Peril!
Sergeant major Koa asked thoughtfully, "Sir, would it do the Connie much
good to launch boats this close to the sun? They'd have to use too much
fuel just keeping position."
"You could be right," Rip said slowly. Koa had a point! To counter
gravitational attraction took velocity, which meant consumption of fuel.
Maneuvering boats meant rapid velocity changes. Against the sun's
terrific gravity at this distance, it also meant maximum thrust and
maximum fuel flow most of the time. The asteroid, in a planned orbit with
the correct velocity, was safe enough, and the Connie cruiser would
simply match the asteroid's orbit. But boats, which had to maneuver, were
another matter.
Rip figured quickly. In accordance with Newton's Law, gravitational
attraction increased rapidly on approaching a body. If he could put the
asteroid even closer to the sun, the boat problem would become worse,
until even a small velocity change in the wrong direction could leave
a boat in the terrible position of not having enough thrust for a long
enough time to keep from being drawn into the sun.
But to change the asteroid's orbit was dangerous! It meant losing just
enough velocity to be drawn closer to the sun, and then picking up a much
higher velocity to get free again!
Rip got his instruments and pulled out a special slide rule designed for
use in space. He had Koa stand by with stylus and computation board and
take down his figures.
He recalculated the safety factor he had used when deciding how close
to the sun to put the asteroid, then took quick star sights to determine
their exact position. They were within a few miles of perihelion, the
point at which they would be closest to Sol.
Rip tapped gloved fingers on his helmet absently. If they could blast out
of the orbit and drive into the sun.... He estimated the result. A few
miles per second of less speed would let them be pulled so far within the
sun's field of gravity that, within an hour or so, small boats would
venture into space only at their peril.
He reviewed the equipment. They had tubes of rocket fuel, but the tubes
wouldn't give the powerful thrust needed for this job. They had one
atomic bomb. One wasn't enough. Not only must they drive toward the sun,
but also they must keep reserve power to blast free again. If only they
had a pair of nuclear charges!
He called his Planeteers together and outlined the problem. Perhaps
one of them would have an idea. But no useful suggestions were
forth-coming--until Dominico spoke up. "Sir, why don't we make two
bombs from one?"
"I wish we could," Rip said. "Do you know how?"
"No, Lieutenant. If we had parts, I could put bombs together. I can take
them apart, but I don't know how to make two out of one." The Italian
Planeteer looked accusingly at Rip. "I thought maybe you knew, sir."
Rip grunted. If they had parts, he could assemble nuclear bombs, too.
Part of his physics training had been concerned with fission and its
various applications. But no one had taught him how to make two bombs
out of one.
The theory behind this particular bomb design was simple. Two or more
correctly sized pieces of plutonium or uranium isotope, when brought
together, formed what was known as a critical mass, which would fission.
The fissioning released energy and produced the explosion.
But there was a wide gap between theory and practice. A nuclear bomb was
actually pretty complicated. It had to be complicated to keep the pieces
of the fissionable material apart until a chemical explosion drove them
together fast and hard enough to create a fission explosion. If the
pieces weren't brought together rapidly enough, the mass would fission
in a slow chain reaction with no explosion.
Rip was trained in scientific analysis. He tackled the problem logically,
considering the design of a nuclear bomb and the reasons for it.
Atomic bombs had to be carried. That meant an outer casing was necessary.
The casing had a lot to do with the design. Suppose no casing were
required? What would be needed?
He took the stylus and computation board from Koa and jotted down the
parts required. First, two or more pieces of plutonium large enough to
form a critical mass. Second, a neutron source--the type of radioactivity
that produced neutrons--to accelerate the reaction. Third, some kind of
neutron reflector. And fourth, explosive to drive the pieces together.
Did they have all those items? He checked them off. Their single five KT
bomb contained at least enough plutonium for two critical masses, if
brought together inside a good neutron reflector. Each mass should give
about a two kiloton explosion. And they did have a good neutron
reflector--nuclite. There wasn't anything better.
"What have we got for a neutron source?" he asked aloud. He was really
asking himself, but he got a quick answer from Koa.
"Sir, some of the stuff left in the craters from the other explosions
gives off neutrons."
