pale blue dot -carl sagan- 第44节

According　to　the　mission　of　Inquiry；　the　cause　of　the　failure　was　probably　a　rupture　of　the　fuel　tank　during　pressurization；　gases　and　liquids　sputtering　out；　and　the　wounded　spacecraft　spinning　wildly　out　of　control。　Perhaps　it　was　avoidable。　Perhaps　it　was　an　unlucky　accident。　But　to　keep　this　matter　in　perspective；　let's　consider　the　full　range　of　missions　to　the　Moon　and　the　planets　attempted　by　the　United　States　and　the　former　Soviet　Union：

In　the　beginning；　our　track　records　were　poor。　Space　vehicles　blew　up　at　launch；　missed　their　targets；　or　failed　to　function　when　they　got　there。　As　time　went　on；　we　humans　got　；）otter　at　interplanetary　flight。　There　was　a　learning　curve。　The　；adjacent　figures　show　these　curves　（based　on　NASA　data　with　NASA　definitions　of　mission　success）。　We　learned　very　well。　Our　present　ability　to　fix　spacecraft　in　flight　is　best　illustrated　by　the　Voyager　missions　described　earlier。

We　see　that　it　wasn't　until　about　its　thirty…fifth　launch　to　the　Moon　or　the　planets　that　the　cumulative　U。S。　mission　success　rate　got　as　high　as　50　percent。　The　Russians　took　about　50　launches　to　get　there。　Averaging　the　shaky　start　and　the　better　recent　performance；　we　find　that　both　the　United　States　and　Russia　have　a　cumulative　launch　success　rate　of　about　80　percent。　But　the　cumulative　mission　success　rate　is　still　under　70　percent　for　the　U。S。　and　under　60　percent　for　the　U。S。S。R。/Russia。　Equivalently；　lunar　and　planetary　missions　have　failed　on　average　30　or　40　percent　of　the　time。

Missions　to　other　worlds　were　from　the　beginning　at　the　cutting　edge　of　technology。　They　continue　to　be　so　today。　They　。ire　designed　with　redundant　subsystems；　and　operated　by　dedicated　and　experienced　engineers；　but　they　are　not　perfect。　The　amazing　thing　is　not　that　we　have　done　so　poorly；　but　that　we　leave　done　so　well。

We　don't　know　whether　the　Mars　Observer　failure　was　due　to　inpetence　or　just　statistics。　But　we　must　expect　a　steady　background　of　mission　failures　when　we　explore　other　worlds。　No　human　lives　are　risked　when　a　robot　spacecraft　is　lost。　Even　if　we　were　able　to　improve　this　success　rate　significantly；　it　would　be　far　too　costly。　It　is　much　better　to　take　more　risks　and　fly　more　spacecraft：。

Knowing　about　irreducible　risks；　why　do　we　these　days　fly　only　one　spacecraft　per　mission？　In　1962　Mariner　1；　intended　for　Venus；　fell　into　the　Atlantic；　the　nearly　identical　Mariner　2　became　the　human　species'　first　successful　planetary　mission。　Mariner　3　failed；　arid　its　twin　Mariner　4　became；　in　1964；　the　first　spacecraft　to　take　close…up　pictures　of　Mars。　Or　consider　the　1971　Mariner　8/Mariner　9　dual　launch　mission　to　Mars。　Mariner　8　Was　to　map　the　planet。　Mariner　9　was　to　study　the　enigmatic　seasonal　and　secular　changes　of　surface　markings。　The　spacecraft　were　otherwise　identical。　Mariner　8　fell　into　the　ocean。　Mariner　9　flew　on　to　Mars　arid　became　the　first　spacecraft　in　human　history　to　orbit　another　planet。　It　discovered　the　volcanos；　the　laminated　terrain　in　the　polar　caps；　the　ancient　river　valleys；　and　the　aeolian　nature　of　the　surface　changes。　It　disproved　the　〃canals。〃　It　mapped　the　planet　pole　to　pole　and　revealed　all　the　major　geological　features　of　Mars　known　to　us　today。　It　provided　the　first　close…up　observations　of　members　of　a　whole　class　of　small　worlds　（by　targeting　the　Martian　moons；　Phobos　and　Deimos）。　If　we　had　launched　only　Mariner　8；　the　endeavor　would　have　been　an　unmitigated　failure。　With　a　dual　launch　it　became　a　brilliant　and　historic　success。

There　were　also　two　Vikings；　two　Voyagers；　two　Vegas；　many　pairs　of　Veneras。　Why　was　only　one　Mars　Observer　flown？　The　standard　answer　is　cost。　Part　of　the　reason　it　was　so　costly；　though；　is　that　it　was　planned　to　be　launched　by　shuttle；　which　is　an　almost　absurdly　expensive　booster　for　planetary　missions—in　this　case　too　expensive　for　two　M。　O。　launches。　After　many　shuttle…connected　delays　and　cost　increases；　NASA　changed　its　mind　and　decided　to　launch　Mars　Observer　on　a　Titan　booster。　This　required　an　additional　two…year　delay　and　an　adapter　to　mate　the　spacecraft　to　the　new　launch　vehicle。　If　NASA　had　not　been　so　intent　on　providing　business　for　the　increasingly　uneconomic　shuttle；　we　could　have　launched　a　couple　of　years　earlier　and　maybe　with　two　spacecraft　instead　of　one。

