Launchers and Propulsion

Question 0

What are the limits of Chemical rockets?

Answer 0

Chemical Rockets exhaust ejection velocity is intrinsically limited by the propellant-oxidizer reaction

Question 1

What is the principle of newtonian rocket propulsion?

Answer 1

Action/Reaction Momentum Transfer

Question 2

How can you get a larger velocity increment of a spacecraft using chemical propulsion?

Answer 2

Larger ejected mass flow

Question 3

Why are chemical rockets not always practical for certain missions?

Answer 3

Chemical rockets require an exceedingly large amount of propellant to be stored aboard.

Question 4

How are electrical propulsions systems limited?

Answer 4

Energy available on board and mission constraints. No intrinsic limitation ot the sped to which the propellant can be accelerated.

Question 5

What are the three basic types of electric propulsion thrusters?

Answer 5

Electrostatic, Electromagnetic, Electrothermal

Question 6

Describe primary propulsion systems.

Answer 6

Primary propulsion systems are launch vehicles or the rockets used to get the spacecraft into orbit.

Question 7

What are the thrust levels/duration for primary propulsion systems?

Answer 7

Thrust at about 60 x 10^4 kN with a burn time of about 100-500 seconds

Question 8

Describe secondary propulsion systems.

Answer 8

Secondary propulsion systems are used for final orbit acquisition or spacecraft attitude and orbit control. Varying level of thrusts and burns.

Question 9

What is required for Launch and Orbit insertion?

Answer 9

very high delta V, high thrust

Question 10

What is required for Orbital transfers and plane changes?

Answer 10

High delta V, engine restart

Question 11

What is required for GEO station keeping?

Answer 11

high total impulse, small I-bit

Question 12

What is required for rendezvous and docking

Answer 12

Precise control, engine restart

Question 13

What is required for Attitude control/orbit maintenance

Answer 13

Redundancy and precise control

Question 14

What is required for Drag compensation?

Answer 14

Very precise control, high delta V

Question 15

What is required for Constellation phasing?

Answer 15

Small I-bit

Question 16

What is required for Proximity manoeuvring?

Answer 16

Small I-bit

Question 17

What is required for Deorbit?

Answer 17

Now a requirement at end of life.

Question 18

What is an ideally expanded nozzle?

Answer 18

Expansion is ideal with Pe=Patm and the nozzle flow is said to be ideally expanded. It maximizes thrust but assumes that nozzle length can be as long as required. In reality it’s limited by weight.

Question 19

What is the difference between solid and liquid propulsion systems and performance?

Answer 19

Solid has a comparatively simple design. No separate propellant storage, feed system, or combustion chamber. Solid has a fixed time-thrust curve determined by the geometry of the fuel grain.

Liquid rocket can vary thrust and has start-stop capabilities.

Question 20

What is the difference between solid and liquid propellant?

Answer 20

Liquid propellants have a higher Isp with a high combustion temperature and a low molar mass of products.

They are storable, hypergolic(if bi-propellant), high density, low toxicity

Thrust curve.

Question 21

Differentiate between pressure and pump fed rocket engines.

Answer 21

Pressure fed rocket engines have two high pressure reservoirs used to push oxidizer and fuel into the thrust chamber. Pump fed rocket engines have two pumps powered by a turbine that is powered by a gas generator.

Question 22

What type of feeding do primary engines use?

Answer 22

Pump-fed

Question 23

What type of feeding do secondary engines use?

Answer 23

Pressure-fed

Question 24

What is considered when choosing pump or pressure fed systems?

Answer 24

Pressure-fed has greater mass but is simpler.

Question 25

What are the factors in selecting a launch vehicle?

Answer 25

- Payload Mass - Payload Dimensions - Operational location (Orbit) - Launch Date - Cost - National Origin - Launcher Reliability

Question 26

How does serial or parallel rocket staging minimise loses?

Answer 26

Optimises thrust to weight ratio to minimise drag and gravity loses

Question 27

Which direction to we launch objects into orbit and why?

Answer 27

We launch objects prograde (eastward) to benefit from the rotational velocity of the Earth (0.47 km/s at the equator)

Question 28

How does the latitude of the launch site come into consideration?

Answer 28

The latitude of the launch site is approximately equal to the orbit inclination.

Question 29

Why is a SSTO launch vehicle not currently possible?

Answer 29

Even with the most energetic propellant combinations currently available, the specific impulse is too low to offer a single stage to orbit capability.

Question 30

Why is multi-staging needed to achieve moderate payload ratios?

Answer 30

- Empty propellant tanks and their associated propulsion systems are jettisioned - Overall vehicle mass is reduced - Less thrust required to accelerate vehicle - Less propellant required to achieve orbital velocity - Greater payload capability

Question 31

What are the general payload ratios?

Answer 31

2-4% payload

Question 32

What percentage of time are launch vehicles considered reliable?

Answer 32

high 90%'s reliability

Question 33

Global launch rate is influenced by ___________ and ____________

Answer 33

Insurance premiums and launcher reliability

Question 34

Commercial spacecraft insurance costs can be as high as ___________

Answer 34

18-22% of the total project costs. Depending on the size of the placement and capacity of the market, premiums can run even higher, with some reaching 28 percent to 33 percent.

Question 35

Launcher reliability is a major factor in _____________

Answer 35

Insurance Premiums