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I was reading an article that said pulsars could be used in the far future, by travelers, by acting as "lighthouses" in space and aiding in interstellar travel. In a galaxy wide civilization, would this be still necessary or beneficial, if they had a method of faster than light propulsion?

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    $\begingroup$ they're more like a gps than lighthouse: as long as there xray signals(astrophysical jet pointing at you) you can triangulate your relative position in space with parallax method and then Doppler shift see if you are approaching/staying away from the source. (Note frequency is just for identification of pulsar mentioned in a4android's answer.) $\endgroup$ – user6760 Oct 12 '17 at 1:56
  • $\begingroup$ What sort of ships are these travelers using? For good pulsar timing, you need a large radio telescope, and those can be a bit bulky. A ship the size of the Space Shuttle likely couldn't detect the requisite pulsars; something a couple hundred meters long could. $\endgroup$ – HDE 226868 Oct 12 '17 at 2:51
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    $\begingroup$ FYI, a Voyager spacecraft carries a pulsar map on its Golden Record. $\endgroup$ – user2851843 Oct 12 '17 at 8:51
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The simple answer is yes. Even with faster-than-light travel spaceships will start from a position below lightspeed they can use the pulsars to orient their direction of travel and initial location. Assume they travel the distant for their voyage, when they are again below lightspeed the spaceship and its navigation systems will be able to determine where they are.

This assumes while in FTL mode spaceships cannot 'observe' the pulsars. If spaceships could 'observe' pulsars while in FTL motion then navigation is much easier.

Essentially pulsars are excellent natural navigation beacons. They can be readily observed effectively anywhere in the galaxy. Each pulsar has a distinctive frequency and they have known positions in the galaxy. If a spaceship had shifted one thousand light years (assume it has used a jump-drive to instantaneously move), then by measuring the positions and frequencies of the reference pulsars it is suing for navigation it can determine where it is in relation to them and how far it has shifted. This is essential if the jump-drive in this example isn't accurate in where it materializes and a course correction is necessary to arrive at its destination.

In summary, if pulsar navigation is useful for sublight, interstellar travel, and pulsars most certainly will be, then it will be equally useful for faster-than-light travel too.

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    $\begingroup$ We are already experimenting with pulsar-based navigation for travel even within our very own solar system -- check out the SEXTANT subexperiment on NICER for details $\endgroup$ – Shalvenay Oct 12 '17 at 1:14
  • $\begingroup$ @Shalvenay Thanks for reminding me. That was something that had slipped my mind. The link is much appreciated. Good one! $\endgroup$ – a4android Oct 12 '17 at 1:25
  • $\begingroup$ To note some problems with pulsars: The cone of pulsar radiation is quite narrow, so you won't see most of known pulsars if you fly far enough. Also their rotation frequency changes and it is hard to say how good we will be able to predict this change. So pulsars would be good lighthouses in known areas, not so good in unexplored ones. $\endgroup$ – Vashu Oct 12 '17 at 4:37
  • $\begingroup$ @Vashu Those are good points. Some of the problems can be overcome by using pulsars that be observed at both departure & arrival points. If pulsars can be 'observed' during FTL that should be less of a problem. Rotational frequency changes will be, hopefully, better known by the time FTL travel is possible. Thanks for the challenging ideas. $\endgroup$ – a4android Oct 12 '17 at 4:47

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