I was recently hired by Professor Kosmatka to work on the California Space Grant High School balloon project with Casey Barrett. Four local high schools with underrepresented minorities were contacted and asked to submit experiments which would fly in their own payload boxes on our near space balloon.
By the time I got involved Casey had already presented to Preuss, Helix Charter, and El Cajon, all of which had provided a class of excited students to work towards creating their own experiment. I was fortunate enough to get to go with Casey to Lincoln, where we donned the Cal Space Grant shirts and did our thing.
The students were introduced to the concept of a near space balloon, what near space is, and what UCSD had done the previous year with their near space balloon. The photos, of course, were a big hit, and by the end of the presentation students were shouting out experiment ideas. “Grilled Chicken,” “Fire,” and “Space Candy” were among them.
With four high school committed and about three weeks left until launch, it was time to get busy designing and building the balloon system.
I was set to work on flight sensors, and decided to once again use Sun SPOTs, very nifty devices which had already been proven to work on the Apteryx mission. For those who are not familiar, a Sun SPOT (Small Programmable Object Technology) is a battery pack + cpu board + radio + sensor board running and programmable in Java. They are extremely customizable to any situation imaginable, involving projects from large scale forest monitoring to flying Google Earth bicycles.
On Apteryx we had rigged up a Sun SPOT with an SHT15 and an SCP1000 to measure temperature / humidity and pressure, respectively. However, this mission didn't require me to measure atmospheric pressure (Stratostar was doing it, more on that later), but I did have to set up a second sun spot with a Geiger counter.
The first SPOT was fairly simple, essentially an easier version of what we had done over the summer. Starting with the project code from Kenai (http://kenai.com/projects/hibal-spot), I added % battery level to the list of stored data points, and removed the SCP1000 from the code. The spot was now storing system time, onboard temperature, onboard net acceleration, SHT15 temperature, SHT15 humidity, and onboard % battery charge every fifteen seconds.
Wiring proved to be a bit of a problem, especially since it was my first time soldering and I was working with my modest equipment in my dorm's study room. I had ordered a protoboard from from Sparkfun (http://www.sparkfun.com/commerce/product_info.php?products_id=8812), and it took me a couple of mind numbing days to figure out that this was a special board with every pad shorted to every other pad, and that I actually need to solder the headers to the spot. With my shameful beginner's errors over, the SHT15 sprang to life and worked perfectly.
The Geiger counter was actually easier, thanks to the help of Mr. Roberts in the MAE electronics lab. We discussed reprogramming the Sparkfun Geiger counter (http://www.sparkfun.com/commerce/product_info.php?products_id=9298)'s microcontroller to store the data, but found that there was not nearly enough flash onboard to store a flight's worth of readings. Instead, I once again used a Sun SPOT, powering the counter from the +5 V pin on the spot and continuously monitoring the counter's output pin.
When a radiation particle hits the Geiger tube it causes a burst of current, which you can see on an oscilloscope and which the Sun SPOT would detect. I had the spot counting the number of events every minute, and storing that in a record along with system time, onboard tempterature, net acceleration, and % battery charge. One can never get enough data.
All in all, the spots turned out pretty nice, though I will do a better job on the wiring next time, since I now have a hang of soldering and know what sort of a protoboard to buy.
My next task was to program two Cannon A590s using CHDK to get them to automatically take pictures during the entire flight. This was not too difficult, and I did manage to add a nifty feature which let me start the camera with the rear display on, then with the CHDK script running, could switch it to turn the display off (to save power).
Finally, I helped Casey put together the payload boxes, which were simply stacked pieces of Styrofoam cut with a hot knife. The boxes were cut for an internal dimension of 9 x 9 inches, with 1.5 inch walls. The top was a separate piece, and was later duct taped / wire tied on.
On the actual day of launch, after running flight simulations, we drove out to just south of the Salton Sea with a big bus full of high school students, parked, and set up. The two guys from Stratostar were there to help us out, and under their supervision we hooked up the payloads. The high schools put their projects in as well. It came out as follows:
- Helix with a cricket experiment, various crickets in plastic bottles set to be exposed to the cold, radiation, and / or pressure. A voice recorder was placed inside to find a correlation to cricket chirps with temperature. A small HD video camera was positioned to record the actions of the crickets inside one of the plastic bottles.
- Preus with a Lego NXT measuring the speed of sound with altitude using sonar with a sensor
- Lincoln with nursery plants and the two Sun SPOTS. (Yes, I could have just used one Sun SPOT, initially I wasn't sure that the two spots would end up in the same payload box) A control group was left on the ground to compare growth to. Plants were only exposed to the radiation
- An expensive Sony HD camcorder pointed up at the balloon
- The camera box, with both of the A590s, a small HD video camera, and a nicer Cannon SX200. All four were positioned radially, pointing out horizontally.
And after a ten second countdown the balloon took to the air.
The main beacon cut out five minutes into flight, and came back online at impact. Stratostar had their sensors set up to report over the air, so we never got that data. We eventually found the balloon, but were disappointed to find that the chords between the top two experiments had severed. We lost everything but the command module, backup ham beacon, parachute, and the cricket experiment. We do, however, remain hopeful in finding the remaining equipment at some point in the desert.