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Pulsar Signals Could Provide Galactic GPS

kdawson posted more than 4 years ago | from the pioneer-10-was-there-first dept.

Space 146

KentuckyFC writes "We're all familiar with GPS. It consists of a network of satellites that each broadcast a time signal. A receiver on Earth can then work out its position in three-dimensional space by comparing the arrival times of the signals from at least three satellites. That's handy, but it only works on Earth. Now astronomers say that the millisecond signals from a network of pulsars could allow GPS-style navigation on a galactic scale. They propose using four pulsars that form a rough tetrahedron with the Solar System at its center, and a co-ordinate system with its origin at 00:00 on 1 January 2001 at the focal point of the Interplanetary Scintillation Array, the radio telescope near Cambridge in the UK that first observed pulsars. The additional complexity of working with signals over these distances is that relativity has to be taken into account (which is why the origin is defined as a point in space-time rather than just space). The pulsar GPS system should allow users to determine their position in space-time anywhere in the galaxy to within a few nanoseconds, which corresponds to an accuracy of about a meter." Pulsars slow down over time, and the arXiv paper doesn't seem to mention this. The paper is mainly about establishing a coordinate system and a reference selection of pulsars. Any proposed Galactic Positioning System would have to take the slowing into account, and since it is poorly understood and not completely predictable, this would limit accuracy.

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146 comments

I would be pedantic, but... (5, Funny)

The_mad_linguist (1019680) | more than 4 years ago | (#28110109)

At this point, I'd normally be ranting about how the G in GPS stands for "Global", and that the summary is making an awful analogy, but then I realized that "Galactic" also begins with a G.

And then I realized that that still doesn't make "Galactic Global Positioning System" any better.

Re:I would be pedantic, but... (0)

Anonymous Coward | more than 4 years ago | (#28110585)

Call it GaPS .. there are sure to be some.

Galactic ? 1m is good enough on earth (1)

OeLeWaPpErKe (412765) | more than 4 years ago | (#28111475)

A good question is whether it would be feasible to receive these signals in a handheld device. Pulsars may not be eternal, but they're quite close indeed to that ideal, certainly much more so than any satellite we'd ever put in orbit.

In other words : could this be used as a GPS system on earth ? I believe 1 meter is more accurate than even recent GPS devices provide. Also, could this be used to have instant clock-sync in just about any computer in 3 components (an RC circuit to tune to the correct frequency) ?

Re:I would be pedantic, but... (1)

Bob3141592 (225638) | more than 4 years ago | (#28111819)

I seriously doubt that this could be made to work, since General Relativity denies the very notion of simultinaity required to coordinate signals. And this results from two monkey wrenches - the various velocities and accelerations of the pulsars, and the varying and unknown distribution of gravitational fields between the objects. Space across galactic distances is not Euclidean, and the degree of curvature is not constant from one place to another on large scales.

Naturally, I didn't RTFA, but I'd be surprised if this scheme is valid even in principle. See sig.

Re:I would be pedantic, but... (1)

RVT (13770) | more than 4 years ago | (#28112811)

Well, pedantic would be to note:

"A receiver on Earth can then work out its position in three-dimensional space by comparing the arrival times of the signals from at least three satellites"

is a wrong statement.
But this is /. Who cares?

Finally! That's a great use for them (0, Offtopic)

BadAnalogyGuy (945258) | more than 4 years ago | (#28110125)

Is there anyone who can help me figure out something to do with my Pulsar's wiper blades?

Re:Finally! That's a great use for them (1)

SEWilco (27983) | more than 4 years ago | (#28110457)

Just make sure that you use at least 50% blinker fluid in your windshield washer reservoir when traveling at relativistic speeds. That will reduce wiper friction and reduce cosmic ray wear.

Relativity also matters for GPS (4, Insightful)

John Hasler (414242) | more than 4 years ago | (#28110145)

> The additional complexity of working with signals over these distances is that
> relativity has to be taken into account...

Also true for high-precision GPS.

Re:Relativity also matters for GPS (4, Interesting)

HonkyLips (654494) | more than 4 years ago | (#28110661)

Yes you're absolutely correct. The current GPS system has to incorporate aspects of both special and general relativity in order to be accurate to the meter. Special Relativity predicts that time slows down proportional to speed and therefore the speed of the satellites becomes a critical aspect of calculating their own "time". Additionally, General Relativity predicts that time slows down as a body is influenced by gravity, and because the GPS satellites do not have circular orbits the influence of the Earth's gravity changes with their position (they move closer and further away from the Earth as they orbit) and this also needs to be taken into account. The overall effect of "relativistic time slowing" is tiny and is in the nano-second ballpark, however when calculating positions using GPS a few nano-seconds can mean a few meters...

