I'll see how interested people are in reading long space diatribes, and how interested I am in writing them, and go from there. From past experience I know that there is a limit beyond which people won't be willing to read on, so I'll try to keep each of these fairly short. In this part, we will focus on two things: the basics of spaceflight and a (highly abridged) history of rocketry, focusing more on the very early and the very recent years of history.
Basic Principles of Rocketry
The basic function of a rocket is quite simple: fire go down, pointy thing go up.
The basic design for a rocket really hasn't changed much since its inception; that's the basic concept for how it works and that's pretty much how it's always been. The conceptual and theoretical aspects of rocketry are remarkably straightforward, and based mostly off of the work of famous physicists from centuries past. Of course, the real devil is in the details. As we all know, rockets have an unfortunate tendency to explode at inopportune times, destroying anything and anyone inside. Every time a rocket launches, we all know that there's a not particularly small risk that it will explode in flight, leaving the owner of that rocket to pick up the pieces and spend months or years trying to figure out what went wrong.
NASA had a really nice article talking about why launching a rocket into space is quite difficult. Bottom line, it takes a lot of fuel used as efficiently as possible in order to generate the kinds of forces you need to be able to beat the gravity of the Earth. The weight of a rocket is disproportionately that of fuel; anywhere from 80 to >95 percent of a rocket's weight is in fuel. It's basically generating a giant explosion and you had better hope that you can control it properly.
While there are other types of rocket fuels used, the ones that generate the massive thrust (the upward force generated by spewing burning gas out the bottom of the rocket) that can actually get you places is pretty much always generated by a chemical reaction optimized to get the biggest bang for your buck in terms of thrust by weight. Those can be divided further into two types of chemical fuels: solid fuels and liquid fuels.
Solid fuels have a very simple design: you place a highly flammable grainy substance into a tube, you light it on fire, and the entire thing ignites and generates thrust until it all burns out. Gunpowder is a great - and early - example of a solid fuel. Light a tube full of it on fire and it will burn until there's nothing left to burn.
The design of that rocket looks quite simple, and it is. Solid rockets are famed for their simplicity, and where that is a priority, solids can't be beat. Rocket missiles these days use solids, and so do strap-on boosters that provide some additional thrust to a rocket. Because missiles are so much more popular than spacebound rockets, most rockets made are actually solid rockets. Their main disadvantages are that they don't burn quite as efficiently as liquid rockets and once you ignite your grain, you can't shut it off (although some clever more modern inventions hope to change that).
Liquid fuels are a whole different story. They involve mixing a flammable liquid, generally liquid hydrogen or a hydrocarbon, in a combustion chamber with a strong oxidizer - usually liquid oxygen (LOX) but also possible is hydrogen peroxide - to generate a nice, powerful explosion.
You can control liquid fuel rockets much more easily than solid fuel rockets but the engine design is always a slight more complicated. But that's the kind of performance you need to actually be able to get into space.
When an object is moving with its own velocity but is also being pulled by another particularly large object, you get an orbit. The traditional example is shooting a cannon from a mountaintop: the harder you shoot, the further your cannonball will go - until you shoot it hard enough that its velocity allows it to curve all the way around the Earth and circle back. If you shoot it hard enough it will curve away and eventually leave the Earth's gravitational field - the velocity at which this occurs is called escape velocity.
There are essentially three shapes that an orbit can take: elliptical, parabolic, and hyperbolic. An elliptic orbit involves circling around an object in a circular shape, possibly a perfect circle, and is the one of most interest here. A parabolic orbit is what happens when you precisely hit escape velocity, and a hyperbolic orbit is anything faster than that. A missile is, from an orbital perspective, little more than an orbit that at some point intersects the Earth.
Because of physics (conservation of angular momentum), an orbit will be along a flat plane of space. Incidentally, the solar system itself is something of a flat plane; if you go up or down rather than in the direction of the plane you will quickly find yourself among a vast expanse of absolutely nothing. While it's possible to change the plane of an orbit, this requires a rather costly (again, in terms of fuel) maneuver - hence, rocket launch reports tend to talk about the orbital angle and why it's so important to get it right.
Pretty much every rocket is either placing something in orbit, or using an orbit to get somewhere. Two orbital maneuvers are worth talking about: Hohmann transfers and plane transfers.
