航天,航天器,航天器环境,空间辐射

N.V.Kuznetsovetal./AdvancesinSpaceResearch36(2005)2003–20112005

Forthepurposesoftheanalysis,thisdatasetshouldbedividedintotwogroups:

1.1965–1977period,whentheP10andP30MeVpro-tons uxesonlyweremeasuredand

2.1985–1997period,whentheP60MeVprotons uxeswerealsomeasured.Thetotal(summarizedwithrespecttoallevents)par-ticle uencedataarepresentedinTable1.ThetotalperiodsT(inmonths)ofproton uencemeasurementsinquietSuntimearealsopresented.

Forcomparison,themeanannualproton uencedataontheSEPeventsthatoccurredwhenthesunspotnumberwas1456ÆWæ6155arepresentedaccordingtothesamedatabasefor1965–1997.

UsingtheTable1data,themean-annualproton u-encesforenergiesP10,P30,andP60MeVwerecalcu-latedandaredisplayedinFig.1.ForthesecondquietSunperioddataandforthe1456ÆWæ6155data,itispossibletoextrapolatetheenergyspectrumtohighenergiesinconformitywiththepropositionthattheen-ergyspectraoftheP30MeVSEPsarepower-lawfunc-tionsofprotonrigidity(Nymmik,1993,1995;Mottletal.,2001;MottlandNymmik,2003b).Forthe rstquietSunperiod,wehaveextrapolatedtheenergyspec-trumtothehigh-energyrangeusingthesameindexoftherigidityspectrum(cp=4.14)asforthesecondquietSunperiod.

Fig.1showsalsothemodel-calculated(Nymmiketal.,1996)annualintegralenergyspectraofgalacticcosmicrayprotonsduringthesametwosolaractivityperiods.ItisseenthatduringthequietSunperiod,itisonlythe10MeVannualintegralsolarenergeticpro-ton uencesthatexceedtheannualgalacticproton u-ence.Duringhighsolaractivity,therecordedsolar

energeticproton uencesexceedthegalacticproton u-encesevenat>60MeV.

Itisthedi erentialenergyspectraoftheparticlesthatdeterminenotonlythespaceradiationenvironmentbutalsotheradiatione ectsinducedbyparticle uxes.Fig.2showsthedi erentialenergyspectrathatcorre-spondtotheintegralenergyspectradisplayedinFig.1.SincethegalacticandSEPeventprotonenergyspec-traareofdi erentforms,thesituationchangesdrasti-cally.Fig.2showsthatthemeanannualSEPeventproton uencesmeasuredintheEarthÕsorbitduringthequietSunperiodsexceedthemodel-calculatedgalac-ticcosmicray uencesunlesstheprotonenergiesreach100MeV,andthe10MeVsolarenergeticproton u-encesareupto3–4ordersashighasthegalacticparticle uences.Duringhighsolaractivity,themeasuredmeanannualSEPeventproton uencesbecomeequaltothecalculatedgalacticcosmicrayproton uencesat400MeV.

Fromtheaboveanalysis,itfollowsthattheSEPeventproton uencescountmuchduringallthesolaractivityperiods,thequietsunincluded.Therefore,iftheSEPeventsduringlowsolaractivityaredisregarded,aninaccuracyofuptoafeworderswilloccurindeter-miningtheparticle uxesininterplanetaryspace.

OuranalysishasdemonstratedthatthechoiceoflowsolaractivityperiodsforinterplanetarymissionsdoesnotexcludetheSEP-inducedhazard.Moreover,thereex-istsasigni cantprobabilityduringlowsolaractivityfortheSEPparticle uencestoexceedU30P1.9108pro-tons/cm2,whichisjustthe6November1997occurrence.Therefore,giventhemodelsthatdescribetheSEP uxesforactiveSunperiodsonly(Feynmanetal.,1993,2002;Xapsosetal.,1998,1999;Tylkaetal.,1997),wecannotdeterminetheradiationhazardforallpossiblespacemissionperiods.

Intheaboveanalysis,weproceededfromourunder-standing(basedonthestatisticalanalysisofexperimen-taldata)thatthemeanSEPeventoccurrence

frequency

Fig.2.Thedi erentialenergyspectraofannualproton uences.Thecurvesarethedi erentialspectracalculatedfromintegralspectradisplayedinFig.1.ThenotationforthecurvesisthesameasinFig.1.