Re:Relativity also matters for GPS (2, Informative)

Anonymous Coward | more than 4 years ago | (#28110993)

Yes you're absolutely correct. The current GPS system has to incorporate aspects of both special and general relativity in order to be accurate to the meter. ...

General relativity generalizes relativity to arbitrary smooth manifolds...

Re:Relativity also matters for GPS (2, Informative)

whoisisis (1225718) | more than 4 years ago | (#28112485)

> The overall effect of "relativistic time slowing" is tiny and is in the nano-second ballpark, however when calculating positions using GPS a few nano-seconds can mean a few meters...

No, it's in the micro-second ballpark (around 38 microseconds a day) which leads to
11 /kilometers/ of inaccuracy a day, if you do not count in relativity.

Re:Relativity also matters for GPS (0)

Anonymous Coward | more than 4 years ago | (#28111233)

> The additional complexity of working with signals over these distances is that
> relativity has to be taken into account...

> Also true for high-precision GPS.

Also true for every day GPS. Without relativity, we'd be off by 11 kilometers a day.

Europe is planning a competing system... (1, Funny)

Anonymous Coward | more than 4 years ago | (#28110163)

...that uses metric pulsars.

Problem with the galactic positioning system (4, Insightful)

kimvette (919543) | more than 4 years ago | (#28110203)

I see a problem with this immediately:

Unlike the global positioning system, the pulsars are always going to be moving relative to each other and to your position AND the reference point, which adds a tremendous amount of error. That combined with the unpredictable changes in chances in pulsars' emissions, makes the "GPS" somewhat unreliable for interstellar travel.

However, given that we're probably centuries if not eons off from traveling outside our solar system, it's a moot point. On the scale we can use it NOW (interplanetary probes, etc.) it should be highly accurate.

Re:Problem with the galactic positioning system (0)

Anonymous Coward | more than 4 years ago | (#28110611)

Unlike the global positioning system, the pulsars are always going to be moving relative to each other and to your position AND the reference point, which adds a tremendous amount of error. That combined with the unpredictable changes in chances in pulsars' emissions, makes the "GPS" somewhat unreliable for interstellar travel.

It would work on the short-term, and by that I mean for the next several million years at least.

Since we know the current relative position and speed of those specific pulsars, we can calculate a starting point for the 0,0,0,0 reference point (notice I include time as well). Since we know the direction/speed of each pulsar we can calculate the amount of shift per time and back-calculate to the original reference point. This also takes into account slowing of the pulsars, and for redundancy we could use more pulsars in case one starts acting goofy.

I would think that (if the theories hold true) that the ultimate point of reference would be the 'center' of the universe itself. I don't know if it's possible, but if we can figure the expansion rate of the universe I'd think we should eventually be able to determine what the starting point was, and use that for the universal zero coordinate.

Re:Problem with the galactic positioning system (0)

Anonymous Coward | more than 4 years ago | (#28111335)

the ultimate point of reference would be the 'center' of the universe itself. I don't know if it's possible, but if we can figure the expansion rate of the universe I'd think we should eventually be able to determine what the starting point was, and use that for the universal zero coordinate.

No.. it doesn't work like that... blow up a balloon(imagine there's no hole to blow it up with). Now the surface of that balloon is the universe... so tell me... where's the center of the surface of that balloon?

Now draw some dots on the balloon surface... those are galaxies. keep blowing it up. Can you determine where the center of the surface would be, if you were inside one of those galaxies and could see the other galaxies moving away from you?

Re:Problem with the galactic positioning system (1)

orgelspieler (865795) | more than 4 years ago | (#28112941)

Interesting analogy. Instead of a balloon it could be an inner tube or some other topology, and your point would be the same. One thing it allows you to envision is that if we could determine the topology, then we could determine the center of the hyper-universe (the balloon/air system), and determine the shortest multi-dimensional routes from one part of the surface of the balloon to another. Also, with the inner tube topology, if it expands too much, part of the universe will eventually collide with another part of the universe that used to be far away. What if that is already happening and we don't know it? Seeing as most of the universe is empty space, the odds of two large bodies (e.g. galaxies) colliding through such a manifold collapse or topology singularity seem slim. My brain hurts now...

