Bigman was at once outraged. "Lucky! Are you going to let him stop the investigation just like that?"

Lucky said, "Not exactly, Bigman. We'll be on board the Agrav ship and we'll continue it there."

"No sir," the commander said flatly, "You will not be on board. Don't think that for an instant."

Lucky said, "Who will be on board, Commander? Yourself, I presume?"

"Myself. Also Panner, as chief engineer. Two of my officers, five other engineers, and five ordinary crewmen. All these were chosen some time ago. Myself and Panner, as responsible heads of the project; the five engineers to handle the ship itself; the remainder in return for their services to the project."

Lucky said thoughtfully, "What type of service?"

Panner interrupted to say, "The best example of what the commander is talking about is Harry Norrich, who-"

Bigman stiffened in surprise. "You mean the blind fellow?"

Panner said, "You know him then?"

"We met him last evening," said Lucky.

"Well," said Panner, "Norrich was here at the very beginning of the project. He lost his sight when he threw himself between two contacts to keep a force field from buckling. He was in the hospital five months and his eyes were the one part of him that couldn't be restored. By his act of bravery, he kept the satellite from having a chunk the size of a mountain blown out of it. He saved the lives of two hundred people and he saved the project, since a major accident at the beginning might have made it impossible to get further appropriations out of Congress. That sort of thing is what earns one the honor of a place on the maiden voyage of the Agrav ship."

"It's a shame he won't be able to see Jupiter up close," said Bigman. Then, his eyes narrowing, "How'll he get around on board ship?"

Panner said, "We'll be taking Mutt, Fm sure. He's a well-behaved dog."

"That's all I want to know then," said Bigman heatedly. "If you cobbers can take a dog, you can take Lucky and me."

Commander Donahue was looking at his wristwatch impatiently. Now he put the palms of his hands flat on the table; and made as though to rise. "We have finished our business then, gentlemen."

"Not quite," Lucky said. "There's one little point to be cleared up. Bigman puts it crudely, but he's quite right. He and I will be on the Agrav ship when it leaves."

"No," said Commander Donahue. "Impossible."

"Is the added mass of two individuals too great for the ship to handle?"

Panner laughed. "We could move a mountain."

"Do you lack room then?"

The commander stared at Lucky in hard displeasure. "I will not give any reason. You are not being taken only because it is my decision that you not be taken. Is that clear?"

There was a glint of satisfaction in his eyes, and Lucky did not find it hard to guess that he was squaring accounts for the tongue-lashing Lucky had given him aboard the Lucky Starr.

Lucky said quietly, "You had better take us, Commander."

Donahue smiled sardonically. "Why? Am I to be relieved of duty at the orders of the Council of Science? You won't be able to communicate with Earth till I return, and after that they can relieve me of duty if they wish."

"I don't think you've thought it through, Commander," said Lucky. "They might relieve you of duty retroactive to this moment. In fact, I assure you they will do so. As far as the government records are concerned, then, it will appear that Agrav ship made its first flight not under your command but under the command, officially, of your successor, whoever he might be. The records of the trip might even be adjusted to show, officially, that you were not on board."

Commander Donahue went white. He rose and for a moment seemed on the point of throwing himself bodily at Lucky.

Lucky said, "Your decision, Commander?"

Donahue's voice was most unnatural when it finally came. "You may come."

Lucky spent the remainder of the day in the record rooms, studying the files on various men employed on the project, while Bigman, under Panner's guidance, was taken from laboratory to laboratory and through tremendous testing rooms.

It was only after the evening meal when they returned to quarters that they had a chance to be alone together. Lucky's silence then was not extraordinary, since the young councilman was never talkative at the best of times, but there was a small crease between his eyes that Bigman recognized as a sure sign of concern.

Bigman said, "We aren't making any progress, are we, Lucky?"

Lucky shook his head, "Nothing startling, I'll admit:"

He had brought a book-film with him from the project's library, and Bigman caught a flash of its title: Advanced Robotics. Methodically Lucky threaded the beginnings of the film through the viewer.

Bigman stirred restlessly. "Are you going to be all tied up with that film, Lucky?"

"I'm afraid so, Bigman."

"Do you mind then if I visit Norrich next door for company?"

"Go ahead." Lucky had the viewer over his eyes and he was leaning back, his arms crossed loosely across his chest.

Bigman closed the door and remained standing just outside for a moment, a little nervous. He should discuss this with Lucky first, he knew he should, and yet the temptation…

He told himself: I'm not going to do anything. I'll just check something. If I'm wrong, I'm wrong and why bother Lucky? But if it checks out, then I'll really have something to tell him.

The door opened at once when he rang, and there was Norrich, blind eyes fixed in the direction of the doorway, seated before a desk on which a checkerboard design carried odd figures.

He said, "Yes?"

"This is Bigman," said the little Martian.

"Bigman! Come in. Sit down. Is Councilman Starr with you?"

The door closed again, and Bigman looked about in the brightly lit room. His mouth tightened. "He's busy. But as for me, I'm filled up on Agrav today. Dr. Panner took me all over, only I don't understand a thing of it hardly."

Norrich smiled. "You're not exactly in a minority, but if you ignore the mathematics, some of it isn't too hard to understand."

"No? Mind explaining it then?" Bigman sat down in a large chair and bent to look under Norrich's workbench. Mutt lay there with his head between his fore-paws and one eye brightly fixed on Bigman.

(Keep him talking, thought Bigman. Keep him talking till I find a hole, or make one.)

"Look here," Norrich said. He held up one of the round counters he had been holding. "Gravity is a form of energy. An object- such as this piece I'm holding which is under the influence of a gravitational field but is not allowed to move is said to have potential energy. If I were to release the piece, that potential energy would be converted to motion-or kinetic energy, as it is called. Since it continues under the influence of the gravitational field as it falls, it falls faster and faster and faster." He dropped the counter at this point, and it fell.

"Until, splash," said Bigman. The counter hit the floor and rolled.

Norrich bent as though to retrieve it and then said, "Would you get it for me, Bigman? I'm not sure where it rolled."

Bigman suppressed his disappointment. He picked it up and returned it.

Norrich said, "Now until recently that was the only thing that could be done with potential energy: it could be converted into kinetic energy. Of course the kinetic energy could be used further. For instance, the falling water of Niagara Falls could be used to form electricity, but that's a different thing. In space, gravity results in motion and that ends it.

"Consider the Jovian system of moons. We're at Jupiter Nine, way out. Fifteen million miles out. With respect to Jupiter, we've got a tremendous quantity of potential energy. If we try to travel to Jupiter One, the satellite Io, which is only 285,000 miles from Jupiter, we are in a way, falling all those millions of miles. We pick up tremendous speeds which we must continually counteract by pushing in the opposite direction with a hyperatomic motor. It takes enormous energy. Then, if we miss our mark by a bit, we're in constant danger of continuing to fall, in which case there's only one place to go, and that's Jupiter-and Jupiter is instant death. Then, even if we land safely on lo, there's the problem of getting back to Jupiter Nine, which means lifting ourselves all those millions of miles against Jupiter's gravity. The amount of energy required to maneuver among Jupiter's moons is just prohibitive."