Ioonos

Carrying your house on your back

To escape the earth’s gravitational pull and deal with friction from the atmosphere, a certain speed must be reached, known by scientists as the “first cosmic velocity”, which is about 7.8 kilometres per second. For this the launcher must be extremely powerful and accelerate very rapidly for a long period. You might think that this would be easier if it was not so heavy. Everything is done to reduce the weight, however, it should be understood that a launcher is unlike any other vehicle. Let’s compare it to an aeroplane. An aeroplane stores fuel in its wings; oxygen in the atmosphere enables this fuel to be burnt in order to produce energy to propel it forward. But as soon as you are a few kilometres into space, there is no more oxygen! So the launcher has to carry not only fuel* but also an oxidizer*, which is often oxygen or nitrogen peroxide. This is why it is so heavy. For example, 90% of Ariane 4’s weight was due to propellant (fuel and oxidizer), 9% to structure and barely 1% to the satellite!

Getting away from earth

The big issue here is thrust. And it is at lift-off that the launcher has to provide the most thrust, because it is still stationary and does not have the benefit of any inertial force, gained once its mass has acquired a certain velocity. Furthermore, all of its tanks are full…So, basically, we are talking about starting from zero. The thrust is obtained by expelling a large volume of gas at a very high speed, which results from the combustion of the propellant. The thrust is proportional to the rate of flow and speed of ejection of the gases. To overcome gravity and lift the launcher’s 700 tons it is therefore necessary to expel a great deal of matter: for every 500 tons, more than two tons of propellant is consumed every second.