Ad Astra by Jack Campbell

component?”
    “Sandra isn’t,” Kevlin insisted. “Her sub-systems are doing it. Just like when humans run short of calcium and the body robs it from bones to keep the teeth strong. Part of the repair sub-system thinks some other part of Sandra needs those components more.”
    The last remnants of the boat had vanished along with the drones which had digested it for Sandra. The captain and another engineer tugged at the emergency release on the outer hatch with no results. “I’ll have to blow it using the explosive bolts.” She yanked open a panel, pulled out a battery, connected leads to two attachments behind another panel, then pushed a button.
    Faint echoes of the explosions reached Kevlin through his handhold on the ship as the hatch swung out. The captain turned to face them. “Push yourselves clear of the ship. We don’t dare wait here for rescue from the chase ship. Go!”
    They went. Kevlin shoved off, looking back to see Sandra’s shape diminishing behind him, the captain’s suited figure going last out of the hatch. He heard her calling the chase ship on the distress frequency. “SOS. We need emergency pick up. Full macro and nano-scale decontamination required. Remain clear of Sandra. Repeat, remain clear of Sandra.”
    Kevlin wondered how long the recirc unit would keep him alive. Full scale decontamination took a while. But then, he couldn’t argue with the captain’s order, either.
    #
    Yasmina joined him at the display, looking like she’d been vigorously scrubbed with sandpaper over every part of her body, every hair shaved clean. Kevlin knew he looked the same, and knew she also felt like her insides had been similarly sandpapered. He would probably shudder for the rest of his life whenever someone mentioned a full macro and nano decontamination.
    She gestured at the image of Sandra. “What’s happening? Any guesses?” Sandra’s clean lines had been distorted by random bulges. Remote readouts showed system failures cascading through the ship.
    “She’s dying,” Kevlin stated. “Pure and simple. Some of her repair functions evolved into harmful out-of-control infections. Other parts of her are attacking her. See this stuff? Any immune system risks getting too efficient. At that point it starts attacking itself. You can see where all the control system filaments in this part of Sandra are dead. I’ll bet her own repair system is destroying them.”
    “Auto-immune diseases,” Yasmina observed in a shocked voice.
    “Yeah. The testing process matched with learning routines and an ability to improve repair capabilities inevitably pushed Sandra into becoming better and better at identifying and fixing damage. Unfortunately, living organisms are obvious lessons that there’s no optimum point at which that stuff stops. It keeps trying to get better even after it gets so good at its job that it turns harmful.”
    The captain had come to stand with them, her face sober. “It shouldn’t have happened. We knew everything there is to know about every one of the components on that ship.”
    Another engineer shook his shaved head. “It’s a scientific principle that you can know everything there is to know about something, and still not be able to predict an outcome. We just proved it again.”
    “Assuming you did know everything,” Kevlin snapped. “You tried to make a machine work like a living creature, with self-direction and self-repair capabilities. What made you think you could tell how it would act? Humans are the mature result of millions of years of evolution and we only function halfway well because of an enormous investment in cultural, organizational and medical systems designed to control our actions and compensate for our faults!”
    “What’ll happen to Sandra?” Yasmina wondered.
    The captain glanced at Kevlin. “Do you think she’ll be safe once the power dies and everything goes dark?”
    “The macro stuff, probably. I don’t know about the nanos. It all depends