back to article NASA is pretty pleased with its pulsar-sniffing intergalactic GPS tech

After years of research and testing, NASA has demonstrated spacecraft positioning equipment that relies on measuring X-ray bursts. The hardware will help future spacefarers navigate the galaxy and beyond. Your car or smartphone GPS gear works out its position using signals received from a constellation of satellites orbiting …

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Very impressive.

And very handy

The payoffs for this tech are

1) That in principal you don't have to point the spacecraft to do nav tasks

2) It can work outside the solar system. It's the nav system for going 10s of light years.

That said in space with a big enough star catalog (and modern computers have the memory for quite a big one) visible stars should be able to do the same.

I think there's also some benefit in principle from making the equipment quite small, but obviously that's for V2.0. This was getting the outline of the software developed.

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Re: Very impressive.

Hold on, I'm a bit confused. Is that supposed to mean that current optical instruments of reasonably modest size would be able to detect the interstellar parallax changes caused by... moving three miles or less? Really...?

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Re: Very impressive.

Very impressive indeed. However, my understanding is that we see pulsars because we happen to lie within the path of radiation that is emitted as it rotates, ie, they don't radiate in all directions.

I therefore wonder how far we would need to travel before we are no longer aligned with a particular pulsar's beam and it effectively goes 'out'? The solar system is probably covered, but i would guess that 10's of light years wouldn't be.

Chances are we would begin to see different, new pulsars as we move further out, but wouldn't we need to know their position with some degree of accuracy before they could become a new reference point?

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Re: Very impressive.

> current optical instruments of reasonably modest size

I think they actually work by timing the x-ray pulses rather than by pointing towards them. Which is the reason they've chosen pulsars instead of some big, bright stars. Pulsars have a very precise and stable timing, comparable to a GPS clock.

(BTW it's not me who downvoted you.)

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Re: Very impressive.

It's interesting that x-rays, which is just a shorter wavelength of EMR than visible light, has been used for astronavigation but I'm afraid I don't see the benefit or the point.

X-rays, being shorter wavelength than visible light, are even more 'directional' so the idea that using x-rays means that you 'don't have to point the spacecraft' isn't true - it just means that, as with visible light, you need to use a number of wide-angle lenses to cover the entire sky, and this is more easily and cheaply done with visible light. Working outside the solar system wouldn't be a problem for visible light systems either.

As for working outside the galaxy... well, I don't think we'll have to worry about that for some considerable amount of time, if ever.

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Re: Very impressive.

@ThatOne that's ok, I'm suspecting a confusion is to blame - I'm well aware that the instrument the article talks about doesn't need to be aimed and works based on timings; I was reacting to the original post that alleged simply looking optically at stars could do the same which sounds seriously implausible in the absence of the relevant pulse timing shifts: "That said in space with a big enough star catalog [...] visible stars should be able to do the same."

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Re: Very impressive.

Can I have one for my SUV?

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Re: Very impressive.

Measuring star positions to determine your position in space won't do it. Certainly not yet.

The GAIA astrometric satellite will, we expect, get parallaxes and positions to (roughly) the 20 microarcsecond level. That involves multiple measurements over a multi-year mission, but let's say a future instrument could get to that level of precision. Let's also say that you have some stars within, say, four light-years; those are the reference points from which you're measuring your position. In that case, your positional accuracy is the distance subtended at a distance of four light years by a 20 microarcsec angle, which is... um... I'm getting about 4000 km. Better than I would have expected, actually. But the pulsars would still be the way to go.

Sadly, interstellar travel is still a ways off. But I _could_ imagine optical methods working within the solar system: image three asteroids with known positions (quite well known already, and about to become better due to GAIA), measure their position relative to background stars, and you could have positioning competitive to pulsar timing methods.

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In other news ...

Falcon Heavy wet dress rehearsal was not followed by a static fire test. Blame one of the hold down clamps for this latest delay to the second deep space Tesla.

