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Advances in Space Research 45 (2010) 917–928

Exploration life support technology challenges for the CrewExploration Vehicle and future human missions

Harry W. Jones a,*, Mark H. Kliss b

a N239-8, NASA Ames Research Center, Moffett Field, CA 94035, USAb N239-15, NASA Ames Research Center, Moffett field, CA 94035, USA

Received 6 August 2008; received in revised form 14 October 2009; accepted 19 October 2009

Abstract

As NASA implements the U.S. Space Exploration Policy, life support systems must be provided for an expanding sequence of explo-ration missions. NASA has implemented effective life support for Apollo, the Space Shuttle, and the International Space Station (ISS)and continues to develop advanced systems. This paper provides an overview of life support requirements, previously implemented sys-tems, and new technologies being developed by the Exploration Life Support Project for the Orion Crew Exploration Vehicle (CEV) andLunar Outpost and future Mars missions. The two contrasting practical approaches to providing space life support are (1) open loopdirect supply of atmosphere, water, and food, and (2) physicochemical regeneration of air and water with direct supply of food. Openloop direct supply of air and water is cost effective for short missions, but recycling oxygen and water saves costly launch mass on longermissions. Because of the short CEV mission durations, the CEV life support system will be open loop as in Apollo and Space Shuttle.New life support technologies for CEV that address identified shortcomings of existing systems are discussed. Because both ISS andLunar Outpost have a planned 10-year operational life, the Lunar Outpost life support system should be regenerative like that forISS and it could utilize technologies similar to ISS. The Lunar Outpost life support system, however, should be extensively redesignedto reduce mass, power, and volume, to improve reliability and incorporate lessons learned, and to take advantage of technology advancesover the last 20 years. The Lunar Outpost design could also take advantage of partial gravity and lunar resources.Published by Elsevier Ltd. on behalf of COSPAR.

Keywords: Space life support; Life support systems; Life support technologies; Crew Exploration Vehicle; Lunar Outpost

1. Introduction

NASA is pursuing the U.S. Space Exploration Policyand planning a human return to the Moon and the explo-ration of Mars. Human physiological needs define the

0273-1177/$36.00 Published by Elsevier Ltd. on behalf of COSPAR.

doi:10.1016/j.asr.2009.10.018

Abbreviations: 2BMS, two bed molecular sieve; 4BMS, four bed molecularCM, crewmember; CM, Command Module (Apollo), Crew Module (CEV); dsystems architecture study; EVA, extra vehicular activity; GCMS, gas chromatoISS, International Space Station; LAS, Lunar Architecture Study; LEO, lowTransfer Vehicle; ORU, orbital replaceable unit; SBAR, sorbent-based atmoModule; SPWE, solid polymer water electrolysis; SSF, space station freedom; Tmembrane evaporation system; TOC, total organic carbon; VCD, vapor comp

* Corresponding author.E-mail addresses: Harry.Jones@nasa.gov (H.W. Jones), Mark.Kliss@nasa.

requirements for life support. The Apollo, Space Shuttle,and International Space Station (ISS) life support designsprovide candidate reference systems, but improvementsare possible and needed. NASA is developing advancedlife support systems to better implement the U.S. Space

sieve; CEV, Crew Exploration Vehicle; CHX, condensing heat exchanger;, day; EDC, electrochemical depolarized concentrator; ESAS, explorationgraph mass spectrometer; HSIR, human systems integration requirements;earth orbit; LiOH, lithium hydroxide; LM, Lunar Module; MTV, Marssphere revitalization; SFWE, static feed water electrolysis; SM, ServiceCCS, trace contaminant control system; TIMES, thermoelectric integratedression distillation; VPCAR, vapor phase catalytic ammonia removal

gov (M.H. Kliss).

Table 1Human transport vehicles and habitats.

Destination Transportvehicle

Duration Habitat Duration

ISS/LEO CEV �1–2 days ISS 10 yearsLunar

surfaceCEV, LunarLander

�3 days LunarLander

�10 days

LunarOutpost

CEV, LunarLander

�3 days LunarOutpost

10 years

Mars MTV 6 months Mars base �18 months

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Exploration Policy. The purpose of this paper is to describenew technologies being developed to meet future life sup-port requirements.

2. Space exploration human habitats

The crew habitats required by the U.S. Space ExplorationPolicy are the Crew Exploration Vehicle (CEV), the LunarLander, the Lunar Outpost, the Mars Transfer Vehicle(MTV), and the Mars base. Each of these will be described.

2.1. The CEV

The CEV is sized to support all U.S. Space Explorationmissions to ISS, the Moon, and Mars. The CEV will beable to launch four crewmembers to the Moon, six to dockwith the Mars Transit Vehicle, and up to six to ISS. LikeApollo, the CEV will include a Crew Module (CM) anda Service Module (SM). Both the CEV CM and SM willinclude parts of the life support system. Significant changesfrom Shuttle and Apollo are proposed for CEV. The CEVwill use solar power rather than fuel cells to support theextended uncrewed CEV stay in lunar orbit.

