New Worlds Observer Optical Performance Amy S. Lo, Tiffany Glassman, Chuck Lillie Northrop Grumman Corporation

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1 Nw Wolds Obsv Optcal Pfomanc Am S. Lo Tffan Glassman Chuck Lll Nothop Gumman Copoaton ABSTRACT Nw Wolds Obsv s an tnal occult o stashad msson dsgnd to dtct vsbl wavlngth (lss than mcon) lght fom ath-lk plants aound sola nghbohood stas. A tlscop spaccaft opats n th shadow cast b an stashad spaccaft locatd tns of thousands of klomts awa. Th spcall contoud ptals on th stashad spaccaft contol th dffacton to poduc hgh contast suppsson of th on-as stalght. Th stashad opats n th Fsnl o na fld dffacton gm whch adds complt to numcal smulatons of ts pfomanc. As a valdaton of th numcal modls and a dmonstaton of th stashad capablts w hav bult a tstbd to masu th pfomanc of subscal NWO hpgaussan stashads. W dscb th atonal fo ou tstbd and ts st up. W pct to b abl to pot sults fom th tstbd n a lat pap ths a. Kwods: o-plant Occult Apodaton Stashad Tstbd Tstal Plant Fnd. INTRODUCTION Nw Wolds Obsv (NWO) s a msson concpt dsgnd to dntf ta-sola plants. NWO conssts of a tlscop and an tnal stashad algnd wth a tagt sta. A sktch of th NWO achtctu s shown n Fgu. Fgu : Th basc achtctu of th NWO msson. A gnc tlscop s usd n conjuncton wth th NWO stashad to block out th on-as stalght and dtct and chaact an off-as souc th tasola plant. Dtctng and chaactng an ath-lk ta-sola plant s v dffcult. At vsbl wavlngths shotwad of mcon plants a sn b flctd stalght; th small s and latvl low albdo of th plant mans that a bghtnss dffnc of ~ sts btwn th sta and plant. In addton th plant and th sta a qut clos togth; at pascs awa ath would b onl mas fom th Sun. Ths alts cat th pfomanc qumnts of th sstm w nd to b abl to achv a v hgh contast ato v clos to th sta. Th stashad s capabl of catng a gvn contast ato fo a plant at all angls gat than som mnmum calld th Inn Wokng Angl (IWA).. TH BINARY APODIZD STARSHAD In a cnt pap Cash (6) showd that an tnal stashad wth a hpgaussan tansmsson pofl (quaton ) povds a dp boadband null fo on-as lght and hgh tansmsson fo an off-as souc. Th hpgaussan apodaton functon A() s gvn b: UV/Optcal/IR Spac Tlscops: Innovatv Tchnologs and Concpts III dtd b Howad A. Macwn Jams B. Bckndg Poc. of SPI Vol (7) X/7/$8 do:.7/.735 Poc. of SPI Vol

2 A < a n a () A p a b wh a s th adus of a cntal gon of o tansmsson b s th fall-off adus of th ponntal functon n s th nd that dtmns how quckl th hpgaussan functon falls wth adus and s th stashad adus. Fo mo dtals about how ths functon was dvd and how t cats a dak shadow s Lo Glassman & Anbg (7). Th smooth tansmsson pofl can b bokn up nto P ptals wh th avag facton of sold aa vsus adus s qual to A(). Ths allows us to buld a bna stashad that totall opaqu ath than on wth vaabl tansmsson; a vaabl tansmsson occult s dffcult to manufactu. Th -dmnsonal apodaton functon and th -dmnsonal bna stashad a shown n Fgu. Fgu : Lft: Th apodaton functon A() fo th NWO stashad showng sval dffnt hpgaussan functons. Cnt: A -ptald bna stashad wth n 6. Rght: Illustatons of stashad shaps wth dffnt ptal numbs and valus of n. 3. MODLING OF TH STARSHAD PRFORMANC Now that w hav dvd an apodaton functon w would lk modl th dtald pfomanc of th stashad. Ths wll gv us a confmaton of th thotcal pfomanc lvl and a vsual psntaton of th sultng dstbuton of lght. Th a two mthods to do ths a numcal smulaton of th dffacton of lght aound th stashad and a lab tst nvolvng a sub-scal stashad. Ths mthods a complmnta as th combnaton of both wll show that th sults a obust. Th optcal smulaton and ts sults a dscbd n dtal n Lo t al. (7). H w wll summa th k sults bfo focusng on th lab scal modl. 3.. Numcal Smulaton Th a two plans of ntst n ths smulaton: th shadow plan and th mag plan (s Fgu 3). Th shadow s a gon of hgh stalght suppsson that s bg nough to accommodat th aptu of th tlscop. W wll focus on ths plan snc that s wh w wll b wokng n th lab tst. Poc. of SPI Vol

