US3891851A

US3891851A - Impact position detector for outer space particles

Info

Publication number: US3891851A
Application number: US502136A
Authority: US
Inventors: James C Administrator Fletcher; Siegfried O Auer
Original assignee: National Aeronautics and Space Administration NASA
Current assignee: National Aeronautics and Space Administration NASA
Priority date: 1974-08-30
Filing date: 1974-08-30
Publication date: 1975-06-24
Anticipated expiration: 1992-06-24

Abstract

The impact position of cosmic dust, micrometeoroids and other similar outer space particles is detected with an array including a multiplicity of mutually insulated, metal electrode strips, a first group of which has parallel, longitudinal axes at right angles to a second group of the strips. There is provided a delay line having a multiplicity of taps, each of which is connected to one of the strips. The delay times between adjacent taps of the delay line are approximately the same. One end of the delay line is terminated with a resistor having a value substantially equal to the characteristic impedance of the delay line. The arrival time at a delay line output terminal of pulses induced in the delay line in response to particle impact is determined relative to the occurrence time of a further pulse derived in response to the impact. Circuitry is provided to separate pulses induced in the line from different strips, even though there are substantially simultaneous impacts on the different strips.

Description

United States Patent 1 1 Fletcher et al.

[ IMPACT POSITION DETECTOR FOR OUTER SPACE PARTICLES [76] Inventors: James C. Fletcher, Administrator of the National Aeronautics and Space Administration, with respect to an invention of Siegfried O. Auer, Lanham, Md.

[22] Filed: Aug. 30, 1974 [21] Appl. No.: 502,136

Primary Examiner-James W. Lawrence Assistant ExaminerDavis L. Willis Attorney, Agent, or Firm-Robert F. Kempf; Ronald P. Sandler; John R. Manning June 24, 1975 [57 ABSTRACT The impact position of cosmic dust, micrometeoroids and other similar outer space particles is detected with an array including a multiplicity of mutually insulated, metal electrode strips, a first group of which has parallel, longitudinal axes at right angles to a second group of the strips. There is provided a delay line having a multiplicity of taps, each of which is connected to one of the strips. The delay times between adjacent taps of the delay line are approximately the same. One end of the delay line is terminated with a resistor having a value substantially equal to the characteristic impedance of the delay line. The arrival time at a delay line output terminal of pulses induced in the delay line in response to particle impact is determined relative to the occurrence time of a further pulse derived in response to the impact. Circuitry is provided to separate pulses induced in the line from different strips, even though there are substantially simultaneous impacts on the different strips.

13 Claims, 20 Drawing Figures 9 PROCESSING NEW/MK PATENTEDJUN 24 ms SHEET FIG I PATENTEDJUN 24 ms SHEET 4 FROM 138 XI I23 m MW? r rlZ! rf39 [I40 ANALOG PEAK ANA OG IND'CATOR X A O E DWIDEB 2 I23 w! 12! 43T I40 I25 ANALOG PEAK ANALOG INDICATOR GATE DETECTOR OWTO R 3. I23 x Do-5 1 r [|2T {A39 [I40 4 ANALOG PEAK Y ANALOG NDICATOR x G A 1E EG DWER 4 Y m K IZ F T |40 ANALOG PEAK ANALOG ,WDICATOR Y GAIE DETECTOR DIVlDEj $1 3 us Y2 ANALOG EAK m ANA LO G GATE DETECTOR DIVIDER IND'CATOR Y2 I23 GW 1 T/I39 r' ANALOG PEAK ANALOG GAT E OETEGTOR DlVlDER 'NDICATOR 3 W1 A [I27 FT 39 140 ANALOG PEAK ANALOG IND'C GATEL i DETECTOR OwTOEg ATOR Y4 H8 x Tf|39 14o ANALOG PEAK ANALOG GATE DETECTOR DIVIDER INDICATOR IMPACT POSITION DETECTOR FOR OUTER SPACE PARTICLES ORIGIN OF THE INVENTION The invention described herein was made in the performance of work under a NASA contract and is subject to the provisions of Section 305 of the National Aeronautics and Space Act of 1958, Public Law 85-568 (72 STAT 435; 42 USC 2457).

FIELD OF THE INVENTION The present invention relates generally to apparatus for detecting the impact location of cosmic dust, micrometeoroid and other similar outer space particles and more particularly to apparatus for detecting impact location on a detecting surface wherein the spatial position of the impinging particle is transferred into a time position.

BACKGROUND OF THE INVENTION In Berg US. Pat. No. 3,626,189, as well as in my U.S. Pat. Nos. 3,694,655 and 3,715,590, there are disclosed devices for detecting the impact position of cosmic dust, micrometeroids and other similar outer space particles. These devices are characterized by forming a plasma stream in response to a particle impinging on a film having a bias voltage applied thereto. Electric charges in the plasma stream are either returned to the film or collected by a grid electrode arrangement in proximity to the film. The grid electrode arrangement is biased oppositely from the film so that charges of one polarity are collected by the film and charges of the other polarity are collected by the grid.