2.2. The Lunar Lander

The Lunar Lander will be a two stage – descent andascent – expendable spacecraft similar to the Apollo LunarModule (LM). The ascent stage contains a combined crewcabin and airlock (not provided by Apollo), and both aremounted on top of the descent stage. The Lunar Landerwill support four crewmembers on the lunar surface for7 days, for lunar sortie missions similar to the Apollo mis-sions. Unlike Apollo, all crewmembers land on the Moon;none remain in lunar orbit. (ESAS, 2005).

2.3. The Lunar Outpost

A primary objective of the US Space Exploration Policyis to establish a Lunar Outpost for continuous human pres-ence on the Moon. The current approach to lunar explora-tion is defined by the Lunar Architecture Study (LAS).(Dale, 2006) (NASA Office of Public Affairs, 2006) Wherethe ESAS report anticipated several sortie missions beforethe Lunar Outpost, the LAS places near-total emphasis onthe permanent outpost. The Lunar Outpost will be near thesouth pole of the Moon. The outpost will be assembled andtested by four-person crews on 7-day missions. When con-tinuous habitation becomes possible, 180-day missionswith rotating crews will test exploration methods and sys-tems to prepare for Mars.

2.4. The MTV

The Mars exploration mission requires 6 months to tra-vel to Mars and 6 months to return to Earth. The crew ofsix is sent to Earth orbit in the CEV and rendezvous with

and transfers to the MTV for the trip to Mars. The Marslander is placed in Mars orbit before the crew is launched.After Mars descent, the MTV and CEV remain in Marsorbit waiting for the return to Earth (ESAS, 2005).

2.5. The Mars base

The Mars exploration mission requires an 18-monthstay on Mars. The surface habitat is deployed on the Marssurface before the crew is launched from Earth. The LunarOutpost will provide valuable testing for Mars, but ifin situ resources are used, Mars life support may not beidentical to lunar life support, because of differences inatmosphere and surface resources (ESAS, 2005).

Table 1 shows the human transport vehicles and habitatsproviding life support for the space exploration missions.

Life support requirements and costs increase withincreasing mission distance and duration. Mission durationis a key life support design factor.

3. Life support system requirements

The three most basic life support requirements are toprovide a habitable environment with appropriate atmo-sphere and temperature, to supply the human consumablesof oxygen, buffer gas, drinking water, food, and washwater, and to remove human wastes including carbon diox-ide, waste water, urine, and feces. A space habitat alsorequires environmental control to prevent decompression,detect and suppress fire, and remove gaseous contami-nants. Table 2 lists these life support requirements.

3.1. Crewmember minimum mass flow requirements

The NASA Constellation Program, in the Human Sys-tems Integration Requirements (HSIR, 2006), defines theminimum mass flow needed to support a typical crewmem-ber as shown in Table 3.

The minimum daily beneficial mass flow to support theassumed typical crewmember is 5.82 kg per crewmemberper day (kg/CM-day).

4. Apollo, Space Shuttle, and ISS life support

The Apollo, Shuttle, and ISS life support technologiesare available low risk candidates for future systems. We

Table 2Life support categories and needs.

Human consumables

Provide foodProvide oxygenProvide drinking waterProvide wash water

Process and recycle waste

Remove and recycle carbon dioxideRemove and recycle waste waterRemove and recycle urineRemove and store feces

Other habitable atmosphere

Provide buffer gasRemove atmosphere contaminantsMaintain temperature and humidityPrevent decompressionDetect and suppress fire

Table 3Minimum crewmember daily mass flow needs.

Needs kg/CM-day

Oxygen 0.93Food solids 0.70Water in food 1.29Food preparation and drinking water 2.50Hygiene water 0.40

Total 5.82

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describe the life support systems NASA has implementedfor the Apollo, Space Shuttle, and ISS.

Vent

Suit compressor

Suit CHX

H2O separator

Command Module (CM)

Potable water

storage

Waste water

storage

Solid waste

storage

Urine collection

Carbon & LiOH

Cabin air in

Cabin CHX

Cabin air in

Water out

Atmosphere

Water

Waste

Fig. 1. The Apollo Comma

4.1. Apollo life support

The Apollo lunar mission used three modules. TheCommand Module (CM) carried the three astronauts, theflight controls, and most of the life support. The ServiceModule (SM) housed the power, thermal, and propulsionsystems, and a small part of the life support. The LunarModule (LM) was used for descent to the surface, livingon the Moon, and ascent to the Command Module.

The Apollo Command Module held the potable andwastewater storage, carbon trace contaminant removal,LiOH carbon dioxide removal, solid waste storage, andheat exchangers and cold plates. Only the oxygen storagetanks and the fuel cells providing power and water werein the Service Module (see Fig. 1) (Wieland, 1994; Diamantand Humphries, 1990).

