Antimatter: Space Propulsion, Past, Present, and Future

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Antimatter: Space Propulsion, Past, Present, and Future Powered By Docstoc
					         Antimatter
Space Propulsion, Past Present and Future



               prepared for: Alvin Strauss
               prepared by: T. Brian Jones
         Energy Conversion – December 11, 2003
Table of Contents

THE HISTORY OF ROCKET PROPULSION .........................................................................................3
MODERN ROCKETRY ...............................................................................................................................6
      Example 1 ..............................................................................................................................................6
    SOLID P ROPELLANT ROCKETS ..................................................................................................................6
    LIQUID P ROPELLANT ROCKETS ................................................................................................................7
    WHY OTHER F ORMS OF P ROPULSION?.....................................................................................................7
      Example 2 ..............................................................................................................................................7
ANTIMATTER PROPULSION...................................................................................................................9
    THE HISTORY .............................................................................................................................................9
    THE P HYSICS ............................................................................................................................................10
       Example 3. ...........................................................................................................................................10
    P RODUCTION OF ANTIMATTER................................................................................................................11
    ENGINE DESIGNS ......................................................................................................................................11
    THE DISTANT F UTURE .............................................................................................................................12
CONCLUSIONS..........................................................................................................................................14




                                                                                                                                                            2
The History of Rocket Propulsion
         The first historical account of rocket propulsion comes from the writings of a
Roman, Aulus Gellius, telling the story of a Greek who mystified the citizens of his town
by suspending a wooden bird from a wire and propelling it along with a jet of steam—
circa 400 B.C.1 This earliest demonstration of rocket propulsion used the same concepts
that are used today in modern rocketry, Newton‘s Second Law.
         Newton‘s Second Law states that force equals mass times acceleration (F=Ma).
This basic concept, not developed by Newton until the 17 th century, forms the
conservation of mass law, which states that the mass of object A times the acceleration of
object A equals the mass of object B times its acceleration (M AaA = MBaB, or further
simplified, MA VA = MBVB, where V = Velocity). With this equation in hand, modern
engineers are able to predict the most basic behavior of rockets—up up and away.
         As far as we know, the Chinese had no knowledge of these basic laws of physics
when       they        were        building
fireworks        for       festive     and
religious ceremonies by the first
century A.D. 2         These were the
first true rockets that worked in a
similar manner to the rockets that
we use today to send people into
space. Not until the year 12323
were     these    fireworks,         which
operated     on        a   solid     rocket
propellant made of salt pepper,
sulfur and charcoal dust, finally adapted for warfare for use against the Mongols in the
form of a giant arrow with a firework attached to the front.
         This method of rocket warfare persisted for hundreds of years, until in the early
    th
20 century Robert H. Goddard began experimenting with rockets. In 1919 Goddard

1
  ―Brief History of Rockets.‖ The Space Educators‘ Handbook,
http://vesuvius.jsc.nasa.gov/er/seh/03_Rocket_History.pdf., p. 1.
2
  Ibid, p. 1.
3
  Ibid, p. 2.


                                                                                        3
published a pamphlet entitled A Method of Reaching Extreme Altitudes. In this he
reached some very profound conclusions:

         The velocity required to escape Earth‘s gravitational pull could be reached using multistage
          rockets—crafts that consist of more than one rocket that are triggered in steps as the craft reaches
          higher and higher altitudes.

         Rockets operate with a much higher efficiency when air is not present—in a vacuum like outer
          space. He was immediately mocked for this conclusion as many people at the time believed that
          rockets required air to ‗push off of,‘ but he was correct.

          Goddard‘s work with early rockets was instrumental in modern rocketry. He first
began working with solid rocket propellant, like the Chinese had done, but quickly
became convinced that liquid propellant would better propel his rockets.                           His first
successful flight with a craft of this type came on March 16, 1926. This rocket, seen
below alongside a schematic, climbed 12.5 meters in a time of two and one half seconds,
and came to a crash in a nearby cabbage patch 56 meters away.




