Congratulations to the Buzzin Ballooners team from Georgia Tech for winning Honorable Mention for the Best Design Category this year. Text from their submitted report is below:
The Buzzin’ Ballooners rose into existence with a push from the executive members of the Ramblin’ Rocket Club at Georgia Tech. In part of a restructuring effort for the club several new ventures relating to space took root. The Buzzin’ Ballooners are considered a sub team of the Ramblin’ Rocket Club at Georgia Tech. Beginning in early June last year the High Altitude (HAB) team begin to take shape with selection of the team lead and outlining objectives for the first season of the Global Space Balloon Challenge. The first members of the Buzzin’ Ballooners joined the team in early September just as school started to pick up. The final team was made up of 6 members. The HAB team set two goals for its infant season; 1-successfully recover a full balloon system, 2-break the 75,000 feet barrier. Our team was able to launch two balloons to two respective altitudes and recover both. In our inaugural season, both objectives were accomplished! We will discuss how below.
First, we begin by discussing the system as a whole and will go into detail regarding each successive subsystem. Based off many similar designs and tutorials listed on the GSBC website, our system was comprised of a balloon tethered to a radar reflector, parachute, and finally payload. The payload contained all the electronic systems including the camera, GPS, and pressure, and temperature sensors. A proper launch procedure was developed in accordance to local state and federal guidelines. Contact with the FAA southeast regional office occurred on numerous occasions regarding selection of materials, launch sites, and proper day of launch procedures. A full launch procedure can be found below in the appendix.
The balloons used for this season were both High Altitude Science balloons. Initially Kaymont balloons were considered due to price, however, logistical concerns drove us to pursue High Altitude Science balloons. The initial test flight done at the end of March featured a HAS 350-gram balloon. The competition balloon featured a 1200-gram HAS balloon. Each system was designed to achieve apogee with the balloon popping due to excessive expansion. No timing or cutting mechanisms were employed during these launches. Helium was purchased through Georgia Tech Aerospace Eng. workshop’s supplier Airgas. Two tanks of helium were used 200 cu. Ft. rated for 2200 PSI and 300 cu. Ft. rated for 2400 PSI respectfully. The initial launch used 145 cu. Ft. of helium while the competition launch used 163 cu. Ft. of helium. Launch planning for apogee calculations was done via the High-Altitude Science ‘balloon performance calculator’.
The tether system consisted of three main segments: the payload to parachute (Segment 1), the parachute itself (Segment 2), and the parachute to balloon (Segment 3). Each segment was connected using triple locking carabiners, and the line used for connections in Segments 1 and 3 was 40 pound tensile-strength, braided fishing line. This tether line was selected because it is abrasion resistant and designed to hold knots under stress. The knot used for the tether line through the whole system is called the double modified-uni knot, which is a common knot used in fishing that is designed specifically for braided line and tightens under increasing load.
Beginning from the payload and working up the payload train, the payload itself was supported using a quadpod approach, achieved by wrapping two loops of the tether around the bottom of the payload equidistant from the center of gravity, and attaching the tops of the two loops using a carabiner. From this carabiner, a 4-foot line of tether line was attached to the next carabiner, which also attached to the bottom of the parachute. The radar reflector was then placed along this line, and a thin plastic wrap was placed along the length of tether where the reflector could potentially fray it. The radar reflector was then tethered at the top to the carabiner attached to the parachute and at the bottom to the carabiner attached to the payload. There was intentionally slack left in the tether from the bottom of the reflector to the payload to ensure the radar reflector did not bear any of the load from the payload train. For Segment 2, the parachute itself acts as the payload train. The carabiner attaches to approximately 3 feet of paracord that attached to the circumference of the 1.5-meter diameter parachute. At the top of the parachute, a small loop was used to attach the carabiner that begins Segment 3. A single 12-foot length of tether line is then attached to the carabiner at the top of the parachute on one end, then to the final carabiner at the other end. To attach the balloon to this carabiner, once the balloon is inflated to the desired lift, the neck of the balloon is folded in half around two zip ties and generously duct taped. The zip ties are then used to make two loops, which are attached to the final carabiner. From the bottom of the payload to the final carabiner, the length of the tether system is approximately 24 feet.
