navigating in a galaxy.

Look, we're travelling faster than the speed of light. That means by the time we see something, we've already passed through it. Even with an IQ of 6000, it's still brown trousers time

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As you can see, yes it's definitely a problem. Which is why you need a computer with an IQ of six thousand and nerves of steel.

A virus in the computer would have far more effects than that though. Environmental systems, air supply..you name it. It's brown trousers time.

Yes, but it's probably still safer than driving.

Nicole

Nivarion said:

I was playing a game called Freelancer the other day when a thought hit me. How would we navigate in space, especially between solar systems.

Unless you had a means of keeping track of every single star and your exact position, you could be lost in an instant at FTL speed. I mean, there is no north or south, up or down in space. and in a galaxy you can't really see its center.

and if you did have a means of keeping track of where you were any little problem could send you hurtling into a star or into a black space where you would get lost and not be able to be found.

a problem could be a virus, a power outage or any little thing that computers like to do to us.

just some wondering.

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Good points. Among the problems of FTL, the problem of running into something doesn't often come up (thank God for Hyperspace and subspace and all the other imaginary spaces where there's nothing to run into)...

Lately I've been pondering navigation for my WIP. In my story, people travel from world to world, but only certain points allow travel to certain other points, and I've been trying to figure out how travelers would carry maps of such a thing (short of the map from Time Bandits or something).

I've been pretty intrigued with Polynesian Stick Charts. It's basically a flat 3-d representation of different islands and the currents and winds around them to help navigators who didn't have compasses, maps, clocks, sextants, or astrolabes.

With a detailed enough physical 3-d map of your general corner of the universe (i dunno, made of metal or something, and knowing the distance to and relative location of the stars, wouldn't it be possible to pinpoint where you generally are? I mean, it would be hard, but when your computer breaks down...

Depending on how much fatser than light, wouldn't say, a signal beacon be useful?

Star navigation is still taught today. Calculating your position from surrounding stars is far from impossible, ditto computers identifying main sequence stars and building a 3D model.

I've read Golden Age Sci-Fi stories whose time-hopping characters could calculate the year just by looking at the positions of familiar stars in the distant past or far future -- and no one appeared to think twice about this awesome ability back then, in the days when computers barely existed except as rudimentary mechanical devices.

You're only going to collide with a star if you don't know your speed and heading -- if unpredictable random variables throw off your calculations. Who would even set off under such dangerous circumstances? Then again, maybe that's a story in itself...

For your story, all you have to come up with is something feasible, with one toe grounded in reality.

-Derek

Well, every star has a certain magnitude and spectrum. Particularly bright stars with easily recognisable spectra could be used as landmarks (spacemarks?). Also, there are pulsars here and there which emit pulses (hence the name) of x-rays or gamma rays at various intervals. These easily detected pulses could also help orient your spacecraft.

There is also a possibility of man-made radio beacons at set points to guide spacecraft. Before GPS, and after World War 2 or so, thats how ships primarily navigated on our oceans, it being easier and more reliable to follow a beacon than the sun or stars.

There is another problem that I *never* see discussed.

Ever tried spearfishing? The fish isn't where it appears to be, it's below. The refraction of the water displaces its image.

What does this have to do with navigation, you might ask? After all, space is a vacuum, right?

Well, the problem is that stars aren't where they appear to be. See, light takes time to reach us. What we are seeing is where the star *was*, not where it is. The farther away the star is, the further out of date our position information is.

Well, that seems simple enough, right? Just advance the star to its projected location, in our database, then perform your calculations. Except that isn't so easy, either, because the gravity of other stars will affect its orbit. *Has* already affected its orbit. And they aren't where they appear to be, either. So you have to solve for the current locations of *all* the other stars which can affect the orbits, to get their correct trajectories through time.

By the time you do all that, the map of the galaxy looks quite different than what most star charts look like.

And, when you get where you are going, you're coming in blind, because the news of anything that happened there recently (star collisions, supernovas, etc) never reached you, before you made your FTL jump.

