Chapter 14: Rockets and Launch Vehicles Flashcards
What is impulse?
force during a certain time interval
What is specific impulse?
impulse that is used to compare performances of different types of rockets (efficiency) it is what he get for what we spend
How do you determine how much propellant you need for a rocket launch?
find the velocity change vs the amount of propellant used
What do you use to determine the velocity change?
the ideal rocket equation
∆V = Ispgln(initial mass/final mass)
How do rockets essentially ‘work’?
energy is transferred to propellant and then converted to exhaust
What are the two type of rockets?
- thermodynamic (heat and pressure)
2. electrodynamic (electric charge/magnetic fields)
How do nozzles work?
they convert thermal energy (produced by thermal, nuclear, or electrical sources) into kinetic energy through thermodynamic expansion
What are the assumptions when using the ideal gas law for fluid dynamics?
- no heat transfer (adiabatic flow)
- flow is reversible (energy is conserved) (isentropic flow)
- I dimensional flow, reactions occur in the chamber, steady flow
Specific energy is what?
the measure of total energy
Describe the venturi effect.
decrease in area = increase in velocity and pressure
works for LOW speed flows (high speed works opposite)
How does high speed flow work? What is it called?
increase in area = increase velocity and decrease pressure
Bernoulli’s principle
What are the two contributors to thrust?
- momentum (newtons laws)
2. pressure
What is an ideal nozzle?
when the exit pressure is equal to the atmospheric pressure
Given underexpanded, ideally expanded, and overexpanded nozzles, state the pressure differences and effects.
- under - Pexit > Patm, loss of energy, h not completely converted to KE
- ideally - Pexit = Patm
- over - Pexit<Patm, shock waves form, KE goes back to h
How do you increase Isp?
raise temperature, higher speed of sound
In rocketry, what is the molecular mass?
a measure of mass/molecule of propellant
In brief, how does a rocket engine work?
combustion chamber transfers energy to propellant, the nozzle converts small velocities to high enthalpy (combustion to higher velocity exhaust), the higher velocities = more thrust
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
increase in temp
increase in Isp Idsp, decrease in T
decrease in Isp, Idsp, dec T
increase in Isp decrease in Idsp and Temperature
What is plasma?
electrically neutral mixture of ions and free electrons
What are the 4 rocket propellants?
- cold gas (mechanical)
- chemical (chemical energy to produce heat)
- solar thermal (concentrates solar energy to produce heat)
- nuclear thermal (use heat from nuclear reactor)
What are the three subdivisions of chemical rockets?
- liquid
- solid
- hybrid
List the two types of liquid rockets.
- bipropellant - high Isp
2. monopropellant - low Isp, simple concept
Describe solid rockets.
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
Describe hybrid chemical rockets.
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
What are the two types of electrical rockets?
- ion(electrostatic) - uses electric fields to accelerate ions
- plasma thrusters - uses electric and magnetic fields to accelerate a plasma
What a re electrodynamic rockets?
plasma thrusters
- hall effect
- pulsed-plasma
What are some exotic propulsion methods
solar sails,
tethers
What is the general percent makeup of rocket mass?
5% payload
80% propellant
15% structures etc
What are some advantages to using staged rockets?
reduces total mass over a period of time
increases total payload mass
increases total velocity
