Today Greg, Alex, and I (with Paul, Alejandro, Akshay, and Marc), finally brought to fruition our small-scale and small means near space balloon project we have been working on for some time. Greg already posted some information about the project here, as well as the pictures. In short, the idea is as follows.
Motorola sells the i290, a sleek, cheap, and light phone running Java for just about $50. (It turns out that ebay has it for much less). The i290 is a pay-as you go phone which comes with some starting amount preloaded on the sim card. No additional plan required. However, what makes it truly advantageous is the onboard gps.
Every near space mission requires telemetry, and a good telemetry beacon can cost quite a lot. The system on Apteryx cost us more than $300, limiting the number of high school or middle school level pockets books which could afford a near space balloon project. With a telemetry system available for less than $50 with a little code and perseverance, we figured we could create a repeatable, off-the-shelf launch package for less than $150, or maybe even $100 if we pushed it.
Some of you may remember the MIT students in the news with the near space project for under $150. They also used an i290, only they bought a tracking system application which went on the phone, and later lost contact. What we proposed and carried through was to write our own to cut costs and adapt to our purposes.
Due to the inevitable lack of cell phone coverage in near space, the code was written to store data points and send them out whenever it was within range. Latitude, longitude, and altitude were sent to sensor.network. The phone would crash from time to time on gps read (we would be interested in testing a second phone, perhaps ours was defective), but would automatically reboot and run the application upon restart. Data was saved, so in the event not all coordinates were sent out on a system crash, the phone continued to work.
Since the i290 is extremely light, we tried to construct a balloon system weighting under a pound. We built our own radar reflector from foam core board, spray adhesive, and tin foil, which ended up weighing less than the store-bought reflector from Apteryx. We built our own two foot parachute from rip-stop nylon (which ended up being too small), and wrapped the phone in soft foam. Everything was attached together by tie line.
The balloon was the toughest question, especially considering we had a limited amount of time before school started, New Years is, well, today, and we wanted to do it as cheaply as possible. We ended up getting a 66 inch latex party balloon from People Greeters for $20. Since a party balloon is not nearly as elastic as a sounding balloon, we felt that buying a larger balloon and under filling it would give us the best results.
So we drove into the central valley, tied everything together, filled up the party balloon, and let her go. The balloon had a noticeable seam is it as we let it go, quite unlike the uniform Kaymont sounding balloons.
With the balloon in the air there was nothing to do but wait. Tracking worked perfectly, then fell out after about ten minutes, for the phone had left cell coverage. We sat and waited, and were surprised by a very early burst and return to cell range. The balloon apparently only got as high as 6,000 ft, which is lower than some mountain peaks within a day's drive. (Lake Tahoe, anybody?) Nevertheless we were able to recover everything from a farmer's field after getting adventurous crossing some mud in an aqueduct. The phone was working perfectly, the parachute was a bit tangled, and the latex balloon was in tatters like the sounding one had been.
What we learned from this is that the telemetry system definitely worked, but we will have to try it with a higher-altitude launch, perhaps with a real sounding balloon this time. We would like to buy a more expensive Motorola phone with a built in camera to take pretty pictures as well, to complete our near space kit.
We also learned that party balloons don't cut it when it comes to a near space launch. We will be looking into several alternatives, including the obvious sounding balloon and the more interesting zero-pressure balloon.