          Goddard also developed many other
devices     used     today     including,     payload
compartments, a parachute recovery system
and even a gyroscopic system for flight
control. This is why Goddard is considered
the father of modern rocketry.




                                                                                                            4
       Not until World War II did rocket development reach the pace that would
eventually get us to the moon. After the success of the German V2 rocket, the United
States and Russia began developing rockets for all sorts of military purposes. This race
for technology led to the development of long range intercontinental ballistic missiles
(ICBM‘s) that could deliver a nuclear warhead over the poles and around the world.
Carrying with them the potential to annihilate the human race, these weapons would
eventually serve a different purpose, and missiles like the Redstone, Atlas and Titan
would carry us into outer space.
       On October 4, 1957, the Soviet Union launched the first artificial Earth orbiting
satellite, Sputnik I, following a month later by placing a dog named Laika into orbit
where she survived for seven days before oxygen ran out. A few months after Sputnik I
was launched, the United States put Explorer I into space—The National Aeronautics and
Space Administration (NASA) was formed, and the Space Race was born.
       Men were in space by 1961, and on July 20, 1969 American, Neil Armstrong,
took ―… one giant leap for mankind,‖ and for the first time in human history, stepped out
of the lunar module, and walked on a planetary body other than the Earth. After the
United States reached the moon before ‗The Reds‘ the race to explore outer space died
down. It was no longer part of a struggle for Capitalism and Democracy to devour
Communism; no longer part of national security, and so the budget and drive were
considerably cut.




                                                                                       5
Modern Rocketry
        Returning to Newtonian Mechanics for a discussion of rocket propulsion, lets
consider Newton‘s famous statement; ―For Every action there is an equal and opposite
reaction.‖

    Example 1: A 100 pound man is floating in outer space holding a baseball that weighs 1 pound.
    He accelerates this baseball, by throwing it (or otherwise propelling it away from him), up to a
    velocity of 32 feet per second (ft/s). The force applied to the baseball allowing it to reach a
    velocity of 32 ft/s is also applied to the man. Since he weighs 100 times as much as the baseball,
    he is repelled in the opposite direction of the ball at a velocity of 0.32 ft/s.4

                 Mass of Baseball * Velocity of Ball = Mass of Man * Velocity of Man
                         therefore: Vm = [1 lb * 32 ft/s] / [100 lbs] = 0.32 ft/s

        The principle demonstrated above summarizes, very simply, all of the theory
behind rocket propulsion. Rockets take a fuel and send it out their back end at high
velocities to produce a thrust, thereby causing the firework, missile or space ship they are
attached to, to move in the opposite direction of the fuel.

        Solid Propellant Rockets

        The earliest rockets, like the fireworks used by the
Chinese, were solid fuel rockets. The basic idea behind these
rockets is to fill a chamber with a material that will burn very
rapidly, but will not explode. As the material burns, its gases are
thrown down the rocket and out the back through a nozzle that
increases its velocity.       The diagram to the right shows this
process.
        The benefits of solid fuel rockets are that they are,
relatively, simple, cheap and safe. The big problem with these
engines in terms of space exploration, however, is that once they are ignited, they cannot
be shut off, nor can the predetermined amount of thrust be controlled. This is why they
are only used on the two solid rocket boosters on the side of the space shuttle.


4
 Brain, Marshall, ―How Rocket Engines Work.‖ http://science.howstuffworks.com/rocket.htm. How Stuff
Works Inc.



                                                                                                         6
        Liquid Propellant Rockets

        Just like Goddard‘s early rocket, the main engines on the Space Shuttle use the
vastly more complicated, liquid propellant rocket design. In these engines, a fuel and an
                        oxidizer (Goddard used gasoline and liquid oxygen, respectively),
                        combine in a combustion chamber to burn, releasing high pressure /
                        high temperature gas that is accelerated through a nozzle out the rear
                        of the rocket. Liquid engines are superior to solid rockets in that they
                        are adjustable. Fuel rate is adjustable, as is thrust, and they can be
                        turned off and restarted, not always easily though.                       The major
                        drawback is that with all of the fuel pumps and the cooling
                        mechanisms associated with the high temperatures, they can be
                        expensive, complicated and dangerous.                  The diagram to the left
                        shows a very simplified schematic of a liquid propulsion rocket.



