by Jeanette CainMore articles in Rockets
The Earth - July 20, 1969. The first human space visitors, 3 Apollo astronauts, made history by visiting another planet in our galaxy. The rocket's name, Saturn V. It used 3 tons of kerosene every second for the first 120 seconds, and lift off thrust was equivalent to 32 Boeing 747's on takeoff. How was this feat accomplished? The laws of physics-Newton's 3 laws of motion:
1. Objects remain at rest, or they travel in straight lines unless acted upon by some force.
2. An object's acceleration is equal to the overall force that acts upon it and divided by its mass.
3. For every action there is an equal and opposite reaction.
If a bullet were fired horizontally from a gun, gravity would pull it vertically toward the Earth. If the bullet were fired with enough horizontal force, reaching the ground would be impossible since it would be sent into orbit. To rise above the atmosphere and release satellites, launch vehicles need enough horizontal force to stay in orbit. In satellites, Newton's first law is satisfied by the force of gravity and the horizontal force of the launch vehicle. An object's mass is the measure of how much matter it is made from, and mass is the same everywhere. An object's weight comes from the force of gravity acting on the mass of the object.
For rockets, Newton's second law is satisfied by 2 main forces: thrust and downward gravity. For a launcher to work it will need enough thrust to not only lift its own mass, but also to overcome gravity. Mass and the pull of gravity decrease with increased distant from the Earth.
Newton's third law is the action that occurs from the release of high-pressure gas from combustion. This produces a reaction that gives a lift off. Thrust is achieved from the burning of fuel in the combustion chamber of the launcher. Should the chamber become sealed, it would explode. The build-up of gases is released through a nozzle, but unable to escape upward. Gases put into action a force, which is a reaction, that is equal and opposite to the force, which is an action, of exhaust escape.
Almost half of the world's large commercial sites are launched with Ariane 5. Thrust at lift off is achieved from the main engine and 2 boosters. Together, they create a thrust that is equal to about 1,300 tons, but on the ground the rocket has a total mass of 800 tons. The launcher requires the extra 500 tons to provide enough thrust for lift off. Boosters are emptied of fuel in about 2 minutes and become discards. Afterwards, the main engine burns out and falls away. For the satellite to be sent into orbit, it needs to be released by a small engine. Ariane has the capability of launching multiple satellites, whose numbers will depend on the weight of the satellites when on the ground and what will be needed for the orbit into which they are to be placed.
Payload is the name for the cargo that is carried on a launcher. A few tons of payload will need great combustion and powerful forces to attain lift-off from the Earth's surface. Payload amounts vary in size, and are either upper payloads or lower payloads. To escape gravity, a launcher will need to give a satellite enough horizontal force to reach 7.8 km/s at an altitude of 200 km. Any satellite reaching just over 11 km/s would escape Earth's gravitational force and be sent into space, which speed is called the escape velocity.
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