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