Bearings in space
 

Does anyone know the proper way to navigate in space? Since on earth, the point of reference is the poles for NSEW. But in space (specifically deep space, where there is no gravitational point of reference) what is the method for determining the course, bearing or direction of a target or path? In, say Star Wars, the dialogue seems to be made up of random numbers ("Set course to oh-three-five" - which means ...?).

And before someone says it, I would prefer not to "wing it", as I like to have a modicum scientific realism in my stories. ;)

My first thought was that it would be a target or the ship itself as the 0-point reference on a XY plot circle. But how do you reference from that? Another idea was that there would have to be a target or point of reference. But, what if you are in deep space, and there's nothing around you but you and another ship?

Re: Bearings in space
 

The first thing that comes to mind is to pick a point - any will do, but the center of the known universe would be a good one. How you pinpoint that is going to be a bit tricky too.

From there you can establish a line to another point. Go egocentric this time, and pick our sun. Now that line becomes your x axis. The y axis would be a perpendicular line from one of those points, and the z axis would be another perpendicular line from those two.

Sounds easy, right?

Okay, now the problems. The sun isn't sitting still, so your x axis is rotating. Also, we're pretty sure the universe is expanding and we're also pretty sure that time-space itself is expanding with it. Trouble is, time-space isn't uniform. So now all your axis are wobbly lines.

Re: Bearings in space
 

Actully this very question was answered in at least THREE Star Trek reference books.
After the first season of NEXT GEN they tried to be consistent about the "bearings issue".
Usually they were measured from the centerpoint of the vessel.
OTHER times - they indicated things were measured from the center of the Milky Way Galaxy.

- Ed Charlton

Re: Bearings in space
 

I believe the term is "astrogation"?

And from what I understand, you take a reference "picture" (visible, radio, x-ray) of all the stars you can see, and then tell the computer "calculate the position in the universe/galaxy where the stars would look like this".

The computer could, of course, make some "educated guesses" based on previous navigation logs to make the process go much faster.

Also, afaik all pulsars have unique pulse times, which can make an incredibly useful and indentifiable single points of reference.

This is, of course, assuming a TL of 9+. I believe for the inter-solar space flight of TL 7 and 8 you'd just use fix pointed radio signal beacons to figure out where you're at.

Re: Bearings in space
 

Here was one explanation for the "TREK Universe" :

http://www.fastcopyinc.com/orionpres..._in_star_t.htm


Your Kilometerage may vary....

- Ed Charlton

Re: Bearings in space
 

http://www.memory-alpha.org/en/wiki/Kellicam

... Or "Kellicamage", as your preferences may dictate.

That's a nice discussion, though. The kind of thing that a GM running a Space campaign could use. Thanks for sharing, Q!

-P. Mandrekar

Re: Bearings in space
 

If your concern is just what points of reference a crew could use to set an accurate 3d bearing, that could be accomplished by a set of 3 gyroscopes set to spin on each axis, with deflections caused by acceleration recorded by monitoring instruments.

As long as a fleet calibrates them to all be the same originally, you'd have a ready made standarized method of "up/down, left/right", etc.

Re: Bearings in space
 

This is the way things work in most (but not all, iirc) of Isaac Asimov's books and stories. It's a really bad system for figuring out where you are after a FTL drive malfunction takes you to uncharted space, though, since the computer would need to ignore all 'nearby' stars (which makes the matching process nearly impossible).
Some kind of TL9/TL10 gyroscope system (based on maglev to eliminate friction, etc =-) would probably be a good backup system. It would need to be calibrated perfectly to work long-term, but even the crudest of readings would be helpful when you just want to go back where you came from.

Re: Bearings in space
 

But that's borne out in both ST: Voyager as well as Lost in Space (at least the terrible movie version)?

It's an interesting question on whether moving yourself into a zone where new stars become detectable and old ones are gone, whether the problem is even solvable anymore...

Although, it would seem to only require the detection of a single pulsar with the same timing as one from your old reference point to "pick up the trail" again.

Re: Bearings in space
 

Even with our currently limited technology and viewpoint, we've mapped what we can see in 3D. It's a tricky model to do a match/fit to, but your ideas about known pulsar timings is a good one. Also, exactly how fast do your ships go? The problem is a lot simpler if you limit yourself to one galaxy or corner thereof.