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Joke

Intergalactic satnav

"In 500 parsecs...turn left"

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Re: Intergalactic satnav

"recalculating..."

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Something missing...

The technology is very impressive of course, but what's missing is the terminology. Was the ISS, we need to know, within 3 miles of sector ZZ plural Z alpha?

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3 miles

Can still mean the difference between missing a moon or smashing face-first into a big slab of rock.

That said this is amazing work and a great step forward..well done those boys n girls!

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Accuracy

The goal was to get a position accurate to within 10 miles, yet the team got it down to three – which may not sound that useful, but when you're talking interstellar distances, that's good enough.

Until said spacecraft slams into something, e.g. Mars.

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Facepalm

Re: Accuracy

> Until said spacecraft slams into something, e.g. Mars.

If you get within 3 miles of some planet and you still solely rely on your spacenav for directions, you definitely deserve to crash...

It would be the space equivalent of those who gladly drive off a pier because "the satnav said so".

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Any benefit

Anybody know if there is any benefit to this, whatsoever?* That is, a benefit to anything we currently do and not interstellar travel that is decades if not centuries away. Would this compete with or supplement navigation within the solar system? Maybe map position of objects to a greater degree?

*I need to clarify here that I do mean this as a question, not as a science without an immediate pay-off is stupid kind of statement.

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Re: Any benefit

Given 99% of our space ventures don't leave the (low) orbit of earth one could say it's pretty pointless.

- Until somebody suddenly finds an unexpected use for it.

I think this is more a feasibility experiment, since the idea of using pulsars to calculate position has been around for quite a while. It's not supposed to have some immediate use, just confirm that we can do such a thing if/when the need arises.

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Re: Any benefit

This is extremely useful for deep space probes. Navigation in the outer solar system has been by using very long baseline interferometry to determine space craft position. The problem is that the farther you get away from earth, the worse the position accuracy. Now you can determine spacecraft position to 3 miles anywhere within a few light years of Earth. This will allow much closer approaches to the outer planets as the spacecraft can be located much more precisely. I assume that the accuracy will improve as they refine the system and add more pulsars to the positioning catalog.

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Boffin

Re: Any benefit

That's certainly the idea behind that experiment.

Still, I think that given the budget limitations pulsar positioning would rank quite low on the priority scale. What does a probe (let's assume sent to Pluto) need? Scientific instruments, as many as money can buy, energy to run them, fuel for maneuvers and an efficient means to send back all that precious information. Those 4 points would be what 90% of the probe money would be spent for.

Given common flyby distances, the precision of 3 miles is not really needed I think, and the problem with going much closer isn't the precision of navigation, but the fact we don't know for sure what's out there: You wouldn't want to suddenly discover some unexpected minor moon... Which means that you'll have to fire up the cameras and look out for hazards while you tip-toe your way to a good observation position. Difficult to automate, no matter the precision of your positioning.

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Alien

Re: Any benefit

This is more or less what info is on the Golden Records attached to the Voyager probes. Using the time and location of some known pulsars can help the ETs that find them figure out where Earth is.

The little diagram on the side with all the lines coming from it indicate the position and "pulse rate" of a bunch of pulsars with the Sun in the middle.

Personally if I found one of these things I am not sure I could decode all the graphics on the side to what their intention is to get the record playing and establish where Earth is but I'm an IT guy and not an intergalactic Astroboffin.

Don't want to quote wikipedia, but it's as good a place as any to link the diagram.

https://upload.wikimedia.org/wikipedia/commons/e/ed/Voyager_Golden_Record_Cover_Explanation.svg

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Re: Any benefit

The current tech can only precisely determine the distance to earth. The are 2 more dimensions needing to be measured. Instead, a few x-ray pulsars across the sky allow eventual precise determination of position. It might take a few days each (pulsar) to be sure of the timing.

And the detectors are only a few kg and half a metre across. Much smaller than the current antenna for comms back to earth. The AE-35 is not required.

On a higher level, this enables, or requires, a more autonomous spacecraft. AI, you know.

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