Giving directions in space

[Ford Prefect]

Something which I'm having an endless amount of trouble with is coming up with a system by which positions can be given. Space is a three dimensional place, so you can't just say 'oh, a million kilometres off the port bow' and leave it at that. Who knows how you'll be orientated compared to your enemy. My only idea so far has involved giving positions through degrees from a variety axis on the ship, but that didn't work out so well in my head.

[rhoenix]

The basic idea I'm using for an idea I'm working on for a story uses the galactic center as a reference point to where you are. From there, it's simply x,y,z coordinates.

For a more wanky universe, wherein one could traverse galaxies like Star Trek warp travel does stars, finding the Big Bang Origin Point, and using that as your point of reference works, though the denominations for numbers used for coordinates would likely grow ever larger - km, to parsec, to even lightyear, perhaps something even greater.

[Ford Prefect]

I mean on a more 'tactical' scale, with ships in the same star system. The sort of situation where you enemy could potentially be off your port bow, but more likely to be bit off the towards the left side of main engine cluster.

[Ford Prefect]

Oh, and as an aside, a parsec is bigger than a lightyear.

[Eris]

The way I do it, when I write or RP scifi, is I give it as a vector relative to your ship. For ease of use, I just think of this vector as two circles perpendicularly superimposed onto each other, one along the xy plane, and the other on the xz plane, with a length associated. For instance, say a ship is relatively speaking to the left and above yours, and very far off. The report might come in that there's a contact at 28 by 43 degrees, 500,000 kilometres. That is, oriented 28 degrees off the x axis on your ship's xy plane, and 43 degrees off the x axis on your ship's xz plane, and half a million klicks distant. Substitute axes and units as needed.

It seems to be pretty fast to say and pretty clear, and not too hard to get a mental picture of, which is why I think it at least wouldn't be too implausible to use in a practical navigational setting. The only problem becomes giving coordinates to other people's ships. In that case, you can either give a coordinate relative to one of the ship's, an object in space, or just some average point. Take for instance the "centrepoint" of a fleet, and then have all fleet orders and communications done relative to that point. It's all a bit relative, but that's just a fallout of having no fixed frame of reference, and that's unavoidable.

[Lone_Prodigy]

Why not just two angles in degrees and a distance? Something along the lines of "30.067 degrees (right of the bow), 42.098 degrees (above the bow), 3012.626 kilometers (away)."

[Lone_Prodigy]

Ghetto edit: beaten by a minute.

[Sriad]

The best tactical way would probably be distance, horizontal radians, and vertical radians relative to the ship's current heading. Or degrees if you prefer. If it's in a time sensative tactical situation, whichever has fewest syllables would probably be best. If your world is still on 12-hour time, calling out 900k-8-11 is a lot faster than 900k-240-330.

Or 4/3 pi by 11/9 pi... on second thought, radians probably aren't the best for on the fly directions.

Or perhaps instead of two continuous measures, you could do one horizontal since people are most used to that, then call hours 1-5 up or down. (six would get called out as "straight" or something)

[Ford Prefect]

The way I do it, when I write or RP scifi, is I give it as a vector relative to your ship. For ease of use, I just think of this vector as two circles perpendicularly superimposed onto each other, one along the xy plane, and the other on the xz plane, with a length associated. For instance, say a ship is relatively speaking to the left and above yours, and very far off. The report might come in that there's a contact at 28 by 43 degrees, 500,000 kilometres. That is, oriented 28 degrees off the x axis on your ship's xy plane, and 43 degrees off the x axis on your ship's xz plane, and half a million klicks distant. Substitute axes and units as needed.

This is actually pretty much the idea I had, only I kept on try to work in a third circle, so it got messy. This way you can give 'double zero' or an equivalent as being straight ahead of the ship. Excellent. Thanks everybody.

[kinnison]

I think the standard way would be to define a coordinate system when you enter a new system. For example; Sol system - define zero-zero as the line from Sol to Pluto and the plane as the plane of Pluto's orbit. I'm using Pluto here because it moves the slowest and therefore would require the least frequent corrections, and in any case you could define the direction in terms of its direction at a particular time.

Or if that doesn't suit, use distant quasars as reference points - they are essentially points and of course don't move. Example; zero/zero is the line from Sol to 3C273 and the plane is defined by including another quasar; then with the angles thus obtained you simply define a distance from Sol. Come to think of it, this could be used whenever you come into a new system, without having to make the decision.

This does of course lead to problems with the ecliptic plane of the system bearing no relation to the xy plane you've just defined, but you can't have everything.

The idea of using coordinates relative to a ship's axis is of course that nobody else knows exactly which way you're pointing; however for tactical use on the ship itself the required 3D coordinate transform shouldn't be too much of a stretch. After all, wet navy captains used to learn and use spherical trigonometry. And in any case, if your ship's computer isn't capable of calculations like that you have more problems than navigation.

