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2. Science andExploration Rationale

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2.1 Introduction

Mars is an intriguing and exciting planetwith many adventures and discoveriesawaiting planetary explorers. But before wego, we must provide the tools the explorerswill use, anticipate as much as possible thesituations they will encounter, and preparethem for the unexpected. For the first time ina space exploration mission, it will be up tothe crew and supporting personnel on Earthto create specific activities as the missionprogresses and discoveries are made. Thelength of time spent on the martian surface, aspresented in the Reference Mission, willpreclude development of the detailed, highlychoreographed mission plans typical oftoday’s space missions. The crew will havegeneral goals and objectives to meet withintheir other time constraints (for example,exercise for health maintenance, regularmedical checks, routine systems maintenance,etc.). Based on knowledge gained fromprecursor robotic missions, the crew will landin an area that has a high probability ofsatisfying the pre-set mission objectives.However, due to the extendedcommunications time lag between Earth andMars, the crews and their systems must beable to accomplish objectives in a highly

autonomous manner with only generalsupport from Earth. From the rationalegenerated by the Mars Study Team forsending human crews to Mars, goals andobjectives are derived to provide guidance forthe exploration crews during their extendedstay on the martian surface. This section willdiscuss that Study Team rationale.

2.2 The “Why Mars” Workshop

In August 1992, a workshop was held atthe Lunar and Planetary Institute in Houston,Texas, to address the “whys” of Marsexploration. This workshop brought togethera group of experts (listed in Table 2-1) familiarwith the key issues and past efforts associatedwith piloted Mars missions in an effort toprovide the top-level rationale andrequirements from which the Marsexploration program could be built (Dukeand Budden, 1992). This group was asked togenerate three key products: a Mars missionrationale, Mars exploration objectives, and alist of key issues and constraints, to be usedby the Mars Study Team (members listed inTable 2-2) to define the technical details of aReference Mission. The workshop attendeesidentified six major elements of the rationalefor a Mars exploration program.

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Table 2-1 Mars Exploration Consultant Team

Dr. George MorgenthalerUniversity of ColoradoBoulder, Colorado

Dr. Robert MoserChama, New Mexico

Dr. Bruce MurrayCalifornia Institute of TechnologyPasadena, California

Mr. John NiehoffScience Applications InternationalCorporationSchaumburg, Illinois

Dr. Carl SaganCenter for Radiophysics and SpaceResearchCornell UniversityIthica, New York

Dr. Harrison SchmittApollo 17 AstronautAlbuquerque, New Mexico

Dr. Steven SquyersCornell UniversityIthica, New York

Mr. Gordon WoodcockBoeing Defense and Space GroupHuntsville, Alabama

Dr. David BlackDirectorLunar and Planetary InstituteHouston, Texas

Dr. Michael CarrU.S. Geological SurveyMenlo Park, California

Dr. Ron GreeleyDept. of GeologyArizona State UniversityTempe, Arizona

Dr. Noel HinnersLockheed MartinDenver, Colorado

Dr. Joseph KerwinSkylab AstronautLockheed MartinHouston, Texas

Mr. Gentry LeeFrisco, Texas

Dr. Roger MalinaCenter for EUV AstrophysicsUniversity of CaliforniaBerkeley, California

Dr. Christopher McKayNASA Ames Research CenterMoffett Field, California

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Table 2-2 Mars Study Team

Dr. Geoff BriggsNASA Ames Research CenterMoffett Field, California

Ms. Jeri BrownNASA Johnson Space CenterHouston, Texas

Ms. Nancy Ann BuddenNASA Johnson Space CenterHouston, Texas

Ms. Beth CaplanNASA Johnson Space CenterHouston, Texas

Mr. John ConnollyNASA Johnson Space CenterHouston, Texas

Dr. Michael DukeNASA Johnson Space CenterHouston, Texas

Dr. Steve HawleyNASA Johnson Space CenterHouston, Texas

Mr. William HuberNASA Marshall Space Flight CenterHuntsville, Alabama

Mr. Kent JoostenNASA Johnson Space CenterHouston, Texas

Mr. David KaplanNASA Johnson Space CenterHouston, Texas

Dr. Paul KeatonLos Alamos National LaboratoryLos Alamos, New Mexico

Mr. Darrell KendrickNASA Johnson Space CenterHouston, Texas

Ms. Barbara PearsonNASA Johnson Space CenterHouston, Texas

Mr. Barney RobertsNASA Johnson Space CenterHouston, Texas

Mr. Ed SvrcekNASA Johnson Space CenterHouston, Texas

Mr. David WeaverNASA Johnson Space CenterHouston, Texas

•Human Evolution – Mars is the mostaccessible planetary body beyond theEarth-Moon system where sustainedhuman presence is believed to bepossible. The technical objectives of Marsexploration should be to understandwhat would be required to sustain a

permanent human presence beyondEarth. However, it is not an objective ofthe Reference Mission to settle Mars butto establish the feasibility of, and thetechnological basis for, humansettlement of that planet.

