X-ray Astronomy From Moon

8/9/2019 X-ray Astronomy From Moon

1/8

Pergamon Adv. Space Res. Vol. 14, No. 6, pp. (6)61-(6)68, 1994Ccpyfisht ~ 1994 COSPARPrinted in Great Britain. All rishls reserved.0273-1177/94 $6.00 + 0.00X - R A Y A S T R O N O M Y F R O M T H E M O O N

Paul GorensteinHarvard-Smithsonian Center or Astrophysics, 60 Garden Street, Cambridge,MA 02138, U .S.A.

1 A b s t r a c tAs a platform for x-ray astronomy, the surface of the Moon is outstanding for its stab.ility, the avail-ability of unlimited space for large instruments, and the ability to observe any object continuouslyfor as much as 14 days. There is likely to be three phases of lunar based investigations. The firstwould be the soft landing of simple, self-contained instruments sent from Earth in their operatingconfiguration, that require no assistance to begin functioning. The range of possible instrumentsis limited by the availability of power for survival during lunar night. One candidate instrumentis a very wide field camera system for detecting and positioning bursts, flares, and transients andmonitoring the interesting temporal variations shown by virtually all point-like sources. Anothercandidate for early deployment is a transit telescope that would perform a partial sky survey withbet ter angular resolution, better energy resolution, and at higher energy than the one recentlycompleted by ROSAT. The second stage would consist of the assembly of more complex telescopes,and all-sky monitors with human or robot assistance from components sent from Earth. The third,or ultimate stage would be the robotic fabrication of large telescopes from lunar materials.2 I n t r o d u c t i o nIts proximity to Earth, unlimited space for instrumentation, its slow rotation, stability dueto a low incidence of seismic activity, and the lack of an atmosphere makes the surface of theMoon the ultimate site for a permanent x-ray astronomy observatory. When Earth/Moontransport becomes routine a lunar base will be competitive with operation in Earth orbit.Low Earth orbit is an imperfect site because of the many interruptions that occur overthe 90 minute orbital period due to the object setting, thermal cycling, and radiation beltpassages. High Ear th orbit is free of these problems but too inaccessible to permit theconstruct ion of very large facilities or even repairing, servicing, and upgrading of an existingone. Some unique advantages of a lunar base are listed below in Tab le 1. A lunar baseprovides v irtually unlimi ted accommodations for large instruments, telescopes with long focallengths, and interferometers requiring a stable baseline. A lunar base permits the gradualand incrementa l development of a large facility. Hence, when x-ray observatories grow to thesize of large ground based optical observatories such as the Keck dual 10m optical telescopesand are regarded as permanent facilities tha t are serviced and upgraded to t he same degreeas ground-based astronomical observatories they are likely to be s ituated on the Moon. Ifthe Moon is indeed ultima tely the preferred site for an x-ray observatory then it is certainlyworthwhile to begin the development of lunar based x-ray astronomy now on a modes t scalein order to understand the lunar environment by deploying small experiments.

It could very well turn out that there is no alternative to the Moon as a site for largeinstruments of the future. The "Great Observatories", Hubble Space Telescope, ComptonGamma Ray Observatory, AXAF, and SIRTF represent the limit of what can be launchedby a single space shuttle mission or a Titan IV rocket. Any observatory that is substantiallylarger or more massive than these would require more than one mission plus construction inspace for assembly. If the U.S., Europe, and Russia do select the construction of a base onthe Moon as the next major goal of space exploration, it may not leave the resources to doconstruct ion anywhere else in space other than the Moon. From the astronauts point of view,the 1/6 g gravity of the Moon is superior to zero ~ of Earth orbit as a living and workingenvironment. Lunar gravity provides orientation for tool placement and is less hazardousphysiologically with respect to bone loss and muscle decay. Ten feet of lunar soil provideas much radiation protection as the Earth's atmosphere against cosmic rays and sporadicsolar flare events. Hence, the Moon offers personnel more shelter against radiation hazardsthan Ear th orbit. Furthermore, detectors can be shielded from background by burying the mbeneath the surface.

(6)61


2/8

(6)62 P . Gorenstein

T a b l e 1A d v a n t a g e s o f a L u n ar B a s e

f or X - ra y A s t r o n o m y L a r g e R e a l E s t a t e . Long, S tab le Base l ine .

Very long foca l l engths (> 15 m ) possible. Con t inuous Obse rv ing for 14 Days . L o w T e m p e r a t u r e E n v i r o n m e n t f o r S o lid S t a t e D e t e c t o r s. O u t o f R a d i a t i o n B e l ts . Expandabi l i ty . Service . S t o r a g e o f I n s t r u m e n t a n d P o ss ib i li ty o f I n s t r u m e n t U p g r a d e . A s s e m b l y o f L a r g e I n s t r u m e n t s w i t h S a fe r a n d

B e t t e r H u m a n W o r k i n g C o n d i t i o n s t h a n Z e r o G r a v i t y a n d E a r t h O r b i t . Poss ib i li ty of In S i tu Co ns t ruc t io n f rom Lu na r Ma te r ia l.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

