J . F. WISE

Solid-State conversion concepts for space needs

Various solid-state energy conversion concepts under development hy the U.S, Air Force are discussed from the standpoint of present capahilities to satisfy aerospace vehicle electric-power needs. Performance possihilities based on completely developed concepts are estimated. Energy sources considered are solar, nuclear chemical, and acoustic, with emphasis on solar and nuclear

Research and development are being accomplished today in the fields of solid-state energy conversion because these materials and conversion mechanisms are most nearly ideal for unattended operation in space. They are relatively static (with no moving parts), nonvolatile except at high temperatures, and reasonably resistant to the space environment; and they generally have possibilities of long life. The long-range objective of the applied research programs is to acquire the technology for obtaining reliable, highly efficient, long-lived, lightweight, low-cost energy conversion systems for aerospace vehicles. The lifetime requirements are for essentially unat­tended operation for 2 years by 1965 and for 5 to 10 years by 1970. Generally, high watt-per-pound performance, reliability, and long life are the primary objectives; efficiency and cost are of lesser impor­tance.

PHOTOELECTRICS Photoelectric conversion may be divided into three distinct classes: single-crystal cell research, poly-crystalline cell research and different device concepts as photocmisssion and nuclear photon conversion.

The area of single-crystal photovoltaic cells is quite well developed; these cells have been exten­sively used in aerospace vehicle systems. Their major limitations are lowering of efficiency with tempera­ture, radiation damage, excessive weight, and high initial cost. To reduce the temperature problem and also utilize the solar spectrum more efficiently, research is being undertaken on higher band-gap materials such as gallium arsenide^ and aluminum antimonide.- The results and anticipated performance in these areas are summarized in the upper portion of Table I.

Dendritic silicon cells are being developed to obtain better crystalline structure and lower cost.'^

E s s e n t i a l l y fu l l t e x t of C P 62-1158, p r e s e n t e d at t h e A I E E S u m ­m e r G e n e r a l M e e t i n g , D e n v e r , Co lo . , J u n e 17-22, 1962, at a s e s s i o n s p o n s o r e d b y t h e A I E E A e r o S p a c e T r a n s p o r t a t i o n C o m ­m i t t e e . J. F. W i s e is w i t h t h e F l i g h t A c c e s s o r i e s L a b o r a t o r y , A e r o n a u t i ­c a l S y s t e m s D i v i s i o n , W r i g h t - P a t t e r s o n A i r F o r c e B a s e , O h i o .

The lower cost is achieved by elimination of the laborious crystal-slicing and polishing procedures. Cells up to 12 inches long with 10 per cent efficiency have been obtained to date.

Thin-film polycrystalline cells are being developed to obtain large reductions in the cost and weight of solar cell arrays. An important feature of these cells is that they will probably be more radiation resistant. The major efforts in the film-cell field are in the formation of film cells from the cadmium compounds of CdS,^-> CdSe, and CdTe.« A brief summation of the state of the art is presented in the lower portion of Table I.

Some of the major problems involved with these

Table I · Performance of higher band-gap materials and thin-film polycrystalline cells

Cell Parameter Present Future

Reasonable Possibility

10 to 12. .

Silicon

Dendritic silicon

Gallium arsenide {

Aluminum Antimonide

Cadmium sulfide

Cadmium telluride

Cadmium selenide

Higher Band-Gap Materials

efficiency, per cent temperature effect, per cent

per degree C - 0 . 4 8 . . . radiation resistance poor cost, dollars per watt 400

cost, dollars per watt

efficiency temperature effect, per cent

per degree C —0.25. . . radiation resistance fair cost, dollars per watt

efficiency, per cent 1.0 to 2.0. temperature effect, per cent

per degree C radiation resistance cost, dollars per watt, average

Tfiin-Film Polycrystalline Cells

efficiency, per cent small area 5.0 large area 1.0

temperature effect, per cent per degree C - 0 . 4 5 . . .