3 Fgu 3: Th a two plans of ntst n th optcal smulaton. Th ncomng adaton stks th stashad n th stashad plan and s dffactd b th stashad. Th lght foms a dp shadow n th shadow plan a dstanc awa wh th tlscop aptu s placd. Th tlscop thn foms an mag of th lght t collcts whch s focusd n th mag plan. Th appaanc of th shadow as modld b th numcal smulaton s sn n Fgu 4. Th shadow has a v dak cntal gon that s lag nough to accommodat th tlscop. Na th dgs dffacton fom th ptals cats a compl pattn as th ntnst ss. Ou smulaton can modl th total dpth of th shadow as wll as ts s and how th lght ncoachs at th dgs. Fgu 4: Th shadow cast b th stashad s shown on th lft. On th ght s a blow up of th dg of that shadow and a slc though th shadow showng that th hghst contast gons hav a dpth of ~X Poblms wth Numcal Smulatons Th a sval smplfng assumptons that must go nto an numcal smulaton n od fo th calculaton to b tactabl. Th fst assumpton w mad s that th stashad opats n th Fsnl gm and thfo w can us th Fsnl ntgal. Th full quaton dscbng th dffacton of lght s th Ralgh-Sommfld quaton: ( ) ( ) p( k) cos ( ndd ) () A Poc. of SPI Vol

4 wh s th wavlngth of lght k/ n s th nomal vcto connctng th aptu plan to th obsvaton plan and s th adal vcto connctng th ponts ( ) and ( ). To b abl to solv ths quaton w mak a numb of assumptons that a vald n th Fsnl lmt. Fst w assum that cos n (3) whch s vald to 5% fo angls lss than 8 dgs. Ths stcton s not pctd to b volatd; gvn th lag dstanc btwn th stashad and th tlscop w a onl concnd wth a small gon aound th optcal as. Nt w tak th fst tm of th bnomal panson of so that: ) ( ) ( (4) bcoms:. (5) Ths smplfs quaton () so that t bcoms: A k d d p ) p ( p ) ( (6) whch s th Fsnl ntgal. Th spaaton of vaabls maks ths quaton s much as to solv. Th Fsnl ntgal s vald whn solvd ov th whol aptu whch n ths cas s th nt sk outsd th stashad. W can us Babnt s pncpl to solv fo an quvalnt pnhol wth th sam shap whch maks th ntgal much smpl. Babnt s pncpl stats that th dstbutons of lght sultng fom an occultng spot and fom th sam shapd pnhol n an nfnt plan a latd b: pnhol. k occult. (7) Solvng th Fsnl quaton fo a pnhol s much mo tactabl snc th ntgal s onl ov th aa of th opnng. Howv usng Babnt s pncpl gnall assums Faunhoff condtons. W hav pfomd chcks of flds calculatd usng Babnt s pncpl and flds calculatd usng a v lag gd and fo smpl aptus th a dntcal. Wth a complcatd aptu lk ous th cospondnc ma dgad. Coss chcks usng numcal smulaton a pohbtvl CPU ntnsv. Ou complcatd aptu dos not hav an analtc soluton; w must choos a mthod of solvng th Fsnl ntgal numcall. Solvng th ntgal n a dct but foc wa b numcal ntgaton s too slow to b pactcal so futh assumptons must b mad. On mthod of solvng th ntgal s to wt th Fsnl quaton n pola coodnats: cos d d θ θ φ φ θ (8) and thn pand ths quaton b th Jacob-Ang tansfom: () () cos sn ) ( φ φ mn X d m m J d J m R mn m R (9) wh J mn a Bssl functons of od mn and N s th numb of ptals n th stashad. In od to us ths panson a fnt numb of tms must b takn. If nough tms a chosn ths appoachs th full quaton. Poc. of SPI Vol

