Then K.i5’s ship stopped blasting. It had obviously exhausted its fuel, and was doing a little better than six kilometres a second away from the sun. K.15 must have landed, for his ship was now speeding helplessly out of the Solar System, Commander Smith didn’t like the message it was broadcasting, and guessed that it was running into the track of an approaching warship at some indefinite distance, but there was nothing to be done about that. The Doradus began to move towards Phobos, anxious to waste no time.
On the face of it, Commander Smith seemed the master of the situation. His ship was armed with a dozen heavy guided missiles and two turrets of electromagnetic guns. Against him was one man in a space suit, trapped on a moon only twenty kilometres across. It was not until Commander Smith had his first good look at Phobos, from a distance of less than a hundred kilometres, that he began to realize that, after all, K.15 might have a few cards up his sleeve.
To say that Phobos has a diameter of twenty kilometres, as the astronomy books invariably do, is highly misleading. The word “diameter” implies a degree of symmetry which Phobos most certainly lacks. Like those other lumps of cosmic slag, the asteroids, it is a shapeless mass of rock floating in space with, of course, no hint of an atmosphere and not much more gravity. It turns on its axis once every seven hours thirty-nine minutes, thus keeping the same face always to Mars—which is so close that appreciably less than half the planet is visible, the poles being below the curve of the horizon.
Beyond this, there is very little more to be said about Phobos.
K.15 had no time to enjoy the beauty of the crescent world filling the sky above him. He had thrown all the equipment he could carry out of the air lock, set the controls, and jumped. As the little ship went flaming out towards the stars he watched it go with feelings he did not care to analyse. He had burned his boats with a vengeance, and he could only hope that the oncoming battleship would intercept the radio message as the empty vessel went racing by into nothingness. There was also a faint possibility that the enemy cruiser might go in pursuit, but that was rather too much to hope for.
He turned to examine his new home. The only light was the ochre radiance of Mars, since the sun was below the horizon, but that was quite sufficient for his purpose and he could see very well. He stood in the centre of an irregular plain about two kilometres across, surrounded by low hills over which he could leap rather easily if he wished. There was a story he remembered reading long ago about a man who had accidentally jumped off Phobos: that wasn’t quite possible—though it was on Deimos—because the escape velocity was still about ten metres a second. But unless he was careful, he might easily find himself at such a height that it would take hours to fall back to the surface—and that would be fatal. For K.15’s plan was a simple one: he must remain as close to the surface of Phobos as possible— and diametrically opposite the cruiser. The Doradus could then fire all her armament against the twenty kilometres of rock, and he wouldn’t even feel the concussion. There were only two serious dangers, and one of these did not worry him greatly.
To the layman, knowing nothing of the finer details of astronautics, the plan would have seemed quite suicidal. The Doradus was armed with the latest in ultrascientific weapons: moreover, the twenty kilometres which separated her from her prey represented less than a second’s flight at maximum speed. But Commander Smith knew better, and was already feeling rather unhappy. He realized, only too well, that of all the machines of transport man has ever invented, a cruiser of space is far and away the least manoeuvrable. It was a simple fact that K.15 could make half a dozen circuits of his little world while her commander was persuading the Doradus to make even one.
There is no need to go into technical details, but those who are still unconvinced might like to consider these elementary facts. A rocket-driven spaceship can, obviously, only accelerate along its major axis—that is, “forward”. Any deviation from a straight course demands a physical turning of the ship, so that the motors can blast in another direction. Everyone knows that this is done by internal gyros or tangential steering jets, but very few people know just how long this simple manoeuvre takes. The average cruiser, fully fuelled, has a mass of two or three thousand tons, which does not make for rapid footwork. But things are even worse than this, for it isn’t the mass, but the moment of inertia that matters here—and since a cruiser is a long, thin object, its moment of inertia is slightly colossal. The sad fact remains (though it is seldom mentioned by astronautical engineers) that it takes a good ten minutes to rotate a spaceship through one hundred and eighty degrees, with gyros of any reasonable size. Control jets aren’t much quicker, and in any case their use is restricted because the rotation they produce is permanent and they are liable to leave the ship spinning like a slow-motion pinwheel, to the annoyance of all inside.
In the ordinary way, these disadvantages are not very grave. One has millions of kilometres and hundreds of hours in which to deal with such minor matters as a change in the ship’s orientation. It is definitely against the rules to move in ten-kilometre-radius circles, and the commander of the Doradus felt distinctly aggrieved. K.15 wasn’t playing fair.
At the same moment that resourceful individual was taking stock of the situation, which might very well have been worse. He had reached the hills in three jumps and felt less naked than he had out in the open plain. The food and equipment he had taken from the ship he had hidden where he hoped he could find it again, but since his suit could keep him alive for over a day that was the least of his worries. The small packet that was the cause of all the trouble was still with him, in one of those numerous hiding places a well-designed space suit affords.