Space Propulsion
The following is a research project on Space
Vehicle Propulsion. It shall
consist of four sections, each discussing
specific topics. Section One lays out
the basic ideas of rocketry. Section
Two compares Rocket Propulsion Systems, and
shows the basis for the
comparison. It also shows how each specific Rocket
System works and
Section Three gives a description of how Space Propulsion has
evolved and
contains a conclusion. SECTION 1 The Basics Section One is a
brief
description of the basic properties of Rocket Systems. It defines the
key terms
and shows how a basic rocket works. It also shows the State if The
Art. I have
chosen to do my project on space vehicle propulsion. Basically,
this means that
my research shall be based primarily on rocketry. Rocketry is
a way of
propulsion that has developed in numerous ways since it was first
used to propel
fireworks in the 16th century. It has emerged into an
extremely complicated
science that few actually understand. Most space
rocketry in America is used in
NASA (National Aeronautics and Space
Association) space projects. NASA, a
government association that focuses on
space exploration, is the main user of
rocket technology. It is used mostly
to power their satellites and shuttles into
space. Pushing an object that
weighs as much as a space shuttle does directly
vertical until escaping the
Earth’s atmosphere requires a tremendous amount of
power. This is why NASA
uses rockets. Rockets are essentially the most powerful
forms of propulsion
there is today. Space Vehicle Propulsion is based rocket
engines. The basic
principle of rocket engine is that when fuel is burned in the
engine, the
reaction mass is expelled at high speeds. As a result of Newton’s
law of
action and reaction this pushes the vehicle in the opposite direction of
the
one in which the reaction mass is moving. Thrust is the force that the
engine
exerts on all space behind it in order to "push" the vehicle
forward.
Efficiency is the way that the quality of rocket engines is
measured by. It is
measured by the time it takes for one kilogram of
propellant to create one
kilogram of thrust. The goal of my research is to
find out what makes these
engines more efficient. In rocketry, the state of
the art is extremely hard to
define, since there are so many different forms
of rocketry ranging from liquid
propellant rockets to fireworks. The state of
the art though is probably nuclear
powered rockets. It is much more efficient
because it does not use chemical
combustion like most rockets do. Instead
NFRRs (Nuclear Fission Reactor Rockets)
heat hydrogen in a fission reactor
which expels the propellant at blistering
speeds. Much research is being done
with NFRRs. They are still highly
experimental because of the dangers that
could be associated with them. The
NERVA (Nuclear Engine for Rocket
Vehicle Application) was one of the most
extensive NFRR research projects,
however it failed because of the inability
figure out an approach to putting
the research into a developmental stage.
SECTION 2 Specific Rocket
Propulsion Systems Section One has laid the foundation
for further research
in the are of rocketry. Section two shall discuss
properties of efficiency in
more depth, it shall lay out the types of rockets in
existence now. It shall
also show which type of rocket is the most efficient.
After this section,
the next one shall describe how the reasons for these
specific rockets
efficiency and depending on the outcome of that report, the
topic of the
fourth shall be decided. EFFICIENCY Efficiency is the most
important part of
my research as yet. Since the object of my research is to find
out which type
of rockets are the most efficient and why, the reader of this
paper must have
a basic understanding of efficiency. Once this is established,
new
definitions will come into play, all of these shall be crucial in
the
understanding of the paper. Terms Needed To Understand Efficiency G- a
unit of
acceleration [equal to 9.8 meters/second/second (accelerating at a
pace of 9.8
meters per second every second)] Specific Impulse (Isp)- A
measurement in
seconds of efficiency. Properties of Efficiency Efficiency is
the most accurate
indicator of rockets performance. As stated in the
aforementioned definitions,
specific impulse is the basic unit of measurement
of rocket efficiency. Isp is
found by dividing the exhaust velocity by g
(definition also mentioned above).
Since velocity is measured in m/s
(meters per second) and each g is equal to 9.8
m/s/s (meters per second every
second), the terms cancel to leave just a unit in
seconds. The resulting
figure, is the duration of time for which one kilogram of
propellant can
produce one kilogram of thrust. Thus, a higher number represents
a better,
and more efficient rocket. To give the reader an idea of the average
Isp
of several type of rockets, I have listed some average figures for
efficiency
of certain types of rockets below. Average Efficiencies of
Certain
Rockets Next, I have listed the Isp values for some basic types
of rockets.
