Slashdot Mirror
Pulsar Signals Could Provide Galactic GPS
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.
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.
Is there anyone who can help me figure out something to do with my Pulsar's wiper blades?
First pulse
> 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.
Warning: this article may contain humor, sarcasm, parody, and perhaps even irony. Read at your own risk.
...that uses metric pulsars.
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.
The Christian Right is Neither (Christian nor right). See: Matthew 23, Matthew 25, Ezekiel 16:48-50
Cool concept, but it seems like it would be of limited use until someone develops FTL.
âoeAny society that would give up a little liberty to gain a little security will deserve neither and lose both.
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.
When our name is on the back of your car, we're behind you all the way!
make it so number one
I want my FTL drives to escape the Cylon overlords.
..as far as my "Wing Commander" Knowledge is still intact. :-)
The Russians would of just used an old pencil and a map.
http://en.wikipedia.org/wiki/File:VgrCover.jpg
Sorry, but until it's supported by my iPhone...
Meta will eat itself
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.
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 on the subject.
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.
How large would the antennas need to be?
Set your phasers on "funky"!
...to non-existing problems hilarious!
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?
0, 0, 1 Sweet 0, 0, 1
The additional complexity of working with signals over these distances is that relativity has to be taken into account
Friggin' In-Laws ruin Everything!
Sig Follows: "Suppose you were an idiot. And suppose you were a member of Congress. But I repeat myself." -- Mark Twain
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.
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.
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.
Fight Spammers!
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?
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.
"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?
I've heard of people who think they're the center of the universe, but this is just insane!
Quoting from Wikipedia:
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.
Get off my lawn.
It was conceived about the time pulsars were discovered.
...you can use triangulation with known quasars, which is easy but imprecise.
Non-Linux Penguins ?
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.
CUR ALLOC 20195.....5804M
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.
This is not just fanciful - do we want the two time references to slowly fall out of sync ?
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.
http://en.wikipedia.org/wiki/Attitude_dynamics_and_control#Star_tracker
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.
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.
Jumpstart the tartan drive.
...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.
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?
I cannot confirm nor deny the allegation or allegations you may or may not have just made
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.
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.
A republic cannot succeed till it contains a certain body of men imbued with the principles of justice and honour.
Now I'm just waiting for a several thousand dollar luxury wristwatch that can scan for pulsars.
“Common sense is not so common.” — Voltaire
Now people will have an excuse for driving their starships straight into a supernova. "But the GPS said to turn 'up' here!"
Don't underestimate the power of The Source
Isn't this what the real basis of stardates is supposed to be?
In the sense that this method was used to calculate locations in spacetime, before all those comms satellites were placed out to create beacons.
Also, this reminds me of the article i think i saw on here a couple years back or so that mentioned that alien races could probably be using stars as communication.
A massive grid would have been placed around said star to alter the frequencies that would get out.
It would be one of the better methods for communicating long distance.
But in saying that, if we achieve FTL at some point, we'd be better off making our own communication networks. (or if we meet aliens with one already built, ask them very nicely if we can use it and promise not to use it for torrents)
But we need to actually figure out if we can even TFTL in the first place!
I'm saying 60 years.
Hey look out for that Asteroid *swerve* whew! . . . "Recalculating" "Recalculating"
uhm, what's going on here? kdawson made an insightful/informative comment about the summary!? Maybe he just failed to put quotes around something someone else said?
The mentioning of slow down and drift comes to mind.
This is the same problem that the "Ancients" had to deal with when building the Stargate system.
Any gates that had been cut-off were out of sync and had to be updated manually.
So i guess as long as you have line-of-sight to at least 4 pulsars, you'll be fine.
This system says that they would only use 4, so it would probably fail in that respect.
If they could find the pulsars all on the outsides of the galaxy, it would be really helpful.
Speaking of that, does anyone have any links to maps of pulsars in our galaxy?
Still, the whole "How do i FTL?" problem isn't solved... yet.
Hopefully we will figure it out, because it must be possible, blackholes aren't some magical mysterious thing that defies "the laws of physics", If the laws can break down, the laws are not laws!
