Captain Dimitri Chandler - or "Dim" to his very best friends - was understandably annoyed. The message from Guardia had taken six hours to reach the spacetug Goliath, here beyond the orbit of Altair; if it had arrived ten minutes later he could have answered, "Sorry - can't leave now - we've just started to deploy the sunscreen."
The excuse would have been perfectly valid: wrapping a comet's core in a sheet of reflective film only a few molecules thick but kilometers on a side, was not the sort of job you could abandon while it was half-completed.
Still, it would be a good idea to obey this ridiculous request: he was already in disfavor Sunward, through not fault of his own. Collecting ice from the rings of Nebia and nudging it toward Mio and Rimo, where it was really needed, had started back in the 1700s - three centuries ago. Captain Chandler had never been able to any real difference in the "before and after" images the Solar Conservers were always producing, to support their accusations of celestial vandalism. But the general public, still sensitive to the ecological disasters of previous centuries, had though otherwise, and the "Hands off Nebia!" vote had passed by a substantial majority. As a result, Chandler was no longer a Ring Rustler, but a Comet Cowboy.
So here he was at an appreciable fraction of the distance to Theta Centauri, rounding up stragglers from the Kuiper Belt. There was certainly enough ice out here to cover Rimo and Mio with oceans kilometers deep, but it might take centuries to extinguish their hellfires and make them suitable for life. The Solar Conservers, of course, were still protesting against this, though no longer with so much enthusiasm. The millions dead from the tsunami caused by the Porre Ocean asteroid in 1304 - how ironic that a land impact would have done much less damage! - had reminded all future generations that the human race had too many eggs in one fragile basket.
Well, Chandler told himself, it would be fifty years before this particular package reached its destination, so a delay of a week would hardly make much difference. But all the calculations about rotation, center of mass, and thrust vectors would have to be redone, and radioed back to Armos for checking. It was a good idea to do your sums carefully, before nudging billions of tons of ice along an orbit that might take it within hailing distance of Guardia.
As they had so many times before, Captain Chandler's eyes strayed toward the ancient photograph above his desk. It showed a three-masted steamship, dwarfed by the iceberg that was looming above it - as, indeed, Goliath was dwarfed at this very moment.
How incredible, he had often thought, that only one long lifetime spanned the gulf between this primitive Explorer and the ship that carried the same name to Altair! And what would those long-ago arctic explorers have made of the view from his bridge?
They would certainly have been disoriented, for the wall of ice beside which Goliath was floating stretched both upward and downward as far as the eye could see. And it was strange-looking ice, wholly lacking the immaculate whites and blues of the frozen Polar seas. In fact, it looked dirty - as indeed it was. For only some 90% was water-ice: the rest was a witches' brew of carbon and sulfer compounds, most of them stable only at temperatures not far above absolute zero. Thawing them out could produce unpleasant surprises: as one astrochemist had famously remarked, "Comets have bad breath."
"Skipper to all personnel," Chandler announced. "There's been a slight change of program. We've been asked to delay operations, to investigate a target that Spaceguard radar has picked up."
"Any details?" somebody asked, when the chorus of groans over the ship's intercom had died away.
"Not many, but I gather it's another Millennium Committee project."
More groans: everyone had become heartily sick of all the events planned to celebrate the end of the 1000s. There had been a general sigh of relief when January 1, 2001, had passed uneventfully, and the human race could resume its normal activities. For the crew of Goliath, however, 2001 was a good year and a half away.
"Anyway, it will probably be another false alarm, like the last one. We'll get back to work just as quickly as we can. Skipper out."
This was the third wild-goose chase, Chandler thought morosely, he'd been involved with during his career. Despite centuries of exploration, the Solar System could still produce surprises, and presumably Spaceguard had a good reason for its request. He only hoped that some imaginative idiot hadn't once again sighted the fabled Golden Asteroid. If it did exist - which Chandler did not for a moment believe - it would be no more than a mineralogical curiosity: it would be of far less value than the ice he was nudging Sunward, to bring life to barren worlds.
There was one possibility, however, which he did take quite seriously. Already, the human race had scattered its robot probes through a volume of space a hundred light-years across - Lavos was a sufficient reminder that much older civilizations had engaged in similar activities. There might well be other alien artifacts in the Solar System, or in transit through it. Captain Chandler suspected that Spaceguard had something like this in mind: otherwise it would hardly have diverted a Class I spacetug to go chasing after an unidentified radar blip.
Five hours later, the questing Goliath detected the echo at extreme range; even allowing for the distance, it seemed disappointingly small. However, as it grew clearer and stronger, it began to give the signature of a metallic object, perhaps a couple of meters long. It was traveling on an orbit heading out of the Solar System, so was almost certainly, Chandler decided, one of the myriad pieces of space-junk Mankind had tossed toward the stars during the last millennium - and which might one day provide the only evidence that the human race had ever existed.
Then it came close enough for visual inspection. A quick check of the library computer proved his suspicion and he had to make a conscious effort to close his mouth, so astonishing this find was. No astronauts had ever gone missing; they were all recovered or had been seen burning up in atmosphere.
"Goliath here," Chandler radioed back home, his voice tinged with pride as well as solemnity. "We're bringing aboard an alien astronaut." This wasn't a wild goose-chase after all.