ces out
here. I want to see what they're up to."

"Great Cosmos, sir! They'll go over this rock like Martian beetles. You'll
get it for sure."

"Get inside," Rip ordered. He gathered strength enough to make his voice
firm. "I'm staying here until I figure out some way to call them off. We
can't just stand here and let them blast us. They're our own men."

"Then I'm staying, too," Koa stated.

A pair of snapper-boats flashed overhead, and vanished below the horizon.
Two more swept past from another direction.

Rip watched, curious. What were they up to? Another pair quartered past
them at high speed, then two more. The dozen boats seemed to be
criss-crossing the asteroid in a definite pattern. Why?

A pair streaked past, and something sped downward from one of them,
trailing yellow flame. It exploded in a ball of molten fire that licked
across the asteroid in waves. Rip tensed, then saw that the chemical would
burn out before it reached them.

"Fire bomb," Koa muttered.

Rip nodded. He had recognized it. The Planeteers were trained in the use
of fire bombs, tanks of chemicals that burned even in an airless world.
They were equipped with simple jets for use in space.

The snapper-boats drew off, back toward the _Scorpius_. Rip watched,
searching for some reason for their actions. Then one of the boats pulled
away from the others. It returned to the asteroid with stern jet burning
fitfully.

"Is he landing?" Koa asked.

Rip didn't know. The snapper-boat was moving slowly enough to make a
landing.

Directly over the asteroid it changed direction, circled, and returned
over their heads. Rip could almost have picked it off with a pistol shot.
Santos could have blasted it into space dust with one rocket.

The snapper-boat changed direction, and for a fraction of a second stern
and side tubes "fought" each other, making the boat yaw wildly, then it
straightened out on a new course.

[Illustration: "They're Using Fire Bombs," Muttered Koa.]

"They're Using Fire Bombs," Muttered Koa.

Koa exclaimed, "That's a drone!"

Rip got it then. A pilotless snapper-boat! That's why its actions were a
little uneven. Only one thing could explain its deliberate slowness. It
was bait. The _Scorpius_ had sent piloted snapper-boats over the asteroid
at high speed, criss-crossing in order to cover the thorium world
completely, expecting to have the unknown rocketeer fire at them. Then a
fire bomb had