S i m u l t a n e o u s E a r t h a n d S ol ar V i e w in gT h e d e v e l o p m e n t o f l u n a r b a s e d X - r a y a s t r o n o m y e x p e r i m e n t s m a y o c c u r in t h r e e d is -t i n c t p h a s e s :

1 . t h e s o f t l a n d i n g o f s m a l l c o m p l e t e i n s t r u m e n t s t h a t a r e r e a d y t o o p e r a t e w h e n t u r n e do n ~

2 . t h e a s s e m b l y o f a l a r g e r i n s t r u m e n t b y e i t h e r a s t r o n a u t s o r r o b o t s f r o m v a r io u s c o m -p o n e n t s d e l i v e r e d t o g e t h e r o r s e p a r a te l y .3 . t h e c o n s t r u c t i o n o f a n o b s e r v a t o r y i n s it u f r o m l u n a r m a t e r i a ls .T h e t h r e e p h a s e s a r e s u m m a r i z e d in T a b l e 2 . W e c o n s i d er e a c h o f t h e t h r e e p h a s e s a n do f fe r s o m e e x a m p l e s o f in s t r u m e n t s f o r e a c h p h a se . T h e f i rs t p h a s e i s o f i m m e d i a t e i n t e r e s tb e c a u s e i t c a n b e i m p l e m e n t e d w i t h c u r r e n t t e c h n o l o g y a n d h a s b e e n d i s c u ss e d se r io u s l y b yN A S A .

T a b l e 2T h r e e P h a s e s o f X - r a y A s t r o n o m y

f r o m a L u n a r B a s eS t a r t i n g ~ 1 9 9 7 .

S o f t L a n d i n g o f S m a l l S e l f -c o n t ai n e d I n s t r u m e n t s w i t h o u tA s t r o n a u t P a r ti c ip a ti o n .P r o j ec t A r t e m i s ?

2 0 0 k g , 2 m I n s t r u m e n tsA l l S k y M o n i t o r s .T r a n s i t T e l e s c o p e s f o r H i g h r e s o l ut i o n d e e p s u r v ey s .

S t a r t i n g ~ 2 0 1 0 . A s s e m b l y o f L a r g e r I n s t r u m e n t s f r o m C o m p o n e n t s w i t h

A s t r o n a u t P a r t i c ip a t i o nL a r g e , m u l t i w a v e l e n g t h a ll s k y m o n i t o r s .L o n g f o c a l l e n g t h , b r o a d b a n d f o c u s s i n g t e l e sc o p e s a n d

c o d e d a p e r t u r e s.I n t e r f e r o m e t r y .

Sta r t in g ~ 2040. In S i tu Co ns t ruc t ion of H igh Th rou gh pu t Te le scopes.R o b o t i c M e t h o d s .

L u n a r M a t e ri a ls .


3/8

X-Ray Astronomy rom The Moon (6)63

3 F i r s t P h a s e : S o f t L a n d i n g o f S m a l l I n s t r u m e n t s o n t h e M o o nT h e f i rs t p h a s e o f l u n a r b a s e d x - r a y a s t r o n o m y e x p e r i m e n t s w o u l d o c c u r p r io r t o t h e e s ta b -l i s h m e n t o f a m a n n e d l u n a r b a s e. S i n c e i t is n o t a d i r e c t p a r t o f t h a t p r o g r a m i t is q u i t ep o s s i b l e t h a t t h i s p h a s e m a y b e b y p a s s e d . H o w e v e r , f ir s t p h a s e e x p e r i m e n t s c o u l d b e d e v e l -o p e d n o w , s o t h e y s h o u l d b e c o n s i d e r e d r e a li s ti c a ll y w i t h a t t e n t i o n p a i d t o t h e i r s c i e n t if icv a l u e a n d t h e e n g i n e e r i n g c o n s t ra i n ts . T h e s o ft l a n d in g o f i n s t r u m e n t s o n t h e l u n a r s u rf a cec o u l d b e g i n i m m e d i a t e l y . I n f a c t, i t w a s a l r e a d y d o n e i n t h e m i d 1 9 6 0 's b y t h e S u r v e y o r p r o -g r a m w h i c h p r e c e d e d A p o ll o . N A S A ' s J o h n s o n S p a c e C e n t e r is c u r r e n t l y s t u d y i n g " P r o j e c tA r t e m i s " w h i c h e n v i s io n s s e n d i n g p a y l o a d s t o t h e M o o n v i a D e l t a ro c k e t s . I f D e l t a s c a n b eu s e d t h e n a l u n a r m i s s io n n e e d n o t b e m o r e e x p e n s i v e t h a n a m o d e r a t e s iz e d E a r t h o r b i ti n gs a t e l li t e . A f t e r a m o r e m o d e s t f ir s t m i s s i o n i t is e s t i m a t e d t h a t a p a y l o a d w e i g h t o f a b o u t2 50 k g a n d a v o l u m e o f 1 . 5 m d i a m e t e r x 3 m l o ng c o u l d b e a c c o m m o d a t e d . W i t h i n t h a te n v e l o p e t h e p a y l o a d w o u l d h a v e t o p r o v i d e i ts o w n p o w e r s y s t e m a n d b a t te r ie s .

