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from math import log
from rocketcea.cea_obj import CEA_Obj
C = CEA_Obj( oxName='LOX', fuelName='LH2')
Wpayload = 8500.0 # lbm
Wstg = 5106.0 # lbm
Wpropellant = 45920.0 # lbm
Winit = Wstg + Wpropellant + Wpayload
Wfinal = Winit - Wpropellant
def show_deltaV( Pc=475.0, eps=84.0, MR=5.88 ):
IspVac = C.get_Isp(Pc=Pc, MR=MR, eps=eps)
IspDel = 0.969 * IspVac
deltaV = 32.174 * IspDel * log( Winit / Wfinal ) # ft/sec
print( '%8.1f %8.1f %8.2f %8.1f %8.1f %8.1f '%(Pc, eps, MR, IspVac, IspDel, deltaV))
print(' Pc(psia) AreaRatio MixtureRatio IspVac(sec) IspDel(sec) deltaV(ft/sec)')
show_deltaV( Pc=475.0, eps=84.0 )
for eps in range(100, 251, 50):
show_deltaV( Pc=475.0, eps=eps )
show_deltaV( Pc=475.0, eps=280.0 )
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