Officially, it had a very elaborate name, but it was spoken of as Station Four by those few Earthpeople who had occasion to mention it. From the name it was at once apparent there had been three such objects earlier - none of which were any longer in use, having been cannibalized, in point of fact. There was also a Station Five that had never been finished and had become derelict.

It is doubtful if the vast majority of Earth's population ever thought of the existence of Station Four, which drifted slowly around Earth in an orbit well beyond that of the Moon.

The early stations had been Earth's launching pads for the construction of the first Settlements, and then, when the Settlers themselves took over the job of building Settlements, Station Four was used for Earth's flights to Mars.

One such Martian flight was all that took place, however, for it turned out that the Settlers were far better suited, psychologically, to long flights (living, as they did in worlds that were large enclosed spaceships), and Earth left it to them with a sigh of relief.

Station Four was now rarely used for any purpose and was maintained only as Earth's foothold in space, as a symbol that the Settlers were not the sole owners of the vastness beyond Earth's atmosphere.

But now Station Four had a use.

A large cargo ship had lumbered out in its direction, carrying with it the rumor (among the Settlements) that another attempt - the first in the twenty-third century - would be made to place an Earth team on Mars. Some said it was merely for exploration, some for the establishment of an Earth colony on Mars in order to bypass the few Settlements in orbit around the planet; and some for the purpose, eventually, of establishing an outpost on some sizable asteroid that no Settlement had yet claimed.

What the ship actually carried in its cargo hold was the Superluminal and the crew that was to propel her to the stars.

Tessa Wendel, even though she had been planetbound for eight years, took the space experience calmly, as any Settler by birth would naturally do. Spaceships were far more like Settlements in principle than they were like the planet Earth. And because of that, Crile Fisher, though he had been on many a spaceflight before, was a bit uneasy.

This time something more than the unnaturalness of space contributed to the tension onboard the cargo ship. Fisher said, ‘I can't endure the waiting, Tessa. It's taken us years to reach this point and the Superluminal is ready and we still wait.’

Wendel regarded him thoughtfully. She had never intended to get this involved with him. She had wanted moments of relaxation to rest a mind overcome with the complexity of the project, so that it might return to work refreshed and keener. That was what she had intended; what she had ended up with was something much more.

Now she found herself helplessly tied to him, so that his problems had become hers. The years of his waiting would surely come to nothing, and she worried about the despair that would follow his inevitable disappointment. She had tried to dash cold water on his dreams judiciously, tried to cool down his overheated anticipation of a reunion with his daughter, but she had not succeeded. If anything, over this past year, he had grown more optimistic about the possibility for no obvious reason - at least, none he would explain to her.

Tessa was finally satisfied (and relieved) that it was not his wife Crile was looking for, but only his daughter. To be sure, she had never understood this longing for a daughter he had last seen as an infant, but he had volunteered no explanation and she had not wanted to probe the matter. What was the use? She was certain that his daughter was not alive, that nothing on Rotor was alive. If Rotor was there near the Neighbor Star, it was a giant tomb drifting in space, wandering for ever - and undetectable except by incredible coincidence. Crile Fisher would have to be kept steady and functioning once that inevitable prospect became clearly apparent reality.

Tessa said cajolingly, ‘There's only a two-month wait left - at most. Since we've waited for years, another two months won't hurt.’

‘It's the waiting for years that makes even two months more unbearable,’ muttered Fisher.

‘Tell yourself otherwise, Crile,’ said Wendel. ‘Learn to bow to necessity. The Global Congress simply won't allow us to go any sooner. The Settlements have their eyes on us, and there's no way of being sure that they all accept the notion that we're heading for Mars. It would be strange if they did, considering Earth's poor record in space. If we do nothing for two months, they will assume we're having trouble - something they would readily believe, and find satisfaction in - and withdraw their attention.’

Fisher shook his head angrily. ‘Who cares if they know what we're doing? We'll be off and gone and they won't duplicate Superluminal flight for years - and by that time we'll have a fleet of Superluminal vessels and be moving rapidly forward toward opening up the Galaxy.’

‘Don't take that for granted. It's easier to imitate and overtake than it is to originate. And Earth's government, considering its dismal record in space after the Settlements reached maturity, is obviously anxious to establish unmistakable priority for psychological reasons.’ She shrugged. ‘Besides, we need the time to carry out more tests on the Superluminal under low-gravity conditions.’