The Apollo LM life support was similar to the CM, witha few differences. The LM potable water was providedfrom storage tanks rather than fuel cells, and was purifiedby iodine rather than chlorine (Wieland, 1994; Diamantand Humphries, 1990). The Apollo life support technolo-gies are listed in Table 4, under the system categories ofatmosphere, water, and waste.

4.2. Space shuttle life support

The Shuttle life support technologies are also listed inTable 4 (Wieland, 1994; Eckart, 1996; Diamant andHumphries, 1990). Fig. 2 gives a block diagram of the

Fuel cell

Cabin air out

Service Module (SM)

Oxygen storage

Water

Oxygen

nd Module life support.

Table 4Apollo, Shuttle, and ISS life support technologies.

Apollo CM/LM Shuttle ISS

Destination Moon sortie LEO LEODuration �10 days �10 days 10 years

Atmosphere

CO2 removal LiOH LiOH 4BMSCO2 reduction None None Sabatier (scarred for)TCC Activated charcoal, filters Activated charcoal, filters, oxidizer Activated charcoal, filters, oxidizerTC monitoring none none GCMSAtmosphere storage O2 cryo tanks N2 gas tanks, O2 cryo tanks N2, O2 tanksAtmosphere source O2 cryo tanks N2 gas tanks, O2 cryo tanks CO2 reduction, H2O electrolysisHumidity control Suit CHX CHX, condensate to waste water CHX, condensate

Water

Potable water storage One or several tanks Tanks TankWater source Fuel cell, tanks in LM Fuel cell Shuttle fuel cell, wastewater recycling plannedWater purification Chlorine, iodine in LM tanks Iodine, microbial check valves IodineWater monitoring None None TOC, pH, iodine, conductivityWastewater processing None, vented None, vented MultifiltrationWaste water storage Tank Tank Tank

Waste

Feces processing Fecal bags Feces vacuum dried, compacted Fecal bags compactedUrine processing None, urine vented except LM None, urine to waste water tank VCD

Condensate

Cabin air in

Filter Fans LiOH & charcoal

CHX Cabin air out

Atmosphere

Waste

Fuel cell water

Water tanks

Vent

Crew Waste

water tank Vent

Vent/store

Commode Urine system

EVA suit drain

UrineWater

Fig. 2. The Space Shuttle life support.

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Space Shuttle atmosphere, water, and waste systems(Wieland, 1994; Diamant and Humphries, 1990).

In the Space Shuttle, the cabin air, which is also used tocool cabin equipment, is circulated through a filter, fans,lithium hydroxide (LiOH) and charcoal canisters, and aCondensing Heat Exchanger (CHX). Water from the fuelcells is stored in four tanks and delivered to the crew.Water is used for cooling and excess water can be ventedto space. The Shuttle commode provides for vacuum dry-ing and compaction of feces. Urine and drainage waterfrom the Extravehicular Activity (EVA) suits are piped tothe wastewater tank. Except for the collection and ventingof wastewater, the atmosphere, water, and waste systemsare not interconnected.

Table 4 and Figs. 1 and 2 show that the Apollo andShuttle life support technologies and system architecturesare very similar. LiOH and activated charcoal are usedfor atmosphere purification and tanks for oxygen storage.

Water is stored in tanks, more is provided by fuel cells,and it is purified by iodine. Feces are stored and urine isstored and vented.

The differences between Shuttle and the Apollo CM arefew. The Apollo CM used a pure oxygen atmosphere inflight and required no nitrogen storage. It also used theEVA suit compressor and heat exchanger as part of theCM life support. These differences reduced the mass ofthe Apollo life support, and reflect the additional cost ofmoving mass from Earth orbit to lunar orbit.

4.3. ISS life support

As shown in Table 4, the ISS life support is fundamen-tally different from that of Shuttle and Apollo. The ordersof magnitude longer duration of the ISS mission wouldlead to very large launch costs if all oxygen and water wereprovided directly from Earth. Recycling carbon dioxide,

Water out

Waste water

Fuel cell

water

Atmosphere

Water

Waste

Vent

Store

Commode urinal

Urine processor

O2 & N2

storage

Cabin air in

CO2

removal CO2

storage

Cabin air in

Trace contaminant monitoring and control

Cabin air out

O2

generation O2 out

Waste storage

Water processor

Potable storage

Water out

Storage

Waste storage

CO2

reduction

Fig. 3. The ISS life support.

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wastewater, and urine is planned for ISS. Implementingrecycling was deferred because the Shuttle provided excessfuel cell water to ISS, and this water was used directly or toprovide oxygen by electrolysis. Fig. 3 shows the ISS lifesupport (Diamant and Humphries, 1990; Carasquillo andBertotto, 1999; Bagdigian and Ogle, 2001).

Although all the ISS life support is not yet operational,redundant trace contaminant control and analysis and car-bon dioxide removal units have long been deployedonboard the US laboratory module. The oxygen generatorand the water processor have been flown.

