Advanced Technology in Propulsion - PHOTON PROPULSION

PHOTON PROPULSION

A form of rocket propulsion, still in the earliest stages of development, in which the reaction is produced by electromagnetic radiation. Types of photon propulsion are:

1) Antimatter (photon rocket)

             Antimatter is the opposite of normal matter, of which the majority of our universe is made. The presence of antimatter in our universe was considered to be only theoretical.

            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. Here are some antimatter discoveries of the 20th century:

• Positrons - Electrons with a positive instead of negative charge. Discovered by Carl Anderson in 1932, positrons were the first evidence that antimatter existed.
• Anti-protons - Protons that have a negative instead of the usual positive charge. In 1955, researchers at the Berkeley Bevatron produced an antiproton.
• 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. As of 1998, CERN researchers were pushing the production of anti-hydrogen atoms to 2,000 per hour.

              When antimatter comes into contact with normal matter, these equal but opposite particles collide to produce an explosion emitting pure radiation, which travels out of 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.

              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.

              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. Therefore 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.
• 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 collider on Earth, a long magnetic nozzle will move the energy created by the matter-antimatter through a thruster.

               Approximately 10 grams of antiprotons would be enough fuel to send a manned spacecraft to Mars in one month. Today, it takes nearly a year for an unmanned spacecraft to reach Mars. In 1996, the Mars Global Surveyor took 11 months to arrive at Mars. Scientists believe that the speed of a matter-antimatter powered spacecraft would allow man to go where no man has gone before in space. It would be possible to make trips to Jupiter and even beyond the heliopause, the point at which the sun's radiation ends. But it will still be a long time before astronauts are asking their starship's helmsman to take them to warp speed.

The problems that must be taken care of before antimatter can be put to use as a fuel source. The first is the creation of antimatter in sufficient quantities, next is the storage of antimatter.

             Before addressing the more fundamental problem of creation, it’s instructive to begin with the question of storage. Although positrons (anti-electrons) are relatively easy to create, they are not easy to store in large quantities. By their very nature, positrons are positively charged and therefore exert a Coulombic force of repulsion against one another. This Coulombic force is extremely powerful and only the smallest amounts of positrons can be stored adequately with current technology.

                Because of this, the ideal storage situation would be the case of neutral antimatter, that is, antimatter with no net

Charge. This could be most simply realized with the creation of antihydrogen, a stable and energetically bound atom   consisting of a single positron and antiproton. A few hundred thousand antihydrogen atoms were produced at CERN in 1995. By their very nature, antihydrogen atoms will annihilate the walls of any container they are stored within. For this reason, specially constructed magnetic storage devices called

Penning traps must be utilized. These devices are not suited for high density storage of antimatter that would be required for space propulsion.

             One possibility might be to store antihydrogen in the form of a Bose Einstein Condensate (BEC), a fifth state of matter (BEC, solid, liquid, gas, and plasma) first predicted to exist in the 1920’s. When matter is cooled to a low enough temperature, its macroscopic state can be modeled by a single quantum wave function and individual atoms lose their independent identities. BEC’s were first created experimentally in the mid-90 and are currently an active research area. In this state, Antihydrogen becomes much easier to store

                 It is possible that particles outnumbered anti-particles at the time of the Big Bang. As stated above, the collision of particles and anti-particles destroys both. so we will have to create our own antimatter. There is technology available to create antimatter through the use of high-energy particle colliders, also called "atom smashers." Atom smashers, like CERN, are large tunnels lined with powerful super magnets that circle around to propel atoms at near-light speeds. When an atom is sent through this accelerator, it slams into a target, creating particles. Some of these particles are antiparticles that are separated out by the magnetic field. These high-energy particle accelerators only produce one or two picograms of antiprotons each year. A picogram is a trillionth of a gram. All of the antiprotons produced at CERN in one year would be enough to light a 100-watt electric light bulb for three seconds. It will take tons of antiprotons to travel to interstellar destinations.

              Clearly a multitude of technological hurdles must be overcome before antimatter use becomes routine in space exploration. However, the fundamental theoretical issues have been proved. Antimatter exists, antihydrogen can be created technologically, and antihydrogen can be stored. The rest is progress.