pale blue dot -carl sagan- 第34部分

But　why　Mars？　Why　not　return　to　the　Moon？　It's　nearby；　and　we've　proved　we　know　how　to　send　people　there。　I'm　concerned　that　the　Moon；　close　as　it　is；　is　a　long　detour；　if　not　a　dead　end。　We've　been　there。　We've　even　brought　some　of　it　back。　People　have　seen　the　Moon　rocks；　and；　for　reasons　that　I　believe　are　fundamentally　sound；　they　are　bored　by　the　Moon。　It's　a　static；　airless；　waterless；　black…sky；　dead　world。　Its　most　interesting　aspect　perhaps　is　its　cratered　surface；　a　record　of　ancient　；catastrophic　impacts；　on　the　Earth　as　well　as　on　the　Moon。

Mars；　by　contrast；　has　weather；　dust　storms；　its　own　moons；　volcanos；　polar　ice　caps；　peculiar　landforms；　ancient　river　valleys；　and　evidence　of　massive　climatic　change　on　a　once…Earthlike　world。　It　holds　some　prospect　of　past　or　maybe　even　present　life；　and　is　the　most　congenial　planet　for　future　life—humans　transplanted　from　Earth；　living　off　the　land。　None　of　this　is　true　for　the　Moon。　Mars　also　has　its　own　legible　cratering　history。　It　Mars；　rather　than　the　Moon；　had　been　within　easy　reach；　we　would　not　have　backed　off　from　manned　space　flight。

Nor　is　the　Moon　an　especially　desirable　test　bed　or　way　station　for　Mars。　The　Martian　and　lunar　environments　are　very　different；　and　the　Moon　is　as　distant　from　Mars　as　is　the　Earth。　The　machinery　for　Martian　exploration　can　at　least　equally　well　be　tested　in　Earth　orbit；　or　on　near…Earth　asteroids；　or　on　the　Earth　itself—in　Antarctica；　for　instance。

Japan　has　tended　to　be　skeptical　of　the　mitment　of　the　United　States　and　other　nations　to　plan　and　execute　major　cooperative　projects　in　space。　This　is　at　least　one　reason　that　Japan；　more　than　any　other　spacefaring　nation；　has　tended　to　go　it　alone。　The　Lunar　and　Planetary　Society　of　Japan　is　an　organization　representing　space　enthusiasts　in　the　government；　universities；　and　major　industries。　As　I　write；　the　Society　is　proposing　to　construct　and　stock　a　lunar　base　entirely　with　robot　labor。　It　is　said　to　take　about　30　years　and　to　cost　about　a　billion　U。S。　dollars　a　year　（which　would　represent　7　percent　of　the　present　U。S。　civilian　space　budget）。　Humans　would　arrive　only　when　the　base　is　fully　ready。　The　use　of　robot　construction　crews　under　radio　mand　from　Earth　is　said　to　reduce　the　cost　tenfold。　The　only　trouble　with　the　scheme；　according　to　reports；　is　that　other　scientists　in　Japan　keep　asking；　〃What's　it　for？〃　That's　a　good　question　in　every　nation。

The　first　human　mission　to　Mars　is　now　probably　too　expensive　for　any　one　nation　to　pull　off　by　itself。　Nor　is　it　fitting　that　such　a　historic　step　be　taken　by　representatives　of　only　a　small　fraction　of　the　human　species。　But　a　cooperative　venture　among　the　United　States；　Russia；　Japan；　the　European　Space　Agency—and　perhaps　other　nations；　such　as　China—might　be　feasible　in　the　not　too　distant　future。　The　international　space　station　will　have　tested　our　ability　to　work　together　on　great　engineering　projects　in　space。

The　cost　of　sending　a　kilogram　of　something　no　farther　away　than　low　Earth　orbit　is　today　about　the　same　as　the　cost　of　kilogram　of　gold。　This　is　surely　a　major　reason　we　have　yet　to　stride　the　ancient　shorelines　of　Mars。　Multistage　chemical　rockets　are　the　means　that　first　took　us　into　space；　and　that's　what　we've　been　using　ever　since。　We've　tried　to　refine　them；　to　make　there　safer；　more　reliable；　simpler；　cheaper。　But　that　hasn't　happened；　or　at　least　not　nearly　as　quickly　as　many　had　hoped。

So　maybe　there's　a　better　way：　maybe　single…stage　rockets　that　can　launch　their　payloads　directly　to　orbit；　maybe　many　small　payloads　shot　from　guns　or　rocket…launched　from　airplanes；　maybe　supersonic　ramjets。　Maybe　there's　something　much　better　that　we　haven't　thought　of　yet。　If　we　can　manufacture　propellants　for　the　return　trip　from　the　air　and　soil　of　our　destination　world；　the　difficulty　of　the　voyage　would　be　greatly　eased。

