Me 599 Final Review

Front 1

What are three assumptions using the Rocket Equation (Ziolkowsky)?

Back 1

1.) no external forces (no drag, weightless space)
2.) inertial reference system
3.) thrust vector is parallel to the flight path

Front 2

What is the effective exhaust velocity?

Back 2

The average exhaust velocity in the axial direction.

Front 3

Describe the working principle of chemical thrusters.

Back 3

1.) Propellant must contain energy.
2.) There is an exothermal chemical reaction.
3.) Increase of propellant temperature.
4.) Expansion in nozzle.

Front 4

Describe the working principle of electric propulsion.

Back 4

1.) Propellant may be inert.
2.) Increase of propellant temperature.
3.) Expansion on nozzle (for electrothermal propulsion).
4.) Direct acceleration of ionized propellant through electric or magnetic fields (for electrostatic propulsion).

Front 5

What factors limit the net velocity change (delta-v) of chemical thrusters?

Back 5

Limited by the energy content (energy that the chemical reaction can deliver per kg mass).

Front 6

What factors limit the delta-v in electric propulsion?

Back 6

Can be limited by the amount of electrical energy which can be introduced into the propellant. However, achievable exhaust velocities strongly depend on the acceleration principle.

Front 7

What is the typical range that the maximum exhaust velocities of chemical thrusters fall between?

Back 7

4-5 km/s

Front 8

What are 3 basic acceleration principles with electrical energy?

Back 8

1.) Purely thermal
2.) Electrostatic
3.) Electromagnetic

Front 9

Define specific impulse.

Back 9

This is the mass efficiency. It is a figure of merit relating the thrust generated by the accelerated propellant to the amount of propellant used.

Front 10

What are 5 general selection rules when it comes to propellants?

Back 10

1.) Propellant must not react with the thruster material.
2.) Contamination of spacecraft surfaces (solar cells) must be prevented.
3.) Propellant should be easy to store and heave.
4.) Should not be too expensive and available in sufficient quantities.
5.) High exhaust velocities should be achievable.

Front 11

What are propellant considerations for resistojets?

Back 11

Propellants should be in gas state in the temperature range of concern, and do not destroy the thruster.

Front 12

What are propellant considerations for arc-jets?

Back 12

All gaseous propellants which don't destroy the electrodes (H2, NH3, N2H4).

Front 13

What are propellant considerations for electrothermal thrusters?

Back 13

Should be light as possible.

Front 14

What are propellant considerations for magnetoplasmadynamic thrusters?

Back 14

Should be easy to ionize (single ionization).

Front 15

What are propellant considerations for electrostatic and Hall effect thrusters?

Back 15

Heavy ions.

Front 16

What are propellant considerations for gridded ion / Hall / SPT thrusters?

Back 16

Noble gases, mostly Xenon.

Front 17

What are propellant considerations for field emission thrusters?

Back 17

Easy to vaporize metals.

Front 18

Is electric propulsion applicable to launch a spacecraft from Earth's surface?

Back 18

No, a nuclear reactor would be needed. Chemical rockets are used.

Front 19

What are three categories of electric propulsion?

Back 19

1.) Electrothermal
2.) Electrostatic
3.) Electromagnetic

Front 20

What happens in an electrothermal thruster? What are 2 examples?

Back 20

Electrical heating and nozzle expansion accelerates the propellant.

1.) resistojets
2.) arcjets

Front 21

What happens in an electrostatic thruster? What are 2 examples?

Back 21

Electric field accelerates an ionized propellant.

1.) Hall thrusters
2.) ion engines

Front 22

What happens in electromagnetic thrusters? What are 3 examples?

Back 22

jxB force accelerates an ionized propellant.

1.) MagnetoPlasmaDynamic thruster (MDP)
2.) Pulsed Inductive thruster (PIT)
3.) Pulsed Plasma thruster (PPT)

Front 23

Draw a simple diagram of a resistojet.

Back 23

Front 24

Draw a simple diagram of an arcjet.

Back 24

Front 25

Draw a simple diagram of an ion engine.

Back 25

Front 26

Draw a simple diagram of a hall thruster.

Back 26

Front 27

Draw a simple diagram of an MPD.

Back 27

Front 28

Draw a simple diagram of a PPT.

Back 28

Front 29

What are the ranges of Isps for:

1.) Resistojets
2.) Arcjets
3.) Ion engines
4.) Hall thrusters
5.) MPDs
6.) PPTs

Back 29

1.) 300s (hydrazine), 600s (hydrogen)
2.) 5-600s (hydrazine), 1000s (hydrogen)
3.) 3000-5000s
4.) 1000-3000s
5.) 2000-6000s
6.) 300-3000s

Front 30

What is the working principle of resistojets?

Back 30

1.) Increase of propellant enthalpy through flowing over a Joule heated resistance.
2.) Expansion in a Laval nozzle.

This transforms thermals energy to kinetic energy.

Front 31

How is the propellant in a resitojet heated?

Back 31

Convectively

Front 32

What are 5 different design variations to the resistance part of a resistojet?