In the Berg device, the impact position of a particle on a detector array is determined by segmenting the grid and film into a multiplicity of strips, such that the film strips are orthogonal to the grid strips. An amplifier is responsive to a voltage change induced on each film or strip in response to the plasma stream being derived. To enable the number of amplifiers employed with the device disclosed by Berg to be reduced to a practical number, the systems disclosed in my two previously mentioned patents were developed.

It has been found that particles impinging on the film have a tendency to penetrate the film and emerge as ejecta in the form of a plurality of particles or as liquid droplets. There is interest in determining the flight paths and mass of the ejecta. To this end, there is provided a second array, downstream of a first array which is directly responsive to an initially impacting particle. The ejecta arrive substantially simultaneously at the second array.

In the devices disclosed in my prior art patents, simultaneous impacting of ejecta or other particles causes an erroneous indication of the impact position of the particles on the detector array. When several particles simultaneously impact, there is derived an output that is indicative of a single impact position. The indicated single impact position generally resembles the centroid of the different impact positions on the detector array. For example, if two particles impact substantially simultaneously at different locations on the array, the detector identifies a location on a straight line between the actual impact sites as the virtual location of impact, and there is no apparatus to determine that a double impact actually occurred. In response to three or more simultaneous particle impacts, the prior art device provides an indication of target location inside a triangle or multiangled polygon enclosed by straight lines between the actual impact sites.

BRIEF DESCRIPTION OF THE INVENTION In accordance with a major aspect of the present invention, the problem of the prior art relating to the simultaneous impact is overcome by converting the spatial location of an impact site into a time position. The spatial to time position conversion is provided by connecting each of a plurality of mutually insulated equispaced particle detector strips to a different tap of a delay line. The delay line is arranged so that the delay times between adjacent taps are substantially the same, so that a unique time position to spatial relationship can be derived from a terminal at a first end of the delay line. To prevent reflections from the first end of the delay line, the first end of the delay line is terminated with a resistor having a value equal to the characteristic impedance of the delay line.

In accordance with one embodiment of the invention, the time position is determined by terminating the second end of the delay line with a short circuit, whereby pulses induced in the delay line in response to an impact are reversed in polarity at the second end of the delay line. Thereby, relatively simple apparatus can be provided at the first end of the delay line to distinquish between pulses which arrive at the first end directly and by reflection from the second end of the delay line.

The embodiment wherein the delay line is terminated at its second end with a short circuit has the added advantage of requiring only a single output amplifier. Since only a single delay line is required to derive impact location information in a pair of orthogonal direc tions there is at least a four-to-one reduction in the number of amplifiers required, compared to the devices disclosed in my prior art patents.

By comparing the time postions of the pulses arriving at the first end of the delay line, the spatial location of the impact on the array is determined. To enable detection of simultaneous impacts at different locations, circuitry is provided to be responsive to the pulse at the first output terminal of the delay line. The circuitry isolates the reflected and directly received pulses arriving at the first output terminal from the same strip into pairs. The pulse pairs are supplied to different channels, one for each strip to enable the spatial positions of the different simultaneous impacts to be ascertained.

In accordance with a further feature of the invention, the mass of each of the simultaneous impacts is separately detected in each of a plurality of channels. One channel is provided for each strip and is energized when a pulse for its corresponding strip is derived at the first delay line output terminal. Each mass indicating channel includes means for detecting the peak amplitude of each non-reflected pulse and for dividing the detected peak amplitude by a signal indicative of the velocity of the ejecta travelling between the two arrays.

It is, accordingly, an object of the present invention to provide new and improved apparatus for determining the impact position of cosmic dust, micrometeoroide and other particles on a detector array.

Another object of the invention is to provide a new and improved apparatus for detecting the impact locations of a plurality of simultaneously impacting outer space particles on a detector array.

Another object of the invention is to provide an apparatus for determining impact locations of a plurality of simultaneously impacting outer space particles on an array including a multiplicity of detector strips without requiring a separate driver amplifier for each of a multiplicity of strips.

An additional object of the invention is to provide a new and improved apparatus for studying break up of micrometeoroids, cosmic dust and other outer space particles after they penetrate a thin film.

A further object of the invention is to provide a new and improved apparatus for determining the trajectory of solid or liquid ejecta from an impact site of a micrometeoroid or other outer space particles on a detector array.

A still further object of the invention is to provide a new and improved apparatus for determining the masses of a plurality of simultaneously impacting outer space particles on the apparatus.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of one specific embodiment thereof, especially when taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a partially schematic and partially perspective view of one embodiment of the invention;

FIG. 2 is a block diagram of apparatus employed with the apparatus of FIG. I, particularly enabling the detection of impact site location of simultaneously impacting outer space particles;

FIGS. 3A-3Q are illustrations of waveforms derived in the FIG. 2 system; and

FIG. 4 is a block diagram of apparatus utilized in conjunction with the apparatus of FIGS. 1 and 2 for enabling the mass of particles impacting on the FIG. 1 detector to be determined.

