ECLSS Conceptual Design Schematic. Page 7 of 7