T h e g r o s s w e i g h t a n d v o l u m e c a p a c i t y o f P r o j e c t A r t e m i s is s im i l a r t o t h a t o f a S m a l lE x p l o r e r ( S M E X ) p a y l o a d l a u n c h e d in t o lo w E a r t h o r b i t b y a P e g a s u s r o c k et . H o w e v e r ,th e m a s s a n d v o l u m e a v a i la b l e f o r s c ie n t if ic i n s t r u m e n t s is e f fe c ti v e ly l es s b e c a u s e o f t h en e e d t o d e a l w i t h t h e s e v er e t h e r m a l p r o b l e m s o f l u n a r n i g h t . T h e r e f o re e n e rg y s t o ra g es y s t e m s w i ll o c c u p y a s i g n if ic a n t f r a c t i o n o f t h e p a y l o a d . I n c o n t r a s t t o E a r t h o r b i t w h e r es o l a r e n e r g y i s a v a il a b le w i t h n o o r o n l y b r ie f i n t e r r u p t i o n s , a p o i n t o n t h e l u n a r s u r fa c e i sw i t h o u t s o l a r e n e r g y f o r 1 4.5 d a y s . T h i s p o s e s p r o b l e m s n o t o n l y f o r t h e o p e r a t i o n o f t h ei n s t r u m e n t b u t f or it s s u rv i v a l a t lo w t e m p e r a t u r e a s w e ll. T h e m i n i m u m t e m p e r a t u r e a tt h e e q u a t o r i s a b o u t 1 0 0K . L u n a r d a y i s m u c h le s s o f a p r o b l e m t h a n l u n a r n i g h t d e s p i t e t h eh i g h t e m p e r a t u r e o f t h e l u n a r s u r fa c e ( 38 0 K m a x i m u m ) . T h e c o ld sk y w i ll s u b t e n d a l ar g es o li d a n g le s o t h a t m o d e r a t e s h i e l d i n g f r o m t h e S u n a n d t h e h o t l u n a r s u r fa c e s h o u l d r e s u l ti n a d e s i r a b l e t h e r m a l b a l a n c e .

E n e r g y i s a c t u a l l y m u c h m o r e o f a p r o b l e m fo r p h a s e 1 e x p e r i m e n t s th e n i t w il l b e l a t e r .D u r i n g p h a s e s 2 a n d 3 t h e i n f r a s t ru c t u r e a n d s u p p o r t s y s t e m s t o b e d e v e l o p e d f o r a l u n a rb a s e w i l l c e r t a i n l y i n c l u d e c e n t r a l e n e r g y s t o r a g e a n d d i s t r i b u t i o n . T h e s o l u t i o n s t o t h et h e r m a l p r o b l e m o f p h a s e 1 a re : ( 1) i n c l u d e w i t h i n t h e p a y l o a d a l a r g e b a t t e r y a n d a s o la ra r r a y t o f u l l y c h a r g e it d u r i n g l u n a r d a y , o r ( 2 ) o b t a i n p o w e r f ro m a s m a l l n u c l e a r g e n e r a t o ri n c l u d e d in t h e p a y l o a d , a n d ( 3) f a v o r i n s t r u m e n t s w h i c h c a n o p e r a t e i n a l o w t e m p e r a t u r ee n v i r o n m e n t . T h e f ir st s o l u ti o n w o u ld p r e e m p t m u c h o f t h e m a s s a n d v o l u m e al lo w a n c e .T h e s e c o n d w o u l d a ff e ct t h e s e n s i t i v i t y o f a n i n s t r u m e n t b y r a is i n g t h e p a r t i c le b a c k g r o u n dl e ve l s. T h e t h i r d s o l u t i o n s h o u l d b e s o u g h t a s m u c h as p o s s ib l e c o n s i s t e n t w i t h g o o d s c ie n c e .T h e a n s w e r t o t h e q u e s t i o n o f w h i c h s o l u t io n w i ll b e e f f e ct iv e i s h i g h l y d e p e n d e n t o n t h ep a y l o a d . I t is q u i t e p o s si b le t h a t a n e x p e r i m e n t w o u l d h a v e t o c o m p r o m i s e b y o p e r a t i n go n l y d u r i n g l u n a r d a y a n d d e v o t i n g t h e s t o r e d e n e rg y to m a i n t a i n i n g t h e t e m p e r a t u r e a b o v et h e s u r v i v a l l i m i t d u r i n g l u n a r n i g h t .