DETAILED DESCRIPTION OF THE DRAWING Reference is now made to FIG. 1 of the drawing wherein there are illustrated two spaced arrays 11 and 12 having a common transverse axis. Array 1] is substantially the same as the five electrode configuration illustrated in US. Pat. No. 3,694,655 and includes five sets of electrodes 13-17 arranged in mutually parallel planes. Central electrode 15 includes a multiplicity of vertically extending, metal film strips which are connected to a positive DC. bias voltage, whereby in response to a micrometeoroid, cosmic dust particle or other similar outer space particle impinging on the metal film, an anisotropic plasma stream is generated. The particle can also break up into several fragments which penetrate through film 15 and traverse the space between arrays 11 and 12.

To enable the plasma stream derived from electrodes 15 to be captured by array 11, without affecting the travel of particles impinging on the array 11 and enabling particles emerging from electrodes 15 to travel unimpeded to array 12, electrode screens 13, 14, 16 and 17 are located on opposite sides of electrodes 15. Electrodes l4 and 16 are formed as a multiplicity of horizontally extending screen strips, connected to a negative DC. bias supply to collect positive ions in the plasma stream. Electrodes l3 and 17, most remote from electrodes 15, are formed as screens connected to a positive DC. bias supply, thereby collecting electrons in the plasma stream.

Impact of a single particle on electrode 15 frequently results in the projection of solid or liquid ejecta from the impact site in the space between arrays 11 and 12. It is a primary object of the invention to determine the impact sites of the ejecta on array 12, even though the impacts occur substantially simultaneously on array 12. To enable the impact sites to be determined, array 12 includes a multiplicity of vertically extending, mutually insulated, metal, coplanar strips 21-24, having parallel longitudinal axes, approximately the same breadth and approximately equal spacing between adjacent edges of the different strips. Positioned downstream of grid electrodes 21-24 is a plurality of horizontally extending, mutually insulated coplanar, metal film electrodes 25-28, also having parallel longitudinal axes, approximately the same breadth and approximately equal spacing between adjacent edges of the different strips. Positioned upstream of grid electrodes 21-24 is a further grid electrode 29.

Electrodes 21-24 are connected to a positive DC. bias voltage, while electrodes 25-29 are connected to a negative DC. bias voltage. Thereby, in response to ejecta from array 11 impinging on one of electrodes 25-28, an anisotropic plasma stream or spray having positive ions and electrons therein is generated. Positively charged ions in the plasma stream derived from any of electrodes 25-28 return to the electrode from which the spray was initiated and which corresponds with line of flight of the ejecta from array 11 to electrodes 25-28 because of the attractive force between the positively charged ions and the negative D.C. voltage applied to the electrode. Because of the positive bias applied to grids 21-24, electrons in the plasma spray are collected by electrodes 21-24 in closest proximity to the impact site of the particle on electrodes 25-28 which corresponds with the line of flight of the ejecta through grid electrodes 21-24. Any electrons in the plasma spray having sufficient energy to pass through mesh electrodes 21-24 are repelled by the negative D.C. field applied to mesh electrode 29 and are returned to and/or captured by positively biased mesh electrodes 21-24.

While only four strips are illustrated as being included in the plane occupied by electrodes 21-24 and four strips are illustrated in the plane occupied by electrodes 25-28, it is to be understood that in an actual embodiment having high resolution, the number of strips in each plane is considerably in excess of four, typically being on the order of 100. The detailed description of FIG. 1 to this point is considered to be in the prior art, as disclosed in my US. Pat No. 3,694,655.

To enable detection of the simultaneous impact sites of ejecta on strips 21-24 and 25-28, the spatial impact position is translated into a time position in accordance with the present invention. To this end, a delay line 31 having two series connected

segments

32 and 33 is provided.

Delay line segments

32 and 33 respectively include a multiplicity of taps 41-44 and 45-48 which are connected in DC. circuit with electrode strips 21-24 and 25-28. Positive and negative DC. bias supply voltages are respectively connected to electrodes 21-24 and electrodes 25-28 through

delay line segments

32 and 33 by DC. sources at

terminals

51 and 52 through relatively

large isolation resistors

53 and 54. The positive DC. voltage in delay line segment 32 is decoupled from the negative DC voltage in delay line segment 33 by blocking capacitor 55, connected in series between

segments

32 and 33 and having a sufflciently large value to enable pulses induced in

segments

32 and 33 to propagate easily between the two segments without substantial attenuation or delay compared to one section of the delay line between adajacent taps (e.g., be tween taps 41 and 42 or between taps 41 and 4S).

Delay line 31 is arranged so that the delay time between adjacent taps is substantially the same for pulses coupled to the delay line from electrodes 21-28 so that a unique time position of pulses arriving at one end of the delay line exists for each pulse induced in the delay time from each electrode. The same result can be attained by providing unequal spacing between the electrodes 21-24 and 25-28 and a commensurate proportional delay time displacement between adjacent taps of line 31. Positive pulses are coupled to taps 41-44 in response to electrons in the plasma stream impinging on electrodes 21-24. In contrast, negative pulses are supplied by electrodes 25-28 to taps 45-48 in response to positive ions in the plasma stream returning to electrodes 25-28.

