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attila77 |
2009-04-26
, 10:36
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Posts: 3,319 |
Thanked: 5,610 times |
Joined on Aug 2008
@ Finland
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#11
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Originally Posted by shadowjk
Actually, ballistic systems don't really navigate (in that phase). When they finish acceleration, it's all momentum+gravity (hence the name ballistic). Thus, I wouldnt make it a security issue when there are plenty of simpler tech reasons for it to stop working (like good old overflows, visibility of high number/below horizon satellites, etc).
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2009-04-26
, 13:25
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Posts: 23 |
Thanked: 3 times |
Joined on Apr 2009
@ US
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#12
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Originally Posted by jmjanzen
Since it has a GPS and phone, it knows it's location, and if properly programmed, can use the phone to tell him about it. Then it can be found. Sounds like a fun geocaching end to the experiment
in the end, you're basically throwing away a tablet, GPS receiver, cell phone, and solar panel, right?
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2009-04-26
, 14:13
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Posts: 3,319 |
Thanked: 5,610 times |
Joined on Aug 2008
@ Finland
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#13
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Originally Posted by 987687
Easy to say, hard to track
Since it has a GPS and phone, it knows it's location, and if properly programmed, can use the phone to tell him about it. Then it can be found. Sounds like a fun geocaching end to the experiment
It can land anywhere within a good 100km radius. And that's a quite literal anywhere. Depending on where you launch, that's sea, river, tree branches, mountaintop, private/state/company property, building top/sides, really, the possibilities are endless, firemen are at an advantage here And if it lands in a populated area, add the speed factor to retrieve it before somebody else does - the race factor
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2009-04-26
, 14:19
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Posts: 23 |
Thanked: 3 times |
Joined on Apr 2009
@ US
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#14
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True... I live in rural middle-of-nowhere-ville in the woods, so I was only thinking about the trees getting in the way. And kinda thinking about the fact that there isn't much cell coverage near me.
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2009-09-12
, 16:22
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Posts: 34 |
Thanked: 0 times |
Joined on Sep 2009
@ Mendo
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#15
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Originally Posted by shadowjk
Actually I recently flew to Dallas and was able to get a gps fix by holding the N810 to the window of the plane. Clocked the speed @ 484MPH @ 27000Ft before losing satellite fix. I believe the difficulty in maintaining a fix was due to the aluminum skin of the plane rather than hardware limitations. The unit seemed to be confused as to exactly "where" I was but my guess is this is due to the difference in time dilation between 484MPH & 30,000Ft and sea level (give or take a few thousand feet) and traveling 70MPH on the ground GPS systems have to take into account that clocks on GPS satellites run a bit slower than clocks on Earth in order to get an accurate location fix. So you are most likely correct in that you may mot get accurate data unless you could figure out how to modify the gps software.
iirc gsm has a range limit somewhere around 30km, not in signal but due to signaling... Comercial gps receivers probably refuse to work over 60k ft altitude (wouldn't want 50 dollar components usable for ballistic navigation etc)
You can start by making it all work in your freezer for 24 hours
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2009-09-12
, 16:49
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Posts: 271 |
Thanked: 220 times |
Joined on Sep 2009
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#16
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Originally Posted by lantz
[digs engineering hat from the closet and puts it on]
The unit seemed to be confused as to exactly "where" I was but my guess is this is due to the difference in time dilation between 484MPH & 30,000Ft and sea level (give or take a few thousand feet) and traveling 70MPH on the ground GPS systems have to take into account that clocks on GPS satellites run a bit slower than clocks on Earth in order to get an accurate location fix.
um, no...relativistic effects have nothing to do with it with regards to the speed or altitude of the plane. If you were able to calculate both an altitude and a speed, the system knew exactly where you were. Accurate altitude determination requires a solid 4-sat fix minimum (4 unknowns require 4 equations/satellites) though due to geometric issues altitude determination will have a larger error bar. By accurate, I mean within the limitations of the CA code and use case. With a 3-sat fix you can get a good approximation of altitude (especially if stationary where you can average out errors to increase accuracy) depending on how clever the programmer was.
And speed requires that such a fix is maintained over time to get the deltas in position over time.The software you were using might not have properly displayed that information for some reason (intentional or otherwise), but that's a display issue and not a calculation one.
However, all that said....thanks for the observation
It's always interesting to see people doing novel things with these tablets
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2009-09-12
, 18:31
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Posts: 34 |
Thanked: 0 times |
Joined on Sep 2009
@ Mendo
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#17
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Originally Posted by texaslabrat
Thanks T
[digs engineering hat from the closet and puts it on]
um, no...relativistic effects have nothing to do with it with regards to the speed or altitude of the plane. If you were able to calculate both an altitude and a speed, the system knew exactly where you were. Accurate altitude determination requires a solid 4-sat fix minimum (4 unknowns require 4 equations/satellites) though due to geometric issues altitude determination will have a larger error bar. By accurate, I mean within the limitations of the CA code and use case. With a 3-sat fix you can get a good approximation of altitude (especially if stationary where you can average out errors to increase accuracy) depending on how clever the programmer was.
And speed requires that such a fix is maintained over time to get the deltas in position over time.The software you were using might not have properly displayed that information for some reason (intentional or otherwise), but that's a display issue and not a calculation one.
However, all that said....thanks for the observation
By accurate I meant that it was not able to display the streets on the map. Might have been moving too fast for the display to keep up... Not sure...
Anyway it was still cool. Not sure what the crew would have done had they known I was using the gps. In retrospect it might not have been too pleasant. LOL
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2009-09-12
, 23:25
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Posts: 1,648 |
Thanked: 2,122 times |
Joined on Mar 2007
@ UNKLE's Never Never Land
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#18
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Originally Posted by texaslabrat
I would think the unknowns are 3 (i.e. x,y,z) but the fourth satellite might be needed to reduce errors from timing, approximations used in the algorithms to make the calculations faster or something similar.
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Accurate altitude determination requires a solid 4-sat fix minimum (4 unknowns require 4 equations/satellites) though due to geometric issues altitude determination will have a larger error bar.
...
Basically, my question is what's the fourth unknown?
Thanks.
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2009-09-14
, 07:27
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Posts: 540 |
Thanked: 387 times |
Joined on May 2009
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#19
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2009-09-15
, 20:23
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Posts: 8 |
Thanked: 1 time |
Joined on Sep 2009
@ UK
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#20
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Hehe, a very cool idea, but tricky to pull off. also if you were to have it take pictures, resolution could be an issue? i mean, if you want the pictures to be of 'globe-worthy' quality :P
Also: technically i think it may count as launching a satellite? which requires permission from the government, but i may be wrong!
Also: technically i think it may count as launching a satellite? which requires permission from the government, but i may be wrong!
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