Re:Problem with the galactic positioning system (3, Insightful)

Anonymous Coward | more than 4 years ago | (#28110619)

So you think the current GPS satellite constellation is fixed relative to some reference point on Earth (and therefore eachother as well)? Of course everything is moving relative to everything else in the system. Now that also means we need to know the position of the pulsars with a high degree of accuracy, just like we have to know the position of the GPS satellites now.

Re:Problem with the galactic positioning system (1)

evanbd (210358) | more than 4 years ago | (#28111661)

You don't need to know the pulsar locations that precisely -- it is sufficient to know the *difference* between the distances from the epoch to the pulsar and your spacecraft to the pulsar. To do that, you simply need to start at a known location and count pulses as you move.

Re:Problem with the galactic positioning system (3, Informative)

evanbd (210358) | more than 4 years ago | (#28111149)

It makes the problem more complicated, but it does not add error. You don't think the GPS satellites are stationary, do you? The source of error here is uncertainty in the measurements of those positions. And it actually isn't that bad -- start your spacecraft near Sol, with position well enough defined that you know which pulse you're receiving. (When observing, you can only see the relative phasing of the pulsars, unlike GPS satellites which transmit a time base.) Then you need to count pulses as you move. You then know that, relative to your starting point (or, equivalently, the epoch), you've seen X0 pulses from pulsar 0, X1 from pulsar 1, etc. Knowing how many pulses closer to each of the pulsars you are tells you how far you are from your starting point (in spacetime, not just space, obviously). The error bars get larger as you move enough to get parallax effects -- since from Earth we can only measure the distance to a pulsar with modest precision, and its velocity perpendicular to us with even less. If, however, you have a radio telescope that can resolve the position of the pulsar with good precision, you get to add a long baseline parallax measurement to correct for that. Add a timebase transmitter at Earth as well, and the errors basically disappear -- errors of a few nanoseconds should be readily available. And once you're far enough away from Sol to make that transmitter difficult (more than a few lightyears), you'll know the pulsar trajectories well enough it won't matter as much.

Re:Problem with the galactic positioning system (1)

Rich0 (548339) | more than 4 years ago | (#28112591)

I'd think a bigger source of error in practice is missed pulses. The system depends on counting pulses, and at any point if you get out of sync you are going to lose track of your position.

In GPS the satellites transmit the time that each packet is transmitted. So, the receiver doesn't need to be on continuously to not lose track of its location. Obviously the pulsars aren't going to encode anything in their signals so you're dependent on keeping track.

Wouldn't a simpler solution be to just put some transmitters in a few locations in the solar system for now, and in a few solar systems once we get to a point where we actually care about navigating between them?

Re:Problem with the galactic positioning system (3, Informative)

evanbd (210358) | more than 4 years ago | (#28112837)

Missing pulses isn't a big deal if you have an accurate clock. Phase locked loops can be tuned to handle lots of missing pulses very, very well. If you're not moving, or know exactly how you're moving, you know when the pulses arrive even if you don't actually look at them. If you're moving, and don't know precisely how, then and only then do you need to be actively counting pulses -- and unless you're accelerating by nontrivial fractions of c in between pulse arrival times, you can still miss lots of pulses before your error in predicted pulse arrival time grows terribly large. Somehow I doubt that will be a problem.

Re:Problem with the galactic positioning system (1)

pacificleo (850029) | more than 4 years ago | (#28111261)

I see a problem with this immediately:

your fear are misplaced . Migratory birds have been using Earth's magnetic field to navigate accurately for ages. AFAIK Pulsars are having somewhat simmilar mechanism. additionally any navigation system is supposed to give you a genral sense of direction don't expect it to plot the curve for you.

Far bigger problem: Directionality (1)

Roger W Moore (538166) | more than 4 years ago | (#28111645)

A far bigger problem is the directionality of the emissions. They send out highly directional beams. These will sweep out a hollow cone of some width. However if you move outside that cone you will not get a signal. This will mean that far more pulsars than just the four mentioned in the article will need to be mapped if you want to cover the galaxy.

Re:Far bigger problem: Directionality (1)

Hadlock (143607) | more than 4 years ago | (#28111895)

I'm sure the current 4 will work fine for the next 150 years or so, barring cheap FTL travel.

Turn Left at the Next Nebula (4, Insightful)

ATestR (1060586) | more than 4 years ago | (#28110207)

Cool concept, but it seems like it would be of limited use until someone develops FTL.

Re:Turn Left at the Next Nebula (4, Interesting)

squoozer (730327) | more than 4 years ago | (#28110523)

I wonder if this would actually be useful before we develop FTL travel. Presumably it's a comparatively simple receiver and some very clever software in which case deep space probes could use it to check their position. I would suggest that they use more than four pulsars though to improve accuracy.