Then, when you get to your new location, all the stars will look out of position, because the light reaching your new position has been travelling a while. If you know where you are, and you know where the other stars are, it's not so bad to predict what the sky should look like. But if you don't know where you are, it gets a lot more complicated. You need to solve for the star's location in 4 dimensions, not just 3. You need to solve for multiple stars, to triangulate your position. But to do that you need to first identify the stars. Since we generally identify stars by their position, it's difficult. Their spectrums are often similar.

I suppose you could just stay at home and weed the vegetable garden . . .

The major stars act as Guidepoints for computing your location. It's a little bit more complicated than earthbound triangulation, because the stars and galaxies ARE moving, but its not that much more complicated. Assuming you're far enough into the future to HAVE FTL available, its not small assumption to figure that the computers will compute doppler shifts, and galaxy trajectories when 'taking a heading' off the guide stars.

We're getting smarter everyday regarding this. Take a look here;

http://news.bbc.co.uk/2/hi/science/nature/7813635.stm

Turns out our galaxy is much larger than we thought. And we 'measured' it by good old 'triangulation' between raidio telescope arrays here on Earth.

As to 'running into things' - I recall a discussion I had with an honest to God 'rocket scientist' who laughed at the line from Star Wars about 'winding up in a Super Nova'. He says that there is so much "Nothing" out there, that the chance of hitting anything is incredibly miniscule.

Flying through hyperspace ain't like dusting crops, boy.

WriteKnight said:

The major stars act as Guidepoints for computing your location. It's a little bit more complicated than earthbound triangulation, because the stars and galaxies ARE moving, but its not that much more complicated. Assuming you're far enough into the future to HAVE FTL available, its not small assumption to figure that the computers will compute doppler shifts, and galaxy trajectories when 'taking a heading' off the guide stars.

We're getting smarter everyday regarding this. Take a look here;

http://news.bbc.co.uk/2/hi/science/nature/7813635.stm

Turns out our galaxy is much larger than we thought. And we 'measured' it by good old 'triangulation' between raidio telescope arrays here on Earth.

As to 'running into things' - I recall a discussion I had with an honest to God 'rocket scientist' who laughed at the line from Star Wars about 'winding up in a Super Nova'. He says that there is so much "Nothing" out there, that the chance of hitting anything is incredibly miniscule.

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So are the odds of being hit by lightning.

Or running into an iceberg on the world's largest luxury liner.

But it happens.

MargueriteMing said:

There is another problem that I *never* see discussed.

Ever tried spearfishing? The fish isn't where it appears to be, it's below. The refraction of the water displaces its image.

What does this have to do with navigation, you might ask? After all, space is a vacuum, right?

Well, the problem is that stars aren't where they appear to be. See, light takes time to reach us. What we are seeing is where the star *was*, not where it is. The farther away the star is, the further out of date our position information is.

Well, that seems simple enough, right? Just advance the star to its projected location, in our database, then perform your calculations. Except that isn't so easy, either, because the gravity of other stars will affect its orbit. *Has* already affected its orbit. And they aren't where they appear to be, either. So you have to solve for the current locations of *all* the other stars which can affect the orbits, to get their correct trajectories through time.

By the time you do all that, the map of the galaxy looks quite different than what most star charts look like.

And, when you get where you are going, you're coming in blind, because the news of anything that happened there recently (star collisions, supernovas, etc) never reached you, before you made your FTL jump.

Then, when you get to your new location, all the stars will look out of position, because the light reaching your new position has been travelling a while. If you know where you are, and you know where the other stars are, it's not so bad to predict what the sky should look like. But if you don't know where you are, it gets a lot more complicated. You need to solve for the star's location in 4 dimensions, not just 3. You need to solve for multiple stars, to triangulate your position. But to do that you need to first identify the stars. Since we generally identify stars by their position, it's difficult. Their spectrums are often similar.

Click to expand...

I just use Google Galaxy.

MargueriteMing said:

Well, the problem is that stars aren't where they appear to be. See, light takes time to reach us. What we are seeing is where the star *was*, not where it is. The farther away the star is, the further out of date our position information is.

