Apollo Saturn User Manual download pdf (Page 53)

J-2 EN(; NE OPE,.AI_ON S-If STAGE

T_ ,perating cycle of the J-2 Engine consists of prestart, _ttatt, steady-

..tat, :. _ation and cutoff sequences. During prestart, LOX and L|{2 flow through

tlle e,_},ne to temperature-condltion the engine components, and to assure the

presence of propellant in the turbopumps for starting. Following a t_med cool-

down period, the start signal is received by the sequence controller which ener-

gizes various control solenoid valves to open the propellant valves in the proper

sequence. The sequence controller also energizes spark plugs in the Ras generator

and thrust chamber to Ignite the pTopel!ant. In ,dditlon, the sequence controller

release GH 2 from the steer tank. The GH 2 provides the inlt_al drive for the turbo-

pumps that deliver propell_t to the gas generator and the englne_ The propellant

ignites, gas geo_rator output accelerates the turhopumps, and engine thrust in-

crea es to main StaRe operation. At this time, the spark plugs are de-en-°rgized <

and _he engine is in steady-state operation,

_teady-state operatlcn is malnta._ned until a cutoff signax is received by

the sequence controller. The sequence control]er de-energlze= the solenoid valves

which in turn close the engine propellant valves _n the proper sequence, As a

result, engine thrust decays and the cutoff sequence is complete,

ED%,_aeStart q

Main F_l Valve Open m '

•:'. '.". _,dn Fuel PropelleJ,t Flow ...... -_,_ II _4_lRk_.

Start Tank Discharge Valve Open Ill

Pump Buildup _ _ ' .!

Bypass Flow Through Oxidizer ---,_ __ __

Turbine B'j-pass Valve

• • Main Oxidizer Flow "-" i _' '

[

G_.e Generator Propellant Flow ___ _-T. __ "_-

, . Main Oxidizer Valve Open R .. ,

' Mainstage OK Signal V . i

90 Percent Thruet V

_' IGNFI _ON. SgC ,_.C S¢C Slr.c St:, •

., COM_U,4D

e_TIME FROM I_N|TION

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Apollo Saturn User Manual Page 53