US3441936A

US3441936A - Spherically mounted floating radiation reflector

Info

Publication number: US3441936A
Application number: US443524A
Authority: US
Inventors: Otto R Heine
Original assignee: Lear Siegler Inc
Current assignee: Lear Siegler Inc
Priority date: 1965-03-29
Filing date: 1965-03-29
Publication date: 1969-04-29
Anticipated expiration: 1986-04-29

Description

veto-61% O. R. HEINE April 29, 1969 Sheet fizz INVENTOR. 0/70 f5 #0; BY 7% MZi firm/914%.

0. R. HEINE- April 29, 1969 SPHERICALLY MOUNTED FLOATING RADIATION REFLECTOR Sheet Filed March 29, 1965 3,441,936 SPHERICALLY MOUNTED FLOATING RADIATION REFLECTOR Otto R. Heine, Playa del Rey, Calif., assignor to Lear Siegler, Inc., Los Angeles, Calif., a corporation of Delaware Filed Mar. 29, 1965, Ser. No. 443,524 Int. Cl. H01q 3/00, 19/12 US. Cl. 343-709 ABSTRACT OF THE DISCLOSURE The perimeter of a parabolic reflector is connected to the circular edge defining a hole in a sphere. Preferably, the hole and the reflector have the same diameter, which is substantially smaller than the diameter of the sphere. In addition, the perimeter of the reflector lies in the same plane as the hole in the sphere and extends inside of the sphere. The sphere floats on a fluid and is held in place by three rotatable drive members that are compressively loaded to remain in contact with the sphere. The drive members are adapted for a swivel motion. At least one of the drive members is coupled to a power source to orient the sphere.

7 Claims dam This invention relates in general to radiation reflecting and focusing means and means for controlling its directivity. More particularly this invention relates to a new and improved method and apparatus for mounting a radiation reflector substantially free of distortion and deformation forces commonly known to prior art devices, and relates to new and novel means for directing'simultaneously the reflector and its mounting structure.

In the past, radiation reflectors, such as radio telescopes, or antennas, have assumed a large range of sizes and have employed various mounting structures chosen in accordance with its intended use which may be as diverse as receiving signals from interplanetary stars, or from tracked airplanes, missiles, or satellites. In common with this wide diversity of uses is the general requirement that the reflector be steerable and have precise signal focusing ability. A steerable parabolic reflector is the simplest, most efficient prior art device which more closely approaches a general purpose instrument than any of the other various types of prior art reflectors, and although this invention is discussed in relation to a parabolic antenna, it is not limited to this single form.

A parabolic reflector for reception of low frequency signals is made of a circular section normally of wire mesh which is slightly concave at its center to form the parabolic focusing and reflecting surface. Reception of high frequency signals, however, generally requires a solid surface of sheet metal plates which are held in a parabolic shape by a support structure. In either event, the support structure for the wire mesh or solid sheets is of steel ribs which are riveted or bonded together to form a mounting surface for the reflective material.

While the parabolic reflector is being directed from one part of the sky to another desired location in the sky, it must hold its true parabolic shape to within one-tenth of the length of the shortest possible wave length it may receive. For example, if the signal frequency that is to be received is 10,000 megacycles per second, the wave length is approximately 1% inches and accordingly the structure must not deviate from a true parabola by any more than approximately .12 inch RMS. This distortion limit is achieved with some degree of success for small (less than 100 feet in diameter) parabolic reflectors, but only then by expensive design of the antenna mounting and steering structure. Larger reflectors (such as those greater than li' 'nited States Patent ice feet in diameter and up to 500 or 600 feet and beyond) have presented complex design problems which, prior to this invention, have remained unsolved in any attempt to stay within the allowable distortion limit at reasonable construction costs. A few large reflectors, as a result, are built as fixed parabolic reflectors consisting of wire mesh placed within a scooped-out hollow in the earth. These fixed reflectors of course are extremely restricted in their usefulness because directivity control is mainly that of the earths motion.

