Have you ever gone to a carnival and tried out the shooting gallery: the ones where you use a BB gun to plink over metal duckies as they swim across a shelf in the back of the booth? Even if the carney has not messed with the sights so the BB does not go where you think it will, you may have found hitting a moving target to be a challenge.
If the carnival shooting gallery isn’t challenging enough, try skeet shooting – with a rifle, not a shotgun – and you’ll get closer to the challenge of shooting a space ship from one planet to another, let alone from one star to another.
Galaxy M1 Courtesy NASA
I found a comment left on one of Greta van der Rol’s blog posts interesting: the discussion was of a space ship coasting to a stop in space because the engine failed. This will not happen, but he asked, “Coast to a stop – relative to what?” And he made the point of my next post in an elegantly succinct manner. The biggest issue in flitting around space is that everything is in motion.
If we board an aircraft in New York and fly to London, noodle around for a week then fly back; New York is almost always right where we left it. We can use landmarks, compass headings & distance and now GPS satellite signals to travel from one point on our globe to another with little risk of missing our mark – unless we’re using iMaps: then it’s hard to say where you will end up! But in outer space – even interplanetary space – things are very different. Everything in our solar system orbits around our sun. We can use the sun as one fixed point of reference, but everything else is in motion and moving from one place to another requires a lot of complicated mathematics to calculate a trajectory that will put us in the place our destination will be when we get there. In marksmanship terms, we must “lead the target”: shoot for where it will be, not where it is now.
Once we leave our planetary system, things get a bit more strange, for our sun is no longer a fixed reference point; our solar system is in motion relative to the rest of the galaxy. If you think finding your car in the shopping mall parking lot is a challenge, how would you feel if sections of the lot could move around? What if light pole 6B was not guaranteed to be 4 rows to the left of the Penny’s main entrance, but could be closer to Sears when you were ready to leave? That would throw a wrinkle into things wouldn’t it? I’d be using the valet parking for sure!
We hop on an interstellar space ship bound for a distant star, noodle around for a few months collecting souvenirs and photographing the local flora and fauna, then head back home. But wait: home is not where we left it! Now what?
As Sci-Fi writers we can simply type, “Ensign Saunders, plot a course.” and we’re on our way. No need to wallow around in the details of interstellar navigation. But, isn’t this a bit like saying, “I have a calculator, why do I need to learn the multiplication tables?” Sometimes, as a writer, wallowing in the details can add depth to your writing. So, how might we chart a galaxy so that our ships could reliably navigate through it? What would we use for landmarks when the land is fluid?
Navigation by Coordinates.
There is a galactic coordinate system in use now. The galactic coordinate system is a celestial coordinate system in spherical coordinates, with the Sun as its center, the primary direction aligned with the approximate center of the Milky Way galaxy, and the fundamental plane approximately in the galactic plane. It uses the right-handed convention, meaning that coordinates are positive toward the north and toward the east in the fundamental plane.This is a great way to plot celestial bodies as viewed from Earth, but I think we’ll find its usefulness limited once we start bebopping about in other neighborhoods.
A computer model of the galaxy could, with sufficient memory and processing power, keep track of the gazillion stars and other celestial bodies in our galaxy. Such a computer will need to be powerful enough to make Oak Ridge National Laboratory’s Titan supercomputer (which resides down the road from me in Oak Ridge Tennessee, and is currently the world’s fastest computer) look like a child’s toy. But if you can plunk down a You Are Here pin on the map, you could calculate a course that will put you in the right spot when your destination gets to where it will be when you get there… and, hopefully, avoid hitting anything substantial while en route. This is fine if you have a careful record of where you have been, but how do you figure out where you are if you’re not sure?
Navigating by Beacons
A network of beacons or satellites that emit a constant signal could be established and used as guide posts. Of course the beacons will be moving along with everything else, but if LaGrange points are chosen so the beacons can float along in relatively fixed positions relative to the rest of the galaxy their guidance should be useful. The bigger problem is that radio signals will take tens of thousands of years to span interstellar space and laser disperses quickly. Both signals are likely to become lost in the galactic background noise, making them of use only at relatively close range anyway. And the cost of setting up and maintaining a system of intergalactic lighthouses… let’s not even go there!
A better system would be to use powerful, natural phenomena as sign posts. Like pulsars. The European Space Agency’s Ariadna initiative is examining the feasibility of navigation relying on millisecond pulsars; rotating neutron stars that spin faster than 40 revolutions per second. Each star is unique in its timing interval. Locate three of them in your proximity and you can triangulate your current position on that wondrous computerized star map your ship carries around. A ship with optical sensors could do this autonomously. Galactic GPS.
Using pattern recognition software and constellations comes to mind as well. But again, as we travel around, and view the constellations from different angles, their shape will change. That pat-rec software will have to be really sophisticated to handle that!
My money is on the pulsars and a star map in a bio-mega-super computer, but I’d be very interested in hearing any other ideas you might have.
Others in this series:
Science Fiction Fact & Fancy: Space Travel
Science Fiction Fact & Fancy: Propulsion-Engines
Science Fiction Fact & Fancy: Propulsion-Exotic
Space: A Really Dangerous Place to Live
Science Fiction Fact & Fancy: Navigation