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Design and operations of multi-hour stratospheric solar hot-air balloons

Hough, Emalee E.
Solar balloons, also known as heliotropes, are solar-powered lighter-than-air vehicles. Dueto its many benefits, they have potential use in applications requiring high-altitude balloons. Solar balloons are made from low-cost lightweight materials that absorb solar radiation for buoyant lift and can carry an average two-pound payload up to over 20 km (70,000 feet). Recent developments in zero-pressure solar balloons have demonstrated longer flight times (12-hour flights), more accurate flight path and altitude predictions, rapid deployment, and robust construction. One downside of solar balloons is the lack of control during flight. Since solar balloons float in the stratosphere, it is hard to know in real time how the envelope is reacting to the environment. Non-ideal circumstances at that high of an altitude occur such as if the stratosphere is too turbulent and the balloon envelope is falling apart, or the winds at altitude are changing the predicted path of the heliotrope. To mitigate these types of circumstances potential changes to the design of the balloon envelope and a way to control the balloon’s altitude would be beneficial. Changing the balloon envelope design can provide more robust operations to carry larger payloads aloft and mitigate failures due to circumferential stresses. Tetrahedral shaped balloons ”tetroons’ are one example of this. In addition, a vent system within the balloon envelope can change altitude, and by way provide a method of limited trajectory control, by venting buoyant lifting gas. This effort compares the results of various envelope designs and flight results.
The discussion of multiple flight campaigns is provided in this effort. These flight campaigns vary from month-long campaigns with NASA Jet Propulsion Laboratory and Sandia National Labs studying the effects of infrasonic events from earthquakes at the stratospheric level as a proof of concept for ballooning on Venus, to providing test launches for future campaigns to understand the feasibility of launching a heliotrope pre-dawn or testing multiple envelope designs to provide more robust flight options for larger payloads.