PowerStar_New Energy From Space Concept

8/12/2019 PowerStar_New Energy From Space Concept

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POWER STARTM: A NEW APPROACH TO SPACE SOLAR POWER

David C. Hyland1

Space Solar Power refers to the concept of a space system that collects solar

power via photovoltaics and transmits it to ground collection stations usingvisible or microwave radiation. Previous system designs developed over the past

several decades entail gigantic structures with many moving parts and require

on-orbit infrastructure and in-space construction. Here we combine very new

and very old technologies to form a design that has no moving parts, requires noin-space construction and can be packaged in many existing launch vehicle

payload fairings.

INTRODUCTIONt has been remarked that the prosperity of a civili!ation is in proportion with its skill in

harnessing sources of useful energy. "hether or not the use of fossil fuels will be limited because

of environmental toxicity, the advance of civili!ation will require substantially more powerful

sources of energy than are presently available. #side from the $arth%s supply of radioisotopes, the

abundant supply of fusion-based energy produced by the sun remains to be efficiently harvested.

&he collection of solar radiation in space could potentially be an order-of-magnitude more

effective than ground-based technology because in space, solar insolation is continuous and un-

attenuated by the atmosphere. &hese potential advantages have motivated efforts to design spacesolar power systems since the early '()*s. +eference gives a timely and thorough review of

previously proposed designs.

# solar power system consists of a space segment that collects solar energy, converts theenergy into radiation typically in a wavelength band to which the atmosphere is mostly

transparent, then transmits the radiation to a ground facility that converts the radiation into

electrical power. Since the ground-based power collection technology is well developed, we

concentrate here on the space segment, called the Solar Power Satellite(s) (SPS). /oreover, the

method of solar energy collection assumed here is photovoltaic, and the power transmission to theground is chosen to be microwave radiation with wavelengths near '*cm.

"ithin the above restrictions, there are a wide variety of SPS design concepts. #ll previous

approaches for SPS in this category involve very large, articulated structures, that must be

assembled in most cases robotically in space and require many launches of the component parts

into orbit typically geostationary orbit',. &hese characteristics necessitate very large initial

investments and technology developments to field an operational system. #n example for

comparison that is fairly representative of previous concepts is the 0aval +esearch 1ab, 2/"SSP design'. 3igure ' shows a summary of this concept. "e choose this for later comparisonbecause it resulted from a quantitatively complete engineering design as well as a financial

analysis. #s can be seen from the 3igure, this involves two '4,5** square meter solar arrays and a

'Professor of #erospace $ngineering, #erospace $ngineering 6epartment, &exas #7/ 8niversity, /8 5'9',

:ollage Station &exas ;;495.

'

Pre-Print ndSPACE C!n"eren#e-$1% 11


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one kilometer diameter microwave antenna. +otating relay mirrors direct energy into the solar

arrays, while the remainder of the structure is nadir pointing. &he study assumed an end-to-end

efficiency of ten percent, and sought a 3irst +evenue 8nit design that could transmit 2 /egawatts

of power. &ypically, this type of design cannot be launched by a single vehicle, but must be

assembled on-orbit by either human or robotic agents.

&i'(re 1. S())ary !" t*e #*ara#teri+ti#+ "! t*e NRL ,MW &ir+t Reven(e Unit de+i'n

# significant improvement over previous efforts is the SPS-#1PH# Solar Power Satellite via

#rbitrarily 1arge Phased #rray. &he main structure of SPS-#1PH# does not have to be slewedto follow the sun direction. &he system is highly modular and good use is made of retro-directive

phased array technology. # sandwich design combines the solar arrays with the microwave

transmitters such that high voltage, centrali!ed power distribution is avoided. apton, paper, fabric, etc.. &he printed sheets are


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produced in mass quantities. &he old technology is that of the Echo satellites. 1arge, thin sheets

are assembled into a spherical balloon. 3or launch, the sphere is compactly packaged in a small

container that fits into the launch vehicle payload faring.