After that I shall explain some of the most well known types
of rockets. Basic
Rocket Types An RPS (rocket propulsion system) is a
powerplant that pushes a
vehicle forward by ejecting matter that is stored
within the vehicle. This
matter is called propellant. The propellant is the
most crucial part of moving a
vehicle through space. Their energy source, the
vehicles they are used on, and
the type of propellant classify the specific
types of systems. Liquid Propellant
Rockets All LPRs (Liquid Propelled
Rockets) contain the same basic devices. The
next paragraph shall discuss
these functions and examine their purpose. The
first such device is the
thrust chamber. The thrust chamber contains an
injector, a combustion chamber
and a nozzle. The thrust chamber is the place
where the propellants are
injected, atomized, then mixed and finally burned to
form reaction products
in the form of gas. Next, the products are accelerated
and ejected at
extremely high velocities to create thrust. The injector is a
series of pipes
that allow the liquid propellant to move into the combustion
chamber chamber
to be made into thrust while atomizing and mixing them. The
exhaust nozzle is
the last step in the releasing of thrust. It allows the hot
gas to expand and
then accelerates them to supersonic velocities. On some
vehicles, the nozzle
acts as a steering mechanism by placing it on an electronic
axis for which it
can be turned by an automated steering wheel. There are two
major types of
feed systems used by LPRs; one uses pumps to move propellants to
combustion
chambers; the other, uses high pressure to expel propellants from
their
tanks. On most space vehicles the engines are mounted in pairs at
the
perimeter of the craft. Normally to opposite facing thrust chambers
are
controlled automatedly to turn the ship. Generally, a minimum of 12
thrust
chambers is required for turning. Solid Propellant Rockets Solid
Propellant
Rockets (SPRs) contains a huge number of types of engines. The
propellant that
is to be burned is held in the combustion chamber. The
propellant charge (grain)
contains chemical elements for complete burning.
When it is ignited, it burns on
all its exposed sides. If the design of the
grain is changed, then less can be
exposed; the less exposed, the less fuel
burned. The average burning rate is
around 1.8 cc per second. The rate
normally depends on the propellant
ingredients. The more chamber pressure,
the more propellant burnt. The way to
make an efficient SPR is to pack as
much solid propellant into a chamber volume
as possible. Theoretically, it
would be ideal to burn the propellant like a
cigar, from one end to the
other. For this reason, scientists created an
end-burning grain, which has
proved extremely successful. Electric Rockets There
are three types of
electric propulsion systems (EPS); the three include
electromagnetic,
electrothermal and electrostatic. They are, in some ways more a
rocket of the
future then one of the present, somewhat like the NERVA project
(see next
section). In the electrothermal system the propellant is heated or
vaporized
electric heaters. The hot gas is then expanded through a nozzle the
way it is
in a chemical rocket. In an electrostatic system, interacting
electrostatic
fields and small charged particles such as colloidal particles
achieve
acceleration. In an electromagnetic rocket, acceleration is achieved
by
placing propellant plasma (a high temperature, electrically natural gas
that
contains electrons, ions and neutral molecular species) in an
electromagnetic
field thus causing a reaction that releases thrust. Nuclear
Rockets Unlike the
aforementioned rockets, nuclear rockets do not generate
its power through
chemical combustion. The way its power is formed, is
through nuclear fission. It
heats a propellant like hydrogen in a fission
reactor and the explosion expels
the propellant at amazing speeds, which
exceed twice what any other rocket can
produce. Its efficiency rating is
around 850, as compared to the 450 of the next
best type, the cryogenic
rocket. Unfortunately due to the extreme dangers of
nuclear fission inside a
shuttle, the main project for researching the nuclear
rockets, NERVA, was
scrubbed. Most likely, in the future, scientists will devise
a plan to
minimize the risks, whereupon research will begin again. SECTION 3
A
History INTRODUCTION The third section of this report shall begin by
indicating
the steps in which rocketry was created, as to allow the reader of
this paper to
better understand the way rockets work. It shall show the works
of Tsiolkovsky,
Goddard, Oberth and a few others. The report shall then
end in a detailed
conclusion. The conclusion will be based on the summary and
discuss all that has
been written. It shall end in giving opinions as to the
future uses of the
specific areas found in the research. Development of
Modern Rocketry EARLY
HISTORY In around 1232 AD, in China, rockets were
created. During the war with
the Mongols, the Chinese would strap an early
form of gunpowder to the shaft of
an arrow. This made them fly longer and
faster than any of the regular arrows
that the Mongols used. About ten years
later, in Europe, another major discovery
was made. An Englishman, Robert
Bacon, created a more practical formula for
gunpowder. He did this by mixing
41.2 parts saltpeter, 29.4 parts charcoal and
29.4 parts sulfur. He was
able to distill saltpeter, which produces oxygen, to
allow the rocket to burn
faster. In the 18th century, the British encounter
encountered rocket warfare
with India. The Indians probably learned the secret
of rocket treat from Arab
traders in the 17th century. The Indians, who were led
by Hyder Ali, gave
thousands of men the task of throwing rockets. The rockets
were first thrown,
then propelled itself. They attached an eight foot long
bamboo stalk to six
pound iron tube filled with fuse and powder. The rockets
were able to fly up
to 1.5 miles. Modern Discoveries Tsiolkovsky Tsiolkovsky, a
Russian
teacher, established that a rocket would work in the vacuum of space,
in
1883. In 1903, he wrote a book explaining how space travel was
possible, using
liquid propelled rockets. He created drawings of possible
space ships propelled
by either liquid oxygen and liquid hydrogen or liquid
oxygen and kerosene. The
sketches also show valves to transport the liquid
propellant into a combustion
chamber and showed how vanes could be created in
the exhaust for steering. He
also illustrated the crew lying on their backs
in a pressurized cabin in order
to withstand the pressure of such high
speeds. Tsiolkovsky also thought of
rocket staging. Rocket staging is a
series of rockets that fire one after the
other. When one finishes and the
other fires, the useless rocket is jettisoned.
