US 3698811 A Abstract available in Claims available in Description (OCR text may contain errors) United States Patent W ll 5] Oct. 17, 1972 [54] DISTANCE RANGING SYSTEM [72] Inventor: William M. Weil, Southfield, Mich. Primary Exami',1er Ben-|amm Bwchelt Assistant Examiner-S. C. Buczmski gn et LTV Aerospace Corporation, Dallas, Attorney-H. C. Goldwire and D. W. Phillion Tex. 22 Filed: Dec. 18, 1970 [57] ABSTRACT A missile is traveling from its launch point towards an [21] Appl' 99429 intended target. A signal source, located near the launch point, radiates a train of pulses towards said 52 us. Cl. ..356/5, 356/28, 343/7 ED, missile and towards said g Each radiated Pulse is 343/7 244 313, 244 3 4 24 31 received by the missile as a pair of pulses, one 244/317; 244/3 19 received directly from the signal source and the other 511 Int. Cl. ..G01c 3/08, F41 g7/0O received after being reflected from the target [58] Field of Search ..244/3.13, 3.14, 3.16, 3.17, Puting means on the missile determines the difference 244/319; 343/7 ED 7 356/5, 28 in arrival times of the two pulses of each pair of pulses, and then, from successive ones of such determina- [56] References Cited tions, computes the distance between missile and tar get, missile velocity and acceleration, and finally the UNITED STATES PATENTS expected arrival time of the missile at the target; said computations being updated with the reception of 3,631,485 12/1971 Beazell, Jr. ..244/3.13 each Succeeding pair of pulsm 3,614,025 10/1971 Maillet ..244/3.16 3,527,167 9/1970 Morse ..343/7 PF 10 Claims, 10 Drawing Figures LOCATION OF REARWARD LOOKING s o U R -E RADIATED DETECTOR LOCATION OF SIGNAL MISSILE 15 f DETECTOR q I il TANK H l4 l LAUNCHING SS lLAJ E C TORY I DO l I Ch r d2 SHEET 2 UF 8 PATENTEDncI n 1912 PATENTEDum 17 I972 SHEET 5 OF 8 mm v n no P2300 P4 mmuwznmk mQmDOm x0040 WILLIAM M. WEIL INVENTOR M M ATTORNEY DISTANCE RANGING SYSTEM This invention relates generally to range detecting systems and more particularly to a range detecting system in which a missile contains means for receiving. and detecting pulses radiated thereto both directly from a remote pulse signal generating source and also after reflection of the radiated pulses from an intended target, in order to determine the range of the target from the missile. INTRODUCTION There are many prior art systems for directing a missile towards an intended target. Some of such systems employ a trough of radiant energy in which the missile rides. More specifically a beam of radiant energy is directed at the target and the missile is then caused to assume a trajectory along this beam. The missile contains detecting means which restrict the missile path within said beam. Other prior art structures flood the intended target with radiant energy and the missile then detects the radiant energy reflected from the target. By determining the maximum Doppler effect the missile can be guided towards the said intended target. Other prior art structures employ ambient light reflected from the target to guide the missile towards said target. However, none of the aforementioned prior art means provide means for determining when said missile is in close proximity to said target. A primary object of the present invention is to provide a ranging system which determines when a missile has arrived at the intended target. A second purpose of the invention is to provide a ranging system in which the missile is capable of detecting pulses radiated from a signal source at or near the launching site, both directly from said source and also indirectly after said pulses have been reflected from the intended target, to compute the missiles position with respect to said target. A third aim of the invention is to provide a ranging system in which the missile contains means for computing its position from radiated pulses received directly from a source located at the launching site, and also received indirectly after being reflected form the intended target. A fourth object of the invention is a ranging system in which the missile computes, in a continuously updating manner, the time interval remaining before said missile reaches the intended target. A fifth aim of the invention is a ranging system in which a pulse train is radiated, from a source near the launching site, directly to the launched missile and is also radiated to the intended target and then reflected back to said missile, and in which the said missile contains means for computing its instantaneous position with respect to said intended target, and its expected time of arrival at said target. A sixth purpose of the invention is the improvement of missile ranging systems generally. STATEMENT OF INVENTION In accordance with the invention there is provided a source of radiated pulses located near or at the launching site of the missile which is launched toward an intended target. Receiving and detecting means are located both at the forward end of the missile and at the rearward end of the missile, The detecting means at the rear end of the missile receives the pulses directly from the signal source