1) Introduction Rocket propulsion is any method used to accelerate spacecraft and artificial satellites. There are many different methods. Each method has drawbacks and advantages. However, most spacecraft today are propelled by forcing a gas from the back/rear of the vehicle at very high speed through a supersonic de Laval nozzle. This sort of engine is called a rocket engine. All current spacecraft use chemical rockets (bipropellant or solid-fuel) for launch, though some use air- breathing engines on their first stage. Most satellites have simple reliable chemical thrusters (often monopropellant rockets) or resistojet rockets for orbital station-keeping and some use momentum wheels for attitude control. Soviet bloc satellites have used electric propulsion for decades, and newer Western geo-orbiting spacecraft are starting to use them for north-south stationkeeping . Interplanetary vehicles mostly use chemical rockets as well, although a few have used ion thrusters and Hall Effect thrusters (two different types of electric propulsion) to great success. 2) History Just when the first true rockets appeared is unclear. Stories of early rocket like devices appear sporadically through the historical records of various cultures. Perhaps the first true rockets wer e accidents. In the first century A.D., the Chinese were reported to have had a simple form of gunpowder made from saltpeter, sulfur, and charcoal dust. It was used mostly for fireworks in religious and other festive celebrations. Bamboo tubes were filled with the mixture and tossed into fires to create explosions during religious festivals. lt is entirely possible that some of those tubes failed to explode and instead skittered out of the fires, propelled by the gases and sparks produced by the burning gunpowder. It is certain that the Chinese began to experiment with the gunpowder-filled tubes. At some point, bamboo tubes were attached to arrows and launched with bows. Soon it was discovered that these gunpowder tubes could launch themselves just by the power produced from the escaping gas. The true rocket was born.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
During the latter part of the 17th century, the scientific foundations for modern rocketry were laid by the
great English scientist Sir Isaac Newton (1642-1727). Newton organized his understanding of physical
motion into three scientific laws. The laws explain how rockets work and why they are able to work in the
vacuum of outer space.Newton's laws soon began to have a practical impact on the design of
rockets.Rocket experimenters in Germany and Russia began working with rockets with a mass of more
than 45 kilograms. Some of these rockets were so powerful that their escaping exhaust flames bored deep
holes in the ground even before lift-off.
During the end of the 18th century and early into the 19th, rockets experienced a brief revival as a weapon
of war. The success of Indian rocket barrages against the British in 1792 and again in 1799 caught the
interest of an artillery expert, Colonel William Congreve. Congreve set out to design rockets for use by
the British military.The Congreve rockets were highly successful in battle.Even with Congreve's work,
the accuracy of rockets still had not improved much from the early days. All over the world, rocketresearchers experimented with ways to improve accuracy. An Englishman, William Hale, developed a
technique called spin stabilization. In this method, the escaping exhaust gases struck small vanes at the
bottom of the rocket, causing it to spin much as a bullet does in flight. Variations of the principle are still
used today.
3) Birth of modern rockets
In 1898, a Russian schoolteacher, Konstantin Tsiolkovsky (1857-1935), proposed the idea of space
exploration by rocket. In a report he published in 1903, Tsiolkovsky suggested the use of liquid
propellants for rockets in order to achieve greater range. Tsiolkovsky stated that the speed and range of a
rocket were limited only by the exhaust velocity of escaping gases. For his ideas, careful research, and
great vision, Tsiolkovsky has been called the father of modern astronautic.
Early in the 20th century, an American, Robert H. Goddard (1882-1945), conducted practical experiments
in rocketry. He had become interested in a way of achieving higher altitudes than were possible for
lighter-than-air balloons. He published a pamphlet in 1919 entitled A Method of Reaching Extreme
Altitudes. It was a mathematical analysis of what is today called the meteorological sounding ro
In his pamphlet, Goddard reached several conclusions important to rocketry. From his tests, he stated that
a rocket operates with greater efficiency in a vacuum than in air. Goddard also stated that
multistage or step rockets were the answer to achieving high altitudes and that the velocity needed to
escape Earth's gravity could be achieved in this way.Goddard's earliest experiments were with solid-
Higher energies are possible if other energy are used in conjunction with the chemical propellants on
board the rockets, and extremely high energies are achievable when the exhaust is accelerated
by electromagnetic means
.
