How Rockets Work: Your Simple & Complete Guide
By: Amira M | Writer at Verity Magazine Global
When initially brainstorming ideas on how we could send a functioning vehicle into space, engineers immediately ruled out traditional transportation mechanisms, such as wings and propellers — these mechanisms worked by pushing against a surrounding medium, but space is a vacuum. Another problem identified was that fuel combustion engines wouldn’t work in space due to the lack of oxygen.
What is a rocket?
A rocket is ‘a large cylinder-shaped object that moves very fast by forcing out burning gases, used for space travel or as a weapon’ — Cambridge Dictionary. Simply put, a rocket is a type of spacecraft that we can use to leave our planet and travel in space.
An oversimplified explanation of how rockets work
In order to leave the Earth’s atmosphere, rockets have to generate an upward force that is greater than the force due to gravity. This upward force is called thrust. A rocket generates thrust using a controlled explosion: as the rocket fuel and an oxidant undergo a violent chemical reaction, expanding gases from the reaction are pushed out the back of the rocket at a high speed. As a result, the rocket is pushed in the other direction, in this case, up. This is in accordance with Newton’s 3rd law of motion, which states that every action has an equal and opposite reaction. The oxidant used in the reaction performs the same role as oxygen in Earth’s air, and enables the fuel to combust in space. The rocket launch is one of the biggest challenges faced by engineers: in the beginning, the rocket is carrying all the fuel and oxidant it needs to reach space. Therefore, the rocket’s weight is at its maximum and a large amount of thrust is required to move the rocket. As the rocket starts moving and its mass decreases, weight is reduced and so the same amount of thrust will have a greater effect in terms of accelerating the rocket. It is generally accepted in the world of engineering, that the most efficient rocket to be launched is a vertical vehicle that is made up of separate parts, with each part being able to detach and fall away when it is no longer of use. This is why when you watch a rocket launch, there is always something that intentionally falls off from the rocket — it’s usually not a malfunction, but rather a smaller part of the rocket that is no longer necessary anymore.
Rocket Engines
Most modern rockets use gimballed engines, mounted to ensure the entire rocket motor can pivot and change the direction of its thrust at any given point. Older, solid-fuelled rockets have external vanes to deflect exhaust gases, and auxiliary engines — small thruster rockets mounted on the sides. For older rockets, the rate at which fuel is burnt, and therefore the amount of thrust, can be controlled by changing the amount of surface exposed to ignition at different points in the rocket’s flight. Newer, liquid-fuelled rockets have propellant tanks for its fuel and oxidant, that are connected to a combustion chamber; the rate of supply can be increased or decreased as required.
Reusable Rockets
As previously mentioned, a normal spacecraft is designed to work on one occasion, before being lost permanently. However, a reusable spacecraft is designed to accommodate repeated launches, orbit, deorbit and atmospheric reentry. These spacecraft require mechanisms to prevent the disintegration of the spacecraft and its cargo during reentry into the atmosphere. Reusable spacecraft must have mechanisms to deorbit and reenter the atmosphere in a controlled fashion. The SpaceX Dragon includes its own engines, used for deorbiting, that slows the spacecraft down as it descends to Earth. Thermal Protection Systems need to be employed on these reusable spacecraft as they have to withstand multiple reentries into the planet’s atmosphere. This proves to be extremely difficult, as most heat shields would add an enormous amount of additional weight. Spacecraft that land horizontally on a runway require wings and an undercarriage. This would either reduce the payload of the spacecraft, or increase the size of the spacecraft. Vertical landings can be accomplished with either parachutes or propulsively. The SpaceX Dragon was an example of a reusable space capsule that used a parachute in its landing procedure. Its derivative, Dragon 2, was originally intended to propulsively land on land. However, this concept of propulsive reusability was scrapped in 2017, and now the Dragon 2 uses parachutes to land in the ocean. After the spacecraft lands, it will likely need to be refurbished before its next flight. This process may be lengthy and expensive, and sometimes the spacecraft may not be able to be recertified as human-rated after it is refurbished. With current technology, there is eventually a limit on how many times a spacecraft can be refurbished before it has to be retired.
Blast Off!
After the rocket has launched, as the rocket gains speed, the direction of motion must be kept closely aligned with the direction of the thrust. Gradual adjustments are needed to steer the rocket towards an orbital trajectory, but a severe misalignment can send the rocket whirling out of control. Rockets can only maintain their orbit around a planet if they are not moving fast enough to escape the planet’s gravitational attraction. If the rocket were to increase its velocity past this point, the rocket would be able to leave the planet’s gravitational attraction and explore the universe.
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