radiation resistance good cost, dollars per watt

efficiency, per cent 6.0 temperature effect, per cent per

degree C radiation resistance cost, dollars per watt

no data

15

- 0 . 4 fair 200 50

15 to 20

- 0 . 2 5 good 400

20 to 40

- 0 . 2 good 200

5.0

-0 .40 good 10 to 20 80

0.2 good 20 to 40

864 ELECTRICAL ENGINEERING NOVEMBER 1962

Table II · Performance of photoemissive solar energy converters

Performance

Converter type

Perforated sfieet

Conventional

Reasonable Parameter Present Possibility

efficiency, per cent 0.01 0.08 to 0.1 watts per pound 30 reliability good good

very good radiation resistance very good. good very good

micrometeorite damage resistance poor poor

10 cost, dollars per watt poor 10

efficiency, per cent e.5 4.0 watts per pound 30 reliability good good

very good radiation resistance. very good . good very good

micrometeorite damage resistance none none

cost, dollars per watt 20

films concern their instability, i.e., they deteriorate when exposed to a moist atmosphere; the inhomo-geneity of the films; the high series resistance, leak­age through the grain boundaries; nonadherence of the films to the substrate; and low efficiency.

Encapsulation is being tried as a method of over­coming the deterioration but little success has been achieved to date. Storage in a dry atmosphere or a vacuum has been a partial soludon to this problem."'

Grids of conductive coatings of silver, indium"* and stannic oxide^ are being used on CdS cells to reduce the series resistance.

The leakage through the grain boundaries is being attacked in two ways: by formation of larger crystal­lites using the Van Cakenberghe^ recrystallization process; and by attempting to obtain ultrahigh purity CdS and thus eliminate the sodium and oxygen impurities. It has been found that sodium is present in all sources of cadmium sulfide and this sodium very possibly provides acceptor centers in the CdS bulk."* The exact effect of this has not been deter­mined to date; however, neither has the effect of the oxygen been determined.

Improvement in efficiency, of course, will be the net result of the experimentation thus far discussed.

The exploratory portions of photoelectric energy conversion are principally in the areas of photo-emission, photogalvanic or photolytic conversion, and nuclear photon udlization.

Photoemissive solar energy conversion is being invesdgated in two programs: the use of a single perforated sheet of material with the emitter on one side and the collector on the other (Gold converter)^ and the "conventional" where the electrodes face each o t h e r . I n the Gold converter the electrons are emitted when the solar energy impinges on the emitter. A certain percentage of these electrons passes through the perforations in the converter and are collected on the back side. This conversion con­cept is capable of only about 0.1 per cent efficiency, but it is very light in weight and low in cost. This concept is only useful in space since it relies heavily on the vacuum environment.

The second photoemissive concept being studied involves more or less conventional construcdon in that the emitter and collector face each other in a glass envelope. There may be a small amount of gaseous cesiura present to reduce space charge. The orientation of the electrodes in this configuration permits a much more direct path for the electrons to pass from the cathode to the anode, and conse-quendy a much higher efficiency is possible. The present and future possibilities in the photoemissive area are summarized in Table II.

The table shows that the chief areas of potential for these converters are superior radiation resistance and lower weight and cost. Problems exist, however, in the fabrication of optimum surfaces. This is especially true when the surfaces of the cathode and anode are different, as is required for optimum efficiency.

Photolytic energy conversion is being investigated in the iron thionine s y s t e m . T o date the efficiency of the process has been quite low. Possibilities exist, however, for increasing efficiency through the use of sensitizers. The program was initiated to determine the feasibility of photogalvanic energy conversion systems. The reactions involved in this system are indicated as follows:

Thionine dye (normal state) + light acti­vated dye

Activated dye + ferrous ion - > ferric ion -\-reduced dye

Reduced dye at electrode —> electron + dye (normal state)

Ferric ion (at electrode) + electron —> ferrous ion

The possible potentials of a system of this type in­clude lower cost, ease of fabrication and possible self-contained energy storage. The system does not look promising at present but might if certain addi-dves should be developed which would increase the efficiency by several orders of magnitude above that obtainable today.

