US3457726A

US3457726A - Incrementally controllable-thrust propulsion device

Info

Publication number: US3457726A
Application number: US655486A
Authority: US
Inventors: Jacques Trotel
Original assignee: Compagnie Francaise Thomson Houston SA
Current assignee: Compagnie Francaise Thomson Houston SA
Priority date: 1966-07-26
Filing date: 1967-07-24
Publication date: 1969-07-29
Anticipated expiration: 1986-07-29
Also published as: GB1176956A; BE701441A; FR1502732A

Description

July 29, 1969 I J. TROTEL 3,457,726 1 INCREMENTALLY CONTROLLABLE-THRUST PROPULSION DEVICE I Filed July 24, 1967 4 Sheets-Sheet 1 Z Jicques 790751,

Avnw we i 29, 1959 I J. TROTEL 3,457,726

INCREMENTALLY CONTROLLABLE-THRUST PROPULSION DEVICE Filed July 24, 1967 4 Sheets-Sheet 2 July 29, 1969 J. TROTEL 3,457,726

INCREMENTALLY CONTROLLABLE-THRUST PROPULSION DEVICE Filed July 24, 1967 4 Sheets-Sheet s July 29, 1969. 4. wow... 3,457,726

INCREMENTALLY CONTROLLABLE-THRUST PROPULSION DEVICE Filed July 24, 1967 4 Sheets-Sheet I.

United States Patent Int. Cl. rozk 9/04, 9/06 US. Cl. 60-250 19 Claims ABSTRACT OF THE DISCLOSURE The controllable-thrust motor for manoeuvring of spacecraft and the like comprises a sealed capsule (1) having a jet discharge orifice (13) at its rear end and containing a composite charge consisting of alternating layers of fuel, e.g. ammonium perchlorate (4) and inert material e.g. aluminium foil (5). A heating electrode (6) is spring-pressed against the outermost layer so that the application of a current pulse from an electric source (B) through discharge of condenser C will vaporize the outermost inert layer (5A) and burn only the adjacent fuel layer (4A), generating a predetermined increment of thrust. Reference is had to FIG. 1.

This US. application is based under International Convention on French patent application 70,865 filed July 26, 1966 by the assignees.

Reference is made in the disclosure to co-assigned, U.S. Patent No. 3,398,357.

This invention relates to propulsion devices or motors capable of developing a controllable thrust, of the kind used as auxiliary motors on space vehicles for such purposes as modifying the attitude of the vehicle, controlling its orbit, and similar maneuvering and correcting functions.

Conventional devices of this kind have often used a stored pressure gas, such as nitrogen, to produce a controllable propulsion jet. Such devices are simple and convenient to control, but the need to carry a heavy and bulky pressure vessel to store the gas is a serious hindrance.

In co-assigned, US. Patent No. 3,398,537, there is disclosed a novel form of controllable thrust propulsion device or auxiliary motor, which comprises a charge of solid fuel enclosed in a sealed casing having an outlet orifice for the discharge of a gaseous reaction jet. The fuel charge has a composition so predetermined as to undergo a controllable chemical reaction preferably of a mildly exothermic character on application of heat energy thereto, and a controllable of heat is associated with the charge capable of controlling the progress of the reaction and thereby controlling the thrust developed by the device.

The device just referred to is simple, compact, light and efficient. However, further experimentation therewith has shown that in some circumstances the thrust derived therefrom is difiicult to control as accurately as would be desirable, because the rate of combustion of the charge tends to be unstable, especially depending on the cold or hot condition of the motor and the surrounding temperature, and also on the amount of the remaining charge.

It is an object of the present invention to provide a controllable-thrust propulsion device using a solid fuel charge and having the outstanding advantages of the device disclosed in the co-pending application, and in which moreover the charge combustion has very high stability,

3,457,726 Patented July 29, 1969 making possible precise incremental control over the developed thrust. An object is to provide such a device which can be accurately controlled incrementally as to the timing and amount of the thrust developed thereby, through remote control means such as by digital signals or pulses received from a remote control station or automatic control means. An object is to provide a simple, compact, lightweight, reliable, solid-charge, incrementallycontrollable thrust propulsion device especially suitable for use as an auxiliary motor on board space vehicles, which can be operated intermittently or continuously with a high degree of precision.

