-and its effects on chemical engines and spacesuits-.

It is deeply rooted in the collective imagination that the spacecrafts we see on our television screens, on our computers or mobile phones, are propelled by chemical combustion rockets, and we are also convinced, precisely because the images show it to us, the films show it to us and the various space agencies continually propose it to us, that the same spacecrafts are able to slow down or divert their trajectory through jets of compressed air or something similar. 
Well, let's try to understand for ourselves if this is true:
First of all, we need to understand what a vacuum is and the force with which it acts on the spacecraft. 
We are wrong if we believe that since there is nothing in space, no force acts on the spacecraft.
 

Let's take a very simple example to understand what forces act on astronauts' suits and their spacecraft. We take a balloon and instead of blowing into it, we put it in our mouth from the round side, and holding it with our fingers, leaving out the hole where we normally blow. Now we try to breathe in, allowing the air to enter only the hole in the balloon and keeping the outside of the balloon well sealed with our lips. We immediately realise that the balloon will inflate inside our mouth, the more we inhale, the more it will inflate and put pressure inside our mouth. 
What do we understand from this experiment? That if a small change in atmospheric pressure produces this, what can, for example, a negative pressure of 1.3×10 at -4 degrees Pascal in the atmosphere outside the Earth produce on the astronauts' suits? 
 

To understand what this measure represents, let's take another example, let's take the vacuum created by the hoover at home which is about 0.8 × 10 at 5 degrees Pascal, many of us have put our hand in it to feel the force with which we were sucked into the tube, well, if your hoover hose were to produce 1.3 × 10 at -4 degrees Pascal, which is the vacuum we have just outside our atmosphere, the hose, if it could ever manage not to get sucked in itself, would literally suck us off, your hand and maybe a lot more. 
 

The question arises, how do astronauts walk in space in their flexible suits? Their fabric, if it were not to burst, would inflate like a balloon and the force that would be produced would make it impossible for those inside the suit to bend an arm or a leg. 
 

Let's take another example, let's imagine the force of pressure, but this time in the positive. Let's imagine a diver diving in the sea, divers have completely different clothing, and they have a rigid suit with metal joints and pins, no fabric, and yet their exposure to positive pressure is very small compared to the negative pressure that astronauts are exposed to, and we see them walking around and folding their spacesuits made of fabric that doesn't inflate. 
 

To be clear, the only possible reason for the astronauts' fabric not to inflate is if the pressure outside the suit is equal to the pressure inside. But at this point a human being subjected to those negative pressures would not survive, just as in the depths of the seas.
If we then talk about the Moon, well, we are taught that down there, the force is even 1.3 × 10 at -6 degrees Pascal. 
 

Now let's understand vacuum and its effects by looking at how rockets work on a spacecraft. A rocket produces such a propulsive force that it is able to create an output force from the rockets that pushes the atmosphere behind it away, creating the thrust that makes it rise. Now, in a vacuum situation the rockets cannot propel anything, because in space there is no dense atmosphere like ours to force it up. 
To understand how dense our atmosphere is, let's imagine that we stick our hand out of a running car window and feel the force with which we have to counteract the air that would otherwise push our hand away. This happens because the air is dense, the air is full of matter, but in space this does not exist, a chemical rocket cannot exert thrust on the ship, because everything that comes out of the rocket would be sucked away instantly and dispersed in space. In fact, matter tends to take its place in the vacuum, diluting itself in it, it does not gather in the vacuum according to a principle of gravity, but let's stay on the subject of the vacuum, perhaps this will be material for another article. 
 

We can only think that in the vacuum of space, the spacecraft is only able to travel in it because it has been forced out of the atmosphere, and therefore maintains its inertial thrust even without rockets, but it could never steer the spacecraft, let alone slow down or even stop its race, because in the presence of a vacuum it can do nothing to counteract its flight. Any jets leaving the spacecraft would be sucked away immediately by the vacuum.

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