reparation. The
nonmagnetic stony asteroids are an absolute necessity for the Belt
Cities. In order to live, man needs oxygen, and there is no trace of
an atmosphere on any of the little Belt worlds except that which Man
has made himself and sealed off to prevent it from escaping into
space. Carefully conserved though that oxygen is, no process is or can
be one hundred per cent efficient. There will be leakage into space,
and that which is lost must be replaced. To bring oxygen from Earth in
liquid form would be outrageously expensive and even more outrageously
inefficient--and no other planet in the System has free oxygen for the
taking. It is much easier to use Solar energy to take it out of its
compounds, and those compounds are much more readily available in
space, where it is not necessary to fight the gravitational pull of a
planet to get them. The stony asteroids average thirty-six per cent
oxygen by mass; the rest of it is silicon, magnesium, aluminum,
nickel, and calcium, with respectable traces of sodium, chromium,
phosphorous manganese, cobalt, potassium, and titanium. The metallic
nickel-iron asteroids made an excellent source of export products to
ship to Earth, but the stony asteroids were for home consumption.

This particular asteroid presented problems. Not highly unusual
problems, but problems nonetheless. It was massive and had a high rate
of spin. In addition, its axis of spin was at an angle of eighty-one
degrees to the direction in which the tug would have to tow it to get
it to the processing plant. The asteroid was, in effect, a huge
gyroscope, and it would take quite a bit of push to get that axis
tilted in the direction that Harry Morgan and Jack Latrobe wanted it
to go. In theory, they could just have latched on, pulled, and let the
thing precess in any way it wanted to. The trouble is that that would
not have been too good for the anchor bolt. A steady pull on the
anchor bolt was one thing: a nickel-steel bolt like that could take a
pull of close to twelve million pounds as long as that pull was along
the axis. Flexing it--which would happen if they let the asteroid
precess at will--would soon fatigue even that heavy bolt.

The cable they didn't have to worry about. Each strand was a fine wire
of two-phase material--the harder phase being borazon, the softer
being tungsten carbide. Winding these fine wires into a cable made a
flexible rope that was essentially a three-phase material--with th