# Патент USA US3020556

код для вставкиFeb. 6, 1962 MJLOSHER 3,020,545 RADIO NAVIGATION SYSTEM Filed Feb. 12, 1958 5 Sheets-Sheet 1 Inventor MORTON £05709? By Attorney Feb. 6, 1962 M. LOSHER 3,020,545 RADIO NAVIGATION SYSTEM Filed Feb. 12, 1958 5 Sheets-Sheet 3 _ M k .+ \ . m m u a f AM 02|m|~ HO._ lunb /l‘ A QM“s 5 BM J _ A4 M P. p.54 _ p/_. H -[iv0mlimL _ F .o 0mm V _ M5 w_ |—\ C A FM _ _r we __ _ we pm. __ + _r0 /10_ MR n i _i:.. P M a: 4 pm pa12_ n L+ _ v/ _6//mx _.s_ RWP _ 8 _L_ UA MM _ * _ ,3 m _ |_Laa|.1| j m My % a 0 mp. n{0i_i1| LaWéo/wYl _Q0’ 5 m p P. M NA _ + Inventor M0197’0N LOS/{fR By 6‘ A Horn ey . Feb. 6, 1962 M. LOSHER 3,020,545 RADIO NAVIGATION SYSTEM Filed Feb. 12, 1958 5 Sheets-Sheet 5 Byazeizfwww Attorney es V I aszasis fPatented ,Feb. 6, 19.62 i , the instantaneous position of ‘said receiver relative to a 3,020,545 . known point in response to signals ‘from said Loran re RADIG NAVHGATEGN SYSTEM ‘Morton ‘Losher, Bergen?eld, 'N..l., assignor to ‘Interna .tioual ‘Telephone and Telegraph =Corporation, Nutley, N1, a corporation of Maryland Filed Feb. 12, 1958, Ser. No. 714,751 6 Claims. (Cl. 343-493) ceiver, thereby minimizing the error .in position intro duced by thecraftls velocity. , Another object of this invention is to provide an analog pes'itioncomputer for use with a Loran receiver on a craft and responsive to signals therefrom and ‘manual input signals, to compute said craftls position relative to .a This invention relates to radio navigation systems and known point preferablynear the craft. particularly to systems utilizing the time dilierence in the 10 "It is a feature of ‘this invention to employ an analog propagation of radio energy from synchronized beacons computer responsive to hyper'boliccoord-inate signals from to establish distances. a ,Loran receiver-indicative of a craft’s position, hyper In the past numerous radio navigation systems have ‘bolic coordinate signals indicative of aknown position been employed which utilize the time dilference in propa and signals indicative of the distance \frornsaid known gation of radio wave energy, such as pulses emanating position to the Loran transmitting vbeacons .to- compute from beacons at a known position and detected by~equip~ said craft’s position relative to said knownposition. ment on a craft to establish the position of the craft rela Another feature of this invention is to provide analog tive to the vbeacons. vOne such prior system commonly integrating means to generate forcing ‘function signals called Loran employs pairs of synchronized ground indicative of the Cartesian coordinates of said .craft’s posi beacons, each beacon of a pair transmitting radio wave tion relative to said known, point which may .befed to pulses vat-the same rate with precisely ?xed time relations tbetweengiven pulses from each of the beacons of a pair. Therpulse repetition rate of the beacons in ‘a pair serves analog quadraticxequation solvers yielding signals indica tive of the differences between the craft’s distance to each Loran beacon and the distance from said known point to each Loran beacon and to compare these signals indica‘ to identify the pair of beacons. in operation the pulses .from two or more pairs of such beacons are radiated to tive of differences with 'hyperboliccoordinate signals in ‘a craft or vehicle having radio receiving equipment where dicative of the craft’s position and the position of said an operator by means of this equipment and otherequip known point yielding signals to control said analog inte ment establishes two different pulse time differences, one grating means and, thus, control said forcing ‘function between the pulses from a ?rst pair of beacons and the signals indicative of said Cartesian coordinates. other between the pulsestrom a second pair of beacons. 30 Another feature is to provide two separate analog inte :Each time difference represents a locus of points forming grating means to p-roducesaid Cartesian coordinate signals .a hyperbolic line one special map; thus, the point on they and to provide three separate analog means to solve three special map where the line representative of the time dif different quadratic equations. ‘ ference between received pulses from a ?rst pair of Another feature is to provide means to adjust scale so beacons and the line representative of the time difference that ‘the Cartesian coordinate signal output may signify between pulses from a second pair ‘of beacons cross, indi cates the position of the craft or vehicle. more than one positional displacement of the craft relative to said known position. iOne difficulty with the prior radio navigation systems Another feature is .toyprovide manual input controls to and the Loran systememploying special maps is that an generate signals indicative of the hyperbolic coordinates operator must obtain information