‘There's never any end to tests, is there?’

‘Don't be impatient. This is so new and untried a technique, and so unlike anything humanity has ever had, that it is all too easy to think of new tests, especially since we are a little uncertain as to the manner in which moving into and out of hyperspace is affected by the level of intensity of a gravitational field. Seriously, Crile, you can't blame us for beingcautious. After all, as recently as a decade ago, superluminal flight was considered theoretically impossible.’

‘Even caution can be overdone.’

‘Possibly. Eventually, I will decide that we've done all we can reasonably be expected to do, and then we'll take off. I promise you, Crile, we won't wait unreasonably. I won't overdo caution.’

‘I hope not.’

Wendel looked at him doubtfully. She had to ask. She said, ‘You know, Crile, you're not yourself lately. For the last two months you've seemed to be burning up with impatience. For a while there you had cooled down, and then you suddenly gained excitement again. Has something happened that I don't know about?’

Fisher calmed suddenly. ‘Nothing's happened. What can possibly have happened?’

To Wendel, it seemed he had calmed down too quickly, had wrenched himself into a most suspicious affectation of normality. She said, ‘I'm asking you what can possibly have happened. I've tried to warn you, Crile, that we are not likely to find Rotor a functioning world, or find it at all. We will not find your - we are not likely to find any of its inhabitants alive.’ She waited through his stubborn silence, then said, ‘Haven't I warned you of that - possibility?’

‘Often,’ said Fisher.

‘Yet you sound, now, as though you can hardly wait for what is sure to be a happy reunion. It is dangerous to have hopes that are not likely to be fulfilled, to pin everything upon them. What has suddenly produced this new attitude? Have you been talking to someone who was unjustifiably optimistic?’

Fisher flushed. ‘Why do I have to have been talking to someone? Why couldn't I have come to an independent conclusion concerning this, or any other matter? Just because I don't understand the theoretical physics that you do understand doesn't mean I'm subnormal or brainless.’

Wendel said, ‘No, Crile. I never thought anything of the sort about you, nor did I mean to imply it. Tell me what you think about Rotor.’

‘Nothing terribly deep or subtle. It just seemed to me that there was nothing in empty space that is very likely to have destroyed Rotor. It's easy to say that there might only be the dead hulk of a Settlement at Rotor, if it reached the Neighbor Star at all, but what is it that would have destroyed them either on the way or once they were there? I defy you to give me a specific scenario of destruction - collisions - alien intelligences - whatever.’

Wendel said earnestly, ‘Crile, I can't. I have no mystical visions of something having happened. It's just hyper-assistance itself. It's a tricky technique, Crile. Take my word for it. It doesn't use either space or hyperspace in a steady way, but skids along at the interface, wobbling to one side or another for short periods, and moving from space to hyperspace and then from hyperspace back to space several times a minute, perhaps. The passage from one to the other may therefore have taken place a million times or more in the course of the trip from here to the Neighbor Star.’

‘And so?’

‘And so, it happens that the transition is far more dangerous than is level flight in either space or hyper-space. I don't know how thoroughly the Rotorians had established hyperspatial theory, but the chances are that they had done so in only a rudimentary fashion, or they would have surely developed true superluminal flight. In our project, which has worked out hyperspatial theory in great detail, we've managed to establish the effect on material objects of passing from space to hyperspace and vice versa.

‘If an object is a point, there is no strain on it during the transition. If an object is not a point, however - if it is an extended bit of matter, as any ship would be - then there is always a finite period of time during which part of it is in space and part is in hyperspace. This creates a strain - the amount of strain depending on the size of the object, its physical makeup, its speed of transition, and so on. Even for an object the size of Rotor, the danger involved in a single transition - or a dozen, for that matter - is so small that it can reasonably be ignored.

‘When the Superluminal will travel, superluminously, to the Neighbor Star, we are liable to make a dozen transitions, or possibly only as few as two. The flight will be a safe one. In a flight with hyper-assistance only, on the other hand, there may be a million transitions in the course of the same trip, you see, and the chances of fatal strain mount up.’

Fisher looked appalled. ‘Is the chance of fatal strain certain?’

‘No, nothing is certain. It's a statistical matter. A ship might undergo a million transitions - or a billion - with nothing happening. It might be destroyed, on the other hand, on the very first transition. The chances, however, increase rapidly with the number of transitions.