Mike:
TRWonderful went down that rat hole, George Garboden built the desk sized
peroxide powered steam plant that drew vacuum for the 747 based
“demonstrator”. There will be no follow-up: seems that combusting Flourine
and Oxygen onboard an airplane was a “bridge too far”....
I’ve visited w/ some folks in an idle way about all this and concluded that
the decision to take the Navy all electric was in some major part driven by
the performance of diode pumped fiber optic lasers.
Bill
On Sun, Oct 25, 2020 at 4:38 PM Michael Kelly <dmarc-noreply@xxxxxxxxxxxxx>
wrote:
This is puzzling to me, since combustion-driven gas dynamic lasers have
been around since the early 1970s. When I was doing student labor at
Purdue, the guy who became my MSME major professor had me make his huge
vacuum facility operational so that he could finally get his GDL running
(he never did, as far as I know). But he had the nozzle array for it,
built by Bell Aerospace. It was about a foot long, and an inch and a half
square. Its design power was 5,000 watts, CW. It would be no trick to
build a 150 kW GDL for aircraft use, burning Jet-A along with a little
water and helium injection - and no cooling issues at all. And it
certainly wouldn't weigh as much as what they're talking about here.
On October 24, 2020 at 10:28 PM, ken mason <laserpro1234@xxxxxxxxx> wrote:
This technology may very well be sequestered, I haven;t seen so much as a
diagram or illustration to better visualize what is going on.
This could be the breakthrough that turns lasers from fantasy/toy to a
practical device. An order of magnitude weight reduction is not trivial.
I suspect the cooling they talk about is inside the mirad of laser pump
diodes. Photon coupling efficiencies between the 808nm pump and
808nm absorption band in the fiber laser medium which has an
extremely high surface area to volume ratio easy to cool convectively and
conductivity.
I've read articles about etching micro cooling passages in these laser
diodes increasing cooling efficiency and power density. I just don't see
where the
rectivive index matching comes into the picture. How does the coolant get
in the lasing cavity, the resonator is usually directly attached to the
crystal.
Keep looking for technical briefs coming out of some research lab. I'm
excited.
K
On Sat, Oct 24, 2020 at 10:55 AM Henry Vanderbilt <
hvanderbilt@xxxxxxxxxxxxxx> wrote:
Another interesting question: Is the solid lasing element fiber optic, or
something else?
On 10/24/2020 12:57 AM, ken mason wrote:
"Not clear if the coolant actually takes part in the lasing, or simply
doesn't interfere with it, though the latter seems implied."
If it were the former then it may be analogous to a dye laser so double
your pleasure, nothing wasted, sounds almost too good to be true.
I still need a diagram to see the configurations of all the components
and coolant paths.
K
On Fri, Oct 23, 2020 at 12:10 PM Henry Vanderbilt <
hvanderbilt@xxxxxxxxxxxxxx> wrote:
https://spectrum.ieee.org/tech-talk/aerospace/military/fiber-lasers-face-a-challenger-in-laser-weapons
And now a new contender for high-power defense apps - "liquid lasers".
General Atomics is working on them. Per this article, these are apparently
solid-state lasers with liquid cooling passages through the lasing medium.
Coolant is carefully matched for refractive index with the solid medium,
and coolant flow is managed to avoid turbulence. Not clear if the coolant
actually takes part in the lasing, or simply doesn't interfere with it,
though the latter seems implied.
Also mentioned that they're shooting for a ballpark couple hundred
kilowatts output for useful weapon applications, at lasing-device mass on
the order of 5 kg/kw output. (A DARPA goal of 150kw output at 750kg mass
is mentioned for "a fighter jet", presumably a F-35.)
Also mentioned that apparently they can usefully combine the output of
multiple individual devices, which implies very good phase control. Also
implied that the same is true of fiber optic lasers. With limits (in both
cases?) on how many devices can be usefully combined. Mike Griffin
Congressional testimony is mentioned in this regard.
They also mention "a high-density modular high-power lithium-ion battery
system able to store three megajoules of energy", presumably to allow
periods of high-power laser operation in between longer periods of charging
from lower-power continuous sources. These might actually have rocketry
applications, for running pumps, depending.
Henry
On 10/15/2020 3:38 PM, Henry Vanderbilt wrote:
Bill,
I'm sure they're electrically-powered continuous-wave lasers that are
being reported on as in field-test in the tens of kilowatts power range.
If I was sure they were diode lasers however, I wouldn't have phrased that
part "I presume". It's been a while since I followed the technology
closely.
