Using Pulsars For Spacecraft Navigation 77
Jimme Blue writes "The use of pulsars as a GPS analogue holds the promise of fixing a spacecraft's location to within 5 km, anywhere in the galaxy. While not ready for immediate use, it may be ready for use within the Solar System in the next 10-15 years. From the article: '"The principle is so simple that it will definitely have applications," said Prof Werner Becker from the Max-Planck Institute for Extraterrestrial Physics in Garching.
"These pulsars are everywhere in the Universe and their flashing is so predictable that it makes such an approach really straightforward," he told BBC News.'"
Really old idea (Score:5, Informative)
This has been in use in sci-fi since the dawn of space opera. It gained sufficient use that it was internalized to the point that it's rarely mentioned anymore, you could even say it's why most sci-fi expects a reliable knowledge of location and date even in the face of miss-folds and unplanned time travel.
Re:Too Late. (Score:5, Informative)
Prior art (Score:5, Informative)
This isn't exactly a new idea:
http://en.wikipedia.org/wiki/Pioneer_plaque#Relative_position_of_the_Sun_to_the_center_of_the_Galaxy_and_14_pulsars [wikipedia.org]
Re:Visibility is an issue (Score:5, Informative)
Your logic is flawed. The Milky Way doesn't follow lie along the equator because the earth is tilted on it's axis.
The fact that we can see other pulsars (many of them) from within the Milky Way means that those pulsars are either rotating on an axis nearly perpendicular to the galactic plane (aka galactic equator), or they're tilted relative to to the galactic plane and we happen to be nearly perpendicular to their axis of rotation. Since we know that not all stars rotate in the galactic plane (e.g. the solar systems ecliptic plane is inclined about 60 degrees from the galactic plane, and we have now observed enough other planetary systems to know that isn't uncommon), then it's likely that some of the pulsars we can see are spinning approximately in the galactic plane, and that some are not. But given there are many more random orientations that are not on an axis perpendicular to the galactic plane, it's probable that most of the ones we can observe from earth are nearly perpendicular to the galactic plane, and will thus be visible throughout most of the galaxy. As we travel around the galaxy within the vicinity of the galactic plane, the pulsars we can see from any given point will be those that spin on an axis nearly perpendicular to the galactic plane, plus some smaller number at other orientations that happen to have an axis of rotation approximately perpendicular to a line between that point and the pulsar.
Re:Visibility is an issue (Score:4, Informative)
The earth's tilt and the solar ecliptic plane don't have anything to do with our ability to view pulsars in/near the galactic plane. What would affect it is the solar system's distance from the galactic plane, and by galactic standards, that's pretty small.
What is relevant is the axis of rotation of the pulsar, the angular height of it's beam, it's distance from us, and it's distance from the galactic plane (and any intervening matter than might obscure it). Again, what's probable is that most of the ones we see have an axis of rotation approximately perpendicular to the galactic plane, such that their beam is "approximately in the galactic plane", giving visibility to that pulsar from most stars near the galactic plane. The larger the angular height of the beam, and the more distant the pulsar, the farther outside a perfect "perpendicular line of sight" the pulsar will be visible.
Re:pulsars versus star tracking (Score:2, Informative)
How do we know a pulsar's period cannot change over millenia? I mean all sorts of things can change a pulsars period .. collision with a red dwarf for one.
The periods of pulsars do increase, in a well-measured way, as they age. (Collision with another random star is so nonsensically rare that I doubt it has happened to a single pulsar in the history of our galaxy.) The periods of regular stars also change, but in less well-measured ways, because we know their periods so much less precisely. We can measure the time of arrival of a pulsar pulse to accuracy of less than a microsecond, which gives us a positional accuracy (timing error times the speed of light) of a few hundred metres. A regular star, we can identify the stage of its rotation to an accuracy of ... maybe an hour? Positional accuracy: a billion kilometres.