In our quest towards making controlled ballooning more affordable and accessible, we have recently developed a way to allow our Doongara balloon cut-down device to be remotely triggered. During testing we have been using an Iridium satellite tracker to both track and remotely terminate high altitude balloon flights. Below is a brief overview of our implementation of an Iridium controlled high altitude balloon.
Why Use an Iridium Controlled High Altitude Balloon?
Improve Recovery—Whether you are launching your balloon from a mountain rimmed valley or an island, ensuring that the payload comes down before drifting somewhere inaccessible is crucial for successfully recovering it.
Real-Time Control—Doongara’s pre-programmed pressure altitude and time triggers alleviate a number of ballooning risks, such as a slowly leaking latex balloon envelope and balloon under inflation. If either of these things happen, it can be hard to recover a payload since the flight can travel a very long way. The balloon may not even burst.
Even with the best planning, unforeseen problems can crop up that can jeopardize the success of a flight. Were the wind and trajectory predictions for your flight completely unreliable? Not an issue if you launched an Iridium controlled high altitude balloon. Adding real-time control allows you to detect and respond to an even larger range of unforeseen conditions.
How an Iridium Controlled High Altitude Balloon Works
Single Balloon—The Doongara balloon cut-down device is attached between your payload and the balloon. When the Iridium tracker receives the terminate signal, it passes it on to Doongara, which terminates the flight and your payload descends under the parachute.
Tandem Balloon—Both ‘tow’ and ‘float’ balloons are connected with two different Doongara balloon cut-down devices. At the desired altitude, you send the termination command to the first Doongara and the ‘tow’ balloon is cut away, stopping the rapid ascent. You continue to track the flight with the Iridium tracker and after the desired time, or when the flight is over a good recovery location, you send the termination command to the second Doongara connected to the ‘float’ balloon. This Doongara then ends the flight by releasing the ‘float’ balloon and your payload descends on the parachute.
The External Trigger on the Doongara Balloon Cut-Down Device
The external trigger can be enabled or disabled via the Doongara programming interface. When it is disabled, all external signals are ignored and do not affect the Doongara in any way. When enabled, the Doongara will look for a trigger signal that is at least 500ms in duration.
External Trigger Signal Source—In testing, we have been using a GSatMicro. It is a small, self-contained Iridium tracker with two open-collector outputs and a web-based interface. It is available, by special request, with a high-altitude capable GPS unit appropriate for high altitude ballooning. A major downside of the GSatMicro is that it uses an internal LiPo rechargeable battery that is cold sensitive. For longer flights, good insulation and a heater are required.
There are numerous other Iridium trackers, line-of-sight radio options, and payload-provided ways to generate the external trigger signal for a Doongara balloon cut-down device. We are currently working on a stand-alone GPS based Geo-fence add-on for Doongara that also incorporates a LoRa line-of-sight radio for real-time control.
Hardware Interface—The external trigger input on Doongara is configured so that an external open-collector circuit can generate the necessary signal. This allows either a direct connection to a microprocessor or transistor, in an Iridium tracker or your payload, to generate the signal. Doongara has a 10K resistor that pulls the trigger input high to 3.3V. The Iridium tracker, radio, or payload simply needs to pull the line low for ≥500ms to generate the trigger signal.