The science of high-altitude balloon flight must consider the makeup and dynamics of the Earth's atmosphere, including weather in the troposphere. Since the goal is to loft payloads into the upper stratosphere and recover them, this near-space environment must be understood, including air pressure, air temperature, windspeed, and solar radiation. Finally, while other ascent options are possible (such as rockets), the mechanics of balloon flight must be mastered for success.
postscript
The inspirations of youth that ignited a passion for space: the movie 2001, A Space Odyssey . . . Larry Niven and his mind-boggling tales of Known Space . . . the little TV series with big ideas, Space Battleship Yamato . . . our real first steps with NASA missions such as Viking and Voyager . . . the audacity of Project Orion (Saturn and back in 3 years!) . . . and all the imagining of 'what if?' when thinking about the Fermi paradox and the Zoo hypothesis.