Re: Bearings in space
 

Or perhaps a few such pulsars, to confirm your location in 3-D space.

-P. Mandrekar

Re: Bearings in space
 

In the old DOS game Starflight the following headings were used:

Coreward and Outward: These headings are toward and away from the core (or center) of the galaxy. coordinates are probably measured in light-years from the center of the galaxy, or relative to the distance of the "primary-home-star" (or PHS)*. So, a location of "-100" would be 100 light-years coreward of the PHS, and "+100" would be 100 light-years outward of the PHS.

Downspin and Upspin: These headings take you with or against the rotation or of the galaxy. I'm guessing you'd measure coordinates, in degrees from a "meridian" of sorts. This "meridian" or "Zero-degrees marker" would likely be the line from the "center" of the galaxy passing through the center of the PHS.

* PHS (Primary-Home-Star)= The primary star of the solar system that the dominant race in the galaxy originated from. This is not from the game, I just made it up.


Starflight was a two dimensional game, so it didn't include a third heading, but something like "Galactic-North and Galactic-South", measured along the center axis of the galaxy, seems like it would work just fine.

Once inside a solar system, more accurate coordinates based on the primary sun, first planet, and common orbital disk, would probably be easier to work with

Of course to get accurate coordinates, you're probably going to need very long numbers with several decimal places. For game purposes, I'd just fudge it, let the characters make the astrogation rolls, and say "your're there" or "you're lost", instead of trying to give the players actual numbers to figure out.

You're on your own for intergalactic travel.

Re: Bearings in space
 

That single pulsar's signature will be distorted by the space-warping that gravity causes, and things like dust clouds in the way will significantly reduce the signal's strength. Also, if your situation involves FTL drives, you potentially outrun the signals from the known part of the universe so that you'd have to wait millions of years (or go FTL in the other direction) to get your bearings.
In Asimov's works, the FTL travel was done via 'jumps' that basically could take you any distance instantly, but practical limits (calculating everything, including the path of all significant objects near the destination so you don't end up inside of one, the influence of gravity of everything along the path, etc) meant that it still acted somewhat like tradition travel with speed limits. This meant that in case of an emergency, you really could come out anywhere in the universe if you didn't bother to spend time calculating, and in such situations, a fancy computer with some nice sensors doesn't help much. Realistically, computers would probably be able to handle all the calculations very quickly (and he did that in some of his works as well).

Re: Bearings in space
 

The signature is merely the time between pulses. So even if something did slow the speed of the initial pulse, it would also slow the one after that by the same factor. Even if there were strong relativistic forces at work, you should still be able to calculate the "normalized" spin time by examining the wave-length distortion (e.g. blue or red shift).

Although, again, the original context of that is that all you'd need to do is find *a single* pulsar that was visible from your old galaxy to get on the right trail, not one specific one.

But now i'm geeking out for no appreciable benefit to the original poster.

And I'm certainly not an astrophysicist here, so I bear no liability if you attempt to navigate an FTL drive by any of my ideas presented, cuz they're probably very wrong. =)

Re: Bearings in space
 

Apparently real scieitists think pulsar maps are the way to go with this.

When the voyager probes were launched, they contained pulsar maps printed on gold records that were supposed to let anyone smart enough to find the probes also find earth.

Here's a link to a site that talks about decoding the pulsar maps:
http://www.johnstonsarchive.net/astro/pulsarmap.html

So it looks like pulsars will be to star farers what lighthouses are to seafarers.

Re: Bearings in space
 

To find out where you are in space, you observe multiple pulsars. Scan the sky for these, locate several nearby (there are quite a few in the galaxy), and take readings until you have a firm idea of what their emitted signature is (radiation spectrum and rotation time). This is the pulsar's fingerprint, which will allow you to identify it.

When you know the direction from where you are to four pulsars, locate those four pulsars on your starcharts. Spherical triangulation will tell you where you are in the galaxy, in whatever coordinates you wish to use.

Re: Bearings in space
 

One concern with the pulsar map theory is that there's reason to think pulsars may not be omnidirectional emitters. Within the milky way, locating some combination of Andromeda, the Magellenic Clouds, and Cygnus X-1 should do the trick.

