Option for locating lost rocket? Anyone use this? Pls review

rocket sok
Onebadhawk
eggtimer rocketry
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NattyDread said:
Anyone used this cellular technology for finding a rocket?
https://cart.amwprox.com/index.php?...t_id=767&virtuemart_category_id=19&Itemid=474
Click to expand...

I have not used it but lets look at the specs:

Specification:
GPS Accuracy:10m
Antenna ：Build-in
GSM Band Frequency：850M/900M/1800/1900MHz(Global Use)
Standby time ：About 3 Days
Size：1.75in x 1.5in x 0.5in(L x W x H)

10m is a bit far for modern GPS units, but should be close enough for rocketry.
Three days standby time is good.
While I understand why it needs GSM over CDMA, for my use this makes it worthless. We have Verizon coverage at our main HP launch site, but not AT&T.
Also the size is a bit larger than most other options, but not enough to make it unusable.

gps1.jpg
 
Winston said:
Anyone ever tried one of these? $38.99:

https://www.ebay.com/itm/Mini-Spy-V...10?pt=US_Tracking_Devices&hash=item19e3f9190e
Click to expand...

I cannot speak from experience as I have do not own one, but a quick Bing Search reveals that this device does NOT use GPS. It uses GMS Cell Tower location, triangulating your position from nearby cell towers. In remote areas where launch sites tend to be the error rate can be 500 to 1000 meters or more. Pretty much useless for finding a rocket.
 
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Right Wing Wacko said:
I cannot speak from experience as I have do not own one, but a quick Bing Search reveals that this device does NOT use GPS. It uses GMS Cell Tower location, triangulating your position from nearby cell towers. In remote areas where launch sites tend to be the error rate can be 500 to 1000 meters or more. Pretty much useless for finding a rocket.
Click to expand...

The TK102 uses GPS. Determining location from cell towers requires access to a database of info about the towers which a simple device like the TK102 wouldn't have. There is an app for IOS that is supposed to be able to get the SMS cell info from the TK102 and use it to determine the device's location if it is unable to do so itself using GPS.

-- Roger
 
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jadebox said:
The TK102 uses GPS. Determining location from cell towers requires access to a database of info about the towers which a simple device like the TK102 wouldn't have. There is an app for IOS that is supposed to be able to get the SMS cell info from the TK102 and use it to determine the device's location if it is unable to do so itself using GPS.

-- Roger
Click to expand...
Absolutely correct. The e-bay ad for the TK102 indicates the GPS chip is a SIRF-3 which is one of the more sensitive units.

Bob
 
bobkrech said:
The e-bay ad for the TK102 indicates the GPS chip is a SIRF-3 which is one of the more sensitive units.
Click to expand...

Just be aware that the sirf 3 behaves very poorly under high acceleration. I flew one of these a few years ago and it had about a mile of error at apogee. Fortunately, I saw the impact location by eye as the GPS had barely started to correct by the time it hit at high speed. I don't consider this chip suitable for rocketry.
 
keithp said:
Just be aware that the sirf 3 behaves very poorly under high acceleration. I flew one of these a few years ago and it had about a mile of error at apogee. Fortunately, I saw the impact location by eye as the GPS had barely started to correct by the time it hit at high speed. I don't consider this chip suitable for rocketry.
Click to expand...

I gotta agree with this. I've used sirf3/4 parts in non-rocketry related products and they were barely acceptable for that. stay away from the sirf stuff.
 
keithp said:
Just be aware that the sirf 3 behaves very poorly under high acceleration. I flew one of these a few years ago and it had about a mile of error at apogee. Fortunately, I saw the impact location by eye as the GPS had barely started to correct by the time it hit at high speed. I don't consider this chip suitable for rocketry.
Click to expand...

The tracker would be used to locate a rocket after it lands, so acceleration isn't an issue.

-- Roger
 
jadebox said:
The tracker would be used to locate a rocket after it lands
Click to expand...

Oh, right, it doesn't report position during flight at all. I'll keep using something else then; afraid I've used Troj's favorite recovery technique more than once, and will probably do so again in the future...
 
keithp said:
Oh, right, it doesn't report position during flight at all. I'll keep using something else then; afraid I've used Troj's favorite recovery technique more than once, and will probably do so again in the future...
Click to expand...