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•Comparative Planetology – The scientificobjectives of Mars exploration should beto understand the planet and its historyto better understand Earth.

•International Cooperation – The politicalenvironment at the end of the Cold Warmay be conducive to a concertedinternational effort that is appropriate,and may be required, for a sustainedprogram.

•Technology Advancement – The humanexploration of Mars currently lies at theragged edge of achievability. Some of thetechnology required to achieve thismission is either available or on thehorizon. Other technologies will bepulled into being by the needs of thismission. The new technologies or thenew uses of existing technologies willnot only benefit humans exploring Marsbut will also enhance the lives of peopleon Earth.

•Inspiration – The goals of Marsexploration are bold, are grand, andstretch the imagination. Such goals willchallenge the collective skill of thepopulace mobilized to accomplish thisfeat, will motivate our youth, will drivetechnical education goals, and will excitethe people and nations of the world.

•Investment – In comparison with otherclasses of societal expenditures, the costof a Mars exploration program ismodest.

The workshop attendees then translatedthese elements into two specific missionobjectives. For the first human exploration ofMars:

•A better understanding is needed ofMars—the planet, its history, and itscurrent state. And to answer, as best aspossible, the scientific questions thatexist at the time of the exploration, abetter understanding of the evolution ofMars’ climate and the search for past lifeare pressing issues.

•It is important to demonstrate that Marsis a suitable location for longer termhuman exploration and settlement.

The following sections discuss the detailsof the science and exploration rationale asapplied to the Reference Mission.Implementation details are in Section 3.

2.3 Science Rationale

Mars is an intriguing planet in part forwhat it can tell us about the origin and historyof planets and of life. Visible to the ancientsand distinctly reddish in the night sky, it hasalways been an attractive subject forimaginative science fiction. As the capabilityfor space exploration grew in the 1960s, itbecame clear that, unlike Earth, Mars is not aplanet teeming with life and has a harshenvironment. The images of Mariner 4showed a Moon-like terrain dominated bylarge impact craters (Figure 2-1).

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Figure 2-1 Orbital image of Mars.

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This terrain now is believed to representancient crust, similar to the Moon’s, formed inan initial period of planetary differentiation.Mariner 9 showed for the first time that Marswas not totally Moon-like, but actually

exhibits later volcanic and tectonic features.Large volcanoes of relatively recent activity(Figure 2-2) and large crustal rifts due totensional forces (Figure 2-3) demonstrate theworking of internal forces.

Figure 2-2 Olympus Mons, the largest volcanoin the solar system.

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Figure 2-3 Across the middle is Valles Marineris, a huge canyonas long as the United States.

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The absolute time scale is not accuratelycalibrated; however, by analogy with theMoon, the initial crustal formation may haveoccurred between 4 billion and 4.5 billionyears ago, and the apparent freshness of thelarge martian volcanoes suggests theirformation within the last billion years.

Many scientific questions exist regardingMars and its history and will continue to existlong after the first human missions to theplanet have been achieved. Two key areas ofscientific interest are the evolution of martianclimate and the possible existence of past life.

Mars’ atmosphere now consists largely ofcarbon dioxide with a typical surface pressureof about 0.01 of Earth’s atmosphere(comparable to Earth’s atmospheric pressureat an altitude of approximately 30,000 metersor 100,000 feet) and surface temperatures thatmay reach 25°C (77°F) at the equator inmidsummer, but are generally much colder.At these pressures and temperatures, watercannot exist in liquid form on the surface.However, Mariner 9 and the subsequentViking missions observed features whichindicate that liquid water has been present onMars in past epochs (Figure 2-4).

Evidence for the past existence ofrunning water and standing water has beennoted, and the interpretation is that theatmosphere of Mars was thicker andwarmer—perhaps much like Earth’s earlyatmosphere before the appearance of oxygen.Three questions arise:

•What was the reason for the change ofatmospheric conditions on Mars?

•What are the implications of suchchanges for environmental changes onEarth?

•Were the conditions on early Marsenough like those of early Earth to guidea search for past life?

These questions are part of the Marsscientific exploration addressed by theReference Mission, and these questions can beanswered only by understanding thegeological attributes of the planet: the types ofrocks present, the absolute and relative agesof the rocks, the distribution of subsurfacewater, the history of volcanic activity, thedistribution of life-forming elements andcompounds, and other geologic features.These attributes all have to be understood inthe context of what we know about the Earth,the Moon, and other bodies of our solarsystem.

