main jobs."

"Then it must be the reactant," said Tom. "Did Kit use standard
reactant?"

Sid nodded. "Got it right here at the spaceport. Same stuff everyone
else is using."

Gloomily the four young spacemen turned away from the ramp and headed
for the control tower to hear the latest reports from the ships already
underway. There were only a few more ships scheduled to blast off, and
the cadets had already inspected them.

"Wait a minute," said Tom, stopping suddenly. "The fuel tanks are on the
portside of the ship, and the feeders are on the starboard. Where did
you see this fellow messing around, Sid?"

Sid thought a moment and then his face clouded. "Come to think of it, I
saw him on the portside."

"I wasn't even close to the tanks!" exclaimed Astro.

"There was someone messing around them, then," said Roger.

"Yes," said Tom grimly. "But we don't know _who_--or _what_ he did."

"From the sound of those rockets," said Astro, "Kit's feeders are
clogged, or there's something in his reactant that the strainers are not
filtering out."