These blasts were below, however, on the surface. While they shook the structure of the Bridge heavily, they almost never interfered with its functioning. And they could not, in the very nature of thing, do Helmuth any harm.

Helmuth, after all, was not on Jupiter though that was becoming harder and harder for him to bear in mind. Nobody was on Jupiter; had any real damage ever been done to the Bridge, it probably would never have been repaired. There was nobody on Jupiter to repair it; only the machines which were themselves part of the Bridge.

The Bridge was building itself. Massive, alone, and lifeless, it grew in the black deeps of Jupiter

It had been well planned. From Helmuth's point of view that of the scanners on the beetle almost nothing could be seen of it, for the beetle tracks ran down the center of the deck, and in the darkness and perpetual storm even ultrawave-assisted vision could not penetrate more than a few hundred yards at the most. The width of the Bridge, which no one would ever see, was eleven miles; its height, as incomprehensible to the Bridge gang as a skyscraper is to an ant, thirty miles; its length, deliberately unspecified in the plans, fifty-four miles at the moment and still increasingly squat, colossal structure, built with engineering principles, methods, materials and tools never touched before now.

For the very good reason that they would have been impossible anywhere else. Most of the Bridge, for instance, was made of ice: a marvelous structural material under a pressure of a million atmospheres, at a temperature of 94deg below zero Fahrenheit. Under such conditions, the best structural steel is a friable, talclike powder, and aluminum becomes a peculiar transparent substance that splits at a tap; water, on the other hand, becomes Ice IV, a dense, opaque white medium which will deform to a heavy stress, but will break only under impacts huge enough to lay whole Earthly cities waste. Never mind that it took millions of megawatts of power to keep the Bridge up and growing every hour of the day; the winds on Jupiter blow at velocities up to twenty-five thousand miles per hour, and will never stop blowing, as they may have been blowing for more than four billion years; there is power enough.

Back home, Helmuth remembered, there had been talk of starting another Bridge on Saturn, and perhaps later still on Uranus too. But that had been politicians' talk. The Bridge was almost five thousand miles below the visible surface of Jupiter's atmosphere luckily in a way, for at the top of that atmosphere the temperature was 76deg Fahrenheit colder than it was down by the Bridge, but even with that differential the Bridge's mechanisms were just barely manageable. The bottom of Saturn's atmosphere, if the radiosonde readings could be trusted, was just 16,878 miles below the top of the Saturnian clouds one could see through the telescope, and the temperature down there was below 238deg F. Under those conditions, even pressure ice would be immovable, and could not be worked with anything softer than itself.