Addressing the question of whether lifeever arose on Mars can provide afundamental framework for an explorationstrategy because, in principle, the search forpast life includes investigating the geologicaland atmospheric evolution of the planet. It isgenerally understood that the search forevidence of past life cannot be conductedsimply by a hit-and-miss landing-and-lookingstrategy, but must be undertaken in a step-wise manner in which geological provenancesthat might be suitable are characterized,located, and studied (Exobiology ProgramOffice, 1995). The characteristics of suitableexploration sites are highly correlated withthe search for past or present water on the

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Figure 2-4 Dense tributary networks indicative of past presenceof liquid water on Mars.

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planet. Within the geological framework,strategic questions related to the search forevidence of life can be posed.

•What is the absolute time scale fordevelopment of the major features onMars? This would include determiningthe time of formation of the martiancrust, a range of formation ages forvolcanic plains, and the age of theyoungest volcanoes. With thisinformation as a guide, the age offormation of water-formed channelsshould be boundable, and theorganogenic element content of martianmaterials as a function of time may beobtainable. As is inferred from the SNCmeteorites which are believed to haveoriginated on Mars (Bogard, et al., 1983and McSween, 1994), impacts on Marshave preserved samples of the martianatmosphere in shock-produced glasses.Thus, it may be possible to characterizethe evolution of the atmosphere fromcarefully selected samples of impactglass.

•What is the evidence for the distributionin space and time of water on thesurface? This would include watercombined in widely distributed igneousor clay minerals, in localized depositssuch as hydrothermal vents, insubsurface permafrost, in the polar caps,and in the atmosphere. The distribution,age, composition, and mode offormation (minerals formed by reactionwith or deposition from heated or cool

aqueous fluids, as found in the SNCmeteorites) is of major interest. Can thechannels apparently formed by watererosion be demonstrated to haveexperienced running water? Is thereverifiable evidence for the existence ofponds of water? What is the distributionof subsurface permafrost, and can thefeatures interpreted as permafrostcollapse be verified?

•What are the distribution andcharacteristics of carbon and nitrogen—the organogenic elements? Where dothey exist in reduced form? In whatenvironments are they preserved in theiroriginal state? Is there chemical, isotopic(hydrogen, carbon, nitrogen isotopes), ormorphological evidence that will linkconcentrations of organogenic elementsto the past existence of life?

•If organic remains can be found, howextensive are they in space and time?What are their characteristics, varietyand complexity? How are they similar ordifferent to biological materials onEarth?

Answers to these questions may besought through orbital mapping (for example,to determine the distribution of hydrothermalmineral deposits), in situ studies (surfacemineralogy, distribution of volatile elements),sample return (age of rock units, detailedchemistry, mineralogy, and isotopiccomposition), and human exploration withsample return (similar but with more highlyintelligent sample collection). The scientific

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community debates the precise order ofinvestigative means used to achieve thisstrategy, but generally concludes that thequestion of distribution of past life will be ofsuch a difficult nature that sample return willbe required and that humans will ultimatelychoose to carry out the exploration in person.

Given the assumption that humans willtake on the bulk of this type of exploration,the key questions become:

•What is the appropriate role and place inthe exploration strategy of roboticsample return missions?

•Scientifically, where is the appropriatetransition from robotic missions,conducted routinely, and humanexploration missions, which may besingular, large, and not reproducible?

General guidelines are needed to answerthese questions. Sample return missionsshould be favored when they can be used tosignificantly reduce the number ofsubsequent missions to address the geologicalmodeling of the planet. Sample returnmissions are likely to be more expensive thanone-way missions, so to be cost effective, theymust reduce the need for a proportionallylarger number of subsequent missions orgarner otherwise unobtainable information iftheir justification is purely scientific. From ascientific perspective, the guidelines forhuman exploration are similar. If a humanexploration mission promises to answer themajor strategic questions better than a largernumber of robotic explorers, or opens new

modes of exploration that cannot be achievedrobotically, then the human mission will becost effective on scientific grounds.

2.4 Exploration Rationale

Aside from purely scientific benefits, thehuman exploration of Mars brings with itmany tangible and intangible near-termbenefits such as:

•New associations between groups ordisciplines which previously have notinteracted, but because of commonobjectives in exploration find newstrengths and opportunities (forexample, new international cooperation).

•New technologies which may be usedfor practical application on Earth or inother space enterprises (dual-usetechnologies).

