? To get yourself a Solar Medal?" asked Roger sarcastically.

"What do you think made this tub act up like this, Astro?" asked Tom,
ignoring Roger's remark.

"Using special reactant feed, Tom," replied Astro. "This is a converted
chemical burner--with an old-type cooling pump. It's touchy stuff."

"Well, couldn't we drive boron rods into the mass and slow down the
reaction?" asked Tom.

"No, Tom," answered Astro, "the control for the rods are inside the tube
control box. We can't reach it."

There was a sudden loud ticking from the Geiger counter.

"Astro!" cried Roger. "The mass is building!"

"Here, lemme see!" shouted Astro. He took the instrument in his big hand
and watched the clocklike face intently.

" ... fourteen hundred thirty--fourteen hundred fifty--fourteen hundred
seventy--" He faced his unit-mates. "Well, that does it. The mass is
maintaining a steady reaction without the energizing pumps. It's
sustaining itself!"

"But how is that possible?" asked Tom.

"It's one of those freaks, Tom. It's been known to happen before. The
fuel is just hot enough to sustain a steady reaction because of its high
intensity. Once that baffle worked loose, the mass started wildcatting
itself."

"And if it doesn't stop?" asked Roger tensely.

"It'll reach a point where the reaction comes so fast it'll explode!"

"Let's pile out of here!" said Roger.

The three boys made a dash for their space suits and the jet boat.
Inside the air lock, they adjusted their oxygen valves and waited for
pressure to equalize so they could blast off.

"Blast it," said Astro, "there must be some way to get to that rocket
tube and dump that stuff!"

"Impossible, Astro," said Roger. "The release controls are in the
control box, and with all that radiation loose, you wouldn't last half a
minute!"

Tom walked over to the valve that would open the outside hatch.

"Wonder how Captain Strong is making out with those tough babies on the
_Polaris_?" asked Tom.

"I don't know," replied Roger, "but anything would be better than
sitting around waiting for this thing to blow up!"

"Ah--stop griping," said Astro, "or I'll shove you up a rocket tube and
blast you from here all the way back to Atom City!"

"Hey, wait a minute!" shouted Tom. "Astro, remember the time we were on
the ground crew as extra duty and we had to overhaul the _Polaris_?"

"Yeah, why?"

"There was one place you couldn't go. You were too big, so I went in,
rememb