He thought this was the
only way to put heavy objects such as satellites into
space. Goddard Although
Tsiolkovsky thought up the ideas of advanced rocketry,
still more had to be
considered, and it had to become reality. The next pioneer,
was the father of
American rocketry, Robert Goddard. He first, created a bazooka
type rocket.
The bazooka was fairly large solid-propellant rocket. In 1919, he
wrote a
text called A Method of Reaching Extreme Altitudes. Two years later, he
bagan
to experiment with the liquid fuels that Tsiolkovsky. In 1926,
Goddard
finally launched the first liquid propelled rocket. It was fueled by
gasoline
and liquid oxygen. It rose to a height of 41 feet and traveled at 60
miles per
hour. It only traveled 56 meters but it set the foundation for the
future of
rocketry. In May 1935, he released a rocket that featured gyro
controlled
exhaust vanes which pushed it to travel 1.5 miles above the ground
at a totally
unprecedented 700 miles per hour. GERMAN ROCKET SCIENTISTS In
1923 a German
rocket scientist Hermann Oberth published The Rocket Into
Planetary Space. He
favored liquid propellants, as Goddard, because of their
power. His
experimentation inspired the creation of the Society for Space
Travel. The
society passionately experimented with ways to improve the liquid
propellant
rocket. On February 21, 1931, a member of The Society for Space
Travel, Johannes
Winkler, launched the second liquid fuel rocket.
Winkler’s rocket was
propelled by liquid methane and liquid oxygen. It failed
totally, going a mere
ten feet forward. Three weeks later another rocket
ascended to about 2000 feet.
The entire Society for Space Travel began
working on two rocket series, the
Mirak and Repulsor. The late model
Repulsors could reach an altitude of 1 mile.
When The Society for Space
Travel ran out of money, they made a demonstration of
the Repulsor for the
German Army. A member, Werner Von Braun compiled some
statistics for the army
who gave it to Hitler. They realized that this did not
violate the treaty
which did not allow them to build airplanes. Hitler started
the Army Weapons
Department. Von Braun was placed in charge of rocket
development. Within a
few years Von Braun was experimenting with highly
developed rockets and was
firing them in secret at the island of Birkum. In 1934
he created two
rockets, that could ascend to over 1.5 miles. After that, The
Society for
Space Travel fell apart due to financial problems. In 1937, a rocket
research
station was constructed on the Baltic coast. Here the Germans created
such
rockets as the famous V-1 Buzz Bombs, and the mammoth V-2 which were
really
rocket-powered flying bombs. Conclusion In this research, it has
been
demonstrated how all rocket engines work. It illustrates how propellants
are
moved into a combustion chamber, and expelled at extremely high speeds.
It shows
the properties of efficiency, the basic measure by which all rockets
are
compared. It shows how efficiency is measure by specific impulse, which
is
calculated by the propellants exhaust velocity divided by g. It has given
a
basic comparison as to the efficiency of various rockets and has shown
the
reasons for being at their respective ranks. Also shown, is the
pioneering of
rocketry starting in the mid 1200s. All this has shown the
basic properties of
space
propulsion.
Bibliography
http://www.asi.org/adb/04/03/09/01/ - the
Rocket Engine Specifications page
from the Artemis Project
(http://www.asi.org/ ) Data Book http://www.orbireport.com/Data.html
-the
Orbital Report News Agency's Launch Vehicle database
http://leonardo.jpl.nasa.gov/msl/home.html
- JPL's Mission & Spacecraft
Library http://solar.rtd.utk.edu/%7Emwade/spaceflt.htm
- Mark Wade's
"Encyclopedia Astronautica"
http://www.ksc.nasa.gov/shuttle/technology/sts-newsref/stsref-toc.html
- The
Space Shuttle Reference Manual http://nmp.jpl.nasa.gov/ds1/tech/sep.html
-
Solar electric propulsion on the Deep Space 1 probe "Rockets" Sutton,
George
P Groliers Online
Encyclopedia