Some large steerable reflectors up to 250 feet in diameter have been developed by using the so-called alt-azimuth mount. In this type of mount the parabolic reflector is suspended by a heavy and complex truss structure which is rotatably mounted at either edge between two supporting towers. This approach is not entirely satisfactory for many large antennas because the extreme weight causes difficulty in providing satisfactory bearings in the tower mounts and the supporting structure. Another disadvantage of this prior art structure is that steering is achieved, in part, by placing the towers on locomotive engines running on a circular railway track. This steering arrangement is slow and lacks precise control. In addition, the combined weight of the towers, the reflector and the trussing supports, and the locomotives are all borne by the railway track. Settling of the earths surface under tracks is often uneven and such settling adversely affects the steering and causes stresses to develop in the trussing structure. These stresses, in turn, may cause the allowable distortion limit for the parabola to be exceeded thereby seriously impairing the antennas reflective surface.

This alt-azimuth mounting of the prior art is also adversely affected by distortion-causing factors other than settling of the supporting ground. These other distortion factors include thermal and wind effects, and gravity forces on the trussing. During the day, part of the parabolic surface is often in the sun and the remaining side is in the shade. Contraction and expansion of the metal, both of the reflector itself and its trussing, may cause the allowable distortion limit to be exceeded. This problem has been lessened by employing large circulating fans which attempt to keep the structure within allowable temperature limits. These fans are not totally effective and are expensive to operate; .Moderate to strong winds also cause considerable disto'ftion and often prevent use of the device during a significant portion of the overall operating day.

One further, andas yet unsolved problem of distortion, particularly as it applies to the larger reflectors, is that regardless of the stiffening. and reinforcing design of the trussing for supporting the antenna, it bends under its own weight. This bending becomes particularly pronounced at portions of the reflectors trussing, which are farther removed from the supporting towers, because such portions are subject to large gravity-induced cantilever forces. These cantilever bending forces soon cause distortion beyond the allowable limits, and thus conventional design has, in the past, stopped at the point where the extra stiffening adds further weight which, in itself, adds further bending. This design limit, until the advent of this invention, has precluded the satisfactory construction of large reflectors.

The foregoing disadvantages of the prior art are overcome by this invention which provides a steerable mounting structure capable of horizon-to-horizon coverage; and which can support parabolic reflectors considerably larger than those of the prior art by a new and novel supporting structure which assures the parabolic reflector will, at all times during its scan, be within allowable distortion limits.

In accordance with. the principles of this invention, a

radiation collecting and focusing means, which may be of any type but preferably is a parabolic reflector, is housed in a circular hole of a spherical mounting shell structure. The circular opening of the spherical structure provides full support for the entire periphery of the reflector, and the inherent structural soundness and rigidity afforded by compressive forces of the sphere structure assures that any deviations, at most, result only in insignificant deviations from a true parabola.

This spherical shell structure is floated in a body of fluid contained within an enclosure. This fluid presents small frictional drag and provides for effective directivity of the spherical shell by frictional or other driving means. The fluid may also be piped through the structure for cooling, if necessary, to prevent thermal distort-ion.

Any settling of the earth beneath the fluid enclosure, of course, will not affect the reflector mounting apparatus of this invention because the fluid displacement forces provide the floating support. These forces are uniform for the spherical surface in the enclosure and are not affected by any settling which may take place.

Further, in accordance with the principles of this inven tion, orientation control means are associated with the spherical shell structure and its driving means to provide a hemispherical sky coverage from horizon-to-horizon. In one embodiment, such orientation control means take the form of dual friction drive wheels which are mounted on the fluid enclosure in contact with the sphere, and which are capable of rotational and swivel motion. In another embodiment of this invention, the orientation control means comprises shifting weights or masses within the shell structure itself.

The invention will be more clearly understood when considered in conjunction, with the accompanying draw= ing in which:

FIG. 1 is shows a three-dimensional view of the spher ically mounted floating reflector of this invention;

FIG. 2 shows a three-dimensional view of one section of the reflector of FIG. 1 and discloses details of the fric tional drive wheels;

FIG. 3 shows a side elevation of the spherically mounted reflector of FIG. 1 and includes an enlarged portion, FIG. 3A, displaying cooling pipes for circulation of the fluid;

FIG. 4 shows an alternative manner of mounting a reflector in the recessed portion of the floating spherical shell;

FIG. 5 shows another alternative manner of mounting a reflector in a floating spherical shell; and

FIG. 6 depicts in block form a typical orientation con trol system for a spherically mounted floating reflector.