Once　we're　up　there　in　space；　venturing　to　the　planets；　rocketry　is　not　necessarily　the　best　means　to　move　large　payloads　around；　even　with　gravity　assists。　Today；　we　make　a　few　early　rocket　burns　and　later　midcourse　corrections；　and　coast　the　rest　of　the　way。　But　there　are　promising　ion　and　nuclear/　electric　propulsion　systems　by　which　a　small　and　steady　acceleration　is　exerted。　Or；　as　the　Russian　space　pioneer　Konstantin　Tsiolkovsky　first　envisioned；　we　could　employ　solar　sails—vast　but　very　thin　films　that　catch　sunlight　and　the　solar　wind；　a　caravel　kilometers　wide　plying　the　void　between　the　worlds。　Especially　for　trips　to　Mars　and　beyond；　such　methods　are　far　better　than　rockets。

As　with　most　technologies；　when　something　barely　works；　when　it's　the　first　of　its　kind；　there's　a　natural　tendency　to　improve　it；　develop　it；　exploit　it。　Soon　there's　such　an　institutional　investment　in　the　original　technology；　no　matter　how　flawed；　that　it's　very　hard　to　move　on　to　something　better。　NASA　has　almost　no　resources　to　pursue　alternative　propulsion　technologies。　That　money　would　have　to　e　out　of　near…term　missions；　missions　which　could　provide　concrete　results　and　improve　NASA's　success　record。　Spending　money　on　alternative　technologies　pays　off　a　decade　or　two　in　the　future。　We　tend　to　be　very　little　interested　in　a　decade　or　two　in　the　future。　This　is　one　of　the　ways　by　which　initial　success　can　sow　the　seeds　of　ultimate　failure；　and　is　very　similar　to　what　sometimes　happens　in　biological　evolution。　But　sooner　or　later　some　nation—perhaps　one　without　a　huge　investment　in　marginally　effective　technology—will　develop　effective　alternatives。

Even　before　then；　if　we　take　a　cooperative　path；　there　will　e　a　time—perhaps　in　the　first　decades　of　the　new　century　and　the　new　millennium—when　an　interplanetary　spacecraft　is　assembled　in　Earth　orbit；　the　progress　in　full　view　on　the　evening　news。　Astronauts　and　cosmonauts；　hovering　like　gnats；　guide　and　mate　the　prefabricated　parts。　Eventually　the　ship；　tested　and　ready；　is　boarded　by　its　international　crew；　and　boosted　to　escape　velocity。　For　the　whole　of　the　voyage　to　Mars　and　back；　the　lives　of　the　crew　members　depend　on　one　another；　a　microcosm　of　our　actual　circumstances　down　here　on　Earth。　Perhaps　the　first　joint　interplanetary　mission　with　human　crews　will　be　only　a　flyby　or　orbit　of　Mars。　Earlier；　robot　vehicles；　with　aerobraking；　parachutes；　and　retrorockets；　will　have　set　gently　down　on　the　Martian　surface　to　collect　samples　and　return　them　to　Earth；　and　to　emplace　supplies　for　future　explorers。　But　whether　or　not　we　have　pelling；　coherent　reasons；　I　am　sure—unless　we　destroy　ourselves　first—that　the　day　will　e　when　we　humans　set　foot　on　Mars。　It　is　only　a　matter　of　when。

According　to　solemn　treaty；　signed　in　Washington　and　Moscow　on　January　27；　1967；　no　nation　may　lay　claim　to　part　or　all　of　another　planet。　Nevertheless—for　historical　reasons　that　Columbus　would　have　understood　well—some　people　are　concerned　about　who　first　sets　foot　on　Mars。　If　this　really　worries　us；　we　can　arrange　for　the　ankles　of　the　crew　members　to　be　tied　together　as　they　alight　in　the　gentle　Martian　gravity。

The　crews　would　acquire　new　and　previously　sequestered　samples；　in　part　to　search　for　life；　in　part　to　understand　the　past　and　future　of　Mars　and　Earth。　They　would　experiment；　for　later　expeditions；　on　extracting　water；　oxygen；　and　hydrogen　from　the　rocks　and　the　air　and　from　the　underground　permafrost—to　drink；　to　breathe；　to　power　their　machines　and；　as　rocket　fuel　and　oxidizer；　to　propel　the　return　voyage。　They　would　test　Martian　materials　for　eventual　fabrication　of　bases　and　settlements　on　Mars。

