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Evaluation of Aerodynamic Drag and Torque for External Tanks in Low Earth Orbit.

Evaluation of Aerodynamic Drag and Torque for External
Tanks in Low Earth Orbit.
(1533 K)

Stone, W. C.; Witzgall, C.

Journal of Research of the National Institute of
Standards and Technology, Vol. 111, No. 2, 143-159,
March/April 2006.

### Keywords:

earth orbit; aerodynamics; space shuttle; aerodynamic
drag; aerodynamic eccentricity; aerodynamic torque; free
molecular flow theory; low Earth orbit; shell of
revolution; space shuttle external tank

### Abstract:

*
A numerical procedure is described in which the
aerodynamic drag and torque in low Earth orbit are
calculated for a prototype Space Shuttle external tank
and its components, the "LO2" and "LH2" tanks, carrying
liquid oxygen and hydrogen, respectively, for any given
angle of attack. Calculations assume the hypersonic
limit of free molecular flow theory. Each shell of
revolution is assumed to be described by a series of
parametric equations for their respective contours. It
is discretized into circular cross sections
perpendicular to the axis of revolution, which yield a
series of ellipses when projected according to the given
angle of attack. The drag profile, that is, the
projection of the entire shell is approximated by the
convex envelope of those ellipses. The area of the drag
profile, that is, the drag area, and its center of area
moment, that is, the drag center, are then calculated
and permit determination of the drag vector and the
eccentricity vector from the center of gravity of the
shell to the drag center. The aerodynamic torque is
obtained as the cross product of those vectors. The
tanks are assumed to be either evacuated or pressurized
with a uniform internal gas distribution: dynamic
shifting of the tank center of mass due to residual
propellant sloshing is not considered.
*