C a n d i d a t e x - ra y i n s t r u m e n t s fo r p h a s e 1 a r e th o s e w h i c h c a n m a k e g o o d u s e o f t h ef o ll o w i n g u n i q u e l u n a r p r o p e r t i e s : t h e s t a b i l i ty o f t h e s u r f a c e , t h e s lo w , v e ry c o n s t a n t a n g u l a rv e l o c it y d u r i n g t h e 2 7 - da y s i d e re a l d a y p e r i o d , a n d t h e c o l d e n v i r o n m e n t . T h e y w o u l d ,o f c o u r s e , h a v e t o b e r e l a t i v e l y s m a l l a n d l i g h t w e i g h t. T h e t e l e s c o p e s w o u l d h a v e t o b ec o n s t r u c t e d o f m a t e r i a l s t h a t h a v e v e r y l o w o r t h e s a m e c o e ff ic ie n t o f t h e r m a l e x p a n s i o n i no r d e r t o s u r v i v e t h e r m a l c y c l in g . O n e c a n d i d a t e i n s t r u m e n t is a h i g h r e s o l u t i o n t r a n s i t x - r ayt e l e s c o p e ; o t h e r s a r e a ll s k y m o n i t o r s . W i t h o u t a d e t a i l e d e n g i n e e r i n g s t u d y o f t h e e ff e ct o ft h e l u n a r n i g h t u p o n t h e i n s t r u m e n t h a r d w a r e i t is im p o s s i b le to d i s c u ss t h e c o m p a t i b i l it yo f a n y p a r t i c u l a r e x p e r i m e n t w i t h t h e M o o n . W e c a n o n l y p o i n t o u t s o m e e x a m p l e s t h a tc o u l d m a k e g o o d u s e o f t h e u n i q u e p r o p e r t i e s o f l u n a r o b s e r v i n g . I t is li k e ly t h a t t h e x -r a y d e t e c t o r w o u l d h a v e t o b e a s o l id s t a t e d e v i c e s u c h a s a C C D i m a g e r , o r a s i li c o n , o rg e r m a n i u m s p e c t r o m e t e r w h i c h o p e r a te s a t l o w t e m p e r a t u r e . T e le s c op e s w o u l d h a v e t o b em a d e o f l ow e x p a n s i o n m a t e r i a l s s u c h a s i n v a r, z e r o d u r , o r f u s e d s i li ca .

O n e s i m p l e i n s t r u m e n t w o u l d b e a h i g h e n e rg y r e s o lu t io n h a r d x - r a y / g a m m a - r a y g e r m a -n i u m s p e c t r o m e t e r . S i n ce th i s d e v i ce n o r m a l l y o p e r a t e s a t v e r y lo w te m p e r a t u r e , t h e c o l dl u n a r n i g h t e n v i r o n m e n t w o u l d b e a d v a n ta g e o u s . T h e m a i n o b je c t iv e o f t h e s p e c t r o m e t e rw o u l d b e t o o b t a i n h i g h r e s o l u ti o n s p e c tr a o f g a m m a - r a y b u r s ts . T h i s i n f o r m a t i o n is n o tb e i n g p r o v i d e d b y t h e C o m p t o n G a m m a - R a y O b s e r v at o ry o r b y o t h e r e x p e ri m e n t s . T h es i m p l e s t d e t e c t o r s y s t e m w o u l d b e u n c o l l i m a t e d . A m o r e c o m p l e x m u l t if a c e t e d g e r m a n i u md e t e c t o r s y s t e m c o u l d b e f a b r i c a t e d t h a t p r o v i d e s s o m e s p a t i a l r e s o l u ti o n f o r a s c a n n i n gs u r v e y o f t h e g a l a c t i c p l a n e a s i t t r a n s i t s t h e z e n i t h .


4/8

(6 )64 P . Gorens te in

A s i m p l e a l l s k y m o n i t o r c o u l d b e a f m e p i n h o l e c o d e d m a s k sy s t e m o p e r a t i n g w i t h a v e ryl a r g e a rr a y o f C C D d e t e c t o r s . A l a r g e a re a C C D a rr a y i s n o r m a l l y c o n s i d e r e d t o b e e x t r e m e l yd i f f i c u l t t o d e v e l o p b e c a u s e o f t h e r e q u i r e m e n t f o r c o o l i n g . H o w e v e r , i t m a y a c t u a l l y b e m o r ef e a s ib l e i n t h e l u n a r e n v i r o n m e n t t h a n o n E a r t h . A m o r e c o m p l e x a l l s k y m o n i t o r c o n s i s ti n go f a o n e - d i m e n s i o n a l f o c u s s in g s y s t e m a n d a 1 - D c o d e d a p er t u r e k n o w n a s " L O B S T E R " i ss h o w n i n s i d e t h e l a n d e r o f P r o j e c t A r t e m i s ( F i g u r e 1 ) . " L O B S T E R " d e t e c t s a n d p o si t io n sx - r a y t r a n s i e n t s o n a l l t i m e s c a l e s ( G o r e n s t e i n , 1 9 8 7 ) . I t s p r i m e o b j e c t i v e w o u l d b e t o d e t e c tp o s s i b l e s o f t x - r a y f l a r e s f r o m T y p e I I s u p e r n o v a e a t d i s t a n c e s u p t o 1 0 0 M p c . I t w o u l d a l s op r o v i d e p r e c i s e p o s i t i o n s f o r g a m m a r a y b u r s t s o u r c e s a n d m o n i t o r t h e t e m p o r a l b e h a v i o ro f 2 5 ,0 0 0 x - r a y s o u r c e s s i m u l t a n e o u s l y .

