The Sails of Tau Ceti (4 page)

A human spacecraft must race away from the sun to intercept the light sail before it entered the system. Once well beyond the orbit of Pluto, the explorer craft would turn end for end and begin decelerating. It would shed all of its outbound velocity and then begin accelerating back toward the sun with the light sail in pursuit. If properly done, it would match velocities with the light sail just as the alien derelict overtook it. Humanity would then be able to use the
Starhopper
probe’s instruments to learn what they could about the alien intruder.

All of this maneuvering required a prodigious velocity change. To match orbits with the light sail in time to do any good was the equivalent of accelerating to 15% of light speed. As Hunsacker had said, only
Starhopper
came anywhere close to having the necessary delta V capability.

“All right,
Starhopper
is the only spacecraft in the Solar System that can catch this light sail. That does not mean we
have
to send it out. How do we know we’ll learn anything worthwhile?”

“Damn it, we’re talking about a vessel built by alien sapients,” an exasperated Hunsacker muttered. “How can we
not
learn from it?”

“No sense getting upset, Boris,” Pierce said calmly. “Tory’s questions deserve an answer. What do we know about this light sail?”

Hunsacker put up the hologram showing Tau Ceti, its light ring, and the sail just beyond the ring’s milk-white boundary. “From its infrared spectrum, we estimate the sail temperature to be 50°K. That is a bit high for that distance from Sol, but not excessively so. We can also estimate its size.”

“Surely it isn’t close enough to show a disk,” Groschenko said.

Hunsacker laughed. “No, not anywhere near close enough. We can put an upper bound on its size from the fact that we did not detect it before now. To have escaped our notice, the sail cannot be larger than 1000 kilometers in diameter. It may be smaller.”

Pierce looked at his comely assistant. “They’ve got the proxies of every one of our sponsors on Earth. Even if we wanted to stop them, we couldn’t. How long before we can launch?”

She activated her implant and quickly reviewed the project’s status. A moment later, she answered, “A month, Dard. We will need to accelerate the certification process. That should not be a problem now that the mission has been shortened. There’s a big difference between a voyage lasting a few years and one lasting half a century.”

“What about fuel loading?”

“We’ll need to get priority at the Phobos refinery.”

“I will take care of it, Miss Bronson,” Jorge Contreras, the Mars government representative, said from across the table. He scrawled a note on his electronic notepad.

Pierce nodded. “Then we launch one month from today. Let us talk about what
Starhopper
is going to do when it gets there. Boris, you have had the most time to think about it. What say we begin with you?”

CHAPTER 3

Victoria Bronson sat at the bar and nursed a double scotch, her second. Ben Stalling regarded her with curious eyes.

“What’s the matter with you?” she asked petulantly after intercepting his third sidelong glance in as many minutes.

He sipped from his beer before answering. “Of all people, I would expect you to be the most ecstatic about this discovery.”

“I am … sort of.”

“Then why the long face?”

“It’s hard to explain.”

“I’m listening.”

“I’ve spent the three years of my life working on that damned probe.”

“So?”

“So, we built it to go to the stars, not to take pictures of a bit of space flotsam.”

“It’s damned important flotsam.”

“Why? Just spotting it tells us that we are not alone in the universe. What else can we learn from it?”

“We’ll learn how aliens build light sails, for one thing. If an anthropologist can reconstruct the whole history of a prehistoric people from a few pottery shards, just think what they will be able to do with a light sail to study. You people are going to make it happen! There is not a ship in the system with one-tenth of
Starhopper
’s speed. Without it, we’d have to watch in frustration as the sail zipped right past us.”

“Then what you are saying, my ex-love, is that I made the right decision when I went for that interview?”

She had meant the comment as a jibe. To her surprise, the expected witty rejoinder did not materialize. Both of them sat without speaking for a long time.

For her part, Tory tried to analyze why she had reacted the way she had. Ben was right. Normally she
would
have been ecstatic at the prospect of examining an alien artifact. Her negative reaction had possibly been an unconscious response to the unfairness of it all.

