Follow-up thanks to the GPS/APRS

--> The G.P.S. (Global Positioning System): We used a GPS navigator fixed in the basket. The GPS uses Medium Earth Orbit Satellites that are exactly located. To solve for a position on Earth, the GPS uses the triateration principle: the location of the object is on the flight path of three satellites that orbit in outer space around the object. Using four satellites allows the receiver to measure time, altitude, latitude/ longitude and speed. The ham radio operators in Tours defined these five parameters of our system which were sent us during the flight. Each satellite broadcasts its identification number, its precise orbit and the exact time the message was sent. Thanks to this information and the integrated clock synchronized with the one of the satellites, the receiver computes the signal traveling at the speed of light through outer space and measures the distance to each satellite from which it determines the position of the receiver.

--> Operation of the APRS (Automatic Position Reporting System) :

In order to follow-up our balloon live, we connected the GPS receiver to the APRS composed of:

- The AX 25 which network transfers data encapsulated in packets and proceeds to fast packet forwarding. Tinitrack is a modem which encrypts these data coming from the GPS receiver.

- A VHF radio transmitter that broadcasts encrypted data on the 144,800 MHz frequency dedicated to the APRS network. The ham radio relay stations receive these data in real-time. They are transmitted  anew through radio waves and the Internet (VPN system, Virtual Private Network), especially through the web site http://aprs.fi/. Our system was identified under the following: F6KCI-11. It is possible to have a look at the data concerning our tries on this web site as data remain available for 6 months. Direct transmission of data or relay station-to-relay station transmission allows a real time follow up of the balloon. In fact a receiver is connected to a lap-top which contains, for example, the UI-View program created by ham Roger Barker G4IDE.

GPS