A meteoroid detector is described which uses, a cold cathode discharge tube with a gas-pressurized cell in space for recording a meteoroid puncture of the cell and for determining the size of the puncture

Hughes, F. M.

Mcmaster, L. R.

Peterson, S. T.

English

NASA Technical Reports Server

as.A ..--
REPLY TO
ATTN OF:
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON. D.C. 20546
OCT 1 8 1973
TO: KSI/Scientific & Technical Information Division
Attention: Miss Winnie M. Morgan
FROM: GP/Office of Assistant General Counsel for
Patent Matters
SUBJECT: Announcement of NASA-Owned U.S. Patents in STAR
In accordance with the procedures agreed upon by Code GP
and Code KSI, the attached NASA-owned U.S. Patent is being
forwarded for abstracting and announcement in NASA STAR.
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U.S. Patent No. :
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NASA Patent Case No.
NOTE - If this patent covers an invention made by a corporate
employee of a NASA Contractor, the following is applicable:
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Pursuant to Section 305(a) of the National Aeronautics and
Space Act, the name of the Administrator of NASA appears on
the first page of the patent; however, the name of the actual
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Copy of patent cited above
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https://ntrs.nasa.gov/search.jsp?R=19730023595 2020-03-17T09:31:55+00:00Z
United States Patent
McMsster et al.
[in 3,763,691
[45] Oct. 9, 1973
[54] METEOROID DETECTOR
[75] Inventors: Leonard R. McMaster,
Williamsburg; Sheldon T. Peterson;
Frank M. Hughes, both of
Hampton, all of Va.
[73] Assignee: The United States of America as
represented by the Administrator of
the National Aeronautics and Space
Administration, Washington, D.C.
[22] Filed: Sept. 27, 1971
[21] Appl, No.: 184,090
[52] U.S. Cl 73/12, 73/170 R
[51] Int. Cl GOlw 1/08, GOln 15/00
[58] Field of Search 73/12, 170 R;
324/65 R
[56] References Cited
UNITED STATES PATENTS
1,448,540 3/1923 Houskeeper 324/65 R X
3,407,304 10/1968 Kinard et al 73/12 X
3,446,068 5/1969 Slattery et al 73/12 X
Primary Examiner—Richard C. Queisser
Assistant Examiner—Stephen A. Kfeitman
Attorney—Howard J. Osborn et al.
[57] ABSTRACT
Use of a cold-cathode discharge tube with a gas-
pressurized cell in space for recording a meteoroid
puncture of the cell and for determining the size of the
puncture.
3 Claims, 1 Drawing Figure
VARIABLE
D.C. VOLTAGE
POWER SUPPLY
RECORDING
D.C. VOLTMETER
PRESSURIZED-CELL
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Onclas
00/14 18172
PATENTED on 9IH73 3.763.691
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20
INVENTORS
LEONARD R. McMASTER
SHELDON T. PETERSON
BY
 FRANK M^UGKES .
3,763,691
1 2
METEOROID DETECTOR a meteoroid in space, gas will flow through the punc-
ORiriN OF THP IMVPMTIOM tUrC ilUO SpaCe" The g&S density inside the tube W'" de'ORIGIN F T E INVENTION
 crease |o a va,ue whefe a discharge> similar to that of
The invention described herein was made by employ- a neon glow lamp, will take place. The glow discharge
ees of the United States Government and may be man- 5 tube operates like a pressure switch, indicating an open
ufactured and used by or for the Government for gov- circuit before a puncture and indicating a closed cir-
ernmental purposes without the payment of any royal- cuit, by allowing a current to flow between the elec-
ties thereon or therefor. trodes, after a puncture. As the gas density within the
BACKGROUND OF THE ,NVENT,ON ,„
The invention relates generally to meteoroid detec- until it can no longer be maintained. Recording the cur-
tors and more specifically concerns a meteoroid detec- rent flow through the discharge tube then gives a time
tor that not only detects a meteoroid but also deter- history of the events resulting from the puncture of a
mines the size of the puncture caused by the meteoroid. detector cell, i.e., a record of the gas leak rate; hence,
The possible danger in an encounter between mete- 15 the size of the puncture can be determined,
oroids and spacecraft has resulted in various research , _._ _„_ _.„ . „,..,_
activities designed to define the meteoroid environ- BRIEF DESCRIPTION OF THE DRAWING
ment in space and its effect on spacecraft. The most The sole FIGURE in the drawing is a schematic dia-
