US3093788A - Radioactive power supply system - Google Patents

Description

June 11, 1963 E. G. LINDER 3,093,788

' RADIOACTIVE POWER SUPPLY SYSTEM Filed Aug. 26, 1955 i 2 Sheets$heet 1 IN VEN TOR.

June 11, 1963 E. G. LINDER 3,093,783

RADIOACTIVE POWER SUPPLY SYSTEM Filed Aug. 26, 1955 2 Sheets-Sheet 2 f /5' Z kz/ PIT O Q EV Unite States Patent 3,093,788 RADIGACTEVE PUWER SUPPLY SYSTEM Ernest G. Linder, Princeton, N..l., assignor, by mesne assignments, to the United States oi America as represented by the Secretary oi the Air Force Filed Aug. 26, 1955, Ser. No. 530,863 3 Claims. (Cl. 322-2) This invention relates generally to an improved electrical power supply system. More particularly, but not exclusively, the invention relates to an improved radioactive primary power source for supplying electrical energy for the operation of electrical equipment, for example on guided missiles and rockets.

It is well known that weight considerations severely limit the construction and design of electrical power supply systems for high altitude crait such as guided missiles and rockets. The velocity and range of such craft are appreciably affected by small variations in the overall mass.

Known radioactive primary voltage sources comprise essentially a radioactive emitter and a collector. Two of the 'difliculties of operating such sources with large amounts of emitter material are the excessive generation of heat at the collector and the eventual destruction of the collector due to radiation damage.

It is therefore an object of this invention to provide improved methods and apparatus for radioactively generating electrical energy which obviate the collection of the radiated charged particles.

Another object of the invention is to provide an improved electrical power supply system for guided missiles and the like which does not add appreciably to the weight of the missile.

Another object of the invention is to provide an improved electrical power supply system of reduced mass, which is capable of supplying a predetermined substantially constant potential and especially useful for high altitude apparatus and craft.

These and other objects and advantages of the invention are attained by a system comprising a radioactive charged particle radiator of relatively small size which is connected through a load (or work circuit) to a body of much larger relative size. Such a system may be provided in an electrically non-conductive non-ionizable medium. When the system is located in a readily ionizable medium the ions produced by radiation should be prevented from establishing a conductive path from the radiator to the relatively large body. It is essential that the only path of electrical conduction between the radiator and the large body he that which is established through the work circuit. The charged particles from the radioactive emitter are radiated into the medium adjacent the radiator. In the case of a missile, for example, at a high altitude where a practical vacuum exists, a small portion of the missiles hull is completely isolated from the remainder of the craft except for a connection to the remainder of the missile through the equipment and devices or circuits to be energized. Charged particles, such as beta-particles, are released from this small portion into the space surrounding the missile. The departure of the charged particles from the isolated portion results in the building up thereon of a potential of polarity opposite to that of the released charged particles. Due to the charge re-distribution on the missile as a whole, electrons will flow from the remainder of the missile toward the positively charged portion through the only electrically conductive path therebetween, namely, the work load. The potential difference across this load will be according to Ohrns law, V=Ri, where R is the load resistance and i is equivalent to the radioactive current released from the isolated portion into space. At

low altitudes where a relatively dense and ionizable medium around the missile may be expected, special precautions must be taken to prevent ionization of the surrounding gas by the radioactive emission from establishing a conductive path from the isolated portion to the remainder of the missiles hull. 'To do this the direction of radiation must be such as to preclude the formation of an ion cloud ahead of the missile and the velocity of the missile must be greater than the velocity of the ions formed.

The invention will be described in greater detail with reference to the accompanying drawings in which:

. FIGURE 1 is a partially schematic view of one embodiment of the invention; 7

FIGURE 2 is an elevational view of a guided missile partially in section and partially schematic, embodying the invention;

FIGURE 3 is a plan view of a guided missile as shown in FEGURE 2 embodying the invention;

FIGURE 4 is an elevational, sectional fragmentary view of details of the embodiment of the invention as shown in FIGURE 2;

FIGURE 5 is a schematic diagram of the embodiment of the invention in a missile as shown in FIGURE 2;

FIGURE 6 is a schematic diagram of another embodiment of a power supply system according to the invention; and

FIGURE 7 is an elevational view, partially in section, partially schematic, of still another embodiment of the invention.

Similar reference characters are used throughout the drawings to designate the same or similar parts.