Re:Turn Left at the Next Nebula (2, Informative)

MBGMorden (803437) | more than 4 years ago | (#28110787)

I would suggest that they use more than four pulsars though to improve accuracy.

There's a whole lot of research and development (and a cost/benefit ratio study) that needs to be done before just throwing out claims like that. If 4 pulsars get you down to 1 meter accuracy, yet 5 only increases it by 10% (and the 6th increases accuracy even less), yet costs millions more dollars to upgrade the probe to handle, then it's of no real benefit to use more than 4.

I need that accuracy! (1)

www.sorehands.com (142825) | more than 4 years ago | (#28110861)

Hey, when I am lost in space, that 1 meter difference is a big deal. I'll end up in the water instead of the beach when I travel 18,000,000,000,000 for my long weekend trip.

Several NASA probes already do this optically (2, Insightful)

mbessey (304651) | more than 4 years ago | (#28112277)

http://en.wikipedia.org/wiki/Attitude_dynamics_and_control#Star_tracker [wikipedia.org]

Deep Space 1 and Deep Impact both were equipped with optical navigation software. I think that the big advantage of Pulsar-based navigation would be for missions substantially outside the solar system, where the star atlas would be less reliable. Without really high-speed propulsion at a substantial fraction of light speed, I think you'd be hard-pressed to design a spacecraft that would survive long enough to need to use Pulsars for location information.

Re:Turn Left at the Next Nebula (1)

eth1 (94901) | more than 4 years ago | (#28111453)

"Warp...five point nine...parsecs then exit hyperspace left"

Re:Turn Left at the Next Nebula (1)

psydeshow (154300) | more than 4 years ago | (#28111987)

You're not going to be able to prove that you developed FTL travel until you can prove that you got to somewhere (and back, presumably) at faster than the speed of light. A galactic positioning system would be quite handy for figuring out exactly where that somewhere was, and how to get back home.

Anyway, it would be quite nice to know exactly where you were even if you stayed within our solar system. Plenty of room to get lost out there...

Already been done (1)

camperdave (969942) | more than 4 years ago | (#28110225)

Hasn't that already been done. I thought the starburst pattern on the plaques affixed to the V'ger probes indicated the position of Earth relative to a set of pulsars.

yep:Already been done (1, Informative)

Anonymous Coward | more than 4 years ago | (#28110377)

http://en.wikipedia.org/wiki/File:VgrCover.jpg

Re:yep:Already been done (0)

Anonymous Coward | more than 4 years ago | (#28111161)

Sheesh! I had to reach for my keyboard to copy and paste. Is it really too much trouble to throw a <URL: and > around that? If you had typed <URL:http://en.wikipedia.org/wiki/File:VgrCover.jpg> then we would have seen http://en.wikipedia.org/wiki/File:VgrCover.jpg [wikipedia.org] and we could just click on the link. Not only that, but you'd get karma points. But Nooo. You had to take the lazy way out, and make me do all the work. Shame on you.

Re:yep:Already been done (0)

Anonymous Coward | more than 4 years ago | (#28113049)

So how does an AC get karma points, and where can (s)he spend them?

Re:Already been done (1, Informative)

Anonymous Coward | more than 4 years ago | (#28110567)

Actually the closest we have to an inertial reference frame in the solar system is already using this idea. It has been extended to a terrestrial reference frame later. Informative links:

ICRF: http://en.wikipedia.org/wiki/International_Celestial_Reference_Frame [wikipedia.org]
ITRF: http://en.wikipedia.org/wiki/International_Terrestrial_Reference_Frame [wikipedia.org]

The technique used in both cases (which is prettey cool): http://en.wikipedia.org/wiki/VLBI [wikipedia.org]

Now that we're getting GGPS... (0)

Anonymous Coward | more than 4 years ago | (#28110277)

I want my FTL drives to escape the Cylon overlords.

Over Engineered (0)

Anonymous Coward | more than 4 years ago | (#28110375)

The Russians would of just used an old pencil and a map.

Emperor of Mankind (1, Funny)

Anonymous Coward | more than 4 years ago | (#28110437)

The only galactic GPS system I use is the beacon sent by the Emperor of Mankind. Granted the cost of a thousand psychers a day is high, but it's worth it.

Old news.... (5, Informative)

p_trekkie (597206) | more than 4 years ago | (#28110463)

This is not a new idea. Actually, this idea has been thought about before and dismissed. The researchers referenced propose using millisecond radio pulsars for navigation. This is a poor idea from an engineering standpoint because it requires having a large collecting area of radio dishes in order to get an apporpriate signal level.