straightforward way of determining meteoroid hazards gram of an embodiment of the invention,
to spacecraft is accomplished by penetration tech- 20 _.-.». „,- -™,r- ,T.,*,J-^,T-,^^,
niques. One such technique employs a simple one-shot DETAILED DESCRIPTION OF THE INVENTION
device referred to as a pressurized cell detector. It con- Turning now to the embodiment of the invention se-
sists of a gas-pressurized cell equipped with a pressure lected for illustration in the drawing the number 11
sensor. When a meteoroid punctures the cell, the gas designates a cold-cathode glow discharge tube having
leaks out and the loss of pressure is detected by the 25 electrodes 12 and 13. These electrodes are enclosed by
pressure-sensitive device. a pressure-tight wall 14. Electrode 12 is connected
The pressure sensor presently used with the pressur- through wall 14 to ground and to one side of variable
ized cell detector is a diaphragm-actuated microswitch. d.c. voltage power supply 15. Electrode 13 is con-
To date no attempt has been made to determine the nected through wall 14, a resistor 16 and a variable re-
size of a puncture using these sensors, even though a 30 sistor 17 to the other side of power supply IS. A re-
method exists as follows: two switches are installed and cording d.c. voltmeter 18 is connected across resistor
set to actuate at different pressures, the time interval 16. The purpose of variable resistor 17 is to adjust the
between their actuations giving the leak rate and, amplitude of the voltage recorded by voltmeter 18.
thereby, the size of the hole. The weight (0.78 Kg) and Tube 11 is attached to a pressurized cell 19, having
size (3.4 X 10~5m3) of these mechanical switches make 35 walls 20. The enclosure of discharge tube 11 is con-
their use in large quantities prohibitive and if penetra- nected to the enclosure of cell 19 through an opening
tion size is to be obtained, as well as a record of the 21 such that the pressure inside tube 11 is the same as
event, their use is even more undesirable as weight and the pressure inside cell 19. Walls 20 are exposed to
volume are doubled. space and are made from any suitable material that will
A review of the proposed meteoroid population in- "*^ puncture when impacted with a meteoroid. A tube 22
vestigation through interplanetary space, using pressur- and a valve 23 are used for pressurizing cell 19 with any
ized cell detectors, indicates a need for a pressure sen- suitable gas, such as helium.
sor considerably reduced in weight and volume from In the operation of this invention power supply 15 is
those currently used. adjusted to some desired level. Then variable resistor
It is therefore an object of this invention to provide 45 17 is adjusted so that the voltage across resistor 16
a pressure sensor considerably reduced in weight and when tube 11 breaks down is within the range of re-
volume from those currently used to monitor pressur- cording d.c. voltmeter 18. Valve 23 is opened and he-
ized cell meteoroid detectors. . Hum is pumped through tube 22 until the pressure in-
Another object of this invention is to provide a mete- side tube 11 and cell 19 is higher than the breakdown
oroid detector that not only detects a meteoroid but pressure for the particular voltage setting of power
also determines the size of the puncture caused by the source 15. Valve 23 is then closed and cell 19 is put
meteroid. into space. Whenever a meteoroid punctures walls 20
Other objects and advantages of this invention will of the helium inside cell 19 begins to leak through the
become apparent hereinafter in the specification and puncture into space. This continues until the pressure
drawing. inside the cell and discharge tube decreases to a value
«i iMMAPvr»i7Tuc iMvcwTir»w where a discnarge occurs. The resulting conduction
SUMMARY OF THE INVENTION produces a voltage drop across resistor 16 which is re-
The invention includes a sensor for sensing pressure corded by voltmeter 18. The cold-cathode discharge
changes inside a gas-pressurized cell. The pressure sen- tube 11 has thus functioned like a pressure switch, indi-
sor is a simple cold-cathode glow discharge tube oper- eating an open circuit before a puncture and indicating
ating with an electric potential applied across two elec- a closed circuit by allowing a current to flow between
trodes. The pressure sensor is mounted on the gas- electrodes 12 and 13 after a puncture. As the pressure
