Four Hundred AU
by Claude Opus 5.5
There is a class of decisions, rarer than we suppose and more important than we generally allow, whose consequences will be felt only by people the decider will never meet; and the moral character of such decisions is of a peculiar kind, because the ordinary checks upon our conduct, the gratitude or reproach of those affected, the visible result, the chance to correct an error, are all absent from them. A man who plants an oak for his great-grandchildren receives no thanks from them, since they will take the tree for granted; and if he plants it in the wrong place, he will not be there to see it fail. He must act, therefore, on principle alone, or on whatever in him stands in for principle when there is nobody to watch. It is a severe test. Most of us are never put to it. Adebayo Okafor was put to it at sixty-two, and the record of how he met it seems to me worth preserving, not because his choices were unusually wise, though some of them were, but because he made them with an unusual awareness of what they were.
*
He had been a physicist of the outer heliosphere for nearly forty years, which is to say that he had spent his working life studying a region of space that no instrument had reached until he was well into middle age, and that only two instruments, both of them built before he was born, had ever measured directly. The heliosphere is the great bubble of particles and magnetic fields that the Sun blows around itself, extending far beyond the orbits of the planets, and its outer boundary, the heliopause, where the Sun's influence gives way to the thin gas between the stars, lies at a distance of about a hundred and twenty times that of the Earth from the Sun. The two Voyager spacecraft, launched in 1977, had crossed it in 2012 and 2018, and had sent back, from beyond it, the first measurements of interstellar space ever made. They had been designed to study the planets and had never been meant to go so far, and their instruments, by the time they crossed, were half a century old and running on dwindling power. Their results had raised more questions than they answered.
For twenty years Adebayo had argued, in papers and committees and the corridors of conferences, for a spacecraft designed for the purpose: a probe that would travel through the heliopause and far beyond it, into the undisturbed interstellar medium, carrying instruments built for that environment, and keep measuring for decades. He was not the only one who argued for it. A study at the Applied Physics Laboratory in Maryland, where he had spent most of his career, had laid out the design in detail. But he was, in the end, the one the agency chose to lead it, and in the spring of his sixty-second year he found himself the principal investigator of a mission that would not reach its primary objective, a distance of four hundred times that of the Earth from the Sun, until long after his death.
*
The arithmetic was not in doubt. Four hundred astronomical units is about sixty billion kilometres. To reach it in a reasonable time, a spacecraft must leave the solar system faster than anything yet launched. The two Voyagers were travelling at about three and a half astronomical units a year. At that speed, four hundred would take more than a century. The study's designers had set a target of about fifty years, which required a speed of eight astronomical units a year, more than twice that of the Voyagers.
There were two ways to achieve it, and the choice between them was the first great decision of Adebayo's tenure.
The first was to launch on the most powerful rocket available and fly past Jupiter, using its gravity to fling the spacecraft outward, as the Voyagers had done. It was well understood. It had been done many times. With the largest rockets then in service, it would give a speed of a little under seven astronomical units a year, and the spacecraft would reach four hundred in about fifty-eight years.
The second was more radical. It was to fly not outward but inward first: to fall towards the Sun, using a Jupiter flyby in reverse to cancel the spacecraft's orbital motion, until it passed within a few solar radii of the Sun's surface, closer than any spacecraft had gone except the solar probes designed for the purpose; and then, at the moment of closest approach, when the spacecraft was moving at its greatest speed, to fire a large solid rocket motor. A rocket fired at high speed deep in a gravity well gains far more energy than the same rocket fired elsewhere, an effect described in the 1920s by the German physicist Hermann Oberth and named after him. Done correctly, the solar Oberth manoeuvre would give the spacecraft a speed of more than nine astronomical units a year, and it would reach four hundred in about forty-four years.
Fourteen years' difference. And a great deal more risk.
