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ials　to　generate　oxygen　to　breathe；　water　to　drink；　and　rocket　propellants　to　get　home；　whether　you　land　using　the　thin　Martian　atmosphere　for　aerobraking；　the　degree　of　redundancy　in　equipment　thought　prudent；　the　extent　to　which　you　use　closed　ecological　systems　or　just　depend　on　the　food；　water；　and　waste　disposal　facilities　you've　brought　from　Earth；　the　design　of　roving　vehicles　for　the　crew　to　explore　the　Martian　landscape；　and　how　much　equipment　you're　willing　to　carry　to　test　our　ability　to　live　off　the　land　in　later　voyages。

Until　such　questions　are　decided；　it's　absurd　to　accept　any　figure　for　the　cost　of　the　program。　On　the　other　hand；　it　was　equally　clear　that　SEI　would　be　extremely　expensive。　For　all　these　reasons；　the　program　was　a　nonstarter。　It　was　stillborn。

There　was　no　effective　attempt　by　the　Bush　Administration　to　spend　political　capital　to　get　SEI　going。

The　lesson　to　me　seems　clear：　There　may　be　no　way　to　Send　humans　to　Mars　in　the　paratively　near　future—despite　the　fact　that　it　is　entirely　within　our　technological　capability。　Governments　do　not　spend　these　vast　sums　just　for　science；　or　merely　to　explore。　They　need　another　purpose；　and　it　must　make　real　political　sense。

It　may　be　impossible　to　go　just　yet；　but　when　it　is　possible；　the　mission；　I　think；　must　be　international　from　the　start；　with　costs　and　responsibilities　equitably　shared　and　the　expertise　of　many　nations　tapped；　the　price　must　be　reasonable；　the　time　from　approval　to　launch　must　fit　within　practical　political　timescales；　and　the　space　agencies　concerned　must　demonstrate　their　ability　to　muster　pioneering　exploratory　missions　with　human　crews　safely；　on　time；　and　on　budget。　If　it　were　possible　to　imagine　such　a　mission　for　less　than　100　billion；　and　for　a　time　from　approval　to　launch　less　than　15　years；　maybe　it　would　be　feasible。　（In　terms　of　cost；　this　would　represent　only　a　fraction　of　the　annual　civilian　space　budgets　of　the　present　spacefaring　nations。）　With　aerobraking　and　manufacturing　fuel　and　oxygen　for　the　return　trip　out　of　Martian　air；　it's　now　beginning　to　look　as　if　such　a　budget　and　such　a　timescale　might　actually　be　realistic。

The　cheaper　and　quicker　the　mission　is；　necessarily　the　more　risk　we　must　be　willing　to　take　with　the　lives　of　the　astronauts　and　cosmonauts　aboard。　But　as　is　illustrated；　among　countless　examples；　by　the　samurai　of　medieval　Japan；　there　are　always　petent　volunteers　for　highly　dangerous　missions　in　what　is　perceived　as　a　great　cause。　No　budget；　no　timeline　can　be　really　reliable　when　we　attempt　to　do　something　on　so　grand　a　scale；　something　that　has　never　been　done　before。　The　more　leeway　we　ask；　the　greater　is　the　cost　and　the　longer　it　takes　to　get　there。　Finding　the　right　promise　between　political　feasibility　and　mission　success　may　be　tricky。



IT'S　NOT　ENOUGH　to　go　to　Mars　because　some　of　us　have　dreamt　of　doing　so　since　childhood；　or　because　it　seems　to　us　the　obvious　long…term　exploratory　goal　for　the　human　species。　If　we're　talking　about　spending　this　much　money；　we　must　justify　the　expense。

There　are　now　other　matters—clear；　crying　national　needs—that　cannot　be　addressed　without　major　expenditures；　at　the　same　time；　the　discretionary　federal　budget　has　bee　painfully　constrained。　Disposal　of　chemical　and　radioactive　poisons；　energy　efficiency；　alternatives　to　fossil　fuels；　declining　rates　of　technological　innovation；　the　collapsing　urban　infrastructure；　the　AIDS　epidemic；　a　witches'　brew　of　cancers；　homelessness；　malnutrition；　infant　mortality；　education；　jobs；　health　care—there　is　a　painfully　long　list。　Ignoring　them　will　endanger　the　well…being　of　the　nation。　A　similar　dilemma　faces　all　the　spacefaring　nations。