•Education of a new generation ofengineers and scientists spurred by thedream of Mars exploration.

In the long term, the biggest benefit ofthe human exploration of Mars may well bethe philosophical and practical implicationsof settling another planet.

2.4.1 Inhabiting Another Planet

The dream of human exploration of Marsis intimately tied to the belief that new landscreate new opportunities and prosperity. Inhuman history, migrations of people havebeen stimulated by overcrowding, exhaustionof resources, the search for religious or

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economic freedom, competitive advantage,and other human concerns. Rarely havehumans entered new territory and thencompletely abandoned it. A few people havealways been adventurous enough to adopt anewly found territory as their home. Most ofthe settlements have eventually becomeeconomically self-sufficient and haveenlarged the genetic and economic diversityof humanity. The technological revolution ofthe twentieth century, with high speedcommunication and transportation andintegrated economic activity, may havereversed the trend toward human diversity;however, settlement of the planets can onceagain enlarge the sphere of human action andlife.

Outside the area of fundamental science,the possibility that Mars might someday be ahome for humans is at the core of much of thepopular interest in Mars exploration. Ahuman settlement on Mars, which wouldhave to be self-sufficient to be sustainable,would satisfy human urges to challenge thelimits of human capability, create thepotential for saving human civilization froman ecological disaster on Earth (for example, agiant asteroid impact or a nuclear incident),and potentially lead to a new range of humanendeavors that are not attainable on Earth.

The settlement of Mars presents newproblems and challenges. The absence of anatural environment that humans and mostterrestrial fauna and flora would find livableand the current high cost of transportation arethe main barriers to human expansion there.

The fact that, once on Mars, humans cannoteasily return to the Earth (and then only atspecified times approximately 26 monthsapart) makes it necessary to develop systemswith high reliability and robustness.

At the present level of humantechnological capability, a self-sufficientsettlement on Mars stretches our technicallimits and is not economically justifiable, butit is imaginable. If, however, transportationcosts were to be reduced by two orders ofmagnitude, such settlements might becomeeconomically feasible. What kind of strategyshould be followed to explore the concept ofhumans permanently inhabiting Mars? Threeconsiderations are important.

•Demonstrating the potential for self-sufficiency. This would includeunderstanding the potential to obtain allimportant materials to support humanhabitation from the natural materials ofMars. It is most important that humansbe able to capture energy for drivingprocesses and have access to naturalresources (such as water, oxygen,agricultural raw materials, buildingmaterials, and industrial materials) frommartian rocks and soil. Demonstratingself-sufficiency requires that resources belocated and technology and experiencebe developed to efficiently extract themfrom the in situ materials. Much can bedone robotically to locate resources priorto arrival of the first human crew.Extraction technology depends on amore detailed understanding of the

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specific materials present on Mars andrequires the detailed mineralogical andchemical analyses generally associatedwith sample return missions. Anexception is the production of water,methane, and oxygen from the martianatmosphere, which is now known wellenough to design extraction technology(Sullivan, et al., 1995). In addition to theextraction and use of martian resources,self-sufficiency undoubtedly requireshighly advanced life support systems inwhich most of the waste product fromhuman activity is recovered and reused,and food is grown on the planet.

•Demonstrating that human beings cansurvive and flourish on Mars. This willlikely be first explored by long-durationmissions in Earth orbit and may becontinued in the 1/6-g environment ofthe Moon (Synthesis Group, 1991). Twotypes of needs—physical andpsychological—must be met for humansto survive and flourish on Mars. Physicalneeds will be met through advanced lifesupport systems, preventive medicalsciences (nutrition, exercise,environmental control, etc.), and thecapability of medical support for peopleon Mars. Psychological needs will bemet through the design of systems,identification and selection of work forcrews, communications with Earth, anda better understanding of humaninteractions in small communities. Manyof these can be addressed through alunar outpost program or in the

International Space Station program tobe conducted in the late 1990s. Some ofthese concerns can also be addressed onthe first human exploration missions toMars, in which greater risks may betaken than are appropriate for latersettlement.

•Demonstrating that the risks to survivalfaced in the daily life of settlers on Marsare compatible with the benefitsperceived by the settlers. Risks tosurvival can be quantified through theMars exploration program. However, thebenefits will be those perceived byfuture generations and cannot beaddressed here.

2.4.2 International Cooperation

The space age gained its start in a periodof intense technical and social competitionbetween East and West, represented by theSoviet Union and the United States.Competition during the InternationalGeophysical Year resulted in the Soviet Unionbeing the first to launch a satellite into Earthorbit, which served to challenge and remindthe United States that technologicalsupremacy was not solely the province of theUnited States.

