For a long time nobody—not even Conrad Taylor—spoke a word. All the members of the Committee were marshalling their thoughts about those difficult people, the Hermians, so ably represented here by their Ambassador.

To most people, Mercury was a fairly good approximation of Hell; at least, it would do until something worse came along. But the Hermians were proud of their bizarre planet, with its days longer than its years, its double sunrises and sunsets, its rivers of molten metal… By comparison, the Moon and Mars had been almost trivial challenges. Not until men landed on Venus (if they even did) would they encounter an environment more hostile than that of Mercury.

And yet this world had turned out to be, in many ways, the key to the solar system. This seemed obvious in retrospect, but the Space Age had been almost a century old before the fact was realized. Now the Hermians never let anyone forget it.

Long before men reached the planet, Mercury’s abnormal density hinted at the heavy elements it contained; even so, its wealth was still a source of astonishment, and had postponed for a thousand years any fears that the key metals of human civilization would be exhausted. And these treasures were in the best possible place, where the power of the Sun was ten times greater than on frigid Earth.

Unlimited energy—unlimited metal; that was Mercury. Its great magnetic launchers could catapult manufactured products to any point in the solar system. It could also export energy, in synthetic transuranium isotopes or pure radiation. It had even been proposed that Hermian lasers would one day thaw out gigantic Jupiter, but this idea had not been well received on the other worlds. A technology that could cook Jupiter had too many tempting possibilities for interplanetary blackmail.

That such a concern had ever been expressed said a good deal about the general attitude towards the Hermians. They were respected for their toughness and engineering skills, and admired for the way in which they had conquered so fearsome a world. But they were not liked, and still less were they completely trusted. At the same time, it was possible to appreciate their point of view. The Hermians, it was often joked, sometimes behaved as if the Sun was their personal property. They were bound to it in an intimate love-hate relationship—as the Vikings had once been linked to the sea, the Nepalese to the Himalayas, the Eskimos to the Tundra. They would be most unhappy if something came between them and the natural force that dominated and controlled their lives.

At last, the Chairman broke the long silence. He still remembered the sun of India, and shuddered to contemplate the sun of Mercury. So he took the Hermians very seriously indeed, even though he considered them uncouth technological barbarians.

“I think there is some merit in your argument, Mr. Ambassador,” he said slowly. “Have you any proposals?”

“Yes, sir. Before we know what action to take, we must have the facts. We know the geography of Rama—if one can use that term—but we have no idea of its capabilities. And the key to the whole problem is this: does Rama have a propulsion system? Can it change orbit? I’d be very interested in Dr. Perera’s views.”

“I’ve given the subject a good deal of thought,” answered the exobiologist. “Of course, Rama must have been given its original impetus by some launching device, but that could have been an external booster. If it does have onboard propulsion, we’ve found no trace of it. Certainly there are no rocket exhausts, or anything similar, anywhere on the outer shell.”

“They could be hidden.”

“True, but there would seem little point in it. And where are the propellant tanks, the energy sources? The main hull is solid—we’ve checked that with seismic surveys. The cavities in the northern cap are all accounted for by the airlock systems.”

“That leaves the southern end of Rama, which Commander Norton has been unable to reach, owing to that ten-kilometre-wide band of water. There are all sorts of curious mechanisms and structures up on the South Pole—you’ve seen the photographs. What they are is anybody’s guess.”

“But I’m reasonably sure of this. If Rama does have a propulsion system, it’s something completely outside our present knowledge. In fact, it would have to be the fabulous ‘Space Drive’ people have been talking about for two hundred years.”

“You wouldn’t rule that out?”

“Certainly not. If we can prove that Rama has a Space Drive—even if we learn nothing about its mode of operation—that would be a major discovery. At least we’d know that such a thing is possible.”

“What is a Space Drive?” asked the Ambassador for Earth, rather plaintively.

“Any kind of propulsion system, Sir Robert, that doesn’t work on the rocket principle. Anti-gravity—if it is possible—would do very nicely. At present, we don’t know where to look for such a drive, and most scientists doubt if it exists.”

“It doesn’t,” Professor Davidson interjected. “Newton settled that. You can’t have action without reaction. Space Drives are nonsense. Take it from me.”

“You may be right,” Perera replied with unusual blandness. “But if Rama doesn’t have a Space Drive, it has no drive at all. There’s simply no room for a conventional propulsion system, with its enormous fuel tanks.”

“It’s hard to imagine a whole world being pushed around,” said Dennis Solomons. “What would happen to the objects inside it? Everything would have to be bolted down. Most inconvenient.”

“Well, the acceleration would probably be very low. The biggest problem would be the water in the Cylindrical Sea. How would you stop that from…”

Perera’s voice suddenly faded away, and his eyes glazed over. He seemed to be in the throes of an incipient epileptic fit, or even a heart attack. His colleagues looked at him in alarm; then he made a sudden recovery, banged his fist on the table and shouted: “Of course! That explains everything! The southern cliff—now it makes sense!”

“Not to me,” grumbled the Lunar Ambassador, speaking for all the diplomats present.

“Look at this longitudinal cross-section of Rama,” Perera continued excitedly, unfolding his map. “Have you got your copies? The Cylindrical Sea is enclosed between two cliffs, which completely circle the interior of Rama. The one on the north is only fifty metres high. The southern one, on the other hand, is almost half a kilometre high. Why the big difference? No one’s been able to think of a sensible reason.”

“But suppose Rama is able to propel itself—accelerating so that the northern end is forward. The water in the Sea would tend to move back; the level at the south would rise—perhaps hundreds of metres. Hence the cliff. Let’s see—”

Perera started scribbling furiously. After an astonishingly short time—it could not have been more than twenty seconds—he looked up in triumph.

“Knowing the height of those cliffs, we can calculate the maximum acceleration Rama can take. If it was more than two per cent of a gravity, the Sea would slosh over into the southern continent.”

“A fiftieth of a gee? That’s not very much.”

“It is—for a mass of ten million megatons. And it’s all you need for astronomical manoeuvring.”

“Thank you very much, Dr. Perera,” said the Hermian Ambassador. “You’ve given us a lot to think about. Mr. Chairman can we impress on Commander Norton the importance of looking at the South Polar region?”

“He’s doing his best. The Sea is the obstacle, of course. They’re trying to build some kind of raft—so that they can at least reach New York.”

“The South Pole may be even more important. Meanwhile, I am going to bring these matters to the attention of the General Assembly. Do I have your approval?”

There were no objections, not even from Dr. Taylor. But just as the Committee members were about to switch out of circuit, Sir Lewis raised his hand.