The launch took place earlier than scheduled; at 0932L the balloon was released in some moderate winds from Forney High School. Everything ran ahead of schedule, we arrived at the high school early, the students from DeSoto and Lancaster arrived early, and subsequently the balloon was launched early.
All pre-flight checks went OK. Everything was beaconing properly, APRS data looked good, and the crossband repeater was repeating. There were five payloads that seemed to be functional: Primary Tracking, Telemetry, Secondary Tracking, Slow-Scan Television (SSTV), and the Crossband Repeater.
Once the rigging was complete, the students huddled in a corner and began inflating the balloon. It took nearly all 21 students with their hands in the air to prevent the balloon from making contact with the building when gusts of wind would take control of the balloon. Upon inflation, we zip-tied the payload string to the balloon, and walked it out to the practice football field. After a quick run-down of launch procedure (essentially “release slowly!”) we let the balloon up by feeding the payload string hand-over-hand. At times, the wind was so strong, the string was barely 30° above the ground.
It’s in the air!
Shortly after launch, we realized that the Pi-based tracker was not updating its position. It was sending the same packet over and over. Although not good, it does indicate that the problem was upstream of the TNC, most likely a communication issue with the GPS. Unfortunately, my code is not self-recovering from a GPS connect/disconnect issue. It can easily handle a position unlock, but if the gpsd daemon stalls, it will not recover. I imagine that there was a loose connection that caused this particular problem. Fortunately, the primary tracker functioned exactly as intended.
The telemetry looked good. At the launch site, the balloon measured a pressure of 981mb, an external temperature of just over 30°C and a relative humidity of 47.6%. Tony (W5ADC) was able to calculate the ascent rate – just over 1200ft/min, or 6m/s. With the balloon in the air, the chase began.
Tony (W5ADC), John (KC0L), and myself took off just after the balloon launched. The students loaded up, and went to a local park to play around while the flight took place. Tony, John and I stopped in Seagoville to run flight predictions, talk on the crossband repeater, and plan out our chase. After about 45 minutes of waiting, we determined it would be wise to head towards Ferris.
I made numerous contacts through the crossband repeater. In this mode, it will repeat things heard on 446.050MHz out on 147.5MHz. I talked to AF5MI in Carrolton, K5LUO near OKC, W5TXG near Palestine, and KD5OUG in Richardson. Next time I’d like to work “Balloon DX” through the repeater.
We made it to Ferris rather quickly, and kept heading south on 45. Believe it or not, bladder instinct led us to our next waiting point, a Shell/Sonic combo just outside the city of Palmer. John, Tony and I spent about twenty minutes at this location while the students were rounded up and caught up with us. The balloon peaked at 85,000 feet, and made a quick descent following the same winds that took it up.
The bus driver was kind enough to follow the chase vehicles as we weaved our way through Palmer out to some country roads. John had a slight lead, and informed us that the balloon would be very easy to access, and was nicely strewn out in a field. His assessment was correct; the balloon was 30 yards from CR813 and was waiting for us in a slightly muddy field.
The students hopped off the bus, and helped gather up the payload bits. The landing, although mostly soft, was enough to knock some batteries out of their holder on the primary tracker. The chase was completed after a trip to CiCi’s in Lancaster.
My favorite part of the launches is the data. I love seeing where the balloon can be heard, and watching the telemetry stream in through the flight. This flight had the telemetry basics covered, but not overdone: internal temperature, external temperature, pressure, and humidity. Altitude was handled by the GPS.
- Launch: 9:32AM
- Burst: 10:54AM
- Landing: 11:20AM
- Flight Time: 1:48
- Max Altitude: 84,486ft
- Lowest Temperature: -47.9°C
- Lowest Pressure: 25mb
Even though my primary tracker had failed to accomplish its primary function, it was still useful for ranging the balloon. A handful of IGates were able to directly receive packets from the balloon: N5DTX-5, K5UTD, KB5ASY-4, AF5I-1, WD5DDH-1, WB5QLD, N5HYH-5, AE5PL-10, KE5UUO, W5LHG, N8QVR-10, KC5AFM-1, W5AMZ-1, KD5UMO-1, N5YSQ, KA5WMY-10, W5NGU-4, W5ROX, KA5WMY-5. Remember, to IGate a packet, you must have a good signal from the balloon. This means >-110dBm (or so). The image below represents the areas in which the balloon was definitely heard via RF, and you probably could have talked through the crossband repeater or received SSTV images.
The temperature data is ever so slightly skewed by the color of the temperature sensor: black. As seen in the chart below, the temperature rapidly dropped on the descent and ultimately reached a minimum value of nearly 20°C less on the descent than it did on the ascent. I believe this is caused by the air rapidly moving over the sensor, giving the sun and the internal electronics less of a chance to skew the data.
Another aspect of the data to analyze is the pressure/altitude correlation. The GPS read a max altitude of 85,000 feet, and the lowest measured pressure was 25mb. Using formulas provided by NOAA, I plugged in our meager 25mb to produce a theoretical maximum altitude of 73,499 feet. It’s a good thing our altitude data came from a GPS, as the NOAA formula and our sensor produced over a 15% error between the two numbers.
The humidity data was rather boring, other than inconsistent amounts of moisture at various altitudes. I’m sure the people that paid close attention in Skywarn school would like me to make a Skew-T chart out of this data, but you’ll have to do it yourself.
The data can be downloaded here.
A Successful Launch
All things considered, this launch was very successful. First and foremost, the students enjoyed themselves and learned a lot in the process. On the balloon, there were no catastrophic failures, as the only issue was a GPS failure on the secondary tracker. The Byonics TinyTrak4 once again proved that it is a solid piece of equipment, and that I’m not yet qualified to make flight-ready trackers myself. The GoPros did a great job, and took plenty of photos of the areas surrounding the metroplex. We couldn’t have asked for a better recovery location, and a better chase team to help find it.
Thanks to everybody that made this launch and recovery possible! It was a very enjoyable experience, and I look forward to the next one.