# How Do Rockets Work

If you have been to Cape Canaveral and witnessed the launch of a space shuttle, you must have felt the goose bumps and been left in awe with the burning arrow rising into the sky! One of the most glorious events on Earth is the launch of a space shuttle. It is a moment of triumph for humanity, as the man-made rocket overcomes the grip of gravity and breaks free from its clutches. It is a triumph of human intelligence and effort, which has helped us to emerge out of the Earth's cocoon and go beyond. Rockets make space travel possible. The phrase 'It's not rocket science!' has fortified the notion that rocket science is something very complex and beyond comprehension. However, all it takes to understand how rockets work is the grasping of some very basic principles and phenomena.

Principle Behind the Working of a Rocket

Every machine like a rocket, is based on the harnessing of some fundamental physical principle. To understand how rockets work, all you need to do is get a hang of this fundamental physical principle. The answer to how does a rocket work is a one line answer in principle. It is called the 'Action-Reaction Principle'. It is the third and last of Newton's three laws of motion. It states that:

"Every action has an equal and opposite reaction."

All forces of nature come in pairs. You can see the effects of this principle all around you. When a bullet is fired from a gun, the gun experiences a recoil. That is, the action of the gun pushing out the bullet has a reaction in the form of the bullet pushing back on the gun in the form of a recoil. If you are standing on a stationary skateboard and you throw a ball at a very high speed, then the skateboard moves back. This is again the reaction of the ball on your hand, making you and consequently the skate board move backwards. So, you can never escape from a reaction when you act on something. Every action must be balanced out, by an equal and opposite reaction.

Momentum is defined as the mass of the body multiplied by its velocity. A corollary that follows from the action reaction principle is the 'Conservation of Momentum'. The principle states that:

"Total momentum of any system of reacting bodies should remain constant."

This is just the action-reaction principle stated in different words. Consider the firing of a bullet from a gun again. The total momentum of the system (made up of the bullet and gun) is zero before firing. Therefore, the total momentum of the system after firing should also be zero. The only way to achieve that after firing of bullet is such that the momentum of the gun and bullet are exactly the same, but opposite in direction, which would make their sum come out to be zero!

If you blow a balloon and then release it, air escapes out of its mouth, launching it in the opposite direction! The action of escaping air from the mouth of the balloon, propels the balloon in the opposite direction. The rocket works on the same principle that launches the balloon. Replace the balloon with a rocket and the air blown out with the exhaust fumes of combustion exhaust gases and you understand why rockets move upwards!The rocket is launched up as a reaction to the action of exhaust gases being released downwards at a high velocity from the nozzle of the rocket's combustion chamber. Just like the gun experiences a recoil when it fires a bullet, the rocket also experiences a recoil when it throws out the exhaust gases out of its tail. This recoil is so strong due to the very high velocity of exhaust gases, that it launches the rocket upwards! If you look at this from the perspective of the conservation of momentum, then you will realize that upward thrust of a rocket is a result of the whole system achieving zero momentum in totality.

So, now you must have an idea how do model rockets work. They have a combustible, slowly burning fuel, which burns creating exhaust gases that escape from a fine tail nozzle, which launches the rocket upward. However, when the fuel in a model rocket is exhausted, the thrust that drives it upwards is no more there and eventually, gravity takes over, bringing it down, back on dear Earth!

How Do Rockets Overcome Gravity?

The prime enemy of everything that tries to rise high above the Earth's surface is gravity! Every object is pulled down to Earth with a downward acceleration of 9.8 m/s2. To rise higher, a rocket must over come this downward acceleration with thrust generated by escaping combusting gases. That is why, the choice of fuel for a rocket is important. The fuel should be of the kind that burns slowly, without exploding and generate a high level of heat which can accelerate the exhaust gases to high speeds. A special type of cryogenic, liquid propellant fuel is used in space rockets.

That is why a rocket needs to carry a lot of fuel in separate tanks along with it, as it needs to maintain the thrust against gravity, balance it and overcome it, throughout its journey. If you have seen a space shuttle launch, then you will remember that it consists of the orbiter, fuel tanks and rocket boosters. The problem is that to launch the weight of the rocket, it needs to carry fuel which makes it heavier. To get around this problem, fuel is burnt in stages. After the launch of the rocket, fuel is burnt in three stages generally. In each stage, when a fuel tank gets exhausted, its detached from the rocket. This reduces the load as the rocket rises higher. If the 'payload' that rocket is carrying needs to be put in the orbit around Earth, then by the end of the third stage, rocket has reached an altitude at which the payload (in the form of an orbiter or satellite) can be put in orbit. When the linearly rising rocket reaches this top altitude, it makes a 90 degree shift going into a horizontal orbit around Earth, while detaching the last fuel tanks. This parks the 'payload' into its orbit in space. Once it is parked into that orbit, it becomes an artificial satellite of the Earth as gravity does the rest keeping it in orbit around our planet. That is how the Hubble Space Telescope, the International Space Station (ISS) and every other satellite is placed in orbit.

Rockets don't perform any task other than parking the payload in predetermined orbit. One day humanity will colonize Moon and Mars using advanced rocket systems and space shuttles. Our dominion will expand beyond the little blue dot in space, that is our home, through new inventions in space exploration technology and advanced spaceships.
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Last Updated: September 22, 2011