Antimatter Propulsion

_____________________________________________________________Antimatter propulsion

ANTIMATTER PROPULSION

Humankind has been exploring space for four decades, and in that time our

reach

has

extended throughout the solar system with the use of unmanned

probes. Finally, what about the exploration of other solar

systems?

INTRODUCTION

Humankind has been exploring space for four decades, and in time our

reach has extended throughout the solar system with the use of unmanned

probes. Finally, what abut the exploration of our solar systems?

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These issues are being addressed by the NASA Advanced Space

Transportation Program (ASTP), which is currently investigating new ways to

propel a unmanned spacecraft to Alpha Centauri in the span of a human

lifetime of 50 years Both tasks suffer the same dilemma: chemical propellants

simply will not work. For the first case, chemical propellants lack the energy

needed to boost a space probe up to 10% the speed of light. The overall

mass of such a booster would be unthinkable. For the latter case, the

spacecraft only needs to obtain the velocity necessary to get to Mars within 3-

6 months; however, the mass of a manned payload once again places a

burden on the size of the booster engine.

Many concepts have been devised. For years, scientists have

suggested nuclear fission as an alternative approach for sending a manned

spacecraft to Mars. Although the specific impulse (Isp) is still too low for

interstellar missions, it does open new avenues near the vicinity of Earth.

Unfortunately, environmental issues have all but "grounded" the use of

nuclear fission as a propulsion source. Nuclear fusion is cleaner, and it is a

more exciting prospect with its higher energy density and specific impulse.

However, scientists are still developing such a device that offers beyond

break-even energy (more energy output than input), let alone making the

same device small enough to be sent into deep space. Last, electric

propulsion, as used for Deep Space I, cannot accelerate a spacecraft fast

enough for the tasks mentioned above due to its low thrust-to-weight ratio.

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It is here that antimatter addresses attention. Upon

annihilation with matter, antimatter offers the highest energy

density of any material currently found on Earth. As shown in the

table below, this indicates that antimatter offers the greatest

specific impulse of any propellant currently available or in

development, and its thrust-to-weight ratio is still comparable with

that of chemical propulsion. Simply put, it would take only 100

milligrams of antimatter to equal the propulsive energy of the

Space Shuttle.

Propulsion

Type

Specific

Impulse [sec]

Thrust-to-

Weight Ratio

Chemical

Bipropellant200 - 410 .1 - 10

Electromagnetic 1200 - 5000 10-4 - 10-3

Nuclear Fission 500 - 3000 .01 - 10

Nuclear Fusion 10+4 - 10+5 10-5 - 10-2

Antimatter

Annihilation10+3 - 10+6 10-3 - 1

Antimatter is one of the most recognized and attractive words in

science fiction. It's the stuff that drives fictional starships from one side of the

universe to the other. Now NASA is giving it serious consideration as a rocket

propellant to get around the solar system. A gram of antimatter would carry as

much potential energy as 1,000 Space Shuttle external tanks carry.

The rockets will employ the ages old action-reaction principle in an

interesting meeting of Albert Einstein (E=mc2) and Isaac Newton (F=ma).

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What is Antimatter?

Antimatter is exactly what you might think it is -- the opposite of normal

matter, of which the majority of our universe is made. Until just recently, the

presence of antimatter in our universe was considered to be only theoretical. In

1928, British physicist Paul A.M. Dirac revised Einstein's famous equation

E=mc2. Dirac said that Einstein didn't consider that the "m" in the equation --

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mass -- could have negative properties as well as positive. Dirac's equation (E =

+ or - mc2) allowed for the existence of anti-particles in our universe. Scientists

have since proven that several anti-particles exist.

These anti-particles are, literally, mirror images of normal matter. Each

anti-particle has the same mass as its corresponding particle, but the electrical

charges are reversed.

Positrons –

Electrons with a positive instead of negative charge. Discovered by

Carl Anderson in 1932, positrons were the first evidence that antimatter

existed.

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Anti-protons –

Protons that have a negative instead of the usual positive charge.

Anti-atoms –

Pairing together positrons and antiprotons, scientists at CERN, the

European Organization for Nuclear Research, created the first anti-atom.

Nine anti-hydrogen atoms were created, each lasting only 40 nanoseconds.