Pulses coupled to delay line 31 from taps 41-48 travel in both directions in the delay line. At a first end terminal 49 of delay line 31, where tap 41 is located, the pulses are not reflected, a result achieved by connecting resistor 56, having a value equal to the characteristic impedance of the delay line, between terminal 49 and a ground terminal. At the other, second end terminal 50 of the delay line, adjacent tap 48, the pulses are reversed in polarity and propagate to end terminal 49, a result achieved by short-circuiting end terminal 50 to ground. Delay line 31 is approximately lossless, so the amplitude of pulses coupled to terminal 49 is substantially the same as the amplitude of the pulses initially induced in the delay line by the voitages derived from electrodes 21-28.

The pulses generated across terminating resistor 56 are coupled to a processing electronics network 57 via coupling capacitor 58 and operational amplifier 59. Operational amplifier 59 has a relatively high input impedance, such as provided between the gate and source electrodes of a metal oxide semiconductor field effect transistor.

In response to a pulse being generated in one of electrodes 21-24 or 25-28, a positive or negative pulse is coupled to delay line segment 32 via one of taps 41-48. The pulse propagates directly to delay line terminal 49 arriving at terminal 49 displaced in time from its initial inducement in the delay line by an interval equal to:

where:

T the delay time in propagating from one of taps 41-48 to terminal 49; n the units digit of the number of the tap; t the time for the pulse to travel between adjacent taps of delay line 31. A pulse induced in delay line 31 from one of taps 41-48 also travels to end terminal 50, where it is reversed in polarity and arrives at terminal 49 at a time indicated by:

where:

N the number of tops of line 31. The time displacement between the positive and negative voltages at terminal 49 is given by:

Thereby, by measuring the time displacement between a pair of opposite polarity pulses as supplied to the input of processing electronic network 57, it is possible to convert the spatial impact position on one of electrodes 21-28 into a time position.

The impact time on electrodes 21-28 can be ascertained by determining the instant of time midway between the two opposite polarity pulses derived at terminal 49 from one of the electrodes and subtracting the median instant of time from the total delay time (N1 of line 31.

To enable unique detection of the spatial position of pulses simultaneously derived from different ones of electrodes 21-28, processing network 57 includes circuitry for separating the pulses derived at terminal 49 at different times into different channels, one of which is provided for each of the electrode strips 21-28. The details of the circuitry included in processing electronic network 57 are illustrated in the block diagram of FIG. 2. The circuitry included in FIG. 2 may in many instances be located at a ground station remote from a spacecraft carrying the detector of the present invention, with communication between the detector and ground station being via a suitable R.F. link.

The circuitry included in processing network 57 is described in connection with an exemplary situation, as illustrated in FIG. 3. In FIG. 3, it is assumed that a particle impacting on array 11 causes three particles to impact substantially simultaneously on array 12. The impact site of one of the particles results in positive and negative pulses being respectively derived from

electrodes

22 and 26; the second particle results in positive and negative pulses being respectively derived from

electrodes

23 and 27; and the third particle results in positive and negative pulses being respectively derived from electrodes 24 and 27. The pulses from

electrodes

22, 23, 24, 26 and 27 are simultaneously derived and result in the simultaneous derivation of voltage pulses at taps 42, 43, 44, 46 and 47. The pulses at taps 42-44, 46 and 47 cause pulses to be induced in line 31, resulting in direct and reflected opposite polarity time displaced pulses to be derived at output terminal 49 of delay line 31, as indicated by the waveform of FIG. 3A. In FIG. 3A,

pulses

61, 62 and 63 are derived in response to pulses derived from

strips

22, 23 and 24 and coupled directly to delay line output terminal 49. The pulses at

electrodes

26 and 27 are coupled directly to delay line output terminal 49 as

pulses

64 and 65, and the reflected replicas of

pulses

64 and 65 are respectively derived at output terminal 49 as pulses 66 and 67. The reflected replicas of pulses 61-63 are derived at output terminal 49 as

pulses

68, 69 and 70, respectively.

The pulses at delay line end terminal 49 are coupled via amplifier 59 to an input of threshold detector 71 which functions as a pulse shaper to eliminate noise and derive relatively short, constant duration and constant amplitude pulses, as illustrated in FIG. 3B. Detector 71 is responsive to pulses of both polarities and derives an output pulse having the same polarity as input pulses to the detector.

The output signal of threshold detector 71 is D.C. coupled to a trigger input of flip-flop 72. Flip-flop 72 is of the type which remains in a particular state until the DC level applied to its trigger input is of an opposite polarity relative to the polarity of its previous input pulse. Flip-flop 72 is respectively triggered to binary one and zero states in response to positive and negative pulses being derived from the output of detector 71. As illustrated in FIG. 3C, flip-flop 72 derives a rectangular wave output, having leading edge transitions occurring simultaneously with the leading edge of a first positive output pulse of detector 71 and a trailing edge occurring simultaneously with the leading edge of a first negative pulse derived from detector 71. The output signal of flip-flop 72 is applied to divide-by-two frequency divider 73 which derives a rectangular wave output as illustrated by the waveform of FIG. 3D.