And　they　would　go　exploring。　When　I　imagine　the　early　human　exploration　of　Mars；　it's　always　a　roving　vehicle；　a　little　like　a　jeep；　wandering　down　one　of　the　valley　networks；　the　crew　with　geological　hammers；　cameras；　and　analytic　instruments　at　the　ready。　They're　looking　for　rocks　from　ages　past；　signs　of　ancient　cataclysms；　clues　to　climate　change；　strange　chemistries；　fossils；　or—most　exciting　and　most　unlikely—something　alive。　Their　discoveries　are　televised　back　to　Earth　at　the　speed　of　light。　Snuggled　up　in　bed　with　the　kids；　you　explore　the　ancient　riverbeds　of　Mars。




CHAPTER　16　　　SCALING　HEAVEN

　

　

Who；　my　friend；　can　scale　heaven？

—THE　EPIC　OF　GILGAMESH　（SUMER；　THIRD　MILLENNIUM　B。C。）

What？；　I　sometimes　ask　myself　in　amazement：　Our　ancestors　walked　from　East　Africa　to　Novaya　Zemlya　and　Ayers　Rock　and　Patagonia；　hunted　elephants　with　stone　spearpoints；　traversed　the　polar　seas　in　open　boats　7；000　years　ago；　circumnavigated　the　Earth　propelled　by　nothing　but　wind；　walked　the　Moon　a　decade　after　entering　space—and　we're　daunted　by　a　voyage　to　Mars？　But　then　I　remind　myself　of　the　avoidable　human　suffering　on　Earth；　how　a　few　dollars　can　save　the　life　of　a　child　dying　of　dehydration；　how　many　children　we　could　save　for　the　cost　of　a　trip　to　Mars—and　for　the　moment　I　change　my　mind。　Is　it　unworthy　to　stay　home　or　unworthy　to　go？　Or　have　I　posed　a　false　dichotomy？　Isn't　it　possible　to　make　a　better　life　for　everyone　on　Earth　and　to　reach　for　the　planets　and　the　stars？

We　had　an　expansive　run　in　the　'60s　and　'70s。　You　might　have　thought；　as　I　did　then；　that　our　species　would　be　on　Mars　before　the　century　was　over。　But　instead；　we've　pulled　inward。　Robots　aside；　we've　backed　off　from　the　planets　and　the　stars。　1　keep　asking　myself　Is　it　a　failure　of　nerve　or　a　sign　of　maturity？

Maybe　it's　the　most　we　could　reasonably　have　expected。　In　a　way　it's　amazing　that　it　was　possible　at　all：　We　sent　a　dozen　humans　on　week…long　excursions　to　the　Moon。　And　we　were　given　the　resources　to　make　a　preliminary　reconnaissance　of　the　whole　Solar　System；　out　to　Neptune　anyway—missions　that　returned　a　wealth　of　data；　but　nothing　of　short…term；　everyday；　bread…on…the…table　practical　value。　They　lifted　the　human　spirit；　though。　They　enlightened　us　about　our　place　in　the　Universe。　It's　easy　to　imagine　skeins　of　historical　causality　in　which　there　were　no　race　to　the　Moon　and　no　planetary　program。

But　it's　also　possible　to　imagine　a　much　more　serious　devotion　to　exploration；　because　of　which　we　would　today　have　robot　vehicles　probing　the　atmospheres　of　all　the　Jovian　planets　and　dozens　of　moons；　ets；　and　asteroids；　a　network　of　automatic　scientific　stations　emplaced　on　Mars　would　daily　be　reporting　their　findings；　and　samples　from　many　worlds　would　be　under　examination　in　the　laboratories　of　Earth—revealing　their　geology；　chemistry；　and　perhaps　even　their　biology。　Human　outposts　might　be　already　established　on　the　near…Earth　asteroids；　the　Moon；　and　Mars。

There　were　many　possible　historical　paths。　Our　particular　causality　skein　has　brought　us　to　a　modest　and　rudimentary；　although　in　many　respects　heroic；　series　of　explorations。　But　it　is　far　interior　to　what　might　have　been—and　what　may　one　day　be。



TO　CARRY　THE　GREEN　Promethean　spark　of　Life　with　us　into　the　sterile　void　and　ignite　there　a　firestorm　of　animate　matter　is　the　very　destiny　of　our　race；〃　reads　the　brochure　of　something　called　the　First　Millennial　Foundation。　It　promises；　for　120　a　year；　〃citizenship〃　in　〃space　colonies—when　the　time　es。〃　〃Benefactors〃　who　contribute　more　also　receive　〃the　undying　gratitude　of　a　star…flung　civilization；　and　their　name　carved　on　the