Hello forum members and thank you for letting me post. My question refers to how rocket thrust works in a vacuum. I know this question has been posted before, but I am still confused about how it works. My understanding is that rockets do not move by pushing against air but move by pushing "against their own fuel," as is stated in Newton's Third Law according to which "for every action there is an equal and opposite reaction." The oft repeated analogy to explain how this works is throwing a ball off the stern of a small boat and the resulting forward movement of the boat, or the recoil energy resulting from firing a gun. Ok. So a rocket moves by recoil energy? Is this correct? Here is an analogy of the recoil generated by a a gun, in this case an M16, compared to the mass and force involved in a rocket, in this case a French rocket Ariane 5. (The analogy is not mine.) I would appreciate your comments. Weight of M16 RIFLE: 4kg https://en.wikipedia.org/wiki/M16_rifle Weight of an M16 bullet: 3.6g http://www.defencetalk.com/forums/army-security-forces/m16-vs-ak-47-a-4686-7/ Weight of an Ariane 5 rocket: 760,000Kg http://en.wikipedia.org/wiki/Ariane_5 Recoil Force involved in firing M16 bullet: "A bullet fired from an M16 rifle has approx 1763 Joules of kinetic energy as it leaves the muzzle, but the recoil energy exerted on the gun is less than 7 Joules." http://en.wikipedia.org/wiki/Recoil The kinetic energy exerted on the rifle is thus equal to 250 times less than the energy exerted on the bullet . If we multiply the weight of the M16 by 190,000, we get the weight of an Ariane 5 (760,000Kg). Continuing the analogy, if we multiply the weight of the M16 bullet by 190,000, we get 684Kg (3.6g x190,000). If the giant M16 were ejecting three giant bullets a seconds (2,054Kg), then this would approximately equal the fuel mass ejected by Ariane 5 every second (2,000Kg). Multiplying (by the 190.000 factor) the known kinetic energy exerted on an M16 rifle by a bullet exiting its muzzle (about 7 joules) we get (7X190.000= 1.330.000 joules). The giant M16 rocket will therefore produce a kinetic energy thrust equal to 7 x 190,000 x 3 = 3,990,000 joules, or approximately 4 million joules. Four million joules is approximately equal to 5,400 Horsepower. How can 5,400 Horsepower be sufficient to lift off a 760,000Kg rocket into Low Earth Orbit?