Re: Bearings in space
 

Over significant intergalactic distances, there really aren't any easily discernable landmarks. You'd probably have to do deep maps of the cosmos to find superstructures like the Great Wall, and that's really astronomy beyond the likely capabilities of a normal ship.

Re: Bearings in space
 

As has been pointed out, you only need 2, and mechanical gyriscopes would not be used any more than they are in modern inertial navigation systems. Laser gyroscopes are used in modern systems, and that or some superscience equivalent would be appriate to scifi INS systems.

You still need to correct for drift occationaly with an INS so you still need an external reference.

Re: Bearings in space
 

How about Galactic North?

It might not be highly detailed, but knowing which way is "north" is probably reasonable enough till you get closer to your goal, yes?

Re: Bearings in space
 

I honestly don't know. My understanding is that time-space is expanding outward from where the big bang took place. Again, as I understand it, it isn't just stars and matter flying away from that origin point, but space itself - a tricky concept that I only claim to partially comprehend.

If this is true, then there is an outer edge, outside of which there is no space. I haven't even tried to wrap my head around that one.

For most discussions, I would agree that no point in our known universe is any better than any other for being the origin. If the big bang is science fact, then I think it would make a good origin for a navigation system. On the other hand, the center of one's own galaxy might be better. The scales at which space travel would occur would make the center of the universe too remote. The differences at our distance from it would be too minute to be practical. (Please excuse the stream-of-semi-consciousness here.)

Re: Bearings in space
 

I think it's only 'north' from earth. It's a large globular cluster, but it's not very bright and globular clusters aren't very distinctive.

Re: Bearings in space
 

Your understanding is incorrect. The big bang took place at every point in space, and the big bang is actually space itself expanding, carrying all the matter with it. There is no center, and there is no outer edge.

Re: Bearings in space
 

My understanding (big, big disclaimers in bright neon here) is that it goes something like this: If you map the "location" of the Big Bang in that early Big-Bang-sized universe to the current universe, the "location of the Big Bang" maps to everywhere. So everything is flying away from everywhere, equally, and there is no reference point, and no space-outside-of-space.

Kind of like those "small parallel universes" where great distances in ours map to casual walks in the other universe (a common rationale for FTL travel), only the "small universe" in this case is our early universe, and it was point-sized.

I could be totally wrong, but that's the model in my head.

Re: Bearings in space
 

Essentially correct. The usual model used is a balloon that's blowing up, with the galaxies drawn in marker on the balloon: all the galaxies are moving away from the Milky Way galaxy, and likewise all the galaxies are moving away from the Andromeda galaxy, even though each galaxy is sitting in place on the balloon as it expands.

The Universe, then, forms a 3-dimensional "balloon." When the Big Bang happened, the Universe was extremely small, and the Big Bang happened everywhere; there simply wasn't much everywhere. It didn't have a boundary, though, no more than a circle has a boundary (you can walk indefinitely in the circle's one dimension) or a sphere has a boundary (you can walk indefinitely in its two dimensions). Both are finite, but unbounded.

That circle does have a center. It's just not anywhere on the circle, and if the circle is all of space, then that center isn't anywhere.

Re: Bearings in space
 

To navigate anywhere you need bearings from two or more fixed known reference points. On Earth, that's the Royal Observatory in Greenwich, England and the Equator.

In space, the logical points would be the Galactic Core (the radio signature of Saggitarius A* is easy to locate) and S Doradus (The brightest and most prominent star in the Large Magellanic Cloud, with a very distinctive spectrum). The relative positions of those two would give a rough general notion of where one is located, as well as distance, and could be designated "main markers".

Purely "local" prominent phenomena (pulsars, supernova remnants, and anomalous objects) would help fix the position to greater degrees of accuracy. In our galactic neighborhood, Alpha Cygni (also called Deneb) would be one such local marker, as white supergiant stars are rare and it has an anomalous spectrum (heavy iron concentration).

So a galactic-scale campaigh would require a eight-place coordinate system - the first two indicating the relative position between Sagittarius A* and S Doradus (flat and inclined plane). The third, fourth, and fifth numbers would be the catalog identification of a local marker and it's relative position from the closer main marker; sixth, seventh, and eighth being the same for another marker relative to the further main marker.

With all these numbers, there could only be one location where these objects would be seen at these exact angles. Thus coordinates are fixed.