Referring to FIGURE 1, a small electrically conductive body 1 of relatively low electrical capacity is connected by the conductor 2 to a large body 3 of relatively high electrical capacity through a work circuit 4. The bodies 1 and 3 are shown as spheres for convenience of illustration only, and such shape is not critical or necessary for operation according to the invention. The small sphere is coated or otherwise in contact with a relatively large amount of radioactive charged-particle-emitting material 5. The radioactive material may, for example be a beta particle emitter such as strontium 90. Preferably the radioactive material is of the purest quality so as to minimize the problems arising from gamma ray emission from some impure radioactive material. The two spheres, the connection therebetween and the work circuit are enclosed in a vacuum or other non-conductive non-ionizable medium as indicated by the dash line 22.

Beta particles are emitted from the small radiator sphere l by the radioactive material. Assuming that just prior to such emission there is no potential difference between the large and small spheres, the departure of these particles results in the charging up positively of the small sphere. Hence as more and more negative particles leave the small sphere 1 a greater and greater positive charge will be built up thereon. The difference in potential between the small sphere 1 and the large sphere 3 will in turn result in a charge lfi-dlSlZllblltlOl'l in the entire circuit as it seeks to return to and maintain the same potential throughout. There will be an electron flow from all less positive points of the circuit or large sphere 3 to the more positive small sphere 1. This current must flow through the load 4 across which a voltage is thus developed.

Stated another way, the positive potential built up on the small sphere 1 will result in a charge re-distribution in the entire circuit as it seeks to return to and maintain the same potential throughout. This means that positive charges will be re-distributed throughout the small, relatively low capacity sphere 1, the large, relatively high capacity sphere 3, and the connection theres eaves between including the work circuit 4. By employing a large, relatively high capacity sphere with the work circuit between it and the low capacity sphere, more of these charges will flow into the large sphere and hence through the work circuit 4. This is because the distribution of positive charges between two bodies having electrical capacity is proportional to the ratio of their capacities, the larger the capacity the greater the aflinity thereof for charges. Thus if the electrical capacities of the two spheres were identical, only half the number of positive charges developed on the one would be distributed on the other. Hence by employing a large capacity sphere as compared with the low capacity of the radiator sphere, a large proportion of the charges developed on the small sphere Will be distributed on the large sphere which acts as a sink for these charges. Thus, for example, if the capacity of the large sphere is 100 times greater than the capacity of the small sphere, about the same ratio of charges developed on the small sphere will flow to the large sphere. Preferably the capacity of the large sphere should be considerably greater than the total capacity of the load and small sphere in order to pull the largest possible number or" charges developed on the small sphere through the load.

The current flow through the load thus is substantially equal to the radioactive current i emitted from the sphere 1 into space; hence the potential difference generated across the load 4 is expressed by where R is the load resistance. Since the load resistance and the current are substantially constant the potential diiference developed across the load will be substantially constant. This is true notwithstanding the fact that the system as a whole is developing an increasing positive charge since negatively charged particles are lost therefrom and not returned to the system.

Referring to FIGURE 2, a high-altitude craft 7 such as a guided missile has an electrically-conductive hull 8. A portion 9 of the hull is isolated from the rest of the hull by means of any suitable electrically insulating material 10 such as porcelain or other ceramic material, for example. Any suitable material may be used which is mechanically strong and temperature resistant. It is preferred that the isolated portion 9 and the insulating material it be flush with the exterior portions of the hull for aerodynamic reasons. The exterior of the isolated portion 9 is coated or otherwise provided with a radioactive material 11 capable of releasing or radiating charged particles into the space surrounding the missile 7. In order to protect the radioactive material from the atmosphere and to insure its retention on the isolated portion 9 it may be covered with a plastic material or metal foil to contain it is place. A suitable arrangement is shown in FIGURE 4 wherein the isolated portion 9 is recessed below the main hull line and covered with the radioactive material 11 which in turn is covered with plastic material 12 which is made flush with the hull 8 for aerodynamic reasons. The radioactive material :11 may alternatively be covered with metallic plating. The protecting covering for the radioactive material should be pervious to radiated charge particles. In this arrangement any radiation which is not perpendicular to the flat radiating surface M of the isolated portion 9 will strike the metallic side walls 16 and 16 which act as shields to prevent the radiation from reaching and possibly damaging or ionizing the insulating material 10.