In FIG. 1 the spherically mounted floating radiation reflector of this invention is depicted as having a spherical shell 10 floating on a body of fluid 12, such as water for example, which is contained within a pool structure 13. This spherical mounting shell 10 may be of any suitable material such as, for example, a steel shell, a concrete shell, or a sandwich shell structure having rigid inner and outer surfaces filled with foam or pressurized air. The spherical mounting shell is a frustrated sphere in that a section has been removed to expose a circular opening in the spherical shell. A mounting surface 14 for a reflec tor is formed in the circular opening with its convexity placed inside the spherical shell 10. It is of course well recognized that the structure principles of a sphere provide the utmost in rigidity, and this rigidity allows the mounting surface for the parabolic reflector to be formed or housed in the circular opening, or so-called lantern ring. This lantern ring provides full and rigid peripheral support which greatly reduces any possible cantilever forces on the structure. If the supporting surface 14 is made of cast concrete, for example, the peripheral support of the lantern ring plus primarily compressive for e of th suppor ng s ructure itself assures substantially complete 4 freedom from distortion of the supporting surface during scanning operations.

A parabolic reflective surface 15, partially shown in FIG. 1, is fastened by any suitable means to the parabolic mounting surface. Signals received at surface 15 are reflected and focused to the receiver 17 which is held by supports 18 at precisely the focus point for the parabolic reflector of FIG. 1.

Receiver 17 may be any of the well known types chosen in accordance wtih the particular use of the reflector. For example, it could be a photographic plate, or a camera, or a signal repeater, amplifier and transmitter. This receiver 17, as is generally true in the art, is capable of relatively small areas of movement in a plane shown as 19 in order to achieve precise focusing. Signals from receiver 17 may be transmitted by any suitable means such as by radio to control house 16.

In FIG. 1 the spherically mounted reflector, or radio telescope, is shown floating on a body of fluid 12 which is contained within a pool 13. This pool may either be level with or it may be above, the earths surface. The pool structure, above the ground level, allows complete coverage in that a horizon-to-horizon hemispherical scan may be obtained by driving the sphere 10 by friction drive wheels 20.

Only two drive wheels 20 are shown in FIG. 1. These friction drive wheels 20 are mounted on the pool structure 13 and are compressively loaded by spring or hydraulic pressure in order to contact the spheres surface firmly at all times. Only one friction drive wheel is required to have a driving force, whereas the remaining wheels may act as bumpers or guides to hold the sphere 10 firmly in place. This technique protects the structure from any possible damage caused by shifting due to strong winds.

FIG. 2 discloses the details of one of the driving friction wheels 20 of FIG. 1. Dual drive friction wheels 22 are independently mounted on rotatable axles which are seated in suitable bearings housed in an E-shaped bracket 23. Independent dual driving wheels 22 are necessary to reduce squeegee loads between the driving surface of the wheels and the outer surface of the spherical shell 10, when the wheels are power driven for sphere control. The lE-shaped bracket 22 is securely mounted by any suitable means on a cylinder 24 which is seated into a compression chamber 25 which may contain a spring or a fluid under hydraulic pressure. This chamber 25 is located in the pools enclosure structure as shown in FIG. 1. Its compressive loading against the sphere 10 provides for continual frictional drive.

Two diflferent directions of driving force are achieved by the drive unit 20, and these include a rotational driving force and a swivel driving force. These rotational and swivel forces, control both elevation and azimuth movements of the spherical shell 10. Dual driving wheels 22 are rotated in either a forward or a reverse direction by any suitable rotational drive motor 27. A swivel drive motor 28 provides power for turning the E-shaped bracket 23 through 360 in a plane which is perpendicular to the pressure axis 29, and which is tangent to the point of contact of wheels 22 against sphere 10. Proper antenna orientation is provided by the control system shown in block form in FIG. 6 and discussed in detail hereinafter. By such control of the rotational and swivel movements of driving unit 20, the spherically mounted raido telescope of this invention can be controlled for complete hemispherical coverage at a rate of scan which is significantly higher than any known prior art radio telescopes of com parable size.