while the detecting means at the front end of the missile receives the pulses reflected off the intended target. Computing means are provided within the missile to measure the time interval between each pulse received directly from the launching site and each corresponding pulse received after being reflected off the intended target. The foregoing time measurements are proportional to the distance of the missile from the target, and therefore, from successive ones of such time measurements, the instantaneous velocity of the missile can be determined. Further means are provided to compute the instantaneous acceleration of the missile from the changes in successive computations of instantaneous velocity. From each computed value of distance between missile and target, the velocity of the missile, and the accelerat ion of the missile, the computing means can then compute the instantaneous time interval required for the missile to reach' the target. Minimum time interval detecting means are provided on the missile to indicate when said missile has arrived at the intended target. STATEMENT OF DRAWINGS The abovementioned and other objects and features of the invention will be more fully understood from the following detailed description thereof when read in conjunction with the drawings in which: FIG. 1 is a pictorial diagram of the overall system showing the relationship between the launching site, the signal source, the missile and the intended target; FIG. 2 is a timing diagram showing the time relation between pulses received directly from the signal source and corresponding pulses reflected off the intended target and then received by the missile; FIG. 3 is another pictorial diagram similar to that of FIG. 1 but showing the signal source as a pulsed laser system; FIG. 4 is a diagram showing the general arrangement of the forward and rearward located detecting means on the missile and the relation thereof to the computer logic means contained in the missile; FIG. 5 is a generalized block diagram of the logic means of the entire system and corresponds to the single logic block of FIG. 4; FIGS. 6 and 6a together comprise a detailed diagram of the logic employed to compute the instantaneous velocity of the system; FIG. 6b shows how FIGS. 6 and 6a fit together; FIG. 7 is a detailed diagram of the logic employed to compute the instantaneous acceleration of the missile; and FIG. 8 is still another diagram showing the logic employed to compute the instantaneous time interval required for the missile to reach the target, and utilizing the velocity and acceleration computed by the logic diagrams of FIGS. 6, 6a, and 7. GENERAL DESCRIPTION Referring now to FIG. 1 the missile 12 is launched from a launching site 10 towards an intended target represented by tank 13, the trajectory of the missile being along the dotted line 14. A signal source 11 is constructed to radiate a directive beam which propogates directly to the missile 12 along path 15, and to the tank 13 along path 16. The directive beam can consist of a series of pulses spaced an equal time distance apart. It is apparent from FIG. 1 that a given pulse, propogating along path 15, will be received by the missile before the same to propogating along path 16 and reflected off the tank 13, will be received by the missile. Thus, as far as the missile is concerned, each single pulse radiated from source 11 is a pair of pulses, one pulse being received directly from source 11 and the other pulse being reflected off tank 13. The term pair of pulses will be used herein to denote such a pair of received pulses. The difference in the received times of the two pulses of each pair of pulses is indicative of the distance of the missile 12 from tank 13. More specifically, since the velocity of radiation of the pulses is known, and the time difference between reception of the pulses is measured by logic means on the missile, to be described later herein, the distance represented by said time difference can be measured. It is apparent from FIG. 1 that since the pulse directed at tank 13 must pass beyond missile 12 and then be reflected back to the missile from tank 13, the distance represented by said time difference is equal to twice the actual distance of missile 12 from tank 13. 4 Four pairs of pulses received by missile 12 are shown in the timing waveforms of FIG. 2. More specifically received pulses and 24 originate from a single pulse radiated from signal source 11 in FIG. 1. The pulse 20 is received directly by the rearward detector of missile 12 from signal source 11 along the path 15, and the pulse 24 is received at the forward detector of missile 12 along path 17 after being reflected off tank 13. PUlse 20 arrives at the missile at time t,,, and pulse 24 arrives at the missile at time The time differential between reception of pulses 20 and 24 is designated as A 1,. The distance of missile 12 from tank 13 can then be represented by the following expression. Where Vr is equal to the velocity of radiation of the pulses. Pulses 21 and 25 comprised the next occurring pair of time differentially received pulses. The pulses 22 and 26 comprise yet another pair of pulses received by the missile 12, and the pair of pulses 23 and 27 comprise a fourth pair of such pulses. It is to be noted that the time increment A A t A I, and A L, are progressively decreasing due to the fact that the missile is approaching its intended target, the tank 13 in FIG. 1. It can be seen then at the times t r t and t calculations of the distance between missile 12 and intended target 13 can be made. Specifically the distance between missile 12 and the target 13 at times r and are given by the following expressions; 2 r 2/ Exp.