Pushing Ice (23 page)

“What now?” Bella asked.

“You see this telemetry channel?” Hinks indicated one of the boxed graphs containing a display of some system parameter against time. “That’s data from the free-flier’s onboard accelerometer. It’s like an inertial compass. But look how it starts: flat at one gee for one hour. Then it does a delta function to zero gees: that’s the engine shutting down. All okay so far. Then it holds at zero for another twenty-five minutes, which is the time the free-flier spent in cruise phase.”

“And then it climbs to five gees,” Bella said.

“No — that’s my point. It stays flat at zero, right until the last data packet.”

“That’s… that’s weird,” Bella said. “Let me get this straight: the Doppler telemetry says the free-flier went shooting off at five gees during the last six seconds of transmission.”

“Correct,” Hinks said.

“While the on-board accelerometer says nothing happened.”

“Right.”

“Then one or both channels must be incorrect. So maybe my putative explosion really did happen, and knocked out the accelerometer.”

“Well, no,” Hinks said patiently, “that’s not what we’d see if that had happened. We’d get zero packets on that channel. Whereas the packets we received from the accelerometer were all well formed.”

“According to the accelerometer,” Fletterick said, “the free-flier didn’t feel that five-gee surge at all.”

“But it did accelerate,” Bella said.

“According to the telemetry.”

“So which is right?”

“They’re both right,” Svetlana said. She had just appeared in the puppet booth. Bella had not given her permission to leave her quarters — indeed, her appearance here was a clear violation of the agreed terms of her confinement, which permitted her limited access to ShipNet if she agreed to treat her room as a locked and guarded prison cell. But at that moment Bella felt no inclination to punish her.

“You have an explanation?” she asked.

“I have one,” Svetlana said, “but you’re not going to like it.”

“Just tell me what you think is going on,” Bella said.

“I want Belinda to try something for me first. It shouldn’t take her long.”

“I’m listening,” Pagis said.

“Point the uplink dish back in the direction of Earth, if you haven’t already done so.”

“It’s done,” Pagis said, shaking her head, “and there still isn’t a signal.”

“No, but I think I know where you can find one. You need to shift the bandpass well out of the frequency range you’re searching.”

“We’ve allowed for the Doppler effect.”

“Just try it. Look on the low-frequency side, as if you’d underestimated the degree of red shift.”

“I don’t see —” Pagis began.

Svetlana cut her off impatiently. “Just do it, all right? Start at the nominal frequency and slide the bandpass into the red. Tell me when you hit a signal.”

It took less time than Bella had expected. Pagis entered commands into her flexy, talking directly to the uplink antenna.

Within a few minutes Bella saw her frown and open her mouth in a silent, “
What
?”

“You’ve found your uplink signal, haven’t you?” Svetlana said. “Earth is still on the air. They always were: you were just looking off-frequency.”

“This isn’t possible,” Pagis said. “I’ve had to apply half as much red shift again.”

“That can’t be right,” Bella said, but she could tell from Svetlana’s expression — fearful and triumphant at the same time — that there had been no mistake.

“It’s right,” she said.

“Svieta, what’s happening?”

Svetlana coughed and looked at everyone in the little gathering. “What’s happening is that we’re moving faster than we thought we were,” she said. “That’s why the Doppler shift was wrong. You weren’t allowing for enough motion difference between us and Earth.”

“We know how fast we’re moving,” Bella said.

“No, we don’t. We think we do, but that’s only because we’ve made a terrible mistake.” Svetlana paused; she had their absolute attention. “It wasn’t the free-flier that accelerated away at five gees. It was us. We’re the thing that’s accelerating.”

“At five gees? We’re standing still, Svieta. We’re not even moving as quickly as we expected to be.”

“No,” she said, with a resigned calm. “We’re moving much, much faster than we were.”

“All this since Fletterick lost his signal?”

“No. We’ve been accelerating for a lot longer than that, at least as far back as the time we first lost the Earth signal, and probably for several hours before that.”

“How can you know this?”

“Only thing that fits the data. You’re also having problems with star-trackers. Fine — that’s exactly what I’d expect if we’d suddenly picked up a lot of speed.”

