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CHEMICAL Always thermal Energy / propellant initially together Energy source is combustion Energy limited Best propellants, Ue ~ 4,500 m/s Isp ~ 100-500 s Thrust ~ 0.1 N-10 MN Propellant and Energy decrease with time High Thrust, Low Isp, High mdot, Fast a o , Short t burn
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CHEMICAL Always thermal Energy / propellant initially together Energy source is combustion Energy limited Best propellants, Ue ~ 4,500 m/s Isp ~ 100-500 s Thrust ~ 0.1 N-10 MN Propellant and Energy decrease with time High Thrust, Low Isp, High mdot, Fast ao, Short tburn Thrust independent of tburn tburn ~O(seconds) Earth to orbit missions, low DV ELECTRIC Some are thermal (resistojet, arcjet) Some are non-thermal (ion, hall effect, MPD) Energy source / propellant separate initially Energy source onboard or external Solar, Nuclear Energy conversion equipment onboard (heavy) ‘Unlimited energy’ Very high Ue (10,000-100,000 m/s) Isp ~ 1,000-10,000 s Thrust ~ mN-N Propellant decreases with time Energy remains constant with time Low Thrust, High Isp, Low mdot, Slow ao, Long tburn Thrust inversely proportional to tburn tburn ~O(days-months-years) Station keeping, deep space exploration, high DV CHEMICAL vs. ELECTRIC ROCKET PROPULSION Origin of Thrust: Eject Stored Mass Backwards → Use Reaction Force to Propel Vehicle Rocket Equation is Always True