 Hey guys, it's Amy. A lot of you have asked me some really great questions on different kinds of deep space propulsion. Specifically, you want to know about nuclear methods. Well, before we get into any details, we're going to do a brief overview on different types of deep space propulsion today on Vintage Space. Before we start looking at any deep space propulsion methods today, we're going to look at how rockets get off the Earth in the first place, because there's the very strong misconception floating around that rockets launch off the planet because the exhaust is physically pushing off the Earth and that force is what launches it into orbit. Well, that is not actually at all how it happens. Any rocket, whether it's accelerating off the Earth or accelerating through space, uses Newton's third law, which is that for any action there isn't equal and opposite reaction. In the case of a rocket, the force of hot gas expanding in a combustion chamber and then being directed out through the rocket nozzle is what pushes the rocket off the planet. This is how a rocket can also fly through space. It doesn't need to be pushing against anything physical. It's the force of the expulsion of gas that pushes the rocket in the opposite direction. That said, any kind of rocket, any propulsion method is effectively doing the same thing. The hot gas expanding, being forced out of the rocket nozzle pushes the rocket or the spacecraft that's powered by that rocket in the opposite direction. The most familiar type of propulsion is chemical and there are different arrangements of fuel and oxidizer, but because it's vintage space we're going to talk about the Saturn V as an example. The Saturn V's first stage burned a combination of a refined form of kerosene called RP1 and liquid oxygen. Both of these liquids were stored in separate tanks, force fed by turbo pumps into a combustion chamber where they were ignited, and then the expansion of that gas forced out through the engine bell is what pushed the rocket off the planet. Another kind of chemical reaction uses cryogenics, which are just fuel and oxidizer stored at super cold temperatures. The Saturn V's upper stages used liquid hydrogen and liquid oxygen, both super cold, stored in separate tanks and again fed through turbo pumps ignited in a combustion chamber to propel the upper stages of the rocket. Another type of chemical propulsion uses hypergolics. This is a fuel and oxidizer that ignite on contact and don't need an ignition source, which is great for space flight because there's fewer things to go wrong and fewer moving parts. You can literally open a valve, mix the two, and then you have an ignition to repel your spacecraft towards its destination. This is the same type of propulsion that the Apollo Command Module's service propulsion engine used. And then of course there are solid rockets that have the fuel and the oxidizer packed as a powder in one body. You ignite it and it flies. Getting completely away from a chemical reaction, we have electric or ion propulsion, which is what the Dawn mission used to get to Vesta and then to Ceres. Inside an ion engine, electrons are stripped from atoms and these charged ions are sped up in an electric field before being shot at the end of the engine providing thrust. Another option is nuclear propulsion. A nuclear thermal rocket generates thrust by using cryogenic hydrogen to cool efficient reactor core. The gas is heated and expands and the expanding gas is directed through the nozzle to generate thrust. We see missions leaving the earth riding on chemically propelled rockets because a chemical reaction is the only one strong enough to get a rocket to launch its payload into orbit. But it's not the best reaction. But once that payload is in space and say it's going to a distant planet, a chemical reaction might not be the best way to get it there. We can talk about how good a rocket is by talking about its specific impulse. Specific impulse is a measurement of an engine's efficiency taking into account the rocket or spacecraft's changing mass as it burns its fuel. All engines using a chemical reaction for propulsion have a relatively low specific impulse and we can't make it any better. We can't create a stronger reaction using the same chemicals that got the rocket off the earth in the first place. This is where ion and nuclear propulsion have a bit of a leg up. Both of these methods actually have a weaker thrust but they have a higher specific impulse meaning they need less fuel to generate the same amount of change to the velocity of the spacecraft or Delta-V. You need a lot less fuel in these types of engines for the same acceleration so while neither of them are powerful enough to get a rocket into orbit these are ideal for long duration deep space missions. Of course there are trade-offs to both methods. An ion engine needs the electricity to power the reaction and that comes from massive solar panels. A nuclear engine with its reactor core means you have to deal with the technical and political challenges of launching nuclear material over the earth knowing that if the rocket explodes it might be really bad for the humans. Because of these challenges and because we've been using chemical propulsion almost exclusively since the 1950s this is what we mainly see in spaceflight. Of course there are people who want to see different ways of going to distant planets and this is where the NERVA and Orion projects come in and these are what I will be talking about in future weeks so definitely stay tuned to get more on these insane 1960s programs. I have to give a huge shout out to Scott Manley for helping me get my head around all the technical details because I am not a rocket scientist I'm a rocket historian but Scott Manley is as good as a rocket scientist so if you want more details on all the nitty gritty technicalities of different types of propulsion definitely check out his video right here. See I bet some of you thought that rocket fuel was all about explosions and everything but it is more mundane than that. Of course for most things we think of rock as rockets there's a secondary function to the fuel and that is to undergo some chemical reaction that releases energy. So does that work for you guys as a bit of a primer of different propulsion methods? If you want some more details I've also got a blog linked below that should help you out and if you still have questions leave them in the comment section below and I will do my best to answer as many as I can and of course any other questions you have about anything deep space and of course what you want to see covered in future episodes. Be sure to follow me on Twitter and Instagram for daily vintage space content and you can connect with me on Facebook as well just look for me by name and of course with a new video going up right here every single week subscribe so you never miss an episode.