Charles Sheffield - Starfire

“We cannot proceed with my plan until Sky City and Cusp Station are in their final locations. For what we have in mind, our timing and the killer’s psychological condition will both be crucial. I would prefer to act at the height of the particle storm. Why do you ask?”

“Just thinkin’ ahead.” Seth picked up the battered rolfe. “If I get the answers I’m suspectin’ out of this thing, I might have to make a little trip. But don’t worry, I’ll be back in plenty of time for your fun an’ games.”

He walked out, leaving me to stare at the empty room. I removed the RV helmet, took it back to my study, and stared at the wall clock in disbelief. Everything, from that first flicker of movement at Seth’s door to this moment, had occupied almost no time at all. Five minutes ago I had drifted between fairy stories and the strange no-man’s-land of impending sleep. Now I was totally wired, nerves jangling at the close escape from death.

I told myself this was Seth’s escape, not mine. I was not, and never had been, in the slightest danger. And Seth felt certain that the Sky City killer was in no way involved.

Curiously, I found I believed him. The murderer had done nothing, because the murderer needed to do nothing. We had no evidence. The killer’s safest course of action was continued total inaction.

Why, then, do I believe that Seth and I have a chance of success? Because human beings find it difficult to act on facts alone. We are plagued by overactive imaginations. And of the things that human beings are called upon to do, doing nothing can be the most difficult act of all.

John Hyslop scanned the table of values. If an anomaly was present, he couldn’t see it. “Are you sure?”

Amanda Corrigan nodded. Shy in a group, she was perfectly self-confident one-on-one. “It’s there. Hard to tell from the table of numbers, but when it’s graphed it jumps right out at you. See for yourself.”

She flashed up a different display, this one a curve of particle number against time. It showed a lopsided Gaussian distribution, the smooth mountain of the bell curve rising rapidly and then falling back to zero. On the left side of the mountain a secondary peak jutted up as a steep little hill.

John studied it. “Not much to look at.”

“It’s not, in terms of the maximum particle flux. Less than one percent.”

“But more than enough to cause trouble. Where did this curve come from?”

“Data from the Sniffer that we launched two weeks ago.”

“As a crash priority. What are the chances that something on board isn’t working right?”

“Poor. The Sniffer passed every test we threw at it.”

“Then we’d better start worrying about the earlier Sniffers. They were designed to catch this sort of thing, and they missed it.”

“Not really.” Amanda did more fast work at the pad.

“Here’s what the other Sniffers gave us, the way it was presented for visual analysis.”

John rubbed his eyes. The new curve he was looking at showed a single mountain with no bordering foothills. Maybe he was getting old. He had drunk wine with dinner, but that wasn’t it. After midnight he couldn’t keep up with Amanda’s speed and adolescent energy. She might be twenty-six, but she was like a fourteen-year-old in more than outward appearance.

“No peaks that I can see.”

“Right. No peaks.”

“Amanda, a peak in particle numbers can’t pop up from nowhere. It represents a physical entity.”

“It didn’t come from nowhere. The Sniffers are working correctly — all of them. What you are seeing is a combination of the physical limitations of the earlier instruments and the way we handle their data. I’ll show you.”

More dancing fingerwork from Amanda, and another display flashed into view.

“These are raw counts from one of the old Sniffers. The older models measure only what they find right in front of them, and they make readings every two seconds. That sounds like frequent sampling, but the relative speed of the particles and the Sniffers means we have only one sample every fifty thousand kilometers. I think of the data as a count of the number of particles at each cross section of a long, thin tube stretching from Earth toward Alpha Centauri. The particles come in bunches and clusters, so the counts have high statistical variation. Lots of hash in the data, hard to analyze. The peak I just showed you is present in the counts, but it’s really hard to see because of the noise in the signal. Now I apply a low-pass filter to the input, and there’s the resulting profile. Nice and smooth, but no peak. We see the major increases and decreases. The minor blip disappears.”

“In other words, we averaged away part of the signal.” John leaned back. “Guess the name of the genius who said he couldn’t read the raw hash, and told you to smooth it out.”

“I wasn’t about to mention that if you didn’t.” Amanda was smiling.

“I’d rather you didn’t mention it at all. Colombo will have my scalp if he ever finds out.” John tried to sound worried, but he was smiling, too. This was his arena, his natural playing field. Here he was the best, with the self-confidence that eluded him when it came to personal affairs.

He went back to the first display with its innocent little side peak. “So this is the real thing — no smoothing.”

“You’ve got it. The new Sniffer detects and counts particle bundles over a cross-sectional area a hundred times as big as the old Sniffers could handle. We don’t need averaging to get rid of statistical variations. There’s something else peculiar in the counts from the new Sniffer, but I’d rather not talk about that until I know what I’m doing.”

“Keep me posted. There’s still one key piece of information missing in what we have so far.” John highlighted the companion peak. “About this. I need to know when. It’s going to hit sooner than the main pulse, but how long do we have? A day, a week?”

Amanda breathed out, explosively. “I’m sorry. The scale is shown along the abscissa, but it doesn’t include the origin. We don’t have much time. The particle bundles from the minor pulse will hit their maximum count forty-eight hours from now. Then the count will fall away and by sixty hours it will be back to normal.”

“But maybe we won’t be.”

When things went wrong you could curse; when things went really wrong you didn’t have time for that luxury. John, as a matter of habit, called a flow chart onto the display. It was more for Amanda’s sake than his own, because he already had a good idea of what it would reveal.

“Here’s the master schedule.” He moved the cursor. “And this vertical line at fifteen days shows what we hope will be happening when the big pulse hits. But we’re more interested in what happens here.” He introduced another vertical line on the display. “That’s forty-eight hours from now. As you see, we have no defense system in operation — old or new. We have to take that as a given, and see what everyone will be doing. I show you on Cusp Station, setting up the high-speed computer links with Sky City. Will Davis and his team are there, too, installing the pulse field generator. Cusp isn’t shielded well enough; you’ll all have to fly back and sit out the particle storm on Sky City. Torrance Harbish and Rico Ruggiero have a team outside, fine-tuning the balance of forces to hang Cusp Station and Sky City at the correct distance from Earth. They’ll have to come inside. The people we have to worry about most are Nordstrom’s group, out on the old shield. They’re modifying the superconducting circuits so they work with the low-intensity detection field. They can’t stay out there, even for a pulse this size. It’s at least a ten-hour flight to safety. I want you to pass the word to Nordstrom at once.”