What Are Rocket Aerodynamics?

Ray Hawk

Rocket aerodynamics are the forces expressed on a rocket body in atmospheric flight, and usually include rocket drag, rocket propulsion, or rocket thrust; the rocket's weight; and its aerodynamic lift based on the shape of the body. Aerodynamic forces in regards to rocketry must also take into account ballistics, which is the general effect of gravity on a rocket as it heads in a vertical direction away from the surface of the earth and returns.

The sides of a booster or staged rocket are designed to offer little air resistance.
The sides of a booster or staged rocket are designed to offer little air resistance.

The history of rocketry can be traced back to at least 1045 AD. At this time, the Chinese were already using them as a form of military device. Basic rocket aerodynamics, therefore, tends to have a much broader level of understanding worldwide than aircraft aerodynamics does.

Aerodynamics act on any body that is moving through the air and exhibits two primary qualities: force and vector, or direction. The direct rocket aerodynamics acting on the vehicle body are drag and lift, where drag is the resisting force of the air that the rocket must push through, and is seen to act in direct opposition to the direction the rocket is traveling. Lift acts perpendicular to the motion of the rocket, or at a right angle to the horizon, and its magnitude depends on the shape of the rocket body, and the density of the air it is passing through.

Forces such as lift and drag are only relevant if the rocket is moving compared to that of another body. Examples of such bodies include the earth and operating within the atmosphere. Full-size rockets that quickly rise into space are not affected by lift and drag forces once outside earth's atmosphere.

Lift and drag elements of rocket aerodynamics are also directly affected by the vector of the rocket, or its angle of ascent compared to the surface of the earth. Vector forces come into more direct play in terms of a rocket's weight and thrust compared to its angle of ascent. The more thrust a rocket can generate as directly compared to its weight, the farther it can rise from the earth's surface before running out of fuel.

This component of rocket aerodynamics is often referred to as delta v, and is calculated as a pure figure in the absence of drag caused by the atmosphere and gravitational acceleration that pulls the rocket downwards. The rocket propulsion required for a vehicle to obtain orbit is known as escape velocity. For earth, it is a speed of about 25,000 miles per hour (40,233 kilometers per hour), or 5,300 miles per hour (8,530 kilometers per hour) on the surface of the moon.

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