Key item for Near Space Balloon flights is to know where the balloo and payload is, to record where it is. Two approaches are used, First of all recordng in the payload the position/velocity every second (the solution time for the GPS). Usually recorded to a SD card, this will provide complete flight data when the payload is recovered. But of course this provides no help in flight. For this we have to provide some telemetry via radio to the ground, so that its track can be plotted and retrieval team can find the payload. Although the telemetry will also provide sensor information, this is usually less interesting during flight, and best studied based on complete flight data afterwards.
The main telemetry is usually sent as frames containing the GPS position/velocity data and sensor data. This can be sent up to 1/second but maybe slower if the frames are long and data rates are lower to maintain range. At present our approach is to send the frames as plain ascii coded data, not coded for compactness, but this could change in future.
This is dependent of the payload and mission objectives. For many balloon flights, no control is provided, just the telemetry and tracking. However some flights may require some control over mission instruments and objects, for instance turning on some instrument at an altitude, or releasing some object at an altitude. Complete control includes uplink commands to the payload. As the balloon goes where it goes, this will not include any flight control. Mission planning will discuss the possibilities and capabilities. Technology is moving fast in the area of processors and sensors so a new flight may have more advanced faclitities.