To track the capsule, we planned to purchase a Motorola Iden cellular phone that would be compatible with the Boost Mobile cellular phone network. The cellular phone would be paired with the Boost Mobile “Pay-As-You-Go” data plan to provide a downlink for GPS tracking. Instead of paying for the Boost Mobile GPS service, we planned to use InstaMapper, a free location tracking service that links to an application installed on the phone using the wireless data connection.
To record the flight, we chose to purchase a small, lightweight, and inexpensive digital video camera that supported up to 8 GB of video at 30 frames per second and a resolution of 720 x 480 pixels. A team member offered to allow us to use his 8 GB microSD card. Since the integrated battery can only run the camera for two hours of recording, we planned to connect the camera to an external power supply.
To make the recovery of the craft easier, we planned to add visible and audible beacons. The visible beacons would be LEDs arranged to emit light in all directions, and the audible beacon would be an external buzzer.
To power the various systems in the capsule we decided to use standard AA alkaline cells. The cells would be combined in both series and parallel to make batteries emitting the necessary currents and voltages. To physically manufacture the batteries, we planned to solder the batteries together and duct tape them for strength.
We followed the initial design fairly closely, but did have to make several omissions and modifications. The phone worked better than expected, as we were able to follow the initial plan but were not required to pay for cellular data usage in order to use InstaMapper. This was the one part of the project that did not require any modifications.
In the initial design, we planned to connect the camera to a AA battery pack. When the camera arrived, however, we discovered that it was unable to record on external power, only allowing video to be captured under the power of its own internal battery. After much discussion, it was decided that we had to hard wire external power directly into the camera. A member of our workgroup donated 2 cell phone batteries with the same voltage as the camera, and he set to work taking the camera apart and soldering the new batteries into place. Using duct tape and rubber bands, he fashioned a makeshift battery pack that was connected directly to the camera. We predicted that the pack would provide the camera with a maximum of 12 hours of life, which would exceed the amount of video that would fit on the 8 GB microSD card. Only time would tell if the battery pack would perform as expected.
Because we were unable to get the LEDs and buzzers, we included neither visual nor audio beacons on the capsule. The removal of the beacons and the discovery that the battery of the cell phone would provide it with enough power for up to ten hours reduced the power required from the batteries. Dr. Lovegrove also warned us of the dangers of alkaline batteries at low temperatures, so we switched to lithium batteries. In the end, because of its short battery life, we hacked together a battery pack for the camera.
The phone was tested in four areas: reception, battery life, accuracy, and temperature resistance. To test the reception, the phone was taken on a road trip through much of the southeast while using the InstaMapper software. The phone passed the test flawlessly, sending data points roughly every 30 seconds and doing so fairly accurately. We had more difficulty getting good reception on campus, but we were still able to get an occasional signal.
Knowing now that the phone was accurate and reliable with adequate reception, we tested the battery life using its internal battery. With the InstaMapper software running the battery lasted roughly ten hours, plenty of time for our flight. Lastly, the phone was placed in a refrigerator (near freezing) and it continued to work as designed.
The camera’s internal battery life was tested by putting the camera in both a refrigerator and a freezer. The camera, being fully charged, was left to record until the battery was depleted. In the end, the camera had a battery life of approximately two hours. This test led us to the conclusion that we definitely needed an external power supply. The hacked camera battery pack was unable to be tested in the time allotted without potentially compromising the project, but we were able to predict a minimum of twelve hours of battery life.
Unfortunately, the phone did not work as well as we had hoped on launch day. We were able to get an initial signal when the phone was first turned on, but did not get another for roughly one hour. By launch time, roughly another thirty minutes had passed without a signal. Fearing that we would lose contact after launch, we shuffled the box around the launch site hoping for another signal. Thankfully we were able to get one, relieving our fears that the signal had permanently dropped.
The phone only sent one position during the ascent, and this was but a few seconds after launch. Without any more data points, the phone was not able to help mission control predict the landing site. We received our next (and final) position once the payload had landed, and it was fairly close to mission control’s predicted location. Upon arrival, we were pleased to find that the actual location of the payload was very close to the location specified by the phone, further proving its accuracy.
The camera exceeded expectations as well. While other cameras in similar projects gave out due to low temperatures, our camera recorded everything from pre-launch preparation to the eventual descent and landing. The camera was able to capture a clear picture of the curvature of the earth just before the balloon popped, and it captured many spectacular sights upon its plummeting return to earth. Unfortunately, the the camera went into sleep mode when the memory card was full. When we returned to the school, we tested the camera and discovered the battery still had life in it. The hack-pack was a complete success.
One of the things that future students should realize is that not all part requests will be fulfilled due to budget and time constraints. They also should understand that the project takes considerable effort, and completing it can take a significant amount of time.
Students should plan ahead and remember to not overlook the little things. With our project, the design of the box was completed before the camera and battery pack was completely tested and confirmed. Because of this, the camera was only able to fit stably in the box sideways, so all of our videos were on their side. It may seem like a minor thing, but when you want to put together a professional looking video presentation it is helpful to not need to rotate the videos, and it looks more polished as well.
Also, do your research thoroughly. Our initial camera investigation led us to a device from a Chinese company. The $10 price tag sounded too good to be true, and after further investigation, we discovered that it was. Fortunately, we were able to locate the actual version of the knock-off product. However, we purchased that under the assumption that we would be able to run it on external power which proved to be false. This could and should have been verified through further investigation before purchasing the product.
The cell phone worked for the GPS tracking, but there are better options available. The software used needs strong reception to be able to send data points, and the city of Greenville simply does not provide that reception through its towers. A dedicated GPS unit or true smartphone (on a different network than Boost Mobile/Sprint) would be a better, albeit more expensive, option. These would provide more data than a simple GPS unit can provide.