The three most promising methods for converdng nuclear photon energy to electric energy are de­scribed as follows: ( 1 ) The particle is converted di­rectly to electric energy by collecting the charged particles (either alphas or betas). ( 2 ) The particles are absorbed in a p-n junction semiconductor, form­ing hole-electron pairs which are separated by the junction. ( 3 ) The emitted pardcles are allowed to strike a phosphor or scintillator material for the pur­pose of converting the radiation to lower energy photons. The radiation is then converted to electric energy when the photons strike a semiconductor energy converter such as a silicon solar cell.

The first method, though it will provide electric energy, is not very useful since currents measured in micromicroamperes at about 1 million volts are the output of this type of device. It is extremely difficult

NOVEMBER 1962 ELECTRICAL ENGINEERING 865

to utilize electric power efficiently under these con- ter program has resulted in a laboratory thermoelec-ditions. trie generator with the performance parameters pre-

The second method (particle to p-n junction) will sented in Table III. yield useful power at useful voltages since the volt- This test was conducted in an evacuated chamber age is determined by the band gap of the semicon- at ΙΟ""* mm Hg with liquid N^-cooled walls so that ductor. The disadvantage of this method is that the space radiation conditions were approximated. As proper combination of isotope or source of betas and noted in the data, the results were not up to expec-the p-n junction semiconductor converter is not tations. Excessive internal resistance is believed tc available and consequently radiation damage to the be the reason for this, and it is thought that furthei semiconductor severely limits the useful life of the work will remedy the situation. This device employed power source. Present data indicate that gallium PbTe as the n-type element and ZnSb as the p-type arsenide solar cells are not significantly more resist- element. ant to 800 kev electrons that n-on-p sihcon solar The intermediate range of temperature operation cells. is characterized by two distinct areas of effort: ( 1 )

The third method—the utilization of a phosphor attempting to extend the operational capabilities of to accomplish multiplication of the number of present-day materials such as lead telluride, and photons at correspondingly reduced energy—looks ( 2 ) the development of new materials such as ger-promising as an energy conversion mechanism if the manium silicon. This report is not an attempt to nuclear photons do not severely damage the phos- cover the whole field of materials development but phor and the transmission the phosphor is main- rather to present the philosophy and performance to tained so that the major portion of the photons date. The state of the art in this range is being formed will be transmitted to the semiconductor con- attacked from the standpoint of adapting the avail-verter. This mechanism of conversion could produce able materials such as lead telluride to device con-electric energy from an isotope at an efficiency of cepts. The main problems to be considered here are 5 to 8 per cent. This concept is being actively inves- sublimation (encapsulation), contact formation, and tigated at present. Data on its capabilities should be system integration. It is well known that lead available in about a year. telluride used at higher than 500 C requires some

sort of encapsulant to prevent sublimation. Several THERMOELECTRICS promising techniques are being developed including The thermoelectric field can be divided into three ceramic coatings, cup-shaped couples, and swaged temperature ranges: high temperature, greater than thermoelectric units. The development of suitable 1,000 C; intermediate temperature, 500 to 1,000 C; contacting techniques also appears satisfactory at and low temperature, less than 500 C hot-junction least for n-type PbTe, and the problem will probably generator systems. The development in the low and shortly be solved for the p-type. Component integra-intermediate systems has advanced to the point tion is under way through a contract with Westing-where laboratory devices with several hundred hours house on a cavity-type solar thermoelectric genera-of operation have been achieved, and the high-tem- tor.-̂ * This program is directed toward the utilization perature systems at present are confined to the ma- of thermal storage in lithium hydride which has a terials development. Many possible materials are melting point of 680 C. The hot-junction temperature available for this range such as BiTe, PbTe, AgSbTe, will be lower than this, however, because of the etc. The low-temperature materials programs are too thermal resistance of the contacts, insulation, heat extensive to include in this report. The low-tempera- storage container, etc. ture device efforts by the Air Force to date have The development of high-temperature thermo-been in the study of the "Fuel-Fired Tap" 100, a electrics is largely confined to material work on such 100-watt thermoelectric generator by Westing- compounds as Ce^Ss and MCC50, a p-type material house^" and in the development of the fiat plate solar developed by Monsanto Chemical Corporation. The thermoelectric generator for space use by General Air Force has contracted with Monsanto to integrate Atomics, a division of General Dynamics.^^ The lat- this material into a laboratory device of about 5