In a "local galactic" campaign, the Core and S Doradus might be too large-scale. In which case only six coordinates need be used; the identity of two markers and bearing from them.

In a "local space" campaign (covering only a couple of dozen parsecs), three coordinates showing the bearing and distance from an arbitrary "fixed" zero location is all that is necessary. The small number of stars allow them to be identified by spectrum and relative position. The system used in GURPS SPace 3e is adequate for that.

(A coordinate does NOT mean a one-digit number! It can be as many digits as necessary. Or even have letters, in the case of identifying markers.)

Hope this helps.

Re: Bearings in space
 

The "known reference points" you refer to on Earth are actually two coordinates -- longitude and latitude respectively -- which you need because the surface of Earth is a two-dimensional object. If you do not know where you are on Earth and need to determine your position, you need to find bearings to three markers of known location. The Equator is not a point!

In three-dimensional space, you need bearings to four markers to find your position, which can be marked in three coordinates. In a relatively round, disc-like galaxy, a number of systems can be applied, with the most likely candidates being spherical (two angles from fixed reference lines -- probably convenient bright stars -- and a distance from an agreed central object) or cylindrical (height from a reference disc -- the "galactic equatorial plane" -- radius out projected on that disc, and angle from a reference line on that disc, again probably from a convenient star).

Re: Bearings in space
 

There is no evidence, one way or the other, that the universe "wraps around" on itself like a circle or sphere. It is possible that the volume of the universe is infinite (unlike the surface of a 4-sphere, which would have finite volume). We cannot see all that volume, of course, because for anything beyond roughly 15 billion light years away it would take longer than the lifetime of the universe for light to reach us. In this sense there is an edge to the observable universe, even if the universe were infinite in extent.

Other possibilities involve various ways for the universe to wrap back around on itself (although, it would do this without any curvature), or that the obervable universe sits inside a finite "bubble," outside of which different physics apply (possibly being the hot, dense inflationary "stuff" that prevailed during the first instant of the big bang, or possibly separated from our universe by a boundary known as a "domain wall," which is thought to cut off regions with one type of physics from those with another. Note that when I say that physics is different, gravitation is probably the same but there exist a different combination of particles and the forces that act on them than our everyday up and down quarks, electrons, electromagnetism, weak force, and strong nuclear force).

Despite amazing advances in comsology and lots of very clever ideas and measurements, there is still a lot we do not know about the universe.

Luke

Re: Bearings in space
 

Is Cygnus X-1 really observable all over the galaxy? Or are you thinking of Sag A?

Luke

Re: Bearings in space
 

I was thinking of Sag A*, though Cygnus X-1 is probably visible from most of the galaxy as well, at a distance of 2500 parsecs it's the brightest hard X-ray source in the sky. There are also a few hypergiants in the milky way (such as Eta Carinae and the Pistol Star) which should be identifiable.

Re: Bearings in space
 

And why not extrapolate that to the 'subspace' beacons (Trekkie Subspace radio). Navigating by polar coordinates between beacons should be easy then, as long as the paths were chartered. That would make the most sense for space 'lanes', where beaconing without an expert would be easy. The only problem is that the beacons must be relative fixed items---planets/moons/planetoids, and probably satellites around those. Stationary beacons could be possible with bases that use engines to correct their position (as 3D polar coords) relative to local system features. Probably no two paths in a particular space length will be exactly the same due to the movements of the planetary bodies that the beacons are stationed on.

Re: Bearings in space
 

If I'm not mistaken, there are a couple of additional factors complicating things here:

1) Nothing in the known universe is completely static with reference to any other object. So all of your charts, maps, and calculations will have to factor in the time element as well. Granted, you can incorporate a clock to measure ship's time, or you could use known rates of change (say a known solar system or <possibly?> the rotation of known stars in a given galaxy) to calculate what the current local time is. However:

2) Even knowing the local time may not help much, as you have to take into account relativistic effects. This is especially problematic for astrogation in a large volume: since your reference points are always moving, and because you may be limited to STL or lightspeed sensors, you have to know where you are (and how you're moving) relative to your reference points in order to adjust your observations for the relativistic effects.

Which may very well mean that calculating your position and velocity will have to be done in a series of steps - look around you for known points of reference, calculate where and when you might be, make more observations to refine the data and determine your ship's velocity relative to those points, recalculate your position, make more observations to try and find your local acceleration, recalculate, re-observe, recalculate, ad naseum or until you feel confident in your numbers to set a course for where you're going.

