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