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Comparison of Liąuid Propellant Rocket Engine Feed Systems - 1 - 11

According to the previously exposed, the batteries mass must be estimated with both factors, and it must be chosen as best estimator the one yielding the greatest value. That is why the mass can be determined with the next equation set:

a f	a o	| K	(2.6.3)
Ji Pltf V/MO y		\n „v,mstap
		k„	(2.6.4)
Pm	O
V •"’*»■)			(2.6.5)

where k_b is a safety factor to consider during the system sizing.

2.7. Gas generator mass

The parameters derived from combustion chamber design approaches usually result too smali, because the combustion characteristics inside a gas generator (GG) are quite different [5], To get a good volume estimation the guidelines proposed in [5] were followed. A GG with spherical shape was adopted and the stay time method was used. The GG chamber volume was estimated using the next expression:

V„ =

hPgg

(2.7.1)

where, t_s: Stay time (s).

m_plu: GG propellant buming mass (kg). p_gg: GG exhaut gases density (kg/m³).

Vgg-. GG chamber volume (m³).

From the obtained volume and accepting a spherical GG, their surface can be calculated. In addition, utilizing the Laplace's Law is possible to calculate the GG wali thickness. The formulas to do those calculations are presented be Iow:

, 4 ,
	(2.7.2)
^?.»=^4>rr«	(2.7.3)
- k ^^88 rgg	(2.7.4)

where, GG chamber surface (m²). rgg: GG chamber radius (m). e_gg: GG chamber wali thickness (m). k_gg: GG chamber wali thickness safety factor. Pgg: GG chamber pressure (Pa).

Ogg: GG chamber wali materiał UTS (Pa).