A n o t h e r t y p e o f i n s t r u m e n t i s a t r a n s it s u r v e y t e l es c o p e , b a s e d u p o n t h e W i d e F i e l d T e le -s c o p e ( W F T ) d e s c r ib e d b y B u r r o w s , B u r g , a n d G i a c c o n i , 19 92 . T h e W F T h a s a r e s o lu t i o nt h a t i s b e t t e r t h a n 5 a r c s e c o n d s i n t h e o r y o v e r a f i e ld o f v i e w o f o n e d e g r e e d i a m e t e r a n d h a sa C C D d e t e c t o r w h i c h o p e ra t e s a t l o w t e m p e r a t u r e . T h e t r a n si t t el e s c o p e c o u l d ca rr y o u td e e p s u r v e y s a l o n g a g r e a t c i r c l e i n a n a l o g y t o t h e o p t i c a l C f A " C e n t u r y S u rv ey " ( G e l l e r a n dH u c h r a , 1 9 9 2 ) . S i x m o n t h s o f o p e r a ti o n d u r i n g e it h e r lu n a r d a y o r n i g h t p r o v id e s 4 0 k s e c o fo b s e r v i n g t i m e o n e a ch o b j e c t w i t h i n a s t ri p o f 1 8 0 d e g x 1 d e g . T h e s m o o t h , s te ax iy s c a n ss h o u l d r e s u l t i n a l a r g e n u m b e r o f e x t r e m e l y p r e c i se p o s i t io n s f o r o p t i c a l i d e n t i f i c a t i o n s . I tw i l l a l s o p r o v i d e a h i g h a n g u l a r r e s o l u t i o n i m a g e o f a s u b s t a n t i a l r e g i o n o f t h e s k y f o r t h es t u d y o f t h e e v o l u t i o n o f c l u st e r s o f g a l a x ie s .

MIR R OR V A N (S

" " " m

-

T W O 0 l id [ N S g ON A L P 0 $ 1 T ION$1[NStT V [ D E T [C T On

CO0t[D APIrR T U R %

F ig u re 1. A large area, wide f ie ld x-ray camera system f ixed on the lunar surface in the lander ofProject Artemis . The camera focuses in one dimension, as descr ibed by Gorenste in and Mauche ,1984 and Go renste in, 19 87, and has a coded aperture for angular resolut ion in th e other dimension.I t has s ince been cal led "Large-angle Observatory for Bursts , Supernovae and Transient Event Re-sear c h" (LO BS TE R) . Th i s i ns tr um e nt i s c apable o f m onitori ng tem por al var ia t ions o f m any sourc e ss imultaneously. T he m axim um angle o f re f lect ion, actual ly o nly abo ut 2 , i s great ly exaggeratedin the f igure .


5/8

X-Ray Astronomy rom T h e M o o n (6)65

F ig u re 2 . A h ard x- ray a l l sky cam era sys tem for de tec t ing gam ma-ray burs t sources.4 D e p l o y m e n t o f X - r a y O b s e r v a to r ie s o n t h e M o o n , P h a s e 2D u r i n g t h i s p h a s e l a r g e r a n d m o r e c o m p l e x ob s e r v at o ri e s w o u l d b e s e t u p a n d d e p l o y e do n t h e l u n a r s u r f a ce f ro m i n s t r u m e n t s a n d t e l e s co p e s s e n t f r o m E a r t h . T h i s is th e p h a s et h a t m o s t i n v e s t ig a t o r s c o n s i d e r in s u g g e s ti n g e x p e r i m e n t s fo r t h e l u n a r s u r fa c e b e c a u s e i tis p o s si b le t o i m a g i n e in s t r u m e n t s t h a t a r e s u b s t a n ti a l ly l a r g e r t h a n t h o s e i n E a r t h o r b i t.T h e y c o u l d a l so b e s e r v i c e d a n d a r e m o r e o r le ss p e r m a n e n t . T h e p r a c t i c a l li m i t o n t h e s i z ea n d m a s s o f E a r t h o r b i t i n g e x p e r i m e n t s i s t i le p a y l o a d h a y o f t h e S p a c e S h u t t l e , a b o u t 4 mx 4 m x 1 2 m a n d 2 0 t o n s . L a r g e r i n s t r u m e n t s c o u l d b e s e n t t o t h e M o o n p i ec e w i s e a n dcon s t ru c t ed in s i tu . Te l e scope foca l l eng ths cou ld be ve ry l ong wh ich f ac i l i t a te s h igh angu la rr e s o l u t io n m e a s u r e m e n t s a n d i n c r e a se s th e b a n d w i d t h f o r f o c us s in g . I n fa c t , t h e d e v e l o p m e n to f x - r a y a s t r o n o m y e x p e r i m e n t s fo r t h e M o o n m a y p r o c e e d d i r e c t ly to t h i s p h a s e i f t h a t i sm o r e c o m p a t i b l e w i t h p l a n s f or e s t a b li s h in g a p e r m a n e n t , m a n n e d l u n a r b a s e . I t is a s su m e dt h a t b y t h i s t i m e t h e r e w i l l b e a f r e q u e n t a n d e ff ic ie n t s y s t e m f o r l u n a r t r a n s p o r t a t i o n .T h e t r a n s p o r t a t i o n s y s t e m w o u l d d e v o t e s o m e f r a c t i o n o f i t s p a y l o a d c a p a c i t y t o s c i e n c ei n s t r u m e n t s , t h e c o m p o n e n t s o f an o b s e r v a t o ry b e i n g s en t a s sp a c e b e c o m e s av a i la b l e. I ti s a l so a s s u m e d t h a t t h e i n f r a s t r u c t u r e a n d a s t r o n a u t s u p p o r t t o d e p l o y t h e o b s e r v at o r y ,a n d s u f fi c ie n t p o w e r t o b o t h s u r v i v e a n d o p e r a t e d u r i n g l u n a r n i g h t w i ll b e p r o v i d e d . A tt h e p r e s e n t t i m e t h i s p h a s e i s f a r e n o u g h f r o m r e a l i t y f o r o u r i m a g i n a t io n s t o b e t o t a l l yu n c o n s t r a i n e d .

