An apparatus for measuring the electric field in the atmosphere which includes a pair of sensors carried on a rocket for sensing the voltages in the atmosphere being measured is described. One of the sensors is an elongated probe with a fine point which causes a corona current to be produced as it passes through the electric field. An electric circuit is coupled between the probe and the other sensor and includes a high ohm resistor which linearizes the relationship between the corona current and the electric field being measured. A relaxation oscillator and transmitter are provided for generating and transmitting an electric signal having a frequency corresponding to the magnitude of the electric field

Ruhnke, L. H.

English

NASA Technical Reports Server

United States Patent
Ruhnke
in] 3,760,268
[45] Sept. 18, 1973
[54] ROCKET BORNE INSTRUMENT TO
MEASURE ELECTRIC FIELDS INSIDE
ELECTRIFIED CLOUDS
[75] Inventor: Lothar Ruhnke, Boulder, Colo.
[73] Assignee: The United States of America as
represented by the Administrator of
the National Aeronautics and Space
Administration, Washington, D.C.
[22] Filed: Apr. 28, 1972
[21] Appl. No.: 248,469
[52] U.S. Cl 324/72
[51] Int. Cl GOlr 29/12
[58] Field of Search 324/32, 72
[56] References Cited
UNITED STATES PATENTS
3,273,066 9/1966 Ruhnke.... 324/72 UX
3,283,241 11/1966 Forbes et al 324/72 X
Primary Examiner—Gerard R. Strecker
Attorney—James O. Harrell et al.
[57] ABSTRACT
3,038,154 6/1962
3,121,196 2/1964
3,219,292 11/1965
3,222,562 12/1965
Zworykin et al 324/72 UX
Kasemir 324/72 X
Chubb 324/72 X
Bennett....: 324/72 X
An apparatus for measuring the electric field in the at-
mosphere which includes a pair of sensors carried on
a rocket for sensing the voltages in the atmosphere
being measured. One of the sensors is an elongated
probe having a fine point thereon, which causes a co-
rona current to be produced as it passes through the
electric field. An electric circuit is coupled between the
probe and the other sensor and includes a high ohm re-
sistor which linearizes the relationship between the co-
rona current and the electric field being measured. A
relaxation oscillator and transmitter are provided for
generating and transmitting an electric signal having a
frequency corresponding to the magnitude of the elec-
tric field.
3 Claims, 2 Drawing Figures
FREQUENCY TO
DC CONVERTER
https://ntrs.nasa.gov/search.jsp?R=19730023586 2020-03-17T09:32:57+00:00Z
Patented Sept. 18, 1973 3,760,268
FREQUENCY TO
DC CONVERTER
16
38
3,760,268
1 2
ROCKET BORNE INSTRUMENT TO MEASURE rocket, (2) an elongated probe having a corona point
ELECTRIC FIELDS INSIDE ELECTRIFIED thereon, carried on the front of the rocket, (3) an elec-
CLOUDS trie circuit coupled between the elongated probe and
This invention described herein was made in perfor- one of the fins providing a current path for the corona
mance of work under a NASA Contract and is subject 5 current caused by the difference in voltage at the co-
to the provisions of Sections 305 of the National Aero- rona point and the fin, (4) a high ohm resistor con-
nautics and Space Act of 1968, Public Law 85-568 (72 nected within the circuit in series with the elongated
Stat. 435, 402 U.S.C.P. 2457). probe for substantially linearizing the relationship be-
This invention relates to an apparatus for measuring tween the corona current and the electric field being
electric fields, and more particularly to a rocket pro- 10 measured, (5) a relaxation oscillator coupled in the cir-
vided with sensors for sensing the magnitude of electric cuit for generating a chain of pulses having a frequency
fields. proportional to the difference in voltage at the corona
The space industry particularly since the Apollo 12 point and the fin, and a transmitter coupled to the re-
launch which was struck by lightning has become par- laxation oscillator for transmitting the train of pulses to
ticularly concerned with launching space vehicles 15 a remote station.
through clouds which may discharge causing lightning Accordingly, it is an important object of the present
to strike the vehicle. The chance of the clouds being invention to provide an apparatus for measuring the
discharged by the rocket increases considerably with electric fields of clouds and the like,
the magnitude of the electric field inside the clouds. Another important object of the present invention is
The electric field in such clouds, in particular thun- 20 to provide an apparatus for measuring electric fields
der clouds, is difficult if not impossible to determine and the like, which generates a signal having a fre-
from ground based sensors. Airplanes equipped with quency that varies according to the density of the elec-
electric field sensors have successfully, measured and trie field.
determined the distribution of electric charges inside Another important object of the present invention is
clouds; however, to infer from such measurements the 25 to provide a simple and inexpensive device for measur-
distribution of the electric field, one must make as- ing electric fields in thunder storms and the like,
sumptions about the distribution of the charges in the Other objects and advantages of this invention will
neighborhood of the charge centers. At the present not become more apparent from a reading of the following
enough charge distribution in electric clouds have been detailed description and appended claims taken in con-
observed to specify these needy assumptions. Direct 30 junction with the accompanying drawing wherein:
measurements of the electric field inside thunder FIG. 1 is a pictorial view illustrating a rocket con-
storms require that an aircraft penetrate the cloud at structed in accordance with the present invention gen-