What a cruel joke for God to play on those poor unknowns who had died with their exploding sun. They must have known that another intelligent race inhabited Sol, a mere 12 light years off. Yet, with both species on the verge of a technology that would have made contact a certainty, Tau Ceti had exploded, snuffing out billions of intelligent minds in a single instant. What if it had been the sun that had gone nova rather than Tau Ceti? Would some alien be sitting in a bar on his distant world at this very moment, contemplating the lost bipeds of Sol III?

What
were
the chances of two races at nearly equal technology levels springing up so close together, and at the same moment in history? For a long moment, Tory toyed with the idea of overriding her implant’s safety interlocks and posing the question to the Olympus city computer. She resisted the urge. Compared with operating an implant, driving a groundcar under the influence of alcohol was an exercise in caution.

“There you are!”

Tory and Ben Stalling both turned around at the shouted accusation. Dardan Pierce was striding purposefully in their direction. If anything, his look was even stranger than the one he had worn in his office earlier in the evening.

“Hello, Dard. Drink?”

“We’ve been looking all over for you two. Why aren’t you on the net? Never mind, I see why.”

“Ben and I wanted to talk. We’ve a lot of catching up before I head back to Phobos tomorrow.”

“Not tomorrow and probably not for the rest of the week.”

“What’s happened?”

“Sadibayan received an emergency flash from Earth. Two hours ago the light sail lit up like a Christmas tree.”

“Lit up?”

“Began emitting blue-white light with a black body radiation curve equivalent to 5000°K. It is also emitting charged protons at relativistic velocity.”

“Huh?”

“So far as we can tell,” Pierce continued, “someone is ionizing hydrogen atoms and then using a very strong electrical charge to repel them away from the sail.”

“Why would they want to do that?”

“To slow down, of course. They are sweeping up the interstellar gas in their path and using it to retard their velocity. They’ve turned the sail into an electrostatic brake!”

“They?” Ben asked.

Pierce did not appear to hear the question. “We were wrong about the size, too. The sail is a hell of a lot bigger than one thousand kilometers.” It was probably furled until quite recently.”

“Furled?”

“Folded up! A fully deployed light sail would produce a strong parasitic drag on a 250 yearlong voyage. Better to stow it until you need it to decelerate. Less of a problem with wear and tear, too.”

“You speak as though there’s a crew aboard,” Tory said. Despite the warm fog the scotch had laid over her mind, the implications of Pierce’s statements were beginning to sink in.

“We think there is. Come on; let’s get you a sober pill. We have plans to make. This changes everything.”

#

There were only three people left in the conference room when Pierce returned with Tory and Ben Tallen. Tory walked with a rolling gait as she sought her place at the table. It had been nearly a century since the invention of
Quiksober
, yet the spatial disorientation that was the wonder drug’s primary side effect had never been completely tamed.

She switched on her implant and let it run through its self-test sequence. When she was certain it was operational, she asked, “All right, what do we know?”

Tory’s intention had been to request the file reference for the new data so that she could access it. Boris Hunsacker misunderstood her request, or possibly the data had yet to be input into the computer. He called for the lights to be dimmed and the holocube to be activated.

The familiar starfield was much as it had been. Tau Ceti blazed bright from within its shell of gas. The light sail, which had formerly reflected an anemic version of Sol’s spectrum, now blazed forth like a new nova. The former dim yellow spot was now the blue-white hue of a mercury vapor lamp.

“Brightened some, hasn’t it?”

“An understatement, Miss Bronson,” Sadibayan replied dryly. “When it first happened, Luna thought it had exploded.”

“Did it blaze up all at once?”

Hunsacker nodded. “The time from onset to maximum was only three milliseconds. That is the primary reason we suspect an electrostatic braking device. If friction were the cause, the temperature would not have shot up so precipitously. We also wouldn’t be seeing relativistic protons.”

“Friction?”

“One of the Luna astronomers postulated that the sail had run into a gas bubble surrounding a comet nucleus out in the Oort cloud,” Hunsacker explained.

