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Interstellar Navigation, or Getting Where You Want To Go and Back Again (In One Piece)
by John G. Hemry
Category: Technology/Science
Description: Science fiction stories often deal with travel to other stars. But travel isn't just a matter of being able to cover a distance, it's also about being able to find your way to where you want to go. Navigating to other stars will pose some serious challenges, but by using our experience with earth-based navigation methods it should prove difficult but doable.
eBook Publisher: Fictionwise.com, 2000 Analog
Filament eBookStore Release Date: July 2005
 
39 Reader Ratings:
Available eBook Formats: OEBFF Format (IMP) [24 KB]
Words: 4655
Reading time: 13-18 min.
All Other formats: Printing DISABLED, Read-aloud DISABLED
Introduction
Traveling to another star system involves two fundamental problems. Problem Number One is how to go fast enough to make the journey practical in terms of human lifespan, or alternatively how to design a ship capable of traveling for centuries of real-time. That tends to be the problem Science Fiction writers (and scientists) focus on.
But there's also Problem Number Two. How do you actually get to that other star and back home again? This question is usually covered by a vague reference to 'navigation', but it's actually a very complicated problem. Throw in concerns about obstacles to safe navigation and you've got some major monkey wrenches to deal with if we ever want to actually travel to another star.
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Navigational Basics: Piloting
A look at navigation on the Earth's surface is a good way to provide a context for interstellar navigation. Specifically, this section will discuss navigation on water, because that is where methods of navigation developed and because aeronautical navigation uses essentially the same tools as surface navigation. Until the recent advent of the satellite-based Global Positioning System (GPS) (described in detail in William Walling's YOU ARE HERE! in the October, 1999 Analog), finding your way around the Earth was often a matter of educated guesses. Over millennia of exploration and travel, humans developed two basic forms of navigation.
One is called piloting, under which you receive frequent external input to your position. Prior to GPS, the most accurate form of piloting involved taking compass bearings to objects on the shore for which the exact positions are known, then extending those lines of bearing from the positions of the objects on your chart. Where the lines of bearing intersect is where you are (or rather where you were when you shot the lines of bearing). Ideally, the lines of bearing meet in a single pinpoint, but in practice they tend to form polygons of varying sizes which define the area inside which your position lies. This is especially true if you have to use other (less precise) means of piloting, such as radar. With radar, you determine the range to prominent points of land, then swing an arc out on your chart which is that distance from the point. You should lie somewhere along that arc, though this is less accurate than using lines of bearing because you can't always be sure exactly where your radar signal is bouncing off the point of land you are using.
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