Deep Space GPS

[Malintent]

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.

Oh, oh, oh.. I know, I know... how to be a dick... Spacecraft have self-awareness now? I guess the spacecraft thinks, "gee, I sure am going pretty fast. I better think about how fast I'm going..." Dick.

 

[Bronzeage]

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.

Is it possible to determine the velocity of an object, without comparing it's change in position to an assumed fixed object?

 

[Malintent]

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

Is it possible to determine the velocity of an object, without comparing it's change in position to an assumed fixed object?

If you know a "starting velocity" (relative to what?) then by tracking inertia with accelerometers, one can calculate speed (and direction changes using gyroscopes)... this is called inertial navigation.

 

[barbos]

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..

They don't use spectra to identify stars, they use their relative position on the sky. same way people identify stars.
And Pulsar GPS don't use direction to pulsars at all, first becasue pulsars are pretty damn invisible in optical spectrum and angular resolution of x-ray detectors is pretty bad, and second of all ordinary stars obviously better for determining orientation and they ARE actually used that way in space. In practice you just find two or more bright stars and track them continuously.
Your pilot license have been revoked. not that it had any relevance to this discussion.

 

[Sarpedon]

If you know a "starting velocity" (relative to what?) then by tracking inertia with accelerometers, one can calculate speed (and direction changes using gyroscopes)... this is called inertial navigation.

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

And if that were sufficient, why bother with the pulsars?

 

[fromderinside]

Yours too! EMR includes everything that doesn't involve moving proton and electron systems.

 

[barbos]

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

And if that were sufficient, why bother with the pulsars?

Who says it is sufficient? and sufficient for what?
All I said is that spacecrafts do account for Doppler shift, it's pretty trivial procedure.

 

[Malintent]

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..

They don't use spectra to identify stars, they use their relative position on the sky. same way people identify stars.
And Pulsar GPS don't use direction to pulsars at all, first becasue pulsars are pretty damn invisible in optical spectrum and angular resolution of x-ray detectors is pretty bad, and second of all ordinary stars obviously better for determining orientation and they ARE actually used that way in space. In practice you just find two or more bright stars and track them continuously.
Your pilot license have been revoked. not that it had any relevance to this discussion.

You need to know what stars you are looking at to gain any usable information from them regarding your position. If I blindfold you and move you somewhere on the planet, and then take off the blindfold and you see two trees in front of you, where are you? Well, you are in front of two random trees.. which does not help you find your way anywhere (except around an imaginary coordinate system that is "random tree" based. You are 5 feet to the left and 1 foot away from some unknown location... How brilliant of you. If you actually knew exactly where those trees are relative to where you want to be, that would be usefull... so, how can we tell what tree that is in front of you... if it was a pulsar, it would TELL YOU what tree it was. If it was a 'regular' star, it would tell you it was a pine tree... identical to billions of others and be no help at all.

 

[Bronzeage]

Is it possible to determine the velocity of an object, without comparing it's change in position to an assumed fixed object?

If you know a "starting velocity" (relative to what?) then by tracking inertia with accelerometers, one can calculate speed (and direction changes using gyroscopes)... this is called inertial navigation.

This sounds frightfully close to the navigation technique known as "dead reckoning," where direction and time are used to calculate your position. The great variable is always velocity, which becomes progressively more difficult to measure the farther you move from the original reference point.

 

[barbos]

They don't use spectra to identify stars, they use their relative position on the sky. same way people identify stars.
And Pulsar GPS don't use direction to pulsars at all, first becasue pulsars are pretty damn invisible in optical spectrum and angular resolution of x-ray detectors is pretty bad, and second of all ordinary stars obviously better for determining orientation and they ARE actually used that way in space. In practice you just find two or more bright stars and track them continuously.
Your pilot license have been revoked. not that it had any relevance to this discussion.

You need to know what stars you are looking at to gain any usable information from them regarding your position. If I blindfold you and move you somewhere on the planet, and then take off the blindfold and you see two trees in front of you, where are you? Well, you are in front of two random trees.. which does not help you find your way anywhere (except around an imaginary coordinate system that is "random tree" based. You are 5 feet to the left and 1 foot away from some unknown location... How brilliant of you. If you actually knew exactly where those trees are relative to where you want to be, that would be usefull... so, how can we tell what tree that is in front of you... if it was a pulsar, it would TELL YOU what tree it was. If it was a 'regular' star, it would tell you it was a pine tree... identical to billions of others and be no help at all.

You keep talking random nonsense. you don't have clue.

 

[Treedbear]

Is it possible to determine the velocity of an object, without comparing it's change in position to an assumed fixed object?

If you know a "starting velocity" (relative to what?) then by tracking inertia with accelerometers, one can calculate speed (and direction changes using gyroscopes)... this is called inertial navigation.

Inertial navigation systems are very susceptible to systematic errors which accumulate over time.

All inertial navigation systems suffer from integration drift: small errors in the measurement of acceleration and angular velocity are integrated into progressively larger errors in velocity, which are compounded into still greater errors in position. Since the new position is calculated from the previous calculated position and the measured acceleration and angular velocity, these errors accumulate roughly proportionally to the time since the initial position was input. Therefore, the position must be periodically corrected by input from some other type of navigation system. The inaccuracy of a good-quality navigational system is normally less than 0.6 nautical miles per hour in position and on the order of tenths of a degree per hour in orientation.

Accordingly, inertial navigation is usually used to supplement other navigation systems, providing a higher degree of accuracy than is possible with the use of any single system.

 

[Sarpedon]

Who says it is sufficient? and sufficient for what?
All I said is that spacecrafts do account for Doppler shift, it's pretty trivial procedure.

