"You mean the assignment?" asked Roger, answering his own question in
the next breath. "I don't know. But anything to get out of here. I've
been on Earth so long that I'm getting gravity-itis!"

Tom smiled. "It'll sure be nice to get up in the wide, high, and deep
again," he said, glancing up at the cloudless sky.

"Say it again, spaceman," breathed Astro. "One more lesson on the
differential potential between chemical-burning rocket fuels and
reactant energy and I'll blast off without a spaceship!"

Roger and Tom laughed. They both sympathized with the big cadet's
inability to cope with the theory of atomic energy and fuel conservation
in spaceships. In charge of the power deck on the _Polaris_, Astro
earlier had gained firsthand experience in commercial rocket ships as an
able spaceman and later had been accepted in the Academy for cadet
training. The son of colonists on Venus, the misty planet, his formal
education was limited, and though he had no equal while on the power
deck of a rocket ship, in theory and classroom study he had to depend on
Roger and Tom to help him get passing grades.

The slidewalk moved smoothly and easily toward the gleaming Tower of
Galileo, the largest and most imposing of the structures of Space
Academy. Made entirely of clear crystal mined on Titan, satellite of
Saturn, the Tower rose over the smaller buildings like a giant
shimmering jewel. Housing the administration offices of the Solar Guard
and the Space Academy staff, it also contained Galaxy Hall, the museum
of space, which attracted thousands of visitors from every part of the
Solar Alliance.