(2) 3 r 3/ Exp.(3)- 4 r q/ Exp. (4) Since the time between each of the pulses 24, 25, 26, and 27 is equal to t, the velocity of the missile can be obtained by computing the change in distance between missile 12 and target 13 during the time interval t. It is to be noted that the time intervals between the pulses 24, 25, 26 and 27 are not precisely equal to t since the reflected pulses will tend to move toward coincidence with the corresponding pulse in the waveform of FIG. 2a as the missile approaches very near to the target. However, since the pulses are traveling near the speed of light and the missile is traveling relatively very slowly, the time intervals A A t A 2 A 2,, are all extremely small compared to the time interval t. Thus for all practical purposes the time-intervals between the reflected pulses 24, 25, 26 and 27 are all equal to t. Consequently at time i the velocity of missile 12 can be computed by subtracting the distance S between the missile and the target at time t from the distance S, between the missile and the target at time t and dividing said difference by t, as shown in the following expression. a . 2 1 2/ Exp.(5) Similarlyat times t and t the velocity of the missile can be computed and represented by the following two expressions. the computations of the velocities V and V The mathematical expression for the accelerations a and a are as follows: From the foregoing discussion it can be seen that computations of the distance of the missile from the target, the velocity of said missile with respect to said target and the acceleration of said missile with respect to said target, are made at every time interval t. From these various computations the length of time t required for the missile to reach the target, based on the calculated parameter and assuming that such parameters will remain constant, is computed. It is to be noted specifically, however, that said parameters are recalculated each time a pair of pulses is received by the missile so that the time interval required for the missile to reach the target is constantly updated. The logic for computing distance, velocity and acceleration is shown generally in FIG. 5, which will be discussed later herein. The radiated pulses employed in the system may be in the form of a pulsed laser beam as indicated generally in FIG. 3. A pulse laser source 20 supplies a pulsed laser beam to a beam splitter 21 which functions to supply a portion of the beam directly to the tank 13' along a path 16', from whence it is reflected back to the front end of missile 12' via path 17'. Exp. (8) The pulse laser beam also follows a path through the prism 22, after being reflected off the beam splitter 21, The said prism 22 redirects the beam through lens 23 and then along a path to the rear end of missile 12'. FIG. 4 is a very generalized block diagram of the means for'detecting and processing the received pulses. MOre specifically, in FIG. 4, the lenses 140 and 141 receive the pulsed laser beam at the rear end and the front end of the missile, respectively. The pulses are then supplied to a logic means 142 which computes the distance between missile and target, velocity, acceleration and expected time of arrival of missile at the target. A more detailed but still quite general diagram of the "logic as shown in FIG. 5 The pulses received at the front end of the missile are received on input lead 153 and the pulses received at the rear end of the missile are supplied to the logic via input lead 154. In the logic of FIG. 5 the block 146 functions to compute the distance between the missile and the target after reception of each pair of pulses. The logic within the block 147 is responsive to successively determined computed distances to compute the velocity of the missile at the end of each received pair of pulses. The logic within block 148 functions to respond to consecutive computations of velocity to determine acceleration of the missile after each received pair of pulses. The determined distance S, the computed velocity V, and the computed acceleration a, from blocks 146, 147, and 148 are then supplied to logic means 149 which functions to determine the time interval t required for the missile to reach the target, based on the latest computations of distance, velocity and acceleration. When said time interval I is equal to a time reference interval t which is stored in a logic block 151, and which is compared with the computed time interval t in time comparator 150, then an event signal is