watts' capacity."^ The hot- and cold-junction tem-, peratures in this effort will be in the ranges of 1,200

Table II · Laboratory thermoelectric ^ , ^ , ^ ^ . , r^t^ , generator - flatplate-solar type to 1 -500 C and 500 to 700 C respectively. The two

j^;;;;;;;;^ p,„„„„„„ advantages of operating in this range are: ( 1 ) the incident energy, watts per n,> 1.400 over -a l l W e i g h t C a n probably be reduced because the Panel size, incites 4 by 4 tadiator sizc can bc much smaller; and ( 2 ) the r c , c . . . . . . . . ^ ' ' ' ' ' ' ' ' ' • • • · • · 2 " availability of materials in this temperature range is Power density, viraits another S t e p toward cascading thermoelectric gen-c a S r / o l ' d e n s i t y , e r a t o r s or elements, thus obtain much higher ef-

watts per square foot 2.95 ficicncics than thosc uow available. p S p e r " ' : ' " ' : : : : : : : : : : : : : : : : : The Nemst effect, described in the following, is

866 . ELECTRICAL ENGINEERING · NOVEMBER 1962

being considered as the basis of a system for con­verdng thermal energy to electric energy.

where

X, y , and ζ are three mutual ly perpendicular p lanes electric field strength in the y d irect ion

Ν = Nernst coefficient dT — = temperature gradient m χ direction dx Hz = magnet ic field strength

In this equation the voltage gradient and the ther­mal gradient are mutually perpendicular, which permits the utilization of anisotropic materials with relatively high thermal and electrical conducdvity in one direction and poor thermal conductivity in the direction of the thermal gradient. In this situadon the possibility is good that optimum material proper­ties may more easily be obtained than with conven­tional thermoelectric materials. The problem of maintaining high magnedc fields exists for this converter but is not being considered at present.

Ferroelectric and pyroelectric energy conversion techniques have been considered and may be useful for supplying electric power in space. Ferroelectric energy conversion is accomplished in the following manner: a capacitor employing a ferroelectric ma­terial as a dielectric separator is charged at the Curie point. The temperature of the system is raised and thus the dielectric strength of the ferroelectric ma­terial increases, and addidonal electric energy is accumulated in the generator in accordance with these equations:

Fi = ρ / C i = QlCoka

where

W^ — energy stored in capacitor C i = vol tage across capacitor Ci

Q = quantity of electric charge Xei = dielectric constant at Γι

W ^ W2- Wr = VoQiVi- Vi)

W ^ \

w = y2Qv

With insufficient data on specific heat, insulation strength, and the change* of the dielectric strength with temperature, it is difficult to determine exactly what performance can be expected from materials. The cycling time is limited by how thin the materials can be made and also by how great a temperature excursion is required to obtain the needed change in dielectric strength.

Pyroelectric energy conversion techniques operate in a somewhat analogous way, in that temperature cycling is required for their operation. They differ,

however, in that a charge separation occurs spon­taneously upon headng the material because of a change in domain alignment or change in polari­zation. A pulse of electric energy can then be ob­tained upon both heating and cooling of the material or crystal.

This means of power generation is not being actively pursued at present. Many unknown factors make its ultimate capabiHties uncertain. It suffers a great disadvantage in that rapid temperature cycling is a requirement for efficient operation and can, therefore, cause severe configuration restriction and component restriction in any operable generator for space use.

