Chapter 14: Rockets and Launch Vehicles

Question 1

What is impulse?

Answer 1

force during a certain time interval

Question 2

What is specific impulse?

Answer 2

impulse that is used to compare performances of different types of rockets (efficiency) it is what he get for what we spend

Question 3

How do you determine how much propellant you need for a rocket launch?

Answer 3

find the velocity change vs the amount of propellant used

Question 4

What do you use to determine the velocity change?

Answer 4

the ideal rocket equation

∆V = Ispgln(initial mass/final mass)

Question 5

How do rockets essentially ‘work’?

Answer 5

energy is transferred to propellant and then converted to exhaust

Question 6

What are the two type of rockets?

Answer 6

1. thermodynamic (heat and pressure)

2. electrodynamic (electric charge/magnetic fields)

Question 7

How do nozzles work?

Answer 7

they convert thermal energy (produced by thermal, nuclear, or electrical sources) into kinetic energy through thermodynamic expansion

Question 8

What are the assumptions when using the ideal gas law for fluid dynamics?

Answer 8

1. no heat transfer (adiabatic flow)
2. flow is reversible (energy is conserved) (isentropic flow)
3. I dimensional flow, reactions occur in the chamber, steady flow

Question 9

Specific energy is what?

Answer 9

the measure of total energy

Question 10

Describe the venturi effect.

Answer 10

decrease in area = increase in velocity and pressure

works for LOW speed flows (high speed works opposite)

Question 11

How does high speed flow work? What is it called?

Answer 11

increase in area = increase velocity and decrease pressure

Bernoulli’s principle

Question 12

What are the two contributors to thrust?

Answer 12

1. momentum (newtons laws)

2. pressure

Question 13

What is an ideal nozzle?

Answer 13

when the exit pressure is equal to the atmospheric pressure

Question 14

Given underexpanded, ideally expanded, and overexpanded nozzles, state the pressure differences and effects.

Answer 14

1. under - Pexit > Patm, loss of energy, h not completely converted to KE
2. ideally - Pexit = Patm
3. over - Pexit<Patm, shock waves form, KE goes back to h

Question 15

How do you increase Isp?

Answer 15

raise temperature, higher speed of sound

Question 16

In rocketry, what is the molecular mass?

Answer 16

a measure of mass/molecule of propellant

Question 17

In brief, how does a rocket engine work?

Answer 17

combustion chamber transfers energy to propellant, the nozzle converts small velocities to high enthalpy (combustion to higher velocity exhaust), the higher velocities = more thrust

Question 18

Increase in chamber pressure = _________ temperature?
Increase in chamber temperature ___ Isp, Idsp, ___ in T?
decrease in efficiency ____ Isp, Idsp, ____T?
decrease in mass ____ Isp, ___ Idsp _______ temperature

Answer 18

increase in temp
increase in Isp Idsp, decrease in T
decrease in Isp, Idsp, dec T
increase in Isp decrease in Idsp and Temperature

Question 19

What is plasma?

Answer 19

electrically neutral mixture of ions and free electrons

Question 20

What are the 4 rocket propellants?

Answer 20

1. cold gas (mechanical)
2. chemical (chemical energy to produce heat)
3. solar thermal (concentrates solar energy to produce heat)
4. nuclear thermal (use heat from nuclear reactor)

Question 21

What are the three subdivisions of chemical rockets?

Answer 21

1. liquid
2. solid
3. hybrid

Question 22

List the two types of liquid rockets.

Answer 22

1. bipropellant - high Isp

2. monopropellant - low Isp, simple concept

Question 23

Describe solid rockets.

Answer 23

a. thrust depends on burn rate and burning surface area
b. the faster the burn, the greater the burning surface, the higher the mass flow rate
c. cannot stop a solid rocket burn

Question 24

Describe hybrid chemical rockets.

Answer 24

a. uses a liquid oxidizer and a solid fuel
b. similar to how a log burns in a fire, the log is the solid and the liquid is the oxygen. the more oxygen flow, the higher the log burns

Question 25

What are the two types of electrical rockets?

Answer 25

1. ion(electrostatic) - uses electric fields to accelerate ions
2. plasma thrusters - uses electric and magnetic fields to accelerate a plasma

Question 26

What a re electrodynamic rockets?

Answer 26

plasma thrusters

1. hall effect
2. pulsed-plasma

Question 27

What are some exotic propulsion methods

Answer 27

solar sails,

tethers

Question 28

What is the general percent makeup of rocket mass?

Answer 28

5% payload
80% propellant
15% structures etc

Question 29

What are some advantages to using staged rockets?

Answer 29

reduces total mass over a period of time
increases total payload mass
increases total velocity