Jump to content

a radio based navigation system


Recommended Posts

1 hour ago, magnemoe said:

Did not the pluto nuclear ramjet plan to use star tracking for navigation? It works on earth as its basically old style navigation, not sure how accurate it is. They gave it up on later cruise missiles who used ground features to find its position, or did the 1980s cruise missiles also use it? 

Star tracking has problems if you need real-time navigation. And of course, it is subject to weather. Can't use star tracking if you can't see the stars.

Nuclear missiles need accuracy, but not so much accuracy that a good inertial reference system won't suffice.

Other missiles need more accuracy, but they can now use GPS. This is why the US used to try to "fuzz up" the GPS signal with "selective availability". They stopped doing that, but can still do it in time of war.

Link to comment
Share on other sites

1 hour ago, mikegarrison said:

Star tracking has problems if you need real-time navigation. And of course, it is subject to weather. Can't use star tracking if you can't see the stars.

Nuclear missiles need accuracy, but not so much accuracy that a good inertial reference system won't suffice.

Other missiles need more accuracy, but they can now use GPS. This is why the US used to try to "fuzz up" the GPS signal with "selective availability". They stopped doing that, but can still do it in time of war.

ICBM flight time is around 30 minutes maximum and most of it in space, cruise missiles bump around in the atmosphere for hours. 
Can they edit the data for the public version? as in causing drones to crash. No this don't work if you use the Russian system But against idiots with no friends like isil it would be amusiing. 
Even more so if you had them climb so the AAA got targets. 

Link to comment
Share on other sites

12 hours ago, magnemoe said:

Can they edit the data for the public version? as in causing drones to crash. No this don't work if you use the Russian system But against idiots with no friends like isil it would be amusiing. 

The civilian GPS signal used to be artificially noisy to limit the accuracy. This was called "selective availability." They have turned it off now because augmentation methods and other GNSS systems have made it ineffective plus a lot of civil and merchant activities have become dependent on accurate location. To my knowledge the capability still exist even in the newest satellites. But for example my cell phone's navigation chip picks up (at least) GPS, GLONASS, Galileo and Beidou satellites. The app I check this with lists a couple more systems and has a category for unknown satellites too. So fiddling with just your own system's output may turn out to be ineffective as a drone protection.

For the curious this also is (one way) how the russian GPS spoofing that's been in the news every once in a while works. They drown out the satellites' transmission with their own that causes the calculated position to drift off the real position. Careful calculation should allow them to control how much and where the drift is at least in a limited target area. Less predictable effects will happen outside the target area, of course. Countermeasures include encrypted transmissions that the malicious party cannot create (GPS at least has these), directional antennas that reject the spoofing signal coming from low elevation and listening to a lot of satellites and rejecting the outliers whose transmission suggest a position far from the others.

Link to comment
Share on other sites

On 8/26/2021 at 4:34 AM, YNM said:

Yeah but you can very easily describe their trajectory using a geodesic, which you can't do for a flying or floating thing in the air. That's why TLEs have been around since ages ago.

And what are you basing that maps on ? Ground beacons measured with chains and triangulation ? It's better to just use ground beacons then...

GPS/GNSS literally eliminates all of this, look up the recent proposed changes on geodectic systems (at the very least gravitational models), it's all based on the satellites' geodesics.

you can use normal topographic maps, we already have very precise versions of those, I'm not looking to build a satellite and launch it into space, so not sure why gps/gnss is persistent here, just a though experiment to see if it would be cheaper to make with recent advances in tech

Link to comment
Share on other sites

1 hour ago, Stratennotblitz said:

you can use normal topographic maps, we already have very precise versions of those

Maps only tell you the relative positions of features on the surface of the Earth - at no point does it tell where you are exactly. You can't use a map to adjust for errors - you gotta find a reference with 'known' positions then try to determine where you are. And since the comment was made in reply to airborne positioning beacon it's kinda useless IMO if you have a beacon that in itself have to derive their position from a completely different system already all the time (granted GNSS satellites does this - they're tracked by ground stations with known 'fixed' locations - but as with most celestial bodies space ephemeris are pretty accurate). If those airborne positioning beacons have to derive from ground stations we'd probably need a ton more ground stations (since they'd need one at line-of-sight), so much that it'd probably be easier to use the ground stations directly, and if they derive from GNSS themselves why not just use the GNSS directly ?

1 hour ago, Stratennotblitz said:

not sure why gps/gnss is persistent here, just a though experiment to see if it would be cheaper to make with recent advances in tech

Well GNSS is the advancement in technology we've finally arrived at.

accurate.png

It's suddenly only 1/20th of it's predecessor, and that was with SA.

