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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).

Dynamic simulation of the Lunar Outpost habitat life support was undertaken to investigate the impact of Extravehicular Activity (EVA). The preparatory static analysis and some supporting data are reported in another paper. (Jones, 2008-01-2184) Dynamic simulation is useful in understanding systems interactions, buffer needs, control approaches, and responses to failures and changes. A simulation of the Lunar outpost habitat life support was developed in MATLAB/Simulink™. The simulation is modular and reconfigurable, and the components are reusable to model other physicochemical (P/C) based recycling systems. EVA impacts the Lunar Outpost life support system design by requiring a significant increase in the direct supply mass of oxygen and water and by reducing the net mass savings of using dehydrated food. The mass cost of EVA depends on the amount and difficulty of the EVA scheduled.

NASA is planning to return to the moon and then explore Mars. A permanent base at the south pole of the moon will be the test bed for Mars. At the moon base, two crewmembers are expected to conduct Extravehicular Activity (EVA) six days every week. Current spacesuits are cooled by the sublimation of water ice into vacuum. A single 7 hour EVA near the lunar equator in daylight can expend up to 5 kilograms of water. Because of the high cost of transporting spacesuit cooling water to the moon, the water for one EVA could cost hundreds of thousands of dollars. The lunar south pole and Mars have low surface temperatures that make cooling much easier than at the lunar equator. Alternate cooling methods and staying in cool environments can reduce or eliminate the use of water for spacesuit cooling. If cooling water is not needed, a recycling life support system can provide all the required crew water and oxygen without transporting additional water from Earth.

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 design and mass cost of a starship and its life support system are investigated. The mission plan for a multigenerationai interstellar voyage to colonize a new planet is used to describe the starship design, including the crew habitat, accommodations, and life support. Cost is reduced if a small crew travels slowly and lands with minimal equipment. The first human interstellar colonization voyage will probably travel about 10 light years and last hundreds of years. The required travel velocity is achievable by nuclear propulsion using near future technology. To minimize mission mass, the entire starship would not decelerate at the destination. Only small descent vehicles would land on the destination planet. The most mass efficient colonization program would use colonizing crews of only a few dozen. Highly reliable life support can be achieved by providing selected spares and full replacement systems.

This paper describes engineering rules of thumb for life support system design. One general design rule is that the longer the mission, the more the life support system should use regenerable technologies and recycling. A more specific rule is that, if plants supply more than about half the food, the plants will provide all the oxygen needed by the crew. There are many such design rules that can help in planning the analysis of life support systems or in assessing design concepts. These rules typically describe the results of steady state, “back of the envelope,” trade-off calculations. They are useful in suggesting plausible candidate life support system designs or approaches. Life support system engineers should consider the basic design rules and make quick steady state calculations as a guide before doing detailed design.

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.

The Advanced Life Support (ALS) project uses Equivalent Mass (EM) to report ALS progress and in technology selection. Life Cycle Cost (LCC) is much more widely used. We develop a new metric, Life Cycle Mass (LCM), from EM and a mass-based LCC model. EM, LCM and Mass (M) alone are compared for technology ranking and progress reporting. These metrics are usually highly correlated and typically produce similar technology rankings and ALS progress metrics. Since M is much simpler than EM or LCM, ALS analysis could use M (Mass) alone for initial technology ranking and for ALS metric reporting.

Space power systems include power source, storage, and management subsystems. In current crewed spacecraft designs, solar cells are the power source, batteries provide storage, and the crew performs any required load scheduling. For future crewed planetary surface systems using Advanced Life Support, we assume that plants will be grown to produce much of the crew's food and that nuclear power will be employed. Battery storage is much more costly than nuclear power capacity and so is not likely to be provided. We investigate scheduling of power demands to reduce the required peak power generating capacity. The peak to average power ratio is a good measure of power capacity efficiency. We can easily schedule power demands to reduce the peak power below the potential maximum, but simple scheduling rules may not achieve the lowest possible peak to average power ratio.

The Government Performance and Results Act (GPRA) requires NASA and other federal agencies to use goals and metrics. Many Advanced Life Support (ALS) goals and metrics are described in the ALS Program Plan and others have been used in designing life support for the International Space Station (ISS) and earlier missions. These well-established goals can be monitored using familiar metrics. The most important goal of ALS is to have missions successfully fly new life support technology. A new ALS technology will be flown if it provides better safety, availability, performance, or cost. Improvements in these four criteria are the major supporting goals of ALS. An ideal candidate technology would also provide increased self-sufficiency, be useful on different types of missions, and have high potential for technology transfer, but these are incidental benefits that are not required for successful flight.