several levels. Such penetration leads to safety prob- erating signals proportional to the electric field of a
lems because of dangers of high turbulence and possi- cloud,
ble high lightning activity associated with these clouds. 35 FIG. 2 is a schematic diagram illustrating a rocket.
Balloons do not penetrate clouds fast enough and, also, having a circuit positioned therein for generating sig-
do not have a flight path that can be predicted accu- nals indicating the electric field of clouds and the like,
rately. Referring in more detail to FIG. 1 of the drawing,
Several methods are available to sense the electric there is illustrated a rocket BO traveling through the at-
field in thunder clouds and the like. One in particular 40 mosphere provided with an, apparatus for measuring
includes a field mill on a fast moving rocket for measur- the electric field of clouds and the like. The rocket 10
ing the vertical electric field component. Such is me- shown has a probe 12 with a very fine point 16 carried
chanically too complex and too difficult to design thereon for sensing the voltage produced by the elec-
under present conditions. Radio active probe circuits trie field as such passes through the clouds. Another
involve difficult logistic procedures. Furthermore, such voltage sensing device is one of the fins 14 of the
devices are also difficult to construct for high electric rocket. The electric field through which the rocket is
fields. passing is substantially equal to the potential difference
Because the sense fields vary very rapidly, the time between the point 16 of the probe 12 and the voltage
reviewing each flight, and because measure times are sensing fin 14 divided by the distance between -the
short compared to the relaxation time of air, it is feasi- point 16 and the fin 14. The electric field through
ble to neglect the conductivity of air and consider elec- which the rocket passes creates a corona current which
trostatic measure methods. An exposed conductor, flows through the probe 12, however, such is non-linear
e.g., a small sphere isolated from the body of the rocket with regard to variations in the electric field. To elimi-
and electrically connected to an amplifier with input „ nate the non-linearity, as well as the various factors that
time Constance large compared with the flight time of influence corona currents, the current from the sharp
the rocket will give readings proportional to the elec- point 16 is fed through a high ohm resistor 24 to bias
trie field, if the electric field at the start of the flight can the corona point aginst the instrument ground. This
be neglected. Unfortunately, such an exposed sphere makes the voltage drop over the resistor 24 large corn-
can easily collect charges by impact with precipitation ,_ pared to to the voltage drop between the corona point
particles causing errors. 16 and the environment. Thus, the corona current mea-
In accordance with the present invention, it has been sured is proportional to the electric field to a practical
found that difficulties encountered with other systems degree, if the electric field is higher than a certain
for measuring electric fields in clouds and the like can threshold field. There is shown in FIG. I pulses 88
be overcome by providing a novel electric field measur-
 6J being transmitted from the rocket 10 which have a fre-
ing apparatus. This electric field measuring apparatus quency directly proporational to the current flow be-
includes the following basic parts: (1) A self-propelled tween the point 16 of the probe 12 and the top of the
rocket with fins carried adjacent the rear end of the fin 14. A receiver 20 is provided at ground station for
3,760,268
3 4 -
receiving the pulses and feeding such to a frequency to impacts the ground after about 70 seconds. The cloud
D.C. converter 22 for converting the pulses to an ana- base is reached after approximately 10 seconds at a ve-
log signal having an amplitude directly proportional to locity of 200 meters per second. This velocity de-
trie electric field. creases to about 25 meters per second at maximum alti-
Referring in more detail to FIG. 2 of the drawing, 5 tude. During flight the rocket is probably never further
there is illustrated schematically the rocket 10 having than 10 kilometers from the launch pad. Maximum ac-
an elongated probe 12 mounted thereon. The elon- celeration is SO G's.
gated probe in one particular instance is constructed of The electric field in the atmosphere or cloud varies
1/16 inch Tungsten steel rod and is approximately 4 strongly with position. Every 10 meters along the tra-
inches long. The point 16 of the probe was sharpened 10 jectory at least one reading of the electric field should
by a grinding machine at a 10° angle with the actual be made and telemetered to the ground station if a
point having a radius of approximately 20 microns. In charge pattern is to be derived from the data. Assuming
order that the probe 12 be a voltage sensor under the
 a maximum velocity of ten hundred meters per second
condition desired to be measured, it must be sharp
 at cloud base and assuming that the electric fields are
enough so that a corona current will flow from the 15
 of interest mainly inside clouds, it is necessary that a
point. This is the case if the electric field adjacent the data point be taken every 0.04 second. This means that
point 16 is higher than approximately 3,000,000 volts
 the sensor for the electric field must have a relatively
per meter. The sharper the point the greater the elec-
 fast response. The magnitude of the electric fields vary
trie field at the tip of the point. When there is
 from 30 y^ per meter in fair weather at cloud level
3,000,000 volts per meter at the tip 16 of the corona 20
 to 300>ooo volts per meter inside thunder storms at
