A low hum of the climate control system. The occasional rumble of the same. The nervous rustle of fabric. A cleared throat. A palpable tension saturated the filtered and reprocessed air of Planetary Defense Citadel 4's firing room.

Citadel 4 held authority over the entire northwestern bank of the "Sentinels", massive emag cannons designed for the sole purpose of annihilating any ship, celestial body, or human body that attempted to cross into Astra-V's stratosphere without adequate authorization. Several terawatts of power imbued each and every shot. A misfire would mean that power would have to be directed elsewhere. If one were lucky, it would be into the unfathomably costly, nigh-irreplaceable electronics and mechanics of the cannon. If not…at any rate, the people in the room wouldn't have enough time to worry about it before it disintegrated them.

Currently the person whose job it was to ensure that did not happen was Aria Rostova-Chen. 20 years old (far too young, according to most). Obsessive. Antisocial. Regarded as at least mildly insane by her contemporaries. Unfit for command positions. Aria went through her own mental highlight reel of all the comments her bosses had left in her file over the years. But no amount of red ink on a dossier was worth more than the rare and coveted treasure that was actual technical competence.

She'd spent the past six months overseeing preventive maintenance for Citadel 4's entire compliment, personally tuning half the battery. Today should be the victory lap for her and the teams she'd been supervising.

Should.

But never is.

A warning symbol flashed up on the massive screen in front of Aria. A problem with Sentinel #3, "Dawnbreaker". The cryogenic cooling for the superconductive coils was failing. A massive localized temperature spike in the seventh coil array. Firing in this state would shatter them like glass. The cannon would be slag.

Citadel 4's commander was a portly man in his middle age, Commander Idris Lance. Aria neither liked nor disliked him. She did her job, and he stayed out of her way, as a matter of course. That was how they both liked it.

"Scrub the test. And find out who signed off on Dawnbreaker, when such an egregious technical fault was present." The threat didn't need to be spoken aloud to be heard.

Aria was doing her job. Lance wasn't staying out of her way. This wasn't how she liked it.

"We are not scrubbing. If we sink the caps right now, that's a 12 hour window where the entire 3rd Arc is unguarded. We fix the cryogenics."

"This is my command, Miss Rostova-Chen."

"This is my test, Commander Lance, and those are my technicians in the maintenance tunnels. So save yourself the indignity, and have some faith."

Aria didn't see how he reacted. She didn't care. 180 seconds until the cannon discharged, one way or another. Her eyes flew over the diagnostic information, impossibly dense, yet clear as day to her even at a glance. An anomaly. The magnetic flux readings on 7B and 7C. Erratic. Induction feedback loop between coils. Eddy currents. Rapid localized heating. The coils were baking each other, and the cryogenics weren't rated to handle that sort of rapid temperature spike.

Her fingers moved to orchestrate the fix before she'd even fully comprehended what it was.

"Matsuda, you there?"

Kaelen Matsuda, One of the techs from Aria's own team. She was extremely bitchy and had zero respect for the chain of command. She also got things done quick without asking unnecessary questions. Aria thanked the Stars the woman had ended up being the closest mechanic to the overheating coils.

"Sure am boss. Just wondering, what's my death gratuity look like?"

"It's that bad?"

"Not that bad. I can't hear the coils overheating yet, which is something. What's the diagnosis?"

"Induction feedback. Eddy currents. Thermal spike."

"You know what this means, right?"

"Yep." Induction feedback like this was accounted for in the designs. This sort of thing didn't happen from a maintenance oversight.

"And you're not scrubbing the test."

"Nope. Cause you're gonna fix it. I need you to take a 3.4x7 meter electromagnetic shielding plate, and stick it between the coils."

"Oh, great, I'm pretty sure I've got one of those right here in my pocket. Ah, there it is! Found it!"

"You're flipping me off, aren't you?"

"You're a real woman of the people, boss. Seriously though, where the Hell are we supposed to find one of those?"

"We had a bunch of oversize ones. I had one cut down on its way over to you."

"….Cut down on its way over?"

"The firing room has control over the hallway sentry lasers too, not just the Sentinels. The timing was a pain but it saved us 8 seconds, accounting for deceleration and re-acceleration."

Aria was vaguely aware of Commander Lance saying something about dangling her upside down from the flagpole, as well as the slack jaws of the two junior techs there to watch, but she considered both of roughly equal unimportance at the moment.

