1. Class 4: Fundamentals of Rocket Propulsion
Marat Kulakhmetov

2. Did Buzz Aldrin punch a reporter?

3. Gases
Gas is made up of molecules that fly in random directions
Molecules collide with other molecules and with the walls

4. Temperature Temperature describes how fast the molecules move
At higher temperature, molecules move faster
At room temperature air molecules move at 500m/s ( mi/h)

5. Pressure
How much momentum gases transfer to the surface
How often and how fast the molecules hit the surface

6. Density
How much stuff is in a volume
Solids are high density
Gases are low density

7. Ideal Gas Law
Temperature, Pressure, Density describe what molecules do so they have to be related.
P = Pressure
ρ = Density
R = Gas constant
T = Temperature

8. Thrust
Most vehicles need to overcome weight and drag by generating thrust
There are many ways of generating thrust:
Internal Combustion Engines
Usually found in cars
They are small but require an oxygen supply
Jet Engines
Usually found on fast airplanes
They can generate a lot of thrust but they still need an oxygen supply
Rocket Engines
These generate enough thrust to escape Earth’s gravity and often carry their own oxidizer so they work in space

9. 4 Stroke Internal Combustion Engine
Use gas expansion to rotate the cam shaft
The cam shaft turns the wheel or propeller and makes cars or airplanes go forward
There is no ground or air in space, rockets cant use this

10. Jet Engine Compressor Bypass Fan Combustor Turbine Compresses air
Accelerates Air
Combustor
Burns air
Turbine
Powers compressor and Bypass Fan
Needs Air
Max Speed: 3000 mi/h

11. Thrust Typically, rocket engines produce two types of thrust:
Pressure Thrust
Generate higher pressure behind the rocket
= (Pe-Pa)*A
Jet Thrust
Pushes the rocket forward by throwing gasses out of the back
= mdot Ve
Total Thrust = Pressure Thrust + Jet Thrust
Thrust produced depends on fuel, rocket nozzle, rocket altitude, etc.

12. Pressure Forces Air wants to go from high pressure to low pressure
Pressure Force ( P1 – P2) * A
Remember that Pressure = Force / Area

13. Momentum Forces Action-Reaction
If you throw something out one way it will push you the other way
If the rocket nozzle throws gases down, the gasses push the rocket up

14. Rocket Nozzles
Nozzles push on high gasses and accelerate them out the back
In return, the gasses push on the nozzle and accelerates it forward

15. Control Volume
It is usually easy to study gas flows using control volumes
Forces on the rocket could be calculated by only looking at control surfaces
Fpressure =(Pe - Pa ) Ae
Fgas = ρ Ue2 Ae

16. Isentropic Nozzles
Rockets usually use converging-diverging nozzles. These could also be called isentropic nozzles
The thrust through the C-D nozzle depends on chamber pressure, ambient pressure, and nozzle shape

17. Converging Section
Upstream of the nozzle, in the combustion chamber, the gas velocity is small
All fluids (water, air, etc.) accelerate through a converging section
The fastest they could get in the converging section is Mach 1

18. Diverging Section
If the gases reached Mach 1 in converging section then they will continue accelerating in the diverging section
If the gasses did not reach Mach 1 in the converging section then they will decelerate in the diverging section
This is why our water bottle rockets only had converging section

19. Over and Under Expanded Gasses
Perfectly Expanded
Over Exanded
Separated
Performance of the nozzle depends on outside pressure
Outside Pressure changes with altitude
Over and Under expanded gasses are not as efficient

20. Lets Calculate Rocket Thrust and acceleration
Ambient Conditions:
Pa = 101,000 Pa
Exit Conditions:
Pe = 150,000 Pa
Ve = 100 m/s
Density = 1.2 kg/m3
Example
Area = 0.05 m^2
Mass = 0.5 kg
Lets Calculate Rocket Thrust and acceleration
A = F/m = 3050 / 0.5 = 6100 m/s^2

21. Water Bottle Rocket Debriefing
Why did rockets filled with water go higher than those filled with just air?
Changes
Exit
Pressure
Constant
Ambient Pressure
Constant
Exit Velocity Assumed
Constant
Air Density = 1.2 kg/m^3
Water Density = 1000 kg/m^3

22. ISP ISP is used to classify how well a rocket performs
Low ISP = need a lot of fuel to achieve thrust
High ISP =do not need as much fuel to achieve same thrust

23. Types of Rocket Engines
Pressurized Air
Solid Propellant
Liquid Propellant
Nuclear
Electric

24. Compressed Air
Compressed air leaves out of the back of the rocket
The air pushes the rocket forward

25. Solid Propellant
Propellant is initially in the solid state and it becomes a hot gas during combustion
Pros:
Simple
Cheap
Easy to store
Can be launched quickly
Cons:
ISP only
Cannot turn off after ignition
Cannot throttle during flight

26. Fuel and Oxidizer are both stored separately in liquid form
Liquid Propellant
Fuel and Oxidizer are both stored separately in liquid form
Pros:
Better performance (ISP )
Cons:
More complex
Requires pumps or pressurized gas tanks
Heavier

27. Nuclear
Nuclear Reactor heats working gas that is accelerated through a nozzle
Pros:
Isp
Cons:
Requires shielding, can be heavy
It’s a NUKE

28. Electric Two types: Arcjet: Electricity is used to superheat the gases
Ion Thrusters: ionized (charged) atoms are accelerated through an electro-magnetic field
Pros:
ISP ,000
Cons:
Thrust usually <1N
VASIMR

29. Video