Annihilation –

The complete conversion of matter into energy-releases the most

energy per unit mass of any known reaction in physics.

When antimatter comes into contact with normal matter, these equal but

particles collide to produce an explosion emitting pure radiation, which travels

out opposite the point of the explosion at the speed of light. Both particles that

created the explosion are completely annihilated, leaving behind other

subatomic particles. The explosion that occurs when antimatter and matter

interact transfers the entire mass of both objects into energy. Scientists

believe that this energy is more powerful than any that can be generated by

other propulsion methods.

So, why haven't we built a matter-antimatter reaction engine? The problem

with developing antimatter propulsion is that there is a lack of antimatter

existing in the universe. If there were equal amounts of matter and antimatter,

we would likely see these reactions around us. Since antimatter doesn't exist

around us, we don't see the light that would result from it colliding with matter.

.

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Matter-Antimatter Engine

Scientists announced early designs for an antimatter engine that could

generate enormous thrust with only small amounts of antimatter fueling it. The

amount of antimatter needed to supply the engine for a one-year trip to Mars

could be as little as a millionth of a gram. Matter-antimatter propulsion will be

the most efficient propulsion ever developed, because 100 percent of the

mass of the matter and antimatter is converted into energy. When matter and

antimatter collide, the energy released by their annihilation releases about 10

billion times the energy that chemical energy such as hydrogen and oxygen

combustion, the kind used by the space shuttle, releases. Matter-antimatter

reactions are 1,000 times more powerful than the nuclear fission produced in

nuclear power plants and 300 times more powerful than nuclear fusion

energy. So, matter-antimatter engines have the potential to take us farther

with less fuel.

There are three main components to a matter-antimatter engine:

Magnetic storage rings –

Antimatter must be separated from normal matter so storage rings

with magnetic fields can move the antimatter around the ring until it is needed

to create energy.

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Feed system –

When the spacecraft needs more power, the antimatter will be

released to collide with a target of matter, which releases energy.

Magnetic rocket nozzle thruster –

Like a particle collided on Earth, a long magnetic nozzle will move the

energy created by the matter-antimatter through a thruster. The storage rings

on the spacecraft will hold the antimatter.

The popular belief is that an antimatter particle coming in contact with

its matter counterpart yields energy. That's true for electrons and positrons

(anti-electrons). They'll produce gamma rays at 511,000 electron volts.

But heavier particles like protons and anti-protons are somewhat

messier, making gamma rays and leaving a spray of secondary particles that

eventually decay into neutrinos and low-energy gamma rays.

And that is partly what Schmidt and others want in an antimatter

engine. The gamma rays from a perfect reaction would escape immediately,

unless the ship had thick shielding, and serve no purpose. But the charged

debris from a proton/anti-proton annihilation can push a ship.

Production of Antimatter

Antimatter does not exist in nature or at least certainly nowhere near

us, which is just as well. If it did it would immediately annihilate with matter

and explode with more force than we have ever experienced.

This means we have to manufacture it and then very carefully store it;

it is only produced at certain high-energy laboratories around the world

(probably most famously at CERN in Geneva).

The actual manufacturing is achieved in a particle accelerator creating

extremely high-energy collisions. Over the past 20 years scientists at CERN

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have been using antiparticles in many different ways for their daily work.

Electrons and positrons (anti electrons) do a neat job of it, but protons

and antiprotons are messy. They yield three types of pions that 1) decay to

produce gamma radiation 2) decay to produce muons and neutrinos plus

electrons and positrons that make more gamma rays. Electrons are

lightweight and tough to store in a magnetic model, so scientists have been

working on antiprotons whose greater mass makes them easier to handle.

(Even anti-atoms that might be stored at near absolute zero are a possibility.)

Billionths of a gram of antiprotons are created each year in high-energy

particle accelerators high in the Alps. A billion antiprotons are produced every

10 minutes, but only 1,000 of those are captured and stored.

Antiparticles can be generated by colliding subatomic particles. Before

being delivered to the various physics experiments, they must be isolated,

collected and stored in order to tune their energy to the appropriate level.

Until now, each of these steps has been carried out by a dedicated

machine with the main purpose of providing high-energy antiparticles.

But now the first "self-contained antiproton factory", the Antiproton

Decelerator (or AD), is operational at CERN . It will produce the low energy

antiprotons needed for a range of studies, including the synthesis of

antihydrogen atoms - the creation of antimatter.