The radioactive material may be either a negative particle (beta) emitter or a positive particle (alpha) emitter according to the invention. In the instant example, and for the purpose of explaining the invention, a beta particle emitting material such as strontium 90 is employed. This isolated charged particle radiating section is preferably located as near to the stern of the t missile as possible. This minimizes the possible formation of ion clouds due to the radiation with which contact by the missile is nearly unavoidable (as would be the situation when the charged particle radiator is near the nose of the missile). Locating the radiator near the stern also enhances the possibility of the complete escape of the radiated charged particles from the isolated portion. The isolated portion 9 is electrically connected to the remainder of the hull 8 through the work circuit or load 4 and a switch 13 the purpose of which is explained in detail hereinafter. The circuitry of the power supply system described is schematically v shown in FIGURE 5.

Referring to FIGURE 5, the radioactive emitter will discharge or release negatively charged. particles into the space surrounding the missile 7. The departure of these charged particles will result in the isolated portion 9' becoming charged to a polarity opposite to that of the charge of the lost particles. Hence as more and more negative particles leave the isolated portion 9 a greater and greater positive charge will be built up thereon. The difference in potential between the portion 9 and the remainder of the hull 8 will in turn result in a charge redistribution in the entire circuit as it seeks to return to and maintain the same potential throughout. There will be an electron flow from all less positive points of the circuit or hull 8 to the more positive portion Q This current must flow through the load 4 across which a voltage is thus developed.

Thus the operation is substantially the same as the apparatus described in connection with FIGURE 1. The

isolated portion 9 of the hull 8 corresponds to the small sphere ll; the hull 8 corresponds to the large sphere 3.

This process may be carried out at both high and low altitudes although special precautions must be observed when the missile is operating at a low altitude in a relatively dense ionizable medium. The charged particles being radiated into space will produce only a negligible amount of ionization of any gas present around the missile due to the rarity of the atmosphere at high altitudes. At low altitudes, however, the ionization of the air around the ship and especially in the neighborhood of the isolated portion 9 will result in an effective short-circuit between the emitting portion and the adjacent portions of the hull 3. Thus to ope-rate the power supply system of the invention at low altitudes or in an ionizable medium successfully, the direction of radiation must be such as to preclude the formation of an ion cloud ahead of the missile with which contact cannot be avoided. Preferably the charged particles will be radiated in the backward direction as shown in FIGURE 7. In this embodiment the isolated portion 9 extends above the main hull 8 of the missile and has its fiat radiating surface 14 facing the stern of the missile. The isolated portion in this embodiment should be located Well toward the tail-end of the missile to enhance the possibility of avoiding shortcircuiting effects due to ionization of the surrounding medium. Likewise such a location also minimizes the collection by the missile of radiated charged particles whose trajectory is such as to result in their returning to the radiator itself thus reducing the net number of released charged particles. Collection of radiated particles by the remainder of the hull is not detrimental and special provision for preventing such a return need not be made. In fact the return of radiated particles to the missiles hull enhances the operation of the invention since negatively charged particles are supplied to regions from whence they are being pulled by the positive potential being built up on the radiating portion 9. The radiating portion is enclosed in an aerodynamically streamlined bubble or dome 15 the rearward end of which is closed off for aerodynamic reasons by means of a gas-tight window d7 of material such as thin mica which is transparent to charged particle radiation.

Though preferably the stream of charged particles is radiated in the backward direction, a short-circuit may still occur between the radiating portion 9 and the adjacent portions of the hull 8 due to ionization of the surrounding medium. This is explained by the fact that some of the ions formed by radiation will have a velocity of their own which may be in the direction of travel of the missile. In such a case the missile would not escape the ions formed and short-circuiting would occur. To avoid this possibility the minimum velocity of the missile when in a dense ionizable medium must exceed the velocity of the ions formed. This means that the missile must have a minimum velocity in the supersonic range when in an ionizable medium.

When in an ionizable medium there will always be some return current, i to the radiating portion 9 due to ions, so that the above equation should have a correction term added, and should read,

The direction of radiation is preferably in the backward direction especially where the missile is at low altitudes where a dense ionizable medium is to be encoun tered. However, radiation can be in a generally forward or backward direction or at right angles to the direction of travel of the missile. The more nearly the direction of radiation coincides with the direction of travel of the missile, the greater must be the speed of the missile to escape the ions formed. Contact with ions formed by radiation directly ahead of the missile cannot be avoided at all, hence radiation in this direction is undesirable if short-circuiting effects due to ion formation are to be minimized.