[Winter]

This is actually pretty much the idea I had, only I kept on try to work in a third circle, so it got messy. This way you can give 'double zero' or an equivalent as being straight ahead of the ship. Excellent. Thanks everybody.

Hmm. I don't think 'double zero' would be accepted as military terminology, especially on a ship where everything has to have a different name in order for accurate commands to be given (look at sailing terminology for an example of this).

What they'd probably do is use language similar to that in use in modern submarines. In order to give a point in 360x360 degrees, something like, "47 port/starboard, 20 high/low, X kilometres," to indicate 47 degrees horizontal on the left or right hemisphere, 20 degrees vertical on the top/bottom hemisphere, and a point X kilometres away. This is of course in relation to the ship receiving the orders. It's the only logical measurement system I can think of, given the fact that most other practical measurements require a star as a reference point, and using the galactic core would just be impractical on the tactical scale.

Just goes to show why humans should leave the manoeuvring of their starships to AIs.

Regards,
Winter

[Ford Prefect]

Hmm. I don't think 'double zero' would be accepted as military terminology, especially on a ship where everything has to have a different name in order for accurate commands to be given (look at sailing terminology for an example of this).

Who cares about 'accepted military terminology'? 'Double zero', or whatever shorthand for 'zero degrees off the X axis, zero degrees off the Y axis' is used, could really not be mistaken for anything else when talking about the context of starship positions.

[Nyrath]

Of course, in Star Trek, they use your relative coordinate system, with the two coordinates separated by the word Mark, e.g., "Mr. Sulu, come to a heading of 23.5 Mark 17.2."

Star system centered coordinates could have the zero Right Ascension coordinate set to the intersection of a circle of arbitrary size in the plane of the system with a plane containing both the star and the galactic core, with the plane being at ninety degrees to the galactic plane. This would produce two points, the point closer to the core would be chosen as the zero point.

In Isaac Asimov's THE STARS LIKE DUST, he uses spherical coordinates for a galactic based coordinate system. Rho is the distance to the galactic core, in parsecs. Theta is the angular separation, along the plane of the Galaxy from the Standard Galactic Baseline (the line that connects the Galactic Center and Earth). Phi is the angular separation from the Baseline in a plane perpendicular to the plane of the Galaxy. Theta and Phi are expressed in radians.

[Mr Bean]

You use the local star's position to reference your own. Nothing worth fighting over between stars so it works quite well in the most part.

[Nyrath]

You use the local star's position to reference your own. Nothing worth fighting over between stars so it works quite well in the most part.

Not always. In the Sten series by Allan Cole and Chris Bunch there is something incredibly valuable in a location between stars, though you do not learn about it until the last book.

[rhoenix]

Oh, and as an aside, a parsec is bigger than a lightyear.

...

*smacks forehead*

Thank you - that's what I get for not previewing.

For a more wanky universe, wherein one could traverse galaxies like Star Trek warp travel does stars, finding the Big Bang Origin Point

The problem with that is there is no such thing.

You'd just want to arbitrarily define a center and your planes and work from there, like others have already suggested.

I'd had that concept in my mind due to it being an important plot point in a story I was working on. Pardon my ignorance, but why wouldn't there be any such thing as the point in space where the big bang originally began?

[Darth Yoshi]

Well, presumably the big bang point would be the center of the universe. But if the universe is infinite, then every point is the center. Which does you no good. Granted, I'm most likely wrong about this.

[Darwin]

Something which I'm having an endless amount of trouble with is coming up with a system by which positions can be given. Space is a three dimensional place, so you can't just say 'oh, a million kilometres off the port bow' and leave it at that. Who knows how you'll be orientated compared to your enemy. My only idea so far has involved giving positions through degrees from a variety axis on the ship, but that didn't work out so well in my head.

I'd use a variation of the military brevity code for the same purpose.

"Contact Ten Range 5M 2M Low!"

Object at 10 o-clock measured from our horizontal axis, direct range 5 million km, 2 million km below our plane of travel.

if you need to be more precise, replace the clock reading with a degree.

"Hostile Three Oh One Range 5M 2M Low!"

[Darth Holbytlan]

Well, presumably the big bang point would be the center of the universe. But if the universe is infinite, then every point is the center. Which does you no good. Granted, I'm most likely wrong about this.

Finite or not, there is no center of the universe and no "big bang point". The Big Bang is an expansion of space itself. Essentially, every point was the same at that moment so no point is more special than any other.

[fnord]

ANother option could be using the system's ecliptic as your zero plane, and taking directions from that.

Wait... doesn't work too well with engagements in deep space. Dammit.

Double zero - workable, but what's wrong with dead ahead?

What about directions on a strategic scale?