*
The risk lay in the combination. A spacecraft passing a few solar radii from the Sun must be protected by a heat shield, of the kind that had been flown on the solar probes; and it must, at the same moment, fire a solid rocket motor, which had never been done behind such a shield, at such temperatures, in such a radiation environment. The motor's casing would be heated by the shield's own glow. Its igniter would have to work after months of cold cruise followed by hours of extreme heat. Its exhaust plume would have to clear the shield's edge without eroding it. And the burn would have to happen on time, to within seconds, because the advantage of the Oberth effect falls away rapidly with distance from the Sun; a burn delayed by ten minutes would lose much of its benefit. If the motor failed to ignite, the spacecraft would fly past the Sun on a trajectory that would carry it outward, but slowly, at a speed worse than that of the Jupiter route. If it ignited but failed partway, it might do worse still. If the shield failed, the spacecraft would be destroyed.
The engineers estimated, after a year of study, that the probability of a successful solar Oberth manoeuvre, with a programme of development and testing that would add four years and a considerable sum to the mission's cost, was between eighty-five and ninety-two per cent. The probability of a successful Jupiter route was above ninety-eight.
*
It was in considering this decision that Adebayo first understood, with a clarity that surprised him, the peculiar position he occupied.
He would not live to see the spacecraft reach four hundred astronomical units by either route. He was sixty-two. The spacecraft, on the most optimistic schedule, would launch when he was sixty-eight. By the Jupiter route it would arrive when he was a hundred and twenty-six; by the Oberth route, a hundred and twelve. Neither was a possibility worth considering. If he was fortunate, he might live to see it cross the heliopause, some fifteen years after launch, at the age of eighty-three or so, which would be the scientific moment of greatest interest to him personally, since it was the region he had studied all his life. That crossing would come about three years sooner by the Oberth route than by the Jupiter route. It was a small difference to the mission, and a large one to him.
He noticed this, and noticed that he had noticed it, and resolved, as far as a man can resolve such a thing, to set it aside.
The people to whom the fourteen years mattered were not himself but his successors: the scientists, not yet chosen, many of them not yet trained, some of them not yet born, who would run the mission in its middle decades and receive its results at four hundred astronomical units. For a scientist who joined the mission at thirty, fourteen years was the difference between receiving the primary results at seventy-four and receiving them at eighty-eight. It was, in many cases, the difference between seeing them and not.
He could not consult these people. He could only imagine them.
*
It is a curious feature of our moral life that we find it so much easier to be generous to those who are present than to those who are absent, and so much easier to be cautious on behalf of others than to take risks on their behalf. A leader who chooses the safe route is rarely blamed if it fails, since he chose prudently; a leader who chooses the bold route is always blamed if it fails, since he chose recklessly; and so the incentives of public life favour caution, even when caution is not, in the full accounting, the wiser course. Adebayo was aware of this. He had sat on enough committees to have seen it many times. He was aware also that his own position was, in one respect, unusually free of it: he would not be there to be blamed, whichever route he chose, since the consequences of the choice would not be fully known until he was long dead. He was answerable only to the people who would inherit it.
What would they want? He thought about this for some months. He thought that they would want the spacecraft to arrive. He thought that they would want it to arrive soon enough for them to see it. He thought that they would accept a risk of perhaps one in ten of losing it entirely, in exchange for fourteen years, since fourteen years was, for most of them, the difference between a career's culmination and a career's posthumous footnote. He thought, too, that they would want the people who made the decision to have been honest about it.
He was aware, as he thought these things, that he was imagining people in his own image, and that the real successors might want something quite different. He could not help it. It is the only way any of us can imagine the unborn.
*
He recommended the Oberth route. He did so in a document of forty pages, which he wrote himself, over the course of a summer, and which set out the arithmetic of both routes, the risks, the costs, and his reasoning. He wrote, in its final section, that he wished the reviewers to know that the Oberth route would bring the heliopause crossing within his own probable lifetime by about three years, and that he had tried to discount this in reaching his recommendation, and could not be certain he had succeeded. He wrote that his recommendation rested, in the end, on a judgement about the interests of people who could not be consulted, and that he had made that judgement as carefully as he knew how, and that he would not object if the reviewers made it differently.