The start of the Apollo program was apolitical decision based more on theperception of the political and technologicalrewards to be gained by attacking a trulydifficult objective in a constrained timeperiod. The space race began, the UnitedStates won it, and a relatively few years later,

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the Soviet Union collapsed. Fortunately, theRussians did not view Apollo success as areason to terminate their space explorationprogram, and they continued to developcapabilities that are in many areas on a parwith United States capabilities. Also, duringthe post-Apollo time frame, space capabilitygrew in Europe (with the formation of theEuropean Space Agency), Japan, Canada,China, and other countries. With thesedevelopments, the basis has been laid for atruly international approach to Marsexploration—an objective in which allhumanity can share.

The exploration of Mars will derivesignificant nontechnical benefits fromstructuring this undertaking as aninternational enterprise. It is unnecessary forany country to undertake human explorationof Mars alone, particularly when others, whomay not now have the required magnitude ofcapability or financial resources, do have thetechnological know-how. An underlyingrequirement for the Reference Mission is thatit be implemented by a multinational groupof nations and explorers. This would allowfor a continuation of the cooperative effortthat is being made to develop, launch, andoperate the International Space Station.

2.4.3 Technological Advancement

From the outset, the Reference Missionwas not envisioned to be a technologydevelopment program. The Mars Study Teammade a deliberate effort to use eithertechnology concepts that are in use today orbasic concepts that are well understood.

Section 3 of this report will illustrate thatmuch of the technology needed for a Marsmission is either currently available or withinthe experience base of the spacefaring nationsof the Earth. No fundamental breakthroughsare required to accomplish the mission.However, an extended period of advanceddevelopment will be required to prepare thesystems needed to travel to and from Mars orto operate on the surface of Mars; specifically,high efficiency propulsion systems, lifesupport systems, and an advanced degree ofautomation to operate, and if necessaryrepair, processing equipment. At a generallevel, perhaps two of the most importantways in which the Reference Mission willhelp advance technology that will benefitmore than just this program is to provide theprogrammatic “pull” to bring technologies toa usable state and the “drive” to makesystems smaller, lighter, and more efficient fora reasonable cost.

For any of the technology areasmentioned above (as well as others notmentioned), this program will requiresystems using these technologies to meetperformance specifications and be deliveredon schedule, all at a pace perhaps nototherwise required. This applies to anydevelopment effort. But for the ReferenceMission, many technologies will need to beready at once, causing many of these systemsto advance in maturity much faster thanmight have otherwise been possible. Thesemature systems and related technologies willthen be available to the marketplace to be

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used in applications limited only by theimagination of entrepreneurs.

The matured systems and thetechnologies behind them will be attractiveto entrepreneurs in part because of the effortto make them smaller, lighter, and moreefficient. A kilogram of mass saved in any ofthese systems saves many tens of kilogramsof mass at launch from Earth (depending onthe propulsion system used) simply becauseless propellant is required to move thesystems from Earth to Mars. Smaller, lighter,or more efficient each translate into acompetitive advantage in the marketplacefor those who use these technologies.

Among the specific areas of desirabletechnology advancement is propulsionsystems. Even the earliest studies for sendingpeople to the Moon or Mars recognized thatpropulsion system efficiency improvementshave tremendous leverage in reducing thesize of the complete transportation systemneeded to move people and supplies.Chemical propulsion systems are reachingthe theoretical limits of efficiency in therocket engines now being produced. Furtherimprovements in efficiency will require theuse of nuclear or electrical propulsionconcepts which have the potential ofimproving propulsion efficiencies by a factorof up to 10, with corresponding reductions inthe amount of propellant needed to movepayload from one place to another. Both ofthese propulsion technologies have maturedto a relatively high state of readiness in thepast, but neither has reached the level

necessary to be used on the ReferenceMission. Once developed, these technologiesbecome available for use, perhaps on reusablevehicles, for the ever-increasing traffic in LEOup to geosynchronous altitude.

Another area of tremendous leverage fora mission to other planets is the ability to useresources already there rather than burdeningthe transportation system by bringing themfrom Earth. Focusing on understanding whatis required for eventual settlement on Marsleads quickly to those technologies that allowthe crew to live off the land. Of the knownraw materials available on Mars, theatmosphere can be found everywhere and canbe used as feedstock to produce propellantsand life support resources. Other rawmaterials (such as water) will eventually befound and used, but sufficient detail is notcurrently known about their locations andquantities. This is an objective for initialexploration.

