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clear Isp=2940;

m=dsolve('Dm=-F/Isp/g','m(0)=2400')

U=dsolve('Du=-F/(M - (F*t)/Isp)*(pi/900*t)','u(450)=0')

W=dsolve('DW=F/450*t*Isp/(M*Isp - F*t)-um/ryue^2','W(225)=28.5') r=dsolve('D2r=F/450*t*Isp/(M*Isp-F*t)-um/ryue^2','r(0)=15000,Dr(0)=17000') b=U/r beta=int(b,t)