MAE 5391: Rocket Propulsion Overview of Propulsion Systems

Rocket Technologies Titan IV and Delta IV

Propulsion Technology Options Thermodynamic Systems (TE KE) Cold Gas Thrusters Liquids Monopropellants Bipropellants Solids Hybrids Nuclear (NE TE KE) Electric Systems Electrothermal (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!

Chemical Limitations Why we have thermo! Vexit= nozzle exit velocity (m/s) Ru= universal gas constant (8314.41 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)

Cold Gas Cold Gas: Expand a pressurized gas through a nozzle Gas Molecular Weight Specific Impulse (sec) Air 28.9 74 Argon 39.9 57 CO2 44.0 67 Helium 4.0 179 Hydrogen 2.0 296 Nitrogen 28.0 80 Methane 16.0 114

Liquid Monopropellant MonoProp: Decompose a single propellant and expand the exhaust through a nozzle Parameter Value Catalyst LCH 227/202 Steady-state thrust (N) 11.1 - 31.2 Isp (sec) 228 - 235 Propellant specific gravity 1.023 Average Density Isp ( sec) 236.8 Rated total impulse (Nsec) 124,700 Total pulses 12,405 Minimum impulse bit (Nsec) 0.56 Feed pressure (bar) 6.7 - 24.1 Chamber pressure (bar) 4.5 - 12.4 Nozzle expansion ratio 61:1 Mass flow rate (gm/sec) 5.0 - 13.1 Valve power 27 W max @ 28 VDC Thruster mass (kg) 0.52 3 N2H4  4 NH3 + N2 + 336,280 joules

Liquid Bi-Propellant BiProp: Combust (burn) two propellants (fuel + oxidizer) in a combustion chamber and expand exhaust through a nozzle Storable Isp 250-320 sec finert=0.03-.13 Cryogenic Isp 320 – 452 sec finert=0.09-0.2 Finert = 0.04-0.2 Finert=0.11-0.31

Solids Composite propellant, consisting of an oxidizing agent, such as ammonium nitrate or ammonium perchlorate intimately mixed with an organic or metallic fuel and binder. Advantages Simple Reliable High density Isp No chamber cooling Disadvantages Cracks=disaster Can’t restart Hard to stop Modest Isp Thrust function of burn area, Isp = 250-300 sec Finert=0.06-0.38, 2/3 of motors have fiinert below 0.2

When solids go bad!

Hybrids Hybrid: Bipropellant system with liquid oxidizer (usually) and a solid fuel Isp= 290-350 sec Finert=0.2 Catalyst Pack Combustion Chamber Nozzle Test Stand Load Cell Fuel Element H2O2/PE Hybrid Test Set-Up Polyethylene fuel rod

Nuclear Thermal Propulsion NERVA Program Thrust = 890,000N Isp = 838 sec Working fluid = Hydrogen Test time = 30 minutes Stopped in 1972 Finert=0.5-0.7 (shielding)

Electrothermal-Resistojets Working Fluid Thrust (mN) Isp (sec) Power (W) Cp (kJ/kg K) Tc (K) hydrogen 37 546 100 14.32 1000 water 93 219 2.3 nitrous oxide 141 144 1.0 Electrothermal-- 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

Electrothermal-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

Electrostatic-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 sec 7000 hours of operation is becoming the standard!

Electromagnetic-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 W Stuttgart, Isp=5000sec, F=100N, P=6 MW, hydrogen

Pulsed Plasma Thrusters Isp = 500-1500 sec P = 1 – 100 W Thrust = 5mN/W

Hall Effect Thruster Power = 50W – 25kW Isp = 500 – 3000 sec Thrust = 5 mN- 1N

Propulsion System “Cost” Performance issues Mass Volume Time (thrust) Power Safety Logistics Integration Technical Risk The “best” (lowest “cost”) option optimizes these issues for a given set of mission requirements