L u n a r b a s e d x - r a y e x p e r i m e n t s o f v a r io u s s iz e s f o r t h e M o o n h a v e b e e n s u g g e s t e d b y t h i sa u t h o r a n d o t h e r s . F i g u r e 2 s h ow s a h a r d x - r a y a ll s k y c a m e r a s y s t e m th a t d e t e c t s g a m m a -ray bu r s t sou rces and p rov ides f i ne pos i t ions dow n to l f f ~ ( Goren s t e in an d M anch e , 1984) .R e s u l t s o n s o m e 40 0 g a m m a - r a y b u r s t s o u r ce s d e t e c t e d b y t h e C o I n p t o n G R O B A T S E e x -p e r i m e n t ( F i s h m a n , et al 1992 ) show a h igh deg ree o f i so t ropy in t he i r spa t i a l d i s t r i b u t iona n d a n u m b e r - i n t e n s i t y d is t r i b u t i o n t h a t c e a se s t o r i se a t l o w i n te n s i ty . T h e s e r e s u l ts c a n n o tb e r e c o n c i l e d w i t h a g a l a c t i c p o p u l a t io n u n l e ss i t is a n e w t y p e o f o b j e c t t h a t i s f o u n d o n l yi n t h e h a l o o f o u r g a la x y .T h e m o s t p l a u s i b le e x p l a n a t i o n f o r t h e o r i g in o f g a m m a - r a y b u r s ts is t h a t t h e y a r is e f r o mt h e m e r g e r o f a d o u b l e n e u t r o n s t a r o r n e u t r o n s t a r - b l a c k h o l e c o m p a c t b i n a r y s y s t e m i ne x t e r n a l g a l a x ie s ( N a r a y a n , P a c z y n s k i , a n d P i r a n , 1 99 2, M o c h k o v i t c h , et al 1993). T he da t am o s t l a c k i n g o n g a m m a - r a y s o u rc e s a r e p r e c is e p o si ti o n s a n d h i g h r e s o lu t i o n s p e c tr o s co p y .T h e i n s t r u m e n t s h o w n i n F i g u r e 2 w o u l d f ill t h o s e g a p s. T h e l a rg e c y l i n d r i c a l c a m e r a sp r o v i d e t h e p o s i t i o n s t h r o u g h t h e c o m b i n a t i o n o f a o n e - d i m e n s i o n a l c o d e d a p e r t u r e a n d a n


6/8

(6)66 P. Goreastein

imaging modulation collimator (Gorenstein and Mauche, 1984). Uncollimated germaniumspectrometers provide the spectral and timing information. T~ s system would also monitorthe temporal variations of all sources in the 15-100 keV band. It is particularly useful fordetecting hard x-ray novae which are believed to be compact binary systems containing ablack hole.Another instrument is the the broadband Total Throughput Transient Spectrometer forGamma Sources (Hurley, 1990). It could accompany the LOBSTER instrument shown inFigure 1 and the two would act in synergy to provide a broad band high angular resolutioncapability for all x-ray/gamma ray transients.The stability of the Moon makes it optimum for interferometry in at all wavelengths.Martin, 1990 has described x-ray interferometers that achieve sub-milliarcsecond and sub-microarcsecond angular resolution.Large area, high throughput instruments are also prime candidates for a lunar observa-tory. At the 1990 Annapolis MD workshop, "Astrophysics From The Moon", Wood, 1990described the "XLA" which is a one hundred square foot array of proportional counters.The XLA collects a large number of photons from strong sources for the study of fast timestructure which is expected to emananate from neutron star and black hole compact binarysystems. At the same workshop, Gorenstein, 1990 described a high throughput focussingsystem known as the Large Area Modular Array of Reflectors (LAMAR) which can carryout a variety of scientific objectives. A Lunar based LAMAR is shown in Figure 3. Theseinstruments study specific objects and require pointing systems.

. . 1 , 1 - --- : -

Fi gu re 3. Artist's conception of a lunar-based LAMAR.


7/8

X-RayAstronomy from The M oon (6)67

5 C o n s t r u c t i o n o f L u n a r O b s e r v a t o r i e s I n S i t uT h e u l t i m a t e p h a s e o f l u n a r b a s e d x - ra y a s t r o n o m y w o u l d b e t h e e p o c h w h e n t h e i n s t r u -m e n t a t i o n i s c o n s t r u c t e d i n s i tu f r o m l u n a r m a t e ri a ls . O b v i o us ly , a n y t h i n g s a i d a b o u t t h i sp h a s e i s v e r y s p e c u l a t i v e i n c l u d i n g a g u e s s a b o u t w h e n i t i s li k e ly t o o c c u r , w h i c h is p o s s i b l yt h e m i d 2 1 s t c e n t u ry . I n s i tu c o n s t r u c t i o n is a p p li c a b le t o v e ry h ig h t h r o u g h p u t m o d u l a rf o c u s s in g s y s t e m s b e c a u s e t h e i n s t r u m e n t a t i o n c o n s is ts o f m u l t i p le co p ie s o f t h e s a m e c o m -p o n e n t .