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&i'(re . Ill(+trati!n !" t*e 0a+i# #!n#et !" t*e S!lar-Mi#r!/ave &a0ri#TM.

&i'(re 2. C!)!+iti!n !" t*e i#t!rian Or'ani# S!lar Cell C!n+!rti().

n comparison, /& solar cells9use an ink-=et process to print cells on paper. $fficiency for

most designs is presently 'A to A. However, 9A is a near-term goal and it is quite reasonable to

Substrate layer

&ransmitter

Solar cell Solar cell

:onductive coatingground

Power

connectors

Printed SolarArrays

Printed PatchAntennae

Solar-Microwave

Fabric

TheNew

9


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anticipate 2 to '*A in the future. #s a baseline we can say that A efficiency with rapid

fabrication ability is the current capability.

Printed Mi#r!/ave Pat#* Antenna+

#ntennas can be ink=et printed onto many flexible materials, even including cotton-polyester

/ultiple printing layers can be used to increase efficiency. #s illustrated in 3igure 9, a

microwave patch antenna consists of a metal BpatchC mounted on a grounded, dielectric substrate.

&i'(re %. T*e 0a+i# #!n"i'(rati!n !" a )i#r!/ave at#* antenna.

&he dielectric provides a resonant cavity to amplify the transmitted signal. Since L is the

resonant dimension, we must haveD

L = '

"hereis the operating wavelength. W is usually chosen as'.2L to get higher bandwidth, but

we shall assume W L = = here. &he practical printing resolution is '2 microns and is quitesufficient to satisfy $quation ' to sufficient accuracy. &able ' shows a survey of performance

statistics for existing patch antennas2. $fficiencies of up to ;(A are presently attainable.

Ta0le 1. Per"!r)an#e #*ara#teri+ti#+ !" vari!(+ rinted at#* antenna+.

Substrate Height

in mm

BW = Banwith

Et#*ed at#* !n

&R%, +(0+trate

In34et Pat#*

5t/! layer+ !"

in36 'l(ed !n&R%, +(0+trate

In34et Pat#*

5!ne layer !"

in36 !n "elt

In34et Pat#*

5t/! layer+ !"

in36 !n "elt

Pat#* +i7e5))6 5;.9 x 4.' 5;.9 x 4.' 9;.; x 5).( 9;.; x 5).(

S(0+trate *ei'*t '.) '.) '.( '.(

&re8(en#y

59H76

.5;4 .94* .9*2 .2*2

SII 5d6 -'5.5( -'9.4( -'*.*2 -(.(2

1$ d W

5MH76

.2 9.2 ';.2 0E#

Dire#tivity 5di6 ;.5( ;.22 4.54 4.;9ain 5di6 ).5; 2.*( 9.* 2.(4

E""i#ien#y 56 ;( 2; 5; 25

2


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S(0+trate Material

#lthough solar cells and patch antennas have been printed on a wide variety of materials, we

have focused on two materials that have the closest connection to $cho satellite technology. &he

foremost, and the one with the most heritage, is /ylar, a polyester film made from resin

Polyethylene &erephthalate P$&. &his material retains its full mechanical capabilities at

temperatures ranging from -;* : to '2* *:. ts melting point is 29 *:. ts volumetric density is

'5(* kgEm5. #n attractive alternative is >apton, an organic polymeric material that, effectively

does not melt or burn and functions well at temperatures ranging from -)( : to 9** *:. #t '9*kgEm5, its volumetric density is slightly larger that that of /ylar. :ontinuing studies will explore

print-compatible materials with adequate tear resistance and minimum density.

THE OLD: ECHO SATELLITE TECHNOLO9;

Sheets of the multi-functional fabric described in the previous section are cut into gores

sectors of a sphere and the several gores are assembled to form a spherical balloon onceinflated. ?eyond this point, the Power Star&/system makes full use of $cho satellite technology.