Back 32

Front 33

What are 2 types of discharge-drive thrusters?

Back 33

1.) Arc-jets
2.) Magnetoplasmadynamic thrusters (MPDs)

Front 34

What is the working principle of arc-jets?

Back 34

Joule heating through the discharge produces high average propellant temperatures.

Front 35

What is the main acceleration process of arc-jets?

Back 35

Thermal expansion on the nozzle.

Front 36

What is the main acceleration process in MPDs?

Back 36

Magnetic forces pushing ionized plasma.

Thermal expansion as secondary process.

Front 37

Where are the most losses in arc-jets?

Back 37

Frozen flow losses. 40-60%

Front 38

What are limiting factors of an arc-jet?

Back 38

1.) Erosion and sublimation of cathode tip.
2.) Erosion of the anode.
3.) Clogging of the injector.

Front 39

What is the working principle of electrostatic thrusters (ion thrusters)?

Back 39

Acceleration of positively charged ions through electric fields.

Front 40

What are the main differences in Kaufmann thrusters and radiofrequency ion thrusters?

Back 40

The main difference is the way in which the plasma is generated:

1.)Kauf - generated through electron collision by an arc discharge from the cathode to the anode.

2.) RIT - ions generated through electrodelss high frequency discharges.

Front 41

What is the main benefit of the deceleration grid?

Back 41

There is a chance of the electrons injected by the neutralizers migrating upstream past the acceleration grid.

If this occurs, the electrons will accelerate toward the ion source. This will damage the ion source and disturb the emission process.

The deceleration grid will:

1.) provide restrain of upstream electron migration
2.) control ion exhaust speed

Front 42

What are the main components of a 3 gridded ion thruster? (Draw)

Draw its potential along the thruster axis.

Back 42

Front 43

What are the main components of gridded ion thrusters and what are their functions?

Back 43

1.) plasma source - sustains emission of ions at current density corresponding to space-charge limited flow at the desired voltage over the given gap

2.) acceleration grid - creates an acceleration field since this grid is negatively charged.

3.) extraction grid - ions arrive at this grid from the plasma source through diffusion.

4.) neutralizer - steady stream of electrons equal to the number passing ions are injected, neutralizing the ion beam.

Front 44

In ion thrusters, where is the highest erosion on the grid usually found?

Back 44

Typically around half the grid radius.

Front 45

What is the working principle of field emission thrusters (FEEPs)?

Back 45

Ions are extracted directly from the surface of a liquid metal through application of high voltages. An electric field is generated, causing the formation of Taylor cones at the surface. Spontaneous ionization at the cone tips in conjunction with the accelerators propel the ions.

Front 46

What is the working principle of colloid thrusters?

Back 46

Propellant droplets are ionized in a high electric field and accelerated.

Front 47

Describe the space charge limitation in ion thrusters.

Back 47

Similarly charged particles (ions) repel each other due to Coulomb interactions. Given an acceleration voltage (U) and an acceleration length (d), only a limited ion current can be transported through a cross section (A).

Front 48

What are Kepler's 3 Laws?

Back 48

1.) Law of Planetary Motion - the orbit of every planet is an ellipse with the Sun at one of the two foci.

2.) A line joining a planet and the sun sweeps out equal areas during equal intervals of time.

3.) The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit.

Front 49

Draw a diagram of the Hohmann Transfer.

Back 49

Front 50

What are typically used for sail materials?

Back 50

Foils consisting of three layers:

1.) Front coating (good reflectivity)
2.) Core foil (mechanical stability)
3.) Rear side coating (high emissivity)

Front 51

Define plasma.

Back 51

Mixture of free elections (negative charge), positive ions, and neutrals in different states of energetic excitation.

Front 52

Describe the working principle of a Hall Effect Thruster (HET).

Back 52

The essential working principle of the Hall thruster is that it uses an electrostatic potential to accelerate ions up to high speeds. In a Hall thruster the attractive negative charge is provided by an electron plasma at the open end of the thruster instead of a grid. A radial magnetic field of a hundred gauss (about 100–300 G, 0.01–0.03 T) is used to confine the electrons, where the combination of the radial magnetic field and axial electric field cause the electrons to drift azimuthally, forming the Hall current from which the device gets its name.

1.) Discharge channel with anode and propellant injection.
2.) Hollow cathode/neutralizer.
3.) Magnetic field generator (coils and/or permanent magnets).

a.) Electric field in axial direction.
b.) Magnetic field in radial direction in the discharge channel.

I.) Electron motion in circumference direction inside the discharge channel (Hall current).
II.) Ion motion inside the discharge channel in axial direction.

Front 53

Describe the principle of a Stationary Plasma Thruster (SPT).

Back 53

- insulating discharge channel walls
- magnetic fields prevents electrons from flowing directly to anode
- axial E field between anode and cathode plasma at the discharge channel exit
-electrons in the ExB region ionize the propellant which is injected through the anode
- ions are generated

Front 54

Describe the principle of a Thruster with Anode Layer (TAL).

Back 54

- discharge channel not isolated
-similar ion generation and acceleration in SPT
- anode in a region with high magnetic fields