One serious defect of prior art radio telescopes over= come by this invention concerns the thermal gradient caused by the effects of sun and shade on the reflectors surface and its trussing structure. The spherical shell 10 is not subject to such thermal gradient distortion because the large mass is relatively insensitive to thermal gradients. Thus i resists thermal distortion to a, much greater extent than do the steel ribs and beams of prior art structures which are extremely sensitive to thermal changes. In addition, the sphere 10, to the extent that it does expand or contract, changes size substantially uniformly throughout and thus is not subject to distortion caused by nonuniform expansion and contraction as in the prior art trussing structure.

Further protection against thermal distortion is pro vided by refrigeration unit 30 shown in block form in FIG. 3 which is a side elevation of the sphere of FIG. 1. This refrigeration unit 30 may be any known prior art cooling system and in particular might be a pump for circulating water or other coolant through pipes 29, FIG. 3A, which are embedded in the lantern ring 32 and the supporting surface 14.

Various examples were given hereinbefore as typical construction materials for shell-10. Concrete is a preferred material although the invention is by no means limited to this material. Various approximate dimensions, heights and structural factors of interest with respect to large concrete spherical shells for housing different size radio telescopes are included in Table 1. Although only statistics for larger size telescopes are given, the smaller sizes are comparable as will be apparent to those skilled in the art.

TABLE.APPROXIMATE STRUCTURAL ANALYSIS Reflector (it.) Sphere d D q" p.s.i. PW p.s.i. (it.) h (in.) W (it) (it) In the table, the columns are identified as follows: h is the thickness of the sphere without any rib construction; W is the weight of. sphere in thousands of tons; a is the draft of the sphere; D is the diameter of pool; q is the critical pressure of a perfect sphere before any buckling will take place; and P is the average hydraulic vertical water pressure against the sphere when it is floatably supported.

As shown by preceding table a satisfactory sphere can be constructed of concrete which has a large safety factor as defined by the difference between P and q In FIG. 3, the lantern ring 32 and parabolic reflector supporting surface 14 lessen the structural pressure somewhat, as compared with a perfect sphere, but are well within this safety factor.

FIGS. 4 and 5 depict side elevations of alternative spherical antenna structures which are within the principles of this invention. In FIG. 5, a parabolic antenna 14 is housed in sphere 10 with its mounting structure extending outside the spherical shell. This alternative provides means for mounting an antenna of larger diameter than the diameter of the housing sphere; and still retain the benefits and advantages afforded by the novel concepts of this invention over the prior art discussed hereinbefore.

In FIG. 4, an opening 35 is provided in the spherical shell 10. A parabolic antenna 14 is located within the bottom of the spherical shell 10 in the manner shown. Receiver 17 is positioned within sphere 10 in line with the center of opening 35. This location of the antenna within the spherical shell considerably lessens any possible distortion from wind disturbances. Pool enclosure 13 in this embodiment is lined with a thick layer of shock absorbent material 36 which is useful in supporting the spherical shell 10 when all of water 12 is evacuated from the pool by any suitable means such as valve 37 and pipe 38. This evacuation might be necessary in an emergency such as an extremely strong wind of hurricane proportions.

Only frictional driving wheels have been discussed hereinbefore as supplying the power for controlling the spherical antenna of this invention. It should be understood that other possible ways of orienting the spherical shell which houses the reflector are within the scope of this invention. Such other control means might include an internal pendulosity drive including shifting weights which are either piston or motor controlled for travel within hollow tubes located within the sphere. External cables may be fastened on the surface of the sphere at selected positions. These cables may be wound on drums for controlling cable tension during drum reeling movements.

Other examples of directivity controls which are available for the novel spherical floating reflector of this invention include external water jet orientation which in-= clude nozzles mounted in the sphere and located within the pool and which utilize the force of water expelled from the nozzle opening to steer the antenna. Another alternative would be to utilize water flooding of inner compartments within the sphere similar to techniques employed in submarine controls.

Regardless of the type of turning power employed, it is necessary that some type of orientation control system be employed so that the antenna may initially be directed to a particular target, and once on target remain fixed by automatic tracking techniques. Numerous antenna orientation control systems may be employed, but only one is discussed in detail hereinafter. An orientation control system for this invention may best be explained by reference to FIG. '6 which depicts such a control system in block form. In connection with the following description of FIG. 6 conventional terminology for an altazimuth mounting arrangement as is commonly known in the prior art is used. According to this common mounting principle, a horizontal control is continually operative, and an elevation control and an azimuth control is provided to selectively direct the antenna through horizon-to-horizon coverage.

