A sensor, consisting of a thin dual-capacitor assembly with an outer film of thermal-control material, is used to detect micrometeoroid particles. A coincidence counting circuit is used to count the penetrations

Davison, E. H.

English

NASA Technical Reports Server

NASA TECH BRIEF .
May 1964	 Brief 63-10443 
This NASA Tech Brief is issued by the Technology Utilization Division to acquaint industry 
with the technical content of an innovation derived from the NASA space program. 
Improved Sensor Counts Micrometeoroid Penetrations 
	
Capacitor No.1.._._..
	
I	 ....._.—Capacitor No. 2 
Thermal-Control
uminum Film 
Micrometeoroid 0
Dielectric Sheet Aluminum FiIm– 
Dielectric She
	 Ground Plate
SENSOR DETAIL 
Charging Resistor
	
Ri	 Dl	 D2 D3 
	
C1	
^^k 
R3: : 	 Multivibrator 
Solar Cells	 Counter( 
Charging Resistor	 Sensor 
SENSOR CONNECTED IN

COINCIDENCE COUNTING CIRCUIT 
The problem: To design a simple, rugged device 
which can be used on space vehicles to detect and 
count meteoroid particles that penetrate known thick-
nesses of metal. 
The solution: A sensing device consisting of a thin 
dual-capacitor assembly with an outer film of thermal-
control material on which the micrometeoroids im-
pinge. A coincidence counting circuit is employed to 
record the micrometeoroid penetrations. 
How it's done: The sensor comprises a sandwich-
type construction forming a pair of capacitors, No. 1 
and No. 2. This sensor includes a stainless steel ground 
plate in the form of a thin metal sheet of known thick-
ness and a layer of very thin dielectric material bonded 
to opposite faces of the ground plate. Each of the 
outer surfaces of the dielectric layers is covered with
a film of aluminum. Successful tests have been made 
on representative units in which the ground plate had 
a thickness in the range between 1 mil and 10 mils, 
and the dielectric layers were each 0.25 mil thick. The 
aluminum films were vapor-deposited to a thickness 
of approximately 1,000 angstroms. 
The aluminum surface of the sensor that is exposed 
as a target to the micrometeoroids is coated with a 
thin layer of silicon monoxide to limit the maximum 
temperature of the device by controlling the ratio of 
solar absorptivity to low-temperature emissivity. The 
thickness of the thermal-control coating, of vapor-
deposited silicon monoxide, can range between ap-
proximately 1,000 angstroms and 10,000 angstroms, 
depending upon the maximum temperature that can 
be tolerated.
(continued overleaf) 
Now
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States Govern-
ment. nor NASA, nor any person acting on behalf of NASA: A. Makes 
any warranty or representation, express or implied, with respect to the 
accuracy, completeness, or usefulness of the information contained in
this document, or that the use of any information, apparatus, method, 
or process disclosed in this document may not infringe privately-owned 
ri g hts: or B. Assumes any liabilities with respect to the use of, or for 
damages resulting from the use of, any information, apparatus, method, 
or process disclosed in this document.
https://ntrs.nasa.gov/search.jsp?R=19630000079 2020-03-11T16:47:27+00:00Z
Because of the extreme thinness of the aluminum 
films and the dielectric layers, the net resistance .to 
penetration of the entire sandwich is essentially due 
to the resistance of the ground plate. Complete pen-
etration of the entire sandwich occurs in less than a 
microsecond, making it possible to use conventional 
coincidence counting circuits with the sensor. With 
this counting method, only those micrometeoroids 
that penetrate the entire thickness of the sensor are 
recorded. Spurious counts from other causes, such as 
aluminum-vapor burnoff when the dielectric is punc-
tured or accidental breakdown of the dielectric, are 
thus avoided. 
In the operation of the system, the two capacitors 
(each having a capacitance of 1 to 2d) comprising the 
sensor are charged by the solar cell, placing a negative 
charge on the ground plate and raising the potential 
of each of the aluminum layers to approximately 100 
volts. As a micrometeoroid particle passes through 
the sensor, the two capacitors are sequentially dis-
charged, and if two voltage pulses arrive at diode Dl 
in the counting circuit in a given time interval, a 
pulse will pass through D2 and D3 to a bistable 
multivibrator and be recorded as a penetration in the 
counter.
In the event that the micrometeoroid strikes the 
left side of the sensor and does not pass through the 
entire sandwich, but discharges only capacitor No. 1, 
for example, the resulting discharge of capacitor Cl 
sends a pulse through resistor RI, and not through 
Dl. If the micrometeoroid strikes the right side of the 
sensor, without passing through the entire sandwich, 
and discharges capacitor No. 2, the resulting dis-
charge of C2 sends a pulse through R2 and R3. Be-
cause the resistance of R3 is much greater than that 
of R 1 and R2, the signal is not strong enough to pass 
through D2 and D3 to the counter. 
Note: 
The sensor may act as its own structural support 
which, together with the fact that both sides can be 
used for penetration measurement, minimizes the 
weight of the device per unit area exposed. 
Patent status: NASA encourages the immediate 
commercial use of this invention. It is owned by 
NASA, and a patent application has been filed. When 
patented, royalty-free nonexclusive licenses for its 
commercial use will be available. Inquiries concern-
ing license rights should be made to NASA Head-
quarters, Washington, D.C. 20546. 
Source: Elmer H. Davison 
Lewis Research Center (Lewis-76) 
Brief 63-10443


Improved sensor counts micrometeoroid penetrations

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