The effective exhaust velocity is the figure of merit for rocket propulsion because it is a measure of thrust
per unit mass of propellant consumed — i.e.,
Values of ve are in the range 2,000 – 5,000 metres (6,500 – 16,400 feet) per second for chemical propellants,
while values two or three times that are claimed for electrically heated propellants. Values beyond 40,000
metres (131,000 feet) per second are predicted for systems using electromagnetic acceleration.
In a typical chemical-rocket mission, anywhere from 50 to 95 percent or more of the takeoff mass is
propellant. This can be put in perspective by the equation for burnout velocity (assuming gravity-free
and drag-free flight)
In this expression, M s / M p is the ratio of propulsion system and structure mass to propellant mass, with a
typical value of 0.09 (the symbol ln represents natural logarithm). M p / M o is the ratio of propellant mass toall-up takeoff mass, with a typical value of 0.90. A typical value for ve for a hydrogen – oxygen system is
3,536 metres (11,601 feet) per second. From the above equation, the ratio of payload mass to takeoff mass
Typical temperatures (T) and pressures (p) and speeds (v) in a De Laval Nozzle
The large bell or cone shaped expansion nozzle gives a rocket engine its characteristic shape.
In rockets the hot gas produced in the combustion chamber is permitted to escape from thecombustion chamber through an opening (the "throat"), within a high expansion-ratio 'de Laval'
nozzle.The exhaust speeds vary, depending on the expansion ratio the nozzle is designed to give,
but exhaust speeds as high as ten times the speed of sound are not uncommon.
Rocket thrust is caused by pressures acting in the combustion chamber and nozzle. From Newton's third law, equal
and opposite pressures act on the exhaust, and this accelerates it to high speeds.
About half of the rocket engine's thrust comes from the unbalanced pressures inside the combustion
chamber and the rest comes from the pressures acting against the inside of the nozzle (see diagram).
As the gas expands (adiabatically) the pressure against the nozzle's walls forces the rocket engine in
one direction while accelerating the gas in the other.
4.5) Propellant efficiency
For a rocket engine to be propellant efficient, it is important that the maximum pressures possible be
created on the walls of the chamber and nozzle by a specific amount of propellant; as this is the
source of the thrust. This can be achieved by all of:
heating the propellant to as high a temperature as possible (using a high energy fuel, containing
hydrogen and carbon and sometimes metals such as aluminium, or even using nuclear energy)
using a low specific density gas (as hydrogen rich as possible)
using propellants which are, or decompose to, simple molecules with few degrees of freedom to
maximise translational velocity
Since all of these things minimise the mass of the propellant used, and since pressure is proportional
to the mass of propellant present to be accelerated as it pushes on the engine, and since from
Newton's third law the pressure that acts on the engine also reciprocally acts on the propellant, it
turns out that for any given engine the speed that the propellant leaves the chamber is unaffected by
the chamber pressure (although the thrust is proportional). However, speed is significantly affected
by all three of the above factors and the exhaust speed is an excellent measure of the engine
propellant efficiency. This is termed exhaust velocity, and after allowance is made for factors that
can reduce it, the effective exhaust velocity is one of the most important parameters of a rocket
engine (although weight, cost, ease of manufacture etc. are usually also very important).
4.6) Thrust vectoring
Many engines require the overall thrust to change direction over the length of the burn. A number of
different ways to achieve this have been flown:
The entire engine is mounted on a hinge or gimbal and any propellant feeds reach the engine via
low pressure flexible pipes or rotary couplings.
Just the combustion chamber and nozzle is gimbled, the pumps are fixed, and high pressure feeds
attach to the engine
multiple engines (often canted at slight angles) are deployed but throttled to give the overall
vector that is required, giving only a very small penalty
fixed engines with vernier thrusters
high temperature vanes held in the exhaust that can be tilted to deflect the jet
Rockets can be further optimised to even more extreme performance along one or more of these
axes at the expense of the others.
4.7) Specific impulse
The most important metric for the efficiency of a rocket engine is impulse per unit of propellant, this
is called specific impulse . This is either measured as a speed (the effective exhaust velocity V e in
metres/second or ft/s) or as a time (seconds). An engine that gives a large specific impulse is
normally highly desirable.
The specific impulse that can be achieved is primarily a function of the propellant mix (and
ultimately would limit the specific impulse), but practical limits on chamber pressures and thenozzle expansion ratios reduce the performance that can be achieved.
controllable divert and attitude control motors, and thermal management materials.
