R. Meyer J. Köhler A. Homburg Explosives

Solid Propellant Rockets
by incorporating special accelerating or retarding additives. The propellant
charge must be carefully examined for cracks, since in their
presence the combustion will not proceed uniformly. If case-bonded
charges are employed, adequate cohesion between the wall of the
combustion chamber and the propellant charge (W Case Bonding)
must be ensured.
The advantages of solid rockets are the short time needed for the
actuation, long storage life, and a simple design.
The burning process in the rocket motor is influenced by:
the thermodynamic performance values of the propellant (W Thermodynamic
Calculation of Decomposition Reactions), the burning characteristics
of the propellant grain (W Burning Rate), depending on its
shape, and by the pressure influence on the burning rate. The pressure
exponent can be zero in the case of modern propellants (“Plateau”,
“Mesa”, W Burning Rate). The pressure function of the burning
rate cannot be described by a universal equation, but within smaller
pressure ranges the equation of Saint-Robert or Vieille equation is
applicable:
r = a pa (1)
r: rate of burning normal to the burning surface
p: pressure
a: pressure exponent
a: constant
(W also Burning Rate, Charbonnier equation.) At any time during the
reaction, equilibrium must exist between the gas produced
r · fT · r (2)
fT: burning surface
r: density of propellant
and the gas discharged through the nozzle
p · fm · CD
(3)
fm: nozzle cross section
CD: mass flow coefficient
The ratio fm/fT = nozzle cross section to the burning surface at any
time is called W Propellant Area Ratio (“Klemmung”) K; the equations
(2) and (3) are considered to be equal: equation (1) can be
rearranged to
p = a
CD
290
†K 1
1–a (4)
Equation (4) allows plotting of the gas pressure-time diagram, if a, CD
and a are known and the course of the propellant area ratio K with the
burning time can be assumed. Modification of the pressuretime diagram
may be caused by the pressure falling off along the propellant