Navigation for Spaceships Using X-ray Pulsars: Introducing XNAV

This could be the ultimate galactic GPS system: using pulsars as an interstellar navigation tool. Rapidly spinning neutron stars emit focused beams of X-rays into space and many, with accuracy as good as an atomic clock, have been mapped by astronomers. Now these pulsars may have a very important practical use. These interstellar beacons may be used to get a fix on the position of spacecraft and guide them around space…

Ever since the first X-ray pulsar was discovered in 1967 (called Centaurus X-3, the third X-ray source discovering in the constellation of Centaurus with a period of 4.84 seconds), astronomers have been busy mapping the distribution of these rapidly spinning stellar objects. Pulsars are the embodiment of a neutron star binary system; the neutron star strips the material from its stellar neighbour, accelerating the gas to about half the speed of light, blasting hot collimated X-ray emissions from its poles. As the pulsar spins, these beams of light act like a lighthouse, and should they be directed toward the Earth, we observe a highly accurate periodic flashing of X-rays.

At the beginning of this month, the IEEE/ION Position, Location and Navigation Symposium (PLANS) 2008 conference in Monterey, California featured two interesting concepts for the use of these highly accurate X-ray sources. The first proposal called “Noise Analysis for X-ray Navigation Systems” headed by John Hanson of CrossTrac Engineering, introduces a scaled-up version of terrestrial GPS, using pulsars rather than man-made satellites. The system is called X-ray navigation, or “XNAV” for short. Primarily focusing on space missions beyond Jupiter, XNAV would use the Solar System as the base co-ordinate and then measure the phase of the incoming X-ray emission from the mapped pulsars. As the X-ray pulses are so accurate, onboard systems could measure and compare the signal from multiple pulsar sources and automatically deduce the position of the spacecraft to a high degree of certainty. I suppose it would be an advanced 3D version of the traditional sextant as used by ships to measure the elevation of stars above the Earth’s horizon.

The second concept entitled “Online Time Delay Estimation of Pulsar Signals for Relative Navigation using Adaptive Filters“, is headed by Amir Emadzadeh at the UCLA Electrical Engineering Department. Emadzadeh suggests that the location of two spacecraft can be worked out if both ships are looking at the same, known pulsar. The periodic emission measured by both ships will have a differential time delay proportional to the distance between the ships. In addition, the UCLA group suggest a method to derive their relative inertial position by observing a distribution of X-ray sources throughout the cosmos.

These are very interesting concepts, but until we begin routinely venturing beyond the orbit of Jupiter I doubt we’ll see these ideas come to fruition any time soon…

Original source:
Additional info: IEEE/ION PLANS 2008 conference

28 Replies to “Navigation for Spaceships Using X-ray Pulsars: Introducing XNAV”

  1. The big challenge for this is that pulsars “shine” (emit pulses) in two circular bands; you leave those bands, and you no longer see those pulsars.

    What we’d like is a map not only of the pulsars, but a detailed analysis to know what those circular bands are, and where on the sky they point! This is going to require a lot of powerful observing tools to figure this out, but pulsars are fantastic tools!

    Glad to see that someone else has found great uses for pulsars, I was worried that I was the only one!

  2. Nicholos, Pulsars would clearly make an excellant navigation beacon. However, I don’t believe man will ever leave the solar system. Why? You ask. Because man is extremely fragile both mentally and physically. All this crap about intragalatic space travel is just sci-fi blather. Oh, we will get one or two scientists on Pluto or maybe on one of the further out astroids in maybe a hundred years or so. But no further. Like I said, man is too fragile for a multi-generation deep-space trip. Mankind will need some heretofore unknown phenomenon to get past the speed of light to do any sensible space travel. If Einstein is correct, we aint going anywhere outside the influence of our sun.

  3. This sounds soooooo cool to me. Makes me feel like we are definitely, 100% on our way out of the Solar System once we don’t need to rely on transmissions from our own planet for spacecraft navigation. Cool article!


  4. Nice, this will be useful if we ever decide to launch probes under or above the plane of our galaxy.

  5. In a simpler way, pulsars are already being used for interstellar navigation. The graphic with lines coming from the center on the Voyager record

    and Pioneer plaque

    is a map: Earth is at the center. Each line coming from the center points to a particular pulsar. Along each line (though it’s hard to see) are a pattern of dots that encode the period of the pulsar.

