Page 8 - Curriculum Visions Dynamic Book

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Controlling the projectile
In the arrow and the firework we have the science needed to get people to the Moon and beyond. We know that we need some propellant to make the projectile—that
is what any rocket is—move very quickly. It is always counteracted by the Earthbound force of gravity.
So to leave the Earth and get into space, the propellant has to produce more thrust than the force of gravity
for long enough to get the rocket and its cargo, such as a satellite or a manned spacecraft—called the payload— to beyond the gravitational pull of the Earth.
Most of this time the rocket is moving through an atmosphere of gases that are constantly applying friction (drag) to its surface. Anything moving fast through the
air will heat up because of this surface friction. The buildup of heat in a spacecraft may reach dangerous levels, especially on reentry into the Earth’s atmosphere.
So, first and foremost the rocket needs to be streamlined and well protected against frictional heating. But it also has to be strong to hold the weight of the fuel inside. Also, as the spacecraft goes up, the air pressure on the casing gets less, causing the casing to tend to burst apart.
The rocket also needs some way of controlling the rate at which the propellant is used up. Then it needs some means of steering. And finally, it needs a means of getting back safely to the Earth’s surface, so that it doesn’t just smash up as it returns.
 If a projectile is thrown with
a low velocity, it will soon fall
to the ground. As the velocity
is increased, it will go farther before it falls. At a great enough velocity it will go into orbit ().
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