Pro=ect $cho)was the first passive communications satellite experiment. $ach of the two

satellites were designed as a passive reflector of microwave signal, and each was a metali!ed P$&

film balloon satellite. Soon after the launch vehicle failure of $cho ' in '()*, the 5*.2m diameter$cho '# was successfully placed in orbit by a &hor-6elta vehicle in the same year. t reentered$arthFs atmosphere, burning up on /ay 9, '()4. 3ollowing successful operation of $cho'#, on Ganuary 2, '()9, the 9'.'m diameter $cho was successfully deployed on orbit. $cho

reentered $arthFs atmosphere and burned up on Gune ;, '()(.

&i'(re ,. ari!(+ a+e#t+ !" E#*! +atellite te#*n!l!'y: 5a6 E#*! 1A +t!/a'e #ani+ter< 506 Cani+ter

#l!+ed< 5#6 &!lded +(0-+#ale r!t!tye< 5d6 In"lated +(0-+#ale r!t!tye< 5e6 E#*! d(rin' in"lati!n

te+tin'.

b

a

c d e

)


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3igure 2 shows various aspects of the $cho technology. &he satellites were made of '.; m

thick biaxially oriented P$& /ylar film, coated with a vapor deposited *.m layer of

aluminum to provide +3 reflectivity. Special folding techniques were devised to minimi!e thestowed volume see 3igure 2c and 2d. &his is an important feature since finite material

strength sets a lower limit to radii of curvature in bending so that any fold of a thin sheet

introduces voids that reduce packing efficiency. &he folded balloons for both spacecraft could be

stowed for launch in small spherical canisters See 3igure 2a and 2b. n particular, the 5*.2m

diameter inflated sphere of $cho '# was stowed in a *.;'m seamed spherical canister.


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S;STEM COORDINATION AND OPERATION

n this section we describe how the old and new elements of the Power Star&/system are

combined and coordinated to work together once the system is launched and deployed. 3igure ;

sketches the overall composition and method of operation.

&i'(re @. Overall P!/er StarTM!erati!n !n#e del!yed

&he exterior surface of the sphere is printed with solar cells and microwave transmitters3igure ;, lower right, where the placement of transmitters is somewhat randomi!ed to prevent

grating lobes see below. &here are power connectors between each transmitter and a subset of

the immediately ad=oining solar cells 3igure ;, top, center, red lines in the cross-section.

?eneath the exterior coating is the substrate layer gray band in the 3igure with an embedded

copper grid orange lines in the 3igure for electrical ground and rigidification. &he interior

surface of the substrate is coated solely with transceivers transmitterEreceivers, blue layer on the

bottom of the cross-section. &here are power connections through the thickness of the skin from

the internal transceivers and the immediately proximate external transmitters. Power connections

in the skin are very short a few centimeters and the power collection and transmission devices

are on a microscopic scale, such that we anticipate an eventual halving of the $cho skin thickness

to ) m.

Power is received at several locations on the ground by arrays of rectifying antennas

rectennas. #t the location of each rectenna, a low-power microwave beacon is placed. #t each

patch antenna a local microprocessor records the beacon radiation that the patch receivesI records

the radiation wave formI amplifies the waveform and emits it back in re!erse time or,equivalently with con=ugate phase. #s will be elaborated below, this completely decentrali!ed

transmitter control scheme produces transmitted radiation that, given the si!e and shape of the

Power Star, optimally matches desired power distribution on the ground. 0ote that the system can

absorb power from the sun and transmit power in any other direction without the need for slewing

or mechanical motions. &he system works with electrons and photons and has no mo!ing parts"

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n the next two subheadings, we discuss further details of the power transmission control, and

the specific processes for transferring collected solar power within and across the sphere.