generated by said time comparator 150 and supplied to an output terminal 152. In the case were the missile and target are military in nature, the missile can be caused to detonate upon the occurrence of the event signal, thus presumably destroying the target (tank 13 in FIG. 1). As can be seen from FIG. 5 each of the major blocks 146 through 150 has an input labeled clock pulse thereto. The general purpose of such clock pulses is to step the data along from one logic block to another as the operation within each logic block is completed. In FIG. 6 there is shown a more detailed logic diagram of the blocks 146 and 147 of FIG. 5. More specifically in FIG. 6 the flip-flop 30, the NAND gate 31 and the counter 33 comprise the logic elements included in block 146 of FIG. 5. The logic within the dotted block 52 is a more detailed logic diagram of the timing means 156 of FIG. 5. The remainder of FIG. 6 is a more detailed logic diagram of the block 147 of FIG. 5. Generally speaking the pair of pulses, 22 and 26, function to set and reset flip-flop 30 to permit a number of pulses from clock source 60 to enter counter 33; said number of pulses being proportional to the time differential between the two pulses 22 and 26, and representing the distance S. The subtraction of a currently determined distance S;, from a previously determined distance S is accomplished by means of the registers 35 and 37, the twos complement logic 38, and a binary full adder 39. The subtrahend S is stored in register 37 and the minuend S is stored in register 35. After the subtraction process is completed, S is transferred to register 37 and becomes a subtrahend for the next subtract operation. To perform the divide-by-t function, called for in block 147 of FIG. 5, there is provided the logic within block 54 of FIG. 6a. Such logic includes storage register 40 in which the dividend is stored. The counter 50 and the comparator 51 function to provide the divisor. The output of counter 49 functions to provide the quotient, which is equal to V as indicated on the output terminal 52 of counter 49. The specific operation ofthe division logic will be discussedin detail later herein. The timing means for the entire system is contained within the dotted block 52 and comprises a main clock pulse source 60 from which all timing in the system is derived. More specifically, clock source 60 provides clock pulses through NAND gate 31 to counter 33 to provide an indication of computed distance. The clock source 60 also provides pulses through NAND gate 48, when flip-flop 58 is set, to perform the division function, as will be described later herein. The clock pulse also supplies shift pulses through NAND gate 68 to the two shift registers 35 and 37 to initiate the subtract function, after two consecutive distance computations have been stored in the two registers 35 and 37. The sequence of the foregoing operations is controlled by the l l outputs, 0 through 10, of counter 66 which responds to the output of divider 61 to increment 1 count for each 512 clock pulses. For example, at the count of 1 of counter 66, the NAND gate 34 becomes conductive to pass the contents of counter 33, which represents distance, into storage register 35. At the count of 2 of counter 66, the flip-flop circuit 69 is set to permit the output from clock pulse 60 to pass through NAND gate 68 and into shift registers 35 and 37 to cause the data therein to shift serially therefrom and into the adder 39 to perform the subtract function. At the count of 3 of counter 66, flip-flop 58 is set to energize NAND gate 48 and initiate the division function. Referring now to FIG. 7 there is shown a more detailed block diagram of the block 148 of FIG. 5. The diagramof FIG. 7 is quite similar to that of FIG. 6 in that a subtraction operation is performed between two binary quantities V and V followed by a division function in which the results of the subtract operation are divided by the time t to produce the acceleration a. In FIG. 7 registers 82 and 83 are parallel input in-parallel out, and serial in-serial out registers of the same general type as registers 35 and 37 of FIG. 6. A twos complement function 84 is provided at the serial output of register 83 to permit the subtract operation to be done in adder 85 in a manner similar to that of the structure of FIG. 6. The currently computed velocity V is stored in register 82 and the previously computed velocity V is stored in register 83. The computed difference in velocity is supplied to a dividing means 81 comprising a storage register 86 which stores the dividend V V The divisor is, in effect supplied by means of counter 88 and comparator 87, and functions in a manner similar to the dividing function within the dotted block 54 of FIG. 6. The quotient of the dividing function 81 of FIG. 7 appears at the output 100 of the counter 89 and represents the acceleration, a. The output of counter 66 of FIG. 6 is employed to time the various operational steps of FIG. 7 in much'the same manner as such output control the operational steps of FIG. 6. More specifically the count of 4 of