Aersp 401A Spacecraft Propulsion Subsystem

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Aersp 401ASpacecraft Propulsion Subsystem

• (rocket science in 15 minutes)

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Spacecraft Propulsion Subsystem

• Uses of onboard propulsion systems
• Orbit Transfer
• LEO to GEO
• LEO to Solar Orbit
• Drag Makeup
• Attitude Control
• Orbit Maintenance

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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

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Spacecraft Propulsion Subsystem

• Basics of Rocketry
• Rocket -- Any propulsion system that carries its
  own reaction mass.
• ?v ueln(Minitial/Mfinal)
• ?v 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

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Spacecraft Propulsion Subsystem

• Basics of Rocketry
• t (?m/?t)ue (pe-pa)Ae
• t is the engine thrust
• (?m/?t) 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

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Spacecraft Propulsion Subsystem

• Basics of Rocketry
• ueq ue (pe-pa)/(?m/?t)Ae
• ueq is the equivalent exhaust velocity
• ueq ue for a perfectly expanded nozzle
• t (?m/?t)ueq
• Isp ueq/g
• Specific impulse is a measure of thrust per
  propellant mass flow rate
• g is always gravity at Earths surface, not local

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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)

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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

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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

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Spacecraft Propulsion Subsystem

• Electric Propulsion
• Performance
• Input Power tIspg/(2?)
• ? 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

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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

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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

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Spacecraft Propulsion Subsystem

• System Selection and Sizing (Table 17.2)
• 1) Determine propulsion functions -- table 17.1
• 2) Determine ?v 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

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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