5 Anoth wa to solv th Fsnl ntgal numcall s to us a Fast Fou Tansfom (FFT) tchnqu. Ths tchnqu uss th smlat btwn th last tm of quaton (6) and th FFT: M N mp nq p q m n p. () m n M N Th Fsnl ntgal can thfo b solvd b takng th FFT of th nput lght dstbuton along wth a phas facto. Whl v fast th pma lmt of ths tchnqu s that a lag gd must b usd to psnt th stashad to th qud accuacs. Gvn fnt comput soucs and tm th s of th gd that can b usd to calculat th sum s lmtd. In addton th FFT tslf nvolvs ctan smplfcatons and os that a wll documntd lswh (s.g. Cool & Tuk 965). Th assumptons that must b mad to do optcal smulatons hav bn chckd and an os th mpos a blvd to b wll blow th lvl of accuac ndd. Howv an numcal modl should b tstd aganst alt to mak su that th fundamntal phscs bhnd th modls s vald. 3.. Sub-scal stashad lab tst Th bst wa to tst f th assumptons w mad n th numcal smulaton a vald s to do a laboato tst of th sstm. Ths wll tll us th actual bhavo of an stashad spondng to al photons. Th s of th full flght sstm fo NWO (an stashad that s 3 to 5 mts n damt opatd 3 to 8 km fom th tlscop) pvnts us fom dong a full-scal tst. Instad w can tst a sstm wth th sam Fsnl numb as th full scal sstm. Th Fsnl numb s dfnd as: R F () wh R s th adus of th stashad and s th dstanc fom th stashad to th dtcto. Ths valu spcfs th bhavo of th sstm a stup wth th sam Fsnl numb wll hav th sam dffacton bhavo. If th full scal stashad has R 5 m 8 km and opats at wavlngths shot than 8 nm th Fsnl numb of th sstm wll b to 5. Snc w want to do th subscal tst n vsbl lght as wll th s and dstanc of th stashad wll hav to b scald togth to kp th Fsnl numb about th sam. W a lmtd b th s of th faclt w can us and th s of tst stashad that b constuctd to psnt th fgu accuac of th actual stashad. Th smallst tst stashad w can accuatl buld s ~ mm n adus (s scton 3..). Thfo to match th Fsnl numb th tst dstanc must b 45 to 65 m Pvous Lab pmnt Wbst Cash and collaboatos at th Unvst of Coloado w th fst to pfom a vson of ths pmnt. Th catd a tst stashad that s 45 mm n damt and tstd t n a dak tunnl that was 45 m long. It was llumnatd b sunlght that was ppd nto th sstm b a hlostat. Th masud a suppsson of th stalght of -7 (Cash 6). Ths s stll 3 ods of magntud lss than pctd fom ths stup. W blv that th two pma asons fo th Cash shadow dpth lmt a: ) Th pmnt was n conductd n a so dust and a cunts could scatt th lght fom th bght out gons of th shadow nto th dak nn gons washng out th shadow dpth. ) Th tst stashad manufactung pocss lft os n th shap of th stashad that caus scattd lght and a low contast shadow Cunt Tstbd Stup Th Nothop Gumman mcolctoncs faclt s capabl of hgh pcson waf manufactung and w can thfo attmpt to mpov on th Cash sults b usng hgh fdlt tst stashads. B adaptng th waf constucton pocsss w can dvlop a tst stashad that has appomatl / to / fgu accuac whch s th lvl Poc. of SPI Vol