At that point, you may not worry too much about using a certain standard set of reference points, unless the area is well charted - the relative postion and movement of a standard set of reference points is well known.

Re: Bearings in space
 

Well, that I can think of, two things:

1) Not a relativistic effect per se, but if you happen to be say, 50,000 light years from one of your reference points, and you're observing it by EM radiation or something else thap propogates at c, then you've got to account for 50,000 years of relative drift. Not a big problem, if it's far enough away and you're only navigating a small region of space at STL, non-relativistic speeds.

But, it could be problem in a couple of scenarios:

a) you're 50,000 light years away from reference point A, but all of your charts are based on observations from 2,000 light years away. Your astrogation has to take into account that your observed position for the reference point is 48,000 years off of what your chart says it is (still assuming your sensors are limited to lightspeed). Not a big deal if you are in known space, relatively sure of where you're at, or don't need a high order of percision... something like the FTL astrogation equivilant of magnetic variance. But,

b) If your FTL jump or hyperspace drive has malfunctioned and you have *no* idea where you are, it makes things more difficult. Even if you're sure you're still in the same galaxy and looking at the proper reference point, you're going to need to make some guess as to about how far away it is so you can account for how far off its apparent position is from the recorded position on your star charts. So you'd probably make a rough guess (probably based on apparent magnitude or spectral shift), calculate a rough position, see how that affects the variance between your observation and your chart, refine your position, lather, rinse, and repeat.

2) If your ship is capable of accelerating to a high order of c, say .5c, then the relativistic effects of your motion are going to throw off your observations of your reference points - because of space/time dialation, they will appear to be in a different place or at a different distance than you would observe them at rest with respect to them. Again, not a big deal if you know where you are, are pretty close to your reference point, and know your velocity and acceleration with respect to your references (or if you're not moving at relativistic speeds). But, again, if you're trying to start from scratch and have *no idea* of your present position, velocity, or acceleration with regards to your reference point, you're going to have to make a series of observations and position calculations.

I think. But maybe the effects start to cancel each other out. And I don't know how big of a deal it would be at intra-galactic distances (although it would be significant in inter-galactic astrogation). Mostly it just means more time and computation - easy enough if you've got it, harder to do when the Imperial Star Destroyer is breathing down your neck.

Re: Bearings in space
 

I don't know about the rest of you, but I'm finding this thread incredibly useful.

At minimum, I intend to archive all the pages for use in my next space campaign. And if anyone disputes a ruling I'm going to begin reading right off one of these posts verbatim until their eyes glaze over. =)

That's not a cut at the posts being boring. My friends are all pretty smart and read enough scifi to talk the talk, but I'm pretty sure none of them are *this* smart. =)

Re: Bearings in space
 

Certainly these are "problems" in the sense that your navigational systems will have to account for them, and hand calculation would be extremely tedious if not downright impossible. If you want to travel at FTL or high-sublight velocities, you'll need computers capable of handling such calculations.

To account for 48,000 light-years of difference in observation of a star, you'll need to be able to accurately project that star's trajectory and stellar evolution for either the past 48,000 years or the next 48,000 years, depending on which direction you're viewing it from relative to where the observations were made. When you make your observations and compare it to your starcharts, your computer will be finding the one place in the galaxy it could possibly look like that at the "now" of whatever coordinate frame you're using.

Re: Bearings in space
 

Hi all,

first, sorry for my bad english, esp. with the cake, it could probably explained better, but not by me :-((

Then, I enjoy rading this thread a lot :-))

For the big bang discussion: The best picture I found in books for the expansion was a cake. The galaxies are like raisin in a cake while you bake it. The distance of the raisins is increasing, also the expansion does not have a center.
For the goemetry of the universe: depending on the mass in the universe, the universe is flat, round or formed like a saddle (sorry, bad english again), all in 3 dimensions. This will have effects on the angles you measure on a universal scale, although you need two points each some million or better billion LY apart to notice it.
(You can read this in most cosmological books, I'm reading "Kosmology für helle Köpfe" (in german) at the moment ;-))))