The output signals of threshold detector 71 and frequency divider 73 are combined in logic, counting and comparator circuitry to enable the pulses which are derived from the same electrodes of array 12 to be separated into mutually exclusive pairs; the logic, counting and comparator circuitry for deriving signals indicative of the impact location of vertically extending strips 21-24 is separate from the circuitry employed for determining the spatial location of the horizontally extending strips 25-28. To these ends, a pair of forward backward counters 74 and 75 is provided. Each of

counters

74 and 75 includes a count forward input terminal 76 and a count backward input terminal 77, as well as an internal digital-to-analog converter for converting a count signal stored therein into a DC. analog voltage that is directly proportional to the count stored therein. In response to each pulse supplied to the forward and

backward input terminals

76 and 77 of

counters

74 and 75 the counts of the counters are respectively incremented and decremented by a count of one.

Counter 74 is advanced by a count of one in response to each positive output pulse of detector 71 while a binary one level is being derived from divider 73. To this end, the output signals of detector 71 and divider 73 are applied to input terminals of AND gate 78, having an output which is coupled to count forward input terminal 76 of counter 74. Counter 74 is decremented by a count of one in response to each negative pulse derived from threshold detector 71 while divider 73 is in a binary zero state. To this end, the output signals of threshold detector 71 and divider 73 are respectively applied to inverting gates 79 and 80, having outputs which are coupled to the input terminals of AND gate 81, which derives an output signal which is coupled to count backward input terminal 77 of counter 74. Thereby, at any instant of time, the count stored in counter 74 and the level of the analog signal derived from the output of the counter are, in the interval between

pulses

61 and 68, indicative of the number of pulses that have been or remain to be processed from vertically extending electrodes 21-24, as represented by the staircase waveform illustrated in FIG. 3E.

Counter 75 is incremented by a count of one in response to each negative output pulse of threshold detector 71 while the output of divider 73 is in a binary one state. To this end, the output signal of detector 71 is coupled to inverter gate 82 which supplies one input of AND gate 83, having a second input directly responsive to the output of divider 73. The output of AND gate 83 is supplied to the forward input terminal 76 of counter 75. The count of counter is decremented by a count of one in response to each positive output pulse of threshold detector 71 while divider 73 is in a binary zero state, a result achieved by supplying the output of divider 73 through inverter 84 to one input of AND gate 85, having a second input responsive to the output signal of threshold detector 71. AND gate 85 derives binary one pulses that are supplied to backward input terminal 77 of counter 75. Counter 75 thereby stores a count and derives an analog output voltage having a value equal to the number of pulses derived from horizontally extending strips 25-28 that have been or remain to be processed, as illustrated by the step waveform of FIG. 3F.

As illustrated in FIGS. 3E and 3F, the outputs of

counters

74 and 75 are staircase waveforms, with the amplitude of each step being the same, but the length of the several steps differing from each other. The leading edge of each ascending step of waveform FIG. 3E is in time coincidence with a leading edge of a corresponding positive going pulse in the waveform of FIG. 38, as derived from detector 71. The leading edge of each descending step in FIG. 3E is in time coincidence with the leading edge of each negative going pulse in the waveform of FIG. 3B. The time separation between each ascending and descending step of FIG. 3E indicates the spatial separation between adjacent elec trodes 21-24 from which pulses are derived.

The total separation between corresponding ascending and descending steps in the waveform of FIG. 3E provides an indication of the spatial location of each one of strips 21-24 from which a pulse is derived. For example, the time separation between the ascending step on the extreme left side of the waveform of FIG. 3E and the descending step on the extreme right side of FIG. 3B provides an indication that a pulse was derived from electrode 22. In this connection, it is to be noted that

pulses

61 and 68 are both derived from strip 22 in the exemplary situation. Similarly, the ascending steps in the waveform of FIG. 3F are in time coincidence with the leading edges of the negative going pulses derived from detector 71 in response to

pulses

64 and 65, while the descending steps of FIG. 3F are in time coincidence with the leading edges of the positive going pulses derived from detector 71.

To process the step waveform outputs of

counters

74 and 75 into separate signals for each of the electrodes 21-28, and to enable an indication of the electrodes which derive pulses to be obtained, the output signal of counter 74 is applied to a plurality of parallel channels 91-94, one of which is provided for each of electrodes 21-24, while the output of counter 75 is applied to parallel channels 95-98, which are respectively provided for electrodes 25-28. In each of channels 91-98, there is provided a comparator 99 which is responsive to the output signal of one of

counters

74 or 75. Comparators 99 are designed so that a binary one level is derived thereby in response to the input voltage thereof from

counters

74 and 75 being equal to or greater than a reference input voltage. Each of comparators 99 in channels 91-94 is responsive to a different reference input voltage, having a magnitude corresponding with the output level of the different steps of the stairwave voltage derived from counter 74. Similarly, comparators 99 of channels 95-98 are supplied with different reference input voltages having levels corresponding with the steps derived from the output of counter 75. The output of comparator k of channels 91-94 can be represented as X,,,, where k l, 2, 3, 4 for

channels

91, 92, 93 and 94, while the output of comparator k: of channels 95-98 can be represented as Y where k l, 2, 3, 4 for

channels

95, 96, 97 and 98.