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Making Antiprotons

Antimatter in the form of antiprotons is being made today, albeit in

small quantities. The antiprotons are generated by sending a high-energy

beam of protons into a metal target. When the relativistic protons strike the

dense metal nuclei, their kinetic energy, which is many times their rest-mass

energy, is converted into a spray of particles, some of which are antiprotons.

A magnetic field focuser and selector separates the antiprotons from the

resulting debris and directs the antiprotons into a storage ring. These

collecting rings have stored as many as 1012 antiprotons for day sat a time. To

give some scale as to what has already been accomplished at these research

facilities, 1012 antiprotons have a mass of 1.7 pg. When this amount of

antimatter is annihilated with an equivalent amount of normal matter, it will

release300 J, an engineering significant amount of energy.

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STORING ANTIMATTER

In a recent experiment, a team of scientists took the low energy

antiprotons in one of these rings, slowed them down to almost zero velocity,

and captured a few hundred antiprotons in a small electromagnetic ion trap.

Other experiments planned for late 1987 will attempt to capture many millions

of antiprotons in a trap no bigger than a thermos bottle. The electromagnetic

trap will be made portable so the antiprotons can be transported to other

laboratories for experiments.

In order to use antiprotons as a propulsion fuel, it will be necessary to

find a more compact method of storage than an ion trap, which is limited to

relatively low ion densities. Another Air Force sponsored research program is

looking into adding positrons to the antiprotons in the ion traps and slowly

building up "cluster ions" of antihydrogen. These cluster ions are large

agglomerations of neutral antihydrogen atoms clustered around a single

antiproton ion. The net negative electric charge of the cluster ion allows it to

be kept in the ion trap, yet the mass of each ion can be increased until we

have an ice crystal with enough charge that it can be electrostatically levitated

without touching the walls of the cryogenically cooled trap

Antimatter does not exist in nature - or at least certainly nowhere near

us, which is just as well. If it did it would immediately annihilate with matter

and explode with more force than we have ever experienced.

This means we have to manufacture it and then very carefully store it;

it is only produced at certain high-energy laboratories around the world

(probably most famously at CERN in Geneva).The actual manufacturing is

achieved in a particle accelerator creating extremely high-energy collisions,

which results in the kinetic energy being converted to matter (subatomic

particles), some of which is antimatter.

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Storage is possible because it may be controlled in magnetic fields,

thereby avoiding the obvious problem of trying to store it in structural

containers.

The Penning trap has been developed; it is a portable antiproton trap,

which is capable of storing 1010 (10^10) antiprotons for one week using the

superposition of electric and magnetic fields. The next stage is an

improvement to 1012 (10^12) antiproton storage.

For complete antimatter propulsion it is thought that 1020 (10^20) anti-protons

will need to be stored.

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Storage is possible because it may be controlled in magnetic fields,

thereby avoiding the obvious problem of trying to store it in structural

containers.

APPLICATION TO PROPULSION

Because of the long lifetime and interaction length of the charged pions

that result from the annihilation of antiprotons with protons, it is relatively easy

to collect the charged pions in a thrust chamber constructed of magnetic

fields and to obtain propulsion from them.

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As is shown in Figure the energy in the pions can then either be used

to heat a working fluid, such as hydrogen, to produce thrust, or the high-

speed pions themselves can be directed by a magnetic nozzle to produce

thrust. Even after the charged pions decay, they decay into energetic charged

muons, which have even longer lifetimes and interaction lengths for further

conversion into thrust. Thus, if sufficient quantities of antiprotons could be

made, captured, and stored, then presently known physical principles show

that they can be used as a highly efficient propulsion fuel.

Since antimatter does not exist naturally, it must be made, one particle

at a time. It is a synthetic fuel. It will always require much (~l04 times) more

energy to produce antimatter than can be extracted from the annihilation

process. Its major advantage is that it is a highly concentrated form of energy

storage. A tenth of a milligram, about the size of a single grain of salt,

contains the energy of 2 tonnes of the best rocket fuel known, liquid

oxygen/liquid hydrogen.