Much of the processing technologyneeded to produce propellants fromatmospheric gases already exists and is in useon Earth. However, integrating thesetechnologies into a production plant that canoperate unattended for a period of years,including self-repair, is an area whereadditional development effort will berequired. (Chemical processing plants onEarth are making significant progress towardautonomous operation even now.) In thisarea, the Reference Mission will adapt theexisting technologies at the time of theReference Mission rather than pull those

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technologies up to the levels needed by theprogram. Regardless of how this technologyis developed, the advantages inmanufacturing and materials processing willbe significant.

Life support systems is another specificarea where advancing the state of the art cansignificantly reduce the overall size of thesystems launched from Earth. The sametechnologies that produce propellants canalso produce water and breathable gases forhuman crews. These resources can be used asmakeup for losses in a closed or partiallyclosed life support system, and can also serveas an emergency cache should primary lifesupport weaken or fail. Life support for thisReference Mission can take advantage ofdevelopments already made for InternationalSpace Station and submarine use.Developments in support of the ReferenceMission are likely to return technologies thatare smaller, more efficient, and perhaps lesscostly than those available at the time.

Important in all of these areas is a focuson ensuring that the cost to manufacture andoperate these systems is affordable in thecurrent economic environment. The design-to-cost concept is not currently wellunderstood in the aerospace industry, andany advancements in this area will benefitdevelopment programs well beyond thoseconnected with the Reference Mission.Developing the tools needed to determinecosts that are as easy to use as the tools usedto predict system performance is one of thekey technology areas that will help make the

Reference Mission possible. Equal with this isinstilling an attitude of cost consciousness inthe engineering community that will designand produce these systems. The importanceof cost as a design consideration andproviding the tools to accurately forecast costshould be incorporated in the educationalsystem that trains these engineers.

2.4.4 Inspiration

It can be argued that one role ofgovernment is to serve as a focusing agent forthose events in history that motivate andunify groups of people to achieve a commonpurpose. Reacting to conflicts quickly comesto mind as an example. For the United States,World War II and the Persian Gulf War areexamples of how a nation was unified in apositive sense; the Viet Nam War is anexample of how the opposite occurred.

It can also be argued that a role ofgovernment is to undertake technical andengineering projects that can inspire andchallenge. The great dam building projects inthe American West during the 1930s is anexample of the government marshaling theresources to harness vast river systems forelectrical power and irrigation to allow forpopulation growth. The Interstate HighwaySystem is another example that receives littlefanfare but has changed the way we live. Thegovernment incentives to private entities thatled to the development of the vastintercontinental rail system in the last centuryis another example.

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Few government efforts can collectivelymotivate, unify, challenge, and inspire. TheApollo program was one such example thatfocused a national need to compete withanother nation in a very visible and highprofile manner; the Reference Mission canserve as another. In this instance, theundertaking provides a focus for the humanneed to struggle and compete to achieve aworthy goal—not by competing against eachother but rather against the challengespresented by a common goal.

2.4.5 Investment

Scientific investigation, humanexpansion, technology advancement, andinspiration are not attainable free of charge.Resources must be devoted to such a projectfor it to succeed; and at a certain level, thiscan be viewed as denying those resources toother worthy goals. The Reference Missioncosts are high by current space programstandards, and additional effort is needed toreduce these costs. The total program andannual costs of the Reference Mission rangefrom 1 percent to 2 percent of the currentFederal budget—still far below other Federalprograms. If this program expands to aninternational undertaking, the costs incurredby each partner would be reduced even more.

A debate must still occur to determine ifthis project is a worthwhile investment of thepublic’s resources. But the use of theseresources should be viewed as more than justan effort to send a few people to Mars. Thisproject will be investing in a growing part of

the infrastructure that affects our everydaylife: the use of space for business, commerce,and entertainment. Just as space projects donow, the Reference Mission can serve as afocal point for invigorating the scientific,technical, and social elements of theeducation system, but with a much longerrange vision.

2.5 Why Not Mars?

Several impediments may severelyhamper the implementation of a program forthe human exploration of Mars. Someimpediments are due simply to the fact thatthey have not been evaluated in sufficientdetail to gauge their impact. Others aresimply beyond the control of this or any otherprogram and must be taken into account asthe program advances. The followingparagraphs discuss some of theseimpediments as viewed by the Mars StudyTeam and others considering programs of thistype (Mendell, 1991).

2.5.1 Human Performance

It is a known fact that the human bodyundergoes certain changes when exposed toextended periods of weightlessness—changesthat are most debilitating when the spacetraveler must readapt to gravity. The mostserious known changes includecardiovascular deconditioning, decreasedmuscle tone, loss of calcium from bone mass,and suppression of the immune system. Avariety of countermeasures for theseconditions have been suggested, but none

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have been validated through testing for long-term, zero-g spaceflight. The Russians havehad some success with long periods of dailyexercise to maintain cardiovascular capacityand muscle tone, but monotonous and time-consuming exercise regimes affect theefficiency and morale of the crew.

