The Lost Worlds of 2001

27. Joveday
The parking orbit in which the ship now moved was a million-mile-long ellipse, coming to within only fifty thousand miles of Jupiter and then swinging out to the orbit of Callisto. Discovery could retrace it forever, if she pleased, making one complete circuit every seven days until the end of time. Sooner or later she would pass within a few thousand miles of each of the inner moons, and could survey them all in detail. And though she would be unable to land on any of them, she still carried enough fuel to make any orbit changes that would improve opportunities for observation.

That seven-day period was very convenient. The first turn around Jupiter had been on a Sunday morning, by the Earth calendar; they would skim past Jupiter, therefore, every Sunday for the whole of the mission. By Wednesday evening they would be out at their far point, the orbit of Callisto, and then the fall back to Jupiter would begin again. It was not surprising that Sunday was soon informally christened "Joveday."

On the very first Monday, on the outward leg of their first orbit, Discovery passed within thirty thousand miles of the satellite Europa. There would be closer approaches later, but this was a good opportunity for the crew to practice with their battery of instruments. They had to learn to make the most of the precious moments when the worlds they had come so far to study grew from points to disks and then to swiftly passing globes.

A group of telescopic cameras mounted in a kind of gun turret outside the Control Deck produced images which could be inspected on monitors inside the ship; then they were stored in a solid-state memory unit which could hold several million high-quality pictures. After a fly-by had been completed, these could be played back and examined at leisure under the different degrees of magnification.

There were also several spectrometers, operating from the short ultraviolet out into the far infrared. These should give dues to the chemical composition of the worlds that were being examined, but their records could be fully interpreted only by the experts back on Earth.

The infrared scanner, on the other hand, provided information of immediate value, which could be understood at a glance. It reproduced a "heat map" of the body at which it was pointed, and so would reveal at once any sources of thermal energy. Originally developed for military purposes, it could spot a power plant even if it was buried under a thousand feet of ice. Since any conceivable civilization or technology-or indeed any living creature- must produce heat, the infrared scanner was one of the most promising instruments at Discovery's command.

The most spectacular, and controversial, instrument that the ship carried was a laser spectrograph, which had been developed especially for the mission, despite the protests of a large section of the scientific community. One critic had said sarcastically, "Why not drop an atom bomb and photograph the debris?"

The idea behind the instrument was very simple. An extremely powerful laser beam was focused through a system of mirrors, on to a target which might be an asteroid or satellite a few hundred miles away. In a fraction of a second, the object receiving the laser pulse was heated to incandescence, producing its characteristic spectrum. The optical system that sent out the beam caught the returning flash of light, which was then photographed and analyzed. And so it was possible to find the composition of a cold, dark, and inaccessible body that might be racing past at thousands of miles an hour.

It was immediately pointed out that to be probed by a laser beam, even though the damage was restricted to an area only a few inches across, might be regarded as an unfriendly act. So Bowman had been directed to use the instrument only if he was satisfied, beyond all reasonable doubt, that he was not aiming it at an inhabited body.

He had rather mixed feelings about the device. Although he approved of the expedition's "no weapons" policy, he could easily imagine circumstances when the laser spectrograph's nonscientific applications might be more than useful. It was reassuring to know that they were not completely defenseless.