Hi-Shear Technology, Corp., (HSTC) has designed and built a Laser equivalent NASA Standard Initiator (LNSI). Langlie tests with a laser diode output initiating ZPP were conducted as a part of this effort. The test parameters include time to first pressure, laser power density requirements, and ignition time. The data from these laser tests on ZPP are presented

Callaghan, Jerry D.

Tindol, Scot

English

NASA Technical Reports Server

TORRANCE.CALIFORNIA
N93-20145
Laser Diode Ignition Characteristics of
Zirconium Potassium Perchlorate (ZPP)
By
Jerry Callaghan and Scot Tindol
ABSTRACT
Hi-Shear Technology, Corp. (HSTC) has designed and built a Laser equivalent NASA Standard
Initiator (LNSI). Langlie tests with a laser diode output initiating ZPP have been conducted as
a part of this effort. The test parameters include time to first pressure, laser power density
requirements and ignition time. The data from these laser tests on ZPP are presented.
INTRODUCTION
This paper describes a part of an effort conducted by HSTC to design and build a Laser
equivalent NASA Standard Initiator (LNSI). There is a need to establish a data base on the
interaction between laser energy and pyrotechnic mixtures commonly used in aerospace
applications. One of the standard pyrotechnic mixtures being initiated via a laser system is ZPP.
The ZPP used in this study has been manufactured by HSTC (HSTC P/N 939321-003) since
1964 for use in the NSI.
There have been many efforts and studies using solid-state laser systems (Nd:glass, Nd:YAG,
RUBY and others) as initiation sources. A steady increase in technology relating to high power
laser diodes has resulted in the production of laser diodes with sufficient output power for
initiation of explosive materials. One drawback in the technology of laser initiation is the lack
of published data regarding experimental procedures and test results. Publication of this type
of information in proper format would greatly help designers of new and existing systems in the
selection and incorporation of lasers as an initiation source.
Laser initiation systems offer many desirable features not found in current ordnance systems.
These features include the virtual elimination of inadvertent initiation by stray voltages,
electromagnetic radiation (EMR) and electrostatic discharge (ESD). The inherent safety of a
laser initiation system allows for the installation of the ordnance during the assembly of ordnance
functioned devices resulting in less time required during installation or integration of the final
assembly.
This paper will describe the experimental procedure used to obtain specific statistical data on
laser diode initiation of ZPP. This testing was performed under laboratory conditions at HSTC
and was funded under IR&D program number 970011.
Approved for public release; distribution is unlimited.
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TORRANCE • CALIFORNIA
EXPERIMENTAL PROCEDURE
The laser diode used for these tests was manufactured by Laser Diode, Inc. This diode operates
at 820nm nominal and has an output of 750mW into a 0.29 Numerical Aperture (NA), 100
micron core fiber optic. This fiber optic cable is a hermetic integral pigtail installed by the
manufacturer. The fiber optic cable was terminated at HSTC with an ST-type connector. The
laser diode output was controlled by a Spectra Diode Lab Model 822 laser diode driver. The
test setup is shown in Figure 1.
As the primary objective of this testing is to provide specific data on the initiation of ZPP with
a laser diode, the spot size must be a constant. This was accomplished by pressing the ZPP
directly on the fiber optic which holds the spot size constant at 100 microns. This test method
also allows for the energy output to be measured directly at the pyrotechnic interface. To
preserve the laser diode pigtail from damage when the ZPP initiated and allow for easy loading
of the test initiators, an interface fiber optic cable assembly was used. This interface cable was
terminated on one end with an ST-type connector for mating with the laser diode and an SMA
connector for attaching the test cartridge on the other. The test initiator is shown in Figure 2.
The ST-type connector is a precision fiber optic connector which minimizes the interconnect
losses. Both the test initiator and the energy meter accept the SMA connector. An O-ring is
included in the SMA to provide a pressure seal when the test initiator is functioned. The
interface cables were labeled and calibrated before the Langlie was begun to insure the
repeatability of the interconnect loss through several mate/de-mate cycles. The actual loss due
to this interconnect was not a concern for this series of tests. The calibration of the interface
cables was to insure the losses were repeatable (within measurement error) over multiple
mate/de-mates with the laser diode pigtail.
As stated above, the ZPP was consolidated directly onto the fiber optic face. A nominal 120
milligrams of pyrotechnic was loaded into the cartridge in two equal increments. After several
pre-test firings it was found the cartridge function characteristics were not affected by the
deletion of a closure. The omission of the closure during loading allowed for quicker testing.