Artificial gravity is often put forward as apossible solution. In this case, the entirespacecraft, or at least that portion containingthe living quarters for the crew, would berotated so that the crew experiences aconstant downward acceleration thatsimulates gravity. It is generally assumed thatthe Coriolis effect (the dizziness caused byspinning around in circles) will fall below thethreshold of human perception if thespacecraft is rotated at a slow rate. It is notknown whether simulation of full terrestrialgravity is required to counteract all of theknown deconditioning effects ofweightlessness, or whether the small residualCoriolis effect will cause some disorientationin crew members. No data from a space-basedfacility exists, and the space life scienceresearch community is split over the viabilityof artificial gravity as a solution.

Deconditioning is a critical issue for Marsmissions because the crew will undergo hightransient accelerations during descent to themartian surface. Depending on thephysiological condition of the crew, theseaccelerations could be life threatening. Onceon the surface of Mars, the crew must recoverwithout external medical support and mustperform a series of demanding tasks. The

time required for recovery is particularlyimportant if the surface stay is short (as hasbeen proposed for “opposition-class”missions).

No one knows whether exposure to agravity field lower than the Earth’s willreverse the deconditioning induced byweightless space travel. And if some level ofgravity does halt the deconditioning effects,what level is too low? In other words, if acrew arrives on Mars in good physicalcondition, what will their condition be afterspending an extended period of time undermartian gravity? Artificial gravity cannot beprovided easily on the martian surface, andApollo missions to the Moon were too shortto produce observable differences betweenthe condition of the astronauts who went tothe surface and those who remainedweightless in orbit.

The human body’s reaction to Marssurface conditions, other than gravity, is alsonot yet known. The Viking missions to Marsfound a highly reactive agent in the martiansoil, an explanation for which has not yetbeen agreed to by the scientific community.Without understanding this agent’s chemicalbehavior, its impact on human crews cannotbe determined. No matter how carefully theMars surface systems are designed and nomatter how carefully the crews handle nativematerials, small amounts of the martianatmosphere and soil will be introduced intocrew living compartments during the courseof the mission. It will be necessary to bettercharacterize the Mars environment and assess

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its impact on the crew. Assuring the healthand safety of the crew will be of obviousimportance.

Psychiatrists and psychologists agree thatpiloted missions to Mars may well give rise tobehavioral aberrations among the crew ashave been seen on Earth in conditions ofstress and isolation over long periods of time.The probability of occurrence and the level ofany such anomalous behavior will dependnot only on the crew members individuallybut also on the group dynamics among thecrew and between the crew and missionsupport personnel on Earth. In general, theprobability of behavior extreme enough tothreaten the mission will decrease with anincreased crew size. However, the expense ofsending large payloads to Mars to support alarge crew will limit the number of people inany one crew. At the present time, little efforthas been spent developing techniques forcrew selection that will adequately guaranteepsychological stability on a voyage to Marsand back. Russian experience suggests that acrew should train together for many yearsprior to an extended flight.

2.5.2 System Reliability and Lifetime

The spacecraft and surface elements willlikely be the most complex systemsconstructed up to that point in time, and thelives of the crew will depend on the reliabilityof those systems for at least 3 years. Bycomparison, a Mars mission will be of aduration at least two orders of magnitudegreater than a Shuttle mission, and there will

be no opportunity for resupply. Either thesystems must work without failure or thecrew must have adequate time and capabilityto repair those elements which fail.

Particularly important to the success ofpiloted Mars missions will be testing ofintegrated flight systems under conditionssimilar to the actual mission for periods oftime similar to, and preferably much greaterthan, the actual mission. Integrated flighttesting is truly critical if the flight system isthe first of its kind. Unfortunately, if history isa guide, budget pressures will cause programmanagement to search for substitutions forfull-up flight testing. (For full-up flighttesting, hardware identical to that used inflight is operated for periods of time equal toor greater than the actual mission whichallows weaknesses or failures to be identifiedand corrected. This is the most expensive wayto test, in terms of time and money.) After all,most of the expense of a mission to Mars is inlaunch and operations, two categories ofexpense for a flight test whose magnitudewould be similar to that of an actual mission.And what possible motivation would there befor a crew to spend 2 or 3 years in orbitpretending to go to Mars?