The device of the invention is characterized in that it uses a composite solid fuel charge consisting of alternate layers of fuel and separator material. Heating means, such as an electrode, when energized first evaporates the outermost layer of inert material or separator, and will only then ignite the next adjacent fuel layer, combustion of which then produces the useful increment of thrust. The separator layers are so predetermined that the combustion of a fuel layer cannot vaporize the next adjacent separator layers, so that combustion is arrested, and with it the developed thrust, on complete combustion of each layer. In this way, the device can be operated for accurately predetermined periods of time.

FIGS. 1 to 5 are views in axial section illustrating five different forms of embodiment of the device of this invention.

In the first embodiment, shown in FIG. 1, the device comprises a metal container 1 of generally cylindrical form having one end sealed by a fiat end wall 2 and its other end 12 domed and formed with a central orifice 13 for discharge of the propulsion jet. A flared nozzle 14 is shown as extending around and rearward from the jet orifice 13. The casing or container 1 may be made of any suitable strong material, such as stainless steel.

Within the casing 2 is a composite fuel charge which as shown consists of a stack of combustible fuel layers 4 and inert separator layers 5 in alternation. The fuel stack has one end adjacent the end wall 2 and its other end somewhat short of the domed end section 12 of the casing. The outermost end of the stack is formed by an inert separator layer 5A, and the next adjacent fuel layer immediately below it is designated A4.

The inert separator layers 5 ma comprise thin metal foil, e.g. aluminium foil about 0.05 mm. thick, or they may comprise other suitable materials as later described.

The heating means in this embodiment comprises a conductive electrode rod 6 extending into the casing 1 through the jet discharge nozzle and orifice, and supported in axially centered position through suitable means shown as including a bushing 7 of heat resistant material supported by way of an insulating spider support 14 at the outer end of the nozzle 21. Bushing 7 is extended rearward in the form of a protective sheath 71 surrounding rod 6. Electrode rod 6 is freely slidable in bushing 7 and is pressed at all times into tight contact engagement with the outermost separator layer 5A of the fuel-charge stack by means of a tension coil spring 8 surrounding the rod and having its outer end anchored to the outer end of the rod, while the inner end of spring 8 is anchored to bushing 7. Clearly various other spring biassing arrangements may be used for the purpose of pressing rod 6 against the fuel stack.

A heating circuit is shown as including a voltage source E, which may be any suitable source available aboard the spacecraft, e.g. a solar battery. A capacitor C is connected to source E in series with a resistance R, and one side of capacitor C is connected to the outer wall of easing 1, while the opposite end is connected through a cut-off switch S and a flexible or otherwise deformable connection to the outer end of electrode rod 6.

In operation, capacitor c is at all times charged from the source E through protective resistance R. On closure of switch S, the capacitor discharges through the circuit including rod 6, the outermost layer of metal foil 5A in the stacked charge, and the wall of casing 1. The high voltage discharge from the capacitor C instantly vaporizes the foil 5A, and almost simultaneously ignites the now exposed, underlying fuel layer 4A. Combustion of the fuel produces a large volume of combustion gases which issue out of orifice 13 and through nozzle 21, as a high-velocity jet generating the requisite thrust. The time required for complete combustion of a fuel layer of course depends on the thickness of the layer and the nature of the fuel, and can be varied widely by suitably selecting said thickness. The inert separator elements 5 are so predetermined that the heat generated by the combustion of the adjacent fuel layer is incapable of vaporizing the separator element, nor is said heat capable of igniting the next fuel layer sealed off by the separator. Practical experience has shown that these conditions can be readily achieved while still providing separator elements thin enough to ensure their being completely and practically instantaneously vaporized by the electric discharge passed therethrough as described above.

Thus the combustion and therefore also the thrust from the device is arrested on combustion of each fuel layer. If switch S is again actuated to its closed condition immediately on termination of the combustion of the layer, the above described process is repeated immediately, and there need be virtually no interruption in the thrust developed by the device. If desired however, and this is an outstanding advantage of the device disclosed, the switch S can be retained in its open-circuit condition for any desired period of time, so that impulses of thrust of any desired incrementally controllable duration can be generated at precisely controlled times.

As will be understood, the electrode 6 projects further and further into the casing 1 under the action of spring 8, as the fuel charge is used up.