The payload for the system was comprised of an insulated Styrofoam box roughly 14 inches long by 7 inches wide and 12 inches tall. This was chosen due to the insulation properties that would benefit the electronic systems performances at high altitude. The sensors discussed below were placed in a double Ziplock bag configuration to waterproof them, while the GPS was hung to the top of the payload in a makeshift gyroscope, and the camera system attached via Velcro to a bottom corner of the payload. A whole was made in the corner for the camera to achieve a clear image. The camera system featured a custom mount that was fabricated via Styrofoam to hold the camera in place while also allowing connections for an external battery and handwarmer to be near the camera.
The payload was wrapped in reflective green duct tape to be easily visible. A notice regarding the team information and purpose of the payload was laminated to the front of the payload as well, as a contingency for identifying and recovering the payload should the GPS fail. For the competition launch the payload remained virtually the same with the addition of a stabilizer fin to increase the moment of inertia and prevent random spinning motions. Figure 2 below displays this.
For the camera, we used a Dragon Touch Vision 3 action camera to record videos of the flight. The battery on the camera will not last the entire flight, so we connected an Anker Astro E1 portable battery as an external battery source. Also, we duct taped some hand warmers at the launch site to prevent camera and battery from freezing.
The system was installed onto the payload box by using Styrofoam structure we made. The Styrofoam we used was softer and lighter compared to other Styrofoam, preventing shocks from pushing the buttons on the camera. The Styrofoam structure, along with camera and
battery, was attached to the payload box using Velcro and duct tape. After multiple tests, it proved to be a sturdy structure, keeping the camera in place. Figure 4 displays the custom mount.
The camera was successful in recording the entire flight from launch to touchdown at 2.7K resolution 30fps. We were astonished by the views from high altitude. Our future goal will be to continue with this stable platform and possibly obtain another camera to have it take pictures at 16MP every 3 seconds.
For the GPS, a SPOT Gen3 satellite GPS was used for in-flight tracking. The tracker works by sending out a location ping every 5 minutes, which team members can check via a web app. Once landed, the device sends out three pings before recognizing its location is constant, upon which it ceases to send more pings. One of the key challenges for the implementation of this device was that it must always remain facing upward. Thus, we secured it to a makeshift gyroscopic rig, ensuring it would face up under any conceivable orientation. The Spot 3 had a counterweight glued to the bottom face of it to ensure a stronger gravitational pull for this side. Next two tethers were connected to the Spot at each corner and around the body and brought to a point 2 inches above the top face. These tethers were connected to four tethers going to each corner of the box via a single tether in a circle, acting as a ball bearing. This allowed the Spot to rotate freely in every direction including being swung or tilted upside down.
We were able to rely solely on the SPOT Gen3 for tracking and recovery in launches; however, in the future it may be prudent to invest in other systems such as APRS tracking and/or other smaller range devices, to aid in recovery. The APRS would serve as a backup to the SPOT, since in the last launch, the SPOT failed to ping for just under 60 minutes. One intriguing hypothesis for why this occurred comes from the video we recovered, which showed the payload rotating rapidly during that part of the descent. The high rate of spin may have affected our gyroscopic rig. To effectively trace the flight path and predict the landing site, we had to rely on flight path modeling rather than real-time data. In addition, another smaller range device with a higher level of precision would aid in balloon recovery if the terrain at the landing site is very rough.
