3Propulsion Technology Options Thermodynamic Systems (TE KE)Cold Gas ThrustersLiquidsMonopropellantsBipropellantsSolidsHybridsNuclear (NE TE KE)Electric SystemsElectrothermal (Resistance Heating)Electrostatic (Ion with E field F=qE)Electromagnetic (plasma with B field F=JxB)With the exception of electrostatic and electromagnetic, all use concept of gas at some temp flowing though a converging/diverging nozzle!
4Chemical Limitations Why we have thermo! Vexit= nozzle exit velocity (m/s)Ru= universal gas constant ( J/kmol*K)T0= chamber temperature (K)Pe= exit pressure (Pa)P0= chamber pressure (Pa)M= molecular mass of gas (kg/kmol)g= ratio of specific heats (no dimensions)
5Cold Gas Cold Gas: Expand a pressurized gas through a nozzle Gas MolecularWeightSpecificImpulse (sec)Air28.974Argon39.957CO244.067Helium4.0179Hydrogen2.0296Nitrogen28.080Methane16.0114
6Liquid Monopropellant MonoProp: Decompose a single propellant and expand the exhaust through a nozzleParameterValueCatalystLCH 227/202Steady-state thrust (N)Isp (sec)Propellant specific gravity1.023Average Density Isp ( sec)236.8Rated total impulse (Nsec)124,700Total pulses12,405Minimum impulse bit (Nsec)0.56Feed pressure (bar)Chamber pressure (bar)Nozzle expansion ratio61:1Mass flow rate (gm/sec)Valve power27 W 28 VDCThruster mass (kg)0.523 N2H4 4 NH3 + N ,280 joules
7Liquid Bi-PropellantBiProp: Combust (burn) two propellants (fuel + oxidizer) in a combustion chamber and expand exhaust through a nozzleStorable Isp secfinert=Cryogenic Isp 320 – 452 secfinert=Finert =Finert=
8SolidsComposite propellant, consisting of an oxidizing agent, such as ammonium nitrate or ammonium perchlorate intimately mixed with an organic or metallic fuel and binder.AdvantagesSimpleReliableHigh density IspNo chamber coolingDisadvantagesCracks=disasterCan’t restartHard to stopModest IspThrust function of burn area, Isp = secFinert= , 2/3 of motors have fiinert below 0.2
10HybridsHybrid: Bipropellant system with liquid oxidizer (usually) and a solid fuelIsp= secFinert=0.2Catalyst PackCombustion ChamberNozzleTest StandLoad CellFuel ElementH2O2/PE Hybrid Test Set-UpPolyethylene fuel rod
11Nuclear Thermal Propulsion NERVA ProgramThrust = 890,000NIsp = 838 secWorking fluid = HydrogenTest time = 30 minutesStopped in 1972Finert= (shielding)
12Electrothermal-Resistojets Working FluidThrust (mN)Isp (sec)Power (W)Cp (kJ/kg K)Tc (K)hydrogen3754610014.321000water932192.3nitrous oxide1411441.0Electrothermal-- electrical energy is used to directly heat a working fluid. The resulting hot gas is then expanded through a converging-diverging nozzle to achieve high exhaust velocities. These systems convert thermal energy to kinetic energy
13Electrothermal-Arcjets In an arcjet, the working gas is injected in a chamber through which an electric arc is struck. The gas is heated to very high temperature (3000 – 4000 K), Arc temp =10,000K on average, and much greater in certain regions in the arc.Power = 1.8 kW, Isp = 502, Thrust = 0.2N, Propellant = hydrazine
14Electrostatic-Ion Propulsion Electrostatic-- electrical energy is directly converted into kinetic energy. Electrostatic forces are applied to charged particles to accelerate the propellant.Deep Space 1 = 4.2 kW, Thrust = 165 mN, Isp = 3800 sec7000 hours of operation is becoming the standard!
15Electromagnetic-MPD Thruster Electromagnetic-- electromagnetic forces directly accelerate the reaction mass. This is done by the interaction of electric and magnetic fields on a highly ionised propellant plasma.NH3 MPD, F=23 mN, Isp= 600 sec, P=430 WStuttgart, Isp=5000sec, F=100N, P=6 MW, hydrogen
18Propulsion System “Cost” Performance issuesMassVolumeTime (thrust)PowerSafetyLogisticsIntegrationTechnical RiskThe “best” (lowest “cost”) option optimizes these issues for a given set of mission requirements