Well, that seems simple enough, right? Just advance the star to its projected location, in our database, then perform your calculations. Except that isn't so easy, either, because the gravity of other stars will affect its orbit. *Has* already affected its orbit. And they aren't where they appear to be, either. So you have to solve for the current locations of *all* the other stars which can affect the orbits, to get their correct trajectories through time.

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I've seen this handled through "course corrections". You make one jump, look ahead, rerun your calculations with the updated data and jump again. Do a few jumps like this and you should be able to minimise any surprises, I would have thought.

Nivarion said:

Unless you had a means of keeping track of every single star and your exact position, you could be lost in an instant at FTL speed. I mean, there is no north or south, up or down in space. and in a galaxy you can't really see its center.

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Actually, you only need three known stars to get your location in space (Yes, Stargate got it really about as wrong as claiming the moon is made from cheese), and finding three known stars is very easy for a computer. Basically, you just have a 3D map of the stars in your computer and whenever you get lost you just map out the position of the nearest three stars and let the computer find them on the map. This will also be greatly helped by the fact that you could also find them by emitted spectrum and size as well as by relative position.
And saving the 3D position of every known star including spectrum and size is pretty trivial even given today's harddisk space.

and if you did have a means of keeping track of where you were any little problem could send you hurtling into a star or into a black space where you would get lost and not be able to be found.

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Uh, no. There is no "black space". Since space is really really empty, stars are visible from everywhere. There's nothig to stop the light. And also, if you know one fact about space make it "Space is empty". It is very, very hard to hit something in space, even if you aim for it. Not accidentally crashing into planets (or stars) is about as much of a safety concern as meteorite proofing for cars. Actually. Much less.
The real problem is not getting lost or crashing, but getting stuck inbetween stars if your FTL drive doesn't work. You know where you are but you can't get away, and noone is ever going to find you. (remember, space is emtpy) And your standard communication laser will get the message to the nearest settled world in ten years time. Have fun surviving until then.

a problem could be a virus, a power outage or any little thing that computers like to do to us.

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That's why you always have physical backup computers for anything vital. We do it for powerplants (actually, we do it for accounting and tax records) so we'd definitly do it for spaceships.

MargueriteMing said:

<snip>Well, the problem is that stars aren't where they appear to be.<snip>

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While certainly problems, it's nothing that can't be compensated for. We today can do, with ever advancing calculation power of computers it will never be a problem in future. And add the fact that those are not effect on an order of magnitude that is important for space navigation. I.e. until you travel in your space ship for a few hundred years, you don't need to care about itragalactic movement of stars. Just update you starcharts at the planetary university's astrography department every 50 years or so and you're good to go.

An interesting thing i notice is that many people have no real conception of what things are easy for a computer to do and what things aren't. Not that i blame them for not being geeks, but take it as a good advice for any aspiring S-F writer to ask your geekiest buddies on topics like that.
Not that it hurts sales, Weber sells pretty well and has no friggin clue about what is a possible task for a computer and what isn't as he prominently displays in his Honorverse.

ElaraSophia said:

I've seen this handled through "course corrections". You make one jump, look ahead, rerun your calculations with the updated data and jump again. Do a few jumps like this and you should be able to minimise any surprises, I would have thought.

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Actually, making multiple jumps is more dangerous.

You see, since you are FTL, you never get accurate info about where you are jumping to. So, each jump you make, you have the same chance of running into some surprise. So, each additional jump adds to your risk.

Lhun said:

Actually, you only need three known stars to get your location in space (Yes, Stargate got it really about as wrong as claiming the moon is made from cheese), and finding three known stars is very easy for a computer. Basically, you just have a 3D map of the stars in your computer and whenever you get lost you just map out the position of the nearest three stars and let the computer find them on the map. This will also be greatly helped by the fact that you could also find them by emitted spectrum and size as well as by relative position.
And saving the 3D position of every known star including spectrum and size is pretty trivial even given today's harddisk space.

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I don't think you understood my post at all.

I'll try again. You make a jump, have a malf, and are off course. You could be anywhere. You want to figure out where you are.