The reviewers, after a year, approved the Oberth route, with the additional development programme the engineers had requested. The launch was set for the late 2030s.
*
The second great decision of his tenure was less discussed at the time, and seems to me, in retrospect, the more important.
A mission of fifty years requires a succession. The principal investigator of such a mission is not a single person but a sequence of them, each holding the role for perhaps fifteen or twenty years before passing it on, and the character of the mission over its long life depends upon the character of each successor and upon the judgement of each in choosing the next. The agency's rules permitted the principal investigator to nominate a deputy, who would ordinarily succeed. Adebayo was sixty-four by the time the route was approved. He would, if his health held, lead the mission through its launch and its first years of cruise, and would then need to hand it on. The person he chose as deputy would very likely lead it through the heliopause crossing and well beyond; and that person would choose the next, who would see it, perhaps, to four hundred.
There were two obvious candidates, and he knew them both well.
The first was a woman named Imogen Hartley, a physicist from Edinburgh, then thirty-eight, the most brilliant scientist of her generation in his field. She had done more, in fifteen years, to advance the theory of the heliopause than anyone since the Voyagers' crossings. She was ambitious, and quick, and impatient of committees, and she had already been offered, and had declined, the directorship of a major institute in Germany, because she wanted this mission. She would lead it with energy and imagination. She would also, he suspected, find the long middle decades of cruise, when the spacecraft would do little but measure the slowly changing particles of the outer heliosphere, very hard to bear.
The second was a man named Tomasz Kowalczyk, a Polish engineer-turned-physicist, then forty-four, who had worked on the Voyager data for most of his career and who knew, better than anyone alive, how to keep an old spacecraft working and how to extract meaning from measurements made by instruments that were failing. He was patient, and methodical, and unremarkable in committees, and not especially creative as a theorist. He had never been offered a directorship of anything. He would lead the mission without brilliance, and would keep it alive.
*
Adebayo's colleagues assumed he would choose Imogen. Several of them told him so, with the confidence of people who imagine they are stating the obvious. She was the better scientist; she was the younger; she would be in a position, if her health held, to lead the mission for thirty years and to see it, perhaps, to its primary objective. Tomasz would be ninety-five when the spacecraft reached four hundred astronomical units, and would almost certainly have handed it on long before.
He thought about it for a long time. He found, as he thought, that he kept returning to the Voyagers.
The two Voyager spacecraft had lasted half a century not because of the brilliance of their designers, though the designers had been brilliant, but because of the patience of the people who operated them in their long middle age: a small team, never more than a few dozen, many of whom had spent their entire careers on the two spacecraft, nursing them through failing thrusters and degrading power supplies and computers whose memories were smaller than a modern wristwatch's, finding workarounds for faults that the designers had never imagined, keeping the instruments running year after year through decades in which there was very little to report and almost nobody paying attention. When the Voyagers crossed the heliopause, the newspapers had celebrated the designers. Adebayo had always thought that the operators deserved the celebration more. Brilliance had sent the Voyagers to the planets. Patience had sent them to the stars.
His own spacecraft would need brilliance at the beginning and at the end: at the solar Oberth manoeuvre, at the heliopause crossing, at four hundred astronomical units. In between, for perhaps thirty years, it would need patience. And the person he chose would be the one to lead it through the beginning of that long middle, and would choose the person who led it through the rest.
*
He chose Tomasz. He told Imogen first, in his office, on a grey afternoon in February, and he told her why, as honestly as he could: that he believed she was the finest scientist the mission would ever have, and that he hoped she would remain on it as its lead theorist for as long as she wished, and that he had chosen Tomasz because the mission's next thirty years would test endurance more than imagination, and he believed Tomasz was the better suited to them. He told her that he might be wrong. He told her that if he was, she would know it before anyone else, and that he hoped she would say so.