point there is only approximately 5 kilovolts per mter conditions when lightning is initiated. This range, how-
m the surrounding air.
 ever does not have to ^ covered by the instrument
The sharp edge of the fin 14 acts as another potential
 since the objective is to survey electric fie,ds only in the
sensor. An electric circuit including linearizing resistor
 range of interest to artificially initiate lightning. A real-
24, relaxation oscillator 26, and the shell of the rocket 25 .^
 estimate ., tha{ the e,ectric fie,ds from 5 Q00 v<j|ts
28 is interposed between the two voltage sensors, the
 metef to 10Q QQQ ^  meter shou,d fee mea
point 16 of the probe 12 and the fin 14, respectively.
 sured Because of a hj h availablit of the j.
The resistor 24 is a high ohm resistor, and in one partic-
 tude Qf e,ectric fields inside doudi in as we,, as
ular embodiment ,s in the order of 5,000 megaohms.
 m u and because of ^ , uncerta-nties involved
This creates a voltage drop over the resistor 24 which 30
 jn dicti tri d H htnin* from Aeoitical consid.
.s large compared with the voltage drop between Uie
 e^ ^ £ no » h * demands Qn accu
corona point 16 and the environment. Such makes the measurements. Therefore, an accuracy of 20
corona current flowing through the circuit substantially ' . . „ „ . ' '
proportional to the electric field if the electric field is P%c.ent ls generally sufficient
higher than 5 kilovolts per meter in the surrounding air. 35 The position of the rocket at anytime during the
It has been found that resistors between 1,000 and flight muit be known to relate the electric field to the
10,000 megaohms operate satisfactory for linearizing locatl°n of observation. Also, here the accuracy re-
the corona current flowing through the circuit. <»u!'ed IS "ot extrkeme' An accuracy of 20 percent of the
Connected to the linearizing resistor 24 is the relax- a'tll"de ab°ve the f ou"d » *f'"ent. The trajectory
ation oscillator 26, which includes a capacitor 32 con- 40 °fthe rof«' may be calculated by computers or syn-
nected in shunt with a neon bulb 34. A lead 36 is pro- ch™n'zed *™& radar information,
vided for coupling the relaxation oscillator to the shell ; Whlle a .preferred embodiment of the invention has
28 of the rocket for completing the circuit. The relax- been described us.ng specific terms, such description is
ation oscillator produces a chain of pulses 18, the fre- for '"ustratwe purposes only, and it is to be understood
quency of which is directly proportional to the corona 45 that changes and variations may be made without de-
current flowing through the circuit. A transmitter 38 is Partm8 from the 8Pmt or 8COPe of the following claims:
carried in the rocket and is coupled to the relaxation l-An apparatus for measuring the electric field in the
oscillator 26 by means of a capacitor 40 for transmit- atmosphere comprising:
ting the chain of pulses back to a receiving station A- self-propelled rocket capable of being propelled
which includes the receiver 20 and the frequency to 50 through the atmosphere,
D.C. converter 22 located at the control center. In one B- an elongated probe carried by said rocket con-
particular embodiment, the corona current flowing structed of 1/16 inch diameter tungsten steel rod
through the circuit is 1 micro amp, therefore, the volt- and having a point being sharpened at a 10° angle,
age drop across the 5,000 megaohm resistor 24 is 5,000 c- fins carried by said vehicle spaced a predeter-
volts. This voltage drop is much larger than the voltage mined distance from said elongated probe,
drop at the corona point 16 which causes the current D- an electrical circuit connecting said elongated
flow to vary substantially directly proportional to the probe and at least one of said fins,
variations in the electric field surrounding the rocket. E- a high ohm resistor coupled in said electrical cir-
From tests conducted in laboratories using simulated „ cuit between said, elongated probe and said one of
electric fields for creating corona current flow through said fins, and
the circuit, the electric field through which the rocket F. a relaxation oscillator coupled in said circuit for
is passing can be determined. generating a chain of pulse having a frequency pro-
In one particular application, the rocket was approxi- portional to the difference in voltage at, said elon-
mately two meters long and reached burn out after ap-
 65 gated probe and said one of said fins,
proximately two seconds at an altitude of about 1,000 whereby the frequency of said chain of pulses is pro-
meters. After burn out the rocket ballistically reaches portional to the electric field through which said
an altitude of about 6,000 meters after 30 seconds and vehicle is traveling.
3,760,268
2. An apparatus for measuring the electric fields in
clouds and the like comprising:
A. a self-propelled rocket,
B. fins carried adjacent the rear end of said rocket,
C. an elongated probe having a corona point thereon
carried on the front of said rocket,
D. an electric circuit coupled between said elongated
probe and said one of said fins providing a current
path for corona current caused by the difference in
voltage at said corona point and said one of said
fins,
10
E. a high ohm resistor connected in said circuit in se-
ries with said elongated probe for substantially lin-
earizing the relationship between said corona cur-
rent and said electric field being measured, and
F. means for transmitting a signal having a frequency
corresponding to the amplitude of said corona cur-
rent.
3. The apparatus as set forth in claim 2, wherein said
resistor is a 5,000 megaohm resistor.
15
20
25
30
35
40
45
50
55
60
65


Rocket borne instrument to measure electric fields inside electrified clouds

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server