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Authors: Ben Bova

BOOK: Battle Station
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“Your own medical science can bring a man back from clinical death, in certain cases,” the Black Saint said gently. “Our science is somewhat more advanced than that.”
“And the agency … Lyle …”
“Mr. Lyle was present at your cremation. He was given your ashes, since you had no next of kin listed in your personnel file.”
Keating thought swiftly. “You switched bodies at the crematorium.”
“Something like that,” said Rungawa.
“Then you really are … what you said you were.”
Rungawa's smile broadened. “Did you doubt it? Even when you risked your life on it?”
“There's a difference between knowing here,” Jeremy tapped his temple, “and believing, here in the guts, where …”
He stopped in midsentence and stared at the hand that had moved from his head to his midriff.
It was not his hand
.
“What have you done to me?” Jeremy's voice sounded high, shrill, frightened as a little child's.
“It was necessary,” Rungawa's deep voice purred softly, “to give you a new body, Mr. Keating.”
“A new …”
“Your former body was destroyed. We salvaged your mind—your soul, if you want to use that term.”
“Where … whose body … is this?”
Rungawa blinked slowly once, then replied. “Why, it is your own body, Mr. Keating.”
“But before … ?”
“Ahh, I understand. We did not steal it from anyone.” The black man smiled slightly. “We created it for you especially, just as this body of mine was created for me. You would not expect a being from another world, thousands of light-years from your Earth, to look like a human being, would you?”
Jeremy swallowed once, twice, then managed to say, “No, I guess not.”
“It is a very good body, Mr. Keating. A bit younger than your former shell, quite a bit stronger, and with a few special sensitivities added to it.”
Jeremy threw back the bedclothes and saw that he was naked. Good strong legs, flat ridged midsection. His hands looked heavier, fingers shorter and somewhat blunter. His skin was pink, like a baby's, new and scrubbed-looking.
Wordlessly, he swung his legs to the floor and stood up. No dizziness, no feeling of weakness at all. He padded to the bathroom, Rungawa a few steps behind him, and confronted himself in the mirror.
The face he saw was squarish, with curly red-blond hair and a light sprinkling of faint freckles across its snub nose and broad cheeks. The eyes were pale blue.
“Christ, I look like a teenager!”
“It is a fully adult body,” Rungawa said gravely.
Jeremy turned to the black man, a nervous giggle
bubbling from his throat. “When you say born again, you really mean it!”
“You spared my life, Mr. Keating,” said Rungawa. “Now we have spared yours.”
“So we're even.”
Rungawa nodded solemnly.
“What happens now?” Jeremy asked.
The black man turned away and strode slowly back toward the hospital bed. “What do you mean, Mr. Keating?”
Following him, Jeremy said, “As far as the rest of the world is concerned, Jeremy Keating is dead. But here I am! Where do I go from here?”
Rungawa turned to face him. “Where do you wish to go, Mr. Keating?”
Jeremy felt uncertain, but only for a moment. He was slightly shorter than he had been before, and the Black Saint looked disconcertingly taller.
“I think you know what I want,” he said. “I think you've known it all along.”
“Really?”
“Yes. This has all been an elaborate form of recruitment, hasn't it?”
Rungawa really smiled now, a dazzling show of pleasure. “You are just as perceptive as we thought, Mr. Keating.”
“So it has been a game, all along.”
“A game that you played with great skill,” Rungawa said. “You began by sparing the life of a man whom you had been instructed to assassinate. Then you quite conspicuously tried to get your employers to murder you.”
“I wouldn't put it that way …”
“But that is what you did, Mr. Keating. You were
testing
us! You set up a situation in which we would have to save your life.”
“Or let me die.”
Rungawa shook his head. “You accepted what I had told you in Athens. You believed that we would be morally bound to save your life. Your faith saved you, Mr. Keating.”
“And you, on your part, have been testing me to see if I could accept the fact that there's a group of extraterrestrial creatures here on Earth, masquerading as human beings, trying to guide us away from a nuclear holocaust.”
Nodding agreement, Rungawa said, “We have been testing each other.”
“And we both passed.”
“Indeed.”
“But why me? Out of five billion human beings, why recruit me?”
Rungawa leaned back and half sat on the edge of the empty hospital bed. “As I told you in Athens, Mr. Keating, you are a test case. If
you
could accept the fact that extraterrestrials were trying to help your race to avoid its own destruction, then we felt sure that our work would meet with eventual success.”
Keating stood naked in the middle of the antiseptic white room, feeling strong, vibrant, very much alive.
“So I've been born again,” he said. “A new life.”
The Black Saint beamed at him. “And a new family, of sorts. Welcome to the ranks of the world saviors, Mr. Keating. There are very few of us, and so many of your fellow humans who seem intent on destroying themselves.”
“But we'll save the world despite them.”
“That is our task,” Rungawa said.
Keating grinned at him. “Then give me some clothes and let's get to work.”
High-powered lasers have many more uses than to “merely” shoot down ballistic missiles.
Someday, sooner than most people think, spacecraft will lift off planet Earth propelled by nothing more than a beam of light.
The work described here started at Avco Everett Research Laboratory, when I was still working there. It has been carried on by a group of Avco Everett “alumni,” who started their own company—Physical Sciences, Inc.
While I was editing
Analog
magazine, I encouraged Jerry Pournelle to develop the concept of laser propulsion in a cover story he was writing. Kelly Freas painted the cover illustration, which ran in the March 1974 issue. I estimate that thirty years after that story appeared, we will be able to go out to Cape Canaveral and check on the accuracy of Kelly's painting.
 
