def lf_needed_fuel(dv, I_sp, m_p, f_e): m_c = m_p/f_e * ((1/f_e) / (1+(1/f_e)-exp(1/g_0*fsum([dv[i]/I_sp[i] for i in range(len(dv))]))) - 1) if m_c < 0: return None return m_c