The subminister shook his head. “Anything dense enough to make it glow like that would have ripped it apart.”

“Can we detect any deceleration yet?”

“No way to tell, damn it. We could judge its speed well enough when it was reflecting sunlight. It is a simple matter to measure Doppler shift from a known spectrum. Now that it is emitting light on its own, we’ve lost even that clue.”

“So we don’t know how fast it is slowing?”

“Not directly. If they intend to stop inside the Solar System, they have to decelerate at something around one-thousandth of a standard gravity.”

“That isn’t very much.”

“More than enough to halt short of the sun. Remember, they’ve got one hell of a long distance to fall.”

“If they’re slowing, they won’t arrive as quickly.”

“True. We now estimate that the sail will reach us in five years rather than three-and-a-half. A precise figure will have to await a better estimate of their deceleration constant.”

Tory had been reviewing the technology of electrostatic brakes ever since activating her implant. The idea had a surprisingly long history. An electrostatic brake was essentially a device for sweeping up hydrogen across a vast region of space and funneling it into a spacecraft’s path. In effect, the spacecraft would plow through an artificially enhanced solar wind. Every impact on the craft robbed it of momentum, causing it to slow.

The literature contained dozens of proposals on how to accomplish the trick. All relied on the fact that there are some 100,000 hydrogen atoms per cubic meter even in deep interstellar space. Most used a tuned laser to ionize the hydrogen over a large region in front of the ship, and then attracted the ions with a powerful negative electrical charge. The electrical field acted as a giant invisible funnel that concentrated the interstellar gas onto a collecting device such as a light sail. If the surface of the sail was then negatively charged, the ions could be reflected back the way they had come before impact. Reflecting the ions allowed twice the momentum transfer of merely bombarding the sail, while protecting the sail’s surface from erosion at the same time.

“Electrostatic brakes work well enough when a ship is moving at high speed,” Tory said, quoting from an encyclopedia article she had just scanned, “but their efficiency drops off drastically with reduced velocity.”

“Once close to the sun, they’ll transition to light pressure braking,” Hunsacker replied.

“I think not,” Pierce responded. He, too, had been busy with his implant. “Tory’s right. Electrostatic braking efficiency falls off rapidly as you slow. Even with optimistic assumptions for both electrostatic and light pressure, they would still be going too fast to stop by the time they reached the sun. They must be planning an aerobraking maneuver near the sun to finish the job. That is a ticklish thing. If they hit that soup too fast, the passengers will be turned to red mush.”

“How do we know the mush would be red?” Ben asked. The question sounded like a joke and drew him a baleful look from Sadibayan. In truth, he had been completely serious.

Tory felt a small shiver run up her spine. The aliens were using their light sail like a giant parachute. If they were to go into solar orbit, they would practically have to dive into the sun. Whoever had thought up this scheme must have been truly desperate. After a moment’s thought, however, she chuckled quietly to herself.

Sadibayan turned his disapproving look from his aide to Tory. “What’s so funny?”

“We are,” she replied. “Here we’re worried that they will fly too close to the sun and end up like Icarus. Yet, they launched from out of the heart of an exploding nova. I doubt they will be frightened by the prospect of diving headlong into our little star!”

#

“All right,” Pierce said after the technical discussion had gone on for nearly an hour, “now that we have all reviewed the new information, what do we do about it?”

“Luna makes their announcement!”

“I’m sorry, Miss Bronson,” Sadibayan said, “but that is not going to happen. My orders from Earth are that no mention will be made of this discovery for the time being.”

“Why the hell not?” Pierce demanded.

“We need time to study the implications of the situation. We don’t know how people will react.”

“But that’s censorship!”

“Nevertheless, that is the way things are going to be. Anyone who divulges a word about the light sail beyond this room will not be allowed to participate in the investigation. Is that clear?”

The three scientists in the room nodded, grudgingly.

“Perhaps we should look to our defenses,” Contreras said.