Mission SammyOne

The Tracking Device



If you want to find your payload back, you will need a tracking device. I had seen on the internet that most groups did this with HAM radio. Sending back radio signals with GPS location. As I do not have a radio license, I couldn't do that.

Most obvious solution was using GSM+GPS. GSM cellphone coverage is very good in the Netherlands and I had an old HTC phone with a GPS receiver. However, research revealed that due to some military restrictions almost all GPS receivers do not work above 18.000 meter. I also read that some GPS receivers do not get a fix when they get back below 18,000 meter due to faulty software. That scared me. Then I found out that a GSM cellphone is only capable of sending a text message out until a max altitude of about 1km (though there are cases reported from GSM phones working at above 5km). So there will be a huge black hole in telemetry data. GSM+GPS seems worthless for tracking the balloon but can be of great value for retrieving the balloon. It only has to send one text message with the correct GPS location when the it has landed.

Anyway, I decided to go on with the GSM+GPS solution and created a test. I bought a cheap prepaid SIM card with lots of free text messages. I found software called ReliRescue that I could use to program my HTC to text me a GPS location every 5 minutes. That worked flawlessly. I carried the phone in my car, to my work, in my pocket, left it outside. It just kept updating me about it's position. So GSM+GPS seems very reliable.

The HTC works for about 5 hours on a battery charge, sending text messages every 5 minutes. A good option for payload retrieval.

Then, at the last minute I found a better solution. The old HTC (a TMobile MDA Compact III) is pretty heavy and it is one of my daughters favorite toys. And I also could use the HTC as a portable tracking device when the balloon is landed. I started looking for other GSM equipment and found a tiny GSM tracker. This is a cheap little device used for tracking the position of a car or a person. It holds a SIM card and a battery but has no display. This means more battery life! I decided to go ahead with that device and keep the HTC for tracking and retrieval. I tested it the same way as I did with the HTC and it performed about the same. Very good! It holds a small lithium Ion accu that lasts for about a day. So battery life will probably not be a problem.

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The Tracking Device

The GSM tracker I used to recover the balloon. It’s as big as a box of matches and weighs almost nothing.