Is rocket science easier than you think?

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1. A universal problem

We’ve all used the phrase ‘rocket science’ to mean something extremely complicated. But when you break down the ideas behind it, it’s really pretty simple.

Firing rockets into space is all about overcoming the force of gravity. We face that same challenge whether we’re launching a NASA mission into space or firing a homemade rocket in the park.

So using three types of model that you can make yourself, we’ll launch some of our own mini-rockets. By understanding how these small-scale examples work, we'll be able to see some of the underlying principles used by experts who build real life space rockets.

2. Equal and opposite forces

To get a rocket into the air, the first thing you need to do is overpower gravity. Like everything on Earth, a rocket will remain motionless until a force acts on it to get it moving. The rocket’s engine supplies this force in the form of thrust. 

Follow the instructions in the video to create your own matchstick rocket.

You will need:

Two matches, one small square of tin foil, one safety pin and one paperclip.

Safety:

Children should get an adult to help them build and launch this rocket. Be aware that the safety pin will be sharp and that the lit match and matchstick rocket both require careful handling to avoid burns. The foil that wraps the match head will remain hot for some time after it has been lit. Make sure you go outside to fire the rocket and be sure that the area is free of people and animals.

How does it work?

When the match head reaches ignition temperature, gas molecules are released. We see these as smoke and the only place they can exit is through the narrow exhaust. The gas escapes very quickly here, creating enough thrust to make the matchstick overcome the pull of gravity and blast off. This demonstrates Newton’s third law of motion, which states that every action has an equal and opposite reaction.

3. Achieving greater forces

For a rocket to make it into space it has to fly incredibly fast. To make it to flight-speed, a rocket’s engine has to create the greatest thrust possible in the shortest amount of time. Launching your own water bottle rocket is a great way to understand how this works.

Follow the instructions in the video to create your own water bottle rocket.

You will need:

One empty fizzy drink bottle, one cork, one paper nose cone, three pencils, one air pump with a needle adaptor, sticky tape and safety goggles.

Safety:

Children should get an adult to help them build and launch this rocket. Be careful of your fingers when making a hole through the cork. Take the rocket outside to launch and only ever fire into an area that is clear of people, animals and breakable objects. Wear safety goggles at all times and stand at least three metres back during launch, as the rocket will fire with little or no warning and could fly in a random direction. We recommend using something like the handle of a garden fork to angle the rocket away from yourself or any other on-lookers.

How does it work?

Just like a real life rocket, it’s the force of what is being ejected out the back that lifts your rocket towards the sky. Compared to the bottle, the water is heavy, so pushing it out under pressure gives the bottle a quick burst of thrust. Streamlining the rocket’s shape by adding a nose cone helps the rocket fly faster by reducing air resistance, or ‘drag’.

Newton’s second law of motion states that force is equal to mass multiplied by acceleration, which means that the rate your rocket accelerates depends on its mass. This is why a lightweight rocket will accelerate faster than a heavy one under the same force. It’s a fine balance between carrying plenty of fuel whilst keeping the rocket light. You could try filling your water rocket with different amounts of water to find how much you need for your rocket to reach its maximum speed.

4. Creating thrust from a chemical reaction

We’re used to seeing an explosion when a rocket blasts off, but actually it’s not an explosion that makes a spacecraft leave Earth. Most rocket engines work on the principle of combustion. This is a fast chemical reaction between a fuel and an oxidiser. During the reaction, the fuel gets 'oxidised' releasing a tremendous amount of energy.

Follow the instructions in the video to create your baking soda/vinegar rocket.

You will need:

One empty plastic water bottle, one piece of white tissue, one cork, one paper nose cone, three pencils, sticky tape, baking soda and vinegar.

Safety:

Children should get an adult to help them build and launch this rocket. Take the rocket outside to launch it and only ever fire into an area that is clear of people, animals and breakable objects. Wear safety goggles at all times and stand well back.

How does it work?

Modern rocket engines work the same way as our homemade rocket. An oxidiser and a fuel are mixed within a combustion chamber at high pressure. Hot gas produced by the chemical reaction then escapes through the bottom of the rocket, creating enough thrust to blast it high into the sky.

5. Principles in practice

Labelled diagram showing similarities between a baking soda and vinegar rocket and a real rocket

Our baking soda and vinegar rocket actually uses similar principles to a real life rocket.

Model rockets might be simpler than real space rockets but everyone, including NASA, are up against some similar challenges. A propulsion system is needed to generate thrust to get any rocket off the ground. While the baking soda and vinegar slowly reacted in our combustion chamber, NASA keeps the fuel and oxidiser in separate containers and pumps them into the combustion chamber when required. Both these types of reactions release gas that is expelled through the exhaust port to generate thrust. And of course, once the rocket has lifted-off, the shape needs to stay aerodynamic - regardless of whether it’s soaring through a park or blasting through the stratosphere.

6. Launching the Space Shuttle

Press start and drag the arrow to see how these principles come into play during a real life rocket launch.

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7. What methods are used by rocket scientists?

Which of the following principles used in the model rockets are applied by scientists to power real rockets into space? (Image: NASA)

Water exhaust

Water is propelled out of the second rocket to generate thrust for lift-off. Is a water exhaust ever used in real rocket design?

You selected

Water exhaust

Yes

Although not in liquid form, some combustion chambers in rockets such as Delta IV generate water vapour, which is ejected as the exhaust. Credit: NASA

Burning solid fuel

Our matchstick rocket burns solid wood to create a smoke exhaust. Do space rockets ever burn solid fuel to propel into space?

You selected

Burning solid fuel

Yes – sometimes

Although liquid fuel is most common, some rockets such as Atlas V use additional solid rocket boosters to generate extra thrust at lift-off. Credit: NASA

Conical nose cone

The nose of our two bottle rockets are covered with a pointed paper cone. Do the nose cones of all space rockets have this shape for optimal aerodynamics?

You selected

Conical nose cone

Not always

Nose cone shapes vary. The blunted sphere of Space Shuttle's external tank created unstable buffeting. It was replaced with a 'biconic' nose cone. Credit: NASA

Straight exhaust port

The foil exhaust port in our matchstick rocket runs straight down. Is a straight nozzle the most common design in space rockets?

You selected

Straight exhaust port

No – not commonly

Most rockets such as the Space Shuttle use an hourglass-shaped nozzle that varies the exhaust flow rate, controlling the exit pressure and thrust. Credit: NASA