 
The shuttle orbiter opens its big cargo bay doors. Its long manipulator arm lifts a set of six communications satellites, one by one, out of the cargo bay and leaves them floating freely in empty space. Then the orbiter fires its maneuvering jets and departs from the area.
A brilliant pencil-thin beam of light lances up from
the ground, reflects off a mirror orbiting hundreds of miles away, and reaches its dazzling finger to a small rocket nozzle on one of the satellites. The rocket flares to life, propelling the satellite toward its desired final destination in an orbit higher than the shuttle could reach. Within a few minutes, each of the satellites has been sent on its way, propelled by the energy of the laser's beam.
Riding such a beam of light may become the most efficient and economical way to maneuver satellites in space, according to Anthony N. Pirri, a vice-president of Physical Sciences, Inc., a fifty-five-man research company in Andover, Massachusetts.
“We've shown that laser propulsion works in the laboratory,” says Pirri. “Now we're investigating the details of the physics so that we can optimize the concept and make it work in the practical world.”
Small models of rocket thrusters have been propelled by laser light in laboratory experiments at PSI. The idea of using a laser to provide propulsion energy for a rocket is also being studied at Penn State University, the University of Illinois, the University of Tennessee Space Institute, and at the NASA Marshall Space Flight Center in Huntsville, Alabama.
Like an automobile engine, a rocket needs to deliver power and fuel efficiency. In an auto, power is measured in terms of horsepower, efficiency in terms of miles per gallon. In a rocket engine, power is measured in terms of pounds of thrust, and fuel efficiency is rated by a factor called
specific impulse
, which is usually expressed in units of seconds.
Chemical rockets, such as those used to boost the space shuttle into orbit, can provide thousands of pounds of thrust, but are not very efficient. The shuttle's main engines, for example, have a specific impulse of less than four hundred seconds.
On the other hand, there are electrical rockets,
which are very efficient, but produce very low power. An ion rocket, for example, which uses electrostatic forces to accelerate ionized atoms of cesium to very high velocities, can yield specific impulses of many thousands of seconds. But it produces only micropounds of thrust because it is very small and very little cesium actually flows through the rocket's nozzle. To make electric rockets larger would mean making their electrical power plants too huge to lift off the ground. An ion rocket, therefore, would be highly efficient, but it would take months for it to lift a communications satellite from low orbit to geosynchronous orbit.
A laser-powered rocket can give specific impulses of one thousand to two thousand seconds, and thrust of up to one hundred pounds. It may be ideal for the task of quickly raising a satellite's orbit or otherwise maneuvering satellites once they have been placed in low orbit by the shuttle.
Laser propulsion offers two basic advantages: one, the laser itself does not have to be lifted off the ground; most of the weight of the propulsion system never leaves the earth. Two, the laser beam can heat propellants to far higher temperatures than can be obtained by chemical burning; the higher the propellant's temperature, the faster it flows through the rocket nozzle; the faster it flows, the higher the specific impulse.
A laser-driven rocket would carry hydrogen or possibly argon in its fuel tank, laced with a small amount of water, ammonia, or another compound that absorbs laser energy well.
Hydrogen would make the best propellant, since it is the lightest element and therefore would produce the highest flow velocity per watt of laser power input. High flow velocity is much more important to high specific impulse than the mass of the propellant. But
hydrogen tends to link into a two-atom molecule, so some laser energy would be used up in dissociating the molecules. Argon, although nearly forty times heavier than hydrogen, is a monatomic gas and would not have to be dissociated.
Experiments at PSI have included both pulsed and continuous-wave lasers. The pulsed laser beam is fired right into the rocket nozzle itself. Pulsing the beam every few microseconds allows the rocket exhaust gases to clear away from the nozzle before the next burst of laser energy comes in. But this means that fast-acting valves may have to be built into the system to pulse the propellant flow on and off within microseconds. A continuous-wave laser would not require gas valving, but needs a window of some sort and a complicated optical system to allow the beam into the rocket chamber upstream of the nozzle.
There are several practical problems facing laser propulsion. Nelson Kemp, a principal scientist at PSI, points out that the materials of the rocket nozzle must handle “a very large amount of energy in a very small volume of gas.” Gas temperatures at the core of the rocket chamber may be as high as 20,000°K and pressures can go up to one hundred atmospheres.
Conventional chemical rockets can run at equally high chamber pressures, but the gas temperature in a chemical rocket is limited to the amount of energy released by the combustion of the rocket's propellants. In a laser-driven rocket, says Kemp, “there's virtually no limit to how high you can heat the gas,” because the energy comes from the laser, rather than from the propellants' inherent chemical energy.
The Hungarian recipe for an omelet begins, “First, steal some eggs …” Laser propulsion depends on the development of lasers of unprecedented power—ten megawatts or more—and pointing systems of astronomical precision. The low-level research efforts currently
funded by NASA and the Air Force Office of Scientific Research are many orders of magnitude too small for such hardware development.
But the White House's Strategic Defense Initiative (i.e., “Star Wars”) is aimed at developing lasers powerful and accurate enough to destroy ballistic missiles. Such lasers would be more than adequate for raising a satellite's orbit or otherwise maneuvering it in space. The Star Wars weaponry may have broad peaceful applications.
“There's no reason why laser propulsion can't be a practical system,” says Robert F. Weiss, president of PSI. He foresees satellites lifted from the ground by high-flying airplanes or air-breathing ramjet boosters, then propelled into orbit from the upper fringes of the atmosphere by laser energy, by the late 1990s.
Robert L. Forward, of Hughes Research Laboratories in Malibu, California, looks even farther ahead and envisions huge lasers in orbit near the Earth that propel spacecraft through the far reaches of the solar system, and even out toward other stars.
No rocket engine even conceivable today could propel spacecraft across interstellar distances. But Forward believes that laser-pushed lightsail systems using “known laws of physics and fairly reasonable engineering extrapolation of known technologies” could send spacecraft to the stars—riding a beam of light.

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