A Hohmann transfer is a way to change from one orbit to a larger orbit using an intermediate orbit, that allows you to make the transition while using the least amount of fuel possible. It's used for anything from launching a satellite from a lower orbit into a higher Earth orbit to launching a probe from Earth to another planet by taking a larger orbit around the Sun. Of course, this orbit comes with the catch that it's the slowest way to go from point A to point B, but the fastest way (burning your engines at full blast directly toward where you want to go) is a great way to run out of fuel.
An orbital plane transfer is a way to change the plane of your orbit by adding some thrust at the right time in the right direction.
Figure 4.13: Blatant Plagiarism
One particularly important equation in rocketry is, quite aptly, called the rocket equation. It relates the mass of the vehicle (before and after fuel is expended) to the velocity of the exhaust (the fuel you burn and shoot out the back of the rocket) to the change in velocity of the rocket (the "delta V"). This delta V is, in a roundabout way, analogous to fuel, and you try to conserve it. You do an orbital maneuver, you pay some delta V to accomplish it. You run out, and you're just sitting in the middle of a vast expanse of nothing with no way to move around. Similarly, unless you have a good reason to do otherwise, you launch to the east to get some velocity boost from the spin of the Earth, preferably in a place where your boosters won't drop and hit someone on the way down. Hence, rockets are generally launched as close to the equator as possible, to the east, and preferably in a place where people don't live to the east.
An orbit is defined in terms of a certain number of orbital elements, six of which are needed in order to be able to pinpoint the orbit of an object. If you're interested in reading more about them, use the previous Wikipedia link; for now, it simply suffices to say that when tracing an orbiting object, the goal is to get a "six element lock" on that object. That requires at least six independent measures of that object's state, but given that we live in the real world where measurements are imperfect, "the more the merrier" applies. The image below gives one example of a six-element lock on an orbit.
A rocket seldom, if ever, consists of just one engine firing. In general, it's multiple smaller rockets all put together in a cylinder and launched together. Each individual independent piece is a "stage" of the rocket. At the very top lies the package to be delivered. An example of a rocket (United Launch Alliance's Atlas) showing each stage is given below - note the solid rocket boosters on the side of the large "first stage" booster.
The first stage is the big bulky part that gets you into space. As soon as it's done firing, it detaches from the rest of the structure ("stage separation") and falls back to Earth, hopefully into the ocean (or, in the case of SpaceX's Falcon 9 first stage, landing on a pad for that rocket). Generally the biggest and most expensive part of the rocket. In general these are powered by some fuel that does a good job of making a lot of thrust - the consensus these days tends to be around using a highly purified version of kerosene called RP-1 as a fuel, although hydrogen is also used (with lower effectiveness) and methane is being explored as a potential future option (most notably SpaceX's Raptor engine and Blue Origin's BE-4 engine, both in development).
The second stage and on are significantly smaller and use that boost from the first stage to get to where they want to go. When you clear the bulk of the Earth's gravitational pull lifting off, you're left with a much smaller and weaker engine, but any amount of thrust will give you far more bang for your buck. So even very small improvements in efficiency on these engines can make a huge difference. One planned second stage known as the Advanced Cryogenic Evolved Stage (made by United Launch Alliance) will increase efficiency of the upper stage enough to essentially double the amount that the entire rocket can lift into space. Hydrogen or a (nasty, but particularly versatile) compound called hydrazine is often used in the most effective second stage engines, although counterexamples (e.g. SpaceX's Merlin kerosene second stage) exist.
All this work is done in order to get some relatively small package into space - whether that package is a satellite, a lander for another planet, an astronaut inside a capsule, or even a box of chocolates for your special someone living on Venus. If it hasn't become clear yet, gravity is kind of annoying for trying to get anything done in space.
A Brief History of Rocketry
I assume that we are all fairly familiar with the history of rocketry during the Space Race; it was a glorious battle of who can be "first" to achieve a certain number of prestigious goals in space travel. If not, or if you would just like to read more about it, Wikipedia's history of spaceflight will be a good place to start - and from there, it's not hard to do a deep dive to learn more about any specific topic you want. Instead, I'm going to focus on the more distant past, the founding era of rocketry, and the much more recent future, covering only the major highlights of the Space Race era.
While not precisely related to rocketry, it's worth acknowledging the physicists who laid the foundation for rocketry. Among them are Galileo, Copernicus, Kepler, and of course Newton. Einstein's work on both general and special relativity also contributed to the space world. I won't spend much time on them, but they certainly deserve mention.
Chinese Fire Arrows
The idea for solid rockets goes back to ancient China and the invention of gunpowder. The Chinese found that if you strap a small capsule of gunpowder to a flighted arrow and lighted the capsule, you would get a primitive form of powered rocket flight. This was essentially an early form of solid rocket.
