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A rocket burns propellant and throws hot gas out of its nozzle very fast. Pushing that gas backward pushes the rocket forward (Newton's third law). It carries its own oxidizer, so it needs no air and works in a vacuum.
Specific impulse (Isp) is thrust divided by the weight of propellant used each second: Isp = F/(ṁg₀). Newtons divided by newtons per second leaves seconds. It is not a burn time. Higher Isp means less propellant for the same push.
Liquid: fuel and oxidizer sit in separate tanks and are pumped into a chamber. They give higher Isp and can be throttled. Solid: fuel and oxidizer are premixed into one solid block that burns from its surface. Simple and ready on demand. Hybrid: a solid fuel with a liquid or gas oxidizer, so it can be throttled, shut down and restarted.
Tsiolkovsky's equation, Δv = Vₑ ln(m₀/m_f), gives how much a rocket can change its speed. It depends only on exhaust speed and on how much of the starting mass is propellant. Because of the logarithm, doubling propellant does not double Δv.
The nozzle narrows to a throat, where the flow reaches the speed of sound, then widens so the gas keeps expanding and speeding up. A bigger exit-to-throat area ratio gives faster exhaust, but a nozzle sized for vacuum overexpands at sea level and loses thrust.
Empty tanks and engines are dead weight. Dropping each stage when its propellant runs out lets the next stage start with a better mass ratio, so the whole rocket reaches more Δv than one big stage could.
They are gases at room temperature. To store them densely as liquids, NASA keeps oxygen at about −297 °F and hydrogen at about −423 °F. The payoff: hydrogen–oxygen engines have the highest chemical Isp. The cost: heat leaks make them boil off, so tanks need heavy insulation.
They use electric power to shoot propellant out extremely fast, giving very high Isp. But thrust is limited by power (F = 2ηP/Vₑ): faster exhaust means less thrust for the same power. They suit long, patient missions, not launch.
Above 1. At exactly 1 the rocket just hovers. The extra above 1 sets its starting acceleration: a₀ = F/m − g.
Yes. NASA reports its RS-25 engines flew 135 Space Shuttle missions, with more than 3,000 starts. Four RS-25s now power the SLS core stage. Reusing proven hardware saves building new engines for every flight.
A jet engine breathes air: it takes in oxygen and uses the air itself as its working gas. A rocket carries all its propellant, oxidizer included, so it works in space where a jet cannot. Jets are efficient by moving lots of air a little; rockets rely on very fast exhaust.
Build the base first: calculus, physics, chemistry, thermodynamics, fluids and heat transfer, then a propulsion course. Our free four-year path does this in order, and MIT's free 16.512 covers solid, liquid and hybrid rockets in depth. Propulsion work sits inside aerospace engineering careers.