5.2) Hybrid rocket
A hybrid rocket is a rocket with a rocket motor which uses propellants in two different states of matter -
one solid and the other either gas or liquid. The Hybrid rocket concept can be traced back at least 75
years.
Hybrid rockets exhibit advantages over both liquid rockets and solid rockets especially in terms of
simplicity, safety, and cost.Because it is nearly impossible for the fuel and oxidizer to be mixed intimately
(being different states of matter), hybrid rockets tend to fail more benignly than liquids or solids.
Like liquid rockets and unlike solid rockets they can be shut down easily and are simply throttle-able. Thetheoretical specific impulse( I sp) performance of hybrids is generally higher than solids and roughly
equivalent to hydrocarbon-based liquids. I sp as high as 400s has been measured in a hybrid rocket using
metalized fuels.]Hybrid systems are slightly more complex than solids, but the significant hazards of
manufacturing, shipping and handling solids offset the system simplicity advantages.
atmosphere the air enters the front of the tube, where it is compressed via the ram effect. As it travels
down the tube it is further compressed and mixed with the fuel-rich exhaust from the rocket engine, which
heats the air much as a combustor would in a ramjet. In this way a fairly small rocket can be used to
accelerate a much larger working mass than normally, leading to significantly higher thrust within the
atmosphere.
5.5) Air turborocket
The air turborocket is a form of combined-cycle jet engine. The basic layout includes a gas generator,
which produces high pressure gas, that drives a turbine/compressor assembly which compresses
atmospheric air into a combustion chamber. This mixture is then combusted before leaving the device
through a nozzle and creating thrust.There are many different types of air turborockets. The various types
generally differ in how the gas generator section of the engine functions.
Air turborockets are often referred to as turboramjets, turboramjet rockets, turborocket expanders, and
many others.
Turborocket
A turborocket is a type of aircraft engine combining elements of a jet engine and a rocket. It typically
comprises a multi-stage fan driven by a turbine, which is driven by the hot gases exhausting from a series
of small rocket-like motors mounted around the turbine inlet. The turbine exhaust gases mix with the fan
discharge air, and combust with the air from the compressor before exhausting through a convergent-divergent propelling nozzle.Once a jet engine goes high enough in an atmosphere, there is
insufficient oxygen to burn the jet fuel. The idea behind a turborocket is to supplement the atmospheric
oxygen with an onboard supply. This allows operation at a much higher altitude than a normal engine
would allow.The turborocket design offers a mixture of benefits with drawbacks. It is not a true rocket, so
it cannot operate in space. Cooling the engine is not a problem because the burner and its hot exhuast
gases are located behind the turbine blades.
Air turboramjet
The air turboramjet engine is a combined cycle engine that merges aspects of turbojet and ramjet engines.
Air passes through an inlet and is then compressed by an axial compressor. That compressor is driven by
a turbine, which is powered by hot, high pressure gas from a combustion chamber. These initial aspects
are very similar to how a turbojet operates, however, there are several differences. The first is that
the combustor in the turboramjet is often separate from the main airflow. Instead of combining air from
Hall effect thrusters accelerate ions with the use of an electric potential maintained between a cylindrical
anode and a negatively charged plasma which forms the cathode. The bulk of the propellant
(typically xenon gas) is introduced near the anode, where it becomes ionized, and the ions are attractedtowards the cathode, they accelerate towards and through it, picking up electrons as they leave to
neutralize the beam and leave the thruster at high velocity.
The anode is at one end of a cylindrical tube, and in the center is a spike which is wound to produce a
radial magnetic field between it and the surrounding tube. The ions are largely unaffected by the magnetic
field, since they are too massive. However, the electrons produced near the end of the spike to create the
cathode are far more affected and are trapped by the magnetic field, and held in place by their attraction to
the anode. Some of the electrons spiral down towards the anode, circulating around the spike in a Hall
current. When they reach the anode they impact the uncharged propellant and cause it to be ionized,
before finally reaching the anode and closing the circuit.
