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PhantomWolf
2004-Oct-04, 06:36 AM
Not quite sure if this is the right forum, but figured it was worth a shot.

In a story I'm working on I'm introducing a device for pilots to locate their positions after a crash landing on an unknown planet.

The idea is to have a database of 3D locations of stars, then compare the local star pattern to the that database thus giving the position iof the pilot systemwise. It would use magnetic field variations along with local time, north and the stars to predict the pilot's position on the planet, thus giving them a map of the area if the world has been catalogued for such.

Is this sort of devise realistic given a jump in computing power?

01101001
2004-Oct-04, 06:46 AM
In a story I'm working on I'm introducing a device for pilots to locate their positions after a crash landing on an unknown planet.
Is this confined to one galaxy, part thereof, or the entire (known) Universe?

PhantomWolf
2004-Oct-04, 06:52 AM
Just one, and even then just one area (sector?) of it.

Robert Andersson
2004-Oct-04, 08:14 AM
It is remotely possible. Say they do have a database of stars, the computer can generate a star map (not graphical like in movies, though) from the vantage point of each known star (system), and then compare it to what is out there.

I cannot think of a way to logically deduce your position, so I see trial & error as the only way. You might be able to optimize the lagorithm, eg. if you know the direction of the galactic center, or known globular clusters, etc.

The problem is solvable by current technology, but we don't have that big database (much of our galaxy we cannot even see from here), a single supercomputer might need months to try out enough positions to find a match. However, I think you can safely ignore the latter factor. You may or may not choose to make a deal out of the first.

Evan
2004-Oct-04, 03:39 PM
Totally possible. Does this look at all familiar?

http://vts.bc.ca/pics/plaque.jpg

Kaptain K
2004-Oct-04, 04:38 PM
Very possible. Look for type "O" and "B" stars. They are all super bright - visible for thousands of light years. If you *know* which stars you have found, three will give your location. If not it will take some "trial and error" matching to come up with a solution (something that computers are real good for).

Evan
2004-Oct-04, 05:15 PM
The best reference is the one used on the Pioneer plaque. Those lines indicate the direction and distance to 14 pulsars. The period of a pulsar is exceptionally stable and can be detected from anywhere in the universe. Pulsars are like natural lighthouses on a universal scale.

Andreas
2004-Oct-04, 05:17 PM
Very possible. Look for type "O" and "B" stars. They are all super bright - visible for thousands of light years. If you *know* which stars you have found, three will give your location.
But how would you know exactly which stars you have found? That is, without knowing where you are in the first place?

Robert Andersson
2004-Oct-04, 06:11 PM
If you *know* which stars you have found, three will give your location.
Actually, you need four to determine your position in 3D space. One gives you any point on a sphere, two gives you any point on a circle, three gives you one of two points, the fours the definite point. Usually you can guess the latter though.

EDIT: Eh, we will also need to know the distance to the stars for it to work. It is probably possible to do it without distances, but it will be a *lot* more complicated.

Evan
2004-Oct-04, 06:27 PM
No need to determine distance at all. All you need is direction.

eburacum45
2004-Oct-04, 06:30 PM
You could probably do it by clusters alone;

first get four or more globular clusters- they are all well known, and vary in size so you could identify them pretty well from a wide range of angles; then you would be able to narrow your location down to a volume maybe a hundred light years on a side. If you need more confirmation open clusters will be well mapped by any star-faring civilisation.

Then just sort through the few thousand stars in that volume until you find one which has exactly the right sky; this is where the O and B class stars come in handy.

a program like Celestia (http://www.shatters.net/celestia/), corrected by centuries of astronavigation, would be essential in a situation like this.

tofu
2004-Oct-04, 06:37 PM
The best reference is the one used on the Pioneer plaque. Those lines indicate the direction and distance to 14 pulsars. The period of a pulsar is exceptionally stable and can be detected from anywhere in the universe. Pulsars are like natural lighthouses on a universal scale.

That's a good idea, but how big of a telescope would you need to carry and how long would it take to survey the sky and find the Pulsars?

If, for whatever reason, you have to use regular stars (or visible stars) I think that just from a computational standpoint you should try to constrain the search as much as possible. Obviously, you can't use only stars of a particular brightness because the apparent magnitude wont be the same everywhere in the galaxy. You might be able to use color though. So, if your database contained only blue stars and you filtered for that the search would be easier.

Another idea is to somehow figure out which way is galactic north before beginning the search. Are you still in space when you use the computer to determine your position? If so that wouldn't be too difficult. You could scan along the plane of the milky way until you found Sagittarius and then use it orient yourself toward whatever direction we decided to call North. But, again I guess that requires a pretty heavy duty telescope. Maybe that's not a big deal for a civilization advanced enough to get lost though.

tofu
2004-Oct-04, 06:44 PM
You could probably do it by clusters alone;

That's a good idea too. All you need to spot a globular cluster is a pair of binoculars.

I was just thinking, you could actually make a pretty good science fiction story around this idea alone. The story could be that a ship with some sort of wierd drive that allows it to get lost in the first place finds itself in a solar system with an industrial age civilization. The telescope on the ship is broken, but the computer and database still works. So the pilot has to sneak down to the planet and make friends with an astronomer who can help him access the civilizations records of globular cluster surveys.

