Rockets11.28 - Understand that a space probe must reach the Earth’s escape velocity, the energy requirements of which can be met only by the use of rockets
9.4 - Understand that a spacecraft traveling to the Moon must reach the Earth’s escape velocity, the energy requirements of which can be met only by the use of rockets
A rocket needs to reach a certain speed to break free of Earth’s gravity. This amount is 11.2 km per second (7 miles a second) and is known as Earth’s Escape Velocity. If it fails to reach this speed the rocket will stay well within Earth’s gravity and probably crash.
It takes an enormous force for a rocket to achieve this speed. To do it rerquires a controlled explosion where the rocket is filled with liquid propellant usually Liquid Oxygen or Nitrogen. It is easier to control liquid propellant rather than solid propellant. A rocket also consists of smaller rockets that are called stages. The Space Shuttle uses three rockets to get into space. To reach the Moon NASA used the Saturn V rockets which were the largest built.
Fly-by for speed increase
Spacecraft can gain speed by using the gravity of Planets and Satellites to propel themselves, change their trajectory (direction) and increase speed.
New Horizons performed a fly-by of Jupiter on it's way to Pluto. While it was an opportunity to test its systems and to take measurements and to send back images, it was primarily used to speed up the spacecraft. The Galileo spacecraft orbited Earth and Venus several times to gain enough speed to get to Jupiter. This is known as the slingshot or gravitational assist.