Rocket Science

In previous sections, equations of motion and Newton's laws were applied only to Terrestrial (on-Earth) examples. In this section, this will be expanded to include rocketry, both within and outwith the atmosphere.


History of Rocketry

Rockets are based on technology that dates back hundreds of years to the Song Dynasty in the 13th century CE China who used gunpowder in small rockets as weapons.

Modern rocketry began in the decade prior to World War Two, with the Germans, Russians and Americans all working independently researching rocket technology. During World War Two, it was German scientists who led the field, creating the V-2 Rocket, which was the world's first long-range Ballistic Missile.

By the end of the war, many German scientists had either defected or had been captured by the Allies, and their technology was used to push american rocket technology quickly forward.

The video below shows newsreel footage of the launch of a captured V-2 rocket in New Mexico, America:-

In the 1950's, the West and the Soviet Union entered a state of Cold War. Part of this revolved around both sides trying to outdo each other technologically, especially in terms of space flight.

The 'Space Race' was at first led by the Soviet Union, who put the first artificial satellite (Sputnik 1) into orbit in 1957, and then the first man into space (Yuri Gagarin) in 1961.

The video below shows newsreel of Yuri Gagarin's first space flight:-

In the years following this flight, the American's took the lead, ultimately winning the space race with the Apollo missions and Neil Armstrong walking on the Moon.

The video below shows a detailed look at the Apollo 11 mission to the Moon:-

Moon Landings - Truth or Conspiracy?

The video below shows a lecture entitled "Did we really land on the Moon?" by Martin Hendry MBE, Professor of Gravitational Astrophysics and Cosmology at the University of Glasgow:-

Physics of Rocketry

In previous sections, all the required Physics concepts have been covered. This is because there is no difference between Physics on Earth and Physics in space, or even Physics across the Universe.

The only difference that must be taken into account is the lack of air, or more usefully, the lack of air resistance.

In order to reach orbit, a spacecraft must 'overcome' gravity. But what does this mean?

In the above diagram, the two main forces to be taken into account are the Weight acting downwards, and the engine thrust acting upwards.

In order for the spacecraft to launch, an unbalanced force upwards is required to give an upwards acceleration (following Newton's second law).

Example 1 -

The Space Shuttle (mass = 1.8x106 kg) is launched using two solid rocket booster engines and three shuttle main engines. What is the acceleration experienced by the Space Shuttle at launch?

Engine thrust data:-

Solid rocket booster - 13.8x106 N

Shuttle main engine - 1859x103 N

Funbalanced = Fup - Fdown

Fup = ( ( 13.8x106 ) x 2 ) + ( ( 1859x103 ) x 3 )

Fup = 33.2x106 N

Fdown = m x g = 1.8x106 x 9.8

Fdown = 17.6x106 N

Funbalanced = 33.2x106 - 17.6x106

Funbalanced = 15.6x106 N

acceleration = Funbalanced / mass

a = 15.6x106 / 1.8x106

a = 8.7 ms-2 upwards

Note - In comparison, the maximum acceleration of a Bugatti Veyron is ~ 11.6ms-2.


Movement in Space

Once a spacecraft leaves the Earth's atmosphere, the method of controlling speed and direction becomes completely different. The major change, however, is that engines are required only for maneuvering, they are not required to maintain speed.

Newton's first law states:-

"An object will remain at rest or travel in a straight line at a constant speed, unless an unbalanced Force acts upon it."

In the atmosphere, a vehicle must have its engines active to provide thrust, overcoming the frictional forces which act to slow it down. Without the engine thrust, the vehicle would slow down, due to the unbalanced Force acting against motion, until its forward Velocity became zero.

Once outside the atmosphere, there is no air resistance acting to slow the craft down. So once out of the atmosphere, a spacecraft will travel at a constant Velocity in a straight line, without the need of engine thrust.