US 3392941 A
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July 16, 1968 c CASON 3,392,941
MAGNETOHYDRODYNAMIC RUDDER FOR REENTRY DEVICE Filed Sept. 22, 1966 United States Patent ice 3,392,941 MAGNETOHYDRODYNAMIC RUDDER FOR REENTRY DEVICE Charles M. Cason III, Huntsville, Ala., assignor to the United States of America as represented by the Secretary of the Army Filed Sept. 22, 1966, Ser. No. 582,204 3 Claims. (Cl. 2443.21)
ABSTRACT OF THE DISCLOSURE An improved means for guidance of a nose cone upon reentry into the atmosphere, employing magnetohydrodynamic effects. The improvement comprises a means for providing a more perfect ionization of the gases about a reentry nose cone which allows an enhancement of the magnetohydrodynamic effects and a means of causing the ionization to provide an electromagnet to react with the ionized gases.
This invention relates generally to the art of magnetohydrodynamics in a reentry device and more particularly to an improved means for guidance of a nose cone upon reentry into the atmosphere, employing the magnetohydrodynamic effects. The improvement comprises a means for providing a more perfect ionization of the gases about a reentry nose cone which allows an enhancement of the magnetohydrodynamic effect.
The present invention is an improvement of the magnetohy-drodynarnic principles applied to the guidance of a nose cone upon reentry as shown in US. Letters Patent 3,162,398 issued Dec. 22, 1964 and entitled Magnetohydrodynamic Control Systems.
Previously, when a device reentered the atmosphere, it might start tumbling violently and thus be highly unpredictable as to its return trajectory. A problem of guidance of a reentry device is that conventional rudders would be burned off upon reentry. However, with a magnetohydrodyna-mic rudder, no projected portion of the nose cone need be involved.
It has long been known that when a plasma is passed through a steady magnetic field at a changing hypersonic velocity and at right angles to the field, a self-loading circulating current is generated orthogonally in the plasma, and the circulating current in turn reacts with the magnetic field to cause a force which obeys the Left Hand Rule, and which is of a magnitude directly proportional to the magnetic field strength and the current density. If the magnetic field strength is a constant value, the force will be determined by the current density, and the current density, in turn, is developed directly from the velocity of the plasma.
The present invention is predicated upon the use of characteristics exhibited by electrically conductive gases in the presence of magnetic fields, whereby the fields induce very high rotational velocities in the gases. Accordingly, the ionized gases flowing around the nose cone upon reentry would tend to be decelerated at the skin of the nose cone, if it were not for the electromagnetic field present.
Gases, about a nose cone upon reentry, reach rather high temperatures. At these high temperatures the gases are easily ioniza-ble, but another way may be used to insure a more perfect ionization about the nose cone. To insure better ionization, place a reservoir of some easily ionizable material in the nose cap section of the nose cone. Upon reentry, the reservoir in the nose cap will be heated to a high temperature and the material inside will be vaporized and build pressure to such a degree as to break open the reservoir and spill the heated vapors into the ionized stream of gases about the nose cone. The flow 3,392,941 Patented July 16, 1968 rate of gases out of the reservoir can be accelerated by winding electrical heater coils around the reservoir, with the coils being actuated upon reentry. This process is known as seeding. Seeding is generally useful whenever the effective amount of ionization at a given temperature is to be increased. With increasing degrees of ionization of plasma, the charged particles will increase in number and the neutral particles will decrease in number. Therefore, as the degree of ionization of the plasma is increased, the electrical conductivity of the plasma is increased. Also, seeding decreases ablation of the nose cone surface.
With a high degree of ionization, the drag forces generated by interaction of the magnetic field and the velocity of the plasma can be better controlled by regulating a direct current circulated in coils wound around electromagnetic cores located in the nose cone. With increased current circulation in the coils, there will be more circulating current in the plasma, with resulting increase in drag force. This will make guidance more effective. Drag forces can be controlled by a method of switching the circulating currents, independently, in the coils wound around the various electromagnetic cores, and thus, controlling the flight angle of attack to a high degree.
It is an object to provide improved means for stabilizing a device upon reentry into the atmosphere.
It is a further object to provide improved means for controlling the angle of attack of a reentry nose cone.
It is a further object to provide means to produce additional ions in ionized gases about a reentry device.
