Rocket science has been around since the 280s BCE, when ancient Chinese alchemists invented gunpowder.
Initially used in fireworks, gunpowder was soon put to use in weaponry as fire-arrows and bombs among other things. Throughout the centuries, rockets continued to be used as weapons until the early-20th Century.
In 1912, Robert Goddard built the first liquid-fuel rocket (previous rockets were solid-fuel) and began the age of modern rocketry. To date, there have been somewhere in the region of 500 rocket launches from NASA’s Cape Canaveral, and more than five thousand satellites launched by rockets from spaceports throughout the rest of the world.
While the term ‘rocket’ can be used to describe everything from cars to jet packs, most of us think space travel when we see rocket. Most rockets follow the same basic design.
Typically they are tube-Iike, with stacks of components. Rockets carry propellants |a fuel and an oxidizer), one or more engines, stabilization devices, and a nozzle to accelerate and expand gases. However, there’s a lot of variation among those basic elements.
There are two main types of rockets: solid-fuel and liquid-fuel. The former have some similarities to those early gunpowder rockets. For space applications, solid-fuel rockets are often used as boosters to lower the amount of needed liquid fuel and reduce the overall mass of the vehicle as a whole. A common type of solid propellant, used in the solid rocket boosters on the NASA space shuttles, is a composite made of ammonium percholate, aluminium, iron oxide and a polymer to bind it. The propellant is packed into a casing. Solid-fuel rockets are used alone sometimes to launch lighter objects into low-Earth orbit, but they cannot provide the type of overall thrust needed to propel a very heavy object into Earth orbit or into space. They can be difficult to control once ignited.
The difficulty in getting off the ground is due to the strength of Earth’s gravity. This is why thrust -a rocket’s strength – is measured in pounds or Newtons. One pound of thrust is the amount of force that it takes to keep a one-pound object at rest against Earth’s gravity. A rocket carries fuel that weighs much more than the object that it’s trying to move (its pay load -a spacecraft or satellite). To understand why, think about what happens when you blow up a balloon and then release it. The balloon flies around the room because of the force exerted by the air molecules escaping from it. This is Newton’s third law in action. But the balloon is only propelling itself; rockets need to generate thrust greater than their mass, which includes the weight of the fuel. For example, the space shuttle in total weighs about 4.4 million pounds, with a possible payload of about 230,000 pounds. To lift this, rocket boosters provided 3.3 million pounds of thrust each, while three engines on the main tank each provided 375,000 pounds of thrust.
Liquid-fuel rockets have the benefit of losing mass over time as their propellant is used up, which in turn increases the rate of acceleration. They have a higher energy content than solid-fuel rockets. Typically they consist of a fuel and an oxidizer in separate tanks, mixed in a combustion chamber. Guidance systems control the amount of propellants that enter, depending on the thrust needed. Liquid-fuel rockets can be stopped and started.
Launch location can also help rockets become more efficient. European Space Agency member country France chose to build a spaceport in French Guiana not only for its location near water, but also its location near the equator. Launching a rocket near the equator, in an easterly direction, makes use of energy created by the Earth’s rotation speed of 465m per second. This also means that putting a rocket into geosynchronous orbit is easier, because few corrections have to be made to its trajectory.
Escape velocity – How rockets break free of Earth’s gravity
Throw an apple into the air and it will keep travelling away from Earth until gravity overcomes the force of your throw. At this point the apple will fall back down to the ground. If, however, you launched that apple from a cannon at a speed of 40,000km/h (25,000mph) – that’s a nippy 11km(7miles) per second-the apple will reach what’s known as escape velocity. At this speed, the force of gravity will never be stronger than the force causing the apple to move away from Earth, and so the apple will escape Earth’s gravity.
Multi-stage rockets are essentially multiple rockets (each with their own engines and fuel systems) stacked on top or beside each other. Sometimes this assembly is known as a launch vehicle. As the fuel burns, the container holding it becomes dead weight. When a stage separates from the main body, the next stage is capable of generating more acceleration. The downside of a multistage rocket is that they’re more complex and time-consuming to build, and there are multiple potential failure points. However, the fuel savings are worth the risk.