A study that compared antihydrogen propulsion systems with chemical

propulsion systems found that antiproton propulsion could possibly be cost

effective for space propulsion. More importantly, it was mission enabling, in

that it would allow missions to be performed that are essentially impossible to

perform with chemical fuels.

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There are four main designs for an antimatter rocket; they are listed here

in increasing specific impulse:

Solid Core - Annihilation occurs inside a solid-core heat exchanger, the

reaction superheats hydrogen propellant that is expelled through a nozzle.

High efficiency and high thrust, but due to the materials the specific

impulse is only 1000secs at best.

Gas Core - Annihilation occurs in the hydrogen propellant. The charged

pions are controlled in magnetic fields and superheat the hydrogen; there

is some loss in the form of gamma rays that cannot be controlled. Specific

impulse of 2500secs.

Plasma Core - Annihilation of larger amounts of antimatter in hydrogen to

produce hot plasma. Plasma contained in magnetic fields, again some

loss in form of gamma radiation, and the plasma is expelled to produce

thrust. There are no material constraints here so higher specific impulse is

possible (anywhere from 5,000 to 100,000secs).

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Beam Core - Direct one to one annihilation, magnetic fields focus the

energetic charged pions that are used directly as the exhausted propellant

mass. These pions travel close to speed of light.

ADVANTAGES:

1. Antimatter is hundred percent efficient. When Antimtter comes in contact

with Matter it annihilates and the whole is converted into Energy.

2. For propulsion of spacecraft the amount of Antimatter required will be very

less. A ten-gram of Antimatter would be enough to send manned

spacecraft to Mars.

3. Specific impulse of Antimatter is very high. The specific impulse could be

greater than 10,000,000secs.

4. Speed of Antimatter particles is about 94% that of speed of light. The

spacecrafts with fuel as Antimatter will almost travel at the speed of light.

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DISADVANTAGES:

1. Problem with developing Antimatter is that it does not exists naturally.

2. Production of Antimatter is a problem .A few gram of Antimatter will take

many years. Large-scale production techniques are not yet developed.

3. Storing Antimatter is very difficult. It requires special vessels to store.

4. Time of existence of Antimatter is very less. When scientist made Anti-

atoms, each of which lasted for about 40 billionths of second.

5. Energy from matter-antimatter reaction is released in the form of particles

moving about one third speed of light. Speed is very high.

6. Antimatter is the most expensive substance on Earth about $62.5 trillion a

gram.

OTHER APPLICATIONS:

1. Antimatter can be used in medicine for scanning.

2. It can be used for medical diagnosis where positrons are used to identify

diseases with positron emission Tomography or PET-scan.

3. Antimatter can be used to propel the future cars.

4. It is possible to built Antimatter weapon.

5. By beaming Anti-protons through large metal structure to detect flaws and

even to cure flaws internally.

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PLANS FOR ANTI-MATTER PROPULSION:

Because antiproton propulsion promises a major advance in Space

propulsion capability, the recently completed Air Force Systems Command

Project Forecast II study recommended that their Force start a new program

in antimatter propulsion. As a direct result of the Project Forecast II

recommendations, the Air Force Astronautics Laboratory at Edwards AFB in

California has reorganized its advanced propulsion activities and formed a

new project called ARIES (Applied Research In Energy Storage). The project

has two major thrusts - chemically bound excited states and antimatter.

The Air Force Office of Scientific Research has initiated a new

program on antimatter research in the Physical and Geophysical Sciences

Branch under Col. Hugo Weichel. The Program Manager for Antimatter is

Maj. John Prince, who evaluates unsolicited proposals for research on

antimatter sciences. In Europe, an Antimatter Research Team (ART) has

been formed atTelespazio, SpA per I.e. Communication Spaziali in Italy. Their

research work will cover antiproton and positron production and storage, and

engine simulations, leading ultimately to technology demonstrations.

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CONCLUSION:

After analyzing the whole topic, it can be concluded that the Antimatter

propulsion even though it is under development ,but it will certainly bring

revolutionary change in conventional propulsion systems. Now mankind can

think about the journey beyond the Galaxy.

Scientist believe that the speed of an Matter-Antimatter powered

spacecrafts would allow man to go where no man has gone before in space.

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BIBLIOGRAPHY:

Various internet sites www.howstuffworks.com www.nasa.org www.psu.com www.sciam.com

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Antimatter Propulsion