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Perhaps　the　chemical　or　fossil　remains　of　early　Martian　life　can　still　be　found—subsurface；　safely　protected　from　the　ultraviolet　radiation　and　its　oxidation　products　that　today　fry　the　surface。　Perhaps　in　a　rock　face　exposed　by　a　landslide；　or　in　the　banks　of　an　ancient　river　valley　or　dry　lake　bed；　or　in　the　polar；　laminated　terrain；　key　evidence　for　life　on　another　planet　is　waiting。

Despite　its　absence　on　the　surface　of　Mars；　the　planet's　two　moons；　Phobos　and　Deimos；　seem　to　be　rich　in　plex　organic　matter　dating　back　to　the　early　history　of　the　Solar　System。　The　Soviet　Phobos　2　spacecraft　found　evidence　of　water　vapor　being　out…gassed　from　Phobos；　as　if　it　has　an　icy　interior　heated　by　radioactivity。　The　moons　of　Mars　may　have　long　ago　been　captured　from　somewhere　in　the　outer　Solar　System；　conceivably；　they　are　among　the　nearest　available　examples　of　unaltered　stuff　from　the　earliest　days　of　the　Solar　System。　Phobos　and　Deimos　are　very　small；　each　roughly　10　kilometers　across；　the　gravity　they　exert　is　nearly　negligible。　So　it's　paratively　easy　to　rendezvous　with　them；　land　on　them；　examine　them；　use　them　as　a　base　of　operations　to　study　Mars；　and　then　go　home。

Mars　calls；　a　storehouse　of　scientific　information—important　in　its　own　right　but　also　for　the　light　it　casts　on　the　environment　of　our　own　planet。　There　are　mysteries　waiting　to　be　resolved　about　the　interior　of　Mars　and　its　mode　of　origin；　the　nature　of　volcanos　on　a　world　without　plate　tectonics；　the　sculpting　of　landforms　on　a　planet　with　sandstorms　undreamt　of　on　Earth；　glaciers　and　polar　landforms；　the　escape　of　planetary　atmospheres；　and　the　capture　of　moons—to　mention　a　more　or　less　random　sampling　of　scientific　puzzles。　If　Mars　once　had　abundant　liquid　water　and　a　clement　climate；　what　went　wrong？　How　did　an　Earthlike　world　bee　so　parched；　frigid；　and　paratively　airless？　Is　there　something　here　we　should　know　about　our　own　planet？

We　humans　have　been　this　way　before。　The　ancient　explorers　would　have　understood　the　call　of　Mars。　But　mere　scientific　exploration　does　not　require　a　human　presence。　We　tan　always　send　smart　robots。　They　are　far　cheaper；　they　don't　talk　back；　you　can　send　them　to　much　more　dangerous　locales；　arid；　with　some　chance　of　mission　failure　always　before　us；　no　lives　are　put　at　risk。



〃HAVE　YOU　SEEN　ME？〃　the　back　of　the　milk　carton　read。　〃Mars　Observer；　6'　x　4。5'　x　3'；　2500　kg。　Last　heard　from　on　8/21/93；　627；000　km　from　Mars。〃

〃M。　O。　call　home〃　was　the　plaintive　message　on　a　banner　hung　outside　the　jet　Propulsion　Laboratory's　Mission　Operations　Facility　in　late　August　1993。　The　failure　of　the　United　States'　Mars　Observer　spacecraft　just　before　it　was　to　insert　itself　into　orbit　around　Mars　was　a　great　disappointment。　It　was　the　first　post…launch　mission　failure　of　an　American　lunar　or　planetary　spacecraft　in　26　years。　Many　scientists　and　engineers　had　devoted　a　decade　of　their　professional　lives　to　M。　O。　It　was　the　first　U。S。　mission　to　Mars　in　17　years—since　Viking's　two　orbiters　and　two　landers　in　1976。　It　was　also　the　first　real　post…Cold　War　spacecraft：　Russian　scientists　were　on　several　of　the　investigator　teams；　and　Mars　Observer　was　to　act　as　an　essential　radio　relay　link　for　larders　from　what　was　then　scheduled　to　be　the　Russian　Mars　'94　mission；　as　well　as　for　a　daring　rover　and　balloon　mission　slated　for　Mars　'96。

The　scientific　instruments　aboard　Mars　Observer　would　have　napped　the　geochemistry　of　the　planet　and　prepared　the　way　for　future　missions；　guiding　landing　site　decisions。　It　might　have　cast　a　new　light　on　the　massive　climate　change　that　seems　to　have　occurred　in　early　Martian　history。　It　would　have　photographed　some　of　the　surface　of　Mars　with　detail　better　than　two　meters　across。　Of　course；　we　do　not　know　what　wonders　Mars　Observer　would　have　uncovered。　But　every　time　we　examine　a　world　with　new　instruments　and　in　vastly　improved　detail；　a　dazzling　array　of　discoveries　emerges　just　as　it　did　when　Galileo　turned　the　first　telescope　toward　the　heavens　and　opened　the　era　of　modern　astronomy。

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。　Y