As shown in Fig. 3, the trace contaminant control andmonitoring equipment operate directly on the cabin atmo-sphere. High pressure oxygen and nitrogen are stored intanks in the air lock. The Node 3 four bed molecular sieve(4BMS) carbon dioxide removal system currently allowsthe carbon dioxide to be vented to space. In the future, itcould be delivered to a scarred-for Sabatier carbon dioxidereduction system. The electrolysis oxygen generator pro-vides oxygen directly to the cabin atmosphere. The hydro-gen produced by water electrolysis is now ventedoverboard but could be used later in Sabatier carbon diox-ide reduction.

Waste hygiene water and cabin condensate are stored inNode 3 and routed through the potable water processor toa product storage tank. Fuel cell water from the Shuttle isstored in the US laboratory module and used directly whenthe potable water processor product is insufficient. Storedwater can be manually sampled and tested. Urine ispumped from the urinal to the urine processor and the dis-

tillate is combined with other wastewater. The commodeprovides for bagging and compacting feces.

5. Open loop direct supply versus closed loop recycling

The two ways to provide space life support are (1) thedirect supply of all the air, water, and food to be consumedby the crew (all open loop), or (2) physical/chemical regen-eration of air and water with direct supply of food (oxygenand water recycling).

Direct supply is adequate for short CEV trips to ISS andthe Moon, and for short lunar sorties in the Lunar Lander.The CEV and Lunar Lander life support will be open loopas are Apollo and Space Shuttle. Oxygen and water recy-cling will be needed to reduce launch mass for the longduration lunar base, the MTV trip to and from Mars,and the Mars base. Long duration life support will use oxy-gen and water recycling as planned for ISS.

5.1. Recycling breakeven date

The mass of oxygen and water needed per crewmemberper day is about 5 kg per crewmember per day (kg/CM-d)including the water in food. To estimate the breakevendate, the mass is doubled to 10 kg per crewmember perday to allow for tankage and storage structure.

The recycling system mass should include allowances forthe power, cooling and structure needed to support thesystem, using the concept of equivalent system mass.The equivalent system mass of the recycling system can

Habitat Air and water

Urine Purification

Condensate Purification

Oxygen Supply

Wash Water Purification

Urine System

Drink & Food Water

Habitat Atmosphere

Wash System

Fig. 5. Proposed functional architecture of the oxygen and water systems.

922 H.W. Jones, M.H. Kliss / Advances in Space Research 45 (2010) 917–928

be estimated as about 400 kg per crewmember. The recy-cling equipment has a daily material cost of about 1 kg/CM-d. (Jones and Kliss, 2005) It is assumed that oxygenand water recycling is 90 percent efficient.

The purpose of recycling is to save the daily mass ofoxygen and water provided in direct resupply. But savingthis resupply mass requires providing a large recycling sys-tem plus the daily material the resupply equipment con-sumes. If the mission is short, the total mass for resupplywould be much less than the mass of the recycling system.For short missions, recycling does not pay for its mass, so itdoes not break even. But the total daily resupply masssaved by recycling increases directly with the missionlength. The date when the resupply mass saved by recyclingjust equals the mass of the recycling equipment plus itsdaily material is called the recycling breakeven date.

The breakeven date is computed as the time when theresupply mass equals the recycling mass. The daily materialmass requirement is 10 kg/CM-d. Ninety percent of this isrecovered by recycling, so recycling saves 9 kg/CM-d. Therecycling equipment requires 1 kg/CM-d of support materi-als, so the net savings of recycling is 8 kg/CM-d. Thebreakeven date is (400 kg/CM)/(8 kg/CM-d) = 50 days.This recycling breakeven date calculation indicates thatoxygen and water should be supplied directly for missionsof much less than 50 days but provided by recycling onmissions longer than 50 days (see Fig. 4).

Directly supply for missions that are longer than thebreakeven date costs much more than recycling. If directprovisioning is used out to 100 days, twice the breakevendate, its total cost is 10 kg/CM-d � 100 d = 1000 kg/CM.The cost of recycling for 100 days would be 400 kg/CM + (1 kg/CM-d recycling supplies + 1 kg/CM-d recy-cling losses) � 100 d = 600 kg/CM. Using direct supplyfor 100 days costs 400 kg/CM more than recycling (thebreakeven date computation does not consider the differentreliabilities of resupply or recycling).

Fig. 4. Cumulative mass versus duration for direct supply and recycling.

Typical breakeven analyses indicate that water recycling“should be used for a mission longer than a few weeks,”“oxygen regeneration technologies should be applied formissions longer than a few months,” and that breakevenon food production “is unlikely” (Doll and Eckart, 2000).

6. Oxygen and water recycling system architecture for longduration missions

The top-level functional architecture of the oxygen andwater recycling systems and the crew habitat interfacesare shown in Fig. 5.

The oxygen and water systems includes four subsystems:Oxygen Supply, Condensate Purification, Urine Purifica-tion, and Wash Water Purification.

The Oxygen Supply subsystem includes different compo-nents for carbon dioxide removal and its reduction to waterand for oxygen generation from water. The components ofthe Oxygen Supply subsystem are shown in Fig. 6. Theflows of carbon and hydrogen are not shown because theydepend on technology selection for carbon dioxidereduction.

