Shape optimization of solar balloons for ultra high altitude flights

Paper number

IAC-08.E2.1.6

Author

Mr. Zsolt Várhegyi, Budapest University of Technology and Economics, Hungary

Year

2008

Abstract

A solar radiation heated hot air balloon is a low cost and energy-effective device to lift a heavy payload into the atmosphere. Solar balloons use renewing energy source and may be built from recycled material, therefore they can teach lessons to everyone about thinking in environment friendly solutions regarding aerospace flight as well.

Despite these advances compared to helium-filled meteorological balloons, solar balloons are rarely used to lift scientific payloads. One reason for this is the small specific lift force of the heated air compared to helium. The aim of the investigation was to find such envelope shapes wich can give optimal possible performance of these balloons.

An algebraic model describing the thermal processes inside and outside a solar balloon envelope, with prescribed shape and given height, velocity, and elevation angle of Sun was set up. Direct and diffuse irradiation, inner convection and heat losses by outer boundary layer convection and radiation were taken into account. Temperature distribution in the filling air was found by solving the above system for thermal equilibrium.

Using numerical optimization methods, several meridional curve families were found wich optimize different cost functions, such as maximum lift, maximum climb height, maximum incident solar energy per unit surface area, or maximum incident solar energy per unit area of sheet material required to taylor out the given shape. 

Results show that envelopes wich are optimal for ultra high altitude flights are typically elongated along the vertical axis, with an H/D ratio of 3 to 5. Conservative models of the heat convection resulted in an almost cylindrical shape wich maximized several cost functions. Predicted temperature differences are varying between the usual 30 K close to the ground and 150 K in the upper atmosphere. Results can also serve as a good starting point for further investigation using a more accurate description of the thermal and hidrodynamic processes coupled with the dynamical system of the balloon flight. The conclusion is drawn that ultra high altitude flight of solar balloons is clearly possible and the choice of solar balloons instead of helium balloons in some low budget near-space missions is a desireable option. 

Abstract document

IAC-08.E2.1.6.pdf

Manuscript document

IAC-08.E2.1.6.pdf (🔒 authorized access only).

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