"We're really cutting it that close, huh boss?"

"We'd be cutting it a lot closer if I was sane. Or sensible. Or cared about still having a job after this. Now catch."

Deceleration would've cost valuable time. Aria had programmed the logistics drones to simply let go of the shielding plate when they got to the maintenance tunnel.

A shout of surprise came over the comms, followed by a grunt of effort immediately after, and then profuse swearing. The high-pitched whirring of the integrated power drill on the technician's exosuit signaled the plate being put in place, and Aria breathed a sigh of relief as she saw the magnetic flux in the coils drop back to nominal levels.

90 seconds left.

The thermal spike was resolved.

The current thermal load was well within the rating of the cryogenics.

It should work.

It wasn't going to be enough.

Again her hands moved before she'd fully comprehended what she was doing. "Matsuda, I need you to open the valve for the redundant coolant line."

"Just to be clear, you mean the empty, depressurized coolant line that was decommissioned five years ago and only has a manual valve? That coolant line?" Her words were punctuated by grunts of effort as the cold, locked up release valve turned for the first time in over half a decade.

"Not empty anymore. You'd be shocked what you can scrounge up when you've got the whole northwestern octant to pull from."

Aria held her breath and watched the temperature on the coils tick down. It was a delicate balance. Too much coolant, and they would quench and shatter just the same. Too little, and they'd slag themselves from the excess heat generated within the tungsten ferrite slug.

30 seconds until the slug reached Coil Array 7.

At the current rate, it would take 20 seconds to cool the coils to safe operating temperature, just barely.

15 seconds would shatter the coils.

There was a path through this. Aria decided to thread the needle.

"Close the coolant valve on my mark."

No response. None needed. They both understood what would happen if they didn't get this perfect.

10 seconds. That was the eye of the needle.

8 seconds. "Mark."

10 seconds. Matsuda finished closing the valve, in spite of its best efforts.

15 seconds. The coils didn't shatter. A good sign, or at least roughly the same shape as one.

20 seconds. No more interventions. The maintenance tunnel had to be cleared. Anything still in the tunnel when the slug passed would get broiled.

25 seconds. The coils were still too hot.

26.

27.

28.

29 seconds. Too hot. Just barely. It would hold. It had to.

30 seconds. For a brief, beautiful moment, temperatures are nominal. The slug passes the coils at 0.001c. Massive thermal spike. It will take 150 seconds to cool to within safe operating range, at the current rate. No one present can bring themselves to care. Certainly not the junior techs, forgetting their decorum in the presence of an officer as they stand up and cheer.

From the firing room's window, Dawnbreaker's roar was beheld. An argent lance, blindingly bright, puncturing the atmosphere too fast to perceive anything more than the pillar of lightning left in its wake.

For almost a full minute, complete silence. What could one possibly say in response to such a profound display of power?

Then, the acoustic shockwave. A low, thunderous rumble that rolled through the mountain that the Citadel was carved into. Through the walls, through the floors, and into the bones, into the very souls of all present to witness.

One of the junior techs ran out and retched in the hallway. The other barely seemed to hold it back. Witnessing that shockwave at such close proximity was nauseating the first time, so Aria didn't blame them. Still, she sent them both out to clean up the mess. She didn't want them in the room for this conversation.

Aria turned to face Commander Lance. He was sitting back in his chair, a cold sweat rolling down his beet-red face, his breathing hurried. She didn't blame him. They'd all come terrifyingly close to dying or, worse, having to handle an absolutely massive maintenance bill.

"Commander Lance."

"Technician Rostova-Chen. I oughta have you dressed down and jettisoned for insubordination…but it did work, so you're spared. For now."

"I imagine it goes without saying, Technician Matsuda is owed hazard pay for the maneuver she pulled off."

"Naturally."

"Good. Cancel the rest of the test fires for Citadel 4. Send in a forensics team to inspect every coil isolator gasket on every array in the NW Octant. I will be filing a formal recommendation that the same be done for all other Citadels."

The Commander nodded. "You noticed something?"

"I personally oversaw Dawnbreaker's maintenance. Not only do I have the reports, I have the logs from the dry fires. Coil Array 7's isolator gaskets were in perfect condition. Those things don't just malfunction, not like this."

Lance's expression turned grim. "You don't mean to say…"

Aria nodded. "Someone wanted to destroy Dawnbreaker."