Schematic of a Hall Thruster
Field emission electric propulsion
Field emission electric propulsion (FEEP) thrusters use a very simple system of accelerating
liquid metal ions to create thrust. Most designs use either caesium or indium as the propellant.
propulsion is a proposed method of spacecraft propulsion that uses the fusion of helium-3 atoms as a
power source. Helium-3, an isotope of helium with two protons and one neutron, could be fused
with deuterium in a reactor. The resulting energy release could be used to expel propellant out the back of
the spacecraft. Helium-3 is proposed as a power source for spacecraft mainly because of its abundance on
the moon. Only 20% of the power produced by the D-T reaction could be used this way; the other 80% is
released in the form of neutrons which, because they cannot be directed by magnetic fields or solid walls,
would be very difficult to use for thrust.
Magnetized target fusion (MTF) is a relatively new approach that combines the best features of the more
widely studied magnetic confinement fusion (i.e. good energy confinement) and inertial confinement
fusion (i.e. efficient compression heating and wall free containment of the fusing plasma) approaches.
Like the magnetic approach, the fusion fuel is confined at low density by magnetic fields while it isheated into a plasma, but like the inertial confinement approach, fusion is initiated by rapidly squeezing
the target to dramatically increase fuel density, and thus temperature. MTF uses "plasma guns" (i.e.
electromagnetic acceleration techniques) instead of powerful lasers, leading to low cost and low weight
compact reactors
A still more speculative concept is antimatter catalyzed nuclear pulse propulsion, which would use tiny
quantities of antimatter to catalyze a fission and fusion reaction, allowing much smaller fusion explosions
to be created.
6.4) Bussard ramjet
Bussard proposed a ramjet variant of a fusion rocket capable of fast interstellar spaceflight, using
enormous electro-magnetic fields (ranging from kilometers to many thousands of kilometers in diameter)
as a ram scoop to collect and compress hydrogen from the interstellar medium. High speeds force the
reactive mass into a progressively constricted magnetic field, compressing it until thermonuclear fusion
occurs. The magnetic field then directs the energy as rocket exhaust opposite to the intended direction of
travel, thereby accelerating the vessel.
A major problem with using rocket propulsion to reach the velocities required for interstellar flight is the
enormous amounts of fuel required. Since that fuel must itself be accelerated, this results in an
approximately exponential increase in mass as a function of velocity change at non-relativistic speeds,
asymptotically tending to infinity as it approaches the speed of light. In principle, the Bussard ramjet
avoids this problem by not carrying fuel with it. An ideal ramjet design could in principle accelerate
indefinitely until its mechanism failed. Ignoring drag, a ship driven by such an engine could theoretically
accelerate arbitrarily close to the speed of light, and would be a very effective interstellar spacecraft. In
practice, since the force of drag produced by collecting the interstellar medium increases approximately
as its speed squared at non-relativistic speeds and asymptotically tends to infinity as it approaches the
speed of light (taking all measurements from the ship's perspective), any such ramjet would have a
limiting speed where the drag equals thrust. To produce positive thrust, the fusion reactor must be capable
of producing fusion while still giving the incident ions a net rearward acceleration (relative to the ship).
The collected propellant can be used as reaction mass in a plasma rocket engine, ion rocket engine, or
even in an antimatter-matter annihilation powered rocket engine. Interstellar space contains an average of
10−21
kg of mass per cubic meter of space, primarily in the form of non-ionized and ionized hydrogen,
with smaller amounts of helium, and no significant amounts of other gasses. This means that the ramjet
scoop must sweep 1018
cubic meters of space to collect one gram of hydrogen.
The mass of the ion ram scoop must be minimized on an interstellar ramjet. The size of the scoop is large
enough that the scoop cannot be solid. This is best accomplished by using an electromagnetic field, or
alternatively using an electrostatic field to build the ion ram scoop. Such an ion scoop will use
electromagnetic funnels, or electrostatic fields to collect ionized hydrogen gas from space for use as
propellant by ramjet propulsion systems (since much of the hydrogen is not ionized, some versions of a
scoop propose ionizing the hydrogen, perhaps with a laser, ahead of the ship.) An electric field can
electrostatically attract the positive ions, and thus draw them inside a ramjet engine. The electromagnetic
funnel would bend the ions into helical spirals around the magnetic field lines to scoop up the ions via thestarship's motion through space. Ionized particles moving in spirals produce an energy loss, and hence
drag; the scoop must be designed to both minimize the circular motion of the particles and simultaneously
maximize the collection. Likewise, if the hydrogen is heated during collection, thermal radiation will
represent an energy loss, and hence also drag; so an effective scoop must collect and compress the
hydrogen without significant heating. A magnetohydrodynamic generator drawing power from the
exhaust could power the scoop.
