May 17, 2013
After waiting through several delays because of poor weather and wind conditions, Catholic University's Physics 240 students finally saw their class project head upward into the blue sky on an early morning last month.
As a project of the class titled "The Earth-Sun Connection," the students' helium-filled, instrument-laden weather balloon ascended to 73,000 feet before bursting and parachuting back to earth, where it was successfully retrieved by the students about two hours later.
The course, which is aimed at non-science and education majors, is team-taught by Fred Bruhweiler, professor of physics and director of the Institute for Astrophysics and Computational Sciences (IACS); Ekaterina Verner, research scientist at IACS; and Elizabeth Montanaro, assistant professor of education.
The Outdoor School at Fairview in Clear Spring, Md., about 11 miles west of Hagerstown, was the launch site. The balloon lifted off at 9:40 a.m., carrying a payload containing a Global Positioning Satellite (GPS) transponder, temperature and height instrumentation, biological samples, and a camera.
At pre-launch, the balloon was inflated with helium to a diameter of 6 to 7 feet. Its size then slowly grew as it ascended into the thin, less dense air of higher altitudes, expanding to about 20 feet in diameter before bursting.
Winds on the descent carried the payload to about 10 miles northwest of York, Pa., where it hit the ground.
The students used GPS tracking to follow the balloon on its travels and later to locate the payload package.
"I was praying real hard that it wouldn't be stuck in a tall tree 80 feet above the ground," said Bruhweiler. Using coordinates from the GPS tracker, Google Maps showed it about 100 feet from a road, well away from houses.
Once launched, the balloon was carried by the winds and the jet stream. This made preparing for the flight with computer-generated simulated routes of the balloon prior to the anticipated launch date very important, said Bruhweiler. These were relayed to the Federal Aviation Administration so that the balloon did not fly over restricted airspace around Washington, Baltimore, or Camp David, Md.
The students had been trying since March to launch the balloon, but simulated tracks keep indicating unfavorable outcomes, said Bruhweiler.
Bruhweiler also said there was a "very nervous period" of about an hour where the GPS wasn't updating. "Our retrieval crew was nervously hanging out at a Burger King in Gettysburg waiting to hear what to do."
But then the updates resumed and indicated the payload was on the ground. "I thought we were extremely lucky because they indicated that the payload was less than 100 feet from the road," he noted.
"I'm extremely delighted with our results," Bruhweiler said. "The video from the payload camera is truly superb. The flight path of the balloon and time of burst were almost exactly as we had predicted."
The video showed the temperature decreasing to minus 70 F at around 60,000 feet. The balloon burst at around 73,000 feet.
In the video, viewers can see the black sky of near-space and the earth's curvature. The balloon burst at 55 minutes after launch, compared to the 58 minutes that was originally predicted, he said.
Bruhweiler added he plans to have more balloon launches in the near future that will include bigger balloons with more sophisticated equipment onboard.
Also, he said it is important to find favorable launch sites, such as the Hagerstown area, where retrieval of the payloads is possible for the students. Lower altitude winds and the jet stream at higher attitudes in some locations could put the payload into the Chesapeake Bay or the Atlantic Ocean.
Such hands-on experiences help students learn science in a practical way, Montanaro said."One goal of this course is to show to non-science college students and our valuable future teachers that science can be quite fun," said Montanaro.