Thursday, May 24, 2018

Installment 5.4: EMP...the life of the party

Walt retransmitted “Repeat: I have six columns approaching.Estimated speed is fifty miles per hour.  They must have removed the governors.  I got a laser on them and the data says they are moving at fifty miles an hour.”

“Holy shit!” Chad exclaimed off-mic.

“Do you have a firing interval figured?” Chad asked.

“According to my calculator, in total, we need to drop a round on them every four seconds if we want a round ‘shingled’ every 300 feet.” Walt said.  He was something of a whiz at math.  "Or we can salvo every fifteen seconds or so an paint a quarter mile of pavement."

"I direct the teams to salvo.  Team alpha sets the cadence, everybody else tweak time in flight to match." Chad said.

“I should have asked this earlier.  Does anybody know how many rounds of EMP we have?” Chad asked.  He could tell that he was handicapped by his lack of sleep.

“Our team has two pallets of EMP ammo.  I counted out one pallet and it had sixty rounds. So that means we have 120 rounds.” Team alpha responded.

The other teams concurred.  They all had two pallets of EMP ammo.

Walt chimed in, “Works out to 720 rounds or about fifty minutes worth of firing.  Do you want us to try to stretch it out?”
The "Kill zone" the Cali attack force must travel through.
“Nope.” Chad said.  “I want to give the defenders down the line a clear break point.  Start firing just before they enter the ‘kill zone’ and drop one round every four seconds on them.  Walt, you have the ping-pong paddles.  Everybody else, light them up when Walt gives you the word.”

Chad switched channels.  ““Izzo-to-Pitoitua.  Izzo-to-Pitoitua.  Come in.” Chad transmitted.

“Pitoitua here.”

“Cali columns proceeding south at fifty miles per hour.  I repeat, five-zero miles per hour, measured with laser.  Traveling in four columns and running without lights.  Anticipate arrival at highway 138 at 2:40 AM.”

“Are you under fire?” Pitoitua asked.

“Negative.  We can see artillery mixed in with personnel carriers.  They are all making fifty mph.  No return fire.  No drones.  We just about to start painting column with the EMP weapons.  No confirmation regarding effectiveness.” Chad transmitted.

The radio transmissions became uneven, even behind two ridges.  The squelch was fighting the bursts of static each time four EMP shell went off.

Walt and Kenny would have been a good musical conductors.  Kenny directed the teams to where the shells were coming in 100 yards apart and Walt tuned up the time-to-targets so they were bursting nearly simultaneously.

Each team had two loaders.  The first one picked it off the pallet and put it on the charging cradle.  The charging cradle was a capacitor with the size and appearance of a very large beer cooler.  A black box converted the 120V AC that into 30,000V DC was plugged into the generator and pumped up the capacitor banks in the charging cradle.  The charging cradle, in turn, charged the small capacitor bank in the EMP shell just prior to firing. 

Capacitor-to-capacitor charging is instantaneous.  The only complication when using high capacity capacitors is that instantaneous charging vaporizes the charging lugs.  Consequently, the process has to be de-tuned.  As it was, the charging was nearly instantaneous by human standards and accompanied with a loud “SNAP!” that stood everybody's hair on end.

The small capacitor bank on the EMP shell were the most expensive part of the system and comprised the rear 2/3s of the shell.  They combined reliability, capacity and compactness.  The electrical charge carried by the on-board capacitor was the primer for the EMP.

The front third of the shell was comprised of a drawn aluminum can wrapped with heavy gauge wire.  The can assembly was nested within a surprisingly thin shell of high explosive.  Protruding out of the can assembly was patch antenna that was made of pure silver and supported with carbon fiber scaffolding.

The shell detonated when the angle of descent pass the specified level.  A copper BB rolled down a "straw" and closed a contact which energized a relay.  The relay dumped the energy in the capacitor into the heavy gauge wire.  The copper sphere also initiated a timing circuit which fired the high explosive shell just as the coil was fully energized.  The explosive crushed the can-coil assembly and generated a very short, very intense power surge.  The explosive charge also severed the “return” leg of the coil.  Having nowhere else to go, the power surge energized the patch antenna in the nose of the shell.

The explosions three hundred feet above the pavement were less than impressive to mortar crew who were used to shells made by 24 ounces of TNT.

What they could not see was the havoc the EMP pulse did to the electronics on-board the vehicles.

Every electronic device that was connected to an antenna or was powered by exposed wiring was damaged.  Fuses melted, then vaporized as the pulse leapt the gap created by the fusible links.  The surge flooded into integrated circuits.  It arced across capacitors leaving carbon traces of charred shellac that turned the capacitors into conductors.  It broke down diode and transistor junctions and the thermal shock cratered the silicon substrate.

The problem was exacerbated by the recent upgrades the Cali technical people made to the electronics package.  They had looked at the military grade electronics and scoffed at the ferrite beads and abundance of chokes.  They laughed at the heavy wire, and in the case of the fire control package in the old Soviet self-propelled artillery, the vacuum tubes.

They replaced all of the military grade electronics with state-of-the-art commercial electronic; electronics that ran 50 times faster, consumed 5% of the electricity, occupied 20% of the space and in audio applications did not clip the high frequency content.  The Cali tech people did not have a very high opinion of their military counterparts.

Next Installment


  1. Oopsie... So much for those 'upgrades'...

  2. One note: contrary to the common perception, most vehicles don't just speed up by removing the governor, and those that do usually seize up in a few minutes.
    Road speed is a combination of engine RPM and transmission gearing; above a certain point the wheels (or tracks) won't turn faster no matter how much power you give them.


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