Robert Andersson
2004-Oct-04, 06:49 PM
No need to determine distance at all. All you need is direction.
Yeah, you're right; I must be totally out. I mixed it up. If you know the (absolute) position of four points, and their distance to you, you can exactly determine your (absolute) position. With relative angles and positions, it is a completely different algorithm (of which I'm not very familiar).

Evan
2004-Oct-04, 07:42 PM
It requires spherical trignometry to solve the problem. Quite a bit different from plane trignometry, in spherical trig a triangle may be made with three 90 angles.

Swift
2004-Oct-04, 08:50 PM
The best reference is the one used on the Pioneer plaque. Those lines indicate the direction and distance to 14 pulsars. The period of a pulsar is exceptionally stable and can be detected from anywhere in the universe. Pulsars are like natural lighthouses on a universal scale.
I agree, pulsars are the way to go. Particularly within a given sector of a galaxy, the pulse rate of a given pulsar is extremely characteristic. You'd need a radio telescope. There was at least one episode of ST:NG that did this trick, some good astronomy from Star Trek.

You might also do a combination technique. I think you'd need a good radio telescope to get precise directions to the pulsars. Use a small one to get general directions, narrow down your location broadly, then use the visible stars to narrow it further by optical means.

I think it is well within physical possibility.

PhantomWolf
2004-Oct-05, 08:50 AM
I'm not sure that a radio telescope would be a lot of help really since it's got to be rather more portable, probably about the size of a PDA or a Tablet at the most.

Anyone got any guesses on how much of the sky would have to be visible to get a match?

Kaptain K
2004-Oct-05, 11:00 AM
If you *know* which stars you have found, three will give your location.
Actually, you need four to determine your position in 3D space. One gives you any point on a sphere, two gives you any point on a circle, three gives you one of two points, the fours the definite point. Usually you can guess the latter though.

EDIT: Eh, we will also need to know the distance to the stars for it to work. It is probably possible to do it without distances, but it will be a *lot* more complicated.
:oops: You are right! I plead "brain fade".

skrap1r0n
2004-Oct-05, 07:20 PM
Not to be a killjoy, but what happens if you crash land on a planet with a thick atmospehere so that the device cannot really see the stars?

Evan
2004-Oct-05, 07:30 PM
Start practicing how to say "Take me to your leader." :D

PhantomWolf
2004-Oct-06, 10:00 AM
Not to be a killjoy, but what happens if you crash land on a planet with a thick atmospehere so that the device cannot really see the stars?

Pray your emergency locator beacon works?

kucharek
2004-Oct-06, 10:13 AM
What kind of vehicle is used for travelling in the story? I mean, usually you should have a pretty good idea where you are when you crash land, so you don't have to check the whole galaxy. When you crash land with your Piper, you usually know pretty well which continent you're on...

PhantomWolf
2004-Oct-07, 09:02 AM
The main ships being used by those in the stories are snub-fighters. Basically a one man fighter craft (they use a variety of anti-grav devices and manoever jets for flight. In an atmosphere they act like a jet fighter, in space they can do a lot more if they have a good pilot. Poor pilots treat them like Jet fighters and rely on a computer to control the jets to control, good ones can turn them on and off themselves to literally be able to do almost anything.) They are typically planet or carrier launchedand have limited hyperspce capability. Hyperspace works as a '5th' dimension that can be accessed by basically tearing a hole in space. Inside of it distances are different because of the way it maps to realspace, the trouble is that gravity distorts it into mountains and valleys, so most travel is not in straight lines in side it, nor does it correspond to a straight line in realspace. If a calculation is wrong, or the ship exits early or late, it could end up light years off track, hence the ability to get lost.

ZaphodBeeblebrox
2004-Oct-07, 11:05 AM
The main ships being used by those in the stories are snub-fighters. Basically a one man fighter craft (they use a variety of anti-grav devices and manoever jets for flight. In an atmosphere they act like a jet fighter, in space they can do a lot more if they have a good pilot. Poor pilots treat them like Jet fighters and rely on a computer to control the jets to control, good ones can turn them on and off themselves to literally be able to do almost anything.) They are typically planet or carrier launchedand have limited hyperspce capability. Hyperspace works as a '5th' dimension that can be accessed by basically tearing a hole in space. Inside of it distances are different because of the way it maps to realspace, the trouble is that gravity distorts it into mountains and valleys, so most travel is not in straight lines in side it, nor does it correspond to a straight line in realspace. If a calculation is wrong, or the ship exits early or late, it could end up light years off track, hence the ability to get lost.

Babylon 5 used a similar FTL System.

They Compensated, by having Hyperspace Beacons, that Ships could Track.

If you fell off the Beacon, you'd have just the Situation, you described, However, I would Imagine the Greatest Danger, would Lie in Getting Lost in Inter-Stellar Space, with a Broken Hyper-Drive ...

sidmel
2004-Oct-07, 04:04 PM
What about having your PDA type locator take a sample of the local galactic gravity 'finger' print? If we can assume it's far enough in the future to detect distant sun's gravity influence on the local star system with such a small instrument.