There was also a sense of danger here that was wholly novel to his experience. In every earlier landing he had known what to expect; there was always the possibility of accident, but never of surprise. With Rama, surprise was the only certainty.

Now Endeavour was hovering less than a thousand metres above the North Pole of the cylinder, at the very centre of the slowly turning disc. This end has been chosen because it was the one in sunlight; as Rama rotated, the shadows of the short enigmatic structures near the axis swept steadily across the metal plain. The northern face of Rama was a gigantic sundial, measuring out the swift passage of its four-minute day.

Landing a five-thousand-ton spaceship at the centre of a spinning disc was the least of Commander Norton’s worries. It was no different from docking at the axis of a large space station; Endeavour’s lateral jets had already given her a matching spin, and he could trust Lieutenant Joe Calvert to put her down as gently as a snowflake, with or without the aid of the nay computer.

“In three minutes,” said Joe, without taking his eyes from the display, “we’ll know if it’s made of antimatter.”

Norton grinned, as he recalled some of the more hair-raising theories about Rama’s origin. If that unlikely speculation was true, in a few seconds there would be the biggest bang since the solar system was formed. The total annihilation of ten thousand tons would, briefly, provide the planets with a second sun.

Yet the mission profile had allowed even for this remote contingency; Endeavour had squirted Rama with one of her jets from a safe thousand kilometres away. Nothing whatsoever had happened when the expanding cloud of vapour arrived on target—and a matter-antimatter reaction involving even a few milligrams would have produced an awesome firework display.

Norton, like all space commanders, was a cautious man.