3.1 How to launch a rocket
How can you launch a rocket into space? Obviously, you need something to push it upwards, so providing a force. This force is often called a ‘thrust’, which is measured in newtons (N). Burning rocket fuel to provide this force is one obvious solution. Opposing this motion, in addition to gravity, is air resistance. This is often called ‘drag’ and is also measured in N.
You then need to consider the mass of the rocket – measured in kilograms (kg) – and how long the fuel burns – measured in seconds (s). As the fuel is gradually exhausted, there is a reduction in the overall mass of the whole rocket. This is because the mass of fuel is reduced as time increases. This change of mass in time is given in kg/s.
Now complete Activity 4.
Activity _unit2.4.1 Activity 4 Launching your own rocket
Using the link below to simulate a rocket launch, try to overcome the gravitational ‘pull’ of the Earth – the Earth’s gravitational field. In the following simulation you can change the mass, thrust, thrust time, drag and mass change. See how far you can launch a rocket into space. [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] Now record what happens when you change the parameters as follows.
Task 1
- Mass change = ‘off’
- Drag forces = ‘on’
- Time = 5 s
- Thrust = 400 N
- Mass = 1 kg
Answer
Your rocket exploded because the thrust was too high for the size of rocket you selected. Try again by selecting a smaller thrust or a larger mass for your rocket.
Now try Task 2 where the mass has been increased but all the other variables have been kept constant.
Task 2
- Mass = 20 kg
- Thrust = 400 N
- Time = 5 s
- Drag forces = ‘on’
- Mass change = ‘off’
Answer
You should have made a successful launch. Did your rocket also reach a maximum height of 267 m?
The ‘extra challenge’ is to switch off drag and mass change to see how the flight of the rocket would be different. Try this now in Task 3. Again, we have only changed one variable, keeping the others constant.
Task 3
- Mass = 20 kg
- Thrust = 400 N
- Time = 5 s
- Drag forces = ‘off’
- Mass change = ‘off’
Answer
Again, you should have made another successful launch. This time the rocket reached a maximum of 270 m, only 3 m more than the last one.
Task 4
Now see if you can beat our best result of a maximum height of 14 769 m (14.769 km) and a maximum speed of 517 metres per second (m/s).
Discussion
To do this, you need to use the following parameters.
- Mass = 5 kg
- Thrust = 400 N
- Thrust time = 5 s
- Drag forces = ‘off’
- Mass change = ‘on’
There are many other online rocket simulations. Here are a few to explore if you have time.
So now, when people say ‘It’s not rocket science’, you can reply by saying that it is!