The oxygen and water recycling systems must provide:

1. Oxygen2. Drinking and food preparation water

H2O CO2

O2 H2O

O2 Store

CO2Removal

CO2Reduction

O2 Generation

Fig. 6. Components of the Oxygen Supply subsystem.

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3. Urine flush water4. Wash water

They must generate these products by recycling inputwaste streams:

1. Exhaled carbon dioxide2. Respiration and perspiration condensate3. Urine and urine flush water4. Used wash water

A direct but too-simple design approach would be to uselargely independent recycling processors for each input–output pair; carbon dioxide–oxygen, condensate–drinkingwater, urine–urine flush, and wash water. However, theoutput and input mass flow rates are not identical andtransfer between the processor streams is necessary. Ifwater is supplied in hydrated food, there may be excesswater.

7. Short mission (CEV, Lunar Lander) life support

The CEV and the Lunar Lander could have beendesigned to use the life support technologies originallydeveloped for Apollo and Shuttle. However, innovativetechnologies are planed for and offer compellingadvantages.

7.1. Legacy life support technologies for CEV and LunarLander

Since the CEV takes crews to ISS and lunar orbit, likethe Shuttle and Apollo CM, it can use the Shuttle and

Table 5Legacy Apollo and Shuttle approach for CEV and Lunar Lander.

CEV, Lunar Lander

Destination ISS, lunar orbit, MTVDuration �10 daysLegacy basis Shuttle, Apollo

Atmosphere

CO2 removal LiOHCO2 reduction NoneTCC Activated charcoal, filtersTC monitoring NoneAtmosphere storage N2, O2 tanksAtmosphere source N2, O2 tanksHumidity control CHX

Water

Potable water storage TanksWater source TanksWater purification IodineWater monitoring NoneWastewater processing None, ventedWaste water storage Tank

Waste

Feces processing Fecal bagsUrine processing None, urine to waste water tank

Apollo CM life support approach. A later CEV will launcha larger crew for Mars, but it operates for a short durationand can also use a similar life support architecture. TheLunar Lander will support a crew for several days on theMoon, like the Apollo LM, and can also use a similar lifesupport. Table 5 gives a possible legacy life supportapproach for the CEV and Lunar Lander, using the sameformat as Table 4.

7.2. New life support technologies in the CEV

The CEV life support will use new life support technol-ogies described in the ESAS. Unlike the Shuttle and ApolloCM, the CEV will use solar arrays, not fuel cells, forpower. The CEV will use solar power because of therequirement for 7 months inoperative time in lunar orbitwhile one crew is conducting its Lunar Outpost mission(ESAS, 2005). The use of fuel cells on CEV missions couldhave provided more than enough water for the crew andalso excess water, as with Shuttle, that could have beentransferred to ISS or other spacecraft.

Unlike the Shuttle and Apollo CM, the CEV will use aswing bed, not LiOH and not a condensing heat exchanger,to remove carbon dioxide and water from the atmosphere(ESAS, 2005). Respired and perspired water captured bythe condensing atmosphere heat exchangers could havebeen a significant source of recycled water.

7.2.1. Amine-based swing bed carbon dioxide removal

An amine-based swing bed carbon dioxide and humidityremoval technology is being developed for the CEV toeliminate both carbon dioxide and water. It eliminatesthe need for the previously used condensing heat exchan-ger, phase separator, and low-temperature thermal control.The swing bed system is shown in Fig. 7.

The regenerable amine sorbent absorbs carbon dioxideby first combining with water vapor to form a hydratedamine and then reacting with carbon dioxide to form bicar-bonate. The exothermic heat of reaction of the absorbingbed combined with exposure to space vacuum providesthe energy necessary for carbon dioxide removal. A sepa-rate dedicated trace contaminant control system will beneeded with the swing bed system (Papale et al., 2009;Barta and Ewert, 2009).

7.2.2. Sorbent-based carbon dioxide removal

A sorbent-based carbon dioxide removal system is alsobeing developed for possible use in the CEV. The technol-ogy uses a molecular sieve and silica gel sorbents, whichhave been successfully used on Skylab and the ISS. Likethe amine-based system, sorbent-based atmosphere revital-ization (SBAR) does not require a condensing heat exchan-ger, a water separator or a low-temperature coolant loop.The vacuum swing adsorption process requires only thevacuum of space for low-power sorbent regeneration.SBAR combines the carbon dioxide, latent water, and tracecontaminant removal functions in a single system, and may

Air inlet

Valve housing

Manifold

Vacuum port

Air outlet

Vacuum port

Fig. 7. The amine-based swing bed carbon dioxide removal system.

924 H.W. Jones, M.H. Kliss / Advances in Space Research 45 (2010) 917–928

be suitable for longer duration missions (Miller and Knox,2009; Ebner et al., 2009).