A better idea, which is currently being researched, and was suggested four years ago (at least the earliest I recall it being mentioned) was using x-ray pulsars, which require much smaller collecting area. See for example this thesis [umd.edu] on the subject.

Re:Old news.... (2, Interesting)

Anonymous Coward | more than 4 years ago | (#28111097)

This is a poor idea from an engineering standpoint because it requires having a large collecting area of radio dishes in order to get an apporpriate signal level.

Well at least it means we'll be able to move the Earth throughout the universe with a high degree of accuracy using huge radio dishes! Now to work on building a propulsion system capable of moving the entire fucking planet. :-D

Re:Old news.... (1)

maxume (22995) | more than 4 years ago | (#28112509)

Better to move the entire solar system, the sun makes it nice and easy to maintain low entropy here on Earth.

Re:Old news.... (0)

Anonymous Coward | more than 4 years ago | (#28112649)

This is a poor idea from an engineering standpoint because it requires having a large collecting area of radio dishes in order to get an apporpriate signal level.

But that creates jobs man, and jobs right now are much more important than silly things like efficiency and productivity.

How accurate does it need to be? (2, Insightful)

wjousts (1529427) | more than 4 years ago | (#28110487)

Any proposed Galactic Positioning System would have to take the slowing into account, and since it is poorly understood and not completely predictable, this would limit accuracy.

Since we're dealing with interstellar distances, just how accurate do you need to be? Being off by a few million miles might be pretty good if you're talking about light-years of travel.

Re:How accurate does it need to be? (1)

Ackmo (700165) | more than 4 years ago | (#28110609)

"We've been thrown off course just a tad."

"What's that mean?"

"In space terms, about 70 million miles."

Re:How accurate does it need to be? (1)

skelterjohn (1389343) | more than 4 years ago | (#28110793)

Hide something in interstellar space, note its current GalacticPS coordinates and velocity, and come back years later to find it. Probably needs to be fairly accurate.

Re:How accurate does it need to be? (1)

dorix (414150) | more than 4 years ago | (#28111377)

And thus is born the sport "Galactocaching".

Re:How accurate does it need to be? (0)

Anonymous Coward | more than 4 years ago | (#28111765)

And thus is born the sport "Galactocaching".

"See that big black circle with the lens-like distorted stars around it? It's in there!"

Re:How accurate does it need to be? (1)

wjousts (1529427) | more than 4 years ago | (#28111519)

Ok, so maybe it won't work for interstellar pirates hiding their space booty, but if all you're trying to do is get from Earth to Alpha Ceti IV, you'll probably be close enough to see where you need to go.

geocentrism (1)

shadowofwind (1209890) | more than 4 years ago | (#28110547)

Fixing the coordinate system to a point near Cambridge will obviously cause the "galactic coordinate system" to oscillate around the sun. And they would try to fix the coordinate system's rotation relative to what? Absolute, or the earth, or the quasars, which are moving relative to each other?

Re:geocentrism (1)

shadowofwind (1209890) | more than 4 years ago | (#28110641)

Or rather, they are fixing it to an inertial reference frame that was centered near Cambridge at the appointed time in 2001? That still seems hard to nail down precisely over a long period of time.

Re:geocentrism (3, Informative)

Morphine007 (207082) | more than 4 years ago | (#28111349)

Not really ... it's just a point in space. They can figure out where everything else in the observable universe was, relative to that point. I mean, the reality is, that nothing in space is really all that fixed (since galaxies are spreading apart), but as far as intra-galaxy positioning goes, one point is just as good as another for a standard point of reference. We know where that point was, relative to most other points, at a specific time. That point doesn't complete an orbit of the sun every 12 months, even though the object it was based on does. Small distinction, but it's all that matters. They're going to be measuring position relative to the pulsars, and not measuring it relative to the focal point of a telescope in Cambridge.

Also, there's a bit of silliness in the summary - the braking index of pulsars is fairly well established. It's the causes that aren't really understood, since most pulsars apparently differ from the theoretical index (IANAP). The slowdown also seems to be constant, and gives pulsars a lifespan of 10^6 years. In a modern GPS system, one needs to know two things from each of the satellites Where the signal came from and when (the reality is that you really just need to know when it was sent, and you program the "where" into the receiver-unit in a manner that lets you know where the object would have been at that time). In a modern GPS system, they put really expensive and accurate clocks into the satellites, and the signal they send out encodes the time that the signal was sent. You figure out where you are, by calculating how long it took that signal to get to you, based off of the time received from other satellites

How the hell would a pulsar encode the time it sent its signal? Simple, the period of the signal from each pulsar changes over time... that's your clock. You know what the period was at 0000hrs 1 Jan 2001, and by how much it increases. So, when you receive the signal, you calculate how long, from 0000hrs 1 Jan 2001, it would take for the signal to have a period matching the one you received. You now know when the signal was sent from, and, the information on where it was sent from is programmed into the receiver-unit. Measure the same from the other pulsars and *bam*, there's your location.

