When the Four rose up to join him, Conal fell in with the larger plane and flew to the right and slightly behind it.
"Here's the plan," Cirocco said. "The radar is good for about thirty kilometers in all directions. An angel can do about seventy kilometers per hour, and can maintain that for maybe two hours. He's been gone slightly under one hour. We will assume he's headed for Pandemonium, which is currently in southern Hyperion. We're going up to twenty, that's two zero, kilometers, and we'll fly fifty kilometers apart, with the same heading. We will fly at one two zero kilometers per hour for another thirty minutes, and hope that puts us in his general area. We will then throttle back to sixty and attempt to locate him by radar. If that doesn't work, we will move ahead at high speed until we're sure we're in front of him, and conduct a search pattern, diagonally across his project path, until we find him or one of us thinks of something better to do. Comments?"
Conal worked it out in his laborious but methodical way. Cirocco did not interrupt him. He realized that, aside from Chris, with whom she had already discussed this, he knew more about Gaea than anyone else.
"What if he goes higher?" Conal finally said. "Should the search pattern be vertical as well as horizontal?"
"I'm making the assumption that he's going to be fairly low."
Conal worked that out, too, and wasn't sure it was a valid assumption to make. Angels might not like clinging to the curved rim roof, but they could do it if they had to. Cirocco was obviously counting on some sort of relay maneuver, since no single angel could move Adam from Dione to Hyperion, and she must think the most likely place for the later carriers to hide was the outer rim of Gaea.
But Gaea was an unusual place for flying. You could climb a full hundred and fifty kilometers before running into the roof. And if you flew through a spoke, you could go even higher than that. If the angel went up to sixty kilometers, they could fly right under him, and never see him.
"Hyperion is about halfway around," Conal pointed out. "He might just go up a spoke, through the hub, and down again."
"You're absolutely right, Conal," Cirocco came back. "But for now, I'm going to assume the rim route. If we don't find anything in two or three revs, we can reassess."
"You're the boss," Conal said.
"Yeah, but don't let that stop you from giving me ideas. And besides, I'm going to do my best to cheat, in just a few minutes."
Conal could tell from Nova's frown that she had no idea what the Captain was talking about. Conal could make a pretty good guess, but kept his mouth shut.
"Weather advisory," the computer said. "You are entering a region where severe turbulence has-" Conal hit the override and the computer shut up.
"What was that about?" Nova asked. Conal glanced at her. She seemed to be feeling better. She must be, he thought, if she was willing to talk to him. He had not been looking forward to a long trip in the small space with somebody who hated him.
"The brain carries a model of Gaea in its head," he told her, calling up a cut-away side view of the wheel-world. "This plane and all the others share the model, and they make a note of places where the storm probability is high, based on past experience. Mostly it's a nuisance."
"I'd think it would be helpful."
"Not too much. Look." He zoomed in on the segment of wheel rim that contained Dione, showing part of the spoke that loomed above it. Two blue dots winked on and off near the bottom of the picture, labeled 2 and 4. "That's us," he said, pointing to the 2. "We're moving toward Iapetus, and we're getting close to the twilight zone, which means warmer air coming up from the ground. When air rises in Gaea, it moves into masses of air that are traveling slower, because they're nearer the hub. So it sort of curls over, like a breaking wave. You get a lot of quick downdrafts in the transitional zone."
He glanced at her to see if she understood. It had taken him a while to get it straight, with his Earth-based thinking. The equivalent effect on Earth was the rotation of air masses caused by north-south currents, and depended on the fact that air at the equator was moving faster with the turning of the planet than air to the north or the south. When the effect was very intense, it was called a hurricane.
"Sure," she said. "The Coriolis effect. We have to take that into account when we go soaring at home."
"It's not as bad here. Gaea's much bigger than the Coven. I don't have to think about it when I'm flying the plane, but the computer takes it into account for navigation." He pointed to the screen again. "The thing is, the weather's pretty regular in Gaea. Bad weather comes out of the spokes. Gaea sucks up a lot of air in one spoke, moves it through the hub into another one, and then lets it all fall out over a night region. It's all done by a schedule. So that's what the computer was telling me: I'm moving into a boundary line between day and night, which means I'm coming out from under a spoke, which means we can expect some bumps. The thing is," and he pointed up at the gargantuan mouth of the Dione Spoke looming above them, "I can see that easy enough."
She didn't say anything, but looked around her, studying the spoke, the curved roof ahead of them that arched over Iapetus, comparing them to the model on the screen. He knew the convoluted geometry of Gaea took some getting used to. It was one thing to look at a map of it, and something else to stand on the hurtling rim and get an ant's-eye view.
"I see what you mean about finding the angel," she finally said. "What's to prevent him from just going so high we'd never find him? It's shorter that way, too."
"All air distances in Gaea are shorter than ground distances," he said. "And if you wanted to go from Dione to Rhea, all the way around the wheel, the shortest way is straight up the spoke, through the hub, and down the Rhea spoke. It gets easier as you go, because you get lighter. And once you're in the hub, it's downhill all the way."
"Why does Cirocco think he won't do that?"
"A couple of reasons. Different flights of angels live in different spokes. They don't like each other and they're jealous of their territory. No matter which flight this one comes from, he'll have to go through unfriendly territory if he goes through two spokes. They might kill him, and he'd have a lot of trouble getting food. He'd do better foraging on the rim. It'd be easier for the others to hide on the rim, where no other flight has nesting rights."
"Why are you assuming he's going to Hyperion?"
Conal shrugged. "You'd have to ask the Captain about that. She has special knowledge which she doesn't always tell me about. Then again, that angel grabbing Adam was one hell of a surprise to her, I can tell you that."
They were in the west end of Iapetus when Cirocco gave the order to throttle back. Conal's plane was far to the north, invisible to the eye but making a strong steady blip when the computer displayed the ground map.
When the three-dimensional display was used, Robin found it hard not to be discouraged.
In that mode, Gaea's rim was a gently curved tube. The angel's possible locations made a hemisphere with Tuxedo Junction at the center. The search profile of the planes was a lengthening tube a hundred kilometers wide and fifty high. When compared with the region where the angel might be, it didn't seem enough. There was so much space above them where it could be, and a vast amount behind them.