In the exemplary situation described in connection with the waveforms of FIG. 3, the output signals of the comparators of

channels

93, 94 and 95 are respectively represented by the waveforms of FIGS. 36, 3H and 3|, respectively having leading and trailing edges in time coincidence with the leading edges of the first, second and third ascending and descending steps of the waveform of FIG. 3E. Similarly, the comparators of channels 97 and 98 respectively derive the rectangular waveforms illustrated in FIGS. 3.] and 3K, which respectively have leading and trailing edges in time coincidence with the ascending and descending first and second steps of the waveform of FIG. 3F.

The length of each of the rectangular waveforms derived from comparators 99 of FIGS. 36-314 is indicative of the time separation between the unreflected and reflected pulses arriving at terminal 49, as indicated by Equation (3). The time interval of each of the rectangular waveforms derived from comparators 99 is measured by including in each of channels 91-98 an AND gate 101 that is responsive to the comparator of the channel. Each of AND gates is also responsive to an output signal derived from clock pulse source 103, having a period between adjacent pulses of 2T seconds, as illustrated by the waveform of FIG. 31.. For the exemplary situation, the output signals of the AND gates 101 of

channels

93, 94, 95, 96 and 97 are respectively illustrated by the waveforms of FIGS. 3M-3Q. The number of clock pulses in each of the waveforms of FIGS. 3L-3K is equal to the Ns complement of the number of taps in delay line 31 minus the number of the tap in which the pulse was induced plus one, i.e., the number of counts equals (Nn 1). Each of channels 91-98 includes a separate counter 103 having a count input responsive to the AND gate 101 included in the respective channel. Counters 103 thereby indicate the location, in Cartesian coordinates of each horizontal and vertical strip in array 12 on which ejecta substantially simultaneously impact.

To determine the mass of the ejecta impinging on each of the strips in array 12, the mass on each of the electrodes 21-28 is determined by gating the signal derived from amplifier 59 into a plurality of parallel channels 111-118 (FIG. 4), one of which is provided for each of the electrodes 21-28. in each channel, the peak amplitude of the pulse derived from amplifier 59 is determined and combined with a signal indicative of the velocity of the impacting ejecta between arrays 11 and 12, as indicated by the travel time between the two arrays.

To these ends, each of channels 111-118 includes an analog gate 121 that is open only in the interval when a direct, unreflected pulse from a particular electrode can be derived from output terminal 49 of delay line 31. For each of the vertically extending electrode strips, except for the last strip, (i.e., for strips 21-23),

this result is achieved by providing in channels 111-113 an analog gate 121 that is opened to pass signals during the interval when the binary outputs of comparators 99 of channels 91-93 are represented by X -X Similarly, in each of the channels 115-117, i.e., the channels for the horizontally extending strips, except for the last strip, (i.e., for strips 25-27), an analog gate 121 is opened during the interval while the outputs of the comparator of channels 95-97 are represented by Y Y,

Channels

114 and 118, which process the signals derived from the last vertically and horizontally extending strips 24 and 28, as derived from amplifier 59, include analog gates 121 that are respectively opened in the interval when unreflected pulses from the last vertically extending strip 24 and from the last horizontally extending strip 28 arrive at terminal 49.

To these ends, each of channels 111-117 includes an AND gate 123 which drives the analog gage 121 of its respective channel with a binary one signal that opens the analog gate so it can pass its input signal to its output terminal. One input of AND gates 123 of channels 111-117 is responsive to the binary signal respectively derived at the outputs of the comparators of channels 91-97. The other input of each of AND gates 123 of channels 111-117 is respectively responsive to the complement of the signals derived from the comparators of channels 92-98, as coupled through inverter gates 125, one of which is included in each of channels 111-117. Analog gate 121 of channel 118 is directly responsive to the output signal of comparator 99.

The variable amplitude pulses selectively coupled through analog gates 121 of channels 111-118 are applied to a different peak detector 127 included in each of the channels. Each of peak detectors 127 derives a steady output signal in response to the direct, nonreflected pulse derived from the output of amplifier 59. The magnitude of the output voltage of each of peak detectors 127 is directly proportional to the energy of the line of flight of ejecta impinging on the portion of array 12 aligned with each of strips 21-28.

To determine the mass of each of the solid particle or liquid droplets in the ejecta, the output signal of each of peak detectors 127 is divided by a signal indicative of the propagation velocity between arrays 11 and 12. The propagation velocity is determined by measuring the time interval between impingement of a particle on any of film 15 of array 11 and the impact time of the resulting ejecta on any of films 25-28 of array 12. Since the spacing between films 15 and 25-28 is a constant, predetermined quantity, the velocity can be determined from the travel time between the films.