An early prototype of the Grad missile system.
Three individuals are mentioned among the founders of the liquid rocket: Konstantin Tsiolkovsky, a Russian; Robert Goddard, an American; and Hermann Oberth, a German.
The three pioneers and their respective successors
Tsiolkovsky was the first pioneer of rocketry who laid much of the groundwork for the physics of space travel. While in his own lifetime he never managed to build rockets, he did create the rocket equation (also known as Tsiolkovsky's Rocket Equation). His work was noticed by an American physicist named Robert Goddard, who created the first rockets. Compared to modern, 99% fuel efficiency rockets, his were rather primitive - he used gasoline and liquid oxygen and only managed a 63% fuel efficiency, and a top speed of 550 mph. In his time, his work was scarcely acknowledged and he died before the advent of the rocket era.
Enter Hermann Oberth, and his student (and an important player in American rocketry), Wernher von Braun. They improved upon Tsiolkovsky's principles and Goddard's designs to create some of the first viable rockets, starting with gasoline/LOX mixtures but eventually moving on to many alcohol-based rockets (I always imagine drunk German rocket scientists pouring vodka into a rocket). One of their most famous works was the V-2 rocket, one such alcohol-LOX combination which, while ineffective as a weapon, did help make future rocketry possible. Though their work was ultimately used for rockets "that go to the wrong planet" in Nazi Germany, their work was indeed eventually used for the right kind of rockets.
As an aside, although it's not commonly used anymore (due to there being better fuels), alcohol is actually a pretty good fuel. It makes a very nice, hefty flame.
After WWII, the missile technology developed by the Germans was improved upon to create space rockets. The Sputnik program put the first satellite into orbit, then a research capsule, then two dogs, and finally a dog with a human dummy. The Vostok program put multiple humans into space, including the first man (Yuri Gagarin, Vostok 1) and woman (Valentina Tereshkova, Vostok 6). Mercury launched the first American (Alan Shepard) and first American orbit around the Earth (John Glenn). And of course we have the Apollo 11 mission, in which Neil Armstrong, Buzz Aldrin, and Michael Collins the Forgotten (the pilot who didn't leave the craft) landed on the Moon. This is the best known era of spaceflight; I need not describe it in excruciating detail.
Shortly after the 1969 Moon landing, interest in space sort of rapidly fell apart. On the Soviet side, many attempted projects ended in unfortunate failure due to budget issues and one particularly glaring flaw (a lack of development of hydrogen engines, which would have been great for a Moon mission). The US sought to create a cheap rocket and created the rebuildable ("reusable") Space Shuttle, which was anything but. The Soviets, and later Russians, undertook some projects, but for many years mostly just kept the lights on, making upgrades to their vehicles but hardly being in a position to make anything new and special - though this capacity did survive the collapse of the USSR and the following disaster.
One new development that was actually interesting during the 1970s and on was the launch of space stations, including Skylab, Mir, and eventually the International Space Station. Each had their own degree of success, but it's hard to deny that the ISS was by far the most successful - it's still orbiting and still one of the most important achievements of spaceflight. Much of the modern work in spacefare involves servicing this station. In a large way this was the dawning of a much more cooperative era, in that the ISS was built with the help of multiple nations rather than as part of a race.
Era of Old Spacers
At the turn of the century, one particularly interesting development was the development of a commercial space market - launching satellites for private companies for money. Although a satellite is an expensive thing to make and launch, a well-planned satellite can rake in hundreds of millions of dollars over its lifespan, easily paying for its launch costs many times over. The European aerospace giant Aerobus created the Arianespace organization to launch commercial payloads, and took a leading position in that market. The Russian space program, suffering from a sudden and severe collapse in potential government funding in the 1990s, kept afloat by selling launches, most notably on its Proton heavy rocket (also Sea Launch, but that's a story for another time).
The US at this time was not really at the top of its game. While I could describe it myself, this report does a better job than I could do, so I'll just quote it instead:
The period spanning the late 1980s to the early 1990s was a particularly difficult era for spaceflight in the United States. After the tragic Challenger disaster in 1986 and the Titan rocket launch failures quickly thereafter, all military launches were halted for almost a year. The fall of the Soviet Union in 1991 led to a decline in the U.S. defense budget, which included military program consolidations. There was also a growing concern that the commercial space launch market could shift away from the United States. The United States needed a new launch vehicle that could provide assured access to space for the military and stay cost competitive over time.