What would that be? I seem to recall him saying something about Big Red Bee at some point...
 
keithp said:
Uh, "bucket" recovery...
Click to expand...

:facepalm:

Seriously, except for Kevin :wink:, in any expensive rocket, a good GPS unit with a radio that reports inflight position is the best solution, because if the GPS fails, you still can use RDF to find the rocket on the ground. Having an audio beeper in the mix is also not a bad idea either.

Bob
 
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Those GPS/cellular text-me-your-location devices will supposedly send you periodic location updates, although I can't get it to work on the one that I got. I have my doubts whether or not this is a viable technology, I'll find out this weekend at ROC. If you have to ping it to get it to respond then it is probably not a viable option, because if the GPS patch antenna happens to land face-down it's unlikely that you'll ever hear from it; they only respond back if they have a good GPS signal.

bobkrech said:
:facepalm:

Seriously, except for Kevin :wink:, in any expensive rocket, a good GPS unit with a radio that reports inflight position is the best solution, because if the GPS fails, you still can use RDF to find the rocket on the ground. Having an audio beeper in the mix is also not a bad idea either.

Bob
Click to expand...
 
I picked up one similar before Christmas and tried it out. The problem I found was the accuracy was very bad. Not just bad, very bad. To the point in some areas I tried it was one kilometre off. Made it quite useless for finding rockets. No where was it within 400m either. In talking with people who know more about the GPS receiver type information they said it was because of the type of technology, not anything else. I looked at a few of the pet finder type things as well, and they also lie about their accuracy. Gave up and bought a BRB900
Andrew
 
Out of curiosity, how is the cellular coverage at your flying field? That may (or may not...) have something to do with the accuracy; these things can only send you the location IF they have a GPS reading AND they can get a cell.
 
It's all in the details of the units architecture. You should be able to ping it on the pad to make sure it's working before you launch. If it's programmed in a logical manner, I would hope it transmits the last valid fix if it looses lock, but that's not a given.

cerving said:
Those GPS/cellular text-me-your-location devices will supposedly send you periodic location updates, although I can't get it to work on the one that I got. I have my doubts whether or not this is a viable technology, I'll find out this weekend at ROC. If you have to ping it to get it to respond then it is probably not a viable option, because if the GPS patch antenna happens to land face-down it's unlikely that you'll ever hear from it; they only respond back if they have a good GPS signal.
Click to expand...
 
Hal8472 said:
... they said it was because of the type of technology, not anything else. I looked at a few of the pet finder type things as well, and they also lie about their accuracy. Gave up and bought a BRB900
Andrew
Click to expand...

GPS technology is around quite for a long while already. Even these cheaper receivers uses standard GPS IC's for the L1 carriage that are pretty accurate (from 3m to 15m usually), so if a device fail so bad in pointing out locations it's most probably because a bad design (how received data is processed e.g.). Advances is GPS receivers in last years does not affect accuracy but receiving efficiency, modern ones (the most common), uses boost reception. Well, maybe cheaper ones are still using old IC's and such but if they got signal received properly, accuracy is just the same.

Most confusion about location comes from misinterpretation on the received data (decimal degree X plain lat long). Other source of confusion is the current Datum (earth ellipsoid) being used as reference by the GPS. Datum misinterpretation can add 70 or more meters error to the data being read. As reference, most uses WGS84, as well common programs like GoogleEarth. Other factors can help adding error readings like GPS constellation changes.

I use one of these cheap receivers to track my car, its called TK-102 (tons of offers on ebay), it proven be accurate and you can set it to send location at intervals or by issuing it by SMS message. It can even communicate to a server to log path etc. For this one though, never tried it inside anything like a rocket.

I suggest you guys to take a look into a software called TrackMaker. Its very easy interface and useful to make location conversions, download tracks from GPS (handhelds ones), among other nice features. Its free version is unlimited/unlock usage and you got all the needed basic functions there.

Well, sorry for my bad English.
 
Thinking a bit more about this subject: Seems that lot's of guys flying rockets do it in very open, large and plane surfaces like deserts or even worse, salt deserts. I guess GPS signal reflection can be a issue in such places? From GPS satellites that are too low on the horizon, maybe there's some chance that the receiver gets ground reflected signals, messing a bit the location.