Somewhere in a large, complex program,a manager will take a shortcut under pressurefrom budget or schedule reasons, and theconsequences will not always be obvious toprogram management. As a result, thereliability of the product will beoverestimated. And management alwaysexpresses a very human tendency to believe

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good news. (This can be illustrated by thechange in the official estimates of thereliability of the Shuttle before and after theChallenger tragedy.) In short, significant riskis introduced when relying on a product thathas not been tested in its workingenvironment, whether it is a new car, acomplex piece of software, or a spacecraft.

2.5.3 Political Viability and SocialConcerns

The human exploration of Mars is likelyto be undertaken for many of the reasonsalready cited as well as others not presentedhere. To a large degree, the responsibility fortaking action based on these reasons is in therealm of political decision makers as opposedto commercial concerns or other spheres ofinfluence. Thus, support for this type ofprogram must be sustained in the politicalenvironment for a decade or more in the faceof competition for the resources needed tocarry it out.

Perhaps the closest analogy to a possibleinternational Mars exploration program is theInternational Space Station, which has beenan approved international flight program forover 10 years. During those 10 years, theconfiguration of the Station has changedseveral times and the number of and level ofcommitment from partners has changedsignificantly. Also during this time, Russia,initially a significant competitor, has turnedinto one of the larger partners in theendeavor. And all of this has taken place priorto launching the first element of the Station.

Shortening development time can bebeneficial if the project remains focused on itsrequirements and can avoid changes imposedby external forces.

If an institution wishes to be supportedwith public funds for a long-duration project,then the institution must be sophisticatedenough to plan visible milestones, which arecomprehensible to the public, at intervalsappropriate to the funding review process.Historically, NASA has been reasonablysuccessful at maintaining funding of decade-long programs in the face of an annual budgetreview. The vast majority of the programs areunderstood by all to have a finite duration.After a satellite has been launched andoperated for a given period of time, it eitherfails or is shut off. Neither NASA nor the U.S.Congress are yet comfortable with open-ended programs such as the Shuttle orInternational Space Station or humansettlement of the solar system.

The decades-long time frame for humanexploration of Mars cannot be supported untilthe role of the space program is wellintegrated into the national space agenda andthe exploration of space is no longerconsidered a subsidy of the aerospaceindustry. To accomplish this, the spaceprogram must show concern for national andinternational needs (visible contributions totechnology, science, environmental studies,education, inspiration of youth, etc.) whilemaintaining a thoughtful and challengingagenda of human exploration of space inwhich the public can feel a partnership.

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Finally there is the political concern ofback-contamination of Earth. This is as mucha social issue as a technical one. Somesegments of the population will object to anyMars mission on these grounds. The twotenets of a successful defense against suchopposition are to ensure that prudent stepsare taken at all phases of the project tominimize risks and to demonstrate that thevalue of the mission is high enough to meritthe residual minuscule risk.

2.6 Summary

This section has woven together severalkey elements of a rationale for undertakingthe Reference Mission: human evolution,comparative planetology, internationalcooperation, technology advancement,inspiration, and investment. Severalchallenging aspects must be resolved beforethe first human crews can be sent to Mars. Butthe Reference Mission has a longer rangeview and purpose that makes thesechallenges worth the effort to overcome. If, atsome future time, a self-sufficient settlementis established on Mars, with the capability ofinternal growth without massive importsfrom Earth, the benefit will be to the eventualdescendants of the first settlers, who will havetotally different lives and perspectivesbecause of the initial investment made bytheir ancestors.

2.7 References

Bogard, D. and P. Johnson, “MartianGases in an Antarctic Meteorite,” Science,Vol. 221, pp. 651-654, 1983.

Duke, M. and N. Budden, “Results,Proceedings and Analysis of the MarsExploration Workshop,” JSC-26001,NASA, Johnson Space Center, Houston,Texas, August 1992.

Exobiology Program Office, “AnExobiological Strategy for MarsExploration,” NASA SP-530, NASAHeadquarters, Washington, DC, April1995.

McSween, H., “What We Have LearnedAbout Mars From SNC Meteorites,”Meteoritics, Vol. 29, pp. 757-779, 1994.

Mendell, W., “Lunar Base as a Precursorto Mars Exploration and Settlement,” 42ndCongress of the International AstronauticalFederation, IAF-91-704, Montreal, Canada,October 5-11, 1991.

Sullivan, T., D. Linne, L. Bryant, and K.Kennedy, “In Situ-Produced Methane andMethane/Carbon Monoxide Mixtures forReturn Propulsion from Mars,” Journal ofPropulsion and Power, Vol. 11, No. 5, pp.1056-1062, 1995.

Synthesis Group, “America at theThreshold: Report of the Synthesis Groupon America’s Space ExplorationInitiative,” U.S. Government PrintingOffice, Washington, DC, May, 1991.