Bearings in space

[Pmandrekar]

Originally Posted by laserdog

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.

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

-P. Mandrekar

[Digganob]

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.

[Extrarius]

Originally Posted by laserdog

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.

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).

[laserdog]

Originally Posted by Extrarius

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.

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. =)

[I, Cylon]

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.

[William]

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.

[Anthony]

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.

[Anthony]

Originally Posted by Agemegos

Are pulsars detectable over intergalactic distances? Or are you thinking of quasars?

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.

[Hai-Etlik]

Originally Posted by laserdog

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 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.

[Archangel Beth]

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?