Astronomy Stratospheric Balloon Flight 1
On September 22, 2016 an Astronomy-student led balloon project carried a custom payload to an altitude of 111,028 feet. As part of Astronomy’s “Tutorial” course (ASTR4993) two students (Chloe Downs and HeeSeok Joo) spent a semester working alongside physics student Nina Mazzarelli designing a payload capable of reporting it’s altitude and position through the APRS (Automated Packet Reporting System) amateur radio network, collecting images with a simple GoPro camera as well as with a camera attached to a Raspberry Pi flight computer, and acquiring flight telemetry on the environments and health of the payload. The students also investigated, from the ground up, the intricacies, management, procurement, rules and regulation, etc. of the end-to-end balloon development and flight process including materials and design, flight path prediction, ascent rate calculation and FAA regulation working loosely in the context of a NASA spacecraft development. The students designed a lightweight balloon gondola in Solidworks and 3D-printed the structure. Chloe Downs spent a second Tutorial semester finishing the payload design, particularly solving the puzzle of placing all the sub-components into the cage, and preparing for the flight returning from the subsequent summer ready to fly. When the winds became acceptable early in the Fall 2016 semester she was ready and, after a week of waiting out low clouds and fog, conditions were right on a Thursday morning in late September.
Figure 1: The flight 1 payload was designed to demonstrate the ability to launch and recover more ambitious future payloads. The balloon gondola is a 3D-printed cage with instrumentation attached (largely by cable ties and caulk) to the inside. Insulation surrounds the payload to protect against ambient temperatures as low as -60C during ascent.
Monitoring of potential ground tracks day-by-day showed a series of good launch opportunities during the week of September 19 where the balloon would not travel far between launch and landing (typical tracks can be hundreds of miles). The first two potential launch days were too cloudy, but Thursday September 22 looked like it had good potential. On the morning of September 21 a Notice to Airmen for an unmanned untethered balloon was filed with the FAA launching from near Keswick, VA on September 22. Keswick was the launch location because the winds that day, uncharacteristically, would carry the balloon southwest toward the Blue Ridge and launching from an easterly location provided enough margin for a landing prior to reaching the heavily wooded mountains. South Plains Presbyterian Church near Keswick had a large parking lot that would be unoccupied on a weekday morning. The church was contacted and permission obtained to use the parking lot. The crew (Chloe Downs, Astronomy graduate student Robby Wilson, and Mike Skrutskie) arrived at the Astronomy Building at 6 a.m., loaded up helium cylinders and other equipment and departed for Keswick at 7:10. The team arrived on site at 7:30 and launched the balloon at 8:20 (time lapse here). Spectators included the reverend and church elders at South Plains (special thanks to them). Pictures and captions below tell the story.
Figure 2: The predicted ground track of the balloon on the morning of September 22. The direction of travel (that ordinarily is eastward) dictated a launch point to the east of Charlottesville. The red dot is at the launch point. The orange star indicates the likely location at the time descent begins (triggered by the inevitable popping of the balloon at around 100,000 feet). The green dot is the predicted landing point.
Figure 3: On site at South Plains Presbyterian Church. Helium cylinders remain in the back of the truck. While Robby holds the filling balloon, Chloe completes the assembly of the payload. Special thanks to Professor Chris Goyne in the Engineering School at UVa who provided the regulator and fill assembly (yellow hose) that he has used for similar student-led stratospheric balloon flights.
Figure 4: Chloe indicates flight readiness.
Figure 5; Chloe images payload. Payload images Chloe.
Figure 6: Ready to release.
Figure 7: Balloon release seen from the inside.
Figure 8: The moment of free release of the balloon and payload. The APRS antenna is now clearly visible on the outside of the insulated payload box.
Figure 9: Ascent begins. Although directed toward the moon we’ll only get one ten thousandth of the way there.
The balloon headed southwest upon release passing just south of Monticello as it passed through 10,000 feet and reaching the area of the Ragged Mountains at the point where it entered the stratosphere. Stratospheric winds were quite gentle that day. During the nearly three-hour ascent to 111,000 feet the balloon wandered in circles above that point reporting its altitude, position, and temperatures to APRS every thirty seconds. The match between predicted and actual track was impressive. The longer than predicted track west was largely due to the slower ascent in the lower atmosphere that was not captured but the flight path predictor. The GoPro camera imaged the ascent every 0.5s until it ran out of memory at an altitude of 70,000 feet. The Raspberry Pi camera system operated throughout (and after) the flight acquiring frames every 9 seconds. The Raspberry Pi camera, however, had problems with its automated exposure setting so most of the frames at high altitude were saturated. A few good exposures, though, provided a stunning perspective. The balloon burst, as planned, at just over 111,000 feet beginning a descent to ground level that required only 50 minutes. At first the payload fell unhindered in the near vacuum of near-space at a speed of 50 meters per second (120 miles per hour). As the atmosphere thickened the parachute became effective with the final speed of descent near landing of 5 meters per second, as planned. The last APRS transmission arrived while the payload was still 800 feet above the ground, but the more sparse (every 10 minutes) backcountry tracker continued to report providing a position accurate to 10 feet. The students were all in class so Mike Skrutskie and Matt Nelson mounted the recovery expedition. Prior to landing the payload had descended over dense forest. It was a pleasant surprise (and a relief) to see the bright red parachute on the ground in an open field adjacent to the forest.
Figure 10: Charlottesville in the morning seen from the southeast at an altitude of 7000 feet.
Figure 11: University of Virginia seen from high over Monticello.
Figure 12: Best image from the GoPro from an altitude near 70,000 feet looking northeast along the Blue Ridge. Luray is near the left edge of the image. Charlottesville Airport is near the bottom right of center. Costco on Rt. 29 is in the lower right .
Figure 13: Best Raspberry Pi camera image from 98,000 feet looking northeast along the Blue Ridge. Luray is on the left. Madison is near the image center.
Figure 14: A Raspberry Pi image from 110,000 feet just after the balloon burst The payload is tumbling at this point and the image is blurred as a result of the motion.
Figure 15: The actual ground track of the flight.
Figure 16: The predicted vs. actual ground track.
Figure 17: Final approach to landing (x marks the spot).
Figure 18: The Raspberry Pi camera view during final approach.
Figure 19: The landing site as seen by the payload.
Figure 20: Parachute and radar reflector on the ground. The payload is in the bush -- a welcome sight for the recovery team (who didn’t want to end up fishing things out of a tall tree).
Figure 21: The payload top up in the brush. The top up orientation permitted the backcountry tracker to report a final position.
Figure 22: Parachute and balloon remnants (more than half of the balloon mass (680 grams of latex) remained attached to the experiment).
Figure 23: Matt Nelson shows the intact recovered payload.
Figure 24: Mike Skrutskie, imaged by the payload camera, drags the parachute, balloon remnants, and radar reflector out of the brush.