In an alt-azimuth mount for the sphere of FIG. 1, a horizontal control requires that an axis X--X which may pass through the center of the sphere 10 in the manner shown, continually hold its position in a plane parallel to the ground. This plane would be defined by rotating the axis X'X about the vertical axis Y--Y of FIG. 1. Different positions of axis X-X in this hori zontal plane represent different azimuths for the antenna of FIG. 1.

An elevation control for the antenna of FIG. 1 may be provided by rotating the elevation axis Y-Y about the horizontal axis XX. Axis Z-Z represents an on target position for the antenna of FIG. 1 as is provided by the control system of FIG. 6. In a similar manner axis Y'Y is established in a plane trans-verse to axis X X and any angular displacement of axis Y-Y from an initial reference position, such as is shown in FIG. 1, may be provided by a second pendulous accelerometer. This second accelerometer is shown as an elevation angular displacement sensor 43 in FIG. 6. Other prior art de vices are available which can provide the amount and rate of angular displacement of the axes XX and YY simultaneously. As one other example, vertical and di rection gyroscopes in combination with rate integrating gyroscopes could be substituted for the

pendulous accelerometers

42 and 43 discussed above.

An azimuth reference for the antenna of FIG. 1 may be provided in any well known manner. For example optical prism devices are available in the art for sighting on an external reference source such as 44 of FIG. 1. As axis X-X rotates about axis YY in its horizontal plane the optical prism device, shown as an azimuth angular displacement sensor 45 of FIG. 6, would generate an output signal proportional to the amount and rate of azimuth deviation from the reference source 44. As de scribed above the three output signals from the

angular displacement sensors

42, 43, and 45 initially position the spherical antenna of FIG. 1 in a two axis earth-space reference position. Any movement of the antenna away from this initial reference, whether by drift or on command, will develop output signals from the

angular displacement sensors

42, 43, and 45..

For tracking purposes a command unit 46 is provided which monitors the angular output signals from the sensors. This command unit includes manual operated or computer operated controls for establishing any desired ascension and declination angles required by the antenna in order to pick up a. selected target. These angles are converted in command unit 46, in a well known manner to earth-space angles for comparison with the angular output signals from

sensors

42, 43, and 45. After this comparison between the present position of the antenna and the desired position the output signals from control command 46 are applied to control gyroscopes 47 mounted in the antenna. These signals precess the gyroscopes. The control gyros 47 are stable in inertial space and thus will maintain the desired ascension and declination, and also counteract the earths motion, once the antenna is suitably positioned by the resolution unit 48 of control command 46. This resolution unit 48, may be a computer as is well known in the antenna and automatic tracking art, for converting the error signals from control gyroscopes 47 into suitable drive coordinates for the rotational and swivel drive motors 2.7 and 28 of frictional drive wheel 20. These drive coordinate signals from resolution unit 48 drive frictional wheels an appropriate amount in the proper direction and rate to continually create a zero error condition,

If the target being tracked is a point source such as a missile, or a non-point source such as a gas cloud, normal drift in the control gyroscopes 47 might cause the antenna to lose its target. This drift may be compensated for in any well known manner such as the use of an automatic tracking receiver 49 to torque the control gyroscopes 47. This automatic tracking device 49, as is known, responds to incoming signals picked up from the target, and produces error signals proportional to any deviation of the antenna from its target line of sight as represented by a weakening of the received signal. In the case of a non-point source a clock reference 50 may be employed to torque the control gyroscopes 47 and thus compensate for normal gyroscope drift.

It is to be understood that the above described arrangements are illustrative of the principles of this invention, Numerous other arrangements may be devised by those skilled in the art without departing from the spirit and scope of this invention.

What is claimed is:

1. In a radio telescope the combination comprising a parabolic signal collecting and focusing bowl, a unitary mounting and supporting structure to hold said bowl in a true parabola of desired focusing curvature to within less than one-tenth of the smallest wave length selected to be received by said bowl, said unitary structure comprising a spherical shell having a parabolic indentation for supporting said bowl in a position to collect and receive signals from the sky, an enclosed body of fluid for floatably supporting said spherical shell, an enclosure for supporting the body of fluid, and means associated with said shell structure for selectively orienting said floating shell whereby said bowl is directed to any selected point in the sky from horizon to horizon, said orientation control means comprising a plurality of friction wheel units mounted on said fluid enclosure with the wheels of each unit touching said spherical shell and means for rotating the wheel of at least one of said plurality of units and for swiveling the wheel of said one unit through a plane tangent to the point of contact of said wheel and said spherical shell surface.

