Basic Rocket Science! (January 2025)
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Rockets first evolved from missiles used created during World War II and those missiles themselves borrowed heavily on the ingenuity of arrows and fireworks that came during the centuries before them. A conventional rocket, as pictured further below, is a long cylindrical vehicle that manages to expel a huge amount of gas vertically downwards, which, in turn, pushes it upwards into space. The total force of the gases pushing downwards will always equal the force pushing back on the rocket in the opposite upward direction. The rocket is, of course, much heavier than the gases and that is why it moves up much slower than they move downwards and why so much gas is needed in the first place. The gases come from burning fuel inside the rocket and as the rocket continues on its journey upwards it begins to travel faster and faster as it becomes lighter and lighter as more of its internal fuel is burned. Space is about 100km above the ground. The higher one goes up the less dense the air becomes and the easier it is again for the rocket to ascend as it suffers less air resistance. It has plenty of insulation between its skin and its internal fuel tanks to avoid any leakage, especially if the fuel could be ignited by something else or the air pressure inside is different from that outside. If there was to be a sudden leak all the fuel could be ignited and explode the rocket or it could immediately escape to the outside if the air pressure there was much less so it was forced out from inside the rocket (just like opening a door in a plane during flight). The tops of rockets also have a thick extra layer of metal known as a heat shield to protect the rocket from the intense heat created from the friction of all the air running passed it at such an incredible speed on its way up. Scientists usually toss and turn between which rocket designs to use, what materials to make them out of, how large they should be and how much fuel they need. The heavier the rocket the more fuel it needs to carry itself into space and the more fuel it needs the heavier it becomes again causing even more fuel to be needed to carry the first lot of fuel into space! It may seem that the answer is to simply make a rocket as light and as strong as possible. However, it is desirable to carry as much as you can into space so you can do something useful when you are there and there are cost implications with using the strongest materials in rocket construction. This is where the complexities start to come in. However, the basic principles of rocket propulsion are quite simple.
It is now time to detail the rocket specific of fuel, commonly known as propellant, as it tends to be about 90% of the rocket’s weight and is absolutely crucial to any mission. Again, scientists will toss and turn between using solid propellants or liquid propellants and then which exact solid or liquid propellants at their corresponding costs. Liquid propellants are usually preferred as they tend to be more powerful and, unlike solid propellants, can be ‘switched off’ whenever needed as the flow of fuel can simply be shut off to cut off all power. This is not possible with solid propellants because once they are lit they keep burning, like a log of wood in a fire. Hydrogen and oxygen is one of the best propellant combinations. Sometimes a combination of both solid and liquid propellants are used. Basic physics tells us that in order to create fire or combustion we need not only fuel but also oxygen and heat. Therefore, rockets also need to carry oxygen with them to mix with their internal fuel as they cannot use the oxygen from outside like planes do with their jet engines. The heat is then created by simply igniting both the fuel and oxygen when needed. All this adds to the overall complexities of rocketry but the basic principles remain fairly simple.
Once we know how rockets work and have chosen their propellants we need to examine their structure, as shown in the below diagram of a Saturn V one which sent men to the Moon in 1969. As labelled below, the rocket has three stages counting upwards from its bottom that create its upward thrust from their internal propellant and boosters. The ‘stabilizing fins’ labelled there are to steer the rocket and keep it on the right course of venturing not only upwards but in the right direction. Some rockets have internal ‘rudders’ at their boosters. The very top part of the rocket, as labelled, is known as the ‘payload’ and this is actually what is sent into space to achieve the mission’s objective. Since the earth’s gravity is so strong everything below the payload is needed for it to escape into space. The three stages of the rocket ignite one by one starting at the bottom first stage to gradually lift the whole rocket into space. Once the first stage has exhausted all its propellant it drops off from the rocket back to earth (as commonly seen on TV documentaries and movies). Then the second stage ignites its propellant with its own boosters and engines below and continues to push the rocket further upward until it too is exhausted and drops away before the third and final stage repeats the process and lifts the payload into outer space.
Since the Apollo era rockets have changed in shape and size with the fascinating space shuttles (that look more like planes and which can return to earth and land like them) coming out in the 1980s (as pictured below) and all sorts of futuristic designs coming out in more recent years.
Once a rocket is in space it pushes itself further towards its destination with its own onboard rocket. Since there is no air in space to slow it down a simple push from its onboard rocket (as mentioned earlier) will send it going in one direction for eternity until it either collides with another object or gets caught in a gravitational field. It turns itself around and keeps the right way up with miniature boosters on its sides that release quick bursts of force. These are called ‘gyros’ and are very popular on probes. All systems on a rocket on the ground before takeoff, during its ascent and in space are constantly and individually monitored back on earth to make sure all is as it should be and this is why we normally see images of NASA staff at a ‘Mission Control (or Command) Centre’ working at numerous workstations full of screens and buttons.
In a nutshell that is how rockets work. The principles are quite simple but the many complexities that immediately come into the picture along with their never-ending costs and risks is what makes the task so difficult. However, if there is anything that anyone should be reminded of when trying to achieve any goal, big or small, it is the simple fact that everything is always hard before it is easy.
In a nutshell that is how rockets work. The principles are quite simple but the many complexities that immediately come into the picture along with their never-ending costs and risks is what makes the task so difficult. However, if there is anything that anyone should be reminded of when trying to achieve any goal, big or small, it is the simple fact that everything is always hard before it is easy.