Deep Space GPS

[Malintent]

https://news.vice.com/story/china-m...ne-of-the-big-challenges-of-deep-space-travel

Currently, the only way a spacecraft knows where it is, is via Earth-based radio transmission. In order to travel farther (as in, out of our solar system), craft will not be able to rely on radio waves emanating from Earth.

A new technology is being tested by China, and soon the US, that uses very precise measurement of the x-ray emanations from Pulsars. Like Earth's GPS system of satellites, craft would be able to triangulate their position in space using readings from multiple Pulsars.

Very cool.

 

[Treedbear]

GPS isn't simply triangulation. It uses the time it takes for the signal to reach the receiver. And if the pulsar-based GPS only uses triangulation I think the change in angular position is too small to locate position to any accuracy within the radius of the Solar System.

 

[Elixir]

GPS isn't simply triangulation. It uses the time it takes for the signal to reach the receiver. And if the pulsar-based GPS only uses triangulation I think the change in angular position is too small to locate position to any accuracy within the radius of the Solar System.

Good explanation.

 

[bilby]

GPS isn't simply triangulation. It uses the time it takes for the signal to reach the receiver. And if the pulsar-based GPS only uses triangulation I think the change in angular position is too small to locate position to any accuracy within the radius of the Solar System.

I can't read the article; but even if the accuracy is fairly poor, then that doesn't render this concept useless. If your spacecraft is in the Solar System, then the current systems can be used for greater accuracy; This seems to me like the sort of thing that would be useful in getting an interstellar probe to the intended star system. If you can get 5 light-hour (5 billion km) accuracy, that's enough to ensure you don't completely miss the target star.

 

[barbos]

GPS isn't simply triangulation. It uses the time it takes for the signal to reach the receiver. And if the pulsar-based GPS only uses triangulation I think the change in angular position is too small to locate position to any accuracy within the radius of the Solar System.

Well, GPS is not triangulation at all. That is It does not use any angles. And pulsar based GPS does not use angles either. I mean it would be pretty pointless because ordinary stars and planets are much better for triangulation. Pulsar based GPS use phases of the signals from pulsars, same thing with ordinary GPS.

 

[rjh01]

GPS isn't simply triangulation. It uses the time it takes for the signal to reach the receiver. And if the pulsar-based GPS only uses triangulation I think the change in angular position is too small to locate position to any accuracy within the radius of the Solar System.

I can't read the article; but even if the accuracy is fairly poor, then that doesn't render this concept useless. If your spacecraft is in the Solar System, then the current systems can be used for greater accuracy; This seems to me like the sort of thing that would be useful in getting an interstellar probe to the intended star system. If you can get 5 light-hour (5 billion km) accuracy, that's enough to ensure you don't completely miss the target star.

I have just read the article. That is what the article does in fact say. The main problem is that the number of pulsars that can be detected with a small telescope is very small.

Though I am not sure why you would need such a system. Just use ordinary nearby stars. Two stars in particular - Our sun and the destination star. Plus a few extra stars to confirm the position.

 

[barbos]

Though I am not sure why you would need such a system. Just use ordinary nearby stars. Two stars in particular - Our sun and the destination star. Plus a few extra stars to confirm the position.

Using stars does not give much precision.

 

[skepticalbip]

I can't read the article; but even if the accuracy is fairly poor, then that doesn't render this concept useless. If your spacecraft is in the Solar System, then the current systems can be used for greater accuracy; This seems to me like the sort of thing that would be useful in getting an interstellar probe to the intended star system. If you can get 5 light-hour (5 billion km) accuracy, that's enough to ensure you don't completely miss the target star.

I have just read the article. That is what the article does in fact say. The main problem is that the number of pulsars that can be detected with a small telescope is very small.

Though I am not sure why you would need such a system. Just use ordinary nearby stars. Two stars in particular - Our sun and the destination star. Plus a few extra stars to confirm the position.

I would think that the reason pulsars would be preferable references would be that they are so easy to detect in the RF spectrum rather than optically. Plus their great distance would mean that their position would change little with respect to the movement of the space ship.

ETA:
I just thought that this idea isn't new. The Pioneer 10 probe launched in 1972 carried a plaque that included a diagram identifying Earth's position with respect to several pulsars.

 

[Treedbear]

GPS isn't simply triangulation. It uses the time it takes for the signal to reach the receiver. And if the pulsar-based GPS only uses triangulation I think the change in angular position is too small to locate position to any accuracy within the radius of the Solar System.

Well, GPS is not triangulation at all. That is It does not use any angles. And pulsar based GPS does not use angles either. I mean it would be pretty pointless because ordinary stars and planets are much better for triangulation. Pulsar based GPS use phases of the signals from pulsars, same thing with ordinary GPS.

Oh I see. It measures phase change so not actual distance to the pulsars but relative change in distance. It sets a reference point (e.g.; the Earth) and tracks phase change in the intensities of 4 or more pulsars. If the frequency of rotation is 1000 Hz a resolution of .01Hz would provide a maximum resolution of 186,000 miles/sec / 1000 / 100 = 1.86 miles. Right? I say maximum because that would only be true along the axis of motion. But phase could probably be measured fairly accurately even with a small detector since it's basically either on or off. So with a really accurate clock, who knows? But you probably need to maintain tracking with continuity (I love how that word feels ) because missing one cycle would throw it off by 1860 miles. Maybe not a problem though under zero acceleration.