7.2.3. Thermal catalytic oxidizer for trace contaminant

control system

The trace contaminant control system (TCCS) used onthe ISS is comprised of three main components; an expend-able granular activated carbon bed, a thermal catalytic oxi-dizer, and an expendable post-sorbent bed. The activatedcarbon bed is treated with phosphoric acid to preventammonia not removed by the condensing heat exchangerfrom contaminating the thermal catalytic oxidizer. Becausethe CEV atmosphere revitalization system will not includea condensing heat exchanger, more contaminants must beremoved by the TCCS. The activated carbon bed accumu-

Fig. 8. The prototype catalytic reactor being developed for chemical tracecontaminant control.

lates chemical contaminants removed from the spacecraftatmosphere. Off-nominal increases in temperature or rela-tive humidity may release the adsorbed contaminants fromthe activated carbon bed back into the cabin atmosphere.Because of these problems, a regenerable thermal catalyticoxidizer is being developed for CEV. A photograph of theprototype catalytic reactor is shown in Fig. 8.

This ultra-compact, lightweight, regenerable trace con-taminant control system will reduce TCCS system weightand operational complexity and can be utilized for futuremissions (Perry, 2009).

7.2.4. Water disinfection

Water disinfection on the Space Shuttle and the ISS usesresidual silver or iodine. Before stored water is consumedby the crew, the iodine must be removed to avoid adverseeffects on the thyroid. It is desirable to replace iodine asthe disinfectant for future missions. Advanced disinfectiondevelopment efforts are investigating the use of ionic sil-ver, its compatibility with materials such as stainless steel,and its efficacy on target microbial organisms (Adam,2009).

7.2.5. Urine pretreatmentUrine can either be collected and disposed of or pro-

cessed to recover the water. Chemical pretreatment of urineinhibits microbial growth, prevents the hydrolysis of ureato ammonia, and prevents the precipitation of solids. Thecurrent US pretreatment approach uses oxone for disinfec-tion and sulfuric acid for pH reduction, while the Russianpretreatment system uses chromium trioxide for disinfec-tion and sulfuric acid for pH reduction. These pretreatmentchemicals are toxic and have poor compatibility withfuture requirements to recover water from urine. Alterna-

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tive urine pretreatment compounds with reduced toxicityand minimal volume and mass are being investigated(Verostko et al., 2004; Carter et al., 2008).

7.2.6. CEV waste management

Spacecraft waste management to date has largely reliedon the collection and storage of trash and human waste.Trash has been typically compacted by hand and stored.Early metabolic waste collection systems consisted of bags,while the ISS uses microgravity-compatible commodes.Near-term efforts for CEV are focusing on developing animproved commode that combines the desirable wasteentrainment feature of the ISS commode with the muchlower mass and volume features of the Apollo bag system(Yuan et al., 2009).

8. Long mission (Lunar Outpost, MTV, Mars base) life

support

The Lunar Outpost, MTV, and Mars base are longduration missions that could use the life support technolo-gies developed for ISS, but improvements are needed.

8.1. Legacy ISS life support technologies for Lunar Outpost,

MTV, and Mars base

Table 6 gives an ISS-based legacy approach for theLunar Outpost, MTV, and Mars base life support.

However, compared to ISS, the Lunar Outpost, MTV,and Mars base have much higher mass launch cost, muchlonger travel time, and lesser or no capability for resupplyfrom Earth.

Table 6Legacy ISS approach for Lunar Outpost, MTV, and Mars base.

Lunar Outpost, MTV, Mars base

Destination Moon, Mars orbit, MarsDuration 10 years, 6 months, 18 monthsLegacy basis ISS

Atmosphere

CO2 removal 4BMSCO2 reduction SabatierTCC Activated charcoal, filters, oxidizerTC monitoring GCMSAtmosphere storage N2, O2 tanksAtmosphere source CO2 reduction, H2O electrolysisHumidity control CHX, condensate to waste water

Water

Potable water storage TanksWater source Tanks, wastewater recyclingWater purification IodineWater monitoring TOC, pH, iodine, conductivityWastewater processing MultifiltrationWaste water storage Tank

Waste

Feces processing Fecal bags, dried compactedUrine processing VCD

8.2. Needed improvements for Lunar Outpost, MTV, and

Mars base

The ultimate goal of the U.S. Space Exploration Policyis Mars, with the Moon serving as a test bed. Gaining expe-rience and proving capability is the reason to return to theMoon and establish a permanent base there.

The Mars trip has much greater distance and travel timethan visiting ISS or the Moon. The mass emplacement costper kilogram is much higher for Mars and the Moon thanfor ISS. Because of the impossibility of rapid resupply orcrew return, the required reliability of life support is muchhigher for Mars than for ISS or the Moon. The life supportfor the Lunar Outpost, MTV, and Mars base must havemuch lower mass and much higher reliability than theISS systems. The Lunar Outpost and Mars base life sup-port can take advantage of gravity and planetary resources,unlike ISS and MTV.

The long mission ISS life support should be extensivelyredesigned to reduce mass and improve reliability. There isan opportunity to incorporate ISS lessons learned and totake advantage of technology advancements over the last20 years.