P!/er ea) C!ntr!l

t is a rigorous result in electromagnetic propagation that the beacon-based control that

coordinates the numerous transmitters as described above optimally approximates, in a mean-

square sense, the desired power distribution on the ground. &his power delivery scheme is a

generali!ation of retro-directive beam technology and has been applied to many areas. 3orexample +eference ( discussed its application to acoustics for medical technology.

ndeed, the ground distribution actually produced is the spatial convolution of the desired

distribution as set by some pattern of beacons with the Power Star aperture point#sprea

$unction PS3, which is essentially the tightest, most concentrated beam that the total

configuration of transmitters can produce. &his PS3 function depends on the si!e, shape and

distribution of the transmitters on the external surface of the power star. &hus, if the beacons can

be approximated by point sources, then the ground distribution consists of several PS3 BspotsC,

each centered at one of the beacon locations.

+ecording the beacon signals, then amplifying them and playing them back in reverse time

occur concurrently. &o simplify the explanation, we illustrate these steps separately. 3irst,

consider the beacon propagation, illustrated in 3igure 4 by means of a simple two-dimensional

wave propagation simulator. Here there are three approximately point sources that is, a single

pixel in extent unevenly distributed along the vertical line to the left, representing the ground

plane. &he circular region to the right represents the Power Star sphere. n part a, radiation

commences with a widening interference pattern. &hen part b, each pixel on the circumference

of the circle records the time signal of the field amplitude measured at its location. 3igure (

shows what happens when each pixel representing a single patch transmitter transmits the signal

it recorded in reverse time. n part a, note the converging wave fronts of the initial field

amplitude. n part b


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same remark pertains to ,S B , and ,S B% . &he sector that a particular transmitter and itsad=acent solar cells are located is indicated by their output signals. Jiven this information, the

power supply

a

b

'*


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&i'(re . Initial Pr!a'ati!n !" 0ea#!n radiati!n. 5a6 Radiati!n #!))en#e+B 506 Cir#(lar *a+ed

array re#!rd+ 0ea#!n in"!r)ati!n.

a

''


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b

&i'(re . P*a+ed array r!a'ate+ a)li"ied 0ea#!n in rever+e ti)e. 5a6 Tran+)i++i!n

#!))en#e+B 506 T*ree #!n#entrated +!t+B #entered at t*e 0ea#!n+ aear !n t*e 'r!(nd lane.

&i'(re 1$. 9e!)etry !" t*e !/er di+tri0(ti!n +y+te). An'le den!te+ t*e an'le 0et/een t*e

dire#ti!n+ t! t*e +(n and a 0ea#!n.

algorithm is indicated in &able . 0ote that no processing is needed for this algorithm. n

essence, the transmitters that need to be active because they receive a beacon signal arepowered by either the proximate solar cells or by the proximate internal transceivers,

whichever is actually producing power. 0o beacon signal means the transmitter is blocked.

$ach transmitting antenna draws power from the solar cells in its immediate vicinity within a

few centimeters, or through the thickness of the skin. $ach transmitter receives =ust a few

"atts, so there are no high voltages or large wires. &his locali!ed architecture means

robustnessagainst partial damage.

Ta0le. P!/er tran+"er al'!rit*)

Se#t!r P!/er Tran+"er

( ),S B $xternal surface transmitter draws power from the ad=acent solar cells

( ),S B%

Solar cells transfer power through the skin to their immediately proximateinternal surface transceivers. &he internal transceivers emit power beams

through the center of the sphere to fall on the internal transceivers in sector

( ),S B% .

'


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( ),S B% nternal transceivers transfer received power through the skin to theirimmediately proximate external surface transmitters

( ),S B%% 0o action taken.

PER&ORMANCE CHARACTERIATION

Having described the basic design of the satellite, we next consider the analysis of its

performance characteristics, vi!. power transmitted to the ground, beam width, etc., under

separate subheadings.

