EXTROVERT Space Propulsion 01

Welcome to AE6450 Space and Rocket Propulsion

Dr. Narayanan Komerath, Professor School of Aerospace Engineering, Georgia Institute of Technology

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

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.

EXTROVERT Space Propulsion 01

Section 1. Rocket Engine Basics

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

In this section we will cover:

EXTROVERT Space Propulsion 01

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.

Test of the crew escapesystem used on the ApolloLauncher. Source: Boeing/Rocketdyne

Rocket

Propellant

EnergyAddition

Acceleration ExhaustFeed

• 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.

EXTROVERT Space Propulsion 01

Thrust Equation for a General Jet Propulsion System

Momentum Conservation gives:

Steady:

( )f e e a eT m U P P A= + −&Rocket: No air mass flow rate.

EXTROVERT Space Propulsion 01

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

( )ee e e a

Ac U p pm

= + −&

Note on Thrust Generation

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.

EXTROVERT Space Propulsion 01Modern Examples of Rocket Propulsion Systems

STS (See Sutton p. 16)

3 Orbiter Main Propulsion Engines 2 Solid Booster engines

2 Orbit Maneuver Engines38 Primary Reaction Control Thrusters 6 Vernier Reaction Control Thrusters8 forward booster separation engines 8 aft booster separation engines

Titan IVB launcher2 solid boosters (+16? booster separators?)2 liquid core engine (Aerozine / N2O4)1st stage1 liquid engine 2nd stageCentaur upper stage2 main engines LOX/LH2(2?) roll thrustersCassini spacecraft2 hydrazine/ nitrogen tetroxide main engines3 Radioisotope Thermal Generators16 hydrazine ACS control thrusters

Cassini-Huygens Mission 1997

EXTROVERT Space Propulsion 01

We consider several types of rockets briefly: • Cold gas thrusters• Chemical thrusters

monopropellantbipropellant (Liquid)solid propellanthybrid

• Nuclear thermal• Solar thermal• Electric• Matter-antimatter

At the end we also consider “propellantless” means of Propulsion, as opposed to rockets.

Rocket Engines

EXTROVERT Space Propulsion 01

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 Programhttp://www.mech.uq.edu.au/hyper/hyshot/hyshot_thruster.jpgwww.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.”

EXTROVERT Space Propulsion 01

Energy from chemical decomposition or reaction generates thermal energy used to expand the gas Monopropellant – single working fluid converted to gases in the presence of a (metallic or thermal ) catalyst. For example,

Chemical Thrusters

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.

EXTROVERT Space Propulsion 01

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

EXTROVERT Space Propulsion 01Bipropellant 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.

http://www.seas.upenn.edu/courses/meam203/class/ssme.jpghttp://www.boeing.com/defense-space/space/rdyne/sightsns/images/ssmetest.gif

Space Shuttle Main Engine: LOX/LH2

Rocketdyne (Rockwell)

F-1 engine. LOX/RP1

EXTROVERT Space Propulsion 01Bipropellant Engine Examples

Bipropellant Apogee Engine (ETS-VI)http://www.wtec.org/loyola/satcom/c2_s5b.htmCourtesy wtec 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.

http://www.atlanticresearchcorp.com/docs/space_biprop6.shtml

EXTROVERT Space Propulsion 01

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)

EXTROVERT Space Propulsion 01

Example: Space Shuttle Solid Booster

http://history.nasa.gov/rogersrep/v1p56.jpg

EXTROVERT Space Propulsion 01

Star-Grained Solid Rocket Motor

http://www.nf.suite.dk/stargrain/ After 1 minute of burn

EXTROVERT Space Propulsion 01

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).

EXTROVERT Space Propulsion 01

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 overlong period.

EXTROVERT Space Propulsion 01

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

EXTROVERT Space Propulsion 01

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 Centerhttp://www.msfc.nasa.gov

EXTROVERT Space Propulsion 01

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?

EXTROVERT Space Propulsion 01

“Propellantless” Space PropulsionTethers

–       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.

M2P2 propulsion: courtesy Dr. Winglee, U. Washington and NIAC. http://www.niac.usra.edu

Solar Sail Propulsion. Courtesy NIAChttp://www.niac.usra.edu

EXTROVERT Space Propulsion 01Questions

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?