Piezoelectric energy conversion is being studied as a means for generating electric power utilizing the acoustic energy of a rocket or jet. Some related information is available on this process through the background of the Navy in sonar. Efficiencies of 80 per cent or higher are achievable if the converter is optimized for a single frequency. This, however, is not the case for the applications being considered and consequently much less efficiency will be at­tained. An efficiency of about 20 per cent is an­ticipated for the aforementioned configuration.

CONCLUSIONS The area of solid-state energy conversion is of prime importance in providing electric power for aerospace vehicle systems. There are many types of power required from missions of several weeks to several years, with power requirements ranging from 10 watts to 10 Mw. Most of the concepts discussed in this report are for applications of less than 30 kw with the solar cells probably Hmited to less than 10 kw. For larger power systems, reflectors can be made much lighter in weight than an equivalent area of solar cell.

There are applications for more than one type of solid-state energy converter. For small power require­ments of up to 100 watts, the single-crystal solar cells or the thin film cells will probably be used exclusively. The thin-film cells are, of course, much less expensive than the single-crystal variety. The silicon dendritic cell will probably have wide appli­cation; it should provide electric power at virtually the same efficiency as has been achieved by the ingot-grown single-crystal cell, but at a greatly re­duced cost.

The flat-plate thermoelectric generator also offers potential in small power applications if orientation of the panel can be provided. It is very light in weight and as with most thermoelectric materials it probably will not be damaged by Van Allen radia­tion.

It is somewhat premature to speculate on the eventual applications of the exploratory efforts pres­ently under way such as the Nernst generator or nuclear photon conversion.