"You're right," Rip agreed instantly. A small piece from one of the
craters, when combined with half of the neutron source in the bomb,
should be enough. As for the explosive, they had exploding heads on their
attack rockets.
In other words, he had what he needed--except for a method of putting all
the pieces together to create a bomb.
If only they had a tube of some sort that would withstand the chemical
explosion--the one that brought the critical mass together!
He told the Planeteers what he had been thinking, then asked, "Any ideas
for a tube?"
"How about a tube from the snapper-boat?" Santos suggested.
Rip shook his head. "Not strong enough. They're designed to withstand the
slow push of rocket fuel, not the fast rap of an explosion. When I say
slow, I mean slow-burning when compared with explosive. Any more ideas?"
Kemp, the expert torchman, said, "Sir, I can burn you a tube into the
asteroid."
Rip grabbed the Planeteer so hard they both floated upward. "Kemp, that's
wonderful! That's it!" The details took form in his mind even as he
called orders. "Dominico, tear down that bomb. Santos, remove two heads
from your rockets and wire them to explode on electrical impulse. Kemp,
we'll want the tube just a fraction of an inch wider than a rocket head.
Get your torch ready."
He took the stylus and began calculating. He talked as he worked, telling
the Planeteers exactly what they were up against. "I'm figuring out where
to put the charge so it will do the most good, but my data isn't
complete. If our homemade bomb goes off, I don't know exactly how much
power it will give. If it gives too much, we'll be driven so close to the
sun we'll never get free of its gravity."
Bradshaw, the English Planeteer, said mildly, "Don't worry, Lieutenant.
If it isn't the solar frying pan, it's Connie fire."
A chorus of agreement came from the other Planeteers. "What a crew!" Rip
thought. "What a great gang of space pirates!"
He finished his calculations and found the exact place where Kemp would
cut. A few feet away from the spot was a thick pyramid of thorium. That
would do, and they could cut into it horizontally instead of drilling
straight down. He pointed to it. "Let's have a hole straight in for six
feet. And keep it straight, Kemp. Allow enough room for a lining of
nuclite. Koa, cut a sheet of nuclite to size."
Kemp's torch already was slicing into the metal. Rip asked, "Can you weld
with that thing, Kemp?"
"Just show me what you want, sir."
"Good." Rip motioned to Trudeau. "Frenchy, we'll need a strong rod at
least eight feet long."
The French Planeteer hurried off. Rip consulted his chronometer. Less
than ten minutes had passed since the call from Terra base.
He went over his plan again. It had to work! If it didn't, asteroid and
Planeteers would end up as subatomic particles in the sun's photosphere,
because he had calculated his blast to drive the asteroid past the limit
of safety. It was the only way he could be sure of putting them beyond
danger from Connie landing boats or snapper-boats. The Connie would have
only one chance--to bring his cruiser down.
If he tried that, Rip thought grimly, he would get a surprise. The second
nuclear charge would be set, ready to be fired. The Connie cruiser was
so big that no matter how it pulled up to the asteroid, some part of it
would be close enough to the charge to be blown into space dust. No
cruiser could survive an atomic explosion within five hundred yards, and
the Connie would have to get closer to the nuclear charge than that.
Dominico reported that the bomb had been dismantled. Rip went to it and
examined the raw plutonium, being careful to keep the pieces widely
separated.
This particular bomb design used five pieces of plutonium which were
driven together to form a ball. Rip made a quick estimate. Two were
enough to form a critical mass. He would use two to blast into the sun
and three to blast out again. He would need the extra kick.
There was only one trouble. The pieces were wedge shaped. They would have
to be mounted in thorium in order to keep them rigid. Only Kemp could do
that. They had no cutting tool but the torch.
Santos appeared, carrying a rocket head under each arm. They had wires
wound around them, ready to be attached to an electrical source.
Rip hurried back to where Kemp was at work. The private was using a
cutting nozzle that threw an almost invisible flame five feet long.
In air, the nozzle wouldn't have worked effectively beyond two feet, but
in space it cut right down to the end of the flame. Kemp had his arm
inside the hole and was peering past it as he finished the cut.
"Done, sir," he said, and adjusted the flame to a spout of red fire. He
thrust the torch into the hole and quickly withdrew it as pieces of
thorium flew out. A stream of water hosed into the tube would have worked
the same way.