counter 66 functions via lead 98 to set flip-flop 97 to supply shift pulses to registers 82 and 83 to initiate the subtract operation within block 80. The count of 5 sets flip-flop 90 to initiate the division operation within logic block 81. The count of 6 functions to transfer to contents of register 82 into the register 83 where it will be employed as a divisor for the next subsequent occurring computation of the acceleration a. In FIG. 8 there is shown a detailed logic diagram of the logic block 149 of FIG. 4. As can beseen from FIG. 8 each of the blocks performs a single arithmetic function. For example the multiplier blocks 110 and 111 function respectively to compute V 2 and the product 2as. The adder 114 adds together the products of the said blocks 110 and 111. The square root function 118 then determines the square root of the output of adder 114. Another adder 123 sums the output of the square root function 118 plus V The output from adder 123 is then supplied to divider 127 which divides said output by the acceleration a. As will be discussed in more detail later the output of divider 127- is equal to time interval t needed for the missile to reach the target. Said time interval 1, is computed at the end of each pair ofinput pulses. Since the missile is moving towards the target the computed time I, becomes increasingly less in value, i.e., decreases with each computation thereoffA time comparator 133 functions to compare the computed time t from divider 127 with a time 2,, generated in time reference 130, and when said time intervals are equal produces an event signal on output lead 28 which can function, for example, to detonate the missile as described in connection with FIG. 1. OPERATION OF THE SYSTEM A detailed description of the operation of the system will now be set forth utilizing the timing waveforms of FIG. 2. In FIG. 2 the train of pulses 20, 21, 22 and 23 are periodically received by the missile at substantially equal time intervals t. It is to be understood that such pulses through 23 originate at the signal source 1 1 in FIG. 1 at equal time intervals t. The reception of said pulses by the missile at equal time intervals t is predicated upon the assumption that the missile velocity remains constant. However, even if the missile velocity should vary, the time spacing between the received pulses, for all practical purposes, is still equal to t since the speed of the missile is very small compared to the propagation velocity of the pulses. Each of the transmitted pulses is also directed at a target such as tank 13 and then is reflected off the target along path 17 and back to the front end of the missile. Such reflected pulses are represented in waveform b of FIG. 2. Specifically the received reflected pulses 24, 25, 26 and 27 correspond respectively to the pulses 20, 21, 22 and 23, which are directly received by missile 12. The time intervals A l A A t;,, A t, then represent the distance of the missile from the target at the time each pair of pulses is received by the missile. Such distances are represented by the four expression for S S S and S, as shown in FIG. 2. The specific logic by which the A t time intervals can be converted into a train of pulses representing distance is best shown by the logic of FIG. 6. More specifically assume that the pair of pulses 22 and 26 are received by the missile,separated by a time interval A t The first received pulse 22 functions to set flip-flop 30, thereby opening NAND gate 31 and permitting the output from clock pulse source to pass therethrough and into counter 33. A time interval later, 66 t the pulse 26, reflected off the target, arrives at the front end of the missile and functions to reset flipflop 30, thereby closing NAND gate 31 to cut off the supply of clock pulse to counter 33. The counter 33 will now contain a count which is proportional to the time interval A t It is now necessary to transfer the count contained in counter 33 to shift register 35 so that the subtract operation can be initiated Such transfer are'accomplished in the following manner. The system is designed so that the count contained in counter 33 is always substantially less than a predetermined number, which in the present embodiment of the invention is assumed to be 512. Consequently, the output of the divide-by-512 circuit 61 will produce an output pulse only after the count in counter 33 is complete. Each the output pulses from divide circuit 61 passes through NAND gate 62 to cause the counter 66 to increment by one. It should be noted that while the output pulses from divide circuit 61 are continuous they will only enter the counter 66 when flip-flop circuit 63 is set. The setting of flip-flop 63 is effected by the occurrence of the corresponding received reflected pulse, such as pulse 26 of FIG. 2. As will be discussed later the flip-flop 63 is reset at the end of a cycle of computations and before the reception by the missile of the next pair of pulses. It is also to be noted that the counter 66 is reset to 0 at the end of the computation cycle initiatedby the reception of each pair of