1159. Space Shuttle External Tank Fluid Center of Gravity Bias Versus Acceleration Angle

Paper

Abstract

This paper presents the analysis for development of a parametric method of determining the effect of acceleration angle developed during the ascent phase of the Space Shuttle launch on propellant mass properties. The Space Shuttle is a complex flight vehicle comprised of four major elements: orbiter, external tank , main engines, and solid rocket motors . The resulting Shuttle configuration was a compromise between typically cylindrical booster and spacecraft to a fully reusable/recoverable configuration. The Space Shuttle is a unique flight vehicle because it is a hybrid airplane-spacecraft launched by a combination of three liquid propulsion engines, mounted in the orbiter, and two solid rocket propulsion engines, attached on each side of a 331 inch diameter external tank. Unlike the conventional launch vehicle, the thrust vector produced as a resultant from the combination of axial and normal force vectors. The resultant force form an acceleration angle with respect to the axial force plane through the symmetrical centerline of the external tank .
The resultant acceleration angle is equivalent to tilting the tank to that angle. This forms a wedge of propellant on one side of the tank centerline and removes a wedge of propellant on the other side of the tank. Integration routines were programmed to compute the volume and center of gravity of the wedges. The resultant moments of the wedges are summed to the increment
Propellant loads of the tank with the fluid level at right angles to the center line of the external tank.
The external tank consists of a liquid oxygen tank and a liquid hydrogen tank. The liquid oxygen tank has three geometric shapes; forward section is a no give, center section is cylindrical, and the aft bulkhead is an elliptical shape. The liquid hydrogen tank has a forward and aft elliptical bulkhead with a cylindrical, section joining the two bulkheads. The standard equations for the shapes were programmed for the Hewlett-Packard Model 9830 computer. Iteration loops were developed to compute the resultant center of gravity for the selected acceleration angle. Parametric data was developed for acceleration angles of 0, 10, 15 and 20 degrees. These data, in look-up table form, were incorporated in the Shuttle Ascent Performance Evaluation computer program.