Performance Characterization of Heliotrope Solar Hot-Air Balloons during Multihour Stratospheric Flights

eliotropes are passive solar hot air balloons that are capable of achieving nearlylevel flight within the lower stratosphere for several hours. These inexpensive flight platforms enablestratospheric sensing at scale, but their performance has not yet been assessed systematically.During the summer of 2021, 29 heliotropes were launched from Oklahoma and achieved floataltitude with data as part of the Balloon-based Acoustic Seismology Study (BASS). All of theheliotrope envelopes were nearly identical with only minor variations to the flight line throughoutthe campaign. This creates a relatively large sample size for this new technology to characterize thetypical flight behavior during launch, ascent, float, and descent. Each flight stage is characterized,dependence on various parameters quantified, and discussion of nominal and anomalous flightsprovided.