        Why Other Forms of Propulsion?

        The Space Shuttle consists of the orbiter (The craft that carries people and cargo
into, and around in, space.), the external liquid fuel tank (This carries fuel for the orbiters
three rockets.) and the two solid rocket boosters on either side. The purpose of this
combination of parts is to get the crew, the cargo and the orbiter into space.

    Example 2: The orbiter weighs 165,000 lbs empty, and with a full payload, 330,000 lbs. When
    full of fuel, the solid rocket boosters, together, weigh 2.57 million lbs, and the full liquid fuel tank
    weighs an additional 1.59 million lbs—a total weight of 4.65 million pounds. To get the orbiter,
    its crew and its cargo into space, 15 times the original weight must be launched from the ground.5

        Now let‘s consider sending craft to other planets. When the Unites States sent the
Cassini Spacecraft on its voyage to Saturn, it had to go through the following steps:

       A liquid propulsion rocket was used to get it into space.
       A second liquid propulsion rocket was used to get the craft out of near-Earth orbit.


5
 Freudenrich, Craig, Ph.D., ―How Space Shuttles Work.‖ http://science.howstuffworks.com/space-
shuttle.htm. How Stuff Works Inc.



                                                                                                               7
      Finally the craft used the principles of planetary gravity to slingshot itself around Venus, back
       around Earth, and around Jupiter before it was finally on its way to Saturn.

       This process is extremely complicated and very slow. Cassini was launched in
1997 and will not enter orbit around Saturn until July of 2004. This may be a practical
means of travel to the moon, and even Mars, but it leaves the rest of the universe
unreachable by humans.         Even if we did send ships, it would take thousands of
generations just to reach Proxima Centauri—the nearest star to the Sun.
       The major problem with current rocket propulsion is the inefficiency of the
energy conversion process involved with current fuels. For spacecraft to achieve speeds
necessary to reach other stars, they would have to carry unimaginable amounts of fuel—
putting the ratio of fuel to cargo in the thousands or even millions. Plus the same amount
of fuel must be available for stopping once the craft reaches its destination, and the more
fuel we pack in the ship for later, the more we need to accelerate it in the first place.
       To help explore our universe we need a source of power that is vastly more
efficient than anything we have today—solid, liquid and even nuclear.




                                                                                                      8
Antimatter Propulsion
       The History

       In December of 1929, a paper was published by a young physicist named Paul
Dirac. Dirac had set out to combine some of the greatest theories in modern physics—as
discrepancies existed, and still do today, between predictions made by Einstein‘s
equations of special relativity, Maxwell‘s equations for electromagnetism and
Schrödinger‘s equations for quantum mechanics. In this paper, Dirac had suddenly
uncovered something surprisingly fresh and quite bizarre about the universe. Sometimes
the solutions of his new equations resulted in a particle with the same mass as an
electron, but with opposite energy.




       A few years later in 1932, while doing experiments to study cosmic rays, Robert
Millikan and Carl Anderson, observed unexplainable symmetric trails of particles
through what they called a cloud chamber. Without
knowing about Dirac‘s predictions a few years
earlier, the two finally came to the conclusion that
the symmetric lines they had seen in their clouded
magnetic field were those of the electron and the
positron—the electrons anti-particle.   The cloud-
chamber photograph to the right, shows the track of
a positively charged particle of electronic mass
slowed down by passing upward through a lead
plate—Anderson, 1932.6


6
 LBNL Image Library, http://imglib.lbl.gov/ImgLib/COLLECTIONS/BERKELEY-LAB/PARTICLE-
DETECTION/CLOUD-CHAMBERS/index/pg09_cloudchamber.html.


