Leaving Earth
To leave earth a space ship must fight against some problems, being those:
Gravitational force;
Friction;
Thermal issues;
Air pressure;
Speed in space;
Gravitational force
To surpass this problem powerful engines are used to boost the ship to the space. These engines use liquid hydrogen as fuel.
Hydrogen - a light and extremely powerful rocket propellant, has the lowest molecular weight of any known substance and burns with extreme intensity (5,500°F).
In combination with an oxidizer such as liquid oxygen, liquid hydrogen yields the highest specific impulse, or efficiency in relation to the amount of propellant consumed, of any known rocket propellant.
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Friction
On earth we have an atmosphere and due to that when a rocket try to go into the space, its affected by friction. Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other ( rocket and air, that is a fluid).
To fight this problem, the ships use aerodynamic concepts together with powerful engines, that allow the ship to leave earth atmosphere.
Thermal issues and air pressure
When the ship is leaving earth it is affected by the air pressure as a consequence of the high speed and the friction on the materials on the fuselage, that causes high temperatures and thus a ship must resist to forces and high temperatures.
To fight this challenges we need to choose the right materials, considering features such as weight savings, reusability, and operating in the space environment. Besides that, there are regulations that must be followed and manufacturing challenges.
The final solution we have found was innovations such as large composite payload bay doors, nondestructive materials evaluation, the super lightweight tank, and the understanding of hydrogen effects on materials.
Speed in space
On space there is no atmosphere and due to that the ship can not use the engines used to leave earth because it would be needed too much fuel. So, how can the ship gain speed in space?
The answer to this question is the use of the centripetal force effect.
​The centripetal force is the force that exists between one center fixed object and one second object that is orbiting around it. The centripetal force is what makes the second object always keep the same trajectory, because do not let it fly away, and due to this effect the object that is orbiting is always gaining speed.
The scientists use this effect and let the ship fly around the earth for months gaining speed, then with the help of the engines they release the ship from its trajectory what lets the ship travel on the space with high speeds.​