NOVEMBER 1962 ELECTRICAL ENGINEERING · 867

REFERENCES Photo electrics 1. G a l l i u m A r s e n i d e S o l a r Ce l l s . R. W. R u n n e l s . A S D T R 61-88 , report o n c o n t r a c t A F 33 ( 6 1 6 ) - 6 6 1 5 . R C A S e m i c o n d u c t o r D i v i ­s i o n , S o m e r v i l l e , N .J . 2 . I n t e r i m R e p o r t s o n C o n t r a c t A F 33 ( 6 1 6 ) - 7 8 4 2 , E l e c t r o - O p t i c a l S y s t e m s , In c . , P a s a d e n a , Calif . 3. R e s e a r c h o n I m p r o v e d P h o t o g e n e r a t o r , R. K. R i e l et al. F i n a l report o n c o n t r a c t A F 3 3 ( 6 1 6 ) - 6 6 1 2 , W e s t i n g h o u s e E l e c t r i c Corp . , S e m i c o n d u c t o r D e p t . , Y o u n g w o o d , Pa . 4. S o l a r Ce l l A r r a y O p t i m i z a t i o n , M. R i t t e r et al. A S D TR 6 1 - 1 1 , v o l s . I a n d II , c o n t r a c t A F 3 3 ( 6 1 6 ) - 7 4 1 5 . R C A A s t r o - E l e c t r o n i c s D i v i s i o n , H i g h t s t o w n , N .J . 5. C a d m i u m Sul f ide S o l a r Ce l l R e s e a r c h , F . A . S h i r l a n d et al. A S D T D R 62-69 . i n t e r i m report , c o n t r a c t A F 3 3 ( 6 1 6 ) - 7 5 2 8 , H a r s h a w C h e m i c a l Co. , C l e v e l a n d , O h i o . 6. U n i q u e P h o t o v o l t a i c Ce l l s . J. F . E l l io t . A S D TR 61-242, r e p o r t o n c o n t r a c t A F 33 ( 6 1 6 ) - 7 1 8 3 , G e n e r a l E l e c t r i c S e m i c o n d u c t o r P r o d u c t s D e p t . , S y r a c u s e , N.Y. 7. P h o t o e m i s s i v e So lar C o n v e r t e r , M. P . H n i l i c k a et al. A S D T R 61-80 , final report c o n t r a c t A F 33 ( 6 1 6 ) - 7 5 3 4 , N a t i o n a l R e s e a r c h Corp . , C a m b r i d g e , M a s s . 8. I n v e s t i g a t i o n of P h o t o e m i s s i o n S o l a r E n e r g y C o n v e r s i o n , H. A . S t a h l , W. K. P e i f e r . A S D TR 61-619, final repor t o n c o n t r a c t A F 3 3 ( 6 1 6 ) - 7 1 6 5 , R C A E l e c t r o n T u b e D i v i s i o n , L a n ­c a s t e r , P a . 9. P h o t o g e n e r a t o r R e s e a r c h A n a l y s i s , I g o r L i m a n s k i . A S D T R 62-213 , final repor t o n c o n t r a c t A F 3 3 ( 6 1 6 ) - 7 9 1 0 , W e s t i n g h o u s e E l e c t r i c Corp . , E l e c t r o n i c T u b e D i v i s i o n . B a l t i m o r e , M d . 10. I n t e r i m R e p o r t s o n Contrac t A F 3 3 ( 6 1 6 ) - 7 9 1 1 . S u n d s t r a n d A v i a t i o n D i v i s i o n , D e n v e r , Co lo . 11. F o u r K i l o w a t t S o l a r P h o t o v o l t a i c P o w e r S y s t e m D e s i g n S t u d y , R. W. B r i g g s et al. A S D T D R 61-158, final r e p o r t o n c o n t r a c t A F 3 3 ( 6 1 6 ) - 8 1 9 8 , W e s t i n g h o u s e E l e c t r i c Corp . , A e r o ­s p a c e E l e c t r i c a l D e p t . , L i m a , O h i o . 12. D e s i g n S t u d y of a S t a t i c S o l a r Ce l l E l e c t r i c a l P o w e r S y s t e m , L . U h l . J . S m a t k o . W A D C T N 59-380, i n t e r i m r e p o r t c o n t r a c t A F 3 3 ( 6 1 6 ) - 6 6 1 7 , H o f f m a n E l e c t r o n i c s Corp. , L o s A n g e l e s , Calif . 13. I n v e s t i g a t i o n o f S o l a r C o n c e n t r a t i n g P h o t o v o l t a i c P o w e r G e n e r a t o r s , D . M c C l e l l a n d et al. A S D T N 60-849, i n t e r i m r e p o r t

c o n t r a c t A F 3 3 ( 6 1 6 ) - 7 3 4 6 , E l e c t r o O p t i c a l S y s t e m s , I n c . , P a s a ­d e n a , Calif . 14. T e s t R e s u l t s o n 50 W a t t S o l a r C o n c e n t r a t i n g P h o t o v o l t a i c G e n e r a t o r , R. S p i e s . A S D T N 6 1 - 3 f 8 . i n t e r i m r e p o r t c o n t r a c t A F 33 ( 6 1 6 ) - 7 3 4 6 , E l e c t r o O p t i c a l S y s t e m s , I n c . 15. D e s i g n S t u d y S o l a r E n e r g y M e a s u r e m e n t T e c h n i q u e s , B . R o s s . D . B i c k l e r . A S D T N 61-156, i n t e r i m r e p o r t c o n t r a c t A F 3 3 ( 6 1 6 ) - 7 9 4 6 . H o f f m a n E l e c t r o n i c s C o r p . , S e m i c o n d u c t o r D i v i ­s i o n , E l M o n t e . Calif . 16. T e m p e r a t u r e C o n t r o l T e c h n i q u e for S o l a r E n e r g y C o n v e r t e r s , J. K. B a k e r . A S D T R 61-689 , final r epor t c o n t r a c t A F 3 3 ( 6 1 6 ) -7889, G e n e r a l E l e c t r i c Co. , M S V D , P h i l a d e l p h i a , P a . 17. R e s e a r c h S t u d y of P h o t o v o l t a i c S o l a r C e l l P a r a m e t e r s , W . S h o c k l e y , H. Q u e i s s e r . A S D T R 61-423 , final r epor t c o n t r a c t A F 33 ( 6 1 6 ) - 6 7 0 7 , S h o c k l e y T r a n s i s t o r U n i t , C l e v i t e Corp . , M o u n ­t a i n V i e w , Calif .

