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1. Welcome to AE6450 Space and Rocket PropulsionDr. Narayanan Komerath, Professor School of Aerospace Engineering, Georgia Institute of Technology Ice geyser from the moon Enceladus near Saturn. Image from the Cassini spacecraft. The Cassini-Huygens mission used gravity assist from several planets to reach the Saturn environment with minimal expenditure of fuel. • Worried about Prerequisites? • Check out • Introduction to Aerospace Engineering http://www.adl.gatech.edu/classes/dci/intro/dci01a.html • Jet Propulsion • http://www.adl.gatech.edu/classes/ae4451/ • High Speed Aerodynamics/Compressible Flow http://www.adl.gatech.edu/classes/ae3021/ http://apod.nasa.gov/apod/image/0710/PIA08386_enceladus_rc.jpg

2. Section 1. Rocket Engine Basics In this section we will cover: • Types of rocket engines • The rocket equation, and a simple solution process for a launch to orbit. • Simple orbital mechanics considerations related to mission requirements. • Calculation of rocket thrust via momentum equation • Definition of Isp, thrust coefficient, c*, • Ideal expansion, over/under expansion • Typical nozzle designs

3. Propellant Feed Exhaust Acceleration Energy Addition Rocket A Rocket carries with it all of the propellant mass which is accelerated to produce thrust. “Jet” engines are generally considered to be those which combine stored propellant with atmospheric gases. There are some propulsion systems which combine airbreathing and rocket propulsion. A rocket engine includes means for heating propellant and accelerating it into an exhaust. • The feed system may use gravity, tank pressure, • pumps, vaporization, pyrolysis, electric fields or something else. • The energy addition may be by chemical, nuclear or matter-antimatter heat release, • electrostatic, electromagnetic, or external solar, laser or microwave radiation. • The acceleration may use gasdynamics (nozzles) or electromagnetic fields. Test of the crew escape system used on the Apollo Launcher. Source: Boeing/Rocketdyne

4. Thrust Equation for a General Jet Propulsion System Momentum Conservation gives: Steady: Rocket: No air mass flow rate.

5. Note on Thrust Generation Thrust comes from: a) Increase in momentum of the propellant fluid (momentum thrust) b) Pressure at the exit plane being higher than the outside pressure (pressure thrust). Where does the thrust act? In the rocket engine, the force is felt on the nozzle and the combustor walls, and is transmitted through the engine mountings to the rest of the vehicle. Effective Exhaust Velocity is the thrust divided by the mass flow rate Specific Impulse (Isp) is the effective exhaust velocity divided by a standard value of acceleration (taken as 9.8 m/s2). Note that you use the same value of 9.8 even on the Moon! Isp = ce / 9.8 expressed in seconds. Obviously, all else being the same, ce is higher in a vacuum, so “vacuum specific thrust” is the Isp value quoted by engine manufacturers. The STS main engines are claimed to achieve 455 seconds.

6. Modern Examples of Rocket Propulsion Systems STS (See Sutton p. 16) Cassini-Huygens Mission 1997 3 Orbiter Main Propulsion Engines 2 Solid Booster engines 2 Orbit Maneuver Engines 38 Primary Reaction Control Thrusters 6 Vernier Reaction Control Thrusters 8 forward booster separation engines 8 aft booster separation engines Titan IVB launcher 2 solid boosters (+16? booster separators?) 2 liquid core engine (Aerozine / N2O4)1st stage 1 liquid engine 2nd stage Centaur upper stage 2 main engines LOX/LH2 (2?) roll thrusters Cassini spacecraft 2 hydrazine/ nitrogen tetroxide main engines 3 Radioisotope Thermal Generators 16 hydrazine ACS control thrusters

7. Rocket Engines • We consider several types of rockets briefly: • Cold gas thrusters • Chemical thrusters • monopropellant • bipropellant (Liquid) • solid propellant • hybrid • Nuclear thermal • Solar thermal • Electric • Matter-antimatter At the end we also consider “propellantless” means of Propulsion, as opposed to rockets.

8. Cold Gas Thrusters Energy comes from high gas storage pressure expelled via a simple blow-down system. Typical propellants (pressurized) include He and N2. Features: ·   Low thrust ·   Low performance ·   Simple and cheap ·   No need for a heat addition system ·   Non-toxic (e.g.: rendezvous with ISS) ·   Used primarily for attitude control. Courtesy, U. Queensland, HYSHOT Flight Program http://www.mech.uq.edu.au/hyper/hyshot/hyshot_thruster.jpg www.mech.uq.edu.au/ hyper/hyshot/ “.. approx. 300N of thrust w/ bottle pressure of 21MPa. .. could also turn valve on and off reliably in 1 ms.”

9. Chemical Thrusters Energy from chemical decomposition or reaction generates thermal energy used to expand the gasMonopropellant – single working fluid converted to gases in the presence of a (metallic or thermal ) catalyst. For example, In the second type shown above, the hydrazine decomposes to ammonia and nitrogen. The ammonia further decomposes in an endothermic reaction (heat is absorbed) to form nitrogen and hydrogen. This is a simple, but rather low-performance thruster. Hydrazine is storable for long missions, but is toxic to humans.