 

EDIT : Although to add, why I brought up the datum as well, is because we haven't been using a unified global datum until GNSS comes along.

Spoiler

Bit old video for him, so there might be a few things off, but still communicates the point well.

 

Edited by YNM
Link to comment
Share on other sites

On 8/26/2021 at 10:40 AM, magnemoe said:

Did not the pluto nuclear ramjet plan to use star tracking for navigation? It works on earth as its basically old style navigation, not sure how accurate it is. They gave it up on later cruise missiles who used ground features to find its position, or did the 1980s cruise missiles also use it? 

it didn't matter because the radioactive trail could kill anything in it's path, so they only needed approximate location and circle around it, by the 70's we already had guidance for cruise missiles, the tomahawk was developed in the 1980's too, the reason why they needed star trackers was because of the amplifying of errors from the radio navigation, so star trackers would help at night snd also offset that error

On 8/29/2021 at 3:05 AM, YNM said:

Maps only tell you the relative positions of features on the surface of the Earth - at no point does it tell where you are exactly. You can't use a map to adjust for errors - you gotta find a reference with 'known' positions then try to determine where you are. And since the comment was made in reply to airborne positioning beacon it's kinda useless IMO if you have a beacon that in itself have to derive their position from a completely different system already all the time (granted GNSS satellites does this - they're tracked by ground stations with known 'fixed' locations - but as with most celestial bodies space ephemeris are pretty accurate). If those airborne positioning beacons have to derive from ground stations we'd probably need a ton more ground stations (since they'd need one at line-of-sight), so much that it'd probably be easier to use the ground stations directly, and if they derive from GNSS themselves why not just use the GNSS directly ?

Well GNSS is the advancement in technology we've finally arrived at.

accurate.png

It's suddenly only 1/20th of it's predecessor, and that was with SA.

 

EDIT : Although to add, why I brought up the datum as well, is because we haven't been using a unified global datum until GNSS comes along.

  Reveal hidden contents

Bit old video for him, so there might be a few things off, but still communicates the point well.

 

https://en.wikipedia.org/wiki/Decca_Navigator_System

this is what I'm trying to do, as you saw in the graph it's only less accurate than the gps, what I'm wondering is if it can work in land, be more precise with the addition of new inertial and traditional tracking systems like star trackers and better pre disposed software and maps, I'm not looking for gps, I already have that

On 8/29/2021 at 3:05 AM, YNM said:

Maps only tell you the relative positions of features on the surface of the Earth - at no point does it tell where you are exactly. You can't use a map to adjust for errors - you gotta find a reference with 'known' positions then try to determine where you are. And since the comment was made in reply to airborne positioning beacon it's kinda useless IMO if you have a beacon that in itself have to derive their position from a completely different system already all the time (granted GNSS satellites does this - they're tracked by ground stations with known 'fixed' locations - but as with most celestial bodies space ephemeris are pretty accurate). If those airborne positioning beacons have to derive from ground stations we'd probably need a ton more ground stations (since they'd need one at line-of-sight), so much that it'd probably be easier to use the ground stations directly, and if they derive from GNSS themselves why not just use the GNSS directly ?

Well GNSS is the advancement in technology we've finally arrived at.

accurate.png

It's suddenly only 1/20th of it's predecessor, and that was with SA.

 

EDIT : Although to add, why I brought up the datum as well, is because we haven't been using a unified global datum until GNSS comes along.

  Reveal hidden contents

Bit old video for him, so there might be a few things off, but still communicates the point well.

 

Maps only tell you the relative positions of features on the surface of the Earth - at no point does it tell where you are exactly. You can't use a map to adjust for errors - you gotta find a reference with 'known' positions then try to determine where you are. And since the comment was made in reply to airborne positioning beacon it's kinda useless IMO if you have a beacon that in itself have to derive their position from a completely different system already all the time (granted GNSS satellites does this - they're tracked by ground stations with known 'fixed' locations - but as with most celestial bodies space ephemeris are pretty accurate). If those airborne positioning beacons have to derive from ground stations we'd probably need a ton more ground stations (since they'd need one at line-of-sight), so much that it'd probably be easier to use the ground stations directly, and if they derive from GNSS themselves why not just use the GNSS directly ?

Well GNSS is the advancement in technology we've finally arrived at.

 

[well yes, but I'm pretty sure some navigation systems use maps to offset errors as soon as they have food measurement systems and a good initial "ping", gps satellites would be over worked if vehicles pinged them every second, there are better ways]

On 8/27/2021 at 4:32 AM, monophonic said:

The civilian GPS signal used to be artificially noisy to limit the accuracy. This was called "selective availability." They have turned it off now because augmentation methods and other GNSS systems have made it ineffective plus a lot of civil and merchant activities have become dependent on accurate location. To my knowledge the capability still exist even in the newest satellites. But for example my cell phone's navigation chip picks up (at least) GPS, GLONASS, Galileo and Beidou satellites. The app I check this with lists a couple more systems and has a category for unknown satellites too. So fiddling with just your own system's output may turn out to be ineffective as a drone protection.