But I thought GPS normally measures the actual distance to satellites having known positions.

ETA: And it should maintain that absolute accuracy over any distance, rather than as a percentage.

 

[fromderinside]

Stars for guidance? Amazing Idea. I think somebody like Minoans or Greeks did it first about 3400 years ago.  History of navigation

Yeah I know its locating, but self locating is very important too.

 

[barbos]

Well, GPS is not triangulation at all. That is It does not use any angles. And pulsar based GPS does not use angles either. I mean it would be pretty pointless because ordinary stars and planets are much better for triangulation. Pulsar based GPS use phases of the signals from pulsars, same thing with ordinary GPS.

Oh I see. It measures phase change so not actual distance to the pulsars but relative change in distance. It sets a reference point (e.g.; the Earth) and tracks phase change in the intensities of 4 or more pulsars. If the frequency of rotation is 1000 Hz a resolution of .01Hz would provide a maximum resolution of 186,000 miles/sec / 1000 / 100 = 1.86 miles. Right? I say maximum because that would only be true along the axis of motion. But phase could probably be measured fairly accurately even with a small detector since it's basically either on or off. So with a really accurate clock, who knows? But you probably need to maintain tracking with continuity (I love how that word feels ) because missing one cycle would throw it off by 1860 miles. Maybe not a problem though under zero acceleration.

Well, 1.86 miles is awfully optimistic, but 50 miles is achievable and more than enough.

But I thought GPS normally measures the actual distance to satellites having known positions.

In the end yes, they measure the distance to the satellites but it works pretty much the same except satellites can send out any signals you want, so they send something which is easier to work with.

ETA: And it should maintain that absolute accuracy over any distance, rather than as a percentage.

 

[Malintent]

The advantage of pulsars over other stars is that the direction to a specific pulsar can be determined with great precision. Determining a specific star for 'old fashioned visual' navigation is error-prone due to countless stars having nearly identical spectra, as detected from a distance. Pulsars are 'self-identifying', like navaids for aviators that send out Morse code identifiers.

 

[Sarpedon]

Wouldn't the relative speed of the vessel affect the apparent frequency of the pulses? Thus making a specific pulsar harder to identify? Possibly that's why one needs multiple pulsars.

 

[Treedbear]

Wouldn't the relative speed of the vessel affect the apparent frequency of the pulses? Thus making a specific pulsar harder to identify? Possibly that's why one needs multiple pulsars.

The New Horizons space probe that visited Pluto left Earth's orbit at a velocity of 36,373 mph. The distance light from a really fast 1000 Hz pulsar travels in one cycle is 186 miles. In an hour that's 669,600 miles. So New Horizons would see a frequency change of about 5% when headed directly toward or away from the pulsar. I think it would be proportionally less for slower pulsars. But when using it to identify specific pulsars that might not amount to much. How many visible pulsars are there anyway? Probably just search in a general direction. A minimum of 4 pulsars are required because you still need to triangulate between them to determine position, even though it's done by comparing phase change rather than angular change. You still need to know the angular positions very accurately, even though they won't change appreciably.

 

[Bronzeage]

Shouldn't bistromathematics be used for this kind of thing?

 

[Malintent]

Shouldn't bistromathematics be used for this kind of thing?

All out of napkins.

 

[Bronzeage]

Shouldn't bistromathematics be used for this kind of thing?

All out of napkins.

That will affect the tip, even though it's something over which the waitress has no control.

 

[barbos]

The advantage of pulsars over other stars is that the direction to a specific pulsar can be determined with great precision. Determining a specific star for 'old fashioned visual' navigation is error-prone due to countless stars having nearly identical spectra, as detected from a distance. Pulsars are 'self-identifying', like navaids for aviators that send out Morse code identifiers.

I am sorry but you have no clue whatsoever.

 

[barbos]

Wouldn't the relative speed of the vessel affect the apparent frequency of the pulses? Thus making a specific pulsar harder to identify? Possibly that's why one needs multiple pulsars.

Spacecraft is aware of its own velocity and can account for that and in fact that's how they determine velocity actually.

 

[Malintent]

The advantage of pulsars over other stars is that the direction to a specific pulsar can be determined with great precision. Determining a specific star for 'old fashioned visual' navigation is error-prone due to countless stars having nearly identical spectra, as detected from a distance. Pulsars are 'self-identifying', like navaids for aviators that send out Morse code identifiers.

I am sorry but you have no clue whatsoever.

um.. apology accepted? Crappy apology, though. Being a licensed, instrument rated pilot, I know exactly what I am talking about with respect to navaids and how they identify themselves. As for the content of the article I enjoyed, and linked for your enjoyment, that is what the author was indicating the advantage was... determining what star you are pointing at is far harder than determining what pulsar you are pointing at, precisely because most stars basically look alike from afar, but pulsars basically identify themselves by their pulses.
If you would like to explain how the article is wrong, or how this is a misunderstanding of it, feel free to sound slightly less like a total dick..