Re:geocentrism (1)

Morphine007 (207082) | more than 4 years ago | (#28111423)

Which is to say, that receiving signals from pulsars whose signal period NEVER deviated, would tell you absolutely nothing about where you are, unless you're using a really narrow directional antenna to figure out exactly where (directionally, but not positionally) the pulsars are. Which is akin to visual triangulation... something that'd likely be a nightmare to engineer around. What you need is a clock in each of the sats, and the slowing *is* that clock.

Re:geocentrism (1)

mlyle (148697) | more than 4 years ago | (#28112025)

Nope. Phase difference between the pulses can tell you about changes in distances and thus your position; no slowing needed, just a knowledge of period and initial phase at a known reference time.

Then, a very approximate clock running from that reference time would tell you the expected phase differences between the next pulses at earth for the next pulse; differences from this lets you solve for x, y, z, and t at your location. If you are going to travel further than the pulsars' periods light distance from earth, you'd better have been tracking your position the whole time to remove ambiguities (or, with additional references and overdetermination it is possible to overcome this).

Re:geocentrism (1)

Morphine007 (207082) | more than 4 years ago | (#28112303)

Yeah, that would be an easier way to calculate distance from the pulsar (like I said, IANAP). However, the onboard clock from which you calculate the expected phase would need to take the change in period with respect to time (ie. the slowing of the pulsar) into consideration. You obviously have a better grasp on how to determine the distance than I do; I was mostly pointing out that, no matter what you do, the braking of the pulsar is understood and either forms the basis for your distance calculations or must absolutely be taken into consideration. It was mostly in response to the since it is poorly understood and not completely predictable crap that was written by Kdawson.

Pulsars slow down over time, and the arXiv paper doesn't seem to mention this. The paper is mainly about establishing a coordinate system and a reference selection of pulsars. Any proposed Galactic Positioning System would have to take the slowing into account, and since it is poorly understood and not completely predictable, this would limit accuracy.

Re:geocentrism (1)

skelterjohn (1389343) | more than 4 years ago | (#28110815)

It doesn't rotate around the sun. It is fixed in both time and space.

Re:geocentrism (1)

shadowofwind (1209890) | more than 4 years ago | (#28110995)

That statement doesn't seem to define the velocity, there being no absolute fixed space.

Re:geocentrism (1)

Morphine007 (207082) | more than 4 years ago | (#28111463)

correct, space is not fixed... unless you're talking about a fixed position in time. The point referring to the focus of the radio telescope in Cambridge UK *does* move. But the point referring to the focus of the radio telescope in Cambridge UK at 0000hrs 1 Jan 2001 does NOT.

Re:geocentrism (5, Informative)

PTBarnum (233319) | more than 4 years ago | (#28110977)

The native coordinate system is not a euclidean grid. Think of the pulsars as being clocks that are continuously broadcasting their local time. The 4 spacetime coordinates they define are just the values of those 4 clocks. In order to normalize this, I need to choose a 0 point for each clock, and the authors chose the values of the clocks as observed in Cambridge at the beginning of the millenium. Apparerently, by observing the signals, I can decide how much time (to the nearest 4 ns) had elapsed at each pulsar, at the time it broadcast the signal I'm now receiving. I can then define a transform that maps those 4 numbers into whatever local coordinate system I want. I could convert it to longitude/lattitude/UTC for terrestrial navigation, or some sort of heliocentric system for planetary navigation, or a galactic system for interstellar navigation.

Relativity, huh? (1)

mandark1967 (630856) | more than 4 years ago | (#28110689)

The additional complexity of working with signals over these distances is that relativity has to be taken into account

Friggin' In-Laws ruin Everything!

origin (1)

fortunatus (445210) | more than 4 years ago | (#28110757)

I think origin (0,0,0) [(0,0,0,0,0)?] should be at the Sun upon the start date - since the earth orbits the Sun _and_ rotates, this could remove a couple curliques from the system - of course I know the sun orbits the galactic center and other things, I'm just saying it would simplify the system some when it comes to resolving positional issues to some fine resolution in the future.