    The idea is, when an alien civilization finds Voyager or Pioneer, there’s a chance they, too, will have discovered the same pulsar (the periods are unique, given enough precision on the measurement.) The map will allow the alien civilization to triangulate back to Earth.

    Sounds just like GPS to me!


  6. Two comments:

    – If these are only visible to us if we happen to be in the direct line of fire of the “beacons” then there must be a heck of a lot more of them than we have catalogued so far. If they do point in random directions, only a very tiny fraction would be aimed at us, given all the other directions they could point in.

    – I have always found it a bit difficult to picture a natural event that would result in something that big rotating that fast without flying apart. So to get a little woo-woo, tin-foil hat-like here: what if these actually ARE artificial beacons, similar to our own lighthouses or warning signs?

    Perhaps we are looking for the wrong thing with SETI. Wouldn’t intelligent species advanced enough for interstellar travel have progressed to communicating with vastly different technologies then primitive EM waves? Perhaps they even send their email equivalents through the same channels as they travel, none of which we could detect at present with our relatively stone-age tools.

    Maybe we should think a little bigger here. It might be child’s play for an advanced civilization to set up a traffic system on an interstellar scale.

    Just askin’…

  7. Chuck, an individual may never get past our sun, but slowly, generation by generation we will get furthur out, in a millienia (if we still exist) imagine how far we could get even if we cant get past the speed of light (someone calc that distance?)

  8. Sounds like something the Zalkons use to navigate interseller space.

    Star Trek: The Next Generation
    Transfiguration. Episode 25
    First Aired 6/4/1990.

    Anybody know of an earlier reference to a pulsar based navigation system in Sci-Fi?

  9. @geokstr

    Just as a figure-skater spins more quickly as they tuck their arms in close, so must a star spin more quickly as it collapses, in order to conserve angular momentum.

    In the case of something like a pulsar, you have a spinning object more massive than our Sun collapsing into an object just 20km in diameter. That’s a lot of angular momentum in an awful tiny package. 🙂

  10. Neil, Do the numbers just to get to Alpha C. Base the calculations on, say, a ten-fold or twenty-fold increase in speed over what man can do currently. The trip duration is mind boggling. Multi-generation space travelers will most likely suffer extreme mental disorders assuming no life-support system breakdowns kill them first. Not to mention intra-breeding problems. Neil, I don’t think deep-space travel will be part of man’s destiny. We are simply to fragile.

  11. Steven, Clearly you have a problem with reality. The road to “hell” is paved with the bodies of those who believe they can do anything. Keep on dreaming. I suspect dreams are all you have.

  12. Peter and Geokstr, Actually any large galaxy will do as a navigation beacon. It can be seen from any direction where pulsars can’t. Triangulation would be much simpler.

  13. -Chuck Lam

    “man is extremely fragile both mentally and physically”

    This is of topic but I am so sick of this crap. I have no idea what your definition of a Human is, but it seems to me to be a definition of some pathetic backward scared creature.

    Don’t base a definition of a Human on yourself Chuck.

    If you have ever read even once in your life about what Humans have done and overcome to do in many situations throughout recorded history you find out we are NOT fragile both mentally and physically but are one of the toughest, adaptable creatures and are up for the challenge of space exploration.

  14. Chuck Lam, If it takes a few bloody noses or worst a few thousand dead bodies to get Humanity to the stars, that is a price worth paying.

    It it you that needs a reality check on what Humanity can do, its only a matter of time before we reach the stars. History is repeat with nay-sayers of one type or another, you and your kind will be laughed at in years to come.

  15. Steven, Stop and think about a multi-generation space trip to Alph C for a moment. Do you honesty believe that a small crew of hand picked scientists can procreate for dozens of generations without losing something genetically critical to the safety of the flight? Ok, let’s assume that all of the technical and biological challenges are overcome and this imaginary flight succeeds. Then what? It the trip took a millennium to complete, how would success be communicated back to earth? Modulated EM transmissions simply won’t make it. Do the math. Maybe a return trip back to earth? Who would be interested after so many generations passing on earth? Steven, there is nothing logical about an intra-galactic trip to Alph C, our closet star system neighbor. The time problem is the painfully slow speed of light. I have said this several times before, If man or any alien intelligence can not overcome the speed of light by several orders of magnitude, we ain’t going anywhere outside the influence of our sun. This is the reality of space travel. Anything else is sci-fi babble.

