Arthur Clarke - Earthlight

But there was just one nagging frustration in Sadler’s mind. He hated to leave a job undone, yet in the nature of things this mission of his might remain forever uncompleted. He would have given so much to have known whether or not there had been a spy in the Observatory.

The liner Pegasus, with three hundred passengers and a crew of sixty, was only four days out from Earth when the war began and ended. For some hours there had been a great confusion and alarm on board, as the radio messages from Earth and Federation were intercepted. Captain Halstead had been forced to take firm measures with some of the passengers, who wished to turn back rather than go on to Mars and an uncertain future as prisoners of war. It was not easy to blame them; Earth was still so close that it was a beautiful silver crescent, with the Moon a fainter and smaller echo beside it. Even from here, more than a million kilometers away, the energies that had just flamed across the face of the Moon had been clearly visible, and had done little to restore the morale of the passengers.

They could not understand that the law of celestial mechanics admit of no appeal. The Pegasus was barely clear of Earth, and still weeks from her intended goal. But she had reached her orbiting speed, and had launched herself like a giant projectile on the path that would lead inevitably to Mars, under the guidance of the sun’s all-pervading gravity. There could be no turning back: that would be a maneuver involving an impossible amount of propellant. The Pegasus carried enough dust in her tanks to match velocity with Mars at the end of her orbit, and to allow for reasonable course corrections en route. Her nuclear reactors could provide energy for a dozen voyages— but sheer energy was useless if there was no propellant mass to eject. Whether she wanted to or not, the Pegasus was headed for Mars with the inevitability of a runaway streetcar. Captain Halstead did not anticipate a pleasant trip.

The words MAYDAY, MAYDAY came crashing out of the radio and banished all other preoccupations of the Pegasus and her crew. For three hundred years, in air and sea and space, these words had alerted rescue organizations, had made captains change their course and race to the aid of stricken comrades. But there was so little that the commander of a spaceship could do; in the whole history of astronautics, there have been only three cases of a successful rescue operation in space.

There are two main reasons for this, only one of which is widely advertised by the shipping lines. Any serious disaster in space is extremely rare; almost all accidents occur during planetfall or departure. Once a ship has reached space, and has swung into the orbit that will lead it effortlessly to its destination, it is safe from all hazards except internal, mechanical troubles. Such troubles occur more often than the passengers ever know, but are usually trivial and are quietly dealt with by the crew. All spaceships, by law, are built in several independent sections, any one of which can serve as a refuge in an emergency. So the worst that ever happens is that some uncomfortable hours are spent by all while an irate captain breathes heavily down the neck of his engineering officer.

The second reason why space rescues are so rare is that they are almost impossible, from the nature of things. Spaceships travel at enormous velocities on exactly calculated paths, which do not permit of major alterations—as the passengers of the Pegasus were now beginning to appreciate. The orbit any ship follows from one planet to another is unique; no other vessel will ever follow the same path again, among the changing patterns of the planets. There are no “shipping lanes” in space, and it is rare indeed for one ship to pass within a million kilometers of another. Even when this does happen, the difference of speed is almost always so great that contact is impossible.

All these thoughts flashed through Captain Halstead’s mind when the message came down to him from Signals. He read the position and course of the distressed ship—the velocity figure must have been garbled in transmission, it was so ridiculously high. Almost certainly, there was nothing he could do— they were too far away, and it would take days to reach them.

Then he noticed the name at the end of the message. He thought he was familiar with every ship in space, but this was a new one to him. He stared in bewilderment for a moment before he suddenly realized just who was calling for his assistance…

Enmity vanishes when men are in peril on sea or in space. Captain Halstead leaned over his control desk and said: “Signals ! Get me their captain.”

“He’s on circuit, sir. You can go ahead.”

Captain Halstead cleared his throat. This was a novel experience, and not a pleasant one. It gave him no sort of satisfaction to tell even an enemy that he could do nothing to save him.

“Captain Halstead, Pegasus, speaking,” he began. “You’re too far away for contact. Our operational reserve is less than ten kilometers a second. I’ve no need to compute, I can see it’s impossible. Have you any suggestions? Please confirm your velocity; we were given an incorrect figure.”

The reply, after a four-second time-lag that seemed doubly maddening in these circumstances, was unexpected and astonishing.

“Commodore Brennan, Federal cruiser Acheron. I can confirm our velocity figure. We can contact you in two hours, and will make all course corrections ourselves. We still have power, but must abandon ship in less than three hours. Our radiation shielding has gone, and the main reactor is becoming unstable. We’ve got manual control on it, and it will be safe for at least an hour after we reach you. But we can’t guarantee it beyond then.”

Captain Halstead felt the scalp crawl at the back of his neck. He did not know how a reactor could became unstable, but he knew what would happen if one did. There were a good many things about the Acheron he did not understand—her speed, above all—but there was one point that emerged very clearly and upon which Commodore Brennan must be left in no doubt.

“Pegasus to Acheron,” he replied. “I have three hundred passengers aboard. I cannot hazard my ship if there is danger of an explosion.”

“There is no danger, I can guarantee that. We will have at least five minutes’ warning, which will give us ample time to get clear of you.”

“Very well—I’ll get my airlocks ready and my crew standing by to pass you a line.”

There was a pause longer than that dictated by the sluggish progress of radio waves. Then Brennan replied:

“That’s our trouble. We’re cut off in the forward section. There are no external locks here, and we have only five suits among a hundred and twenty men.”

Halstead whistled and turned to his navigating officer before answering.

“There’s nothing we can do for them,” he said. “They’ll have to crack the hull to get out, and that will be the end of everyone except the five men in the suits. We can’t even lend them our own suits—there’ll be no way we can get them aboard without letting down the pressure.” He flicked over the microphone switch.

“Pegasus to Acheron. How do you suggest we can assist you?”

It was eerie to be speaking to a man who was already as good as dead. The traditions of space were as strict as those of the sea. Five men could leave the Acheron alive, but her captain would not be among them.

Halstead did not know that Commodore Brennan had other ideas, and had by no means abandoned hope, desperate though the situation on board the Acheron seemed. His chief medical officer, who had proposed the plan, was already explaining it to the crew.