Rip took a block of plutonium from Dominico and handed it to Kemp. "Cut
a plug and fit this into it. Then cut a second plug for the other piece.
They have to match perfectly, and you can't put them together to try out
the fit. If you do, we'll have fission right here in the open."
Kemp searched and found a piece he had cut in making the tube. It was
perfectly round, ideal for the purpose. He sliced off the inner side
where it tapered to a cone, then, working only by eye estimate, cut out a
hole in which the wedge of fission material would fit. He wasn't off by a
thirty-second of an inch. Skillful application of the torch melted the
thorium around the wedge and sealed it tightly.
Koa was ready with a sheet of nuclite. Trudeau arrived with a pole made
by lashing two crate sticks together.
Rip gave directions as they formed a cylinder of nuclite. Kemp
spot-welded it, and they pushed it into the hole.
Nunez found a small piece of material in one of the earlier craters. It
would provide some neutrons to start the chain reaction. Rip added it to
the front of the plutonium wedge, along with a piece of beryllium from
the bomb, and Kemp welded it in place.
They put the thorium block which contained the plutonium into the hole,
the plutonium facing outward. Trudeau rammed it to the bottom with his
pole. The neutron source, the neutron reflector, and one piece of
fissionable material were in place.
Kemp sliced another round block of thorium out of a nearby crystal and
fitted the second wedge of plutonium into it. At first Rip had worried
about the two pieces of plutonium making a good enough contact, but
Kemp's skillful hand and precision eye removed that worry.
The torchman finished fitting the plutonium and carried the block to the
tube opening. He tried it, removed a slight irregularity with his torch,
then said quietly, "Finished, sir."
Rip took over. He slid the thorium-plutonium block into the tube, took a
rocket head from Santos, and used it to push the block in farther. When
the rocket head was about four inches inside the tube, its wires trailing
out, Rip called Kemp. At his direction, the torchman sliced a thin slot
up the face of the crystal. Rip fitted the wires into it and held them in
place with a small wedge of thorium.
Kemp cut a plug, fitted it into the hole, and welded the seams closed.
The tube was sealed. When electric current fired the rocket head, the
thorium carrying the plutonium wedge would be driven forward to meet the
wedge in the back. And, unless Rip had miscalculated the mass of the two
pieces, they would have their nuclear blast. Rip surveyed the crystal
with some anxiety. It looked right.
Dominico already had rigged the timer from the atomic bomb. He connected
the wires. "Do I set it, sir?"
"Load the communicator, the extra bomb parts, the rocket launcher and
rockets, the cutting equipment, my instruments, and the tubes of fuel,"
Rip ordered. "Leave everything else in the cave."
The Planeteers ran to obey. Rip waited until the landing boat was nearly
loaded, then told Dominico to set the timer for five minutes. He wondered
how they would explode the second charge, since they had only the one
timer left, then forgot about it. Time enough to worry when faced with
the problem.
"I'll take the snapper-boat," he stated. "Santos in the gunner's seat.
Koa in charge in the landing boat. Dowst pilot. Let's show an exhaust."
He fitted himself into the tight pilot seat of the snapper-boat while
Santos climbed in behind. Then, handling the controls with the skill
of long practice, he lifted the tiny fighting rocket above the asteroid
and waited for the landing boat. When it joined up, Rip led the way to
safety. As he cut his exhaust to wait for the explosion, he sighted past
the snapper-boat's nose to the asteroid.
Even though both boats had been careful to match velocity with the
asteroid as closely as possible, the slight difference remaining caused
them to drift sunward. Rip cut his jets in to compensate, and saw Dowst
do the same.
Another few miles toward the sun, and the landing boat wouldn't have the
power to get away from Sol's gravity. A few miles beyond that, even the
powerful little snapper-boat would be caught.
Below, the timer reached zero. A mighty fan of fire shot into space. The
asteroid shuddered from the blast, then swerved gradually, picking up
speed as well as new direction.
Rip swallowed hard. Now they were committed. They would reach a new
perihelion far beyond the limits of safety. _P_ for perihelion and _P_ for
peril. In this case, they were the same thing!