  16. Hi guys,
    I posted this on the MRO string about pheonix lander before I read this post and thought it could save all of you some bloody noses.

    It’s almost like 1969 again, America is at a war ,nobody likes it, people are unhappy with political leadership, but throught out all this paul we still can move our, this human foot print, futher into the heavens for all mankind.

  17. Chuck:

    But what if they are warning signs, to keep travelers away from very small specific regions? Kinda tough to use other galaxies for that, I would think.

  18. Qev:

    Thanks for the angular momentum lesson. I never got much past the figure skater analogy.

    However, it still boggles that something even that size could spin hundreds of times a second.

  19. Chuck:

    To give an example closer to home, sailors (before GPS) could navigate using the stars and other far away signposts, but those more local lighthouses were still the best protection against hitting the rocks.

  20. Chuck – In London before the 19th century ended, people saw a problem in the future, the streets of London where going to fill up with horse dung, an expected 8 meters high level was predicted for the early 21st century then someone invented the car around the dawn of the 20th century.

    All I am saying we should all keep an open mind of what is to come.

    I understand your point of view, but all the relative facts will change in the future, that is what science is all about.

    Further more its pointless arguing about this as nether of us will live to see who will be correct.

  21. Steven, My mind is open to the possibility of multi-generation deep space travel. It just will not be with human cargo. Robotics yes! Humans no! I chuckled at your reference to the late 19th century London dung problem. Just imagine for a moment having to deal with a millennium’s worth of a few space travelers and their offspring’s fecal matter requiring ongoing recycling. We’re talking hundreds of tons of material. I’m not joking. Every molecule of material and joul of energy on a human occupied space ship has to be positivetly accounted for and dealt with very efficiently or there will be a catastrophic trip failure. The slightest miscalculation will result in disaster. I really believe most people fail to understand the technological or biolological magnitude of what is involved in space travel we are discussing. Positive “we can do anything given enough time” thinking will not make it. for human or alien intelligence deep-space travel. Space is not a human friendly place. Another thought for consideration concerning why extended space travel won’t happen and that is the mind boggling cost and return on investment for a high risk prototype venture. In fact cost and ROI may be the largest single obstacle to long range space exploration. And by the way, we are not arguing, we are debating the possibility of space travel. Steven, open your eyes, it isn’t going to happen with humans. Man will make it to Mars, Pluto and maybe an asteroid or two beyond pluto, but no further.

  22. Zeb, The human species will not survive long enough to develop the surgery and reconstituting techniques you suggest. Your second sentence should read in part . . . “sending dozens of generations of human bodies across light years of deep space.” I suspect if an attempt is made to build a bio-sphere space vehicle in the next couple hundred years for a trip to Alph C; it will most likely be larger than the Merchandise Mart in Chicago. A guess is this would be a minimum size vehicle to support, say, a half dozen science engineers ready for a millennium nightmare . Hmm . . . I wonder who will put up the billions of dollars required to build this folly and who will volunteer for the mission. I sure would like to be around to see what develops.

  23. We can solve the problem of manned interstellar trips with robotics. The main problem seems to be with sending a human body across light-years. Ok, then, don’t send the human body. Remove the brain, put it in a hermetically sealed jar, and send that. Hook the brain up to a virtual reality system and you’re all set.

    On the way there, the only space a human would need to take up is about three liters. The ship could be the size of current day space probes. Life support and radiation protection are highly simplified, and there is no danger of going crazy because of the nearly unbounded virtual worlds that the crew would “live” in.

    On arrival, use robotic bodies that have been stored along with the ship (again, very little space needed to do that).

    A human body IS fragile, so it would a lot easier if we got rid of it.

  24. I suspect that once computers have achieved both superiority to the human brain both in calculating and cognitive superiority that all bets are off in what we can do. And that achievement is expected in the next 30-50 years. But I agree with Chuck that humans won’t be leaving the solar system anytime soon, if ever. That doesn’t mean our children (intelligent and sentient machines) won’t be. Seems to be the next logical step in evolution to me.

  25. Gary, It won’t be we, it will be them. The thought of sentient machines scares the hell out of me.

  26. Guess that re-deifines the term ‘Sat-Nav’

    ok, crap joke

    But will such a system send hordes of unwary space-travellers down dead-ends, careening into black holes, even though the darn hardware used swaers blind it’s safe to proceed?

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