Thermoelectrics

18. E x p e r i m e n t a l M e a s u r e m e n t s a n d A n a l y s i s o f D e g r a d a t i o n F a c t o r A f f e c t i n g L o n g L i f e F e a s i b i l i t y of T h e r m o e l e c t r i c G e n ­e r a t o r s , A . M. B e r n a r d . A S D TR 61-107, c o n t r a c t A F 3 3 ( 6 1 6 ) -7515, W e s t i n g h o u s e E l e c t r i c Corp . , L i m a , O h i o . 19. P r e p a r a t i o n of S o l a r T h e r m o e l e c t r i c C o n v e r s i o n P a n e l s , E . L . B r a d y , A . N . H i m l e . A S D T D R 62-214, final r epor t c o n t r a c t A F 33 ( 6 1 6 ) - 7 6 7 6 , G e n e r a l A t o m i c , S a n D i e g o , Calif . 20. S o l a r T h e r m o e l e c t r i c G e n e r a t o r C o n c e p t , C o n t r a c t A F 33 ( 6 5 7 ) - 8 0 8 9 , W e s t i n g h o u s e E l e c t r i c Corp . , L i m a , O h i o .

21. H i g h T e m p e r a t u r e T h e r m o e l e c t r i c G e n e r a t o r . C o n t r a c t A F 3 3 ( 6 5 7 ) - 7 3 8 7 , M o n s a n t o R e s e a r c h L a b o r a t o r i e s , D a y t o n , O h i o . 22. F e r r o e l e c t r i c E n e r g y C o n v e r s i o n . C o n t r a c t A F 3 3 ( 6 1 6 ) - 7 9 4 0 , I n t e r n a t i o n a l T e l e p h o n e a n d T e l e g r a p h Corp . , N u t l e y , N.J . 23 . T h e r m o p i l e G e n e r a t o r F e a s i b i l i t y S t u d y — P a r t s I - I V , R. L . G e s s n e r , J . H. B r e d t , D . K e r r . W A D D T R 60-22 , final r e p o r t c o n t r a c t A F 3 3 ( 6 1 6 ) - 5 2 8 1 , G e n e r a l E l e c t r i c Co. , S c h e n e c t a d y , N.Y. 24. S o l a r T h e r m o e l e c t r i c G e n e r a t o r S y s t e m . A S D T R 61-315 , final r e p o r t c o n t r a c t A F 3 3 ( 6 1 6 ) - 7 3 5 8 , H a m i l t o n S t a n d a r d , W i n d ­s o r L o c k s , C o n n . 25 . E n e r g y C o n v e r s i o n S y s t e m s R e f e r e n c e H a n d b o o k , J . F i s h e r et al. W A D D T R 60-699, v o l s . IV, V , I X . c o n t r a c t A F 3 3 ( 6 1 6 ) -6791, E l e c t r o O p t i c a l S y s t e m s Inc . , P a s a d e n a , Calif .

U N D E R W A T E R A R T I L L E R Y R E A D I E D F O R S O U N D - O F F

Underwater artillery to "shoot" telephone conversations under the Pacific Ocean undergoes final check at the plant of α British affiliate of International Telephone and Telegraph Corp. Known technically as submarine telephone re­peaters, these gold-plated "guns" are part of α transpacific cable to be laid between Australia and Canada. The cable will be capable of carrying 80 two-way telephone calls simultaneously.

868 · E L E C T R I C A L E N G I N E E R I N G · N O V E M B E R 1962