The solid fuel used in the laminated or stacked charge of the invention may include any of the compositions known as suitable for use as a solid fuel. Examples of suitable fuel compositions include the following (compositions are by weight):

Ammonium perchlorate (80%) and asphalt (20%);

Ammonium perchlorate (75%) and polyurethane (25% Ammonium nitrate (76%) and cellulose acetate (14%);

Nitrocellulose (55%), nitroglycerine (25%) and plasticizer.

The above list is not exhaustive but merely indicative. The compositions also are only indicative and may generally be varied over a substantial range without impairing results.

As the inert constituent in the separator layers, it will be understood that in the embodiment of FIG. 1 this must be an electrically conductive material in order to establish a conductive path through the discharge circuit for capacitor C. Conveniently, the separator layers in such cases may comprise aluminium foil about from to A mm. thick, through other suitable conductive media may be used.

FIG. 2 illustrates a modification of the controllablethrust motor of FIG. 1 in which similar components are designated by similar numerals. The only important difference here is that the metal container 2 is provided with an end sealing wall 2 which, rather than being flat as in FIG. 1, is conically convex with a rounded central apex. correspondingly, both the combustible fuel layers 4 and the intervening inert separator layers 5 are of a similar generally conical concave configuration as the end wall 2. An advantage of this arrangement is that the combustion area of each fuel layer is substantially greater, for a given volume, than in the case of FIG. 1. Moreover the recessed charge configuration obtained with such an arrangement creates a concentration of heat tending to improve combustion.

In the further embodiment shown in FIG. 3 the controllable-thrust device comprises a generally cylindrical container 1 made of a suitable ferromagnetic material, e.g. suitable grade of magnetic steel, and there is provided a rod or post 9 of the same material extending from the flat end wall 2 of the container axially thereof. The free end of axial post 9 lies substantially flush with the rear wall 25 of casing 1 and defines an annular gap 22 with a central aperture in said front wall for the discharge of combustion gases. The annular gap 22 is surrounding by a suitable converging-diverging wall defining the jet nozzle orifice 13. Positioned within the front end of easing 1 near the end wall 2 thereof is a coil winding 10 surrounding post 9. The coil 10 has its ends led out of easing 1 and connected to a condenser discharge circuit similar to the one described for FIGS. 1 and 2. Overlying coil 10 in the container is a separator disc 23 of non-magnetic material. The remaining part of the container 1 to the rear of disc 23 and extending over the major part of the axial length of the device is an assembly of coaxial cylindrical lamina tions including active fuel layers 4 and electrically conductive separator layers 5 in alternation. The radially innermost separator layer 5 is radially spaced from the circumference of post 9 to provide an annular cylindrical gap in which initial combustion can take place. In the operation of this device, it will be understood that coil 10 constitutes the primary of a transformer of which each of the conductive separator layers 5, made e.g. of aluminum foil as in the preceding embodiments, constitutes a partial secondary. On closure of switch S, the COndenser C discharges into coil 10, creating a high primary current pulse through the coil winding. It will be evident that the impedance of the secondary circuits constituted by the metal foil layers 5 increases stepwise from each such layer to the next radially outward layer owing to the increase in radius, hence, every time switch S is closed the primary current pulse generated in coil 10 induces a secondary current pulse predominantly or exclusively in the innermost separator foil 5 present at the time. The high current pulse produces a sudden and sharp discharge of heat which vaporizes the foil, exposing the adjacent fuel layer for combustion as earlier described. This embodiment is considered advantageous in that it eliminates the provision of a movable heating electrode in the path of the gas jet, as required in FIGS. 1 and 2.

In the embodiment of BIG. 4, the general lay-out of container 1 with its active and inert stacked layers 4 and 5 is similar to that in FIG. 1. However, the heating means used in this case comprise a resistive wire 11 disposed e.g. in the form of a flat grid in container 1 some distance from the rearmost inert layer 5A. The ends of resistor 11 are connected to

rigid conductors

15 and 16 which serve as supports therefor and are led out of container 1 for connection to a pulse circuit which may be similar to the condenser discharge circuit shown in the preceding embodiments. A reflective screen 17 made of a suitable metal sheet element having a polished rear surface, is supported a short distance rearward of register grid 11, e.g. from the rigid resistance-support ing wires or other suitable supporting means not shown. Reflector 17 is shown flat but may be concave if desired. On application of a current pulse to resistor 11, the resulting heat is reflected by screen 17 as a beam of heat radiation which evaporates the nearest inert layer 5, exposing the underlying fuel layer 4 for combustion as earlier described.