2. A signal receiving device comprising a substantially distortion-free sphere having a circular indentation therein as a supporting surface in the shape of a paraboloid of revolution as defined by rotating a parabola about an axis passing through the center of said sphere and the center of said circular indentation, signal collecting means supported by said surface for reflecting and focusing such collected signals at a common point in front of said signal collecting means, signal detecting means mounted at said common point, a utilization circuit, means for transmitting the detected signals from said detecting means to said utilization circuit, temperaturetcontrolling means at said supporting surface for maintaining it at substantially the same constant temperature, an enclosure for containing a body of fluid to floatably support said sphere, and a plurality of guides mounted in spaced relation on said enclostire and in contact with said sphere for stabilizing said sphere from wind or other shifting forces.

3. A signal receiving device as defined in claim 2 and further comprising a layer of shock absorbent material on the inside surface of said fluid enclosure and means for evacuating fluid from said enclosure to settle said sphere firmly in place.

4. A signal collecting device comprising a parabolic signal reflector for reflecting collected signals at a common focus point for said reflector, a spherical structure of a diameter larger than the diameter of the circular periphery of said reflector having a circular hole cut therein for receiving said reflector, means for mounting said reflector in a substantially distortion-free parabolic shape in said circular receiving hole, a closed pool enclosing abody of water sufficient to floatably support said spherical structure in said water, a plurality of friction wheel pairs with each pair rotatably mounted in an E-shaped bracket, a plurality of pressure chambers equally spaced in mounted relationship around said pool enclosure for turnably receiving said equal number of wheel parts and for holding said wheels in frictional contact with said spherical surface, a pair of motors mounted on at least one of said E brackets for providing rotational and swivel power to said wheels, orientation control means connected to said motor pair for selectively rotating both wheels in either the same or opposed directions, signal-detecting means at said common focus point for said parabolic reflector, a utilization circuit, means between said signaldetecting means and said utilization circuit for transmitting said focused signals to said utilization circuit, and means associated with said orientation control means for supplying control signals to said motors to direct said reflector to any selected point in the sky.

5. In a radio telescope, the combination comprising:

a parabolic surface for collecting and focusing received signals;

a spherical structure for housing said parabolic surface;

means for floatably supporting said spherical structure;

means for controllably rotating said spherical structure within said supporting means, the rotating means comprising a plurality of frictional driving means mounted around said supporting structure in spaced relationship and in contact with the outer surfaces of said spherical housing structure; and

means for supplying rotational power to at least one of said plurality of frictional driving means, the rotational power supplying means being capable of transmitting a swivel motion to said frictional driving means in a plane defined by rotating a tangent to said spherical surface about the point of contact of said frictional driving means and said spherical housing structure.

6. An antenna arrangement comprising:

a parabolic reflector with a circular perimeter having a first diameter;

a spherical supporting structure having a second diameter substantially larger than the first diameter;

a circular hole having the first diameter formed in the spherical structure, the circular edge of the spherical structure that defines the circular hole lying in a given plane;

means for connecting the circular perimeter of the reflector to the circular edge of the spherical structure such that the center of the reflector extends in- 9 16 side the spherical structure and the circular perimeter References Cited of the reflector lies in the given plane; UNITED STATES PATENTS a fluid on which the spherical structure floats;

a base unit for containing the fluid; and 2,260,396 10/1941 g at least three compressively loaded rotatable drive 5 g i members mounted on to the base unit in spacedm y 3,141,168 7/1964 Ashton 343-709 apart relationship around the sphere so as to maintain firm contact with the sphere, the drive members OTHER REFERENCES being adapted for swivel motion relative to the base 1) S K d & C Catalog, June 6, 1958, page 12 unit while in contact with the sphere. 10 7. The antenna arrangement of claim 6, in which at ELI LIEBERMAN PH-mw'y Examine least one of the drive members is coupled to a source of US. Cl. XLRQ power to change the orientation of the sphere. 343-765, 840, 872