Nearly　every　one　of　these　matters　could　cost　hundreds　of　billions　of　dollars　or　more　to　address。　Fixing　infrastructure　will　cost　several　trillion　dollars。　Alternatives　to　the　fossil…fuel　economy　clearly　represent　a　multitrillion…dollar　investment　worldwide；　if　we　can　do　it。　These　projects；　we　are　sometimes　told；　are　beyond　our　ability　to　pay。　How　then　can　we　afford　to　go　to　Mars？

If　there　were　20　percent　more　discretionary　funds　in　the　U。S。　federal　budget　（or　the　budgets　of　the　other　spacefaring　nations）；　I　probably　would　not　feel　so　conflicted　about　advocating　sending　humans　to　Mars。　If　there　were　20　percent　less；　I　don't　think　the　most　diehard　space　enthusiast　would　be　urging　such　a　mission。　Surely　there　is　some　point　at　which　the　national　economy　is　in　such　dire　straits　that　sending　people　to　Mats　is　unconscionable。　The　question　is　where　we　draw　the　line。　plainly　such　a　line　exists；　and　every　participant　in　these　debates　should　stipulate　where　that　line　should　be　drawn；　what　fraction　of　the　gross　national　product　for　space　is　too　much。　I'd　like　the　same　thing　done　for　〃defense。〃

Public　opinion　polls　show　that　many　Americans　think　the　NASA　budget　is　about　equal　to　the　defense　budget。　In　fact；　the　entire　NASA　budget；　including　human　and　robotic　missions　and　aeronautics；　is　about　5　percent　of　the　U。S。　defense　budget。　How　much　spending　for　defense　actually　weakens　the　country？　And　even　if　NASA　were　cancelled　altogether；　would　we　free　up　what　is　needed　to　solve　our　national　problems？



HUMAN　SPACEFLIGHT　In　general—to　say　nothing　of　expeditions　to　Mars—would　be　much　more　readily　supportable　if；　as　in　the　fifteenth…century　arguments　of　Columbus　and　Henry　the　Navigator；　there　were　a　profit　lure。*　Some　arguments　have　been　advanced。　The　high　vacuum　or　low　gravity　or　intense　radiation　environment　of　near…Earth　space　might　be　utilized；　it　is　said；　for　mercial　benefit。　All　such　proposals　must　be　challenged　by　this　question：　Could　parable　or　better　products　be　manufactured　down　here　on　Earth　if　the　development　money　made　available　were　parable　to　what　is　being　poured　into　the　space　program？　Judging　by　how　little　money　corporations　have　been　willing　to　invest　in　such　technology—apart　from　the　entities　building　the　rockets　and　spacecraft　themselves—the　prospects；　at　least　at　present；　seem　to　be　not　very　high。

*　Even　then　it　wasn't　easy。　The　Portuguese　chronicler　Gomes　Eanes　de　Zurara　reported　this　assessment　by　Prince　Henry　the　Navigator：　〃It　seemed　to　the　Lord　Infante　that　if　he　or　some　other　lord　did　not　endeavor　to　gain　that　knowledge；　no　mariners　nor　merchants　would　ever　dare　to　attempt　it；　for　it　is　clear　that　none　of　them　ever　trouble　themselves　to　sail　to　a　place　where　there　is　not　a　sure　and　certain　hope　of　profit。〃

The　notion　that　rare　materials　might　be　available　elsewhere　is　tempered　by　the　fact　that　freightage　is　high。　There　may；　for　all　we　know；　be　oceans　of　petroleum　on　Titan；　but　transporting　it　to　Earth　will　be　expensive。　Platinum…group　metals　may　be　abundant　in　certain　asteroids。　If　we　could　move　these　asteroids　into　orbit　around　the　Earth；　perhaps　we　could　conveniently　mine　them。　But　at　least　for　the　foreseeable　future　this　seems　dangerously　imprudent；　as　I　describe　later　in　this　book。

