A technique is described for breaking ice in the path of a ship. A laser is placed on the bow of the ship with apparatus to scan the ice in the path of the ship with the laser beam. The beam cuts or shatters the ice, enabling the ship to break the ice in its path

Hess, R. V.

Lucht, R. A.

Saunders, A. R.

English

NASA Technical Reports Server

NASA Case m. LAR 10815-1i ji
| A TECHNIQUE FOR BREAKING ICE IN THE PATH
j OF A SHIP
The invention relates to the use of a laser for cutting or shattering
ice in the path of a ship thereby enabling the ship to move through
the ice.
The invention consists essentially of a laser 11 on the bow of a ship
12. The beam 16 from laser 11 strikes a scan mirror 14. The reflected
beam 17 scans the layer of ice 13 in front of ship 12. Beam 17 either
cuts or shatters ice 13 thereby enabling the ship to move through the
ice.
The apparatus used in this inventi. on is shown in more detail in FIG.
2. The beam 16 from COo laser 11 is directed into a beam splitter 18.
The part of beam 16 that is reflected is again reflected by mirror 19
onto photodetector 20 which indicates the intensity of beam 16. The
part of beam 16 that passes through beam splitter 18 is reflected by a
parabolic mirror 21 onto a rotating scan wheel mirror 22 which is
driven in a clockwise direction by a clock drive 23. Scan mirror 22
has five surfaces, hence each time the mirror rotates through 72 degrees,
the laser beam will be reflected by a different surface. Consequently,
each time the mirror rotates through 72 degrees, the reflected beam 17
will scan from a point in front of the ship to the left through 72
degrees. The scan mirror can have any number of reflecting surfaces
other than two as shown in FIG. 1 or five as shown in FIG. 2.
C02 laser 11 usually operates in a continuous mode. Q- switching of
laser 11 is required for operating it in a high power, rapid-pulsed-
mode. In this mode, the inversion densities are built up to high levels
to be discharged in one large pulse at power levels several times above
the continuous wave output of the same cavity. Q- switching of laser 11
is accomplished by removing the output mirror of its resonating cavity
and replacing the mirror with a rotating mirror. The rotating mirror is
rotated by a constant speed synchronous motor 24 at about 3000 rpm. :
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The novel feature of the invention appears to lie in the use of a laser
to cut (continuous mode) or shatter (pulsed mode) ice in the path of a
ship thereby enabling the ship to move through the ice.
Inventors: Andrew R. Saunders; Robert V. Hess; Roy A. Lucht
Employer: NASA/Langley Research Center
r^ g^^ age^ ^^ fecon C. Ellis
Prepared by: William H. King
Serial No.: 233,587
Filing Date: 3/10/72
https://ntrs.nasa.gov/search.jsp?R=19720014870 2020-03-23T10:29:05+00:00Z
CASENO.NASA-LAR-10815-l
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DJVENTOR(S): ANDREW R. SAUNDERS
ROBERT V. HESS
ROY A. Ll^CHT
FIG. 1
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ROY A. LUCHT
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NOTICE
The invention disclosed in this document resulted from
research in aeronautical and space activities performed under
programs of the National Aeronautics and Space Administration.
The invention is owned by NASA and is therefore available for
licensing in accordance with the NASA Patent Licensing Regu-
lation (14 Code of Federal Regulations 1245.200).
To encourage commercial utilization of NASA-owned inven-
tions, it is NASA policy to grant nonexclusive, royalty-free,
revocable licenses to any company or individual desiring to use
the invention while the patent application is pending in the U. S.
Patent Office and within a specified period, presently two years,
after issuance of the patent to NASA. If commercial use of the
invention does not occur during this period, NASA may grant a
limited exclusive, royalty-free license thereby adding an incen-
tive to further encourage commercial development. Any company
desiring to make, use, or sell this invention is encouraged to
obtain a royalty-free license from NASA.
Address inquiries and all requests for licenses to Assistant
General Counsel for Patent Matters, Code GP-1, National
Aeronautics and Space Administration, Washington DC 20546.
NASA-HQ
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provide a new technique for breaking the ice in the path of ships
which eliminates or decreases the disadvantages found in prior
art techniques.
SUMMARY OF THE INVENTION
In this invention a laser is placed on the bow of the ship
and a mirror means is used to scan the beam of the laser across
the layer of ice in front of the ship. There are two modes of
operation used in this invention. In the first, the laser beam
is a continuous beam which cuts the layer of ice; and in the
second, the laser beam is pulsed causing it to shatter the layer
of ice. In both modes of operation the structure of the ice is
weakened thereby enabling the ship to break the ice with much
less ramming force than would be otherwise required. The laser
used in this invention is a C02 or other gas laser with output
powers of 2500 watts or larger, operating in continuous wave or
pulsed modes at 10.6 microns.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic drawing of an embodiment of the
invention;
FIG. 2 is a block diagram of the apparatus used in the
embodiment in FIG. 1; and
FIG. 3 is a graph of ice cutting rate in meters per hour
versus beam power in kilowatts for gas lasers.
DETAILED DESCRIPTION OF THE INVENTION
Turning now to the embodiment of the invention selected
for illustration in the drawings, the number 11 in FIG. 1 desig-
nates a laser that is attached to a ship 12. The ship is
traveling through water that has a layer of ice 13 on top. As
was discussed above, in the past the layer of ice 13 was broken
by explosives or by ramming with the ship. It is the purpose of
this invention to use the laser 11 to break the ice or to aid