Navigation: a) Inside a galaxy or near one galaxy
I do not see a problem. Either you are travelling with sublight speed, then you can measure your position all the time and probably don't get lost. Anyway, even if you travel 10000 y through the galaxy with light speed, not much has changed. If you travel by FTL, then not much time will have passed, so you can use the reference point system (there have been very good suggestions before).
For navigation inside a solar system there might be a second coordinate system necessary, which can be used down to kilometers or so?

b) far distance (billion LY):
That is really, really tricky. One problem is, if you, lets say, instantly travel 10 billion LY, first, 2/3rd of what you see now, was not visible before (the universe is just not old enough that light has reached your starting point). A lot of things you've seen from your starting point is now no longer visible...
To further complicate things, objects near your new position are 10 billion years older than how you saw them before, so e.g. quasars will have changed to ordinary galaxies, galaxy clusters have formed, other galaxies might have collided, transforming from spiral to eliptic etc.
Your starting point is now 10 billion years younger, maybe still a Quasar instead of your lovely habitable home galaxy, the great wall may not have formed etc.
Solution? Make small hops, not big one or create a system of FTL beacons...

Mark

Re: Bearings in space
 

Well, what I meant is that navigation might be based off of "where am I" and "where is 'galactic north'" -- without getting into the fiddly bits of which landmarks one is using to determine "north."

I.e., as I understood the original question, the "set a course" could be based off of the direction the ship should be pointing, with the other referent being "which way is up."

E.g., The Bullet has come through a stargate between civilized sectors. The pilot, having 3-D Spatial Sense, quickly figures out where "up" is and sets a course to the near-by planetary system. The Bullet's nose is pointed 30 degrees from "up," and the planet will be another 20 "down" and 20 degrees to the right. While she could -- having 3-D Spatial Sense -- just joystick the ship around till she got within visual scan range of the place (she's been there before), her AI assistant would like to get a chance to crunch the numbers, so the pilot goes off to take a nap. (And meanwhile, the AI generates some code or other which indicates "Course 23d, 21.45729r, 3.14695 minutes, adjust for that other system there, and continue at heading 1d, 22r for the rest of the trip.")

Assigning a latitude/longitude/othertude coordinate system for star systems would be a whole 'nother kettle of asteroids, of course.

Re: Bearings in space
 

The easy one is if you are using some short lived object, so if you look at it at certain distances, it simply isn't there.

Solution - use only long lived beacons, with a lifetime = (diameter of the galaxy)/c

Re: Bearings in space
 

The universe is flat. This is predicted by the generally accepted inflationary models of the big bang, and confirmed experimentally by COBE and the discovery of dark energy. What is unknown is the topology of the universe. You know those old computer games like Asteroids with "wrap around screens," where if you go off one side you end up at the corresponding point on the other side? This is a 2D manifold that is geometrically everywhere flat but with a finite area. The universe might be similar, except it would be flat in 3+1 dimensions.

Luke

Re: Bearings in space
 

You're right. Relativistic was a misapplied label. Signal propagation delay is a better term. It's related to relativity only in that relativity gives a fixed speed for light in a vacuum.

It can be solved in one step as long as you know to a rough degree of approximation of where you are already (by dead reckoning or initial observation). I would think to get really precise results, though, you'd need to calculate your rough position, account for space velocity and signal propogation delay (based on that calculated position), calculate a finer position which gives you better numbers for signal propogation delay, use that more percise value to calculate a more percise position, and so on until you reach the desired number of significant digits.


Exactly. Although it also depends on if you've got a limit on your FTL range. If you know you're in the same galaxy you started out in, then it depends on how good your charts are.

Good point. I wasn't sure how significant the space velocities would be (I'm a philosopher, not an astronomer). It also depends, I think, on if a few tens of parsecs is good enough for your astrogational purposes or not, which depends on the setting and its realism and tech assumptions.

I honestly hadn't thought of using the spectroscope to measure your velocity, but that would be the best way to do it.

Exactly. Given enough time or computing power, these "problems" are reasonably trivial. However, they do allow a GM to set up a scenario that says "You come out of jump space. Even though jump travel is instantaneous, it does take x amount of time to set up the next jump." without breaking realism.