It is still another object of the present invention to provide means to seed ionized gases about a reentry device, to enhance the torque produced about the device by the interaction of a magnetic field in the device with the seeded ionized gases.
The invention, as to its organization and operation, together with further objects and advantages thereof, will best be understood by reference to the following description taken in connection with the single drawing in which:
The drawing figure illustrates a sectional view of a nose cone structure including a magnetohydrodynamic system with an ionized gas seeding, and a current producing charged rnetal plate system in accordance with the invention.
In the figure, there are illustrated portions of a nose cone 5 included in the guidance system. The skin of the nose cone is of an electrically insulative material. When nose cone 5 reenters the atmosphere, a bow shook 7 is formed outward from the leading edge. Within this how shock 7 there exists an ionized boundary layer 9 wherein ionized gases exist to form an electrically conductive plasma zone of interaction 11, from the boundary layer 9 to the surface of nose cone 5. By an interaction of the electrically conductive plasma with a magnetic field that is normal to the nose cone surface, drag forces will be formed which cause the boundary layer to become thicker. For the purpose of creating these drag forces, an electromagnet with north pole 13 and south pole 15 is energized by coils 23 and 25 that are connected to metal plates 36 and 38 in the forward and rearward portions of the nose cones outer layer. A potential difference will exist upon reentry into the atmosphere between metal plates 36 and 38. Metal plate 36 thermionically emits electrons causing a difference in electric potential between it and metal plate 38. The reason for this is that the boundary layer is more highly ionized at the front portion of the nose cone than at the surface on further back, where the boundary layer gets increasingly thicker. By operation of controlling switch 17 drag forces may be controlled. A number of these electromagnets, for example, three, can be located around the nose cone section with independent switching. With the combined effort of the three drag forces, spaced apart, and energization of each of the three being controlled individually, the reentry device can be guided to its target.
To insure a more perfect ionization of the gases about the reentry nose cone 5, a reservoir 20 containing easily ionizable material 22 is located in the forward section of the nose cone in such a manner that when the temperature rises upon reentry this easily ionizable material 22 will be vaporized and pressurized then ejected into the plasma zone of interaction 11. More control can be effected by more perfect ionization of the plasma zone of interaction 11. A heater coil 26, wound around reservoir 20, is electrically connected to metal plates 16 and 18 in the forward and rearward portions of the nose cones outer layer. Upon reentry, a potential difference exists between metal plate 16 and metal plate 18 for reasons stated above. Controlling switch 37, serially connected between metal plates 16 and 18, comprises a temperature sensitive device actuated when a predetermined temperature exists at the outer surface of the nose cone.
From the foregoing, it is seen that this invention provides an improved method of guidance for reentry device by use of a magnetohydrodyn'amic rudder effect, by insuring a more perfect ionization of the thermionic media. While the reference has been to a nose cone in the above description, the present invention could be used in guidance of any reentry device, such as a spent booster motor.
The easily ionizable material could be a gas, a liquid, or a readily vaporizable solid. Some easily ioniza-ble materials that can be used are cesium nitrate, potassium nitrate, saltpeter, etc.
While the skin of the nose cone has been described as being insulative, it obviously could be metallic, in which case it would be necessary to insulate metal plate 16 from the nose cone.
1. A magnetohydrodynamic nudder guidance system for a reentry device in an ionized rnedia comprising: a magnetic means for producing a magnetic field normal to the fiow of gas about said reentry device; means for energizing said magnetic means; and a means for providing additional ions in said ionized media, said means for energizing said magnetic means including two electrical conductors longitudinally displaced on the surface of said reentry device, and a pair of windings electrically connected through a controlling switch between said electrical conductors, whereby the forwardmost of said electrical conductors thermionica'lly emits electrons causing a difference in electrical potential between said electrical condoctors, as said reentry device passes through an ionized media.
2. The combination as set forth in claim 1 wherein said means for producing additional ions includes means for introducing easily ioniza-ble material.
3. The combination as set forth in claim 2 wherein said material is an easily ionizable fluid.
References Cited UNITED STATES PATENTS 3,095,163 6/1963 Hill 24442.49 3,162,398 12/1964 Clauser et al. 2443.1 3,224,375 12/1965 Hoff 102-105 FOREIGN PATENTS 635,784 4/1950 Great Britain. 542,359 4/ 1956 Italy.
ROBERT F. STAHL, Primary Examiner.