You say "Simple, triangulate on 3 stars".

Not so simple.

To start with, there are roughly 400 billion stars in MW. This is an estimate, we can't count them. Actually, we can't even really see the other side of the galaxy too well, it is obscured by the galactic core, and a lot of the disc is obscured by dust clouds. So if you jump far enough you are in uncharted territory.

But even if you can see stars that you know, you can't just triangulate on them. They move, depending on where you are. Hmm, this is hard to explain.

Let's try this:

We'll clear the sky out, mostly, to make things easier. Imagine the MW core, and a star, Marker1, orbiting it, 25K LY out. Now, put your position at 50K LY out, looking back at our marker star. Trace a line from your position to the star. Add a few more stars Marker2, Marker3, Marker4, and draw lines to them, and you can triangulate your position, right?

Here is the problem. In your original position, your data is 25,000 years old. You see where the star was 25,000 years ago. Imagine that you now coast in 1000 LY over a few seconds. Your data is now 1000 years newer. You are now seeing where the star was 24,000 years ago. In other words, the star moved along its orbit 1000 years as you changed position. Your line of bearing to the star changes based on where you are, but worse, the location of the star changes based on where you are. So you can't just pick a star, take a sighting, and figure out where you are. You need to figure out how far away the star is, so you know where it looks to be.

The problem is, you don't know your own position, so you can't tell how far away the star is, so you don't know where it should be. It's a catch-22.

Lhun said:

While certainly problems, it's nothing that can't be compensated for. We today can do, with ever advancing calculation power of computers it will never be a problem in future. And add the fact that those are not effect on an order of magnitude that is important for space navigation. I.e. until you travel in your space ship for a few hundred years, you don't need to care about itragalactic movement of stars. Just update you starcharts at the planetary university's astrography department every 50 years or so and you're good to go.

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There aren't all that many stars within 100 LY. To go anywhere, you're going to be moving around a lot. That makes temporal stellar location of critical importance.

An interesting thing i notice is that many people have no real conception of what things are easy for a computer to do and what things aren't. Not that i blame them for not being geeks, but take it as a good advice for any aspiring S-F writer to ask your geekiest buddies on topics like that.
Not that it hurts sales, Weber sells pretty well and has no friggin clue about what is a possible task for a computer and what isn't as he prominently displays in his Honorverse.

Click to expand...

I have a BS in computer science, I have some idea. Nothing is simple or hard for a computer to do. Things are simple or hard for programmers to do.

Recording stellar spectrums is all well and good, but what evidence do we have that spectrums remain constant over time? We only have 100 years of photographic evidence. Stars are fusion engines, their composition (and hence their radiated spectra) change with time. The best thing to do is visit each star. record it's spectrum up close, to get current data. Then travel away from the star for 25K or 50K LY, recording the changes, so you can match the spectra based on how far away you are. But, there are 400 billion stars in MW, there are bound to be a lot of similarities, since stars tend to follow the same rules, fusing hydrogen into heavier and heavier elements, up to iron.


But, there is another solution. Assuming your jump didn't take you out of MW, use bearings to other galaxies for astrogation. With their greater distance, you will get less temporal drift in their locations based on your location.

But anyway, I brought this up because I've never seen it mentioned in a novel before. Hard science fiction is supposed to contain hard science, but a lot of them don't do that good a job.

Lhun said:

The real problem is not getting lost or crashing, but getting stuck inbetween stars if your FTL drive doesn't work. You know where you are but you can't get away, and noone is ever going to find you. (remember, space is emtpy) And your standard communication laser will get the message to the nearest settled world in ten years time. Have fun surviving until then.

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Oh, they can find you. You made that very clear in another thread here (realistic space warfare). If you run out of gas, just light up a cigarette.

Granted, it may take AAA awhile to get to you, depending upon which stars you ran outta gas between.

MargueriteMing said:

There aren't all that many stars within 100 LY.

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There are several thousand within 100 LY. It's peanuts next to the galaxy as a whole, but it's certainly enough to keep explorers and colonists occupied for quite some time.