rocket engineering. It is a well-known
fact that the greater the velocity of a fluid stream, the less the side-
pressure. Those tubes were designed for the greatest possible velocity,
naturally, and since that meant almost no side-pressure, tons of metal could
be shaved from the rocket tubes. Only the great pressure blocks seemed, and
were, capable of resisting strain bracing the egg-shaped combustion chambers.
Hour after hour the tubes moaned and droned. They were running almost white
hot, but they were polished more carefully than the finest telescope mirrors,
and they were in vacuum jackets equally polished, so that almost no heat
escaped from them-for heat, where it isn't wanted, is not only a nuisance, but
a warning of inefficiency.
Presently, the song of the fuel pumps started. They had been feeding the tubes
on the original pressure hi the tanks at first, but now this was falling. Pure
hydrogen and oxygen were 'being taken from the tanks at seven tons, pressure,
and stepped up to the necessary eight for efficient running in the tubes. It
was a gas-but under that pressure, denser than water.
That might have warned them, had they stopped to think then. But it was a
hastily conceived and carried out thing, throughout. They'd raced against time
all the way. When, after seven days they landed on Mars North City field with
wings spread and the parachute air-brake spread to stop them, the ships needed
repair and final adjustment, so much so that the three-month wait on Mars was
no ordeal of monotony. There were plenty of trained mechanicians at Mars North
City to help them, and still it was more of an ordeal of labor. And still
there wasn't any time for recalculation that might have stopped the expedition
then and there.
They loaded up with water-fuel-that is, hydrogen and oxygen gases, at Mars
North City where the gases were cheap, and pulled out to Phobos running heavy.
They replaced the burned fuel there, and at last the "Mercury" and her
companions pulled out on the real trip.
So far they had gone. This trip out to Mars and her moons was old, charted and
laid out by a pair of generations and more of space travel. Over a hundred and
fifty years of exploration, over seventy years of commercial exploitation of
the Minor Planets, and still no human being had passed beyond the magic ring
of the Planetoids.
You have seen a scale map of our system. You know the dimensions. Forty,
seventy, one hundred and one hundred-forty millions of miles are the orbits of
the Minor Planets. Then-the Great Gulf. It's five hundred million to Jupiter,
nine hundred million to Saturn, a billion and three quarters to Uranus. When
the Lord made this system, he used two scales. Maybe he started out with one,
and didn't like the looks of the dinky little system he got -planets with
diameters measured in thousands of miles, orbits with diameters measured in
millions. Maybe he threw that scale away, and decided to start all over with
something worth while. The dust specks he /had, he just forgot, and worked
with a scale reading hi billions instead of millions for the orbits, and he
used tens of thousands of miles for planet diameters.
At any rate, there are two systems really, the Inner System, and the Outer
System, and they're as different as two entirely strange systems might be.
Four, seven, ten and fourteen tens of millions for the Inner System. Four,
eight, seventeen, twenty-eight hundreds of millions for the Outer System.
The "Mercury" was trying to be the Messenger of the Gods, from the Lesser Gods
to Mighty love. And she was the first ship that really stood a chance of
crossing that gulf.
That's quite a hill, there between the Inner and Outer systems. Nearly four
hundred million miles-and every blasted mile of it uphill-with old Sol
dragging, dragging, dragging on the other end. Four hundred million miles of
uphill climb had stopped exploration for a hundred and fifty years and more.
The "Mercury" lifted off Phobos, with her train of three service ships,