It also allows for scenarios like "you are trying to evade the Imperial fleet, but it will take your astrogation computer <clatter> x more minutes to calculate the jump into hyperspace. The AI politely informs you that it would be easier if you'd maintain a constant position or velocity, so could you please stop all of that evasive manuvering for a while?" or "the FTL drive malfunctioned. It's going to take Chief Astrogator Sulu at least a few hours to figure out where in the galaxy you are and where the closest star base is. Meanwhile, the following things start happening..."

Re: Bearings in space
 

We may have wandered from the original question, though. My 3e GURPS Space (Steve Jackson and William A. Barton, (c) 1988) says Is this in the new edition of Space? And are these terms used in rela world astronomy, does anyone know?

Re: Bearings in space
 

Galactic north has a meaning. It seems to be what Space is calling Galactic 'up'. Coreward is galactic longitude 0

Re: Bearings in space
 

Depends on whether it vanishes within a hundred thousand years or so, which is something that, given FTL, can be determined fairly quickly.

Given a bit more time, you can probably locate the black hole at the center of the Large Magellenic Cloud. That's not going away any time soon.

Re: Bearings in space
 

Very well done. This must be why I'm not a professional astrogator/astrogation computer programmer. I must admit I did miss the more elegant mathematical solution here.

Re: Bearings in space
 

Not on topic I know, but every time I see this thread title my first thought is that it has something to do with using ball bearings as weapons in space.

Re: Bearings in space
 

Well, really all I need is something for dialogue purposes. I don't want to wing it. I want to use something that actually has some merit to it.

For example, what would be an efficient dialogue for a sensor operator warning of a unidentified blip 3 miles to the right of the vessel, 1 mile down, and on a tangent course?

I'm sure if I want to pull a Star Wars "wing it" / ad lib type dialogue, the NPC or player could simply say, "Bogey, at 0-53". But ... what the frak does that mean? I would prefer an actual system, even if it's simplified.

Re: Bearings in space
 

On the local scale, just treat bearings relative to the ship. Take a line straight forward from the ship. An object is at some number of degrees port or starboard of that line (up to 180 degrees, a.k.a. 'aft' or 'dead astern'), and a number of degrees elevation, positive 90 to negative 90.

"Bogey 40 degrees to port, 20 degrees elevation" might get shortened to "Bogey, port 40 plus 20." For detail on its current relative heading, its directions of travel might be "closing", "orbiting" or "moving away," "heading to our port or starboard," and "climbing" or "diving."

Re: Bearings in space
 

I think there may be two things here getting mixed (into a deliciously scientific slushie!) - which boil down to piloting the ship and navigating the ship. The following is from wargame-design experience in trying to keep it simple.


For general GMing use, I'd want something that orients everything else to your ship. ie: "Bogey detected at +25°, -35°, range of 500", where "0°,0°" is directly ahead on your current course, + is to the right/starboard, and the second digit is the detected objects elevation.

At +25°, -35°, that's ahead and a little to the right, but well below and 500(units) away...

Maintaining accurate ranges wouldn't be impossible, but would require some fast trigonometry.




(If you want to accurately map everything in 3d (such as for a dogfight), I'd use a 2d grid to act as the X,Z plane, and book-keep Y axis seperately. The origin point is arbitrary. You maintain values of your speed in the 3 axes, and simply add them on with any acceleration each turn.)




Navigation is a whole different beast, and has been well covered in the other posts.

Re: Bearings in space
 

The Star Trek Next Generation Tech Manual describes a system where dead ahead is 0° by 0° (000 mark 0), with the bearing continuing all the way around the ship up to 359° by 359°. Azimuth (right/left rotation) comes first then elevation/declination.

Thus a course of "24 mark 35" means 24° to the right of the current course, 35° up above it. Since the numbering continues all the way around, this means that in the azimuth 90° would be a course directly to the right, while 270° would be a course directly to the left, 180° would be directly behind. An elevation of 90° is straight up, 270° straight down, and 180° straight behind.

Re: Bearings in space
 

Excellent! I really like those ideas, EricBSmith and William. I wonder if there is a way to incorporate them together, or use the pros of both together ...

Re: Bearings in space
 

I believe we basically used the same system. ^_^ I used -90 to 90 for elevation, and Eric (or, Star Trek) used 270 to 90. Theoretically, there's another half a circle behind us (Eric's 180-degree elevation), but in practice you almost never use those coordinates since that gives every point in space two names.