In　his　classic　science　fiction　novel　The　Man　Who　Sold　the　Moon；　Robert　Heinlein　imagined　the　profit　motive　as　the　key　to　space　travel。　He　hadn't　foreseen　that　the　Cold　War　would　sell　the　Moon。　But　he　did　recognize　that　an　honest　profit　argument　would　be　difficult　to　e　by。　Heinlein　envisioned；　therefore；　a　scam　in　which　the　lunar　surface　was　salted　with　diamonds　so　later　explorers　could　breathlessly　discover　them　and　initiate　a　diamond　rush。　We've　since　returned　samples　from　the　Moon；　though；　and　there　is　not　a　hint　of　mercially　interesting　diamonds　there。

However；　Kiyoshi　Kuramoto　and　Takafumi　Matsui　of　the　University　of　Tokyo　have　studied　how　the　central　iron　cores　of　Earth；　Venus；　and　Mars　formed；　and　find　that　the　Martian　mantle　（between　crust　and　core）　should　be　rich　in　carbon—richer　than　that　of　the　Moon　or　Venus　or　Earth。　Deeper　than　300　kilometers；　the　pressures　should　transform　carbon　into　diamond。　We　know　that　Mars　has　been　geologically　active　over　its　history。　Material　from　great　depth　will　occasionally　be　extruded　up　to　the　surface；　and　not　just　in　the　great　volcanos。　So　there　does　seem　to　be　a　case　for　diamonds　on　other　worlds—on　Mars；　lied　not　the　Moon。　In　what　quantities；　of　what　quality　and　size；　and　in　which　locales　we　do　not　yet　know。

The　return　to　Earth　of　a　spacecraft　stuffed　with　gorgeous　multicarat　diamonds　would　doubtless　depress　prices　（as　well　as　the　shareholders　of　the　de　Beers　and　General　Electric　corporations）。　But　because　of　the　ornamental　and　industrial　applications　of　diamonds；　perhaps　there　is　a　lower　limit　below　which　prices　will　not　go。　Conceivably；　the　affected　industries　might　find　cause　to　promote　the　early　exploration　of　Mars。

The　idea　that　Martian　diamonds　will　pay　for　exploring　Mars　is　at　best　a　very　long　shot；　but　it's　an　example　of　how　rare　and　valuable　substances　may　be　discoverable　on　other　worlds。　It　would　be　foolish；　though；　to　count　on　such　contingencies。　If　we　seek　to　justify　missions　to　other　worlds；　we'll　have　to　find　other　reasons。



BEYOND　DISCUSSIONS　OF　PROFITS　and　costs；　even　reduced　costs；　we　must　also　describe　benefits；　if　they　exist。　Advocates　of　human　missions　to　Mars　must　address　whether；　in　the　long　term；　missions　up　there　are　likely　to　mitigate　any　of　the　problems　down　here。　Consider　now　the　standard　set　of　justifications　and　see　if　you　find　them　valid；　invalid；　or　indeterminate：

Human　missions　to　Mars　would　spectacularly　improve　our　knowledge　of　the　planet；　including　the　search　for　present　and　past　life。　The　program　is　likely　to　clarify　our　understanding　of　the　environment　of　our　own　planet；　as　robotic　missions　have　already　begun　to　do。　The　history　of　our　civilization　shows　that　the　pursuit　of　basic　knowledge　is　the　way　the　most　significant　practical　advances　e　about。　Opinion　polls　suggest　that　the　most　popular　reason　for　〃exploring　space〃　is　〃increased　knowledge。〃　But　are　humans　in　space　essential　to　achieve　this　goal？　Robotic　missions；　given　high　national　priority　and　equipped　with　improved　machine　intelligence；　seem　to　me　entirely　capable　of　answering；　as　well　as　astronauts　can；　all　the　questions　we　need　to　ask—and　at　Maybe　10　percent　the　cost。

It　is　alleged　that　〃spinoff〃　will　transpire—huge　technological　benefits　that　would　otherwise　fail　to　e　about—thereby　improving　o