For the curious this also is (one way) how the russian GPS spoofing that's been in the news every once in a while works. They drown out the satellites' transmission with their own that causes the calculated position to drift off the real position. Careful calculation should allow them to control how much and where the drift is at least in a limited target area. Less predictable effects will happen outside the target area, of course. Countermeasures include encrypted transmissions that the malicious party cannot create (GPS at least has these), directional antennas that reject the spoofing signal coming from low elevation and listening to a lot of satellites and rejecting the outliers whose transmission suggest a position far from the others.

I was saying that to someone before, satellites can only give so much accuracy, you need better points of reference 

Link to comment
Share on other sites

On 8/30/2021 at 6:48 PM, Stratennotblitz said:

[well yes, but I'm pretty sure some navigation systems use maps to offset errors as soon as they have food measurement systems and a good initial "ping", gps satellites would be over worked if vehicles pinged them every second, there are better ways]

GNSS Receivers does not transmit any signals - they just compare the clocks they have on-board (which is synced - value-wise when first started with terrestrial time signals, and step/rate-wise as long as the receiver is turned on) with the continuously transmitted messages from the satellites. Satellite position is both contained in the transmission and there are backup ephemeris within the receiver that allows operation under degraded accuracy. By comparing the time right now and the time at transmission it's possible to tell how far away you are from the beacon, and if you have the data from at least 3 beacons the intersection of the 3 circles of radius/distance it gives you your position - roughly (in reality I think you need a 4th one due to 3-dimensional sphere rather than circles that it produces). Directional transmission is available but obviously only certain receivers get this treatment (like some random joe's phone probably won't but military airplanes probably would).

On 8/30/2021 at 6:48 PM, Stratennotblitz said:

what I'm wondering is if it (Decca) can work in land

Yes, and with more fixed transmission beacons you'd increase the accuracy.

The problem is that the world isn't a single country, and there're seas.

They had >75 LORAN-C stations to serve mostly the northern hemisphere's seas (none would work well in-land since that wasn't the focus) - there're only 31 GPS satellites on-orbit right now providing coverage anywhere on Earth (excluding mines and tunnels), with merely 1/20th the error (20x more accurate).

Edited by YNM
Link to comment
Share on other sites

... That being said, GNSS satellites (and other satellites) still derive their final position from a ground observatory.

I've heard that at least one collaboration have up to 500 observatories - if they could be a fairly accurate source while providing enough high-accuracy coverage for ground-based positioning signals, maybe it'd work ? idk.

Edited by YNM
Link to comment
Share on other sites

On 8/30/2021 at 6:01 AM, YNM said:

(in reality I think you need a 4th one due to 3-dimensional sphere rather than circles that it produces). 

Three is enough. Extra signals allow for an estimate of the error (by comparing solutions from the different sets of three), and also allow for fine tuning of the GPS receiver's internal clock (by tweaking the time to minimize the error).

The computation of position using three distances from three known points is called trilateration. It is how my old Kerbal GPS mod (Figaro) does it. In that mod, just like in the real GPS system, extra combinations of three are used to estimate the error.

(A relevant link for anyone who's interested: https://gisgeography.com/trilateration-triangulation-gps/)

Link to comment
Share on other sites

15 hours ago, PakledHostage said:

Three is enough. Extra signals allow for an estimate of the error (by comparing solutions from the different sets of three), and also allow for fine tuning of the GPS receiver's internal clock (by tweaking the time to minimize the error).

The computation of position using three distances from three known points is called trilateration. It is how my old Kerbal GPS mod (Figaro) does it. In that mod, just like in the real GPS system, extra combinations of three are used to estimate the error.

(A relevant link for anyone who's interested: https://gisgeography.com/trilateration-triangulation-gps/)

Think many systems like phones and cars uses the 3rd to synchronize the clock if you only has 3 as you presumably is at the ground there height is know by the map. In an plane you don't want that, but then you don't have so much stuff blocking the signals and you should use an gps system designed for planes not an phone. 
Was on one flight from US to Europe there they had to abort and return as they lost two of the navigation systems and they needed two cross the Atlantic. (was they flying with two and the second broke before it could be replaced? plausible)
Anyway most on that flight had an phone with gps, but obliviously the navigation system probably had other features like streaming positions of other planes you might catching up on an slower plane. 
 

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...