ss than a half hour, Corbett," said Connel nervously. "I'd better
check on Shinny and Alfie." He called into the audiophone. "Major Connel
to Shinny and Higgins, come in Shinny--Higgins!"

"Shinny here!" came the reply. "We're just finishing up the last unit.
Should be back in five minutes."

"Make it snappy!" said Connel. "Less than a half hour left!"

"We'll make it," snorted Shinny.

"Coming in for a touchdown," said Tom. "Better strap in, sir!"

Connel nodded. He laced several straps across his lap and chest,
gripping the sides of the seat. Tom sent the jet boat in a swooping
dive, cut the acceleration, and brought the small ship smoothly inside
the huge air lock in the side of the _Polaris_.

"I'd better get right up on the control deck and start warming up the
circuits, sir," said Tom.

"Good idea, Tom," said Connel. "I'll try and pick up Manning and Astro."

Tom left the officer huddling over the communicator in the jet boat.

"Major Connel to Manning and Astro, come in!" called Connel. He waited
for a moment and then repeated. "Manning--Astro, come in! By the rings
of Saturn, come in!" There was the loud roar of an approaching jet boat.
Shinny guided the ship into the _Polaris_ with a quick violent blast of
the braking rockets. The noise was deafening.

"Belay that noise, you blasted space-brained idiot!" roared Connel. "Cut
that acceleration!"

Shinny grinned and cut the rockets. The jet-boat catapult deck was
quiet, and Connel turned back to the communicator.

"Come in, Manning--Astro! This is Major Connel. Come in!"

On the opposite side of the airless satellite, Roger and Astro were busy
digging a hole in the hard surface. Near by lay the last of the
explosive units to be installed. Connel's voice thundered through their
headset phones.

"Boy, is he blasting his jets!" commented Roger.

"Yeah," grunted Astro. "He should have to dig this blasted hole!"

"Well, this is where it's got to go. If the ground is hard, then it's
our tough luck," said Roger. "If we stick it anywhere else, it might
mess up the whole operation."

Astro nodded and continued to dig. He held a small spade and jabbed at
the ground. "How much--time--have we got left?" he gasped.

"Twenty minutes," replied Roger. "You'd better hurry."

"Finished now," said Astro. "Get the reactor unit over here and set the
fuse."

Roger picked up the heavy lead box and placed it gently inside the hole.

"Remember," Astro cautioned, "