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• November 26, 2015 Create Date
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Space Vehicle Design Criteria - Propellant Slosh Loads

Sloshing of propellants may adversely affect the stability of a space vehicle and the
integrity of the tank structure. Sloshing describes the free-surface oscillations of a fluid
in a partially filled tank. These oscillations result from lateral and longitudinal
displacements or angular motions of the vehicle. Such displacements or motions can be
caused by several factors, alone or in combination.

Examples:
0 Wind gusts daring powered flight

o Programmed changes in vehicle attitude
o Attitude-stabilisation control passes
0 Separation impulses

1' Elastic deformations of the vehicle.
Once propellant sloshing begins, it is maintained by the continued tank motions; or in
the absence of tank disturbances, the interchange of kinetic energy and the potential
energies due to gravitational and surface tension forces will cause free vibrations to
persist. Since the damping provided by the wiping action of the fluid against the tank

walls is small, free oscillations may persist for long periods, and forced oscillations may
produce large free—surface waves unless suitable damping devices are provided.

The magnitude of propellant sloshing and hence of forces and moments acting on the
vehicle depends upon these parameters:

0 Tank geometry

O Propellant properties

0 Effective damping

0 Height of propellant in the tank
O Acceleration field