T h e t e c h n o l o g i c a l d e v e l o p m e n t s t h a t w i ll t r a n s f o r m t h i s i d e a f ro m s c i e n c e f i ct i o n t o r e a l i t ya r e p r o g r e s s i n r o b o t i c s a n d a r ti fi c ia l i n te l li g e n c e . C o m p a r e d t o e x p e c t a t i o n s g r o w t h o ft e c h n o l o g y in t h e s e a r ea s h a s b e e n s o m e w h a t d i s a p p o i n t i n g o v e r t h e p a s t t w e n t y y e a r s.H o w e v e r d u r i n g t h e n e x t t w e n t y y e a rs t h i s s i tu a t i o n w i ll p r o b a b l y c h a n g e r a d ic a l ly . O n c et h e i r d e v e l o p m e n t a ch i e v e s a c e r t a i n t h r e s h o l d , p ro g r e s s i n r o b o t ic s a n d a r ti fi c ia l i n t e ll i g e n c ew i l l be ve r y r ap i d .T h e d e v e l o p m e n t o f an o b s e r v a t o ry w o u l d b e c a r ri e d o u t u n d e r a d i ff e re n t p a r a d i g m w i t hr e s p e c t t o t h e r o le s o f t h e s c ie n t if ic g r o u p s a n d N A S A a s c o m p a r e d t o t h e w a y s a t e l l it ee x p e r i m e n t s a r e c u r r e n t l y b u i l t. N A S A ' s r o l e w o u l d c o n s is t o n l y o f t r a n s p o r t i n g e x p e r i -m e n t e r s ' t o o l s t o t h e m o o n , p r o v i d i n g e n e rg y , s p a ce a n d c o m m u n i c a t i o n l in k s t o t h e E a r t h .

A f t e r d e p l o y m e n t , a s t r o n a u t s u p p o r t w o u l d b e r e q u i r e d o n l y o n o c c a s i o n f o r r e p a i rs . S c ie n -t if ic g r o u p s w o u l d c o n s t r u c t t h e o b s e r v a t o r y t h r o u g h t e l e -r o b o t i c o p e r a t i o n s c o n t r o l l e d f r o mE a r t h w i t h t h e a i d o f a rt if ic i a l i n t e ll i g e n c e . T h e t a s k w i ll r e s e m b l e th e c o n s t r u c t i o n o f a l a r g ee x p e r i m e n t f or t h e f l o or o f a p a r t i c l e a c c e l e ra t o r li k e F e r m i l a b ' s o r C E R N ' s m o r e t h a n t h ec o n s t r u c t i o n o f a n i n s t r u m e n t fo r E a r t h o r b it . I n c o n t ra s t t o i n s t r u m e n t s t h a t a r e h o i s te d t oE a r t h o r b i t , t h e r e i s n o i n t r in s i c w e i g h t o r v o l u m e r e s t r ic t i o n o n t h e s iz e o f t e l e sc o p e s . T h eo n l y l i m i t i s g r a v i t a t i o n a l d i s t o r t i o n i n a 1 / 6 g e n v i r o n m e n t .T h e m e c h a n i c a l p r e c i s i o n r e q u i r e d o f t h e r o b o t s is n o t b e y o n d c u r r e n t t e c h n o l o g y . T h ee n t i r e p r o c e s s c a n b e t h o r o u g h l y t e s t e d o n E a r t h . I n d e e d , t h e r e i s n o a l t e r n a t i v e t o te l e -r o b o t i c o p e r a t io n s b e c a u s e t h e a m o u n t o f a s t r o n a u t t i m e a n d l a b o r n e e d e d to a c c o m p l i s ht h e s e t a s k s b y m o r e c o n v e n t io n a l m e a n s is p r o h i b it iv e . T h e t i m e a l lo t t e d to c o n s t r u c t i n g1 00 m 2 o f x -r a y o p t i c s w o u l d b e a b o u t 1 0 y e a r s , c o m p a r a b l e t o w h a t i s r e q u i r e d t o c o n s t r u c t

