# EXTROVERT Space Propulsion 01

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Nov 16, 2013 (4 years and 7 months ago)

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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.

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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:

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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 escape

system used on the Apollo

Launcher. Source: Boeing/Rocketdyne

Rocket

Propellant

Energy

Addition

Acceleration

Exhaust

Feed

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.

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Space Propulsion 01

Thrust Equation for a General Jet Propulsion System

Momentum Conservation
gives:

Steady:

Rocket: No air mass flow rate.

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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

Note on Thrust Generation

Specific Impulse (Isp)

is the effective exhaust velocity divided by a standard value of acceleration

(taken as 9.8 m/s
2
). Note that you use the same value of 9.8 even on the Moon!

Isp = c
e

/ 9.8 expressed in seconds. Obviously, all else being the same, c
e

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.

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Space Propulsion 01

Modern Examples of Rocket Propulsion Systems

STS (See Sutton p. 16)

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

Cassini
-
Huygens Mission 1997

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Space Propulsion 01

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.

Rocket Engines

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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 N
2
.

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.”

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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.

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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

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Space Propulsion 01

Bipropellant liquid thrusters

Very common type of rocket with separately stored “oxidizer” and “fuel”.
Examples include: LOX/LH
2
, LOX/RP, N
2
O
4

/ N
2
H
4
.

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.jpg

http://www.boeing.com/defense
-
space/space/rdyne/sightsns/images/ssmetest.gif

Space Shuttle Main Engine:
LOX/LH
2

Rocketdyne (Rockwell)

F
-
1 engine. LOX/RP1

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Space Propulsion 01

Bipropellant Engine Examples

Bipropellant Apogee Engine (ETS
-
VI)

http://www.wtec.org/loyola/satcom/c2_s5b.htm

Courtesy 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

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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)

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Space Propulsion 01

Example: Space Shuttle Solid Booster

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

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Star
-
Grained Solid Rocket Motor

http://www.nf.suite.dk/stargrain/

After 1 minute of burn

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Hybrid Thrusters

Use a solid fuel (a plastic
-
like hydrocarbon polymer) and a liquid or gaseous oxidizer
(typically LOX or H
2
O
2

).

Higher performance than solids

Controllable and can be throttled by varying liquid flow rate.

Uneven burning

Significant “Inert mass” (unburned propellant).

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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 over

long period.

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Space Propulsion 01

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

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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

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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?

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Space Propulsion 01

“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.

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

Solar Sail

Propulsion.

Courtesy NIAC

http://www.niac.usra.edu

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Space Propulsion 01

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?