The energy levels were monitored by a Photodyne Model 66XLA optical power/energy meter
with a Model 350 integrating detector head. This detector head has adapters to allow any style
of fiber optic connector to be accurately placed into the head, including a bare, unterminated
fiber optic. The values calculated during the Langlie testing were measured at the SMA
connector before installation into the test initiator. The various output values were obtained by
varying the current supplied to the laser diode. The test initiator was then attached to the SMA
connector and the ZPP loaded.
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TORRANCE • CALIFORNIA
LASER DIODE
DRIVER
LASER DIODE _
ENERGY
METER
ST CONNECTORS
DD _
............. ' l
TEST INITIATOR
TRIG
@
O'SCOPE
1Oct
CLOSED
BOMB
I 1
XDUCER
AMP
TRANSDUCER
Figure 1
Test Set-up
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TORRANCE'CALIFORNIA
5/B HEX
IN _ /_O-RING
CLOSURE _ WVVV_ _ _u
,3750-24UNJF-3A / ,250-36UN5-2^
CONNECTOR
Figure 2
Laser Test Initiator
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TORRANCE.CALIFORNIA
The test initiator was installed into a 10cc test bomb equipped with a pressure transducer to
monitor pressure and function time. All tests were performed at room ambient temperature and
humidity. A total of 30 trials were used in the test series. Of these 30 devices a total of 14
devices functioned. This even split between fire and no-fire indicates proper bracketing of the
energy. A typical pressure verses time curve is shown in Figure 3. A typical NSI output is
shown in Figure 4. The output monitor from the laser diode driver was used to trigger the
O'scope and is used to find the function time.
TEST RESULTS
The Langlie statistical approach has an advantage over other test methods used in determining
the function characteristics of ordnance devices. The Langlie method finds both the mean and
standard deviation efficiently without requiring a detailed test procedure as does a Bruceton. An
upper and lower limit of the mean firing point are chosen and the Langlie testing begins halfway
between these two points. As the test continues the next level selected is calculated on the
response of the previous firings - fire or no-fire. The statistical results from the Langlie test are
shown in Table 1.
For information purposes the test initiators that did not function at the Langlie stimulus were
fired at the calculated 99.9% at 95% confidence point. All 16 test initiators functioned.
The function time of an NSI when fired with 3.5 Amps constant current is 1.0 mSecond
minimum and 6.0 mSeconds maximum. The maximum jitter in a test series is 3.5 mSeconds.
The 1.0 mSecond minimum time is based on a NASA study which followed the function times
of NSI lots over several years. No NSI's were found to function less than 1.0 mSecond when
fired with 3.5 Amps. The LNSI function times ranged from 0.39 mSeconds to 2.5 mSeconds.
This discrepancy in the minimum function time is not a true comparison to the NSI as the LNSI
does not have a bridgewire.
CONCLUSIONS
The use of laser diodes as the ignition source of ZPP is a viable approach. Conventional testing
of these devices produces repeatable results. The current laser diode technology can supply
twice the all-fire energy into a 100 micron core fiber optic cable.
Additional studies planned by HSTC include the environmental dependance (temperature, shock
and vibration) on the all-fire energy level. Other analysis includes a Taguchi test on the
assembly process/procedures involved in the manufacture of the LNSI. Testing is planned on
other pyrotechnic materials as well as secondary explosive materials.
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TORRANCE - CALIFOI_NIA
i
t
-500,000 us
l i _
Vmarker2 r 2 )
Vmarker I( 2 )
delta V( 2 )
I 200 mVldlv
offset: 400,0 mV
1.000:1 dc
_-.- _.__. : _ _
.................................................: ........__ 2 5oo
offset:
I, 000 :I
........................ --............................ ,,
.]
4.50000 ms 9,50000 is
1,00 msldiv
0.00000 V stop marker: 300.O00us
1.75000 V start marker: 0.00000 s
-1,75000 V delta t_ 300,O00us 1
11aelta t: 5,33333kI_
mVldlv
1.500 V
dc
240,0 IV
Figure 3
Typical LNSI Pressure Curve
Channel 2 Calibration 300 psig/Volt
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TORRANCE'CALIFORNIA
v ......
,i. offset: 0,000
:i: 1,000 : 1
.!-
_ ...... 'i 2 500
offset:
1, 000 : 1
S
, -_
:i: i
-500,000 us 4,50000 ms 9,50000 ms
1,00 ms/div
Vmarker2(2 ) 1,75000 V stop marker: 2,62000ms
Vmarker1( 2 ) 31,250 mV start marker, 0.00000 s
delta V(2) 1.71875 V delta t: 2.62000ms '1 ...1r"
11del ta t: 381,679
I I00 mVldiv
V
dc
iVl{Iiv
I.500 V
dc
75, O0 IV
Figure 4
Typical NSI Pressure Curve
Channel 2 Calibration 300 psig/Volt
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TORRANCE. CALIFORNIA
TABLE 1
LANGLIE TEST RESULTS
MEAN FIRE (50%)
SIGMA
ENERGY DENSITY
1.24 mJoules
0.12mJoules
15.75 J/CM2
NO-FIRE POINT
0.1%
0.1%
0.1%
CONFIDENCE
90%
95%
99%
ENERGY
0.27 rrdoules
0.23 mJoules
0.18 mJoules
ALL-FIRE POINT
99.9%
99.9%
99.9%
CONFIDENCE
90%
95%
99%
ENERGY
5.65 mJoules
6.56 mJoules
8.65 mJoules
222


Laser diode ignition characteristics of Zirconium Potassium Perchlorate (ZPP)

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