pulses, in preparation for the computations to be made at the reception of the next pair of pulses. Thus the first output pulsefrom divider 61, after the setting of flip-flop 63, will advance the counter 66 from a count of 0 to a count of 1, at which time the counter 33'will contain its distance representing count. The count of 1 output of counter 66 is supplied to the input of NAND gate 34 and functions to transfer the count in the counter 33 to the register 35 which consists of N stages, where N is equal to 9 in the preferred form of the invention being described herein It is assumed that shift register 37, which also has N stages, contains the count representing the A t time interval determined by the previous pair of received pulses 21 and 25 of FIG. 2. equal to N. The clock source supplied to the shift inputs of registers 35 and 37 functions to shift the contents of said registers therefrom in a serial manner and into the adder 39, More specifically the contents of the shift register 35 is shifted directly into the adder 39 and the contents of the register 37 is shifted into adder 39 through twos complement 38. As is well known in the art, the use of the twos com plernent logic 38 and the adder 39 function to subtract the contents of register 37 from the contents of register 35. Thus when register 35 contains a count representing a distance S and resister 37 contains a count representing a distance of the output of adder 39 represents the difference S S Such difference is supplied to a third shift register 40 in serial manner. It is to be noted that the capacity of counter 73 is equal to the number of stages in registers 35 and 37. Consequently when counter 73 counts to its capacity N and then recycles to 0, the flip-flop 69 is reset via the count of lead 72. It is to noted that the output of the shift register 35 has a feedback connection 29 which functions to recirculated the words shifted serially therefrom back into the input of the register 35. Thus upon completion of the shift function the original word remains in register 35. Next the difference function S S stored in register 40 is divided by the time t, as called for by the block 147 of FIG. 5. Such division is performed in the follow ing manner. At the count of 3 of counter 66, the flipflop 58 is set to permit clock pulses from clock pulse source 60 to pas through NAND gate 48 and into the time representing counter 49, The clock pulses are also supplied through NAND gate 48 into counter 50. The said counter 50 has a capacity which is at least equal to the greatest number to be stored in the register 40. When said counter 50 reaches a count which is equal to the number stored in register 40 the comparator 51 function to produce an output signal on its output terminal 47, which output signal performs several functions. Specifically said output signal resets flip-flop 58 to close NAND gate 48 and thereby cut off the supply of clock pulses to counter 49. Also said output from comparator 51 functions to reset to 0 the shift register 40, the counter 50, and the counter 49. Referring more particularly to counter 49, the function thereof is to produce at its output terminal 52', an output signal proportional to missile velocity. More specifically the counter 49 has a count capacity which is proportional to the time interval t as shown in block 147 of FIG. 5. Each time the counter 49 fills to its capacity it produces a signal on its output terminal 52'. The recycling of counter 49 will continue until the count in counter 50 is equal to the binary word in shift register 40 and the comparator 51 produces an output signal on its output terminal 47, as discussed above. The number of recyclings of the counter 49 is indicated by the number of output pulses on its output terminal 52 which in turn is directly proportional to the missile velocity V. It is to be noted that the contents of register 35 are transferred to the register 37 by means of a count of 3 input signal supplied to lead 36 of register 35 Thus the distance 5;, will be stored in the register 37 so that when the next distance 8,, is computed and stored in the register 35, the next subtraction function 8, 5,, can be performed. Referring now to FIG. 5 it can be seen that the velocity indicating signal V at the output terminal 52 of logic block 147 is supplied to the logic block 148 where the acceleration is computed. As discussed above the acceleration is computed by taking the difference between two consecutively computed velocities and dividing the difference by the time interval between said velocity computations. The detailed logic em ployed to compute acceleration is shown in FIG. 7 and is quite similar to the logic of FIG. 6 employed to compute velocity. In FIG. 7 it is assumed that the velocity V has been previously computed and is stored in the shift register 83, The velocity V has just been determined by the logic of FIG. 6 and stored in shift register 82 via lead 52'. It is to be understood that the completion of the computation of velocity occurs .a finite time after the reception of the reflected pulse. Such finite time