Which Burning is Better Axial or Radial of Solid Propellant grain used in Solid Rocket Motors? How Someone Determines which to choose according to the Mission requirements ?
Radial burn is usually preferred.
Axial burn rockets (solid rockets that burn from the bottom up – otherwise known as end burners) suffer from the problem that the centre of gravity of the rocket changes as the rocket burns.
Radial burn rockets do not tend to suffer from this problem as they mostly burn from the inside out along the length of the rocket.
The thrust of a solid rocket is dependent on the amount of propellant that burns in a given time and that is dependent on the geometry of the burn tube. A circular burn tube will provide less thrust for longer, a star shaped cross section will provide more thrust for a reduced period. An end burner has a much smaller circular burn surface.
Once lit it is not possible to throttle a solid rocket motor in the same way as a liquid propellant rocket. But it is possible to design a variable burn rate by adjusting the cross sectional area of the burn surface on a radial burn rocket. This can be seen for example in a Finocyl Grain (star cross section) rocket. Could 3D printing be used to achieve perfect grain geometry of solid and hybrid rocket motors? It is also possible to adjust the shape of the burn tube along the long axis of the rocket. https://www.hindawi.com/journals/ijae/2019/3060173/fig5/