Airborne lasers (Pulsed?)

Pat Flannery :

Allen Thomson wrote:

Note that the referenced slide says they're shooting at the
ullage volume, i.e., the volume that's above the liquid level. My
interpretation of this is that they're trying to heat up the thin
metal tank skin enough that it will weaken and existing internal
pressure will cause a blow-out.

In other words, they're trying to heat up the air and propellant vapor
in the tanks, not the propellants themselves?
Since the propellants will be at the bottom of the tankage during
ascent, if one were to put a ring of pressure activated blow-off valves
at the front of the tank, that would retain enough tank pressure to give
the missile structural rigidity, but activate and release tank pressure
if it became high enough to threaten to rupture the tank...
I was assuming that they were trying to heat up the hydrazine to the
point where it detonated.

No, I think they want to damage the wall of the tank itself, that just
happens to be easyier if the other side of the wall where the laser hits has
gasses as a heat sink, vs liquids which do make good heat sinks.

Plus, if they are going the explosion route (Ultra fast, ultra high energy
pulse) then the gasses offer less resistance to an explosion on the outside
of the tank and likely a larger hole per given units of power.

Earl Colby Pottinger

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Earl Colby Pottinger wrote

No, I think they want to damage the wall of the tank itself, that
just happens to be easier if the other side of the wall where the
laser hits has gasses as a heat sink, vs liquids which do make good
heat sinks.

Yes, exactly.

Plus, if they are going the explosion route (Ultra fast, ultra high energy
pulse) then the gasses offer less resistance to an explosion on the outside
of the tank and likely a larger hole per given units of power.

At least in the current version, steady if rapid heating rather than
ultra fast pulses is envisaged. Think of a hot blowtorch being applied
to the side of a thin, pressurized tank. The heated spot on the wall
softens, weakens, and at some point is unable to resist the internal
pressure.

Back in SDI days -- and probably in the future -- fast pulses that
cause vaporization and explosive blow-off were contemplated. That's
a much different damage mechanism, rather similar to the x-ray
ablation encountered in the nuclear weapons world but using visible
or IR radiation rather than x-rays.

Speaking of airborne laser weapons, there's an interesting
article on their history (in the US) by Hans Mark at
http://www.ndu.edu/inss/DefHor/DH12/DH12.pdf