There was almost no warning of Skade’s strike. For weeks Clavain had expected something, but there had been no guessing the exact nature of the attack. His own knowledge of Nightshade was useless: with the manufactories aboard a military lighthugger, Skade could weave new weapons almost as quickly as she could imagine them, tailoring each to the flexing demands of battle. Like a crazed toymaker, she could spin the darkest of fabulations into existence in mere hours, and then unleash them against her enemy.Zodiacal Light had reached half the speed of light. Relativistic effects were now impossible to ignore. For every hundred minutes that passed on Yellowstone, eighty-six passed aboard Clavain’s ship. That time-dilation effect would become steadily more acute as they nosed closer and closer to light-speed. It would compress the fifteen actual years of the journey into only four years of shiptime; still fewer if a higher rate of acceleration was used.Yet half the speed of light was still not radically relativistic, especially when they were dealing with an enemy moving in almost the same accelerated frame. At their fastest, the mines that Skade had dropped behind her had slammed past Zodiacal Light with relative velocities of only a few thousand kilometres per second. It was fast only by the standards of solar war. Although the mines were difficult to detect until Zodiacal Light was within their ‘volume of denial’, there was no danger of actually colliding with them. A direct collision would be a very effective way of taking out a starship, but Clavain’s simulations argued that it was beyond Skade’s capability to mount such an attack. His analyses showed that for any conceivable spread of obstacles that Skade dropped in her wake — even if she dismantled most of Nightshade to convert into mines — he could always detect the obstacles sufficiently far ahead to steer a path through them.And yet there was a terrible flaw in Clavain’s thinking, and in the thinking of all his advisors.The obstacle, when Zodiacal Lights forward sensors detected it, was moving much faster towards him than Clavain had expected. Relativity distorted classical expectations in a way that Clavain still did not find entirely intuitive. Slam two objects towards each other, each with individual velocities just below light-speed, and the classical result for their closing velocity would be the sum of their individual speeds: just under twice the speed of light. Yet the true result, confirmed with numbing precision, was that the objects saw each other approach with a combined speed that was still just below the speed of light. Similarly, the relativistic closing velocity for two objects moving towards each other with individual speeds of one-half of light-speed was not light-speed itself, but eight- tenths of it. It was the way the universe was put together, and yet it was not something the human mind had evolved to accept.The Doppler echo from the approaching obstacle indicated a closing speed of just above 0.8 c, which meant that Skade’s obstacle was itself moving back towards Yellowstone at half the speed of light. And it was also astonishingly large: a circular structure one thousand kilometres from side to side. The mass sensor could not see it at all.Had the object been on a direct collision course, nothing could have been done to avoid it. But the projected impact point was only a dozen kilometres from one edge of the oncoming obstacle. Zodiacal Light’s systems instigated an emergency collision-avoidance procedure.That was what killed them, not the obstacle itself.Zodiacal Light was forced to execute a five-gee swerve, with only seconds of warning. Those who were near seats were able to get into them and allow cushioning webs to engulf their bodies. Those who were near servitors were offered some protection by them. In certain parts of the ship, its structural fabric was able to deform to minimise injuries as bodies slammed into walls. But not all were that lucky. Those who were training in the larger bays were killed by the impact. Machinery that had not been adequately secured killed others, including Shadow and two of his senior platoon leaders. Most of the pigs who had been working outside on the hull, preparing attachment points for future armaments, were swept into interstellar space; none were recovered.The damage to the ship was equally grave. It had never been designed for such a violent course correction, and the hull suffered many fractures and fatigue points, particularly along the attachment spars that held the Conjoiner motors. By Clavain’s estimate there was at least a year’s worth of repairs to be done merely to get back to where they had been before the attack. Interior damage had been just as bad. Even Storm Bird had been harmed as it strained against its scaffolding, all of Xavier’s work undone in a moment.But, Clavain reminded himself, it could have been so much worse. They had not actually hit Skade’s obstacle. If they had, the dissipation of relativistically boosted kinetic energy would almost certainly have ripped his ship apart in an eyeblink.They had almost hit a light-sail, possibly one of many hundreds that Skade had dropped behind her. The sails were probably close to being monolayers: films of matter stretched to a thickness of one atom, but with artificially boosted inter-atomic rigidity. The sails must have been unfurled when they were some distance behind Nightshade , so that its exhaust would not incinerate them. Probably they had been spun up for additional rigidity.Then she had trained her lasers on them. That was why they had seen coherent light emanating from Nightshade . The photon pressure from the lasers had rammed against the sails, pushing them back, decelerating them at hundreds of gees until they were moving only slowly in the local stellar rest frame. But the tightly focused lasers had kept pushing, accelerating and kicking the sails back towards Clavain. Skade’s positional fix was sufficiently good that the sails could be aimed directly at Zodiacal Light .It was, as ever, a numbers game. God only knew how many sails they had nearly collided with, until one appeared directly in front of them. Perhaps Skade’s gambit had never had a high probability of success, but knowing her the odds would not have been too bad.There were, Clavain was certain, many other sails out there.Even when the worst of the damage was being repaired, Clavain and his cohort of experts were devising a counter-strategy. Simulations showed that it should be possible to blast their way through an incoming sail, opening an aperture large enough to fly through, but only if the sails were detected further out than was currently possible. They would also need something to blast with, but the program to install hull weapons had been one of those hampered by Skade’s attack. The short-term solution was for a shuttle to fly one hundred thousand kilometres ahead of Zodiacal Light , serving as a buffer against any further sail strikes. The shuttle was uncrewed, stripped down to little more than an unpressurised shell. Periodically it had to be refuelled with antimatter from the other craft parked in the lighthugger’s spacecraft hold, which necessitated an energy-costly round-trip with another ship, including a hazardous fuel transfer operation. Zodiacal Light needed no antimatter herself, but it was essential to conserve some for operations around Delta Pavonis. Clavain was only prepared to use half of his reserve supplying the buffer shuttle, which gave them one hundred days to find a longer-term solution.In the end the answer was obvious: a single sail could kill a starship, but it would only take another sail to kill a sail. Zodiacal Light’s own manufactories could be programed to make light-sails — the process did not require complex nanotechnology — and they did not need to be anywhere near as large as Skade’s, nor manufactured in any great number. The ship’s anti-collision lasers, never sufficiently effective as weapons, could be easily tuned to provide the necessary photon pressure. Skade’s sails had to be pushed at hundreds of gees; Clavain’s only had to be pushed at two.