“Explain,” Bella said. Her mouth felt dry.

“The trackers are set up to recognise bright stars in fixed constellations. They’re programmed to ignore stars that don’t fall at exactly the right angular separations from each other.

The problem is that now the stars have moved relative to each other, so they can’t find the matches they expect. It’s called aberration: an apparent displacement in the positions due to speed.“

“I don’t get it,” Hinks said. “What has speed got to do with where the stars are?”

Bella was afraid that Svetlana was going to lash out at the robotics technician for not knowing basic astrogation theory, but instead she seemed drained of all fury.

“It’s like this. You’re driving at night, in snow. There’s no wind, yet the snow seems to be falling horizontally, heading towards your windshield from the direction you’re driving — even though you know it’s really falling vertically. Well, the same thing’s happening with starlight, only to a much smaller degree. Trouble is, it’s still enough to throw the trackers.”

“And the trackers don’t know that?” Hinks asked.

“No, they do know it, and they’re programmed to correct their expected stellar positions to allow for aberration. But to do that properly they need to know how fast they’re moving.”

“The free-fliers hitch a ride with
Rockhopper
,” Saul Regis said, speaking for the first time since Svetlana’s arrival. “They assume that
Rockhopper
knows how fast it’s moving, so they query
Rockhopper
to keep their kinematic parameter file up to date.”

“In other words, they ask the ship how much of a correction to allow for, and the ship tells them,” Svetlana said. “But this time the ship got it wrong.”

“We can check this as well,” Bella said. “It won’t be difficult. But it still doesn’t answer my basic question: what
the hell
is happening?”

* * *

Bella called Svetlana and Craig Schrope to her office. Before Schrope could lodge an objection to Svetlana being there, Bella said, “These are exceptional circumstances, which is why I’m turning a blind eye to Svetlana’s presence. She’s already solved the uplink problem, and I believe she has an explanation for the star-tracker errors as well.”

Schrope’s pen glittered in his hand like a twirling six-shooter. “Let’s hear it.”

“It looks as if Janus is dragging us with it,” Svetlana said. “We’re caught in some kind of slipstream.”

Schrope pulled a face. “It’s moving through vacuum. You don’t get slipstreams in vacuum.”

Svetlana kept her composure. “There’s a lot here we don’t understand. Adding one more thing to the list doesn’t strike me as the worst crime imaginable.”

Schrope responded with a noncommittal shrug.

“Explain what you think is happening,” Bella said, “then what you think we should do about it.”

“I think we should reverse, and reverse
fast
. We should be doing it already, not sitting around discussing it.”

“I still need to hear your argument,” Bella said patiently. “If I’m swayed by it, I promise I’ll act with all due swiftness.”

Svetlana leaned forward. “I’ll tell you, but you have to act as soon as I’m done. Every second we spend —”

“Just tell us,” Schrope said.

“Janus never slowed its rate of acceleration. Our only point of reference was the laser we were shining on Janus, and suddenly we were closing the distance too quickly. So we throttled back our engine in response. By the time we reached the initial study position, we thought we were nearly in free fall. But we weren’t. We were still accelerating.”

“Then why didn’t we feel it?” Schrope asked.

“Because we’re in an accelerated reference frame that just happens to feel inertial. I have no idea what this implies. Janus must be doing something weird to space-time, and we’re caught up in that weirdness.”

Bella fingered her shark’s-teeth necklace. “So what happened with the free-flier?”

“My best guess is that we let it drop far enough behind us to fall out of the slipstream,” Svetlana said. “It went from being caught in this accelerating field to not accelerating at all. We read that as the free-flier suddenly accelerating for no reason — but it was
us
, all along.”

“But five gees — that’s ridiculous. Janus was never accelerating that hard.”

“Something’s changed, in that case. When Janus left Saturn it was shedding ice, just as we’d expect if it were a physical object experiencing stresses due to its own acceleration. But at some point the ice-shedding stopped: we saw that in the images. We just didn’t think about what it meant.”

“Which was?”