from the receiver, then 40 of said known point relative to said Loran beacons, the subsequently transpose this information to a coordinate distance from said known point toeach Loran beacon and system on a special map to locate his own position. This the bearing of said known point to each Loran beacon so that during the course of navigation, said known point process of obtaining information and transposing it is time consuming, and if the operator’s craft is moving at an appreciable speed, its position will have changed ap preciably between the time the information is ‘received may be frequently changed manually. Other and further objects and features of this invention will ‘be more apparent from the following speci?c descrip tion taken in conjunction with the ?gures,_,in which: . and obtained from the receiver and ‘the time it is ‘trans posed to yield ,position from the special map. Thus the FIG. '1 is a map view of a Loran hyperbolic coordinate signal ?eld from which the geometry and equations com operator is not able to establish the instantaneous position of his craft on the map within the accuracy inherent to the Loran receiver. puted by the positioncomputermay be better understood; Therefore, the primary object of this invention is to provide an improved radio navigation system. had; FIG. 2 is a block diagram of the position computer item which a general understanding of its operation may be Another object is to provide a navigation system rem ploying a position computer responsive to signals indica tive of a craft’s position relative to a ?rst known position and responsive also to signals indicative of a second known positionrelative to said ‘?rst known position-to thereby compute :the craft’s position relative to said-second-known position. Another objectof this invention is to ‘provide a naviga tion system responsive -.to'signals'indicative-of a craftis position relative to a knownposition to establishtthe craftls ‘FIGS. 3 and 3A are a detail ‘block diagram and elec 55 trical schematic of the position computer; and FIG. 4 is a detail schematic of one of the three quad-p ratic equation solvers shown in FIG. 3A. Referring ?rst to FIG. 1, there are shown three Loran beacons, a master M and slaves S1 and S2, transmitting signals from which two .sets of hyperbolic coordinate lines may ‘be established. One set of hyperbolic coordi nate lines which are established by signals from beacons M and S1 are shown as broken lines, while the other set position relative to :another ‘.known position, which is of hyperbolic coordinate :lines established bysignals from preferably nearer to thecraft, thereby permitting the sys 65 beacons M and S2.are shown as solid lines. tem to deal with ‘and compute shorter, distances resulting It‘ a vehicle containing a Loran receiver is located at in more accurately locating the position of said craft. point P within range of tthe beacons M, S1, and Spat ,Anotherobject .of this invention is to provide a position distances Dm', D1’ and D2’ vfrom the beacons, respective computer for use with a LLoran receiver to establish the ly, and it is desired to ?nd the coordinates Xp and YD position ;of ‘the receiver. relative to. a known point. 70 of point P relative to a known point at O and the-dis Another object of invention is to provide a com puter for use with a Loran receiver to rapidly establish l i Hi i tances Dm, D1 and D2 of point 0 from beaconsM, S1, and S2, respectively, are accurately known, as well asithe ' 3,020,545 and by similar analysis the following can be shown: angles ¢m, (p1, and p2, and the exact hyperbolic coordi mates of point 0 are known, then there is sufficient in formation available to compute Xp and Yp thereby lo cating the craft’s position at P relative to the known point 0 which may be at the center of a small area map 1. It should be noted that the positions of the Loran beacons as shown in FIG. 1 are arbitrary and the tri and solving the above equations for AD2, AD,,, and ADl, the following quadratic equations are obtained: angle they form is not necessarily a right triangle and, furthermore, the known point 0 is well outside the tri' 10 angle formed by the beacon positions. The arbitrary lo cation of the beacons and point 0, shown in FIG. 1, is purposely employed to show the versatility of the em bodiment of the navigation computer herein described. It might be preferable from the standpoint of accuracy that the beacon positions form a right triangle and that ‘small map 1 be smaller than shown and located within (5) the right triangle formed by the beacons. In order to show that there is enough information AD,,, z 21),, 1 available as outlined in the above paragraph to compute Xp and Yp, consider the following strict derivation of quadratic equations in terms‘of the precisely known fac Referring next to FIG. 2, there is shown a general