P!/er Tran+)itted

&o begin, a geometrically regular arrangement of the patch antennas on the exterior surface

would produce an aperture PS3 having, besides a main concentrated spot the central lobe,

several regularly spaced offset spots thegrating lobes. &his tends to have a disastrous effect onthe accuracy with which a desired power distribution may be approximated, since the actually

produced distribution is the convolution of the desired distribution and the PS3. However, a slight

randomi!ation of the transmitter antenna placements that retains the same average number of

antennas per unit area suffices to disburse the grating lobes so that the central lobe alone remains

the only power concentration in the emitted radiation. n this case, the main lobe is proportionalto the characteristic function the 3ourier transform of the probability density function of patch

antenna locations. 3or example, if the locations of all patch antennas are statistically independent

Jaussian distributions, then the angular distribution of radiated power, ( )P produced by theentire phased array isD

( )

' exp

% %& &sPs

v v

where is the unit vector from the phased array to a point of observation, and whereD

operating wavelengthballoon diameter

average distance between the centers

of neighboring patch antennas

%&

s

L W

===

= =

5.a-d

&he last equation repeats the assumption made in the remarks under 3igure 9 that the patch

antennas are roughly squares that are half a wavelength on a side. 0ote that the maximum value

of s has to be unityI in which case, patch antennas cover the entire exterior surface of

the balloon, leaving no room for the solar arrays. &hus the phased array must be sparse,

and of necessity s > .

$quation is a reasonable approximation for many different antenna position probability

distributions. &hen accordingly, the total power transmitted to the ground from the central lobe isD

'5


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( )

&otal power input from the solar arrays

and internal transceivers

t sa

sa

P P Ps

P

=

=

v

9.a,b

0ote that the factor appropriately reflects the sparse aperture theorem.

3or a given s' the fraction of the frontal area occupied by the solar arrays is ( )

' s ,thereforeD

' 9

aggregate efficiency of solar arrays

and patch antennas

Solar insolation '5);"

sa % e$$ s

e$$

S

P & (s

( m

= =

=

2.a-c

&he aggregate efficiency, e$$ is a function of both the solar array and transmitter

efficiencies and the beacon-sun angle, . #ssuming roughly the same efficiencies for theexterior and interior transmitters, we haveD

( )

[ )

'

' ' cos

*,

Solar array efficiency

&ransmitter efficiency

e$$ ) S ) )

S

)

= + +

==

).a-d

:ombining $quations 9-), we have in summaryD

( )

'

'

9

' ' cos

t % e$$ s

e$$ ) S ) )

P & (

s s

= = + +

;.a,b

3rom this relation, it is clear that the optimal average spacing of the transmitters is

optimal

s = . &his means that the surface area of the balloon is equally divided between

the solar cells and transmitters. #lso, the total power to the ground becomesD

{ }

( )

max

'

'

9 9

' ' cos

t % e$$ s

e$$ ) S ) )

P & (

= = + +

4.a,b

0ote that the factor'9 arises from the sparseness of the array.

3rom $quation 4, we see that if the satellite is at geostationary altitude with the ground

station beneath, the power transmitted rises to a maximum at midnight *'4* and declines

'9


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to a minimum at noon * . &his conforms to the daily electrical power usage profilefor street lighting of typical municipalities.

&o see what $quation 4 predicts for power transmitted to the ground given current device

capabilities, we let AS = and, consulting &able ', set ;(A) = . 3igure '' shows theranges of transmitted power over all sun-beacon angles for S equal to A current

&i'(re 11. P!/er tran+)itted a+ a "(n#ti!n !" 0all!!n dia)eter "!r vari!(+ val(e+ !" t*e +!lar #ell

e""i#ien#y.

capability, and for 2A, '*A, and 2A , representing different stages of development, all

as functions of the balloon diameter. "e see that even with the presently lowly

capabilities of printed solar cells, a one kilometer balloon can deliver from 5 to 9/egawatts K comparable to the design of 3igure '. /oreover, efficiency of 9A is

expected soon, in which case, a ' km system gives ) to '* /". Printed cell technology

is still in an early stage of development wherein cheap manufacturability is paramountover cell efficiency. ?ut one can expect a progression toward the efficiency levels of

presently Bone-offC laboratory devices, where 2A is typical. n this case the 'km balloon

might be capable of 5* to 2*/". :ompare this with the system of +eference '.

