Lesson 2

Instructions

All engines that are classified as rocket engines work on Newton's 3rd law of motion. Expelling mass backwards to provide thrust forwards. There are 3 main types of rocket engines. 1. Chemical These are what we discussed in Lesson 1, where an Oxidizer and a Fuel burn to create pressure. The pressure causes the exhaust to expel out the nozzle at extreme speed. The higher the exhaust velocity is, the higher the Isp is. CH4 has an Isp of ~380, but if its exhaust velocity were higher without increasing its mass, its Isp would also become higher. To achieve the highest Exhaust Velocity engines utilize the De Laval nozzle. The De Laval nozzle allows the gas to be pushed through a choker, a choker is anything that chokes the flow of something, in a rocket this is the throat, which creates pressure, nothing pushing through a choker can go faster than Mach 1. However if you give it room to expand right after, it can achieve higher speeds, like Mach 3+, which is why a rocket has a smaller throat (the choker) than the bell. Every material has its own Mach1, which is speed of sound, heat also affects its speed of sound, which is why we want the temperature to be as high as it can be so its Exhaust Velocity is maxed and therefore so is its Isp. 2. ETR (External Thermal Rockets) These utilize fuel but skip the oxidizer, the most common is NTR (Nuclear Thermal Rocket). ETR’s use a heat source to heat fuel to temperatures that combustion couldn't achieve, which means something like CH4 would have a higher Isp than ~380. NTR’s use nuclear fission as the heat source, it super-heats the fuel to the point where its speed of sound dwarfs the Mach1 of a combustion, causing the De Laval Nozzle to be even more effective. 3. Ion Drives These also utilize fuel and skip the oxidizer. It ionizes the fuel, meaning it strips the electrons away, giving it a charge, which allows it to be affected by electromagnetic fields. After ionization, it will use an electromagnetic nozzle, to accelerate the plasma (the result of ionizing something) to high exhaust velocities. The major trade off here is it takes a lot of power to ionize things and accelerate them. Where it is a beast when it comes to Isp, it can only use a little of its fuel at a time, instead of being able to provide 300 Tons of thrust with an Isp of 5,000-10,000 (which would be insanely good), it usually can’t even provide the thrust required to lift a piece of paper, which makes it useful for long missions, like to the edge of the solar system, but you could not lift off the planet with it. Ion Drives can also utilize the De Laval shape, but Gridded Ion drives do not benefit from it, though Plasma Ion thrusters gain noticeable efficiency boosts from a magnetic De Laval nozzle.