is required in order to perform the computations Thus in FIG. 2 the computation of V occurred a certain interval of time after the reception by the missile of reflected pulse 25, and the computation of the velocity V occurs a finite time after the reception of reflected pulse 26. The composition of the computation of the velocities V and V is indicated as occuring at the the count of 3 of counter 66 in the waveform of FIG. 2, and specifically as occurring at times t and t,,. Counter 66 of FIG. 6 is also employed to control the operational steps of the logic of FIG. 7. More specifically the counter 66 continues to count after the velocity computation has been completed and at the count of 4 will function to set flip-flop 97 of FIG. 7 via input lead 98. The setting of flip-flop 97 opens NAND gate 95 to permit the output from clock pulse source 60 to be supplied to the shift inputs of shift registers 82 and 83, and also to the counter 96. Both of the shift registers 82 and 83 have N stages therein, which is adequate to indicate the range of velocities that will be computed during the tracking of a missile from launch point to target. The counter 96 has a capacity of N counts and performs a function similar to that of counter 73 of FIG. 6a. More specifically counter 96 functions to reset flipflop 97 after the N bit word stored in registers 82 and 83 have been serially transferred therefrom into adder 85, thereby terminating the flow of shift pulses to registers 82 and 83. As in the case of the logic of FIG. 6 the adder and the twos complement function 84 of FIG. 7 produce a subtract function between the contents of register 83 and register 82. The resulting difference V V is supplied from adder 85 into shift register 86 as shown in FIG. 7. Subsequently at the count of 5 of counter 66, flip-flop is set to open NAND gate 92 and thereby permit the output of clock pulse source 60 to flow into time indicating counter 89 and also into counter 88. The counter 88 corresponds to the counter 50 of FIG. 6. When the count in counter 88 reaches the value of the number stored in register 86 the comparator 87 will respond to produce an output signal on its output terminal 94. Said output signal will reset to 0 the shift register 86, the counter 88, the counter 89, and will also reset flip-flop 90 to block any further flow of clock pulses into counter 89 or counter 88. Thus the division function is completed. The counter 89 corresponds to the counter 49 of FIG. 6. More specifically the counter 89 represents the time interval t and will recycle a number of times during the time required for the counter 88 to reach a value equal to the number contained in shift register 86, thus in effect dividing the contents of register 86 by the count capacity of counter 89. Each time the counter 89 fills to capacity it supplies an output pulse to its output terminal 100. The number of such output pulses is representative of the acceleration a as defined in block 148 of FIG. 5. As can be seen from FIG. 2 the acceleration a, computed from the velocities V and V is defined as acceleration a and is completed at the time 2?. in the waveform of FIG. 2. Thus at time t the distance S the velocity V and the acceleration a have been computed, so that the estimated time of arrival of the missile at the target can be computed. More specifically the measured distance from missile to target S can be expressed in terms of the measured velocity and acceleration in accordance with the following expression: S =V2a t +V t Exp.(l) It can be seen that the expression set forth above is a quadratic expression in t having the following solution: Expression 11 is the relationship which must be solved by the logic within the block 149 of FIG. 5 to determine the expected time of arrival of the missile at the target. Reference is made to the logic of FIG. 8 which will perform the various arithmetic operations required in solving expression 11. The velocity V is supplied to multiplier 110 which functions to square the said velocity V The acceleration a and the measured distance S are supplied to multiplier 111 via input leads 100' and 56' from the logic of FIGS. 6 and 7 to obtain the product 2a S At the count of 6 of counter 66 of FIG. 6, NAND gates 112 and 113 become conductive to pass the products of multipliers 110 and 111 into adder 114, which produces the following sum. At the count of 7, NAND gate 117 is opened to pass the sum computed in adder 114 to the square root function 118 which computes the square root of said sum as shown in the following expression. Subsequently at the count of 8 of counter 66 of FIG. 6, NAND gates 120 and 121 are made conductive to pass the output of the square root function 118, and also the computed velocity V to adder 123 which adds said two quantities together to obtain the follow- At the count of 10 of counter 66,'NAND gates 128 and 131 are caused to become conductive to supply the computed time t from divider 127, and also the time interval t from time reference 130, to the time comparator 133. When said time intervals are equal or when the time interval t