Signal reflection is for sure a issue to be aware of in the GPS world but I'm not sure how it happens in environments like desert and such.

EDITED:

Cool info, specially for developers: https://www.ion.org/publications/abstract.cfm?articleID=6584

"With GPS, multipath occurs when the signal bounces off a building or terrain before reaching the GPS receiver's antenna, meaning that the signal takes longer to reach the receiver . This added time makes the GPS receiver think the satellite is farther away than it really is, which adds error to the overall position determination."

Some empirical data about receivers on (some?) desert: https://www.fao.org/ag/locusts/oldsite/MAUproj/Reports/GPS.pdf

I didnt read it entirely but considering only the results on this experiment its clear to me that receiving on deserts is much much worse than results I got in a city or a forest/montain places. This one study point out a GPS error of 1000m! I swear I never had such a big error with handhelds on my life in usual conditions.
 
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Your reference article was dated 1999, and who knows how much earlier the data was obtained, a 1000M error was possible if the satellite coverage was the minimum number, poorly distributed and mainly overhead. In the days of SA (selective availability), the intentional GPS errors put you within +/-100 meter horizontal and +/-150 M vertical 95% of the time by design and SAs was not turned off till May 1, 2000. WAAS was not turned on until December, 1999 either. With SA disabled the GPS accuracy is within +/-2.5 M horizontal and +/-4.5 M vertical 95% of the time. Using WAAS corrections the GPS accuracy improves to within +/-0.9 M horizontal and +/-1.3 M vertical 95% of the time. Both values assume open signal access over the overhead hemisphere.

It's also easy to be off by 1 km if you decode the GPS data incorrectly. A ham friend was trying to locate a weather balloon payload that landed with a ARPS transmitter. The owner had written a cell phone app to put the data into a google map but incorrectly converted the ARPS data packets. My friend was located at the spot where the payload supposedly landed but he could not hear the audible beeper that was in the payload. He asked about the data format, the owner realized his erron, altered the program and directed him to another location a 1 km away. As he stepped out of his car he faintly heard the beeper and followed it and the gps map location right to the tree the payload landed in.......

If you use a commercial unit, their software is probably correct, however the internal architecture may not sent out the last known fix location if no current GPS fix is available.

Bob


Bob
 
Well pointed Bob,

I knew about the intentional "noise" removal but didnt knew such details, thanks. I heard that US can add noise back anytime (crisis management), but no idea if they really do it or how often. Sure, with poor coverage and/or other issues the actual position is pretty much unpredictable.
It's possible though to build a decent system using (even for cheap), commercial units.

My experience with TK-102: They provide a software you can use to track the GPS to have even the "last seem" position but the last time I tried it, worked only on WindowsXP. If you reinstall their software or uninstall and install in another computer you cannot register the unit anymore. Same chinese companies that sell these units also offers a server based tracking system so no mystery about understanding why you can register GPS just once in the provided software. My final solution for TK-102 to track the GPS and not be depended on other people software/solution was installing OpenGTS https://opengts.sourceforge.net/ on a linux VPS server (though it works on windows as well), of course if you dont have a fixed IP you will need to reprogram the unit (sending SMS to it), every time you got a new IP. OpenGTS have ready to use protocols for TK-102 and many other brands.

Still about the FAO document: They took several sample points along different times so for me the real issue about its reliability is really what you pointed out (added noise). I would like to see the same experiment in recent days. (The multipath issue and how it may happen on ares like deserts still bugs my head).

EDITED: They have now the TK-102-2 model with a SD card. I even emailed then to ask how it works and they responded that it will collect position points when GSM is not available and send all the data to server when GSM becomes available.
 
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"Selective availability" was still in effect in 1999, so those accuracy number reflected in that article are no longer relevant. I routinely get very accurate results in wide open spaces like playas, deserts, and open range.

Greg
 
I've never had access to this proliforation of Affordable Technology in my earlier Days as a Rocket Enthusiast. I used a Compass and Shot an Azimuth, then tried my best to find the Tree.
I still can't afford all that fancy stuff come to think of it. Sometimes, your just going to loose one.
I like to think it's part of the Game.
 

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