Thus by maintaining the missile velocity greater than the ion velocity, the missile can escape the short-circuiting effects of the ionization of the surrounding medium. With reference to FiGURE 1, this suggests that a stationary system can be operated even when in an ionizable medium by causing the ionizable medium to have a velocity in a direction away from the stationary apparatus which velocity is greater than the velocity of the ions themselves. This may be accomplished by blowing the air past the system at the requisite velocity.

Since the static charge on the missile increases as radiation continues, the high charge difference between the missile and the earth might result in some difiiculties if the missile were to abruptly return to earth and discharge itself. In general, however, descent through the atmosphere will result in slowly discharging the missile as it enters the denser atmosphere. It is also possible to limit the charge developed according to another embodiment of the invention as illustrated schematically in FIGURE 6. In the example heretofore described negativelycharged particles are radiated from the iolated portion 9 and the missile as a whole charges up positively. The positive charge developed can be limited to any predetermined value by radiating positively-charged particles into the space surrounding the missile. Thus if the number of positively-charged particles leaving the missile is equal to the number of negative particles leaving the missile, the positive charge developed on the isolated portion 9 no longer increases but becomes constant or stabilized at the potential developed before positively-charged particle radiation commenced. If the number of positive particles radiated is less than the number of radiated negative particles, then the positive charge on the missile will continue to increase but at a slower rate, depending upon the difference in the number of radiated particles. If the number of positive particles radiated is greater than the number of radiated negative particles, then the positive charge on the missile will decrease. In this manner the charge built up on the missile can be controlled and established at any predetermined value.

The preferred means for discharging the missiles positive charge depends upon the surrounding medium. When the missile is at high altitudes and in a relative vacuum it is preferred to release positively charged particles by radiation from a radioactive material such as polonium 210. The alpha particle emitting material 18 may be located upon another portion 19 of the missiles hull and isolated therefrom by means of a gap or the insulating portion 26. When the switch is in position A the radiation of beta particles from the isolated portion 9 will result in the building up of a positive charge on the missile as described previously. When this charge has reached the desired value the switch 13 is thrown to position B so as to connect the alpha emitting isolated portion 19 with both the rest of the missiles hull 8 and the beta emitting isolated portion 9. The departure of the positively charged particles from the portion 19 compensates for the departure of negatively charged particles from the portion 9 as explained previously. Furthermore, this compensation may be controlled so as to bring about a stable charge on the missile, or to decrease the charge, or to permit a retarded charge increase as compared with a free-running charge increase.

When controlling the charge on the missile by emitting alpha particles therefrom the same requirements on the direction of radiation as described in connection with the emission of beta particles should be observed. If, for example, the alpha particles were able to return to the missile nothing would be accomplished by way of reducing the positive charge thereon. If the missile is being char ed positively, then this positive charge will tend to repel alpha particles that might attempt to return. This method of controlling the charge on the missile can also be employed at low altitudes in a relatively dense ionizable medium but further precautions, such as previously mentioned, must be observed to prevent short circuiting due to ionization of the surrounding gas. An arrangement such as described for the radiation of beta particles in a dense medium (shown in FIGURE 7) would likewise overcome difficulties due to ionization by alpha particles in a dense medium.

An alternative method for discharging the positive charge is by the phenomenon of cold emission of positive particles. To accomplish this a sharply pointed electrode is provided which may comprise the nose 21 of the missile as shown in FIGURE 2. The sharply pointed electrode concentrates a very intense electrical field at its point which arises from the charge on the missile. This embodiment is, however, preferred when the missile is in a relatively dense ionizable medium. When in such a medium the field at the point of the electrode 21 causes ionization of the surrounding gas and since the field potential is positive, negative ions or electrons will be attracted to the electrode from whence they will redistribute themselves throughout the hull of the missile to compensate for the positive charge being built up thereon.

It should be understood that a voltage may be developed across the work circuit 4 whether either a positive or negative particle emitter is employed. For example, the isolated portion 9 could become negatively charged by having an alpha particle emitter located thereon. Since this portion would gradually build up a negative charge greater than the potential on other portions of the missile a charge re-distribution would occur with the result that electrons would flow in the opposite direction through the work circuit 4. Likewise, the negative portion build up on the missile would then be controllable by providing a beta particle emitter elsewhere whose function and operation on the isolated portion 19 would be the same as that described in con nection with the embodiment where the missile was being charged positively.

