L10 - Rocket Performance & Staging

Question 1

What parameters describe a rocket?

Answer 1

• Mass ratio (R)
• Payload ratio (p)
• Propellant ratio (l)
• Structure ratio (s)

Question 2

What is the mass ratio?

Answer 2

Ratio of initial mass to burnout (final) mass.

Question 3

What is the payload ratio?

Answer 3

Ratio of payload mass to inital mass.

Question 4

What is the propellant ratio?

Answer 4

Ratio of propellant mass to initial mass.

Question 5

What is the structure ratio?

Answer 5

Ratio of structure mass to mass of structure + propellant.

Question 6

What is the benefit of staged rockets?

Answer 6

Today’s technology gives us a structure ratio of ~ 0.1 hence a single-stage rocket would not be able to deliver enough payload to space.

Multi-staging, vertically or horizontally, helps increasing the payload mass that can be delivered to space for a vehicle of the same size.

Question 7

What are the limitations of multi-stage rockets? (related to the number of stages)

Answer 7

Most launch vehicles have no more than 3 or 4 stages. The more stages are added, the more structural mass starts to dominate the overal rocket mass. Each additional stage adds less and less performance. By 5 or 6 stages, complexity and reduced reliability offset the improvements in performance.

Question 8

What is the difference between a stage and a subrocket?

Answer 8

• A stage is a complete propulsion unit that contains fuel tanks, structure, engine etc…
• A sub-rocket is a complete rocket comprised of one or more stages and a payload.

Question 9

What is the difference between vertical and horizontal staging?

Answer 9

• Vertical stages are mounted on top of eachother and remain disconnected until they are used. (only when at the bottom)
• Horizontal or parallel stages are mounted on the sides of the main stages, usually in the form of booster rockets. They are ignited at the main time as the main engines of the rocket proper.