The Mote In God's Eye

The Face of God. It was a famous sight throughout the Empire, this extraordinary view of the Coal Sack from New Cal. But standing here in the cold of space it was different. In a picture it looked like the Coal Sack. Here it was real.

And something he couldn't see was coming at him out of the Mote in God's Eye.

6 The Light Sail

One gravity only-with queasy sensations as MacArthur lined up on her proper interception course. Elastic webbing held him in the acceleration chair during these few moments of changing but normal gravity-minutes, Rod suspected, that he'd soon look back on with wistful longing.

Kevin Renner had been mate of an interstellar trading vessel before -joining MacArthur as her sailing master. He was a lean man with a narrow face, and he was ten years older than Blaine. As Rod steered his acceleration chair up behind him, Renner was matching curves in a view screen; and his self-satisfied grin was not the expression of a Navy man.

"Got our course, Lieutenant Renner?"

"Yes, sir," Kevin Renner said with relish. "Right into the sun at four gees!"

Blaine gave in to the desire to call his bluff. "Move her."

The warning alarms sounded and MacArthur accelerated. Crew and passengers felt their weight settle gradually deeper into beds and chairs and couches, and they nerved themselves for several days of weighing far too much.

"You were joking, weren't you?" Blaine asked.

The Sailing Master looked at him quizzically. "You knew we were dealing with a light-sail propulsion system, sir?"

"Naturally."

"Then look here." Renner's nimble fingers made a green curve on the view screen, a parabola rising sharply at the right. "Sunlight per square centimeter falling on a light - sail decreases as the square of the distance from the star. Acceleration varies directly as the sunlight reflected from the sail."

"Of course, Mr. Renner. Make your point."

Renner made another parabola, very like the first, but in blue. "The stellar wind can also propel a light sail. Thrust varies about the same way. The important difference is that the stellar wind is atomic nuclei. They stick where they hit the sail. The momentum is transferred directly-and it's all radial to the sun."

"You can't tack against it," Blaine realized suddenly. "You can tack against the light by tilting the sail, but the stellar wind always thrusts you straight away from the sun." -

"Right. So, Captain, suppose you were coming into a system at 7 percent of the speed of light, God forbid, and you wanted to stop. What would you do?"

"Drop all the weight I could," Blaine mused. "Hmm. I don't see how it'd be a problem. They must have launched the same way."

"I don't think they did. They're moving too fast. But pass that for a minute. What counts is they're moving too fast to stop unless they get very close to the sun, very close indeed. The intruder is in fact - diving right into the sun. Probably it will tack hard after the sunlight has decelerated it enough -...rovided the vessel hasn't melted and the shrouds haven't parted or the sail ripped. But it is such a close thing that they simply have to skydive; they have no choice."

"Ah," said Blaine.

"One need hardly mention," Renner added, "that when we match course with them, we too will be moving straight toward the sun. .

"At 7 percent of the speed of light?"

"At 6. The intruder will have slowed somewhat by then. It will take us one hundred twenty-five hours, doing four gees most of the way, slowing somewhat near the end."

"That's going to be hard on everybody," Blaine said. And suddenly he wondered, belatedly, if Sally Fowler had in fact gotten off. "Especially the passengers. Couldn't you give me an easier course?"

"Yes, sir," Renner said instantly. "I can pull alongside in one hundred and seventy-hours without ever going over two and a half gees-and save some fuel too, because the probe will have more time to slow down. The course we're on now gets us to New Ireland with dry tanks, assuming we take the intruder under tow."

"Dry tanks. But you liked this course better." Rod was learning to dislike the Sailing Master and his grin that constantly implied that the Captain had forgotten something crucial and obvious. "Tell me why," he suggested.

"It occurred to me the intruder might be hostile."

"Yes. So?"

"If we were to match courses with him and he disabled the engines . .

"We'd be falling into the sun at 6 percent of light speed. Right. So you match us up as far from Cal as possible, to leave time to do something about it."

"Yessir. Exactly."

"Right. You're enjoying this, aren't you, Mr. Renner?"

"I wouldn't have missed it for anything, sir. What about you?"

"Carry on, Mr. Renner." Blaine guided his acceleration chair to another screen and began checking the Sailing Master's course. Presently he pointed out that the Sailing Master could give them nearly an hour at one gee just before intercept, thereby giving everyone a chance to recuperate. Renner agreed with idiot enthusiasm and went to work on the change.