I suspect Ken/Roxanna has it right; the technology involved is likely
fiber optic lasers. Which on hasty reading-up, can be pumped with diode
emitters, so at least I'm not totally off base.
My understanding is that Free Electron Lasers are pulsed, not continuous
output. And my impression is that while they're still being looked at for
defense apps, they're not the frontrunner these days. To the extent one
can trust an impression of an inherently sensitive subject gained purely
from reports in the open press, of course.
Henry
On 10/15/2020 3:06 PM, William Claybaugh wrote:
Henry:
You sure those are diodes? All the one’s I’ve seen were FEL’s.
Bill
On Thu, Oct 15, 2020 at 2:59 PM Henry Vanderbilt <
hvanderbilt@xxxxxxxxxxxxxx> wrote:
Apply a potential difference to a conductive material, and you'll get a
net migration of electrons along the potential direction. "electric".
Oh, you wanted something more specific than that? :-) Current public
reports of tests and prototypes seem to cluster around what I presume are
diode lasers with continuous outputs in the tens of kilowatts range,
mounted with appropriate pointing and beam-forming on ships, aircraft, and
large ground vehicles. Some stories give the impression that the customers
think another order of magnitude of reliable power output (in the hundreds
of kilowatts) will give them a useful area defense against targets heavier
than the small rockets/shells and small drones commonly mentioned as
current test targets.
Henry
On 10/15/2020 1:48 PM, roxanna Mason wrote:
electric lasers these days.
Elaborate on "electric"
Ken
On Thu, Oct 15, 2020 at 1:41 PM Henry Vanderbilt <
hvanderbilt@xxxxxxxxxxxxxx> wrote:
Utility in evading missile defenses aside, one thing to keep in mind
is, for certain targets - among them ships - payload fraction is less
important. A hypersonic impact delivers TNT-equivalent energy for the
entire vehicle mass involved even with no actual warhead on board at
around
Mach 9, and the equivalent energy of a 25%-of-vehicle mass TNT warhead at
Mach ~4.5.
Given that the main penetrating-defenses advantages seem to be
maneuvering beyond an interceptor's ability to follow, and operating in
atmosphere bands where the interceptor loses effectiveness, effective
anti-missile beam weapons will likely negate much of those advantages and
largely obsolete expensive hypersonics. Which may well explain why USN
(and USAF) seems very interested in electric lasers these days.
Henry
On 10/15/2020 2:23 AM, George Herbert wrote:
OT...
It’s not much of a secret I do missiles and nuclear proliferation
research and analysis including threat systems analysis as a side job.
There are a few things you can do with hypersonic weapons. You can
approach targets in the inconvenient altitude and speed band where
there’s too little lift for normal fins and too much for unstreamlined
exoatmospheric interceptors. Midcourse defense gets very difficult...
You can change direction in hypersonic flight, allowing flightpaths
avoiding defenses or attacking simultaneously from different directions,
complicating defenses. Under some circumstances they can use trajectory
changes in target approach to maneuver out of interceptor engagement
envelopes after interceptor burnout. Against rapidly maneuvering targets
there is a better target volume capability. Under some circumstances the
range is longer than a smaller ballistic trajectory Maneuvering Reentry
Vehicle can do.
They are much more expensive and harder to do than maneuvering ballistic
RVs. They can’t carry effective decoys, IR sensors see them thousands of
kilometers away, and avoiding defenses has to be done essentially blind
because they can’t credibly detect incoming interceptors with onboard
sensors.
The payload fraction of ballistic RVs is about 0.5, of maneuvering RVs
0.3-0.4, of hypersonic glide weapons 0.2 or less and Hypersonic cruise
weapons 0.1 or so. For the same payload they’re tremendously larger
missiles to start with, with corresponding ship, aircraft, submarine,
truck, or silo capacity issues.
They make better sense as Chinese antiship Missiles than as US prompt
conventional strike missiles. The countries don’t have analogous needs.
-george
Sent from my iPhone
On Oct 14, 2020, at 10:19 PM, Troy Prideaux <troy@xxxxxxxxxxxxxxxxxxxxx>
<troy@xxxxxxxxxxxxxxxxxxxxx> wrote:
attracted a lot of attention and hype but had no military value
whatsoever.
(For the sponsoring nation, that is -- it had considerable value to their
enemies,
since it pulled desperately-scarce resources away from things that *did*
have
real military value.) The recent hypersonics hype smells much the same to
me...
Henry
I guess the difference now is the "enemy/ies" are all on the same
hypersonic
bandwagon.
Troy