block diagram of the position computer. The quadratic tors outlined in the paragragh above and in terms of XI, equation solvers 2 receive signals from the manual in~ put controls 3 which are indicative of the position of point 0 shown in FIG. 1 relative to the position of the beacons M, S1, and S2, also shown in FIG. 1. Quad ratic equation solvers 2 are also fed signals indicative of and Yp yielding the factors ADm, ADI, and ADZ which are equivalent by de?nition to the following: Xp, Yp, and Xpz-l-Yp2 from error integrating and squar ing circuit 4 so that the factors ADm, AD1, and ADZ may be computed by quadratic equation solvers 2. Signals Let up and 51, be the time differences of radio pulses detected from beacons S2 and M and S1 and M, respec tively by the Loran receiver in the craft at P; therefore: indicative of ADl and ADm are fed to comparing circuit 5, while signals indicative of ADZ and ADm are fed to comparing circuit 6. Comparing circuit 5 is also fed signals indicative of air-4x0, While comparing circuit 6 is also fed signals indicative of tip-{30. These compar~ ing circuits 5 and 6 compute Equations 1 and 2, respec tively, yielding output signals indicative of 40 and ?;,—,60—AD2+ADm, respectively. and consider triangle (APSZ). It follows by the Pytha gorean theorem that: antennas 12. (AP)2=(XI,~D2 cos 11:2)? since cos ¢2 is negative and: (S2B)=D2 Sin ¢2 The factors nip-a0 are computed by comparing means 7 in response to do from manual input controls 3 and up from Loran receiver 8, while the factor [Sp-Bo is obtained from com paring means 9 in response to ,60 from manual input controls 3 and pp from Loran receiver 8. The Loran receiver 8 receives signals via antenna 10 which are transmitted from the Loran beacon transmitters 11 via The action of error circuit 4 in response 50 to error signals from circuits 5 and 6 is to vary the out- - put signals indicative of Xp, Yp, and Xp2+Yp2 fed to quadratic equation solvers 2 until said solvers yield sig nals indicative of ADm, ADl, and AD2 which when com pared in circuits 5 and 6 with the 0c and it signals yield zero error signals. In other words, error circuit 4 varies therefore: (Dz')2= (D2-i-AD2)2 therefore: the values of XI) and YB until the error signals from cir~ cuits 5 and 6 are nulled. The Xp and Y1, indicators, 13 and 14 respectively, coupled to circuit 4, are provided to indicate the coordinates of the craft’s position relative 60 to known point 0. Referring next to FIGS. 3 and 3A, there is shown a detail diagram of the position computer. In operation signals from beacons M, S1, and S2 are detected by antenna 10 and fed to Loran receiver 8 wherein up and tip signals are computed as shaft rotations and coupled to synchros 15 and 15a, respectively, which in turn energize synchros 16 and 17, respectively, whose output and in this equation: shaft positions are applied to differential gear boxes 18 and 19, respectively. Shaft rotations 20 and 21 from 70 manual controls 3, indicative of a0 and 50, respectively, are applied to gear boxes 18 and 19, respectively, which in turn drive potentiometers 22 and 23, respectively. Thus, the voltage output from potentiometer 22 is equiva lent to tap-a0, while the voltage output from potenti ometer 23 is equivalent to ?p—,80. 3,020,545 6 Meanwhileshaft rotations 24 through 29 are fed from tentiometer 65 is proportional to XI,2 and the voltage in arm 67 of potentiometer 69 is proportional to Ypg. Arms 63 and 67 ,feed voltage signals to summing ampli input controls 3 to potentiometers 30 through 35. These potentiometers, 36 through 35, are energized by signals from double pole switches 36 through 41, each of which ?er 52 wherein XD2 and Y;,2 are added and their sum is positioned from manual controls 3. The poles of then fed to each of quadratic equation solvers 46, 47, switches 37, 39, and 41 are energized by signals indica and 48. The outputs of ampli?ersltd and 45 are each tive of +Yp or —Y,, from ampli?ers 44 and 45, respec fed to one pole or the other of the polesof double pole tively, in the manner shown, while the poles of switches switches 37, 3?, and 41, while the outputs of ampli?ers 36, 38, and 4% are energized by signals indicative of 42 and 43 are each fed to one or the other of the poles -|-Xp or ~Xp from ampli?ers 42 and 43, respectively. 