6 w blv s ndd fo th NWO stashad. Onc a good tst stashad s avalabl w catd th bascs of th Cash st up wth th cpton that w dsgnd fo vacuum capablts. Th tst stashad pattns a tchd on a S substat wth a photosst la that s thn mtald. Vaous mtallaton optons w plod and an altnatng la of NC and Au was th bst soluton fo a stabl fnal poduct wth mnmum wapng. Th substat s thn thnnd and tchd to val th fnal stashad. Th sultng tst stashad s appomatl 4 mm n damt wth dgs fatus small than.5 mcon and hgh mtologcal accuac. Th tuncaton pont of th stashad s vaabl fom tp to tp wth som of thm tapng down to lss than mcon. Unqu to th NWO stashad dsgn s th fact that ts suppsson s panchomatc. Th stashad s dsgnd fo adquat pfomanc at th longst wavlngth ncssa and s capabl of smla lvls of suppsson on all shot wavlngths. Its bandpass s thfo v lag wll ov %. Fo ampl ou tst stashad s dsgnd to gv a contast suppsson of - at 8 nm; t s pctd to pfom as wll o btt at shot wavlngths and n wht lght. Ths wll b an mpotant pat of ou tst Constucton and Calbaton of th Tstbd W hav constuctd a 6 m long vacuum tub out of.3 m damt PVC pps. Ths a boltd togth n 3 mt sgmnts and mountd on sawhoss (s Fgu 6). Th tubs a lnd wth alumnum nsts that a pantd black to mnm scattd lght n th tubs. Th a also baffls placd at man locatons along th tub that a dsgnd to futh cut down on scattd lght. Th nds of th tub hav alumnum caps wth 5 cm damt quat wndows to lt th bam though. Fgu 6: Th tstbd vacuum tub showng th souc-nd optcal bnch and th vacuum pump n th backgound. Th nt tub s 6 m n lngth. Th stashad s mountd n a salabl bo halfwa down th tub (Fgu 7). Th stashad tslf s glud to a mountng scw that s hld nto a ng usng th guta ws. Th stashad assmbl can b usd to otat th stashad fom outsd of th tub to tst th ffcts tltng th stashad. Poc. of SPI Vol

7 Fgu 7: On th ght s th tst stashad mountd n a ng b guta stngs. On th lft a cloth has bn placd n th sstm so that th lght dstbuton and th shadow of th stashad can b sn. Th lght souc w a usng s cuntl a Nd:YAG las wth an addtonal fant HN las to hlp wth algnmnt. As wth all long basln optcal pmnts kpng th bam algnd s ou bggst optcal challng: a small adjustmnt of th st up causs th bam to bcom msalgnd. Thmal dstotons and buldng vbatons qus us to algn th sstm bfo ach masumnt. W thfo hav placd sval sts of mos to ) dtmn th magntud and souc of msalgnmnt and ) adjust th bam n poston and pontng wth hgh pcson (Fgu 8). Th s a pnhol just bfo th ntanc to th tub that s usd to clan up th wavfont of th bam. W hav a wak halogn souc fo wht lght algnmnt but nd a bght lamp fo pop llumnaton of th stashad. Fgu 8: Th souc-nd optcal tabl s sn wth th ntanc to th vacuum tub n th backgound. Th two lass that a bng usd as a lght souc (th Nd:YAG) and an algnmnt las (th HN) a sn n th fogound. Th dtcto w a usng s an SBIG CCD cama wth a v small fld of vw so th s no contamnaton fom th bght aas of th stashad shadow. It dos not contan a lns and s usd to captu th photon dstbuton of th shadow plan. It s wat coold to -3ºC. Th optcal bnch at th dtcto nd also contans sval oth camas and montos that a usd n algnng th sstm (Fgu 9). Poc. of SPI Vol