8.2.1. The ISS life support design raises several issues

The life support design and technology selection processfor the ISS indicates that the ISS life support design maynot be optimum for future long duration missions. The ini-tial technology screening eliminated low technical maturitytechnologies. Baseline and alternate life support subsystemtesting began in the mid 1980s, 20 years before the oxygenand water systems could be launched to ISS. The ISS lifesupport recycling technologies have not yet been flightproven.

The oxygen generation, water purification, and urinepurification technologies chosen for ISS were selected moreon qualitative than quantitative analysis. The EquivalentSystem Mass, a standard metric in life support design,was not computed. Reliability was not compared quantita-tively. The oxygen, water purification, and urine technolo-gies selections all changed between the earlier Space StationFreedom (SSF) baseline identification and the final ISSselection. The technologies not selected by ISS seem nearlyas good as those selected.

A paper by ISS life support team members explains theneed for improvements to the ISS design,

“The baseline environmental control and life support(ECLS) systems currently deployed on board the Interna-tional Space Station (ISS) and that planned to be launchedin Node 3 are based upon technologies selected in the early

1990s. While they are generally meeting or exceedingrequirements for supporting the ISS crew, lessons learned

from years of on orbit and ground testing, together withnew advances in technology state of the art, and the unique

requirements for future manned missions prompt consider-ation of the next logical step to enhance these systems toincrease performance, robustness, and reliability, and

Table 7Potential lower mass Lunar Outpost, MTV, or Mars base life support.

Lunar Outpost, MTV, Mars base

Destination Moon, Mars orbit, MarsDuration 10 years, 6 months, 18 monthsAnalog ISS

Atmosphere

CO2 removal EDC or 2BMS

CO2 reduction SabatierTCC Activated charcoal, filters, regenerable oxidizer

TC monitoring GCMSAtmosphere storage N2, O2 tanksAtmosphere source CO2 reduction, H2O electrolysis

Humidity control CHX, condensate to waste water

Water

Potable water storage TanksWater source Tanks, wastewater recyclingWater purification IodineWater monitoring TOC, pH, iodine, conductivityWastewater processing MultifiltrationWaste water storage Tank

Waste

Feces processing Lyophilization

Urine processing TIMES or VPCAR

The approaches changed from ISS are given in bold italics.

926 H.W. Jones, M.H. Kliss / Advances in Space Research 45 (2010) 917–928

reduce on orbit and logistical resource requirements”

(Emphasis added) (Carasquillo et al. 2004).Problems cited with the ISS life support design include

high power consumption, difficult maintainability andlogistics, sensitivity of several components to particulatesand fouling, gravity related problems in multi-phase fluidflow and separations, and the lack of fine particle settlingin microgravity. There are potential improvements inrobustness, performance efficiency, and capability (Caras-quillo et al., 2004).

The ISS life support design process may not have pro-duced the best design for the Lunar Outpost, MTV, andMars base, especially considering their differing require-ments. We consider mass and reliability requirements inmore detail.

8.2.2. Lower mass needed for Moon and Mars missions

The Lunar Outpost life support system will have to betransported beyond LEO to lunar orbit and then theMoon’s surface. The MTV life support must be taken fromLEO to Mars orbit and then returned to LEO. The Marsbase life support must be taken from LEO to Mars orbitand then to Mars’ surface. The mass emplacement costsfor Lunar Outpost, MTV, and Mars base are about anorder of magnitude higher than the costs to transport massto ISS in LEO.

The higher mass emplacement cost makes more attrac-tive the lower mass life support alternatives that were con-sidered but not selected for ISS. An electrochemicaldepolarized concentrator (EDC) and a two bed molecularsieve (2BMS) have lower mass than a 4BMS, a static feedwater electrolysis (SFWE) oxygen generator has less massthan a solid polymer water electrolysis (SPWE), and a ther-moelectric integrated membrane evaporation system(TIMES) or Vapor Phase Catalytic Ammonia Removal(VPCAR) urine processor has less mass than vapor com-pression distillation (VCD) (Jones and Kliss, 2005). Lyoph-ilization, or freeze-drying, can be used to recover a smallamount of water from feces.

Table 7 lists a potential lower mass Lunar Outpost,MTV, or Mars base life support, using the same formatas Table 6. The approaches changed from ISS are givenin bold italics.

Mass and launch cost can be reduced up to one half bysubstituting EDC or 2BMS for 4BMS, SFWE for SPWE,and TIMES or VPCAR for VCD.

8.2.3. Greater reliability needed for Mars missions

Since it is not possible to send additional material orequipment, or to return ahead of schedule during a missionto Mars, life support for the MTV or Mars base must havemuch greater reliability than for ISS or the Lunar Outpost.For any particular system, the probability of failure-freeoperation declines exponentially with mission duration.

