A controlled explosion was the only solution, despite the danger to the crew within. But as the demolition squad placed their charges against the ventral hatchway, the shutter of an observation window opened for the first time. Captured on film, the faces of Colonel Irwin and Commander Merritt looked down at the limpet mines, the detonators and fuse wire. They gazed calmly at the NASA officials and engineers gesticulating at them, and shook their heads, rejecting the world with a brief wave before closing the shutter for the last time.

Needless to say, NASA allowed nothing of this to leak to the public at large, and claimed that the crew had alerted their ground controllers to the possible dangers of a virulent interplanetary disease. NASA spokesmen confirmed that they had ordered the crew to isolate themselves until this mystery virus could be identified and destroyed. The Zeus IV was hitched to its tractor and moved to an empty hangar on a remote corner of the airbase, safe from the TV cameras and the thousands still camped around the perimeter fence.

Here, over the next weeks and months, teams of engineers and psychologists, astrophysicists and churchmen tried to free the crew from their self-imposed prison. Right from the start, as the doors of the hangar sealed the Zeus IV from the world, it was taken for granted that the astronauts’ immolation was entirely voluntary. Nonetheless, an armed guard, backed by electronic security devices, kept careful watch on the craft. Sets of aircraft scales were manoeuvred under the landing wheels, so that the weight of the Zeus IV could be measured at all times, and instantly expose any attempt at escape.

As it happened, the spaceship’s weight remained constant, never fluctuating by more than the accumulated dust on its hull. In all senses the Zeus IV constituted a sealed world, immune to any pressures from within or without. A controlled explosion strong enough to split the hull would also rupture the engines and disperse the craft’s nuclear fuel supply, provoking a worldwide political outcry that would doom NASA forever. There was no way of starving the crew out — to deal with the possibility of the Zeus IV missing its rendezvous with Mars and stranding itself forever in deep space, a 200-ton stock of food had been placed aboard, enough to last the crew for 40 years. Its air, water and human wastes were recycled, and there were enough episodes of Dallas in the video-library to amuse the astronauts for all eternity.

The Zeus, in fact, no longer needed the Earth, and the NASA officials accepted that only psychological means would ever persuade the crew to leave their craft. They assumed that a profound spiritual crisis had afflicted the astronauts, and that until this resolved itself the rescuers’ main task was to establish a channel of communication.

So began a long series of ruses, pleas and stratagems. The puzzled entreaties of relatives, whose tearful faces were projected onto the hangar roof, the prayers of churchmen, the offer of huge cash bribes, the calls to patriotism and even the threat of imprisonment, failed to prompt a single response. After two months, when public curiosity was still at fever pitch, the NASA teams admitted to themselves that the Zeus IV crew had probably not even heard these threats and promises.

Meanwhile an impatient President Quayle, aware that he was the butt of cartoonists and TV comedians, demanded firmer action. He ordered that pop music be played at full blast against the spacecraft’s hull and, further, that the huge ship be rocked violently from side to side until the crew came to their senses. This regime was tried but discontinued after two hours, partly for its sheer ludicrousness, and partly for fear of damaging the nuclear reactors.

More thoughtful opinion was aware that the crisis afflicting the Zeus crew merited careful study in its own right, if mankind were ever to live permanently in space. A prominent theologian was invited to the Edwards airbase, and surveyed the claustrophobic hangar in which the Zeus was now entombed, draped like Gulliver in its cables and acoustic sensors. He wondered why the crew had bothered to return to Earth at all, knowing what they probably faced, when they might have stayed forever on the vast and empty landscapes of Mars. By returning at all, he ventured, they were making an important point, and acknowledged that they still saw their place among the human race.

So a patient vigil began. Concealed cameras watched for any signs of internal movement and electronic gauges mapped the smallest activities of the crew. After a further three months the daily pattern of life within the Zeus IV had been well established. The crew never spoke to each other, except when carrying out the daily maintenance checks of the spacecraft systems. All took regular exercise in the gymnasium, but otherwise stayed in their own quarters. No music was played and they never listened to radio or television. For all that anyone knew, they passed the days in sleep, meditation and prayer. The temperature remained at a steady 68°F., and the only constant sound was that of the circulation of air.

After six months the NASA psychiatrists concluded that the crew of the Zeus IV had suffered a traumatic mental collapse, probably brought on by oxygen starvation, and were now in a vegetative state. Relatives protested, but public interest began to wane. Congress refused to allocate funds for further Zeus missions, and NASA reluctantly committed itself to a future of instrumented spaceflights.

A year passed, and a second. A small guard and communications crew, including a duty psychologist and a clergyman, still maintained a vigil over the Zeus. The monitors recorded the faint movements of the crew, and the patterns of daily life which they had established within a few hours of their landing. A computerized analysis of their foot-treads identified each of the astronauts and revealed that they kept to their own quarters and seldom met, though all took part in the maintenance drills.

So the astronauts languished in their twilight world. A new President and the unfolding decades of peace led the public to forget about the Zeus IV, and its crew, if remembered at all, were assumed to be convalescing at a secret institution. In 2016, eight years after their return, there was a flurry of activity when a deranged security officer lit a large fire under the spacecraft, in an attempt to smoke out the crew. Four years later a Hollywood telepathist claimed to be in contact with the astronauts, reporting that they had met God on Mars and had been sworn to silence about the tragic future in store for the human race.

In 2025 the NASA headquarters in Houston were alerted to a small but sudden fall in the overall weight of the Zeus — 170 pounds had been wiped from the scales. Was the spacecraft preparing for take-off, perhaps employing an anti-gravity device which the crew had been constructing in the seventeen years since their return? However, the tread-pattern analysis confirmed that only four astronauts were now aboard the craft. Colonel Irwin was missing, and an exhaustive hunt began of the Edwards airbase. But the organic sediments in the trapped gases released from a discharge vent revealed what some engineers had already suspected. Colonel Irwin had died at the age of 62, and his remains had been vapourized and returned to the atmosphere. Four years later he was followed by the Japanese, Professor Kawahito, and the Zeus was lighter by a further 132 pounds. The food stocks aboard the Zeus would now last well beyond the deaths of the three astronauts still alive.

In 2035 NASA was dissolved, and its functions assigned to the immensely wealthy universities which ran their own scientific space programmes. The Zeus IV was offered to the Smithsonian Institute in Washington, but the director declined, on the grounds that the museum could not accept exhibits that contained living organisms. The USAF had long wished to close the Edwards airbase, and responsibility for this huge desert expanse passed to the National Parks Bureau, which was eager to oversee one of the few areas of California not yet covered with tract housing. The armed guards around the Zeus IV had long gone, and two field officers supervised the elderly instruments that still kept watch over the spacecraft.