Aersp 401A Spacecraft Propulsion Subsystem

1. Aersp 401ASpacecraft Propulsion Subsystem (rocket science in 15 minutes)

2. Spacecraft Propulsion Subsystem • Uses of onboard propulsion systems • Orbit Transfer • LEO to GEO • LEO to Solar Orbit • Drag Makeup • Attitude Control • Orbit Maintenance

3. Spacecraft Propulsion Subsystem • Typical Mission Requirements • Orbit Transfer • Perigee Burn -- 2,400 m/s • Apogee Burn -- 1,500 - 1,800 m/s • Drag Makeup -- 60 - 1,500 m/s • Attitude Control -- 3 - 10% of total propellant • Orbit Maintenance • Orbit Correction -- 15 - 75 m/s (per year) • Stationkeeping -- 50 - 60 m/s

4. Spacecraft Propulsion Subsystem • Basics of Rocketry • Rocket -- Any propulsion system that carries its own reaction mass. • Δv = ueln(Minitial/Mfinal) • Δv is the spacecraft velocity change • ue is the rocket exhaust velocity • Minitial and Mfinal are the spacecraft mass before and after the rocket firing, respectively

5. Spacecraft Propulsion Subsystem • Basics of Rocketry • τ = (Δm/Δt)ue +(pe-pa)Ae • τ is the engine thrust • (Δm/Δt) is the mass flow rate of propellant • ue is the rocket exhaust velocity • pe and pa are the exhaust and ambient pressure, respectively • Ae is the nozzle exit area • Most thrust for a “perfectly expanded” nozzle

6. Spacecraft Propulsion Subsystem • Basics of Rocketry • ueq = ue + [(pe-pa)/(Δm/Δt)]Ae • ueq is the “equivalent exhaust velocity” • ueq = ue for a perfectly expanded nozzle • τ = (Δm/Δt)ueq • Isp = ueq/g • Specific impulse is a measure of thrust per propellant mass flow rate • g is always gravity at Earth’s surface, not local

7. Spacecraft Propulsion Subsystem • Chemical Rockets • Performance is energy limited • Propellant Selection • Maximum Performance • Density • Storage (i.e. cryogenic) • Heat transfer properties • Toxicity and corrosivity • Viscosity • Availability (cost)

8. Spacecraft Propulsion Subsystem • Chemical Rockets • Cold Gas Systems • pressurized gas flowing through a nozzle, no reaction • very low performance -- 30-70s Isp • very simple, inexpensive system • Monopropellant Liquid Systems • Single substance with a catalyst – hydrazine, hydrogen peroxide with metal catalysts -- silver, rhodium, platinum • physically simple system • 200-225s Isp

9. Spacecraft Propulsion Subsystem • Chemical Rockets • Bipropellant Liquid Systems • liquid fuel -- hydrocarbons, kerosene or alcohol based • liquid oxidizer -- oxygen, nitrogen tetroxide • more complex pumping/feed systems • better performance -- 300-450s Isp • Solid Propellants • Matrix of fuel and oxidizer • simple system • single burn, no throttling • moderate performance 275s Isp

10. Spacecraft Propulsion Subsystem • Electric Propulsion • Performance • Input Power = τIspg/(2η) • η is efficiency (Kinetic Energy/Input Power) • Electrothermal • Electrical energy is used to heat the propellant to high temperature, and then gas is expanded through a nozzle. • Resistojet • Ammonia, Water • ~300s Isp

11. Spacecraft Propulsion Subsystem • Electric Propulsion • Electrothermal (cont.) • Arcjet • Ammonia, Hydrazine • ~500-600s Isp • Electrostatic • Electrical energy is used to accelerate charged particles with a static electric field • Ion Engine • Xenon, Krypton • 2,500-10,000s Isp

12. Spacecraft Propulsion Subsystem • Electric Propulsion • Electromagnetic • Combination of steady or transient electric and magnetic fields used to accelerate charged particles • Pulsed plasma thruster • Teflon • 850-1200s Isp

13. Spacecraft Propulsion Subsystem • System Selection and Sizing (Table 17.2) 1) Determine propulsion functions -- table 17.1 2) Determine Δv and thrust levels needed -- sec. 7.3, sec. 10.3 3) Determine subsystem options -- ch. 17 4) Estimate Isp, thrust, mass, volume for each option 5) Establish baseline subsystem

14. Spacecraft Propulsion Subsystem • References • Hill and Peterson, Mechanics and Thermodynamics of Propulsion • Sutton, Rocket Propulsion Elements • Micci and Ketsdever, eds., Micropropulsion for Small Spacecraft. • Aersp 430, 530