6.5) Solar sail
Solar sailing is a way of moving around in space by allowing sunlight to push a spacecraft.A solar sail is
a very large mirror that reflects sunlight. As the photons of sunlight strike the sail and bounce off, they
gently push the sail along by transferring momentum to the sail. Because there are so many photons from
sunlight, and because they are constantly hitting the sail, there is a constant pressure (force per unit area)
exerted on the sail that produces a constant acceleration of the spacecraft. Although the force on a solar-
sail spacecraft is less than a conventional chemical rocket, such as the space shuttle, the solar-sail
spacecraft constantly accelerates over time and achieves a greater velocity. Solar sails enable spacecraft to
move within the solar system and between stars without bulky rocket engines and enormous amounts of
fuel.
When the spacecraft is in orbit around the Earth or sun, it is traveling in a circular or elliptical path at a
given speed and distance. To go to a higher orbit (travel farther away from the object), you angle the solar
sail with respect to the sun so that the pressure generated by sunlight is in the direction of your orbital
motion. The force accelerates the spacecraft, increases the speed of its orbit and the spacecraft moves into
a higher orbit. In contrast, if you want to go to a lower orbit (closer to the object), you angle the sail withrespect to the sun so that the pressure generated by the sunlight is opposite the direction of your orbital
motion. The force then decelerates the spacecraft, decreases the speed of its orbit and the spacecraft drops
into a lower orbit.
The pressure of sunlight decreases with the square of the distance from the sun. Therefore, sunlight exerts
greater pressure closer to the sun than farther away. Future solar-sail spacecraft may take advantage of
this fact by first dropping to an orbit close to the sun -- a solar fly-by -- and using the greater sunlight
pressure to get a bigger boost of acceleration at the start of the mission. This is called a powered
perihelion maneuver.
6.6) Magnetic sail
A magnetic sail or magsail is a proposed method of spacecraft propulsion which would use a static
magnetic field to deflect charged particles radiated by the Sun as a plasma wind, and thus impart
Beam-powered propulsion is a class of aircraft or spacecraft propulsion mechanisms that use energy
beamed to the spacecraft from a remote power plant to provide energy. Most designs arerocket
engines where the energy is provided by the beam, and is used to superheat propellant that then provides
propulsion, although some obtain propulsion directly from light pressure acting on alight sail structure,
and at low altitude heating air gives extra thrust.
The beam would typically either be a beam of microwaves or a laser. Lasers are subdivided into either
pulsed or continuous beamed.Many proposed spacecraft propulsion mechanisms use power in the form of
electricity or heat. Usually these schemes assume either solar-electric power, or an on-board reactor.
However, both power sources are heavy. Therefore, one could instead leave the power-source stationary,
and power the spacecraft with a maser or alaser beam from a fixed installation. This permits thespacecraft to leave its power-source at home, saving significant amounts of mass.
6.8) Alcubierre drive
The Alcubierre drive, also known as the Alcubierre metric, is a speculative mathematical model of
a spacetime exhibiting features reminiscent of the fictional "warp drive" from Star Trek , which can travel
"faster than light", although not in a local sense.
In 1994, the Mexican physicist Miguel Alcubierre proposed a method of stretching space in a wave which
would in theory cause the fabric of space ahead of a spacecraft to contract and the space behind it toexpand. The ship would ride this wave inside a region known as a warp bubble of flat space. Since the
ship is not moving within this bubble, but carried along as the region itself moves,
conventional relativistic effects such as time dilation do not apply in the way.
Normally, Einstein's theory of relativity doesn't permit any object to travel faster than the speed of light,
because accelerating up to that speed requires an infinite amount of energy. The Alcubierre drive gets
around this by proposing that the drive would actually manipulate spacetime itself, causing the space in
front of it to contract while the space behind it expands. This "warp bubble" allows the ship to reach a
destination faster than a light beam traveling through "normal" spacetime.According to relativity, space is
malleable, which is how the Alcubierre drive achieves this feat. (The early universe, for example,
expanded faster than the speed of light because spacetime itself can expand faster, even though objects
within spacetime cannot accelerate faster.) In this scenario, the ship containing the Alcubierre drive
actually sits still and is carried along the warp bubble, kind of like a surfboard riding on an expanding
wave. This means that time dilation and other relativistic effects aren't significant