burst into smoky flame
and shriveled, and the thing--still shrieking like a fog-horn in a
tunnel--flopped flat forward with a resounding _clank!_ It was abruptly
silent.

But the total noise was not lessened. Another pushpot came soaring
wildly into view, making hysterical outcries. It touched and banged
violently to earth. Others appeared in the air beyond the construction
Shed. One flopped so hard on landing that its tail rose in the air and
it attempted a somersault. It made ten times more noise than before--the
flame from its tail making wild gyrations--and flopped back again with a
crash. Two others rolled over on their sides after touching ground. One
ended up on its back like a tumble-bug, wriggling.

They seemed to land by hundreds, but their number was actually in
dozens. It was not until the last one was down that Joe could make
himself heard. The pushpots were jet motors in frames and metal skin,
with built-in jato rocket tubes besides their engines. On the ground
they were quite helpless. In the air they were unbelievably clumsy. They
were actually balanced and steered by vanes in the blasts of their jets,
and they combined the absolute maximum of sheer thrust with the
irreducible minimum of flyability.

Crane-trucks went out to pick them up. Joe said anxiously, "We'd better
check our flight plan again. We have to know it absolutely!"

He headed across the floor to the flight data board. He passed the hull
of another ship like his own, which was near completion, and the bare
skeletons of two others which needed a lot of work yet. They'd been
begun at distant plants and then hauled here on monstrous trailers for
completion. The wooden mockup of the design for all the ships--in which
every possible arrangement of instruments and machinery had been tested
out--lay neglected by the Shed wall.

The four stood before the flight data board. It listed the readings
every instrument should show during every instant of the flight. The
readings had been calculated with infinite care, and Joe and the others
needed to know them rather better than they knew their multiplication
tables. Once they started out, they wouldn't have time to wonder if
everything was right for the time and place. They needed to know.

They stood there, soaking up the information the board contained,
forming mental pictures of it, making as sure as possible that any one
of them would spot anything wrong the instant it showed up, and would
i