To these ends, signals derived from each of films 15 are coupled to separate inputs of a single, high input impedance amplifier 131 (FIG. 1). Similarly, the signals derived from films 25-28 are coupled as inputs to a single, high input impedance amplifier 132. The several signals from films 25-28 are coupled to a single amplifier 132 because it can usually be validly assumed that all of the ejecta from array 11 impinges substantially simultaneously on films 25-28 of array 12. The output signal of amplifier 131 is applied to a set input terminal of flip-flop 133, having a reset input terminal responsive to the output of amplifier 132. Flip-flop 133 is thereby in a binary one state during the interval while ejecta is propagating between arrays 11 and 12. A resulting binary one output of flip-flop 133 is coupled to one input of AND gate 134, having a second input responsive to clock pulses from oscillator 135, having a frequency such that a relatively large number of pulses is derived from the oscillator in the interval while ejecta propagate between arrays 11 and 12. Pulses derived from AND gate 134 are coupled to digital-to-analog converter 136, the output of which is a DC. analog signal having a magnitude directly proportional to the travel time of ejecta between arrays 11 and 12.

The output signal of converter 136 is supplied as a divisor input to analog divider 137, having a dividend input equal to the separation between the film electrodes of arrays 11 and 12. The output of divisor 137 is an analog DC signal directly proportional to the ve locity of propagation of ejecta between arrays 11 and 12. The output of divider network 137 is applied to a cubing network 138, which derives an output signal proportional to V, where S is a predetermined constant and V is the propagation velocity. The output signal of divider 138 is applied as a divisor input to an analog divider 139 included in each of channels 111-118. Each of analog dividers 139 has a divider input terminal responsive to the output of the peak detector 127 for the particular channel, whereby each of the analog dividers derives an output signal having a magnitude directly proportional to the mass of the material impinging on an area of array 11 commensurate with the area of the strip for which the channel is associated.

The output signal of each of dividers 139 is applied to a separate indicator 140, such as a voltmeter or analog to digital converter to digital display combination. The output signal of indicator 140, together with the strip indicating signal derived from each of counters 103, enables the impact location of ejecta on array 12 to be determined in each area of array 12 defined by a square that is coincident with overlapping areas of strips 21-28. A correlation between ejecta impact position and mass can be performed manually, or by automatic recording apparatus including vertically and horizontally extending strips that are energized in pairs in response to the output signals of counter 103 and the signals derived from each of channels 111-118. In the alternative, in systems where resolution in two orthogonal directions is not required, information in a single direction can be derived by including only vertically or horizontally extending strips in array 12.

While there has been described and illustrated one specific embodiment of the invention, it will be clear that variations in the details of the embodiment specifically illustrated and described may be made without departing from the true spirit and scope of the invention as defined in the appended claims. For example, delay line 31 can be terminated with an open circuit, rather than a short circuit, at terminal 50, in which case the reflected pulses at the delay line output terminal 49 have the same polarity as the directly received, unreflected pulses. 1n response to the like polarity direct and reflected pulses arriving at terminal 49, logic circuitry must be included to identify the direct and reflected pulses by a reasonable time sequence thereof. Once the direct and reflected pulses have been identified, they can be supplied to the same processing network as is employed with the system described in connection with FIGS. 1-4. A further modification involves connecting a resistor having a value equal to the characteristic impedance of delay line 31 between terminal 50 and ground, rather than shorvcircuiting terminal 50 to ground. If both ends of delay line 31 are connected to resistors having a value equal to the delay line characteristic impedance, there are no reflected pulses and additional signal processing circuitry must be connected to terminal 50. The additional processing circuitry must also be responsive to a signal indicative of the impact time of ejecta on array 12, a result which can be achieved by supplying the output signal of amplifier 132 to the additional circuitry.

The invention is also applicable to other outer space particle detectors, such as those including a thin film covered with thin conductive layers on both sides wherein pulses are derived in response to penetrating meteoroids or the like. Such detectors have been utilized in spacecraft in the past, for example, in the Pegasus Project and on the Mariner 1V spacecraftv What is claimed is:

1.1n an apparatus for determining the impact position of cosmic dust or other similar outer space particles on a detector, an array of electrically conducting, mutually insulated metal strips each having a different impact area for the particles, each of said strips including means for generating a different electric pulse in response to a particle having a line of flight in the impact area thereof, the strips of said array being arranged so that each strip uniquely indicates the spatial location of an impact, at least some of said strips having parallel longitudinal axes and defining an impact area having the same length in a direction at right angles to the longitudinal axes, a delay line having a multiplicity of taps, each of which is connected to one of said strips, the delay time of the delay line between adjacent taps being proportional to the spatial separation between adjacent electrodes, whereby a first pulse is induced in the delay line at the tap connected to the strip in which a line of flight exists and propagates down the delay line to a first end thereof, means for substantially preventing reflection of pulses from the first end of the line, and an amplifier having an input terminal connected to be responsive to pulses arriving at the first end of the line.

2. The apparatus of claim 1 further including means responsive to an output of the amplifier for detecting the first pulse arrival time at the first end relative to the occurrence time of a further pulse derived in response to a line of flight existing in the strip.

3. The apparatus of claim 2 wherein said delay line is terminated at a second end so as to cause the induced pulse to be reflected from the second end, the reflected pulse being coupled to the first end, said means for detecting including means for detecting the relative arrival time at the first end of the first and reflected pulses.