a m a j o r g r o u n d - b a s e d o p t i c a l o b s e r v a to r y . B e c a u s e it is a m o d u l a r s y s t e m , i t c a n b e b u i l ti n c r e m e n t a l l y . A p o r t i o n o f t h e s y s t e m c a n b e o p e r a t i n g a n d o b t a i n i n g s c ie n t if ic d a t a w h i l ec o n s t r u c t i o n p r o c e e d s . I n s i t u c o n s t r u c t i o n o f m o d u l a r x - r a y o p t ic s b y e l e c t r o f o r m i n g f la t sf r o m L u n a r i r o n o r n i c k e l i s d i s c u s s e d b y G o r e n s t e i n , 1 99 0.6 S u m m a r y a n d C o n c l u s i o nF u t u r e l a r g e x - ra y o b s e r v a t o r ie s t o f o ll o w t h e f a c i li ti e s n o w u n d e r d e v e l o p m e n t , i .e . A X A F ,X M M , a n d S p e c t r u m - X - G a m m a , c o u l d v e r y w ell b e l o c a t e d o n t h e M o o n . I n d e e d , if a d e -c i s i o n i s m a d e t o b u i l d a l u n a r b a s e , t h e r e m a y n o t b e a n a l t e r n a t i v e p l a t f o r m w h i c h c a na c c o m m o d a t e i n s tr u m e n t s l a rg e r t h a n t h e m a x i m u m p a y lo a d c a p a c it y o f t h e S p a c e S h u t-t ie . A l u n a r p r o g r a m c o u l d b e b e g u n n o w o n a m o d e s t s c a le b y s of t la n d i n g s e l f- c o n ta i n e di n s t r u m e n t s . P r o j e c t A r t e m i s is b e i n g c o n s id e r e d b y N A S A . T r a n s i t s u r v e y te l e sc o p e s a n da l l s k y m o n i t o r s a r e a p p r o p r i a t e c a n d i d a t e s f o r i n i t i a l e x p e r i m e n t s . T h e m o s t c h a l l e n g i n gt e c h n i c a l p r o b l e m is p r o v i d i n g s u f fi c ie n t p o w e r t o s u r v i v e t h e l ow t e m p e r a t u r e o f l u n a r n i g h t .

7 R e f e r e n c e sB ur r ow s , C . J . , B u r g , R . , and G i accon i , R . , 1992 , Opt i ma l Gr az i ng I nc i dence Op t i c s and i t sAp p l i ca t i on t o W i de - i e ld I mag i ng , A p . J . 3 9 2 , 760 .F i s h m a n , G . J . , et al , 1 99 2, P a p e r p r e s e n te d o n re s u lt s f ro m B A T S E o n t h e C o m p t o n G a m m aR a y O b s e r v a t o r y , W a s h i n g t o n U n i v e r s i ty , S t . L o u i s.G e l l e r , M . J . , and H uchr a , J . P . , 1989 , M appi ng t he Un i ver s e , S c i e n c e 2 4 6 , 8 9 7 .


8/8

(0")68 P. Gor ea.qe ia

Gorenstein, P., and Mauche, C., 1984, All Sky H igh Resolution Cameras for Hard and SoftX-rays, i n H i g h E n e r g y T r a n s i e n t s i n A s t r o p h y s i c s , S . E . W o o s le y , E d. A I PConference Proceedings No. 115, Am erican Ins titu te of Physics, New York.Gorenstein, P., 1987, All Sky Supernova and Transient Explorer, i n V a r i a b i l i t y o f G a l a c t i ca n d E x t r a g a l a c t i c X - r a y S o u r c e s , A T re ve s e d ., A s so c . p e r l 'Q u a n z a m e n t a d e ll 'Astron om ia, M ilano-Bologna.Gorenstein, P., 1988, High Energy Astronom y from A Lunar Base , in F u t u r e A s t r o n o m -i c a l O b s e r v a t o r i e s o n t h e M o o n , J .O . B ur ns a n d W . W . M en de ll E d. N A S AConference P ublic at ion 2489.Gorenstein, P., 1990, H igh Throughput X-ra y Telescope on a Lu nar B ase, in A s t r o p h y s i c sf r o m th e M oo n , M.J . Mum ma and H .J . Sm i th , Eds. AIP Conference P roceed ings207, Am er ican Ins t i tu te of Physics, New York .Hurley, K., 1990, A total Throughput Transient Spectrometer for Ga mm a-Ray Sources, inH i g h E n e r g y A s t r o p h y s i c s i n t h e 2 1 s t C e n t u r y , P .C . Jo ss E d . A I P C o nfe re nc eProceedings 234 , Am er ican Ins t i tu te of Physics, N ew York .M ar t in , C. , 1990, X-r ay Interferom etry for Sub-Mill iarcsecond and Sub-Microarcsecond Imag-ing, i n H i g h E n e r g y A s t r o p h y s i c s i n t h e 2 1 s t C e n t u r y , P .C . Joss Ed. A I PConference Proceedings 211, American Institute of Physics, New York.M ochko vitch , R. , H ernanz, R. , I sen , J . , and M ar t in , X., 1993, Gamma-Ray Bursts as Colli-mated Jets f rom Neutron Star/Blac k H ole Mergers, N a t u r e 3 6 1, 23 6 .Narayan , R. , Paczynski , B. , and Piran , T. , 1992, Gamma Ray Bursts as the Death Throesof Massive Binary Stars, A p . J . L e t t . 3 9 5 , L 88 .Wood, K.S., 1990, An X-r ay Large Arra y fo r Astrophysics at a Luna r Base i n A s t r o p h y s i c sf r om th e M oo n , M.J . Mum ma and H .J . Smi th , Eds. AIP Conference P roceed ings207, Am er ican Ins t i tu te of Physics , New York .

Documents

X-ray Astronomy From Moon