The full report, in fact, gives some nice insight into US Old Spacers - I recommend reading it. Long story short, though, the US was in a pickle because they feared they would be locked out of the growing commercial space industry, their military launches would see trouble, and they needed to create some reliable, cheap rockets to stay afloat. One company, General Dynamics, eyed the Russian RD-170 engine - a monster of a kerosene engine with excellent performance capabilities and a better design than anything they could have made themselves. They made a joint venture with the engine producer, NPO Energomash, to build what was essentially a half-size version of that engine - the RD-180. It was used in the Atlas rocket, which was eventually purchased by Martin Marietta, which after a merger became Lockheed Martin. Another rocket at that time of interest was the Delta series, a hydrogen rocket that eventually got into the hands of Boeing. While they both eventually developed some rather fantastic launch records, the Atlas was clearly superior for most launches, being a far less convoluted design with a fantastic engine.
The plans that the US had for getting into the "growing commercial market" never really materialized, mostly because the market itself never materialized. So it started to be the case that the most important customer for these organizations was the Air Force itself. They wanted to keep two lines of rockets online to ensure that they would never be in a position where they couldn't launch one of their rockets; in the case of military satellites, the cost isn't so much the lost satellite as the cost of what the satellite won't be doing for you, the battle it won't win. Ultimately, Boeing and Lockheed merged their two rocket businesses into the United Launch Alliance, which they claimed would reduce logistics costs and give the US Air Force cheaper launches. Whether or not that's true, ULA is known for two things these days: being very expensive, and not losing a single rocket in the entire history of the joint venture.
I know that India, China, and others started to really develop their space chops at this time, and I wish I could talk more about them. But I simply don't know enough about them to give any meaningful opinion here. I'll make sure to talk about them more if I end up learning more.
The New Spacers on the Block
The most recent development, the one we've all seen develop before our eyes, is the advent of a group of New Space companies which sought to break into the space industry. Funded mostly by the funds of wealthy individuals, they set out to accomplish some lofty goals - create space tourism services, create cheap rockets, colonize Mars, and many more.
Their successes were rather limited in most cases, but one particular New Spacer stands out: SpaceX. Headed by Elon Musk, a man of many talents and an ego the size of Donald Trump, he sought to make fully reusable rockets that would be able to travel to Mars.
Will SpaceX reach those goals? Hard to say. Personally I have my doubts - but even so, it's hard not to acknowledge what they did bring to the table: a focus on designing rockets to reduce cost. Many of their design decisions, while suboptimal from a performance perspective, do make the rocket much cheaper to build. They also chose to build much of their rocket in-house to reduce the size of their supply chain. And they have offered launches for far cheaper than their competitors (possibly at a loss), forcing those competitors to do all sorts of things to try to be competitive with their low price. Some may wonder if they are in over their heads with some of their plans - but it's hard not to acknowledge the things they did do, including designing for cheaper manufacturing and landing a first stage booster (certainly a technical feat).
Blue Origin, perhaps, deserves a parting mention. Bankrolled by Amazon billionaire Jeff Bezos, they have designed a reusable suborbital rocket which they have reused before - and are creating a large, powerful methane engine - the BE-4. ULA, forced to find a replacement for their RD-180 engine due to political troubles with Russia, has played the role of a guardian angel of sorts for Blue Origin - helping them design and improve the BE-4, so that they will sell ULA a good replacement for a new rocket.
So that's about where we are today and how we got there. I know that I skipped over quite a lot of history in each era. You'll have to forgive that; this is already getting pretty long and if I get any more exhaustive then I'll be writing to an audience of no one.
With the advent of the New Spacers, spaceflight has certainly taken an interesting turn towards a cost-based focus. Whether or not any one of those New Spacers will ultimately succeed, many of the expensive, yet highly skilled, Old Spacers have been forced out of their comfort zone and into a much more competitive environment.
In truth, though, I often find this era slightly disappointing - it almost seems like much of the interesting aspects of spaceflight are being ignored in favor of just focusing on SpaceX. What I tried to do here was to give a much broader picture - the physics of a rocket, some of the technical challenges, and many of the players and where they are coming from. Time allowing, I'll probably go into more depth on some of these; much was omitted in order to make this at least somewhat shorter than it was originally planned to be. If anyone wants me to talk about anything specific, let me know.
In any case, props to anyone who actually read through my diatribe - and bonus points to anyone who reads all the links as well. Hope you enjoyed it!