I agree X-ray sources are better than MHz sources.

Re:origin (1)

PhireN (916388) | more than 4 years ago | (#28111325)

No matter where you define the origin, your going to have the same problems.
Everything is going to move, at different velocities in different directions, even the origin.
To find a planet you will need know:
  1. Where it was at the time of origin
  2. Relative to the point of origin at the time of origin,
  3. How much time has passed since the time of origin,
  4. The velocity/acceleration of the point of origin
  5. The velocity/acceleration of planet.

This isn't hard for a computer to calculate. But you will never be able to locate a planet to just by a set of coordinates like you can do with GPS, you will also need to include a series of vectors regarding velocity and acceleration, which could get complex if you need describe complex orbits.

Re:origin (1)

maxume (22995) | more than 4 years ago | (#28112889)

The present position of Cambridge doesn't factor into it. Unless you are trying to compare something to the present position of Cambridge.

Nothing new here, move along (1)

Ancient_Hacker (751168) | more than 4 years ago | (#28110851)

Pulsars have been used for geodesic measurements for about 30 years. The nice short regular pulses make it possible to track the movement of continental plates down to the miliionth of a LOC length.

How accurate? (1)

TheCabal (215908) | more than 4 years ago | (#28110877)

IIRC, one of the methods we use to measure the distance to a pulsar is to look at the effects the interstellar medium has on the latency of the pulse. Assuming the ISM is uniform, I suppose this wouldn't be an issue, but wouldn't this cause accuracy problems if there was an area where the ISM was denser?

Directional GRB (1)

jadedoto (1242580) | more than 4 years ago | (#28110937)

Aren't pulsars directional? How would you see the pulsar if it isn't currently flashing in your direction... They have set orbits and would have a plane where they will be invisible. Not that we'll ever get that far as humans, but it does seem like a major show-stopper.

Re:Directional GRB (1)

the_other_chewey (1119125) | more than 4 years ago | (#28112537)

Aren't pulsars directional?

You fail at using TLAs to enhance your whatever. GRBs, or Gamma Ray Bursts,
are non-recurring events and don't have much to do with pulsars.

The astronomical acronym you might be trying to refer to is LGM, as in LGM-1 [wikipedia.org] .

remember the millennium bug (1)

G3ckoG33k (647276) | more than 4 years ago | (#28111025)

"They propose using four pulsars that form a rough tetrahedron with the Solar System at its center, and a co-ordinate system with its origin at 00:00 on 1 January 2001 at the focal point of the Interplanetary Scintillation Array, the radio telescope near Cambridge in the UK that first observed pulsars."

I really really hope they remember the millennium bug. We don't want to creat another one of those, do we?

Dupe from 37 Years Ago. Pioneer 1 Plaque (4, Informative)

clintp (5169) | more than 4 years ago | (#28111169)

Quoting from Wikipedia [wikipedia.org] :

Relative position of the Sun to the center of the Galaxy and 14 pulsars

The radial pattern on the left of the plaque shows 15 lines emanating from the same origin. Fourteen of the lines have corresponding long binary numbers, which stand for the periods of pulsars, using the hydrogen spin-flip transition frequency as the unit. Since these periods will change over time, the epoch of the launch can be calculated from these values.

The lengths of the lines show the relative distances of the pulsars to the Sun. A tick mark at the end of each line gives the Z coordinate perpendicular to the galactic plane.

If the plaque is found, only some of the pulsars may be visible from the location of its discovery. Showing the location with as many as 14 pulsars provides redundancy so that the location of the origin can be triangulated even if only some of the pulsars are recognized.

The data for one of the pulsars is misleading. When the plaque was designed, the frequency of pulsar "1240" (now known as J1243-6423) was known to only three significant decimal digits: 0.388 seconds. The map lists the period of this pulsar in binary to much greater precision: 100000110110010110001001111000. Rounding this off at about 10 significant bits (100000110100000000000000000000) would have provided a hint of this uncertainty. This pulsar is represented by the long line pointing down and to the right.

The fifteenth line on the plaque extends to the far right, behind the human figures. This line indicates the sun's relative distance to the center of the galaxy.

When out of the galaxy... (1)

dargaud (518470) | more than 4 years ago | (#28111333)

...you can use triangulation with known quasars, which is easy but imprecise.

"Pulsars slow down over time...' (1)

rnturn (11092) | more than 4 years ago | (#28111381)

The GPS ephemerides data stream includes parameters to model clock drift. A similar set of corrections could be included to provide a correction for the change in pulsar frequency.

