Though the HabHub predictions are impressively accurate, they are not good enough to lead us to the exact landing spot required for retrieval, so we need the payload to be able to tell us where it is.
To Pinpoint the Landing Location
Strobe LightDepending on your landing area, you could equip your payload with a bright strobe — get close enough to the landing location using estimates, and hone in on the exact location by looking for the strobe.
The challenge with this method is that a strobe light adds weight and requires power. If it is not recovered in a timely manner the power will eventually run out, disabling the strobe. Additionally, if the payload lands with the strobe light buried or blocked, the strobe will not help you locate the payload.
Audible PingAnother option is for the payload to emit a loud sound so that once you are close by you can hear where the exact location is. Like the strobe solution, this adds weight and consumes power. The noise may also be disruptive or annoying to people near the landing area.
Both of these methods only work for (potentially) finding the location of the balloon when it is near or on the ground — neither allows you to track the balloon in flight.
Cellular CommunicationIn order to track the balloon in flight and track where it lands, we wrote a tracker app that enables the cell phone in the balloon payload to text us its location and altitude while it has cell reception. Once we receive the text, we map the GPS coordinates using Google Maps. Since we already have a cell phone on the payload, there is minimal addtional power use and no extra weight to have the cell phone text us every minute while it has cell reception. But it means we need to launch and land in areas with good cell phone reception and that we do not know where the balloon is while it is above ~20,000 ft, as it is too high to access the cell network.
Radio CommunicationIn order to track the balloon when it does not have cell reception, we place a 433MHz radio onboard the payload and use a directional antenna to receive the signal. This method adds some weight and power drain. It also requires that the operators have at least a Technician Class Amateur Radio License, are within range of the payload, and have an unobstructed path between the transmitter and receiver. Once the payload is on the ground, the transmission will most likely be blocked by the ground or other obstructions, so unless you can track the balloon closely during the entire flight, a radio is not ideal for finding the exact landing location.
We did successfully track the balloon using radio during our third launch, and you can read more about that here.
BackupIf all else fails, you may be able to take advantage of the Android Device Manager to locate your balloon. We had do this on our first launch when one of our cell phones never got a valid GPS fix. Luckily, Android Device Manager was able to triangulate and provide a very accurate location of the payload. Though this was a lifesaver, we would not recommend relying on this service as the main tracking method.
Once we get the GPS coordinates of the payload landing site (from radio communication, cellular communication, or Android Device Manager), we have to get to the landing site. This is often one of the most challenging (and fun!) parts of the day.
In order to automate the process of transferring the cell's texts into a Google Map, we created a web app that plots all received location texts from the cell phones. Here are the results from our fourth launch:
|Launch 4 balloon tracking.|
Though this gives a great overview (and is much more helpful than having to copy and paste GPS coordinates into Google Maps while on the chase), even when zoomed in, Google Maps isn't necessarily helpful in getting you to the exact landing location.
|Landing location of Chuva from launch 4.|
Since we aim to land in unpopulated areas, we're not landing near marked roads. Therefore, in order to get close to the landing location, we rely on Google's satellite imagery and real-time problem solving to get as close as possible to the payload.
Luckily, Chuva landed right alongside a dirt road, and we could drive up pretty close to retrieve.
Other times we have had to walk long distances or find ways around unanticipated obstacles. Always be careful and respectful when recovering your payload!