20 Million Leagues Over the Sea by K. T. Hunter

interruption.
They filed out of the room and followed the young man to the lift,
which took a couple of trips to ferry them all to the Oberth Deck.
Gemma stayed beside Dr. Pugh during the trip down.
    "We did have some ideas of our own once, you
know," Dr. Pugh said to her. "Before the Invasion, that is. There
was some flirtation with chemical rockets. Some people have always
had dreams of going to the stars, and they felt that rocketry was
the key."
    "Rocketry?" Gemma asked. She had heard the
term bandied about during one of her previous jobs, but she had
gleaned very little in the way of useful information.
    "I'll leave it to our good physicist to
explain," Pugh replied as they exited the lift and passed the sign
for the Oberth Deck.
    "Have you ridden a bicycle before, Miss
Gemma?" Hui asked.
    She shook her head. "No, but I have seen them
in London."
    "Well," he continued, "when I ride one, it
looks like I am pushing the pedals to move the wheels. What I am
really doing is pushing against the ground, the Earth itself, to
move forward. That thing I push against is called the working
mass , to use the precise phrase. I can use the brakes to slow
down or stop. And of course, there is friction on the road to slow
me down as well."
    The group turned a corner in the corridor and
waited before a heavy door as their guide turned a large valve
wheel to open it.
    "In space," Hui said, "a ship has no ground,
no gravity, to push against to move. So it has to bring its own
working mass, yes? In rocketry, that working mass is the fuel. It
is funneled out of the rear of the ship, which pushes it in the
opposite direction. And there is no friction to slow it down." The
door swung open as he talked, and they followed the guide through.
"Simple enough, at least in theory--"
    Hui gasped, and so did Gemma as she followed
his eyes up, up, and up. This chamber seemed to have no ceiling!
They stepped deeper into the chill of the cavern before them.
    It was a veritable jungle of brass and steel,
abloom with valve wheels and gauges of every size. Pipes climbed
the walls like strangler vines and ran in every direction. The few
spaces not claimed by pipes were plastered with warning signs that
shouted all the dreadful consequences of a fuel leak or a solar
flare, along with directions to the closest head. Gemma wondered
about this obsession with toilets among the crew, thinking it might
be a sign of some deficiency. Did one make water more often in
space? So far, that had not been her experience.
    A cylindrical tank dominated the vast
chamber. Pipes of all sizes extended from it, running both fore and
aft. Row upon row of barrels marched beside it. Each barrel had its
own large gauge, like a cyclopean eye staring out over its fellows.
The black tank itself had its own great bank of indicators in the
shadows beneath it. A cluster of men monitored these instruments as
they consulted clipboards and muttered amongst themselves.
    "In practice, it wasn't so simple," Dr. Pugh
said, picking up Hui's train of thought. Gemma thought she detected
a note of boredom in his voice. It took her a moment to remember
that he had seen all this before, and to him it was just another
cold section of the ship.
    "The problem was heat," Dr. Pugh said. "Look
at it this way. You have to provide so much kinetic energy to reach
a certain velocity, and you have to get to a certain velocity to go
a certain distance in a reasonable amount of time. To get that
velocity, you have to burn very hot indeed, and that sort of
temperature tends to melt the very nozzle that uses it for
propulsion! What a dreadful pickle! So we had to figure out some
method of producing the thrust without actually melting the ship in
the process! We fought with it and fought with it and there seemed
no way round it ... until the Invasion. Once the little buggers had
been harvested by the grim reaper, we peeked into their cylinders
and found a solution."
    He walked towards the tank. Most of the