The embodiment shown in FIG. 5 is somewhat similar in its method of heating as the one just described, but the general layout resembles that of FIG. 3 rather than FIG. 1. That is, the active and inert layers 4 and 5 are in the form of coaxial internested cylindrical layers coaxial with the cylindrical casing 1 and defining a central recess Within the casing. A heating resistor ,11 in the form of a helical wire is supported in this central recess by way of the

condutcors

15 and 16 connected to a pulsing circuit not shown. On application of a current pulse to the resistor 11, the heat radiated outward from the resistor evaporates the innermost separator layer and causes combustion of the fuel layer 4 thus exposed.

In each of the embodiments of FIGS. 4 and 5 the active fuel constituent may be similar to any of those used in the embodiments of FIGS. 1 to 3. On the other hand, the separator constituent in each of said embodiments last described is not necessarily electrically conductive, but may comprise any of various suitable noncombustible materials capable of being decomposed and/ or evaporated or sublimated by heat. It is also contemplated, in embodiments of the invention of the'character last described, that the constituent comprising the inert or separator layers 5 may be such as to generate a substantial amount of gas capable of contributing to the thrust developed by the device, as said constituent is decomposed by heat. Strictly speaking in such embodiments the materials composing the separator layers are not inert but, to some extent, active. In fact said separator layers may comprise materials similar in char acter to some of those used as the fuel material in the co-pending application Ser. No. 553,814 referred to above.

As examples of materials usable as the relatively inert separator materials in embodiments of the present invention of the type exemplified by FIGS. 4 and 5 the following may be cited: Organic polymers such as polyvinyl chloride, polystyrene and the like; cellulose acetate; urea-formol resins, methacrylates, polyesters, polysulfides, polyurethanes, polybutadiene.

FIGS. 4 and 5 are but examples of embodiments of the present invention in which the source of heat serving to break down the separator layer and ignite the exposed combustible layer, is other than an electric discharge. Various other heat sources of this general character may be conceived for use according to the invention, including the sources disclosed in the above-identified co-pending application, e.g. sunlight or, a source of radioactive substance. Thus, the co-pending application discloses arrangements wherein the casing of the device includes a transparent wall section arranged to be exposed to sunlight by means of a movable opaque shutter, for igniting the charge. In another arrangement disclosed in said copending application, the heat source is an element of radioactive material movable into and out of the casing of the device for controlling charge ignition. Controllable heat sources of either of these types can be used in devices according to the present invention for breaking down the separator layers and igniting the exposed fuel charges of the various devices disclosed herein.

Conveniently, though not necessarily, the individual layers of fuel material in a device according to the invention are so predetermined that the combustion of each layer develops substantially the same thrust increment. Where necessary, as in the embodiments of FIGS. 3 and 5, this condition may require the provision of unequal thicknesses for the various fuel layers. With such an arrangement, the average thrust developed will be constant when the rate of ignition of the charges will be constant. When it is desired to vary the average thrust developed by the device, the rate at which the successive fractional charges are ignited, e.g. the rate at which such as S in FIGS. 1-3 is closed, would be varied correspondingly. Control is thus facilitated. As regards the sensitivity with which the developed thrust can be controlled and varied with the controllable-thrust motors of the invention, this will obviously be increasingly great as the number of elementary fuel charges in the device is large, and the individual quantity of fuel in each elementary charge is correspondingly small.

The means for controlling the ignition of each individual fuel charge, shown as a mechanical switch S in the embodiments of R168. 1-3, may assume a variety of forms, and may be associated with any suitable automatic and/or remote-control instrumentalities, e.g. for operating the control by way of a radio link or under control of gyroscopic and inertial stabilizing arrangements, as will be readily understood.

What I claim is:

1. An incrementally-controllable thrust device com prising:

a casing (1) having an outlet orifice (13) for the discharge of a gaseous jet;

a composite laminated charge in said casing comprising a series of combustible fuel layers (4) and a series of separator layers (5) in alternating relation; and

a single ignition means (S, 6; S, 10; 15, 16, 11) for applying pulses of thermal energy to said charge, each of said energy pulses provided by said single ignition control means causing combustion of a single one of said fuel layers (4) to develop a corresponding increment of thrust from the device.