It is trivial, when the spacecraft is close to earth and can receive signals from its radio beacons. This whole pulsar system is based on the assumption of deep space probes that will have to navigate without that reference point. It just seems to me that in order to identify the reference point, one needs to know one's velocity, and to know one's velocity, one needs a reference point. Perhaps there are few enough pulsars and their pulses are different enough that won't be a problem.

I'm reminded of the story of the military fort which had a sargeant who fired off a cannon each day at exactly noon. A reporter asked him how he knew it was exactly noon. He replied that there was a clock store in the nearby town, and he set his watch when he visited on weekends. The reporter then went to town, and asked the guy at the clock store how he set his clock. He replied, "Oh, you know that fort outside of town, they fire off a cannon every day at noon.."

 

[barbos]

Who says it is sufficient? and sufficient for what?
All I said is that spacecrafts do account for Doppler shift, it's pretty trivial procedure.

It is trivial, when the spacecraft is close to earth and can receive signals from its radio beacons. This whole pulsar system is based on the assumption of deep space probes that will have to navigate without that reference point. It just seems to me that in order to identify the reference point, one needs to know one's velocity, and to know one's velocity, one needs a reference point. Perhaps there are few enough pulsars and their pulses are different enough that won't be a problem.

First, modern aircraft speeds are so tiny and periods of pulsars are so different that problem the way you described will not happen. Second of all, in worst case scenario which is aircrafr completely forgets its velocity it's a matter of scanning different velocities and trying to fit pulsar frequencies. It's not a problem at all.

I'm reminded of the story of the military fort which had a sargeant who fired off a cannon each day at exactly noon. A reporter asked him how he knew it was exactly noon. He replied that there was a clock store in the nearby town, and he set his watch when he visited on weekends. The reporter then went to town, and asked the guy at the clock store how he set his clock. He replied, "Oh, you know that fort outside of town, they fire off a cannon every day at noon.."

Nice story but irrelevant here.

 

[Sarpedon]

Aircraft? I thought we were talking about spacecraft. This whole thing is for projected interstellar space probes that could be travelling at a substantial fraction of the speed of light.

 

[barbos]

Aircraft? I thought we were talking about spacecraft. This whole thing is for projected interstellar space probes that could be travelling at a substantial fraction of the speed of light.

Yes, I meant spacecraft, and no, substantial fraction of speed of light will not be a problem for navigation.

 

[Treedbear]

Regarding their use for interstellar travel, I'm wondering whether the beam would remain visible over interstellar distances? How narrow is it? How far could one travel before moving out of its beam width?

 

[Malintent]

You need to know what stars you are looking at to gain any usable information from them regarding your position. If I blindfold you and move you somewhere on the planet, and then take off the blindfold and you see two trees in front of you, where are you? Well, you are in front of two random trees.. which does not help you find your way anywhere (except around an imaginary coordinate system that is "random tree" based. You are 5 feet to the left and 1 foot away from some unknown location... How brilliant of you. If you actually knew exactly where those trees are relative to where you want to be, that would be usefull... so, how can we tell what tree that is in front of you... if it was a pulsar, it would TELL YOU what tree it was. If it was a 'regular' star, it would tell you it was a pine tree... identical to billions of others and be no help at all.

You keep talking random nonsense. you don't have clue.

You have a very odd way of using the words "random" and "clue". Are you trying to distract from how stupid you look with a "no I'm not, you are" thing? Whatever, you're just being a dick, I guess. If you have something of substance to say, feel free... or fuck off... care less, I cannot.

- - - Updated - - -

If you know a "starting velocity" (relative to what?) then by tracking inertia with accelerometers, one can calculate speed (and direction changes using gyroscopes)... this is called inertial navigation.

Inertial navigation systems are very susceptible to systematic errors which accumulate over time.

All inertial navigation systems suffer from integration drift: small errors in the measurement of acceleration and angular velocity are integrated into progressively larger errors in velocity, which are compounded into still greater errors in position. Since the new position is calculated from the previous calculated position and the measured acceleration and angular velocity, these errors accumulate roughly proportionally to the time since the initial position was input. Therefore, the position must be periodically corrected by input from some other type of navigation system. The inaccuracy of a good-quality navigational system is normally less than 0.6 nautical miles per hour in position and on the order of tenths of a degree per hour in orientation.

Accordingly, inertial navigation is usually used to supplement other navigation systems, providing a higher degree of accuracy than is possible with the use of any single system.

Totally... and worse, gyroscopic procession is a major issue as well. But we aren't really talking about inertial navigation, dead reckoning, or pilotage.. we're talking something similar to GPS.

 

[Malintent]

Aircraft? I thought we were talking about spacecraft. This whole thing is for projected interstellar space probes that could be travelling at a substantial fraction of the speed of light.

I think barbos is just a contrarian looking for attention. He's got problems with statements and then agrees with them a few posts later in order to disagree with a later post. He brought up the speed issue earlier, and now is saying it doesn't matter (by introducing "low speeds")... just to contradict whatever latest post.

 

[barbos]

You keep talking random nonsense. you don't have clue.

You have a very odd way of using the words "random" and "clue". Are you trying to distract from how stupid you look with a "no I'm not, you are" thing? Whatever, you're just being a dick, I guess. If you have something of substance to say, feel free... or fuck off... care less, I cannot.

It is you who is trying to distract from your stupidities. You should have educated yourself a little before claiming your own stupid "ideas" as facts.

 

[barbos]

Aircraft? I thought we were talking about spacecraft. This whole thing is for projected interstellar space probes that could be travelling at a substantial fraction of the speed of light.

I think barbos is just a contrarian looking for attention. He's got problems with statements and then agrees with them a few posts later in order to disagree with a later post. He brought up the speed issue earlier, and now is saying it doesn't matter (by introducing "low speeds")... just to contradict whatever latest post.

Another bulllshit post which has no relation to reality.