Arduino data logger
We used an Arduino Nano and a BMP 280 pressure and temperature sensor and recorded the data to a micro SD card. The power source was a battery bank of 4 AA Energizer Lithium batteries, used for their high voltage, low weight, and low operating temperature. We wrote a script to take measurements at intervals of 1-2 seconds, writing the data on a new line along with a timestamp. We didn’t use a real time clock, so we relied on the Arduino’s processor clock. That worked fine, except for an integer overflow every hour or so (due to the variable type) which had to be corrected manually afterwards. Another function of the data logger was to activate a buzzer to help locate the payload if it was hidden in vegetation. However, the buzzer did not work for the first (practice) flight due to the overflow error, and on the second (competition) flight it was found to be too quiet.
The competition system was launched at roughly 1:48 pm on Saturday April 20th from Cuthbert Georgia. The last ping from the Spot 3 GPS was received at 4:29 pm. The balloon had a 2 hour and 41-minute flight time with an ascent rate of 6.2 m/s and descent rate of 4.455 m/s. The estimated burst altitude was 29580 m above sea level. Launch proceedings began early in the morning with the meeting of the team to gather all needed materials and check the systems. The helium tank was loaded onto the trailer and driving commenced to our launch location 2.5 hours south east of campus. Arriving near 11:30 launch prep began with the assembling and last-minute check of all respective systems. The 160-cu ft. of helium was added into the 1200-gram balloon to generate 2000 grams of lift. Finally, just past 1:30 the balloon was launched. The Spot Gen 3 GPS gave regular 5 min pings up until 2:48 pm. Connection was lost with the GPS and therefore system for nearly an hour until another ping was received at 3:44 pm. The balloon was recovered near 5:00 pm EST just outside Wenona Georgia. The balloon followed the predicted flight path quite well except for the lost data from lost connection between 2:40 and 3:40. Figure 11 and 12 below displays the GPS coordinates.
The Arduino data logger successfully recorded altitude and temperature data to the micro SD card for our first . Our sensor recorded a minimum pressure of 3047.29 Pa for our practice flight and 1077.95 Pa for the competition flight. Using the altitude approximation equation included with the sensor code, we calculated a rough estimate of 21580 m and 25636 m above sea level for the practice and competition flights respectively. However, these estimates must be taken with a grain of salt because we did not calibrate or validate the sensors and the equation, we used an approximation. Examining a standard pressure altitude table, we can also estimate our apogee from pressure readings. Figure 10 below displays a standard pressure altitude table. Looking at this figure and converting our pressure reading of 1077.95 Pascal to PSIA we obtain a pressure of 0.156 PSIA and an altitude of 30627 m above sea level. This was done by plotting the last few points of the standard table altitude vs pressure readings in PSIA and using the line of best fit, a 3rd order polynomial to estimate altitude achieved. Figure 9 displays this plot and best fit equation. These results are quite different, the initial method, estimating an altitude of roughly 85,000 feet while the second method, an altitude of over 100,000 feet. Due to images recovered our team believes the latter calculation is more accurate, signifying that our competition balloon achieved an apogee of 100,484 feet. Proper calibration and testing of our sensors must be done in order to precisely and accurately determine pressure and altitude readings. GPS would give us much more accurate data, however the SPOT 3 is currently beta testing altitude functionality and we found its results to be almost random while in flight. Graphs of the data can be found in the appendix.
As a team we are extremely proud of the work we put into our system this season. None of the team members possessed extensive knowledge relating to high altitude balloon launching or recovery. With proper guidance, curiosity, and passion for the subject we were able to successfully launch two balloons to approximately 70,000 and +100,000 feet and recover both. While a great deal of information was learned during this season, the Buzzin’ Ballooners have only just whetted their appetite for this sport. Goals for the next season include the addition of control systems for more stable flight and precise apogee termination, two-way GPS communication, APRS inclusion for more accurate altitude and pressure data and 5 or more launches. Future goals for the club revolve around the HAB launch being a launching and testing platform for rockets, and avionics research for Aerospace professors involved in CubeSat and other research programs. With the inaugural season behind us, the HAB team of the Ramblin Rocket Club plan to not only aim for the stars but soar among them!