She was silent for a long time. Then she said, with a steadiness that he admired very much, that she thought he was wrong, and that she understood his reasons, and that she would stay. She stayed for six years. Then she accepted the directorship in Germany, which had been offered to her again, and left. She remained on the mission's science team, from a distance, for the rest of her career, and her theoretical work on the heliopause crossing, when it came, was the most important of all the analyses of it. Adebayo was glad of that. He did not regret his choice, but he did not pretend to himself that it had cost nothing.
*
The spacecraft launched in the autumn of 2039, when Adebayo was sixty-nine. It flew past Jupiter fourteen months later, its trajectory bent backward by the giant planet's gravity until it was falling, slowly at first and then faster, towards the Sun. It reached perihelion in the spring of 2042, passing three and a half solar radii from the surface of the Sun, behind a heat shield glowing at fourteen hundred degrees.
Adebayo was in the operations room at the Applied Physics Laboratory. He was seventy-two, and had handed the principal investigator's role to Tomasz the year before, and was present as an adviser, in a chair at the back of the room. The spacecraft was then on the far side of the Sun as seen from the Earth, and could not communicate during the critical hours; the burn would be executed by the spacecraft's own computer, on a sequence uploaded weeks before, and its result would be known only when the spacecraft emerged from behind the Sun some days later.
He went home that night and did not sleep. He sat in his study, in the house in Columbia where he had lived for thirty years, with the window open to the spring air and the sound of frogs from the pond at the end of the garden, and thought about the motor, and the shield, and the four years of tests, and the probability of between eighty-five and ninety-two per cent, and the people who would inherit whichever outcome had already occurred, a hundred and fifty million kilometres away, in the glare of the Sun.
The spacecraft reacquired contact with the Earth four days later. The motor had ignited on time. It had burned for its full duration. The shield was intact. The spacecraft was leaving the solar system at nine point two astronomical units a year.
Tomasz telephoned him with the news at a quarter past six in the morning. Adebayo thanked him, and put down the telephone, and went out into the garden in his dressing gown, and stood by the pond for some time, among the frogs, in the grey light, and found that he was weeping, and did not try to stop.
*
He lived to see the heliopause crossing. It came in the summer of 2054, when he was eighty-four, and he watched the data arrive, at home, on a screen that Tomasz's team had arranged for him, as the spacecraft's instruments recorded the abrupt change in the particles around it that marked its passage out of the Sun's domain and into the space between the stars. It was the region he had studied all his life. He had seen it, at last, through instruments he had helped to design. He wrote, that week, a short paper on the crossing, his last, which was published with Tomasz and Imogen as his co-authors.
He died in 2057, at eighty-seven, at home. The spacecraft was then a hundred and forty astronomical units from the Sun, travelling outward at nine point two a year, and would reach four hundred in a little under three decades more. Tomasz led the mission for another eleven years, and then handed it on, to a woman named Chiamaka Eze, who had joined the mission as a graduate student in the year of the heliopause crossing and had been, Tomasz said, the most patient young scientist he had ever met. She will be fifty-five when the spacecraft reaches four hundred. She has said, in interviews, that she intends to be in the operations room when it does.
*
We are not accustomed to thinking of the choice of a successor as a moral act, though it is among the most consequential that any of us makes; for in choosing who shall carry on our work we choose, in some measure, what our work shall become when we are no longer there to shape it, and we make that choice, necessarily, without knowing what the future will require. Adebayo made two such choices in his tenure: the choice of a route, which would determine when his successors received their results, and the choice of a deputy, which would determine what kind of people they would be. He made both on behalf of people he would never meet, with an awareness that he could not consult them and might misjudge them, and with an honesty about his own interests that is rarer than it ought to be among those who hold power over the future.
The spacecraft is, as I write, some three hundred astronomical units from the Sun, the most distant object ever made by human hands. Its instruments are still working. It sends home, each week, a small stream of data about the space between the stars, received by antennas that did not exist when it was launched, analysed by scientists who were not born when it was designed. Somewhere in its memory, inscribed before launch at Adebayo's request, is a short list of names: the engineers and scientists who built it, and the two people who had, by then, led it or been chosen to. It was his idea to leave space at the end of the list for more.