“Janus must have switched over to a different drive mechanism. Maybe it used one drive to leave the solar system, something relatively slow and primitive by Spican standards but which wouldn’t do too much harm to the neighbourhood. But now it’s a long way from the Sun. It’s engaged something altogether more powerful: something capable of accelerating an entire
moon
at five gees.”

“And we’re stuck in the wake,” Bella said.

Svetlana nodded. “It’s been at least a day. We’ll have a better idea of how fast we’re moving once we have precise numbers on the extra Doppler component. But I’ll give you a good guess: we’ve been sustaining five gees ever since we lost contact with Earth, probably longer. We were moving at three per cent of the speed of light this time yesterday. Now you’d better make that four-and-a-half per cent, maybe even five.”

“What exactly does that mean?” Schrope said, in the voice of a man who had just seen his own ghost. “In terms of the mission objectives, I mean.”

“I don’t know about the mission objectives, Craig, but I’ll tell you what it means to you personally if we don’t get out of this fast. It means you’re fucked. It means we’re all fucked.”

Bella flinched, expecting Schrope to react. But nothing came. He just sat there in a slack-jawed stupor, as if he had been tranquillised.

“If this is confirmed,” Bella said tentatively, “then… what should we do? Can we back out of the slipstream, or whatever it is?”

“We can try,” said Svetlana. “The free-flier didn’t appear to suffer any damage when it left the slipstream: we only lost contact with it because of the sudden shift in frequencies.”

“We’ll need to know that for certain before we try anything. I’ll have Pagis and Hinks see if they can widen the reception bandpass and pick up a signal.”

“We don’t have time for this, Bella. We have to reverse out of this now, before it pulls us any faster than we’re already travelling.”

“Not until we know that the free-flier survived the transition. It shouldn’t take long.” She reached for her flexy, preparing to give the order. She already regretted not having Pagis and Hinks present in her office.

“Bella,” Svetlana said urgently, “listen to me. Every minute you sit here thinking about this is an additional three kilometres per second of speed we have to lose if we ever want to get home. There isn’t time to look into all the angles here. You have to move us
now
.”

Schrope suddenly came back to life. “The free-flier… how long did it take it to clear the slipstream?”

Svetlana answered him with a flat absence of emotion. “It was more than half a light-second out. If we push at half a gee now, we might reach the drop-out point in two or three hours, by which time we’ll be moving even faster.”

Schrope looked at Bella. “Perhaps we should consider a withdrawal —” He said it plaintively, like a child after sweets. Bella saw it plainly: the utter collapse of his neatly ordered corporate world. Until now Schrope had been in control. Now he was at the mercy of something frightening and powerful in equal measure.

Bella’s flexy chimed with an incoming call from Belinda Pagis. She had a hard number on the aberration problem.

“This is… not good,” she said, as if Bella had imagined it could be anything else. “To match the star positions as we see them, we need to allow for —” She lowered her eyes, reading data from another flexy. “Four-point-nine-eight per cent of the speed of light.”

“Good work,” Bella said.

“We’ve picked up a faint signal from the free-flier,” Pagis said, almost apologetically. “We allowed for the excess in our Doppler shift. It’s… worryingly consistent.”

“Does the free-flier telemetry look healthy?”

“No sign of any damage. The accelerometer curve was —”

“Flat,” Bella finished for her.

“Um, yes.”

Bella turned to Svetlana. “Then we could — theoretically — survive exiting the slipstream.”

“Start the process now,” Svetlana urged. “Full burn at half a gee. We’ll ditch the remaining mass drivers — anything we absolutely don’t need.”

“We still have to turn the ship around,” Bella said. “That’ll take two hours, if we don’t want to snap in two.”

Svetlana closed her eyes. “Jesus, I forgot.”

Rockhopper
didn’t take kindly to torsional stresses, any more than a skyscraper took kindly to being tipped on its side. Slewing the ship — bringing the fusion motors around to reverse their thrust — was a delicate operation that could not be hurried.

Normally there was no need to hurry it.

“Belinda,” Bella said, “drop whatever you’re doing and prep for a one-hundred-and-eighty-degree turnaround. Emergency slew speed: I don’t care if we blow the warranty on this one.”

“I’m on it,” Pagis said. “Anything else?”