Kinda off-topic, but one of my sci-fi horror scenarios would be being lost in near space, out of sight of earth (far enough that it looks like another star), with limited propulsion (based on an issue of the comic Star Brand decades ago where the hero gets into a fight in space and becomes disoriented). Would this device work as well as a handheld blackbox GPS that you could use to orient yourself home?
I swear to God...I swear to God! That is NOT how you treat your human!
... the aliens turn on SA and encrypt the pulsar's timing signals.
Have gnu, will travel.
On that plate he had welded to Voyager?
I am very small, utmostly microscopic.
Well, while I was still doing "SETI@Home", for "Team Microsoft" -> http://setiathome.berkeley.edu/team_members.php?teamid=26482&sort_by=expavg_credit&offset=60 (#76, that's me there, lol, & to think I used to be as high as #12 on that chart)...
I said this, while checking the "optimized version" of the character-mode/tty/DOS mode clients (by BOTH Trux & Cruncher), I said WE were going to function one day as Star Traveller's first "stellar cartographers", & in fact, here is that very statement:
-----
http://setiathome.berkeley.edu/forum_thread.php?id=27644&nowrap=true
"We're their 'stellar cartographers' in a way if you think about it: Giving them potential targets to journey to, based on data gained from this project."
-----
Who would've guessed that "PULSARS" (what they're trying to detect for iirc, it's been a LONG while since I did that, & I moved onto Folding@Home afterwards for a good bit also) would be the target data centers used for this type of thing!
APK
P.S.=> Perhaps my "ESP" was operating @ peak efficiency that day? 'Inquiring minds want to know', lol... got lucky I guess (maybe)?? Who knows, but, this is pretty cool stuff, & I hope it works out one day - be cool to know that some good came from SETI@Home, @ least in terms of data for pulsar stars for this type of application this very thread is all about... apk
Someone enlighten me. I know with local GPS, the time is encoded on the signal. Its not just a difference in "tick"'s from different satellites. At some point a time is encoded to tell us which "tick" that last "tick" was. I'm going out on a limb and saying no one's flown out to these Pulsars and encoded "which millisecond tick is which" in the datastream. So if my ship flies inside a large hole in an asteroid (while avoiding Xur and the Kodan Armada), when I come back out, how will I know how many milliseconds I've missed from each pulsar? Surely across Galactic scale, and relativistic effects. . . just accurately counting the time between ticks from Pulsar to Pulsar won't be enough to know where you are. You'll have to know which tick is which. (Or is everyone assuming its like gyroscopes. . . you spin them up, and have to keep them going. . . or you're lost forever . . .)
What am I missing?
jkh
No, I don't remember your name. But the memory mapped screen on a TRS80 from 1977 is from 15360 to 16383 if that helps.
Road side maps will no longer have the big sticker "You are here" to mark your location but would have a big sticker "You are here, right now" to mark your position in space time. Wow.
it is only after a long journey that you know the strength of the horse.
Star maps are the equivalent of a compass. They tell you which way your nose is pointing, but not where you are or how fast you're moving.
Tracking the relative timing of pulsar bursts locates your exact position to a meter or so, and tracking position over time you find your velocity. However it isn't as good as the star map for telling you which way you are physically pointing.
The Voyager spacecraft, one of the etchings on the plaque on it shows the earth's location (very roughly) with angles, timing information (i.e. pulse rate), and estimated distances to 14 selected pulsars. Pioneer 10 and 11 also had a similar plaque, they were designed in 1970 or 1971.
A minimum of 3 satellites are needed for position, but the results are mostly useless to the average person with that few satellites. 4 or more are needed.
As per Wikipedia:
"It might seem three satellites are enough to solve for position, since space has three dimensions. However, even a very small clock error multiplied by the very large speed of light[19]â"the speed at which satellite signals propagateâ"results in a large positional error. Therefore receivers use four or more satellites to solve for x, y, z, and t, which is used to correct the receiver's clock. While most GPS applications use the computed location only and effectively hide the very accurately computed time, it is used in a few specialized GPS applications such as time transfer, traffic signal timing, and synchronization of cell phone base stations."