But　whether　in　single　launches　or　in　pairs；　the　space…faring　nations　have　clearly　decided　that　the　time　is　ripe　to　return　robot　explorers　to　Mars。　Mission　designs　change；　new　nations　enter　the　field；　old　nations　find　they　no　longer　have　the　resources。　Even　already　funded　programs　cannot　always　be　relied　upon。　But　current　plans　do　reveal　something　of　the　intensity　of　effort　and　the　depth　of　dedication。

As　I　write　this　book；　there　are　tentative　plans　by　the　United　States；　Russia；　France；　Germany；　Japan；　Austria；　Finland；　Italy；　Canada；　the　European　Space　Agency；　and　other　entities　for　a　coordinated　robotic　exploration　of　Mars。　In　the　seven　years　between　1996　and　2003；　a　flotilla　of　some　twenty…five　spacecraft—most　of　them　paratively　small　and　cheap—are　to　be　sent　from　Earth　to　Mars。　There　will　be　no　quick　flybys　among　them；　these　are　all　long…duration　orbiter　and　lander　missions。　The　United　States　will　re…fly　all　of　the　scientific　instruments　that　were　lost　on　Mars　Observer。　The　Russian　spacecraft　will　contain　particularly　ambitious　experiments　involving　some　twenty　nations。　munications　satellites　will　permit　experimental　stations　anywhere　on　Mars　to　relay　their　data　back　to　Earth。　Penetrators　screeching　down　from　orbit　will　punch　into　the　Martian　soil；　transmitting　data　from　underground。　Instrumented　balloons　and　roving　laboratories　will　wander　over　the　sands　of　Mars。　Some　microrobots　will　weigh　no　more　than　a　few　pounds。　Landing　sites　are　being　planned　and　coordinated。　Instruments　will　be　cross…calibrated。　Data　will　be　freely　exchanged。　There　is　every　reason　to　think　that　in　the　ing　years　Mars　and　its　mysteries　will　bee　increasingly　familiar　to　the　inhabitants　of　the　planet　Earth。



IN　THE　MAND　CENTER　on　Earth；　in　a　special　room；　you　are　helmeted　and　gloved。　You　turn　your　head　to　the　left；　and　the　cameras　on　the　Mars　robot　rover　turn　to　the　left。　You　see；　in　very　high　definition　and　in　color；　what　the　cameras　see。　You　take　a　step　forward；　and　the　rover　walks　forward。　You　reach　out　your　arm　to　pick　up　something　shiny　in　the　soil；　and　the　robot　arm　does　likewise。　The　sands　of　Mars　trickle　through　your　fingers。　The　only　difficulty　with　this　remote　reality　technology　is　that　all　this　must　occur　in　tedious　slow　motion：　The　round…trip　travel　time　of　the　up…link　mands　from　Earth　to　Mars　and　the　down…link　data　returned　from　Mars　to　Earth　might　take　half　an　hour　or　more。　But　this　is　something　we　can　learn　to　do。　We　can　learn　to　contain　our　exploratory　impatience　if　that's　the　price　of　exploring　Mars。　The　rover　can　be　made　smart　enough　to　deal　with　routine　contingencies。　Anything　more　challenging；　and　it　makes　a　dead　stop；　puts　itself　into　a　safeguard　mode；　and　radios　for　a　very　patient　human　controller　to　take　over。

Conjure　up　roving；　smart　robots；　each　of　them　a　small　scientific　laboratory；　landing　in　the　safe　but　dull　places　and　wandering　to　view　close…up　some　of　that　profusion　of　Martian　Wonders。　Perhaps　every　day　a　robot　would　rove　to　its　own　horizon；　each　morning　we　would　see　close…up　what　had　yesterday　been　only　a　distant　eminence。　The　lengthening　progress　of　a　traverse　route　over　the　Martian　landscape　would　appear　oil　news　programs　and　in　schoolrooms。　People　would　speculate　on　what　will　be　found。　Nightly　newscasts　from　another　planet；　with　their　revelations　of　new　terrains　and　new　scientific　findings　would　make　everyone　on　Earth　a　party　to　the　adventure。

Then　there's　Martian　virtual　reality：　The　data　sent　back　from　Mars；　stored　in　a　modern　puter；　are　fed　into　your　helmet　and　gloves　and　boots。　You　are　walking　in　an　empty　room　on　Earth；　but　to　you　you　are　on　Mars：　pink　skies；　fields　of　boulders；　sand　dunes　stretching　to　the　horizon　where　an　immense　volcano　looms；　you　hear　the　sand　crunching　under　your　boots；　you　turn　rocks　over；　dig　a　hole；　sample　the　thin　air；　turn　a　corner；　and　e　face　to　face　with　。　。　。　whatever　new　discoveries　we　will　make　on　Mars—all　exac