A mission to the ISS or a lunar sortie might require only10 operational days, while the total duration of a Marsmission could be nearly a 1000 days. Suppose we achieve

a life support reliability of 0.99 for a short 10-day mission.The corresponding reliability for 1 day is 0.999, indicatingan expected failure rate of one in a thousand per day. Thisis not sufficient for a 1000-day mission. The reliability overa 1000-day Mars mission would be 0.999 raised to theexponential power of 1,000, or 0.999 ^ 1,000, which equals0.37, so that there would be a 63 percent chance of one ormore failures during the mission. This is not satisfactoryreliability.

To achieve a reliability of 0.99 over a 1000-day Marsmission, the corresponding reliability for 1 day would be0.99999, indicating an expected failure rate of one in onehundred thousand per day. This corresponds to a reliabilityover a 10-day mission of 0.9999. This corresponds to onlyone failure in 10,000 repeated 10-day missions.

Designing a system to be sufficiently reliable for1000 days will be difficult, but it is possible. Ultra reliablespace life support recycling systems can be built by dou-bling their minimum mass. Recycling equipment can bepartitioned to have a large number of components so thatthe failure modes are separated and contained, and so thatthe failure rate of each component is small because the fail-ures are distributed over a large number of components.Ultra reliability can be achieved by providing a single sparefor each component if the number of components is largeenough. This means that ultra reliability for recyclingequipment can be achieved by merely doubling the equip-ment mass (Jones, 2008).

Life support equipment should be designed for ultra reli-ability and tested over the long term to ensure that suchreliability is attained. Systems must be designed, tested,and allowed to fail so that they can be redesigned to

H.W. Jones, M.H. Kliss / Advances in Space Research 45 (2010) 917–928 927

eliminate failure modes. Several cycles of design, long dura-tion test, and redesign will be needed to achieve and dem-onstrate sufficiently high reliability for a Mars mission.

8.3. New life support technologies for long duration missions

In addition to the new technologies being developed forCEV, there are new technologies in water processing andwaste management that are suitable for long durationmissions.

8.3.1. Vapor Phase Catalytic Ammonia Removal (VPCAR)

Vapor Phase Catalytic Ammonia Removal (VPCAR) isa distillation-based/catalytic oxidation water processor. Itsdesign philosophy departs from the traditional concept ofthe on-orbit replaceable unit (ORU) in favor of a highlyintegrated processor configuration. It accepts a combinedwastewater stream of humidity condensate, hygiene water,and urine, and produces potable water in a single step withno pre- or post-treatment required. The design is intendedto require no consumables and minimal maintenance. A

Fig. 9. The Vapor Phase Catalytic Ammonia Removal (VPCAR) waterprocessor.

Fig. 10. Prototype heat melt compa

high efficiency wiped-film rotating disk evaporator removesinorganic salts and nonvolatile organic contaminants fromthe feed stream. The resulting vapor stream is then com-pressed and passed through an oxidation reactor wherevolatile hydrocarbons are converted to carbon dioxideand water, and ammonia is oxidized to nitrogen andnitrous oxide. A second high temperature reduction reactordecomposes the nitrous oxide to nitrogen and oxygen. TheVPCAR converts about 97 percent of the wastewater topotable standards. A photograph of the VPCAR prototypeis shown in Fig. 9 (Duval et al., 2009).

8.3.2. Waste management for long duration missions

The accumulation of trash on spacecraft is a problemand future missions will require improved approaches. Amechanical trash compaction system is being developedto reduce the volume of trash to 10–20% of its original vol-ume. For longer duration missions, a heating element inthe compactor removes the water, stabilizes the waste,and encapsulates the compressed trash in the melted plasticcomponent of the trash. Plastic is typically more than 20%of the trash by mass. A prototype heat melt compactor isshown in Fig. 10.

The compactor recovers the water in the trash, compactsthe trash to 10–20% of its original volume, and encapsu-lates the compressed waste in the melted plastic componentof the trash. Recovering water from both trash and meta-bolic wastes would provide significant water mass launchsavings compared to the existing ISS approach (Paceet al., 2009).

9. Conclusion

The Crew Exploration Vehicle (CEV) life support sys-tem could be similar to the Space Shuttle and Apollo sys-tems, but improved systems are needed and are beingdeveloped. The Lunar Outpost, MTV, and Mars base lifesupport systems could be similar to the ISS system, butthey should be extensively redesigned to reduce mass,improve reliability, incorporate lessons learned, and take

ctor with a sample waste disk.

928 H.W. Jones, M.H. Kliss / Advances in Space Research 45 (2010) 917–928

advantage of technology improvements over the last20 years.

The Lunar Outpost life support should be similar to thatfor Mars base, since the Moon is the test bed for Mars. TheMoon and Mars base life support can take advantage ofgravity and planetary resources. Much more work isneeded to develop satisfactory life support systems forthe Moon and Mars.

Additional life support development challenges includeconducting trade studies to select new or existing technolo-gies, developing new technologies on schedule and in bud-get, integrating life support systems having new andexisting technologies, flight proving technologies andintegrated systems, and interfacing life support with othermission elements, such as a laundry, shower, or saladmachine.

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