There wasn't anything better for the purpose.

"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. Who has another
idea?"

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 well never
get free of its gravity."

Bradshaw, the English Planeteer, said mildly, "Don't worry, Lieutenant.
We're caught either way. 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 spot 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