Pauline said in her ear, “Wang’s qube and some other qubes working on security issues have set up a system to try to lower the detection limit for pebble mob attacks like the one that hit Terminator’s tracks.”
“How?”
“They’ve manufactured and distributed a network of micro-observatories throughout the plane of the ecliptic, from Saturn’s orbit in to the sun. Using the gravity and radar data from these, they have lowered the limits of detection to the size of the pebbles used against Terminator, and even a bit smaller. Wang’s qube now has a time- adjusted map of everything in the plane of the ecliptic bigger than a centimeter across.”
“Wow,” Swan said. “I didn’t know that was possible.”
“No one did, but until now no one had tried it. The need wasn’t perceived. In any case, the system has detected an attack already in progress.”
“Oh no!” Swan said. “At what?”
“At the Venus sunshield.”
“Oh no!”
The other people in the bathroom were beginning to look at her. She went out into the hall and almost took the elevator down to the park, just on instinct; but she had left Wahram at their restaurant table, and besides, she couldn’t run from this. “Damn,” she said. “I have to tell Wahram.”
“Yes.”
“How much time before it hits?”
“Approximately five hours.”
“Damnation.” She thought of Venus-the dry ice seas under their carpet of rock, the cities on the coasts and in the craters. She ran back up the stairs to the picture window restaurant and sat down across from Wahram. He looked at her curiously, alert to her distress.
“All right, I have to make a confession first,” Swan said. “I told Pauline about the strange qube problem because I wanted to hear what she thought of it, and I figured she was isolated in me and it would be all right.” She raised a hand to forestall whatever he was about to say; he was already pop-eyed with alarm. “I’m sorry, I should have asked you I suppose, but anyway it’s done, and now Pauline has been in touch with Wang’s qube, and it’s telling her there’s a new qube security system in place that has lowered the limit of detection, and they’re seeing a new pebble attack in the process of coalescing, an attack on the Venus sunshield.”
“Shit,” Wahram said. He gulped, stared at her more pop-eyed than ever. “Pauline, is this right?”
“Yes,” Pauline said.
“How long before these pebbles hit?”
Pauline said, “Just under five hours.”
“Five hours!” Wahram exclaimed. “Why such short notice!”
“The attack is coalescing in such a way that it will hit edge-on to the sunshield, and so most of the pebbles have been out of the plane of the ecliptic until just recently. There are no new detectors yet distributed out of the plane, so they’re just now showing up. Wang’s qube was just about to warn Wang about it.”
“Can you display your data in a 3-D model?” Wahram asked. Swan put her right hand against the table’s screen, and in the texture of the table appeared a glowing image of the Venus sunshield-a great circular sheet, spinning around the hub at its center point, somewhat like Saturn’s rings around Saturn. Red lines indicating the detected pebbles were coming in from many directions, looking like magnetic lines converging on a monopole. When massed together, they would tear through the thin concentric panels of the shield, and if the conglomerate was large enough, reach the hub and destroy the controls. The remainder of the giant thing would go Catherine- wheeling through the night, mirror banners twisting and knotting in the black vacuum. And Venus would be cooked.
“Has anyone alerted the Venusian defense system?” Wahram asked.
“Yes, Wang’s qube did that, and now Wang too, but the sunshield’s AI did not find that the data transmitted represented a hazard. We suspect something is wrong with it.”
“Did the sunshield AI explain itself?” Wahram asked. “I need to see that whole exchange, please. Display as text,” and then he was reading the table screen so intently that it seemed his exophthalmic eyes might pop out of his head entirely. Swan let him read and conducted her own quick conversation with Pauline.
“Pauline, say we can’t convince the sunshield’s AI to act, is there anything we could do from here?”
Pauline took a few seconds, then said, “A countermass arriving at the pebbles’ meeting point at the rendezvous moment and hitting the mass at a tangent would push the paired mass off to the side, thus missing the sunshield. After the impact, the sunshield’s security system would presumably react to any detritus flying its way. The countermass should have approximately an equivalent momentum to the pebble mob, to vector the paired mass away successfully.”
“How big is the pebble mob?”
“It looks like it will mass about the equivalent of ten ships of this size.”
“This ship? So… if this ship was moving ten times faster than the pebbles?”
“That would make a momentum equivalency, yes.”
“Can this ship get there in time, and going fast enough?”
By now Wahram was listening to them rather than reading.
“Yes,” Pauline said. “But only by accelerating at this ship’s maximum acceleration, and starting as soon as you can.”
Swan looked at Wahram. “We have to tell the ship’s crew about this. And everyone else too.”
“True,” he said, taking up his napkin and patting his mouth. He surged to his feet. “Let’s go up to the bridge.”
B y the time they got there, the officers of the ship were already gathered before their AI’s biggest screen and were looking into a graphic of the pebble array very similar to the one Wahram and Swan had been looking at.
“Oh good,” Wahram said when he saw it. He was huffing a bit from the run down hallways and up stairs. “You see the problem we have.”
The ship’s captain glanced at him and said, “I’m glad you’re here. Indeed a big problem!”
Wahram said, “Swan’s qube says our ship here can serve to ward off the attack, by colliding with the pebbles at their rendezvous point.”
The captain and everyone on the crew looked startled at this idea, but Wahram gave them little time to adjust: “If we decide to do this, are there enough lifeboats for everyone aboard?”
“ ‘Lifeboat’ is not the right word,” the captain said, “but yes. There are lots of small ferries and hoppers on board, and most of the passengers could be put in them. Also there are more than enough personal spacesuits to send everyone out on their own. There are supplies in the suits to last ten days, so in that sense they’re better than the ferries, which don’t carry that kind of emergency supply. Everyone would get picked up, either way. But…” The captain looked around at the ship’s officers. “I should think the Venusian defense system would take this kind of thing on. Are we sure they won’t? And”-gesturing at the screen-“is this image evidence enough for us to change course, accelerate, and abandon ship?”
Wahram said, “We have to trust our AIs here, I think. They’re issuing their warning because we programmed them to react to input like this.”
“But they set up this fine-grained detection system on their own, I’m being told.”
“Yes, but I guess you could say we asked for that too. Wang asked for better protection. So-we’ve already made the decision to trust them.”
The captain frowned. “I suppose you’re right. But I don’t like it that the sunshield security doesn’t recognize this as a problem. If it did we wouldn’t have to throw our ship into harm’s way.”
“That may be balkanization rearing its head again,” Inspector Genette said from the doorway. “The Venus sunshield isn’t connected to the warning system that saw these pebbles, and it’s heavily firewalled from influences just like Wang’s qube. So it may not be equipped to believe the input.”
“What do the Venusians say?” the captain asked.
“Let’s ask them and find out,” suggested Wahram.
Swan said, “We have to tell them immediately, of course, but the Venusian leadership is notoriously opaque. How soon will they reply? And what do we do in the meantime?”
The captain was still frowning. He glared at Swan, as if because she had brought up the problem, it was her
