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The least expensive life support for brief human missions is direct supply of all water and oxygen from Earth without any recycling. The currently most advanced human life support system was designed for the International Space Station (ISS) and will use physicochemical systems to recycle water and oxygen. This paper compares physicochemical to direct supply air and water life support systems using Equivalent Mass (EM). EM breakeven dates and EM ratios show that physicochemical systems are more cost effective for longer mission durations.

This paper considers the design of a life support system for transit to Mars and return to Earth. Because of the extremely high cost of launching mass to Mars, the Mars transit life support system must minimize the amount of oxygen, water, and food transported. The three basic ways to provide life support are to directly supply all oxygen and water, or to recycle them using physicochemical equipment, or to produce them incidentally while growing food using crop plants. Comparing the costs of these three approaches shows that physicochemical recycling of oxygen and water is least costly for a Mars transit mission. The long mission duration also requires that the Mars transit life support system have high reliability and maintainability. Mars transit life support cannot make use of planetary resources or gravity. It should be tested in space on the International Space Station (ISS).

This paper considers the design of a Mars Transfer Vehicle (MTV) water processor. The Constellation Program has begun to consider the first human mission to Mars, and the MTV water processor is of special interest. Mars transit system design is not affected by Extra-Vehicular Activity (EVA) or In-Situ Resource utilization (ISRU). The total duration of Mars transit and return is relatively fixed at about four hundred days, while Mars and lunar surface stays can vary from a few days to many years. The Mars transit water processor will operate in zero gravity, like the International Space Station (ISS) Water Recovery System (WRS), so the ISS WRS design can serve as a reference baseline for the Mars transit system. The paper develops the MTV water requirements and considers the suitability of the ISS WRS for Mars transit. The ISS WRS meets MTV requirements and requires less mass than direct resupply for Mars transfer, but it has excess capacity for the requirements.

This report considers crewmembers’ life support needs for air, water, and food in a long duration lunar surface base. It also considers requirements for washing and clean-up water, waste recycling, and the crew's use of air, water, and food during Extravehicular Activity (EVA). The life support mass flow is described, including the needs of the statistical average crewmember, the expected variation between crewmembers, and the potential range of the total crew's average requirements. To develop the lowest cost, most reliable life support system that meets the crew needs, we must understand how the requirements impose design constraints and cost drivers and provide options and opportunities. We also must be aware of the degree of flexibility and potential change in requirements as their costs and implementation become defined.

Dynamic simulation of the lunar outpost habitat life support was undertaken to investigate the impact of life support failures and to investigate possible responses. Some preparatory static analysis for the Lunar Outpost life support model, an earlier version of the model, and an investigation into the impact of Extravehicular Activity (EVA) were reported previously. (Jones, 2008-01-2184, 2008-01-2017) The earlier model was modified to include possible resupply delays, power failures, recycling system failures, and atmosphere and other material storage failures. Most failures impact the lunar outpost water balance and can be mitigated by reducing water usage. Food solids and nitrogen can be obtained only by resupply from Earth. The most time urgent failure is a loss of carbon dioxide removal capability. Life support failures might be survivable if effective operational solutions are provided in the system design.

The search for alien life in the solar system should include exploring unearthlike environments for life having an unearthly biochemistry. We expect alien life to conform to the same basic chemical and ecological constraints as terrestrial life, since inorganic chemistry and the laws of ecosystems appear to be universal. Astrobiologists usually assume alien life will use familiar terrestrial biochemistry and therefore hope to find alien life by searching near water or by supplying hydrocarbons. The assumption that alien life is likely to be based on carbon and water is traditional and plausible. It justifies high priority for missions to search for alien life on Mars and Europa, but it unduly restricts the search for alien life. Terrestrial carbon-water biochemistry is not possible on most of the bodies of our solar system, but all alien life is not necessarily based on terrestrial biochemistry.

New variable environment Modified Energy Cascade (MEC) crop models were developed for all the Advanced Life Support (ALS) candidate crops and implemented in SIMULINK. The MEC models are based on the Volk, Bugbee, and Wheeler Energy Cascade (EC) model and are derived from more recent Top-Level Energy Cascade (TLEC) models. The MEC models were developed to simulate crop plant responses to day-to-day changes in photosynthetic photon flux, photoperiod, carbon dioxide level, temperature, and relative humidity. The original EC model allowed only changes in light energy and used a less accurate linear approximation. For constant nominal environmental conditions, the simulation outputs of the new MEC models are very similar to those of earlier EC models that use parameters produced by the TLEC models. There are a few differences. The new MEC models allow setting the time for seed emergence, have more realistic exponential canopy growth, and have corrected harvest dates for potato and tomato.

Stored air and water will be sufficient for Crew Exploration Vehicle visits to the International Space Station and for brief missions to the moon, but an air and water recycling system will be needed to reduce cost for a long duration lunar base and for exploration of Mars. The air and water recycling system developed for the International Space Station is substantially adequate but it has not yet been used in operations and it was not designed for the much higher launch costs and reliability requirements of moon and Mars missions. Significant time and development effort, including long duration testing, is needed to provide a flawless air and water recycling system for a long duration lunar base. It would be beneficial to demonstrate air and water recycling as early as the initial lunar surface missions.

Popular depictions of space exploration as well as government life support research programs have long assumed that future planetary bases would rely on small scale, closed ecological systems with crop plants producing food, water, and oxygen and with bioreactors recycling waste. In actuality, even the most advanced anticipated human life support systems will use physical/ chemical systems to recycle water and oxygen and will depend on food from Earth. This paper compares bioregenerative and physical/chemical life support systems using Equivalent System Mass (ESM), which gauges the relative cost of hardware based on its mass, volume, power, and cooling requirements. Bioregenerative systems are more feasible for longer missions, since they avoid the cost of continually supplying food.

This paper considers system design and technology selection for the crew air and water recycling systems to be used in long duration human space exploration. The ultimate objective is to identify the air and water technologies likely to be used for the vision for space exploration and to suggest alternate technologies that should be developed. The approach is to conduct a preliminary systems engineering analysis, beginning with the Air and Water System (AWS) requirements and the system mass balance, and then to define the functional architecture, review the current International Space Station (ISS) technologies, and suggest alternate technologies.

We have developed top-level crop models for analysis of Advanced Life Support (ALS) systems that use plants to grow food. The crops modeled are candidates for ALS use: bean (dry), lettuce, peanut, potato (white), rice, soybean, sweet potato, tomato, and wheat. The crop models are modified versions of the energy cascade crop growth model originally developed for wheat by Volk, Bugbee, and Wheeler. The models now simulate the effects of temperature, carbon dioxide level, planting density, and relative humidity on canopy gas exchange, in addition to the effects of light level and photoperiod included in the original model. The energy cascade model has also been extended to predict the times of canopy closure, grain setting (senescence), and maturity (harvest) as functions of the environmental conditions.