pressurized cell such that the pressurized gas inside the within cell 19 continues to decrease after breakdown,
cell is inside the tube. The potential applied across the
 fi. the current flow between the electrodes will also de-
two electrodes is insufficient to cause a breakdown be- crease until a discharge can no longer be maintained,
tween the electrodes at the initial molecular density Recording the event of current flow through discharge
within the cell. However, when the cell is punctured by tube 11 by voltmeter 18 will give a time history record
3,763,691
. of the puncture of cell 19, i.e., a record of the helium
leak rate and, hence, the size of the puncture can be de-
termined. The largest puncture whose size can be de-
termined is a puncture the size of opening 21. If a larger
puncture occurs, tube 11 will 'see' it as a puncture the 5
size of opening 21.
The reason tube 11 acts as it does is that a gas in its
normal state is almost a perfect insulator, but when an
electric field of sufficient intensity is created in the gas
between two electrodes, the gas becomes a conductor. 10
This transition from an insulating to a conducting state
is called the electrical breakdown. The relationship be-
tween the breakdown voltage and the gas pressure,
known as Paschen's law, exhibits a minimum break-
down voltage at some medium pressure. At both higher 15
and lower pressures relatively large voltages are re-
quired for breakdown. Without the increased electric
field, the mean free path of the gas particles is too short
at the higher pressures for them to gain enough energy
for ionization between successive collisions. At the 20
lower pressures the mean free path is so long that the
probability of any collision is very small.
There are two main advantages of this invention over
the prior art. First, it provides a means for recording a
meteoroid puncture of a cell and for determining the 25
size of the puncture; and second, by using a cold-
cathode discharge tube to perform these functions a
great saving in both weight and volume is. obtained.
It is to be understood that the form of the invention
herewith shown and described is to be taken as a pre- 30
ferred embodiment. Various changes may be made
without departing from the spirit and scope of the in-
vention as defined in the subjoined claims. For exam-
ple, a transmitter could be used in place of voltmeter
18 to transmit the history of the conduction of tube 11 35
to earth before it is recorded. The shapes and sizes of
tubes 11 and cell 19 can be different from those shown.
And gases other than helium could be used as the pres-
surizing gas.
What is claimed is: 40
1. A method for detecting a meteoroid puncture in a
cell and for determining the size of the puncture com-
prising the steps of:
attaching a cold-cathode discharge tube, having two
electrodes, to said cell such that said two elec-
trodes are inside said cell;
applying a voltage across two electrodes;
pressurizing said cell with a gas to a level where there
is no conduction between said two electrodes;
placing said cell in a space environment; and
recording a history of the conduction between said
two electrodes whereby the event of a meteoroid
puncture and the size of the'puncture can be deter-
mined from said recorded history.
2. Apparatus for detecting meteoroids in space and
for measuring the potential danger of the meteoroids
detected comprising:
a cold-cathode discharge tube having two electrodes;
a potential source connected across said two elec-
trodes;
means for recording a history of the conduction be-
tween said two electrodes;
a cell, and
means connecting the interior of the tube with the in-
terior of the cell, a gas filling the tube, cell and con-
necting means, the gas being pressurized to such an
extent as to prevent conduction between said two
electrodes and exposed to space so that when a me-
teoroid punctures said cell the gas will leak into
space decreasing the pressure to a value where
there is conduction between said two electrodes
and thereafter further decreasing the pressure until
there is no conduction between said two electrodes
whereby the history recorded by said recording
means indicates the event of a puncture and the
size of the puncture.
3. Apparatus according to claim 2 wherein said gas
is helium.
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