Mini)() ea) Widt* 5Re#tenna Si7e6

'2


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:ommon to all SPS concepts is the minimum beam width on the ground expressed, byuse of +ayleigh%s angular resolution formula, as a function of wavelength, distance and

transmitting aperture diameter. n the present case this is modified slightly because the

aperture is sparse, not filled. n accordance with the sparse aperture theorem see also$quation , the width of the central beam in the system PS3 is diminished by the factor

of . &herefore the minimum width of the power concentration BspotC that can be put

on the ground, * , is given byD

( )'.'

transmit distance

-52,;4) km for J$


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&i'(re 1. Re#tenna dia)eter 5)ini)() +!t +i7e6 a+ a "(n#ti!n !" 0all!!n dia)eter "!r vari!(+

val(e+ !" t*e !eratin' /avelen't*.

Pa#3a'in' "!r La(n#*

&he Power Star is to be folded compactly into a canister that can be accommodated in existing

launch vehicle payload fairings. "e assume here that the stowed configuration is a sphere ofdiameter S& . f wdenotes the thickness of the skin, the total volume occupied by =ust the skin of

the deployed balloon is

%& w . &he smallest stowed diameter is obtained when this volume is

equal to5 )S

& . However as remarked above, a thin membrane folded many times has an

external volume much in excess of =ust the volume of the material of which it is composed. &hus

we characteri!e the folding system by the packing e$$icienc,' 'e$$p , so that5 )S % e$$ & & wp = ,

orD

( )

( )

' 5)

Skin thickness

Packing efficiency '

S e$$ %

e$$

& p w&

w

p

=

=

=

'*.a-c

&he packing efficiency is difficult to calculate and depends upon the precise geometry of the

folds, the skin thickness, and the material properties. However, we shall take the $cho satellite

';


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characteristics as our guide. &able lists the $cho dimensions and the values of packing

efficiency. &hese are quite close, so in the following we use simply 5.*e$$p .

Ta0le . Di)en+i!n+ and a#3in' e""i#ien#ie+ "!r t*e E#*! +atellite+.

Satellite ( ), mAD ( ), mSD ( ), m/ e$$

$cho ' 5*.2 *.;' *.5L 5.')

$cho 9'.' '.*9 5).*LL 5.*4

Lncludes /ylar, metallic coating and sublimating power coating.

LLncludes /ylar, metallic coating and average thickness due to pillows

?ased on this value, 3igure '5, shows the launch canister diameter as a function of the inflated

balloon diameter. $vidently, a one kilometer Power Star, the same si!e as the 3+S design

microwave antenna of 3igure ', can be accommodated in several existing heavy-lift launch

vehicles. n particularD the 6elta Heavy 2.' m diameter fairing, the #riane 2 2.9m and the

/inataur @ 2.;' m.

Aer!dyna)i# Dra' and Or0it Li"eti)e

#s is the case with the $cho satellites, Power Star would have a very low ballistic coefficient

so that aerodynamic effects can set limits on orbit altitude such that orbit lifetime is more than a

few decades. &o analy!e this situation, we assume an initially circular orbit. 3or lifetimes greaterthan '* years, the lifetime as a function of the initial orbit radius of a circular orbit is nearly

independent of the launch time relative to the solar maxima or minima see +eference '*. &hus

the orbit lifetime can be estimated using the average atmospheric density as a function of altitude,

as given by the 8.S. Standard #tmosphere. 3urther we may assume small drag forces such that

the decaying orbit takes the form of a tight spiral with a slowly varying BinstantaneousC orbit

radius.

