The Leonid 2000 Meteor Shower. Information for spacecraft operators

Transcription

1 Sptmbr 14, 2000 Th Lonid 2000 Mtor Showr Information for spaccraft oprators 1. Scop Th objctiv of this not is to provid background information about th xpctd Lonid mtor showr around 17/18 Novmbr 2000 and to giv advic for spaccraft oprators what kind of prcautions can b takn to minimiz th risk of damag to oprational spaccraft. A similar not was distributd on 28 August 1999 for th 1999 rturn of th Lonids. In this not updatd prdictions for th xpctd tim and intnsity of th Lonid 2000 mtor showr ar givn. Although a smallr activity is xpctd as compard to last yar, prcautionary masurs should b considrd. 2. Introduction Earth orbiting spaccraft ar at risk of bing hit by Earth orbiting dbris but to som xtnt also by mtoroids. For xampl, th dmis of ESA's Olympus spaccraft may b attributd to th Prsid mtoroid stram. Th Lonid mtoroid stram is xpctd to pos a particular risk in th yars 1999 to 2002 around Novmbr 17-18, th tim in th yar whn th Earth passs closly th orbit of comt Tmpl-Tuttl, which is th prognitor of this stram. P/Tmpl-Tuttl, which taks 33 yars to complt on rvolution around th Sun, passd through prihlion in Fbruary Th latst orbital lmnts (J2000) of P/Tmpl-Tuttl ar (Rf. 1): tim of prihlion passag: 1998 Fb ccntricity: prihlion distanc: AU argumnt of prihlion: dg long. of ascnding nod: dg inclination: dg. Bcaus of th rcnt prihlion passag, a strong incras in flux of th Lonid mtoroids is obsrvd. Sinc th Lonids approach th Earth with a vlocity of about 71 km/s, vn small particls can damag a spaccraft. Th damag potntial is similar as during th flyby of th Giotto spaccraft at comt Hally, whr th spd of th impacting dust particls was nar 68 km/s. 1 lonids-warning2000.doc

2 3. Risk for Earth Orbiting Spaccraft 3.1. Potntial damag to spaccraft Oprational satllits can b damagd by high-spd impacting particls in two primary ways: damag through physical impact (dstruction of snsitiv parts) with th high-spd impact a plasma cloud (mixtur of nutral and chargd particls) can b gnratd. This plasma cloud can intrfac with spaccraft lctronics. Th plasma cloud can also triggr an lctrostatic discharg of a prviously chargd spaccraft. Such lctrostatic dischargs can coupl into th spaccraft lctronics and lad to lctronic anomalis. Th liklihood of lctrostatic dischargs will dpnd on th ambint plasma lctron nvironmnt (in th KV to MV nrgy rang) during th showr but also hours and days bfor th showr. Larg impacting particls may also chang th spaccraft attitud du to momntum transfr. Erosion may occur of outr surfacs lik thrmal blankts, mirrors, solar clls by typ of sand-blast ffct Znithal hourly rat (ZHR) Th quantity usd by astronomrs to dscrib th intnsity of mtor strams is th znithal hourly rat (ZHR). It tlls how many mtors pr hour would b visibl if th obsrvd showr wr to com from th dirction of th znith undr optimum obsrving conditions (no moon, no clouds). In dtrmining th ZHR, th limiting visual magnitud is put at 6.5, which is quivalnt to a particl mass of about 100 micrograms (for objcts at 71 km/s) or a diamtr of about 0.5 mm. Th normal background ZHR is around Dat, tim and intnsity of th Lonids in 2000 Th maximum ZHRs ar usually rachd in th two yars following th prihlion passag of th comt, that is for th prsnt apparition of P/Tmpl-Tuttl in 1998 and Indd last yar th ZHR rachd a rat of about 5000 narly xactly at th tim prdictd by Ashr and McNaught on 18 Nov, 1999 at 2:04 UT (s Figur 1). Th activity was at storm lvl (i.. ZHR largr than 1000) for mor than on hour (30 minuts bfor and aftr th pak). 2 lonids-warning2000.doc