from divider 127 is less than the time interval t from time reference 130, the said time comparator 128 will produce an event signal on its output lead 28'. Such event signal can be .employed to detonate the missile or to perform any other desired nstiqa- It is to be understood that the form of the invention shown and described herein is but a preferred embodiment thereof and that various changes may be made therein and various other arrangements of logic be employed, without departing from the spirit or scope of h ny t What is claimed is: 1. A missile ranging system for determining the position of a missile which is traveling towards an intended target and comprising: a signal source for radiating a train of electromagnetic pulses; 1 each radiated pulse being propagated directly to said missile and also to said missile after being reflected off said intended target to form a pair of pulses; .first receiving means positioned on said missile to receive and detect said train of radiated pulses directly from said signal source; second receiving means positioned on said missile to receive and detect said train of radiated pulses after said pulses have been reflected off said intended target; computing means constructed to measure the time difference in the arrival times of the two pulses forming each pair of pulses to compute, in a continuously updating manner, the time of arrival of saiqmissilq sssa nt nsdiarsst- 2. A missile ranging system in accordance with claim 1 in which; said signal source is a pulsed laser signal source; and said train of radiated electromagnetic pulses are laser Ba s... 3. A missile ranging system in accordance with claim 1 in which: said computing means is further constructed to determine the increment of distance traveled between each successive pair of received pulses from said signal source and to compute velocity and acceleration from successive measurements of sai increm nts of sta 4. A missile ranging system in accordance with claim 3 in which; said signal source is a pulsed laser signal source; and said train of radiated electromagnetic pulses are laser pulses. 5. A missile ranging system in accordance with claim 1 .in which said computing means comprises: distance determining means for determining the distance of the missile from the intended target from the difference in arrival times at said missile of the two pulses of each pair of pulses; velocity determining means constructed to compute the differences between successive measurements of distances from said missile to said target to determine the velocity vector of said missile towards said target; acceleration determining means constructed to compare successive determinations of velocity of said missile to determine the acceleration vector of said missile towards said target; and logic means responsive to the determined distance between said missile and intended target, and to the computed velocity and acceleration of said missile to determine the time interval required for said missile to reach said intended target. 6. A ranging system for determining the estimated time of arrival of a body with respect to an object destination towards which said body is moving and comprising: a signal source located behind said moving body with respect to its forward movement and constructed to radiate a continuous train of periodically spaced pulses towards said moving body and also towards said object destination; detecting means contained on said moving body for detecting each pair of pulses received from each radiated pulse, one pulse of said pair being received directly from said signal source and the other pulse of said pair being received after reflec tion off said object destination; means for measuring the time intervals between the pulses of each pair of pulses received by said moving body; computing means on said moving body constructed and acceleration from successivemeasurements of a said increments of distance. 9. A missile ranging system in accordance with claim 8 in which; said signal source is a pulsed laser signal source; and said train of radiated pulses are laser pulses. 10. A missile ranging system in accordance with claim 6 in which said computing means comprises: distance determining means for determining the distance of the missile from the intended target from the difference in arrival times at said missile of the two pulses of each pair of pulses; velocity determining means constructed to compute the differences between successive measurements of distances from said missile to said target to determine the velocity vector of said missile towards said target; acceleration determining means constructed to compare successive determinations of velocity of said missile to determine the acceleration vector of said missile towards said target; and logic means responsive to the determined distance between said missile and intended target, and to the computed velocity and acceleration of said missile to determine the time interval required for said missile to reach said intended target. Referenced by
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