10. Example: Monopropellant engine assembly for the Cassini Mission. http://saturn.jpl.nasa.gov/cassini/Spacecraft/propulsion.shtml Text: “The monopropellant tank assembly (MTA) mounts externally to the PMS cylindrical structure and utilizes a propellant management diaphragm to contain gaseous helium on one side and purified hydrazine on the other side. The hydrazine is expelled, as required, to feed the four thruster cluster assemblies during the performance of attitude control maneuvers and functions.” Courtesy, NASA

11. Bipropellant liquid thrusters Very common type of rocket with separately stored “oxidizer” and “fuel”. Examples include: LOX/LH2, LOX/RP, N2O4 / N2H4 . Bipropellant thrusters can achieve high performance, but are complex and weight more. They enable throttling and control over a wide range of thrust. Rocketdyne (Rockwell) F-1 engine. LOX/RP1 Space Shuttle Main Engine: LOX/LH2 http://www.seas.upenn.edu/courses/meam203/class/ssme.jpg http://www.boeing.com/defense-space/space/rdyne/sightsns/images/ssmetest.gif

12. Bipropellant Engine Examples Bipropellant Apogee Engine (ETS-VI) http://www.wtec.org/loyola/satcom/c2_s5b.htm Courtesy wtec http://www.atlanticresearchcorp.com/docs/space_biprop6.shtml LEROS 20H Station Keeping Thruster: Dual mode attitude control engine. Nominal thrust of 5 lbf (22 N). Uses a high temperature Platinum/Rhodium alloy in its chamber. Isp > 308 seconds steady state, without throughput limitation operating on hydrazine and nitrogen tetroxide propellants. Courtesy Atlantic Research Co.

13. Solid-propellant thrusters • Fuel and oxidizer are premixed into a rubbery mixture (example: Aluminum fuel and ammonium perchlorate oxidizer). The solid propellant generates a mixture of gases when burned. • Solid thrusters are • · Storable • · Simple, low-cost • · Deliver high energy density (i.e., high values of density*(square of specific impulse) • · Performance is moderate, • · Hard to control/ throttle (usually little control once lit) • Exhaust can be toxic and corrosive (e.g., chlorine)

14. Example: Space Shuttle Solid Booster http://history.nasa.gov/rogersrep/v1p56.jpg

15. Star-Grained Solid Rocket Motor http://www.nf.suite.dk/stargrain/ After 1 minute of burn

16. Hybrid Thrusters Use a solid fuel (a plastic-like hydrocarbon polymer) and a liquid or gaseous oxidizer (typically LOX or H2O2 ). • Higher performance than solids • Controllable and can be throttled by varying liquid flow rate. • Uneven burning • Significant “Inert mass” (unburned propellant).

17. Nuclear Thrusters Use nuclear energy source to heat a working fluid to high temperature, and exhaust the fluid through a nozzle (typically hydrogen). ·        High performance·        High reactor/ shielding mass required against radiation emission·        Political/ environmental issues Nuclear RadioIsotope Decay Power Generators Deep-space missions use radio isotope decay to generate a small amount of heat over long period.

18. http://lifesci3.arc.nasa.gov/SpaceSettlement/teacher/lessons/contributed/thomas/Adv.prop/scntr.gifhttp://lifesci3.arc.nasa.gov/SpaceSettlement/teacher/lessons/contributed/thomas/Adv.prop/scntr.gif

19. Solar Thermal •  Like nuclear thrusters, but use solar energy either directly or indirectly to heat a working fluid (typically hydrogen). • Not enough power for constant burns (impulsive thrust generation) Source: NASA Marshall Space Flight Center http://www.msfc.nasa.gov

20. Electric Thrusters Uses a magnetic fluid or electric field to accelerate ions (typically Argon, Krypton, Cesium or Cobalt) to very high exhaust velocity Very high performance (specific impulse above 2000 seconds) Usable only in low-thrust applications Note: energy source can be solar (SEP) or nuclear (NEP) Resistance thrusters?

21. “Propellantless” Space Propulsion Tethers –       rotating (momentum exchange – “catch and throw”) –       electrodynamic (uses Earth’s magnetic field) Sails - Solar sails use the solar wind (high speed charged particles emitted from the Sun) to provide momentum for outbound trajectories. Magnetic sails use magnetic fields instead of a physical fabric to “capture” the solar wind. Solar Sail Propulsion. Courtesy NIAC http://www.niac.usra.edu M2P2 propulsion: courtesy Dr. Winglee, U. Washington and NIAC. http://www.niac.usra.edu

22. Questions How many rocket engines are to be used on the current version of the human mission to the Moon? What types of engines are these? How does this number compare to what was used on the Apollo missions? A cylinder contains compressed air at 2500psi. The lab temperature is 300K. If you could use this air to run a cold gas thruster producing 100 Newtons thrust in the laboratory with no losses, how much air flow (grams per second) would be needed? What is the specific impulse of this rocket?