10 of double pole switches 36, 38, and 4%. The output of Thus the ouput voltages from potentiometers 34) through ampli?ers 42, and 44 also provide signals to Xp indicator 35 provide the factors Xp cos¢ and Yp sin ¢, of the '13 and Yp indicator 14, respectively. proper sign to their appropriate quadratic equation solv The ?eld coils of servomotors '66 and 61 are ener ers 46, 47, and 43, which solve Equations 3, 4, and 5, gized by signals from double pole double throw switch respectively. Mechanical couplings 49, 5tl,land 51 feed ~ 76' so that depending upon the position of switch 76, a shaft rotations proportional to given signal to each servomotor from its associated servo ampli?er will cause the motor to rotate in one direction or the other. Double pole double throw switch 70 isv 1 7 and '27); positioned by mechanical linkage 71, which is operated to quadratic .solvers 46, 47, and 48, respectively. Each quadratic equation solver is also fed a signal propor tional to Xpz-l-Yp2 from summing ampli?er 52 via lines 52a. Thus all the values required to solve, Equations 3, .4, and 5 for ADI, AD2, and ADm are fed to quadratic 25 equation solvers 46, 47, and 48, respectively. The outputs from the quadratic equation solvers 4-5 and 47, which are indicative of AD1 and A132, respectively, from manual input controls 3 depending upon the op eration of the position computer as evidenced by XD and Yp indicators 13 and 14, respectively. if these indi cators present values of XI, and Yp which appear un stable or change considerably more than is expected from the motion of the Loran receiver when switch 70 is in one position, then switch 78 should be positioned in its ‘other position. Potentiometers 30 and 31, 32 and?f’l, and 34 and 35 are mechanically driven from manual are fed to double pole double throw switch 53 which is input controls 3 to yield the sine or cosine function of positioned by mechanical coupling 54 from manual input 30 angles p1, ¢2, and ¢m, respectively, by mechanical cou controls 3. Thus the outputs from quadratic equation plings 24 to 29, respectively, as shown in FIG. 3A. solvers 46 and 47 are each fed to different ones of sum Since the angles ¢1, ¢2, and qbm are known (see FIG. 1) ming networks 55 and 56 of servo ampli?ers 57 and 58, when the Loran receiver 8 is located in any particular respectively, depending upon the position of switch 53. map 1 having its center at known point 0, the sine and Manual coupling 54 also positions double pole double cosine functionsof angles ¢1, 4&2, and rpm are’also known throw switch 59 applying the outputs from the (mp-a0) and may be inserted by the appropriate mechanical cou potentiometer 22 and the (?p—,8o) potentiometer 23 to plings 24 to 29. di?erent ones of summing networks 55 and 56 so that Referring next to FIG. 4, there is shown a detail elec ap—a,, and AD1 are applied toone of the summing net trical schematic of one of quadratic equation solvers 46, works 55 or 56 and (fip—?o) and ADZ are applied to 47, or ‘4%. For purposes of explanation assume this is the other, depending upon which set to the hyperbolic lines running through map 1, shown in FIG. .1, is more quadratic equation solver ‘46 which solves Equation 3 yielding a signal indicative of ADI. The inputs to quad ratic solver 46 are mechanical coupling 45, voltage sig parallel to the north direction N. If the a hyperbolic lines (broken lines) are more parallel to the north di nals from potentiometers Stl'and 31 via lines 30a and 31a rection than the 5 hyperbolic lines, switches 53 and 59 45 and a voltage signal from summing ampli?er 52, via line should be positioned so as to apply ap—<xu and‘ AD1 to 52a. Lines Calla and 31a are coupled to different termi summing network 55 and [Sr-5,, and AD2 to summing nals of input network 78, thereby feeding voltage signals network 56. proportional to Xp cos ¢1 and Yp sin 4&1 from potentiom ' Summing networks 55 and 56 are each also fed‘a sig eters 3t? and 51, respectively, to input network 73. Other ' nal voltage proportional to AD,,, from quadratic equation solver '48. The outputs summing networks 55 and 56 inputs to network 78 are a signal from line 79 indica tive of are coupled to servo ampli?ers 57 and 58, respectively, in such a manner that the output voltages from servo Xp2+Yp2—AD12 2D1 ampli?ers 57 and 58 energize servomotors 6th and 61, respectively, causing these motors to turn at a speed pro portional to the voltage output from its associated servo ampli?er. The outputs of motors 6t} and 61 are coupled to arms 62 and 63 of potentiometers 64 and 65, erespec~ tively, while the output of servornotor 61 is coupled to arms 66 and 67 of potentiometers 68 and 69, respec tively. Opposite ends of potentiometers 64 and 68 are applied opposite polarity A.C. signals, while the center tap of each of potentiometers 64, 65, 68, and 69 is grounded. Thus the signal applied from potentiometer 55 and a signal via line 36 proportional to M31 as shown. Summing network 78 serves to sum the aforementioned voltage signals applying a sum voltage signal to servo ampli?er 81, which in ,turn is coupled to and energizes servomotor :8'2. Motor 82 drives potentiometer arms 83 and S4 of potentiometers 85 and 86, each of which has its center tap connected to ground. Potentiometer. 