set the fuse for two hours."

"No, you're wrong," replied Roger. "I've set the fuses each time,
subtracting the amount of time since we left the _Polaris_. I set this
one for twenty minutes."

"You're wrong, Roger," said Astro. "It's maximum time is two hours."

"Listen, you Venusian clunk," exploded Roger, "_I_ built this thing, so
I know what I'm doing!"

"But, Roger--" protested Astro.

"Twenty minutes!" said Roger, and twisted the set-screw in the fuse.
"O.K., it's all set. Let's get out of here!"

The two cadets raced back to the jet boat and blasted off immediately.
Once in space, Astro turned to Roger.

"Better check in with Major Connel before he tears himself to pieces!"

"Yeah," agreed Roger. "I guess you're right." He flipped on the audio
communicator. "Attention! Attention! Manning to Major Connel. Am making
flight back to _Polaris_. All installations complete."

[Illustration: "_Remember," Astro cautioned, "set the fuse for two
hours._"]

"What took you so long, Manning?" barked Connel in reply. "And why
didn't you answer me?"

"Couldn't, sir," said Roger. "We had a tough time digging a hole for the
last unit."

"Come back to the _Polaris_ immediately," said Connel. "We're blasting
off in fifteen minutes."

"Very well, sir," said Roger.

Presently the jet boat circled the _Polaris_ and made a landing run for
the open port. Roger braked the small craft and brought it to rest
alongside the others.

"That's it, spaceboy," he said to Astro. "All out for the _Polaris_
express back home!"

"Just be sure you give me a good course, Manning," grunted Astro,
heaving his huge frame out of the small cabin of the jet boat, "and I'll
give you all the thrust you want!"

Astro secured the jet boats while Roger closed the air-lock hatch,
shutting out the last view of the rugged little planetoid. Roger threw
the landscape a mocking kiss.

"So long, Junior! See you back home!" The two cadets climbed the ladder
leading to the control deck.

Seated in front of the control panel, Tom watched the sweeping hand of
the solar clock. Connel paced nervously up and down behind him. Shinny
and Alfie stood to one side also watching the great clock.

"How much time, Corbett?" asked Connel for the dozenth time.

"Junior gets his kick in the pants in ten minutes, sir," replied Tom.

"Fine," said Connel. "That gives me just enough time to notify Space
Academy to get ready to receive Junior's signal. You know what