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Inside the High Stakes Missions of NASA’s Oldest Deep-Space Probes
日期:2020-02-22 03:34 作者: 来源:美国新闻周刊网 相似文章:0条
           OnAug.20,1977,NASAlaunchedtheVoyager2probeonamissiontoexploretheouterplanetsofoursolarsystem.Twelveyearslater,havingscannedJupiter,Saturn,UranusandNeptune,the1,600-poundspacecraftcompleteditsinitialmission.Butitkeptgoing.Andgoing.Andgoing.NursedfartherandfartherintospacebyasmallteamatNASA’sJetPropulsionLaboratoryinCalifornia,Voyager2isnowmorethan11billionmilesfromEarth,makingitthesecond-most-distantman-madeobjectfromEarthafteritsspeediertwinVoyager1.InlateJanuary,Voyager2’sdecades-longvoyagealmostcametoanuntimelyend.ThemishapunderscoresthedelicacyofNASA’ssuper-long-rangespacemissions,aswellastheingenuityofthespaceagency’sprobe-operators.AfterzippingpastNeptunein1989,Voyager2tookonanewmission:workingalongsideVoyager1toinvestigatethe“heliosphere,”whichNASAspokeswomanCallaCofielddescribedas“thebubbleofparticlesandmagneticfieldscreatedbythesun.”OnJan.25,Voyager2wassupposedtoexecuteascheduledmaneuver,turning360degreesinordertocalibrateanon-boardmagneticinstrument.Buttheprobenevermadetheturn.Voyager2’soperatorsinCaliforniafoundoutaboutthemissedturn17hourslater—thetimeittakesforaradiosignaltotravelthebillionsofmilesfromthespacecrafttoEarth.“Analysisofthetelemetryfromthespacecraftindicatedthatanunexplaineddelayintheonboardexecutionofthemaneuvercommandsinadvertentlylefttwosystemsthatconsumerelativelyhighlevelsofpoweroperatingatthesametime,”NASAexplainedinarelease.“Thiscausedthespacecrafttooverdrawitsavailablepowersupply.”TheVoyagerprobescarryplutonium-poweredgeneratorsthatcanproduce470wattsofpower—theequivalentofahandfuloflightbulbs.Anysystemthatconsumesevenafewextrawattscouldshaveyearsofftheprobes’lifespans.Toprotectagainstasuddenbatterydrain,theVoyagers’softwareautomaticallyshutsofftheprobes’scienceinstrumentswheneveritdetectsasurgeinpowerconsumption.Ofcourse,withoutinstrumentsthespacecraftarejustuselesshunksofmetalstreaking34,000milesperhourintothecosmos.TheteaminCaliforniagottoworkfixingVoyager2.They’ddoneitbefore.In2010asinglebitinVoyager2’smemoryflippedfromzerotoone,introducingaflawintothedatatheprobewassendingbacktoEarth.Todiagnosetheerror,engineersattheJetPropulsionLaboratoryransimulationsonacomputerrunningthesamesoftwareasthedistantprobe.Ittookafewweeks,buttheywereabletotransmitinstructionstoVoyager2toflipthebitbacktozero.Butthe2010fixperhapsseemeddeceptivelyeasy.Infact,theteamsmanagingtheVoyagersaswellasNASA’sotherdeep-spaceprobe,NewHorizons,canpreventorcausecatastrophewithasinglekeystroke.(NewHorizons,whichlaunchedin2006,isprobingtheKuiperBelt,aregionofthesolarsystembeyondNeptunethatscientistsbelievecontainsalargenumberofcometsandasteroids.)In1982,aNASAteambotchedasoftwareupdateontheViking1Marslander.Thebadcodecausedthelandertopointitsantennainthewrongdirection,permanentlycuttingoffallcommunicationwithEarth.“Theycannevermakeasinglemistake,”AlanStern,theprincipalinvestigatorfortheNewHorizonsmission,toldTheDailyBeast,referringtoNASA’sprobeteams.Andtheteamshavetomaintainthatflawlessperformanceeverydayfordecadesaspresidentialadministrationscomeandgo,budgetsriseandfall,oldstaffretireandnewstaffjoinup.FixingVoyager2’sJanuarymalfunctionendedupbeingfairlystraightforward.Theengineersessentiallyrebootedafewkeysystems.Thenwaited17hourstohearbackfromtheprobe.OnFeb.5,NASAannouncedthegoodnews.“MissionoperatorsreportthatVoyager2continuestobestable,andcommunicationsbetweenEarthandthespacecraftaregood,”NASA’sCofieldtoldTheDailyBeast.“Thespacecrafthasresumedtakingsciencedata,andthescienceteamsarenowevaluatingthehealthoftheinstrumentsfollowingtheirbriefshut-off.”Sternpraisedtheengineerswhosavedtheprobe.“TheVoyagerguys,theywereunderthegunoftimewithhighstakes,”hesaid.“Theydiscoveredaproblemandtheclockwastickingtosavetheday.”Withanyluck,theVoyagershaveanotherfourorfiveyearsworthofpowerleft.NASAplansfortheprobestocontinueinvestigatingtheheliosphereuntilthedaytheyfinallypowerdown,sometimeinthemid-2020s.Withitsfresherbatteries,NewHorizonscouldlastintothe2040s.