7 ms·

In theory this is a much better approach than Earth satellites: the farther away an object is, the smaller its motion will appear. With hundreds or even thousan

In theory this is a much better approach than Earth satellites: the farther away an object is, the smaller its motion will appear. With hundreds or even thousands of "fixed" data points incoming, it should be possible to develop an incredibly accurate model for position in space.

fooker 9y ago
I suspect the latency might kill this idea.
- baseethrowaway 9y ago
  Not at all, if you take it into account.
  - fooker 9y ago
    Would you be happy to wait for tens of minutes to get a position lock?
    - handedness 9y ago
      One wouldn't be transmitting to pulsars and awaiting a response, but treating them as what they are: always-on beacons. The signals would always be present.
      - lorenzhs 9y ago
        Not even GPS transmits to the satellites, it only relies on observations of what the satellites sent. And pulsars are quite a bit further away than tens of light minutes :) Mars is currently 14 light minutes from Earth. PSR J2144-3933 is one of the nearest known pulsars, and it's some 587 light years away.
        pc86 9y ago
        Yes but if we're using it as a beacon the distance is irrelevant, isn't it? It's been "transmitting" for much longer than 587 years, we're already receiving a signal, and that's what we're using?
        lorenzhs 9y ago
        Exactly. The post I replied to said "One wouldn't be transmitting to pulsars and awaiting a response", and I expanded on that. The whole subthread of https://news.ycombinator.com/item?id=16288955 https://news.ycombinator.com/item?id=16288955 doesn't make much sense because nobody defined what they mean by "latency" and people are talking about different things.
    - misnome 9y ago
      Tens of minutes to get a position lock for your location in the entire Galaxy? Yes, that sounds completely reasonable.
    - thaumasiotes 9y ago
      Of course, if that was the best I could do. People will happily spend an entire day becoming unlost if they're lost. As long as they have the means to survive, they'll be willing to spend much longer than that.
    - Maken 9y ago
      Likely, after the first calibration you could keep moving around and updating your location, so as long as the system doesn't go down you always know your (relative) position as you travel through the galaxy.
      - ccozan 9y ago
        I thought of this as well. After the first lock, you can use inertial navigation.
      - kijin 9y ago
        Regular GPS does this, too. It takes about 12 minutes to download the list of currently active satellites and their attributes. The data is part of the signal from the satellites. Most GPS units do this in the background. But if you leave it unpowered for too long, it will need to update itself before it begins to work properly. The GPS in my dad's car used to have a flaky ROM, and it would show the car flying across the wilderness at over 400mph while it was updating.
    - emiliobumachar 9y ago
      If I can then keep the lock indefinitely, I don't see much of a downside.
    - tlrobinson 9y ago
      Yes, especially if it’s just to occasionally recalibrate an inertial guidance system.
- Lewton 9y ago
  What latency? They're talking about measuring millisecond pulsars, there's no latency
  - TheOtherHobbes 9y ago
    Indeed. But if you're travelling significant distances, you're not going to be able to assume the space between you and all your beacons is flat. For good accuracy you'd need a predictive spacetime curvature map for the entire galaxy, and that might not be an easy thing to generate.
    - solotronics 9y ago
      it would probably be an advantage to measure the shift effect from multiple sources as you travel whatever fraction of the speed of light, giving both your position and derivatives such as velocity
widdma 9y ago
This is exactly what is already done! On Earth at least. Radio telescopes around the world observe (mostly) quasars to perform geodesy. This is the main method used to measure the Earth Orientation Parameters which is need for keeping GPS/GNSS calibrated. With it, you can measure distances of several thousand km with a precision on the order of a few millimetres. The problem is that it's really expensive compared to GPS: at each site you need a reasonably size telescope, atomic clock, some serious storage, and a way to ship all the data to a central cluster.

fooker 9y ago

I suspect the latency might kill this idea.

baseethrowaway 9y ago
Not at all, if you take it into account.
- fooker 9y ago
  Would you be happy to wait for tens of minutes to get a position lock?
  - handedness 9y ago
    One wouldn't be transmitting to pulsars and awaiting a response, but treating them as what they are: always-on beacons. The signals would always be present.
    - lorenzhs 9y ago
      Not even GPS transmits to the satellites, it only relies on observations of what the satellites sent. And pulsars are quite a bit further away than tens of light minutes :) Mars is currently 14 light minutes from Earth. PSR J2144-3933 is one of the nearest known pulsars, and it's some 587 light years away.
      - pc86 9y ago
        Yes but if we're using it as a beacon the distance is irrelevant, isn't it? It's been "transmitting" for much longer than 587 years, we're already receiving a signal, and that's what we're using?
        lorenzhs 9y ago
        Exactly. The post I replied to said "One wouldn't be transmitting to pulsars and awaiting a response", and I expanded on that. The whole subthread of https://news.ycombinator.com/item?id=16288955 https://news.ycombinator.com/item?id=16288955 doesn't make much sense because nobody defined what they mean by "latency" and people are talking about different things.
  - misnome 9y ago
    Tens of minutes to get a position lock for your location in the entire Galaxy? Yes, that sounds completely reasonable.
  - thaumasiotes 9y ago
    Of course, if that was the best I could do. People will happily spend an entire day becoming unlost if they're lost. As long as they have the means to survive, they'll be willing to spend much longer than that.
  - Maken 9y ago
    Likely, after the first calibration you could keep moving around and updating your location, so as long as the system doesn't go down you always know your (relative) position as you travel through the galaxy.
    - ccozan 9y ago
      I thought of this as well. After the first lock, you can use inertial navigation.
    - kijin 9y ago
      Regular GPS does this, too. It takes about 12 minutes to download the list of currently active satellites and their attributes. The data is part of the signal from the satellites. Most GPS units do this in the background. But if you leave it unpowered for too long, it will need to update itself before it begins to work properly. The GPS in my dad's car used to have a flaky ROM, and it would show the car flying across the wilderness at over 400mph while it was updating.
  - emiliobumachar 9y ago
    If I can then keep the lock indefinitely, I don't see much of a downside.
  - tlrobinson 9y ago
    Yes, especially if it’s just to occasionally recalibrate an inertial guidance system.
Lewton 9y ago
What latency? They're talking about measuring millisecond pulsars, there's no latency
- TheOtherHobbes 9y ago
  Indeed. But if you're travelling significant distances, you're not going to be able to assume the space between you and all your beacons is flat. For good accuracy you'd need a predictive spacetime curvature map for the entire galaxy, and that might not be an easy thing to generate.
  - solotronics 9y ago
    it would probably be an advantage to measure the shift effect from multiple sources as you travel whatever fraction of the speed of light, giving both your position and derivatives such as velocity

widdma 9y ago

This is exactly what is already done! On Earth at least. Radio telescopes around the world observe (mostly) quasars to perform geodesy. This is the main method used to measure the Earth Orientation Parameters which is need for keeping GPS/GNSS calibrated. With it, you can measure distances of several thousand km with a precision on the order of a few millimetres. The problem is that it's really expensive compared to GPS: at each site you need a reasonably size telescope, atomic clock, some serious storage, and a way to ship all the data to a central cluster.