[Howedar]

The best tactical way would probably be distance, horizontal radians, and vertical radians relative to the ship's current heading. Or degrees if you prefer. If it's in a time sensative tactical situation, whichever has fewest syllables would probably be best. If your world is still on 12-hour time, calling out 900k-8-11 is a lot faster than 900k-240-330.

Or 4/3 pi by 11/9 pi... on second thought, radians probably aren't the best for on the fly directions.

Or perhaps instead of two continuous measures, you could do one horizontal since people are most used to that, then call hours 1-5 up or down. (six would get called out as "straight" or something)

Why do you care how fast it is? In what realistic space scenario is time on the order of seconds important?

To answer the question, really it's just a rephrased version of: how do you define a vector?

You're either going to give angles and magnitude with respect to some origin and coordinate system (presumably your own ship) or an actual set of <x,y,z> coordinates (presumably with respect to your own ship again).

I'd expect the former to be more helpful, as it's a little bit more intuitive and total distance is often more relevant than coefficients, but I don't think it's a big deal. Note that you could specify those angles as precisely (seconds of arc) or loosely (clock-based system) as is useful for that situation. I'd expect the latter to be more common, because I can't think of any time the precision would be useful verbally. It's something Data might babble about, but it's not actually going to help situational awareness.

[PeZook]

I'd expect the former to be more helpful, as it's a little bit more intuitive and total distance is often more relevant than coefficients, but I don't think it's a big deal. Note that you could specify those angles as precisely (seconds of arc) or loosely (clock-based system) as is useful for that situation. I'd expect the latter to be more common, because I can't think of any time the precision would be useful verbally. It's something Data might babble about, but it's not actually going to help situational awareness.

In a realistic space combat scenario, trajectories are going to be much more important for a firing solution than relative positions, anyway. You can fire a torpedo directly at the target from two kilometers away and expect it to find the target with at least some chance, while in space you will probably have to reliably hit enemies at thousands of kilometers and being off by half a degree would mean a clean miss.

And, well...accurately presenting an enemy trajectory is all but impossible verbally. What, are you going to blurt out "Enemy contact, distance 234 thousand, inclination 32 to Earth ecliptic eccentricity 0,0034 periapsis 453 apoapsis...etc."?

It will take much less time to just draw an approximate orbit and enemy position with a light-pen so that the commander can have a nice graphical presentation untill precise data is received.

[Ford Prefect]

It will take much less time to just draw an approximate orbit and enemy position with a light-pen so that the commander can have a nice graphical presentation untill precise data is received.

In all honesty, that's basically how things will be presented, though normally it would presented within a 'simulation', so no pen would be needed (unless something is going horribly wrong, in which case you're going to have to do it by hand. Which might be a little problematic ). I need this sort of information more for myself and the narrative.

[Junghalli]

I think almost certainly one would use straightforward XYZ positions, such as mathematicians usually use to determine coordinates in three-dimensional space. Another ship might be 3 km away on the X axis, 10 on the Y axis, and 1000 on the Z axis, and hence you have a coordinates. It would probably be communicated something like "we have a bogey at X-110, Y- minus 225, Z- minus 40, inbound", or something like that.

For navigation within a system it seems most straightforward to just use the local sun as the 0-0-0 point. For combat manuevers you'd probably use your own position as the center, I'd imagine. The important thing is how everything's moving relative to you, not how everything's moving relative to some distant reference point, as is the case in trying to find your way around a bunch of planets.

For interstellar coordinates I imagine you would probably use either the galactic center or your own home system as the 0-0-0. It's pretty much totally arbitrary, so one is basically as good as the other.

For a more wanky universe, wherein one could traverse galaxies like Star Trek warp travel does stars, finding the Big Bang Origin Point, and using that as your point of reference works

I don't think the expansion of the universe actually has a physical center, so I don't think that would work. It'd probably be a lot easier to just use the center of your own galaxy as 0-0-0.

[Patrick Degan]

I think almost certainly one would use straightforward XYZ positions, such as mathematicians usually use to determine coordinates in three-dimensional space. Another ship might be 3 km away on the X axis, 10 on the Y axis, and 1000 on the Z axis, and hence you have a coordinates. It would probably be communicated something like "we have a bogey at X-110, Y- minus 225, Z- minus 40, inbound", or something like that.

For navigation within a system it seems most straightforward to just use the local sun as the 0-0-0 point. For combat manuevers you'd probably use your own position as the center, I'd imagine. The important thing is how everything's moving relative to you, not how everything's moving relative to some distant reference point, as is the case in trying to find your way around a bunch of planets.

The notation could be even simpler: zero defines the X & Y axial planes, you use a 1000-point compass, and z is distance in parsecs from home point zero. So a positional bearing and heading would be rendered something like "232 by 378 by 040. Course 902 mark 5".