Usage of the term "mark" to separate azimuth and elevation numbers is probably wise, especially for reports like "Bogey 40 mark 2, 500 meters and climbing." Aurally, it's a good sharp divider.

Re: Bearings in space
 

No, he's correct (if perhaps he explained it a little simplistically). If you use a full 360° coordinate for the azimuth (right/left rotation) you only need use a +/-90° elevation/declination (180° total). This is, in fact, how we designate location on the sphere we call planet Earth - if you imagine the "ship" is the center of the earth, pointed directly at the equator (0° latitude), and at 0° longitude.

The only thing using a full 360° elevation would truly give you is a very quick estimate of whether the object is in front or behind the ship - but a person trained to use such a system should already be able to tell that from the azimuth coordinate.

Re: Bearings in space
 

Hi,

I think we shall separate two case: first when your campaign will happen in one particular galaxy like Milky Way. And the second when your campaign will be inter-galactical.
In first case I think very obvious that the travellers will use their galaxy's center as reference. The x axis could be the line through the center and our sun, the y axis perpendicular with that through the center and the z axis is perpendicular both of the previous through the center of the galaxy.
In second case the things are not so easy. I think the only possibility to use the known universe's center but maybe that's too difficult to pinpoint.

Re: Bearings in space
 

I think we actually have three different cases:

First, we have campaigns set in what would be a small piece of the Galaxy. I have one setting where the "frontier" is 20 lightyears from Earth, due to the very slow FTL methods used. These campaigns would likely use the position of the homeworld or ruling world (if different from the homeworld) as 0,0,0 on the X,Y,Z axii respectively, with the XY-plane being the angle of the orbit of the homeworld around the sun. Even Star Trek's Federation uses this method; the Federation doesn't control the entire Alpha Quadrant, after all, and started with a much smaller area. Remember that habits are hard to break (we're still using a degree system, developed at least 6,000 years ago in Sumeria, despite the relatively recent inventions of radians and gradians).

Second, we have the galactic-sized campaign (common for Star Wars and other sci-fi/sci-fan settings), which uses the first method you mentioned. Even then, this doesn't always hold water; in Star Wars, whose system has been in use for 25,000 years, Coruscant (believed to be the homeworld of humans, and capital of the Galactic Republic (and later the Empire and New Republic)) is 0,0,0 on the starcharts, not the black hole at the center of the galaxy.

The third is the intergalactic set up. Even there, we have two set-ups.

In a campaign where galactic-level interstellar FTL is around, you will have the main galaxy and its satellite galaxies (example: our Milky Way and the Megallanic Clouds). Here, the system used for galactic-sized campaigns can be used.

In a campaign that spans something like the Local Group of galaxies (Milky Way, Andromeda, and M33, along with the satellite galaxies and other irregulars in between), the best thing to do is to assign a single galaxy as the "center", and deal with the center of that galaxy as 0,0,0, calculating from there.

It may even be possible for all three of these methods to be used in a campaign; one system for long-range intergalactic travel, one system for galactic travel, and one system for galactic sector travel.

Re: Bearings in space
 

I agree a small scale campaign will probably use Earth or some other reference world as the origin, but the XY-plane need not necessarily be the orbital plane of the reference world. Having a central origin makes for easy math by keeping the numbers small; which way the plane is oriented doesn't really matter. Any one of the reference planet's equator, reference planet's orbital plane, or the galactic plane would be equally likely. Actually scratch that; the most likely is all being used to some extent, with potential confusion if maps aren't labelled accurately.

Re: Bearings in space
 

The biggest problems with using the planet's equator as a reference for the XY-plane are two-fold:

First, as the planet orbits the star, the actual location of the equator changes minutely; the equator is rarely on the same plane as the orbit, causing seasons. This doesn't mean much, but can lead to inaccurate astrogration.

Second, the planet wobbles over time, causing what folks on Earth call precession. Polaris hasn't always been our pole star; during the time the Great Pyramids are commonly believed to have been built, Sigma Draconis was the pole star. In another 16,000 years or so (I'm fuzzy on the actual time frame), Vega will be the pole star. Imagine setting a trip for 0,0,30, intending to hit the vicinity of Polaris and hitting Vega's neighborhood instead.

As far as I know, the planetary plane does not change in regards to the sun it orbits, which would make for a slightly better reference in the long run than the planetary equator.