0531 ISDPメモ
Mission Elements: Propulsion
Requirements
- Delta-V Budget: Based on trajectory
- Performance:
- Thrust
- Specific Impulse
- Operational:
- Restart
- Control
- Throttling
- Gimballing: Change the directions of thrust vector -- attitude control
- Redundancy
- position of the thrusters is important
- Constraints
- Mass/ size (propellant margin: 5% - 20%)
- Power (Electric Propulsion)
- Environment (Temperature, Acceleration, Vibration)
- Structural loads on rocket
- Any combustion reaction generates heat
Components: Chemical Rockets
Liquid rockets
- High Thrust
- Active Control
- Intermediate Isp
- Complex
Solid Rockets
- Simple
- High Thrust
- Low Isp
- Combustion of oxidizer/fuel and other bonds create heavier molecules difficult to accelerate
- No Active Control
Hybrid Rockets
- High Thrust
- Active Control
- Safing Capability
- fuel coal apart from oxidizer -> less chance of explosion
- intermediate Isp
Cold Gas Thrusters
- Simple
- Good Reliability
- Low Thrust
- Low Isp
Liquid Rocket Power Cycles
Pressure-fed
- propellants are stored at high pressures
- Simple
- Requires strong (i.e. heavy) propellant tanks
Gas Generator
- Use a preburner + turbine to generate power, drive propellant pumps
- Powerful
- Wastes propellant (preburner exhaust)
- good Reliability
Expander:
- User propellants to cool the nozzle, then use the heated propellant to power a turbine, drive propellant pumps
- Efficient
- Self-contained
- Only works with certain propellants (near the triple point)
Staged combustion
- Use a preburner + turbine to generate power, drive propellant pumps
- Direct preburner exhaust into thrust chamber
- powerful & efficient
- complex
Electric
- Use electric motors to drive propellant pumps
- Simple
- Requires electrical power
Components: Electric Propulsion
High Isp, Low Thrust
Ion Thruster
- Ionize neutral gas
- Use electrostatic force (charged grids or plasma) to accelerate ions
- electrons fired into gas -> ionized gas
- positive ions are accelerated at very high speed
- there's no ground in space -> spacecraft gets negatively charged -> release some electrons in exhaust gas from neutralizing electron gun
Arcjet/Resistojet
- Use Electrical energy to heat propellant
- Convert internal energy to kinetic with a nozzle
- generally not very efficient
Plasma Propulsion
- Accelerate ionized plasma using an induced electromagnetic field
- require large amounts of power -> small amount of thrust
Laser Propulsion/Photonic Rocket
- Photonic pressure
- May require external source
- require large amounts of power -> small amount of thrust
Solar Sail
Infinite Isp, Very Low Thrust