Thursday, November 10, 2016

How do you leave breadcrumbs in space?

One of the givens in any space opera is the ability to move through space (relatively) quickly from one place to another. Some people use worm holes. Others use plain old hyperspace. In the Star Wars universe moving from one star system seems to be a bit like driving your car across town. Sometimes stories are written about generation ships which travel through normal spacetime over incredibly long time frames.

That's all well and good. But there aren't any roads in space. Of course, all those ships transporting people around have wonderful navigation systems. The issue, though, is that distance and direction on planet Earth are all based on constants. Locations on the surface have precise coordinates, given in latitude and longitude. Latitude is based on the distance north of south from the equator, and longitude is based on the distance east or west from a given base line (0) which we humans have decided passes through Greenwich in the UK. In the past, longitude was found to be exceptionally difficult to measure. It wasn't until the invention of extremely accurate clocks that we could get it pretty right. To quote Wikipedia "Longitude at a point may be determined by calculating the time difference between that at its location and Coordinated Universal Time (UTC)." It's an over-simplification, but we don't need more than that for this discussion.

The point is that in order to navigate between two places, you need to know the position of those two places based on two 'knowns' – your start point, and your end point. Sure, you can recalculate en route. Aircraft do it all the time, because they work in three dimensions: latitude, longitude and height. I assume submarines do, too. If we look at space, working out how to get to other planets has already been done successfully many times. But the further we go, the harder it gets. This io9 article explains it better than I could.

So why do I care? Because my current WIP is very much about following a specific journey made by space-farers in the distant past. There aren't any roads, so I need breadcrumbs, or a ball of string, and I'm not sure how to make it work.

Ah well. That's one of the joys – and the frustrations – of writing science fiction.


  1. I always loved the navigation explanation in Stargate. The geek explains how you needed seven symbols (the co-ordinates) to travel anywhere in three dimensional space: six points = three lines intersecting to pinpoint a destination.
    "But you said seven."
    "Six for the destination. The seventh is your point of origin."
    The gates they use for transportation are all fixed points on their planets (though of course the planets are moving) but all you had to do was dial in the seven co-ordinate address to be instantly transported to the chosen planet. Fun.

  2. Great post, Pippa! Yes, navigation in space is vastly more complicated. On Earth navigating from, say, one port to another doesn't entail the destination point moving, but that happens in space. Where the destination point is going to be when you get there is part of that complex calculation, and it depends on the length of time it takes to travel the distance. Just looking at calculations needed to navigate from Earth to neighboring Mars are boggling enough, just wait until we attempt to travel to other solar systems.

  3. For your story: Maybe, they constantly stopped at planets and carved a comment in stone or built some long suriving obelisk, before leaving. or they scar the planets with a powerful weapon as they pass through, like a trail marker on a tree.

    per your original question: we might have sent stationary beacons in our traveled universe that enables all pilots to have a superb and accurate perception of where they are by the beacons that feed them the proper dimensional info since absolutely nothing is being still, except for the beacons...and maybe not even them since they will probably be tugged around by their galaxy. Just the thought of the math involved gives me a migraine, but my organic computer named Marybell could no doubt figure it out.


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