2. The device claimed in claim 1, wherein said charge comprises a stack of fiat fuel and flat separator layers.

3. The device claimed in claim 1, wherein said charge comprises a stack of internested concave fuel and separator layers.

4. The device claimed in claim 1, wherein said charge comprises a set of internested coaxial cylindrical fuel and separator layers.

5. The device claimed in claim 1, wherein said single ignition control means comprises a source (E) of electric energy, capacitance means (C) connected to be charged from said source, and discharge circuit means (S, 6, 5A, 2; S, 10; 15, 11, 16) connected for receiving discharge pulses from said capacitance means for producing said pulses of thermal energy.

6. The device claimed in claim 5, wherein said casing (1) and said separator layers (5) are electrically conductive and said discharge circuit means includes: a conductor member (6) engageable with an exposed one (5A) of said conductive separator layers and establishing a circuit extending through said exposed layer and said casing; and means connecting said conductor member and said casing to said capacitance means (C).

7. The device claimed in claim 6, including spring means (8) associated with said conductor member (6) for pressing it into resilient engagement with said exposed separator layer (5A).

8. The device claimed in claim 5, wherein said casing has magnetic core means (1,9) associated therewith and said separator layers (5) are electrically conductive, and said discharge circuit means includes an inductance coil (10) associated with said casing to constitute the primary winding of a transformer having secondaries constituted by said separator layers (5), said separator layers (5) being so disposed in said laminated charge that the impedance of each separator layer is greater than the impedance of the adjacent separator layer that has undergone combustion before it.

9. The device claimed in claim 8, wherein said charge comprises a set of internested coaxial cylindrical fuel and separator layers, and said magnetic core means includes a rod (9) extending axially with respect to the cylindrical set.

10. The device claimed in claim 1, wherein said ignition control means comprises a source of electric energy and a resistance (11) connected to said source and arranged to radiate heat on an exposed one (5A) of said separator layers.

11. The device claimed in claim 1, wherein said fuel comprises a solid rocket propellent composition.

12. The device claimed in claim 1, wherein said fuel comprises a compound of ammonium perchlorate and asphalt.

13. The device claimed in claim 1, wherein said fuel comprises a compound of ammonium nitrate and cellulose acetate.

14. The device claimed in claim 1, wherein said fuel comprises a compound of ammonium perchlorate and polyurethane.

15. The device claimed in claim 1, wherein said fuel comprises a compound of nitrocellulose, nitroglycerine and plasticizer.

16. The device claimed in claim 1, wherein said separator comprises thin metal foil.

17. The device claimed in claim 1, wherein said separator comprises cellulose acetate.

18. The device claimed in claim 1, wherein said separator comprises organic polymer material.

19. The device claimed in claim 1 wherein said outlet orifice is substantially centrally located at one end of said casing and wherein said composite laminated charge comprises a stack of alternate generally transversal solid propellent layers and conductive separator layers, the edges of said separator layers engaging the inner surface of said casing, and wherein said single ignition control means comprises:

a conductor members passing through said orifice and engageable with an exposed surface of one of said separators;

a source of pulses of electrical energy; and

terminal means on said conductor member and on said casing coupled to said pulse source;

each pulse delivered by said pulse source vaporizing one separator layer and causing combustion of a single one of said propellent layers to develop a corresponding increment of thrust from said device.

References Cited UNITED STATES PATENTS 2,640,417 6/1953 Bjork et al. 60-2-56 2,918,871 12/1959 Taylor l0246 XR 3,000,175 9/1961 Lawrence 149-76 XR 3,002,830 10/1961 Barr 149-76 XR 3,033,716 5/1962 Preckel 149-96 3,128,600 4/1964 Oldham 6025O 3,247,796 4/1966 Kirshner l0246 3,248,875 5/1966 WOlcott 60250 XR 3,249,049 5/1966 Zimmerman l0246 3,293,855 12/1966 Cuttill et a1 602 56 XR 3,358,452 12/1967 Ehrenfeld et al. 60-200 FOREIGN PATENTS 137,341 9/1952 Sweden. 627,722 8/ 1949 Great Britain.

25 CARLTON R. CROYLE, Primary Examiner US. Cl. X.R.