for fuel. This would give If the motor of a new stage is ignited before the previous stage has been discarded and the simultaneously working motors have a different specific impulse (as is often the case with solid rocket boosters and a liquid-fuel stage), the situation is more complicated. Common misconceptions When viewed as a variable-mass system, a rocket cannot be directly analyzed with Newton's second law of motion because the law is valid for constant-mass systems only. It can cause confusion that the Tsiolkovsky rocket equation looks similar to the relativistic force equation . Using this formula with as the varying mass of the rocket seems to derive the Tsiolkovsky rocket equation, but this derivation is not correct. Notice that the effective exhaust velocity does not even appear in this formula. See also Delta-v budget Robert H. Goddard added terms for gravity and drag in vertical flight Jeep problem Mass ratio Oberth effect applying delta-v in a gravity well increases the final velocity Relativistic rocket Reversibility of orbits Spacecraft propulsion Variable-mass systems Working mass References External links How to derive the rocket equation Relativity Calculator – Learn Tsiolkovsky's rocket equations Tsiolkovsky's rocket equations plot and calculator in WolframAlpha Astrodynamics Equations Rocket Equation Single-stage-to-orbit Rocket propulsion