                                                                                       9
        The Physics

        Today, we know that each elementary particle has an anti-particle—the electron
has the positron, and the proton has the anti-proton. The useful discovery regarding these
anti-particles is that they are part of the most complete
form of energy conversion in the known universe.
When an anti-particle contacts a regular particle, like
the ones everything we know are made of, they
annihilate each other completely, releasing all of their
mass in the form of energy, as predicted by Einstein‘s
equation: E = mc2. The electron / positron collision
releases two gamma ray photons and the proton / anti-
proton collision releases its energy in the form of four pions.                    This result can be
multiplied and applied to actual anti-matter. The collision signature of hydrogen and
anti-hydrogen, consists of two gamma ray photons and four pions.                         The computer
generated image above shows the annihilation of an atom of hydrogen with anti-
hydrogen, forming two gamma rays and four pions. 7
        Although the energy released by the reaction in the earliest H-bombs, about 4.7
meV, is much larger than that released by the electron / positron annihilation, 511keV,
the electron is thousands of times less massive. This collision energy is actually 10
billion times the energy released by chemical reactions like oxygen / hydrogen, 1,000
times more than the energy released in nuclear fission and 300 times more than nuclear
fusion.8
             Example 3: Impulse and thrust to weight ratio for different forms of propulsion.9

              Propulsion Type              Specific Impulse [sec]      Thrust-to-Weight Ratio
            Chemical Bipropellant                200 - 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 Annihilation              10+3 - 10+6                   10-3 - 1


7
  ―Antihydrogen Antics.‖ http://www.physicscentral.com/action/action-03-06-print.html.
8
  Bonser, Kevin, ―How Antimatter Spacecraft Will Work.‖
http://science.howstuffworks.com/antimatter.htm. How Stuff Works Inc.
9
  Smith, Gerald A. Dr., ―Antimatter Space Propulsion.‖
http://www.engr.psu.edu/antimatter/introduction.html. Penn State University, February 27, 2001, p. 1.


                                                                                                        10
            Production of Antimatter

            Antimatter is very difficult to produce, and even by the mid 90‘s antimatter was
only being produced a few particles at a time—even these particles were only being
observed for millionths of a second as they raced away at the speed of light. To make
antimatter, regular particles must be accelerated in giant particle accelerators like the
ones at Fermi lab in Chicago, and CERN in Switzerland.               These accelerators are
enormous circular tubes that use magnetic fields to propel particles to near the speed of
light, and then to collide them with a target, or with other particles traveling in the
opposite direction. After the collision anti-particles must quickly be slowed down and
separated via other magnetic fields and placed into a new magnetic containment device
where they are prevented from coming into contact with any ‗regular‘ matter.
            Researchers at Penn State have developed a portable device called a Penning Trap
that uses liquid nitrogen and helium to slow these antiparticles to manageable speeds, still
fractions of the speed of light, and then to capture them in a magnetic containment field.
From here they have learned to combine anti-protons and positrons to produce anti
hydrogen, more controllably and more efficiently.

            Engine Designs

            This Penning Trap can currently hold 1010 antiprotons for up to a week. The next
generation trap being developed at NASA is going to house 10 12. Fermi lab is also
currently implementing a new Main Injector Ring that will allow their facility to produce
14 ng of antiprotons per year—combined with a recycling ring, production may increase
by ten fold. 10
            Production of this magnitude is enough to fuel the
Antiproton Catalyzed Microfission Engine (ACMF).
This engine uses the energy from antiproton collisions to
induce a fission reaction where all of the material reacting
is used as a propellant for the rocket.        This is vastly
superior to a nuclear fission reactor where much of the
energy from the nuclear reaction is lost in heating a propellant. Using this engine design,
10
     Ibid, p. 2.