Something tells me though, that this is a small problem compared to being able to detect the pulsar signals in the first place. Unless adding an Arecibo-sized dish to your cellphone or pocket-sized locator gizmo is an option.

Re:"Pulsars slow down over time...' (1)

Red Flayer (890720) | more than 4 years ago | (#28112243)

Something tells me though, that this is a small problem compared to being able to detect the pulsar signals in the first place. Unless adding an Arecibo-sized dish to your cellphone or pocket-sized locator gizmo is an option.

There's a much easier way to solve that problem, by centralization.

All you need is one array to detect the quasar pulses and parse them for location. Then, you can use a system to determine your location relative to that array -- combine the two sets of information and you'll have your position as triangulated from the relative quasar locations.

We could possibly use a set of satellites to triangulate & determine our location relative to the quasar-sensing array, so that we can then calculate our location based on the quasars.

This would enable us to replace our Global Positioning System with a Galactic Positioning System, as desired.

GMT - Galactic Mean Time ? (1)

Alain Williams (2972) | more than 4 years ago | (#28112043)

There has to be some base time, so what do we use ? Might as well base it on what we use already - GMT. A couple of things to sort out:
  • Gweenwich Mean Time is subject to Leap seconds - what about Galactic Mean Time ?
    This is not just fanciful - do we want the two time references to slowly fall out of sync ?
  • According to relativity things that occur at the same time to one observer, may not for another observer, see: Relativity of simultaneity [wikipedia.org] , so how meaningful is a Galactic Mean Time ?

Slow down? Pulars can also suddenly speed up (1)

parlancex (1322105) | more than 4 years ago | (#28112149)

Not only do Pulsars slow down over time but they also unpredictably and abruptly speed up. This is thought to be because of a collapse of the outer layers of the Pulsar as it gradually loses energy over time and due to the conversation of angular momentum this collapse will cause an increase in rotational velocity.

Polar or Grid coordinates? (1)

Midnight Thunder (17205) | more than 4 years ago | (#28112325)

Thinking about this, I wonder what sort of coordinate system you would use in your spacecraft? Would you use a polar coordinate system, with certain celestial bodies providing the center of the coordinate system? For example if you are in close proximity of a planet you use that, then outside of those bounds the star and then the galactic center, and so on? Or do you a grid (cube?) system with certain reference points to keep the grid in the right position?

Because reference points in space have this horrible tendency to move, I can see the mapping system being more dynamic that the surface maps we use for planets, so will probably need a planetary simulator to keep it precise.

Four Satellites (1)

matelmaster (1040950) | more than 4 years ago | (#28112433)

...from at least three satellites

That's actually a common misconception. In GPS positioning you have four variables to be determined, your position on the earth (X,Y,Z coordinates) as well as the error of the receiver clock. Because you don't have a high precision atomic clock in your Garmin and the Master Control Station doesn't monitor and adjust the clock in your handheld you need the signal of a fourth satellite to use its high precision clock to calculate exact time differences (distances).

The reason many handheld or car navigation systems also work with three satellites is that they keep one variable, usually the height, fixed in their calculations. You can either use the last known value if a satellite disappears over the horizon or you can just get it from, for example, the navigational maps in your system. When you're driving along some road it generally doesn't matter whether you're 100 meters above or below the road, but it may matter if you're 100 meters to the left or right. This usually doesn't impact the usefulness of the device very much but may allow you to get a fix on your location when you otherwise wouldn't.

Ok, so what are the coordinates of Earth? (1)

SAFH (65236) | more than 4 years ago | (#28112667)

All of this is fine and dandy, but they still don't tell us what the coordinates of Earth are. What good will this do us if we are abducted and need to get home?

As a commenter on Technology Review said, isn't this the same concept as NASA put on Pioneer F?

Just in time for the Touch refresh... (1)

Opr33Opr33 (1180091) | more than 4 years ago | (#28112909)

Here I was just hoping for standard GPS in the next iPod Touch but Galactic GPS - WOW!

Will it have audible turn by turn? If so please let it come with Majel Barrett's voice.

zero position (1)

aquabat (724032) | more than 4 years ago | (#28112981)

If we're going to do this, could we please make the origin at 00:00 Jan 1. 1970? I'd hate to have to write yet another date conversion function.

Galactic [G]PS in a watch? (1)

OrangeTide (124937) | more than 4 years ago | (#28113131)

Now I'm just waiting for a several thousand dollar luxury wristwatch that can scan for pulsars.

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