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in the breaking of the ice. To accomplish this purpose, a scan
mirror 14 is mounted on ship 12 with any suitable mounting means
15 such as a telescope pedestal. The details of scan mirror 14
are disclosed in FIG. 2. The beam 16 from laser 11 is directed
into mirror 14 such that as mirror 14 rotates the reflected
beam 17 scans the layer of ice 13 in the path of ship 12. There
are two modes of operation for this invention: a continuous laser
beam mode and a pulsed laser beam mode. In the continuous laser
mode of operation, a groove is cut into the ice by the laser
beam and in the pulsed mode of operation the ice is shattered
by the laser beam. In either mode of operation, the structure
ofj the ice layer 13 is weakened to the extent that ship 12 will
move through the ice without any ramming or with substantially
less ramming than would be required if no laser beam were used.
Referring to FIG. 2, there is shown a block diagram of the..
I
apparatus used with laser 11 and scan mirror 14 in FIG. 1. The '
beam 16 from C02 laser 11 is directed into a beam splitter 18.
The part of beam 16 that is reflected is 3gain reflected by a
mirror 19 onto a photodetectdr 20 which indicates the intensity
of the beam 16. The part of the beam 16 that passes through
beam splitter 18 is reflected by a parabolic mirror 21 onto a
rotating scan wheel mirror 22 which is driven in a clockwise
direction by a clock drive 23. Scan mirror 22 has five surfaces,
hence each time the mirror rotates through 72 degrees, the laser
beam will be reflected by a different surface. Consequently,
each time the mirror rotates through 72 degrees, the reflected
beam 17 will scan from a point in front of the ship to the left
through 72 degrees. The scan mirror can have any number of
reflecting surfaces other than two as shown in FIG. 1 or five as
shown in FIG. 2 without departing from this invention.
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Q-switching of CC^ laser 11 is required for operating the
device in FIG. 2 in a high power, rapid-pulsed mode. In this
mode, the inversion densities are built up to high levels to be
discharged in one large pulse at power levels several times
above the continuous wave output of the same cavity. Q-switching
of C0« laser 11 is accomplished by removing the output mirror
of its resonating cavity and replacing the mirror with a rotating
mirror. The rotating mirror has a gold-coated optical surface
and is rotated by a constant speed synchronous motor 24 at about
3000 rpm.
The CC>2 laser 11 can be a CO^-N^-He laser with an output
power of 2500 watts or larger in the TEMQQ and TEMQ-, modes com-
bined with an output frequency of 10.6 jum. The beam diameter is
1 cm with a beam .divergence of less than 2 milliradians. Regu-
lated d.c. excitation, flow-through water cooling is used with
 ( i
an input power requirement of 208 volts a.c., 50 to 60 Hz and
at 2500 watts of output power.
All optical components have gold-coated optical surfaces
with provisions for water cooling. The opics and laser cavity
is mounted on an optical bench for accurate alinement. The rota-
ting scan mirror 22 is mounted on a pedestal telescope mount for
vertical and horizontal alinement to scan the target. The mirror
22 is driven by a synchronous motor electric clock drive 23 with
speeds of 1/100 to 1 rpm allowing linear scan rates between
50-5000 m/hr.
In order to prove the feasibility of this invention, an
experimentally cutting rate of 14.8 m/hr was obtained with a
35-watt CW COo laser operated at 10.6 microns in single mode
with the beam focused to 1/250 Cm diameter. Based on this
experimentally obtained cutting rate, cutting rates were
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calculated as a function of CC^ laser beam output power for
0.1-100 KW as shown in FIG. 3.
 : Linear cutting rates in excess
of 1 km/hr can be obtained with beam powers of about 3 KW. Based
on the results of the preliminary experimental studies the
radiative energy conversion efficiencies are near the theoretical
values for melting with only negligible vaporization and
refreezing. Since the 10.6 jam radiation is absorbed by the
hydrogen bonds in the ice crystal lattice the energy will be
used primarily to break these bonds selectively, resulting in
melting with potentially less energy transfer into the trans-
lational modes than in conventional thermal excitation processes.
The advantages of this invention are numerous. It provides
a technique for clearing ice from the path of a ship in which
no explosives are used, thus avoiding a hazard to required
personnel. Substantial structural reinforcement of the ship's1
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hull is not necessary since very little, if any, ramming by '
the ship is required. Close contact with the ice is not needed.
Not as large an expenditure of power is needed in the use of this
invention as was required by previous techniques. When the
technique of this invention is used, the ship's speed will be
substantially greater than when previous techniques were used.
It is to be understood that the form of the invention herewith
shown and described is to be taken as a preferred embodiment.
Various changes may be .made in the shape, size and arrangement
of parts. For example, equivalent elements such as different
lasers, different scanning mechanisms and different means for
pulsing the laser beam may be substituted for those illustrated
and described herein, parts may be reversed, and certain features
of the invention may be utilized independently of the use of
other features, all without departing from the spirit or scope
of the invention as defined in the following claims,
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What is claimed as new and desired to be secured by
Letters Patent of the United States is:
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A technique for breaking ice in the path of a ship

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