rockets

Question 1

Why may liquid rocket motors be preferable to solid rocket motors.

Answer 1

Liquid rocket motors can be throttled and turned on or off at the pilots discression. This is in contrast to solid rocket motors which, when activated, will only turn off once the propellant has run out.

However, liquid propellants are heavier and more complex than solid rocket propellants.

Question 2

Describe the three main categories of solid propellants used in rocket fuel.

Answer 2

1.Double based or homogenous propellants, where the molecule contains both fuel and oxidiser. These are highly explosive ingredients consisting of nitrocellulose and nitroglycerine, and they function as fuel, oxidiser, and binder.

2.Composite or heterogeneous propellants, made up of crystalline oxidisers (such as ammonium perchlorate) and powdered fuel (such as aluminium) dispersed in a hydrocarbon binder, which may also serve as a fuel. The resulting mixture can be cast into any shape. This must then be cured which leads to polymerisation of the binder. This propellant is less hazardous to handle than the double based mixture.

3.Composite double based propellant, which is a combination of the types above containing oxidiser and powdered aluminium in a matrix of double based propellant.

Question 3

What are the four main components of a solid rocket motor?

Answer 3

1.The combustion chamber, which stores and contains propellant during high pressure burning

2.The igniter which starts the propellant burning

3.The solid propellant, which burns and produces gases for propulsion

4.The nozzle, which expands the combustion product gases to high velocity, thus generating thrust

Question 4

What loads would the walls of the combustion chamber be required to withstand?

Answer 4

• Pressure Load during combustion
• Thermal stresses from high temperature combustion and possible aerodynamic heating
• Dynamic loads during launch and flight manoeuvres
• Clustering and Staging loads

Question 5

What is the difference between thrust, T, at the design condition and maximum thrust of a rocket?

Answer 5

Maximum thrust of the rocket only occurs in a vacuum when Pa = 0.

While generating maximum thrust in outer space (pa = 0), rocket engines also operate at optimum thrust only if pe = 0 as well. However, this requires an infinitely large nozzle area expansion (Ae/A* = ∞), which is not realistic.

Question 6

Describe, using diagrams if required, what is meant by progressive, neutral and regressive burning in a rocket motor. Sketch potential propellent geometries for progressive, neutral and regressive burning.

Answer 6

See Slide 436 on the Mega PDF

Question 7

Derive the Tsiolkovsky relation for rockets by considering the force balance equation for purely vertical ascent

T-W-D = M(dV/dt)

where T is the thrust (= 𝑚̇ c), W the weight, D the air drag, M the rocket mass, and dV/dt the acceleration of the rocket

Answer 7

https://app.box.com/s/zrhyh546jdezkzpn8ydytnyht5tunn6t/file/476130785521

Q2 part c

V = Ispgln(M0/M)