Spacecraft Propulsion Subsystem - Courses Server

Aersp 401A Spacecraft Propulsion Subsystem (rocket science in 15 minutes) Spacecraft Propulsion Subsystem Uses of onboard propulsion systems Orbit Transfer LEO to GEO LEO to Solar Orbit Drag Makeup Attitude Control Orbit Maintenance

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

Spacecraft Propulsion Subsystem Basics of Rocketry Rocket -- Any propulsion system that carries its own reaction mass. v = uv = ueln(Minitial/Mfinal) v = uv 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 Spacecraft Propulsion Subsystem Basics of Rocketry = (v = um/v = ut)ue +(pe-pa)Ae

is the engine thrust (v = um/v = ut) 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 Spacecraft Propulsion Subsystem Basics of Rocketry ueq = ue + [(pe-pa)/(v = um/v = ut)]Ae ueq is the equivalent exhaust velocity ueq = ue for a perfectly expanded nozzle

= (v = um/v = ut)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 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)

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

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 Spacecraft Propulsion Subsystem

Electric Propulsion Performance Input Power = Ispg/(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 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

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 Spacecraft Propulsion Subsystem System Selection and Sizing (Table 17.2) 1) Determine propulsion functions -- table 17.1 2) Determine v = uv 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 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