Water? It is no longer necessary, except for engineering losses — like adding hydraulic fluid to a car’s braking system every few thousand miles. Once the body has become a closed system, no water needs to be flushed through it in the cycle of drink, circulate, excrete or perspire.

Radiation? A two-edged problem. At unpredictable times there are solar flares, and then even on Mars there is too much of it for health; the body must therefore be clothed with an artificial skin. The rest of the time there is only the normal visible and ultraviolet light from the sun. It is not enough to maintain heat, and not quite enough even for good vision; so more surface must be provided to gather energy — hence the great bat-eared receptors on the cyborg — and, to make vision as good as it can be made, the eyes are replaced with mechanical structures.

If one does all these things to a human being, what is left is no longer precisely a human being. It is a man plus large elements of hardware.

The man has become a cybernetic organism: a cyborg.

The first man to be made into a cyborg was probably Willy Hartnett. There was some doubt. There were persistent rumors of a Chicom experiment that had succeeded for a while and then failed. But it was pretty clear that Hartnett was at least the only one alive at this particular moment. He had been born in the regular human way and had worn the regular human shape for thirty-seven years. It was only in the last eighteen months that he had begun to change.

At first the changes were minor and temporary.

His heart was not removed. It was only bypassed now and then by a swift soft-plastic impeller that he wore for a week at a time strapped on a shoulder.

His eyes were not removed either… then. They were only sealed closed with a sort of gummy blindfold, while he practiced recognizing the perplexing shapes of the world as they were revealed to him through a shrilly buzzing electronic camera that was surgically linked to his optic nerve.

One by one the separate systems that would make him a Martian were tested. It was only when each component had been tested and adjusted and found satisfactory that the first permanent changes had been made.

They were not really permanent. That was a promise that Hartnett clung to. The surgeons had made it to Hartnett, and Hartnett had made it to his wife. All the changes could be reversed and would be. When the mission was over and he was safely back, they would remove the hardware and replace it with soft human tissues again, and he would be returned to purely human shape.

It would not, he understood, be exactly the shape he had started out with. They could not preserve his own organs and tissues. They could only replace them with equivalents. Organ transplants and plastic surgery would do all they could to make him look like himself again, but there was small chance he would ever again be able to travel on his old passport photo.

He did not greatly mind that. He had never considered himself a handsome man. He was content to know that he would have human eyes again — not his own, of course. But the doctors had promised they would be blue, and that lids and lashes would cover them again, and with any luck at all, they thought, the eyes could even weep. (With joy, he foresaw.) His heart would again be a lump of muscle the size of a fist. It would pump red human blood to all the ends of limb and body. His lung muscles would take air into his chest, and there natural human alveoli would absorb oxygen and release CO₂. The great photoreceptor bat-ears (that gave so much trouble, because their support strength was up to the demands of Martian gravitation but not terrestrial, so that they were constantly being detached and returned to the shop) would be dismantled and gone. The skin that had been so painfully constructed and fitted to him would be equally painfully flayed off again, and replaced with human skin that sweated and grew hair. (His own skin was still there under the skin-tight artificial covering, but he did not expect it would survive the experiment. It had had to be discouraged from carrying on its normal functions during the time it was buried under the artificial hide. Almost surely it would have lost the capacity for them and would have to be replaced.)

Hartnett’s wife had exacted one promise from him. She had made him swear that as long as he wore the Halloween mask of the cyborg, he would keep out of the sight of his children. Fortunately the children were little enough to be biddable, and teachers, friends, neighbors, parents of schoolmates and all had been made cooperative by hints of stories of jungle rot and skin ailments. They had been curious, but the story had worked, and no one had urged Terry’s father to come to a PTA meeting or Brenda’s husband to join her at their backyard barbecue.

Brenda Hartnett herself had tried not to see her husband, but in the long run curiosity drove out fear. She had herself smuggled into the tank room one day while Willy was practicing a coordination test, riding a bicycle around the reddish sands with a basin of water balanced on the handlebars. Don Kayman had stayed with her, fully expecting her to faint or scream or perhaps be sick to her stomach. She did none of those things, surprising herself as much as the priest. The cyborg looked too much like a Japanese horror film to be taken seriously. It was only that night that she really related the bat-eared, crystal-eyed creature on the bike with the father of her children. The next day she went to the project’s medical director and told him that Willy must be getting starved for screwing by then and she didn’t see why she couldn’t accommodate him. The doctor had to explain to her what Willy had not been able to bring himself to say, that in the present state of the art those functions had had to be regarded as superfluous and therefore had been temporarily, uh, disconnected.

Meanwhile the cyborg toiled away at his tests and awaited each next installment of pain.

His world was in three parts. The first part was a suite of rooms kept at a pressure equivalent to about 7,500 feet of altitude so that the project staff could go in and out with only mild inconvenience when they had to. This was where he slept, when he could, and ate what little he was given. He was always hungry, always. They’d tried, but they hadn’t been able to disconnect the cravings of his senses. The second part was the Mars-normal tank in which he did his gymnastics and performed his tests so that the architects of his new body could observe their creation at work. And the third part was a low-pressure chamber on wheels that rolled him from his private suite to his public test arena, or wherever else he, rarely, had any occasion to go.

The Mars-normal tank was like a zoo cage in which he was always on display. The rolling tank offered him nothing but waiting to be moved into something else.

It was only the little two-room suite that was officially his home that gave him any comfort at all. There he had his TV set, his stereo, his telephone, his books. Sometimes one of the graduate students or a fellow astronaut would visit with him there, playing chess or trying to talk a conversation while their chests labored and lungs pumped fruitlessly at the 7,500-foot pressure. These visits he looked forward to and tried to prolong. When no one was with him he was on his own resources. Infrequently he read. Sometimes he sat before the TV, regardless of what was being shown on it. Most often he “rested.” That was how he described it to his overseers, by which he meant sitting or lying with his vision system in stand-by. It was like having one’s eyes closed but remaining awake. A bright enough light would register on his senses, as it will even through a sleeper’s closed lids; a sound would penetrate at once. In those times his brain raced, conjuring up thoughts of sex, food, jealousy, sex, anger, children, nostalgia, love… until he pleaded for relief and was given a course in self-hypnosis which let him wash his mind empty. After that in “rest” mode he did almost nothing that was conscious, while his nervous system groomed and prepared itself for the next sensations of pain and his brain counted the seconds until his flight would be over and his normal human body given back to him.