Flashcards in Launchers and Propulsion Deck (36):
What is the principle of newtonian rocket propulsion?
Action/Reaction Momentum Transfer
What are the limits of Chemical rockets?
Chemical Rockets exhaust ejection velocity is intrinsically limited by the propellant-oxidizer reaction
How can you get a larger velocity increment of a spacecraft using chemical propulsion?
Larger ejected mass flow
Why are chemical rockets not always practical for certain missions?
Chemical rockets require an exceedingly large amount of propellant to be stored aboard.
How are electrical propulsions systems limited?
Energy available on board and mission constraints. No intrinsic limitation ot the sped to which the propellant can be accelerated.
What are the three basic types of electric propulsion thrusters?
Electrostatic, Electromagnetic, Electrothermal
Describe primary propulsion systems.
Primary propulsion systems are launch vehicles or the rockets used to get the spacecraft into orbit.
What are the thrust levels/duration for primary propulsion systems?
Thrust at about 60 x 10^4 kN with a burn time of about 100-500 seconds
Describe secondary propulsion systems.
Secondary propulsion systems are used for final orbit acquisition or spacecraft attitude and orbit control. Varying level of thrusts and burns.
What is required for Launch and Orbit insertion?
very high delta V, high thrust
What is required for Orbital transfers and plane changes?
High delta V, engine restart
What is required for GEO station keeping?
high total impulse, small I-bit
What is required for rendezvous and docking
Precise control, engine restart
What is required for Attitude control/orbit maintenance
Redundancy and precise control
What is required for Drag compensation?
Very precise control, high delta V
What is required for Constellation phasing?
What is required for Proximity manoeuvring?
What is required for Deorbit?
Now a requirement at end of life.
What is an ideally expanded nozzle?
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.
What is the difference between solid and liquid propulsion systems and performance?
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.
What is the difference between solid and liquid propellant?
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
Differentiate between pressure and pump fed rocket engines.
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.
What type of feeding do primary engines use?
What type of feeding do secondary engines use?
What is considered when choosing pump or pressure fed systems?
Pressure-fed has greater mass but is simpler.
What are the factors in selecting a launch vehicle?
-Operational location (Orbit)
How does serial or parallel rocket staging minimise loses?
Optimises thrust to weight ratio to minimise drag and gravity loses
Which direction to we launch objects into orbit and why?
We launch objects prograde (eastward) to benefit from the rotational velocity of the Earth (0.47 km/s at the equator)
How does the latitude of the launch site come into consideration?
The latitude of the launch site is approximately equal to the orbit inclination.
Why is a SSTO launch vehicle not currently possible?
Even with the most energetic propellant combinations currently available, the specific impulse is too low to offer a single stage to orbit capability.
Why is multi-staging needed to achieve moderate payload ratios?
-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
What are the general payload ratios?
What percentage of time are launch vehicles considered reliable?
high 90%'s reliability
Global launch rate is influenced by ___________ and ____________
Insurance premiums and launcher reliability
Commercial spacecraft insurance costs can be as high as ___________
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.