35 . has its ends coupled to opposite A.C. polarities, and the voltage in arm ‘83, which is coupled to input network 87 and thence to ampli?er o8 and which is indicative arm 66 to ampli?er 45 is proportional to +Yp, while of ADI, is reversed .in polarity at the output of ampli?er the signal applied from potentiometer arm 62 to ampli 88; thus, the output of ampli?er 83 is indicative of —AD1. ?er 43 is proportional to -|-Xp and the output from am This —-AD1 output is fed to input network 35 of'ampli?er pli?er 43 is indicative of -—Xp, while the output of ampli 5d and also to one end'of potentiometer 86, while the ?er 45 is indicative of —Y,,. The actions of ampli?ers output of ampli?er 96, which is indicative of +AD1, is fed 42 and 44, which are coupled to the outputs of ampli 70 to the other end of potentiometer 86. The +AD1 output ?ers 43 and 45, respectively, are merely to change the of amplifier 96 is fed back to input network 78 via line sign of X1,, or Yp providing signals indicative of +Xp and —Xp to opposite terminals of potentiometer 65 and signals of +Yp and —Y,, to opposite terminals of potentiometer 69. Thus the voltage in arm 63 of po Stl; thus, the action of shaft rotation from motor 82 cou pled to arm 84 which is proportional to A131 serves to multiply the shaft rotation times the voltage applied to the terminals of potentiometer 86, yielding a signal in 3,0 cases 14 if! a‘) line H which is proportional to ADIZ. Lines 91 andSZa , are coupled to input network §2 of ampli?er 93 whose output is proportional to the sum of voltages in lines 91 I and 52a and thus the sum of (Xlgz-l-YplbADlz). > The generating means to correct the'values of the Cartesian ‘ ' coordinates produced thereby. 3. ,A system according to claim 2, further including in dicating means coupled to said'assumed signals’ generating output of ampli?er 93 is fed to one terminal of potentiom $1 means for indicating said Cartesian coordinates. 4. A radio navigation receiver adapted to be carried ~ star-‘94 whose arm 95 is positioned by shaft 4&9 whose on a craft and cooperating with a plurality of Loran ‘rotation is indicative of beacons for indicating inCartesian coordinates the dis __._L___ placement of said craft with. respect to. a known point 2131 '10 which may be selected to be one of, said plurality of Thus, the voltage, in arm 95, which is coupled to line 79, is indicative of ~ XPZ-FYDLFADIZ 2o1 The output voltage of quadratic ‘equation solver 46 which is proportional to A131 is obtained from arm 33 of potentiometer 85 and is fed to one arm'oi double pole double throw switch 53 shown in PEG. 3. I While I have described above the principles of this in vention in connection with speci?c apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope‘ of ‘ . my invention as set forth in the objects thereof and in the accompanying claims. ‘1. A radio navigation receiver adapted to be carried on a craft and cooperatingwith a plurality of Loran Loran ‘beacons comprising means for receiving signals from said beacons, means for deriving from the received ' signals a pair of time difference signals with one of said time di?erence signals representing the difference in time between signals received from a ?rst pair of said beacons and the other time difference signal representing the dif ference intimebetween signals received from a second pair of said beacons, means to generate a second pair of > time di?erence signals representing similar time difference signals at the known point, means for generating assumed signals indicative of the Cartesian coordinates representing "the displacement of theicraft from the known point, means ‘for generating polar coordinates representing the position of said point with respect to said beacons,>means for computing from said assumed signals and said polar co »ordinate signals ‘the differences inthedistancesof the known point and the craft to each of said beacons and producing computed distance difference signals rcpre~ > sentativethereof, means .for computing from these com- , eacons for indicating in Cartesian coordinates the dis— placement of said craft with respect to a known point 30 puted distance di?erence signals ‘and the time di?erence signals of said craft and said‘point error signals repre which may be selected to be one of said plurality of Loran beacons comprising means for receiving signals from said beacons, means for deriving from the received signals measured distance diiference signals indicative of the craft’s position relative said known point, means for gen senting the error in the values of said ‘assumed signals, and means for applying said errorsignals tosaid assumed signals’ generating means to correct the values of said , assumed signals so that said assumed signals more pre cisely correspond to the said Cartesian coordinates of said craft withrespect to said known point signals. ,5. A system according to claim 4,'whereinsaid means signals indicative of the Cartesian coordinates ‘of ‘said > * for receiving comprisesmeansfor receiving signals from craft’s displacement relative'to said known point, means for computing from said assumed signals, other signals 40 a ?rst, second, and third beacon and wherein said ?rst erating hyperbolic coordinate signals indicative of the. position of said known point, means to generate assumed indicative of ‘the differences between the craft’s‘ distance ‘ > to each said beacon and the distance from said known point to each said beacon, means to compare these com . and second beacons formone of said pairs, and said Sec ond the third pairs form the other of said pairs, 6. A radio navigation receiver adapted to be carried on a craft and cooperating with a plurality of Loran beacons puted difference distance signals with the measured dis tance diiference signals indicative of the craft’s position relative said known point and the position of said known point to yield error signals, and ‘means for applying the for indicating in Cartesian coordinates the displacement error signals to said assumed signals’ generating means means‘for deriving from the received signals a pair of time difference signals with one of said time di?’erence to correct said assumed signals so as to drive said gen erating means to values more precisely indicative of the Cartesian coordinates representing the displacement of the craft’s position from the known point. 2. A radio navigation receiver adapted to be carried on a craft and cooperating with a plurality of Loran beacons for indicating in Cartesian coordinates the displacement of said craft with respect to a known point which may be selected to be one of said plurality of Loran beacons com of said craft with respect to a known point which may be selected to be one of said plurality of Loran beacons comprising means for receiving signals from said beacons, signals representing the difference in time between signals received from a ?rst pair of said beacons and the other time difference signal representing the difference in time between signals received from a second pair of said beacons, means to generate a second pair of time differ ence signals representing similar time diilerence signals at the known point, means for comparing the received time di?'erence signal and the generated time dilierence signal prising means for receiving signals from said beacons, of one pair of beacons to produce a ?rst signal, means to means for deriving from the received signals measured the received time difference“ signal and the gen distance difference signals indicative of the craft’s posi 60 compare erated time diiference signal of the other pair of beacons tion relative said known point, means for generating to produce a second signal, means toproduce assumed hyperbolic coordinate signals indicative of the position of signals indicative of the Cartesian coordinates represent said known point, means to generate assumed signals in ing the displacement of the craft from the known point, dicative of the Cartesian coordinates of said craft’s dis means for generating further signals representing the polar placement relative to said known point, means for gen coordinates from the known point to the different beacons erating signals representing the polar coordinates of said forming said pairs, meansfor computing from the as point with respect to said beacons, means for computing sumed signals and said further known signals the differ from said assumed signals and said generated polar coordi ences in the distances of the known point and the craft to nate signals the differences in the distances of the known point and the craft to each of said beacons, means for 70 each of the beacons forming said pairs and producing sig nals representing each of said distance differences, means computing from these distance differences and said meas for taking the difference ‘between different pairs of said ured distance di?erence signals of said craft and said point distance difference signals to provide a third and fourth the errors in the values of the assumed signals and for signal derived respectively from said ?rst and second pairs producing error signals representative thereof and means for applying said error signals to said assumed signals’ r of beacons, means for comparing said third and fourth sig ' ' 8,020,645 9 10 nals with said ?rst and second signals, respectively, to p_rod1l1ceten'or sigxtlaltil and 11163138 fer allaplyintglthese e?rqr slgna s o correc e assume slgna s un 1 a nu 1s preclsely reached, the Cartes1an corrected coordinates assumed signals expressmg representing the dlsplecemore 5 ment of the craft from the known point. References Cited in the ?le of this patent UNITED STATES PATENTS ' 2:717:735 . Luck 5,1522? ________________ "7 ------------__ ~- Sept. 111;? 13’ g’ 1955

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