'4


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&i'(re 12. St!/ed dia)eter a+ a "(n#ti!n !" t*e in"lated 0all!!n dia)eter.

&hen we have approximately that the orbit life time, $t , isD

( )

( )

nitial orbit radius

+adius of the $arth

Jravitational constant -J/ of the earth

#tmospheric density at orbit radius

'

E

$

i

E

%tm

%tm

ia

-t

a

a

-

a a

aa

=

=

=

=

=

''.a-e

where is the ballistic coefficientD

9

Power star mass

3rontal area@olumetric density of the skin

&

% skin

%

skin

.

/ %

. & w

% &

=

= =

= ==

'.a-c

&hus, for the Power Star and assuming free molecular flow &/ , we getD

skinw = '5

'(


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&i'(re 1%. Or0it li"eti)e a+ a "(n#ti!n !" initial !r0it altit(de.

which is =ust twice the areal density of the BskinC and independent of diameter. &o get a

conservative estimate of orbit life, we assume the smallest practicable thickness, *.**)w mm= .&hen we haveD

( ) ( ) '5(* *.**) *.*'))4skinw mm = = = '9

"ith the above assumptions, $quations '' give a conservative estimate of the orbit lifetime

as a function of initial altitude as shown in 3igure '9. &he results indicate that a long lifetime is

ensured by placing the Power Star at roughly ***km or above. &hus a /$< orbit or above issuitable for a long-term system. 0ote that the de-orbit time function is independent of the

diameter of the system and directly proportional to , which is approximately twice the arealdensity of the skin. Hence results for larger skin thicknesses can be obtained from the 3igure by

multiplying the ordinate by the ratio of new to old thicknesses.

CONCLUSION

n this paper we have proposed a novel design concept for a Space Solar Power Satellite K the

Power Star&/. "ith heritage dating back to Pro=ect $cho, this system is an inflatable balloon

made of a thin, flexible skin whereupon solar cells, and microwave patch antennas are printed via

the most modern mass production technology. Power Star&/operates with no moving parts and

with no slewing or other mechanical motion. #t least up to 'km diameter, it requires no on-orbitmanufacturing or construction. #dvanced adaptive phased array technique and insights from

time-reversed acoustics, combined with low-amplitude beacons yield a beam forming control

algorithm that is entirely local to each patch antenna. &he operation of the phased array is

decentrali!ed and adaptive so that even if severely damaged, the system can retain some level of

useful performance. Power is regulated within the balloon such that transmission through the skin

*


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occurs within a few centimeters at most, obviating the need for a centrali!ed, high voltage power

distribution system. &he power system permits solar power to be gathered from any angle and

power to be beamed in any direction s without slewing or structural deformation.

Preliminary performance calculations show that even with the low efficiencies of presently

available printed solar cells, a ' km Power Star can produce enough power for a 3irst +evenue

System. 8sing $cho technology, a ' km Power Star can be packed for launch in several existing

heavy-lift vehicles. 3inally, despite its low ballistic coefficient, the orbit lifetime is of the order of

a century if the initial circular orbit altitude is greater than approximately ***km.

NOTATION

% 3rontal area of the Power Star

ia nitial orbit radius

&/ #erodynamic drag coefficient

%& ?alloon diameter

S& 6iameter of launch canister

L' W +esonant length, and width, respectively of the microwave patch antennas. /ass of the Power Star

e$$p Packing efficiency

saP &otal power input from the solar arrays and internal transceivers

tP &otal power transmitted from the central lobe

S( Solar insolation at ' #8

E- +adius of the earth

s #verage distance between the centers of neighboring patch antennas

$t


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skin @olumetric density of the skin

#ngle between the sun and beacon directions

RE&ERENCES

'#.:. :harania, G.+.

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PowerStar_New Energy From Space Concept