While according to the preferred embodiment of the invention the charged particle radiator comprises an isolated portion of the vehicles hull and the equipment to be operated is connected between this portion and the remainder of the hull, the invention is not limited to this arrangement. The charged particle radiator could be an aerodynamically streamlined electrode extending from the hull of the craft-and suitably insulated therefrom. Likewise the load circuit could be connected between the charged particle radiator and any suitable conductive mass within the vehicle into which the developed charge could flow. As pointed out previously, however, the electrical capacity of this conductive mass should be large as compared with the electrical capacity of the electrode. Furthermore, as has been mentioned, the isolation of the charged particle radiator could be accomplished by providing a gap between the radiator and the hull of the craft. At high altitudes the radiator would thus be electrically isolated by the relative vacuum constituting this gap. At low altitudes the air itself is a sufficiently good electrical insulator to provide the necessary isolation although the special precautions against ionization referred to previously should be observed.

As used herein and in the appended claims the term missile is intended to describe any object or craft capable of travelling through space, Whether propelled by its own power or projected from the earths surface.

What is claimed is:

1. An electrical power supply apparatus consisting of first means having a relatively low electrical capacity, second means electrically insulated from said first means and having a relatively high electrical capacity, said first means being a small, electrically conductive body having a flat radiating surface for releasing charged particles of one polarity into the space adjacent thereto, said charged particles having a travel path perpendicular to said fiat radiating surface and away from said second means, said charged particles escaping from said power supply apparatus, the release of said particles producing an electric potential of a polarity opposite to said one polarity on said first means, said seconduneans being an electrically conductive body which is large with respect to said first means, an electrical load, third means connecting said load beaween said first means and said second means, whereby current may flow between said first and said second means and through said load, and fourth means connected to said second means for controlling the static charge on said electric supply apparatus.

2. The apparatus of claim 1 wherein said fiat radiating surface comprises a radioactive source of beta-particles.

3. A radioactive power supply consisting of first and second electrically conductive bodies, said first body being small and of relatively low capacity, said second body being large with respect to said first body and of relatively high capacity, said first body being electrically insulated from said second body, said first body having a fiat radiating surface of radioactive material for releasing charged particles of a finst polarity, the release or" said charged particles producing an electric potential of a second polarity on said first body with respect to said second body, a single path of electrical conduction between said first body and said second body, said path of electrical conduction consisting of: a load, a first connector connecting said first body to one side of said load, and a second connector connecting said second body to the other side of said load, whereby current will flow between said first and said second bodies only through said load.

References Cited in the file of this patent UNITED STATES PATENTS 2,517,120 'Linder Aug. 1, 1950 2,552,050 Linder May 8, 1951 2,709,229 Linder May 24, 1955 2,728,867 Wilson Dec. 27, 1955 2,789,241 Frey Apr. 16, 1957

Claims (1)

1. AN ELECTRICAL POWER SUPPLY APPARATUS CONSISTING OF FIRST MEANS HAVING A RELATIVELY LOW ELECTRICAL CAPACITY, SECOND MEANS ELECTRICALLY INSULATED FROM SAID FIRST MANS AND HAVING A RELATIVELY HIGH ELECTRICAL CAPACITY, SAID FIRST MEANS BEING A SMALL, ELECTRICALLY CONDUCTIVE BODY HAVING A FLAT RADIATING SURFACE FOR RELEASING CHARGED PARTICLES OF ONE POLARITY INTO THE SPACE ADJACENT THERETO, SAID CHARGED PARTICLES HAVING A TRAVEL PATH PERPENDIUCLAR TO SAID FLAT RADIATING SURFACE AND AWAY FROM SAID SECOND MEANS, SAID CHARGED PARTICLES ESCAPING FROM SAID POWER SUPPLY APPARATUS, THE RELEASE OF SAID PARTICLES PRODUCING AN ELECTRIC POTENTIAL OF A POLARITY OPPOSITE TO SAID ONE POLARITY ON SAID FIRST MEANS, SAID SECOND MEANS BEING AN ELECTRICALLY CONDUCTIVE BODY WHICH IS LARGE WITH RESPECT TO SAID FIRST

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