say.

As a heat sink, the water provided stability of temperature that would
have been difficult to achieve without it. Bathed in the tenuous solar
atmosphere that extends well beyond the orbit of Earth, and with a
temperature over 100,000 C, maintenance of a livable temperature on
board the big wheel was not the straight-forward balancing of
radiation intercepted/radiation outgoing that had been originally
anticipated by early writers on the subject.

True, the percentage of energy received by convection was small
compared to that received by radiation; but it was also wildly
variable.

As a biological cultural medium, the hydraulic system provided a basis
for both air restoration and food supplies. When the proper balance of
plankton and algae was achieved, the air jets that gave the ship its
spin would also purify the ship's air, giving it back in a natural
manner the oxygen it was now fed from tanks.

As a method of controlling and changing the rate of rotation of the
wheel, the rivers of water had already proven themselves; and as a
method of static balancing to compensate for off-center weights,
masses of it could be stopped and held in counterbalance tanks around
the rim, thus assuring that the observatory, in its stationary
position on the hub, would not suddenly take up an oscillatory pattern
of motion as the balance within the wheel was shifted either by moving
equipment or personnel.

* * * * *

In effect, the entire ship operated against a zero-M-I calculation
which could be handled effectively only by the computer. The moment of
inertia of the ship must be constantly calculated against the moment
of inertia of the hydraulic mass flowing in the rim. And the
individual counterbalance tanks must constantly shift their load
according to the motions of the crew and their masses of equipment
that were constantly being shifted during installation. For already
the observatory was hard at work, and its time must not be stolen by
inappropriate wobbles of the hub.

A continuously operating feedback monitor system was capable of
maintaining accuracy to better than .01% both in the mass inertial
field of centrifugal force affecting the rim; and in overall balance
that might otherwise cause wobbles in the hub.

While such fine control would not be necessary to the individual
comfort of the personnel aboard, it was very necessary to the accuracy
of scientific observation, one maj