4. The apparatus of claim 3 wherein said delay line is terminated at the second end so as to cause the reflected pulse to have a polarity opposite from the first pulse.

5. The apparatus of claim 4 wherein a short circuit terminates said delay line.

6. The apparatus of claim 1 wherein multiple impacts are susceptible to substantially simultaneous occurrence on different ones of said strips causing different first pulses to be induced substantially simultaneously at different ones of said taps, and said means for detecting includes means for separately detecting the first pulse arrival times for different ones of said first pulses.

7. In combination. a plurality of first mutually insulated biased metal strips having parallel longitudinal axes. a plurality of second mutually insulated biased metal strips having parallel longitudinal axes orthogo nal to the longitudinal axes of the first strips, a delay line having a multiplicity of taps each of which is connected to one of said strips. the delay line having a predetermined characteristic impedance and a delay time between adjacent taps commensurate with the spacing between adjacent ones of the strips, and an impedance terminating one end of the delay line having a value substantially equal to the characteristic impedance.

8. The combination of claim 7 wherein another end of the delay line is terminated by a short circuit.

9. In a apparatus for determining the impact position of cosmic dust or other similar space particles on a detector. an array ofclectrically conducting, mutually insulated metal strips each having a different impact area for the particles, each of said strips including means for generating a different electric pulse in response to a particle having a line of flight in the impact area thereof. the strips of said array being arranged so that each strip uniquely indicates the spatial location of an impact. and means for converting the spatial position of the strip on which the line of flight exists into a time position.

10. The apparatus of claim 9 wherein the means for converting includes a delay line having a plurality of spaced taps each connected to a different one of the strips.

H. In an apparatus for determining the impact position of cosmic dust or other similar outer space particles on a detector. an array of electrically conducting, mutually insulated metal strips each having a different impact area for the particles. each of said strips including means for generating a different electric pulse in response to a particle having a line of flight in the impact area thereof, the strips of said array being arranged so that each strip uniquely indicates the spatial location of an impact. whereby a pulse is derived from each strip in which the line of flight exists, means connected to all of the strips for deriving a replica of all of the derived pulses at a signal output terminal. and means connected to be responsive to the pulse replicas at the signal output terminal for distinguishing the spatial location of different impacts that occur substantially simultaneously on different ones of said strips.

12. The apparatus of claim 11 further including means connected to be responsive to the pulse replicas at the signal output terminal for deriving a signal indicative of the mass of the particle of each distinguished impact.

13. The apparatus of claim 11 further including means connected to be responsive to the derived pulses for deriving a signal indicative of the mass of the particle of each distinguished impact.

Claims

1. In an apparatus for determining the imapct position of cosmic dust or other similar outer space particles on a detector, an array of electrically conducting, mutually insulated metal strips each having a different impact area for the particles, each of said strips including means for generating a different electric pulse in response to a particle having a line of flight in the impact area thereof, the strips of said array being arranged so that each strip uniquely indicates the spatial location of an impact, at least some of said strips having parallel longitudinal axes and defining an impact area having the same length in a direction at right angles to the longitudinal axes, a delay line having a multiplicity of taps, each of which is connected to one of said strips, the delay time of the delay line between adjacent taps being proportional to the spatial separation between adjacent electrodes, whereby a first pulse is induced in the delay line at the tap connected to the strip in which a line of flight exists and propagates down the delay line to a first end thereof, means for substantially preventing reflection of pulses from the first end of the line, and an amplifier having an input terminal connected to be responsive to pulses arriving at the first end of the line.

5. The apparatus of claim 4 wherein a short circuit terminates said delay line.

7. In combination, a plurality of first mutually insulated biased metal strips having parallel longitudinal axes, a plurality of second mutually insulated biased metal strips having parallel longitudinal axes orthogonal to the longitudinal axes of the first strips, a delay line having a multiplicity of taps each of which is connected to one of said strips, the delay line having a predetermined characteristic impedance and a delay time between adjacent taps commensurate with the spacing between adjacent ones of the strips, and an impedance terminating One end of the delay line having a value substantially equal to the characteristic impedance.

9. In a apparatus for determining the impact position of cosmic dust or other similar space particles on a detector, an array of electrically conducting, mutually insulated metal strips each having a different impact area for the particles, each of said strips including means for generating a different electric pulse in response to a particle having a line of flight in the impact area thereof, the strips of said array being arranged so that each strip uniquely indicates the spatial location of an impact, and means for converting the spatial position of the strip on which the line of flight exists into a time position.

11. In an apparatus for determining the impact position of cosmic dust or other similar outer space particles on a detector, an array of electrically conducting, mutually insulated metal strips each having a different impact area for the particles, each of said strips including means for generating a different electric pulse in response to a particle having a line of flight in the impact area thereof, the strips of said array being arranged so that each strip uniquely indicates the spatial location of an impact, whereby a pulse is derived from each strip in which the line of flight exists, means connected to all of the strips for deriving a replica of all of the derived pulses at a signal output terminal, and means connected to be responsive to the pulse replicas at the signal output terminal for distinguishing the spatial location of different impacts that occur substantially simultaneously on different ones of said strips.