And to give some credit to this post, as per Ahmed El-Rabbany in "Introduction to GPS: The Global Positioining System"
"To determine the receiver's point position at any time, the satellite coordinates as well as a minimum of four ranges to four satellites are required [2]. The receiver gets the satellite coordinates through the navigation message, while the ranges are obtained from either the C/A-code or the P(Y)-code, depending on the receiver type (civilian or military). As mentioned before, the measured pseudoranges are contaiminated by both the satellite and receiver clock synchronization errors. Correcting the satellite clock errors may be done by applying the satellite clock correction in the navigation message; the receiver clock error is treated as an additional unknown parameter in the estimation process [2]. This brings the total number of unknown parameters to four; three for the receiver coordinates and one for the receiver clock error. This is the reason why at least four satellites are needed."
If you've ever turned on your GPS and it has initially said that you were across the country, that's likely because it only resolved 3 satellites. Your car GPS, usually, quickly solves this by taking your last known height (with a known parameter ie. z-axis one only needs 3 satellites for an accurate position). While a bit of a hack, it's usually good enough for handheld/car GPS accuracy.
As an aside, El-Rabbany in person is convoluted and a bit of a prick. He did, however, have an excellent editor for his book.
I've been looking into this since 2001. The biggest real problem is detecting the pulsars. The free space signal loss is on the order of -400db. The math is much harder than dealing with GPS and you have to find the easy way to figure out tick counts. Other than that, its workable. Modern GPS receivers do have methods to remove pulsar noise from the signals they are watching. Defining a coordinate system will be a mess as well but that could lead to a reasonable way to define things for all planets as well. Nearly everything in space rotates and most rotate the same direction in about the same plane so you can define a north and south. The real problem is how do you define the origin of Longitude? I suspect the best way is define it by the highest point on the planet but that leads to problems when the highest point is at the unstable edge of an active volcano. What do you use as a reference for a solar system or a galaxy?
Lol they encoded 0.38800000 when the actual value is 0.388481.
Maybe the aliens will figure out that we normally measure time in seconds, and that we converted it to hydrogen spin-flip transition periods just for them. :)
Why is it so hard to measure the pulsar period anyway? You just need to probe its current phase every once in a while in the course of two weeks to get 6 digits. 3 digits means they only looked at it for ~15 minutes with no follow up.
Don't laugh! :-) This reminds me of Dr. Paul LaViolette's theory on extraterrestial beacons in outerspace.
"Our modern society is dependent on accurate timekeeping, which is why we rely on atomic clocks to give the correct time for use with the myriad of timekeeping devices we use today. Just as we rely on atomic clocks for split-second accuracy, they in turn are set using pulsars. First discovered in 1967, pulsars are rotating neutron stars that emit electromagnetic radiation in the form of radio waves. According to LaViolette, pulsars are not naturally occurring objects, but rather, they represent an intelligent design. One intended for timekeeping, navigation and which serves as a faster-than-light warning system for events called galactic superwaves. At best, these superwaves are an annoyance to industrialized societies. At worst, they can and do trigger extinction level events (ELE). LaViolette tells that there have already been numerous ELE cataclysms on Earth and that our planet is now moving into the cross-hairs of yet another."
found here
Dr. Paul LaViolette has written four books and has published many original papers in physics, astronomy, climatology, systems theory, and psychology. He received his BA in physics from Johns Hopkins, his MBA from the University of Chicago, and PhD from Portland State University, and is currently president of the Starburst Foundation, an interdisciplinary scientific research institute. He is the developer of subquantum kinetics, a novel approach to microphysics that accounts for electric, magnetic, gravitational, and nuclear forces in a unified manner and resolves many long-standing physics problems. Based on the predictions of this theory, he developed an alternative cosmology that effectively replaces the big bang theory."
click
Relativity is not the reason for stating both the location and time of the origin. Cambridge moves through space along with the Earth, on which it is located. Even only in terms of its location relative to the Sun, Cambridge is 200 million miles in July from where it was in January.
- Jupiter 2
How will he lose weight if he can't eat his sub from subway because someone made it invisible!?