                                                                                         11
the Ion Compressed Antimatter Nuclear (ICAN-II) spacecraft, being developed at Penn
State, could, theoretically, complete a manned mission to Mars with a total transit time of
                                                            30    days       on     only     140    ng   of
                                                                           11
                                                            antiprotons.          At current production
                                                            levels, this is still at least ten years
                                                            away.
                                                                     A more futuristic design uses
                                                            antimatter and a microfission reaction
                                                            to    initiate        repeated    microfusion
                                                            reactions—the          Antiproton      Initiated
                                                            Microfission/fusion            (AIM)    engine.
                                                            This engine design would require three
degrees of magnitude more antiprotons for practical applications, but provides a much
higher impulse than the ACMF engine. The experimental benefits of this engine are that
each reaction only requires 5E8 antiprotons. 12              With the development of its bigger
Penning Trap, NASA hopes to be able to actually test this engine in the near future.
        All of the previously discussed designs use current technology, in combination
with antimatter, to produce thrust for an engine. Theoretically, the simplest, and most
efficient, engine model would be the ―beam-core‖ Matter-Antimatter Annihilation
Propulsion engine. This engine allows the full potential of matter/antimatter annihilation
to be realized converting about 62% of the initial rest mass into energy in the form of
pions.13 These are then focused and directed out a magnetic nozzle for propulsion. This
engine is simple, but in actuality, very difficult to build properly. The pions created in
the mass/energy conversion process are released in every direction at the speed of light
and must be captured and controlled without losing their useful energy.


        The Distant Future
11
   Ibid, p. 2.
12
   Ibid, p. 2.
13
   Frisbee, Robert H., ―Systems-Level Modeling of a Beam-Core Matter-Antimatter,‖
http://ntrs.nasa.gov/index.cgi?method=display&redirect=http://techreports.jpl.nasa.gov/2000/00-
0212.pdf&oaiID=oai:jpl-trs.jpl.nasa.gov:00-0212. Jet Propulsion Laboratory, California Institute of
Technology, Pasadena, California.



                                                                                                         12
       Even with these fantastic engines using the most energy efficient propulsion
method known, the human race will be unable to realistically travel around the universe.
We are not allowed to move faster than the speed of light, and therefore would waste four
years just traveling to the nearest star, other than the Sun. To solve this problem, the
writers of Star Trek developed Warp Drive. In the seventies, when it was first conceived,
Warp Drive was nothing but a literary work of fiction.             The idea, however, was
revolutionary and decades ahead of its time in design and in physics. Warp drive is a
fantastic idea that uses the tremendous power that is created by matter/antimatter
collisions to actually warp space time.
       According to Einstein‘s theory of special relativity, objects only have to move
slower than the speed of light, locally. Assume the Sun is moving locally away from
some hypothetical ‗center of the universe‘ at 9/10 the speed of light. And, then assume
that there is another star directly opposite the sun moving away from the same center at
the same speed. Neither of these stars are moving faster then light relative to the center,
but relative to each other, they are moving at near twice the speed.
       Warp Drive uses this principle.          The energy created by matter/antimatter
collisions is used to create near-black holes that shrink space time in front of the ship,
while stretching it behind. This trick allows the ship to obey Einstein‘s laws, while
allowing the ship to cover tremendous distances very quickly. This sort of manipulation
of the universe is still centuries away—if it will ever be realized.




                                                                                        13
Conclusions
       Until the early part of this century, flight was something that was said to be
impossible. Scientists left this fantastic idea to the whims of dreamers and science fiction
writers. Until the 1960‘s, space travel was something that fell into the same category.
Why then do so many brilliant minds say that mankind will never travel to other stars?
Antimatter seems like something made up for a story, and in fact, something like it had
been many times before its existence was ever predicted or even proven.             As the
progression from Earth to space to Moon to Mars moves us further out into our solar
system, new forms of propulsion and space travel will need to be developed. Antimatter
is the next logical step in a science that will ultimately allow the human race to explore
the universe.




                                                                                         14

				
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Description: This is a paper I wrote my senior year as a mechanical engineering student for a class called 'Energy Conservation.'
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