8 S Fgu 9: Th stup on th dtcto nd s shown. Th scnc dtcto s mountd up aganst th nd of th vacuum tub on th ght. Th s a small tlscop anoth small cama two montos fo us n algnng th sstm. Th laptop on th lft wll b usd to tak th data. Th s a vacuum pump just past th souc nd of th tub (Fgu 6) that can ach / atm n lss than 3 mnuts and /5 atm n lss than hou. Th psstnc at s btt than / atm p hou Plmna Tstbd Rsults Fgu shows an mag takn wth th tstbd that s a mosac of 36 posus. Ths mag has a v good cospondnc to th sults of th numcal smulaton (s Fgu 4). Th man dffnc s a ss of dffacton ngs that a psnt n th tstbd data whch w blv a th sult of a contnud msalgnmnt n th sstm that s causng th bam to clp a baffl. Ths s on of th ssus w a contnung to wok on. Fgu : An mag of th dg of th shadow of th stashad takn n th tstbd. Ths mag s a mosac of 36 mags ach of whch s a mllscond posu stmatd Obtanabl Rsults Fo ou tstbd stup wth 6 nm lght th bst cas would gv us an avag contast n th cama of ~X -9. Th dpst potons of th shadow should hav a suppsson of ~X -4 n ths cas. Th a sval factos that would dgad ths pfomanc. In od of th stmatd mpact ths nclud: Poc. of SPI Vol

9 Non-unfom wavfont fom th lght souc. W pct that w should b abl to achv a wavfont that s unfom to at last pat n 3 and hopfull as good as pat n 5. Fom th numcal smulaton w pct that fo wavfont os of -5 th dpst potons of th shadow would hav a contast no btt than ~X -. Fo os of -4 th hghst contast would b ~X -8 and fo os of -3 t would b ~X -6. Sta lght gttng nto th bam path. W hop to mtgat ths to a lag tnt so that t s no long an ssu. Manufactung os on th stashad shap. Though th stashad manufactung pocss s v good th wll b som manng non-unfomts. Fom ou numcal smulaton w pct that f th dg os a no bgg than pat n th suppsson would onl b mpactd at th lvl of X -. W thnk th stashad os a clos to ths lvl alad so th shouldn t b a sgnfcant mpact fom ths ssu. In addton b cafull masung th os that do st on th stashad dg w can vf th pdctons of th numcal smulaton fo how th os wll affct th pfomanc Futu Wok Th nt stp n ths pocss s to mtgat th ffcts abov to gt som sults out of th cunt tstbd stup. In th futu w would also lk to mpov th tstbd b gttng: A mo snstv dtcto so that w can masu th shadow at v low lght lvls wth adquat S/N. A btt lght souc that s bght nough to gv suffcnt S/N n th shadow and povd a unfom bam. It should also b a wht lght souc nstad of a las to btt match th spctum fom a al sta and to mtgat ssus w a cuntl havng wth th cohnc of th las. A mo stabl nvonmnt to duc vbaton and thmal ffcts. 4. CONCLUSION NWO s a unqu msson concpt usng a bna apodd tnal stashad. Although numcal smulatons can b usd to modl th pfomanc of ths stashad buldng a tstbd to chck th smulaton s an mpotant stp. If th two mthods gv sults that a n agmnt th pfomanc of th stashad wll b full convncng. W hav bult a tstbd fo th stashad that conssts of a 6 m-long vacuum chamb and a 4 mm damt tst atcl. W hav a las lght souc and a CCD cama as a dtcto. W a cuntl n th pocss of undstandng and mpovng th bhavo of th tstbd. W pct to gt a masumnt v soon of th suppsson lvl achvd b ths stashad. In addton to dbuggng th cunt tstbd th a sval mpovmnts that can b mad to th tstbd n th futu to mpov ts pfomanc. Cash W. 6 Pvat Communcaton 5. RFRNCS Cool J. W. & Tuk J.W. 965 Mathmatcs of Computaton 9 97 Lo A. S. Glassman T. G. & Anbg J. 7 ApJ submttd Poc. of SPI Vol