The Dark Side of the Sun by Terry Pratchett

Hrsh-Hgn, 'You'd heard of Ghost Stars, Dom?'
    'Uhuh. So dense that not even gravity escapes from them.'
    'Now this is just an idea to kick about, I'm just dropping it on the plate to see if anyone pours mayonnaise on it, but you could outfit an entire solar system with matrix engines and drop it into interspace,' said Isaac. Dom was about to laugh, but looked sidelong at Hrsh-Hgn.
    'That's the legend of the Prodigal Sun,' said Hrsh-Hgn, 'A low-temperature Creapii story. Yes, you could do it in about fifty years time, at our present rate of technological expanssion. The catalytic power would not have to be too great. But the practical application of the matrix equation makes it impossible.' He caught Dom's blank expression. 'You see, you do not need a great deal of power to drop even a large mass in and out of interspace.'
    Hrsh-Hgn used more technical language to explain that it was the on-board computer that really counted. Since a body in interspace was theoretically everywhere at the same time and would if randomly dropped out almost certainly materialize in the centre of the nearest solar body, the navigational matrix computer was very necessary. It had to be big - 'everywhere' was a large volume to be quantified. The bigger the body, the greater chance of error, so the bigger the computer.
    'The sundog carrying us now registered a current drain in microamps to achieve interspace. 'It's little more than a mental discipline. Four fifths of its body iss a hind-brain designed to locate it accurately with regard to the datum universse, with fortunately just enough sspare capacity to allow for the extra mass of a medium-ssized sship.
    'To get a medium-range star successfully through interspace you'd have to have a computer about one hundred times its mass.'
    'How about one planet?'
    
    
    asked Dom.
    'The graphs meet at planets like Phnobis or Widdershins, small and dense. You could just about do it if you hollowed out the world and filled it with computers. But this is a fruitless line of sspeculation. Personally I believe that the Jokers—'
    Illusion.
     
    Ig was keening. Dom opened his eyes and blinked. He was soaked in sweat. One arm ached.
    At the far end of the cabin Hrsh-Hgn had been thrown like a doll across the gear locker.
    'Isaac?'
    The robot let go of the handrail that ringed
One Jump's
cabin.
    'Rough, huh?' he asked.
    'I feel like someone just hit me with something large, like a planet,' said Dom. 'Or a large asteroid. What's happened?'
    'We're between stars. It looks as though the sundog dropped out rather clumsily.'
    Dom floated up, trying to quieten his stomach. It appeared to be knotted. His head ached.
    Hrsh-Hgn groaned and woke. 'Frghsss—' he swore.
    'Sundog?' said Dom to the empty air.
    Apologies. Journey interrupted owing to circumstances beyond control. Disturbance in interspace matrix space-frame. We must detour in datum space.
    Isaac was glued to the deep radar.
    'It's still several million kilometres away - it must be throwing one hell of an interspace shadow. It's taking its time. It's a cone - oh, my, will you look at that!'
    They stared into the screen. On maximum magnification it showed a pyramid tumbling deceptively slowly through space, flashing faintly as starlight caught its polished faces. There was no mistaking the outline of a Joker tower.
    Dom swam into the pilot seat and asked the sundog to take them in closer. In a few minutes they were a few kilometres away. The tower hung steady against a starfield that spun like a mad planetarium.
    'The Institute of Joker Studies pays a million standards bounty for details of new towers,' said Dom, 'I want to catch it.'
    'In a pig's eye,' said Isaac. 'That mass at that speed? It's
    
    
    a job for twenty sundogs.'
    Right.
    'Well, we can plot its course. There's a reduced bounty for that sort of information. We could split it three ways.'
    Four ways.
    'Okay, four—'
    Dom struggled for breath. Something had caught him in a vice, and was squeezing