3 Howvr, simulations by McNaught and Ashr (Rf. 2) prdict storm lvls also in th yars 2001 and 2002 and may b also this yar. Thy prdict a ZHR of 100 to 5000 on Nov 18, 2000 at 03:44 UT (ncountr with 1733-particls ) and again 4 hours latr at 07:51 UT (ncountr with 1866-particls ). Th work by Ashr and McNaught was manwhil succssfully rpatd by othr rsarch groups. Th tim of th paks ar usually in vry good agrmnt, whil th assssmnt of th intnsity may diffr considrably. A study by Göckl and Jhn (Rf. 3) confirmd th two paks on Nov 18, 2000, howvr, thy xpct th major contribution from particls jctd in Th Earth is passing clos to th cntr of this filamnt of th Lonids on Nov 17, 2000 at 07:53 UT. To summariz, th Lonids may b vry activ for a short tim (about 1 hour) on thr occasions this yar sprad ovr 24 hours. Th xact magnitud of ach showr is prdictd diffrntly by diffrnt rsarchrs Mtor rat (ZHR) Solar longitud (dg) Fig.1 Znithal hourly rat of th Lonids Th maximum occurrd at a solar longitud of dg (18 Nov 1999, 2:04 UT). 3 lonids-warning2000.doc

4 3.4. Radiant and Vlocity Th radiant, i.. th dirction from which th particls approach th Earth, is at right ascnsion = 153 dg and dclination = 22 dg. Th vlocity of th Lonids with rspct to th Earth is 71 km/s. To calculat th vlocity of th Lonids rlativ to a spaccraft, th vlocity of th spaccraft with rspct to th Earth must b takn into account. So a LEO satllit will xprinc impacts btwn about 64 and 79 km/s. 4. Rcommndations for spaccraft oprators Although no damag was rportd on oprational satllits during th 1999 Lonids and although th Lonids ar prdictd to b lss activ this yar, a numbr of prcaution masurs ar rcommndd to avoid unncssary risk of mtoroid impacts on spaccraft: Spaccraft launchs nar mid-novmbr 2000 should b postpond to aftr th Lonid showr, i.. aftr Novmbr 18. It is rcommndd to minimiz th cross sctional ara of th spaccraft facing th radiant of th Lonids. Sinc th dirction from which th particls approach th Earth is almost prpndicular to th dirction to th Sun, th solar arrays will fortunatly b facing th showr dg on (assuming that th solar arrays ar pointing towards th Sun). If possibl, th attitud of th spaccraft should b chosn such that snsitiv parts ar not xposd to th mtoroids. It is rcommndd to apply this and th masurs listd blow from Nov 16, 20 h UT to Nov 18, 20 h UT. It is rcommndd to xamin th possibilitis of damag du to plasma discharging. By turning off snsitiv quipmnt th spaccraft may b configurd to a "saf" mod. Incrasd lctron fluxs could lad to incrasd spaccraft anomalis during th showr. It is rcommndd to rinforc th opration tam prior to and during th showr in ordr to cop with potntial spaccraft anomalis. Th spaccraft status should b continuously monitord prior to and during th showr. 4 lonids-warning2000.doc

5 5. Rfrncs 1. D. K. Yomans, Comt 55P/Tmpl-Tuttl and th Lonid Mtors, Proc. Lonid Mtoroid Storm and Satllit Thrat Confrnc, Manhattan Bach, CA, USA, April 27-28, R. McNaught and D. Ashr, Lonid Dust Trails and Mtor Storms, WGN, th Journal of th IMO, pp , C. Göckl and R. Jhn, Tsting Comtary Ejction Modls to fit th 1999 Lonids and to Prdict Futur Showrs, Mon. Not. R. Astron. Soc., Vol. 317, No. 1, L1-L5, 1 Sp W. Ailor, Th Upcoming Lonid Mtoroid Storm and its Effct on Satllits, Th Arospac Corporation, May 21, Procdings 99 Lonid Mtoroid Storm and Satllit Thrat Confrnc, May 11-13, 1999, Th Arospac Corporation and AIAA. 6. G.E. Ptrson, Dynamics of Mtor Outbursts and Satllit Mitigation Stratgis, Th Arospac Prss, El Sgundo, CA, AIAA, Inc., Rston VA, For furthr information contact: W. Flury, TOS-GMA or R. Jhn, TOS-GMA ESOC ESOC Robrt-Bosch-Str. 5 Robrt-Bosch-Str Darmstadt Darmstadt Grmany Grmany Tl: 06151/ Tl: 06151/ Fax: 06151/ Fax: 06151/ wflury@soc.sa.d rjhn@soc.sa.d 5 lonids-warning2000.doc