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Former Fermilab physicist Gerald Jackson has stated, “Antimatter-driven spacecraft prototype could be tested within a decade. To that end, next month, Jackson and his Chicago-based Hbar Technologies firm are launching a $200,000 Kickstarter campaign to crowdfund the next phase of its antimatter propulsion research.
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. Matter-antimatter reactions release 10 billion times more energy than chemical energy such as hydrogen & oxygen combustion, 1,000 times more powerful than the nuclear fission produced in nuclear power plants and 300 times more powerful than nuclear fusion energy.
Matter-antimatter engines have the potential to take us farther into space, with propulsion velocities of some 40% of the speed of light they would cut the travel times to the nearby Alpha Centauri star system from current 30,000 years to less than a decade and with mass of fuel that is comparative to the payload. The near term applications could include Google Skybox for images of Earth, Samsung and One Web for universal internet, scanning for agricultural data, and military applications.
One of the most difficult challenge in developing antimatter propulsion is extreme scarcity of antimatter existing in the universe. Scientists discovered one of possible deposit of antimatter is the center of our own Milky Way galaxy.
On Earth, by contrast, most antimatter has to be generated in particle physics accelerators at laboratories like Fermilab or CERN. Atom smashers, like CERN, are large tunnels lined with powerful supermagnets 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.
However these high-energy particle accelerators only produce one or two picograms of antiprotons each year. A picogram is a trillionth of a gram. One requires approximately 10 grams of antiprotons fuel to send a manned spacecraft to Mars in one month.
At the highest possible rate at which CERN facilities would be capable of generating antimatter, it would take about one hundred billion years to generate one gram of antihydrogen. Proposals have been made to build facilities that would be capable of generating and capturing antimatter far more economically than CERN facilities, but would be extremely expensive to develop and still only generate minute quantities of antimatter.
Naturally-occurring antimatter could exist in the Van Allen belts of Earth and Jupiter, and if this could be collected with magnetic scoops, it may prove more economically viable than artificially generating antimatter.
Kevin Bonsor in Science enumerates 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.
NASA Institute for Advanced Concepts (NIAC) funds study by Positron Reactor
Another challenge is that some antimatter reactions produce blasts of high energy gamma rays. Gamma rays have high energies to penetrate matter and break apart molecules in cells, so are harmful. High-energy gamma rays can also make the engines radioactive by fragmenting atoms of the engine material.
The NASA Institute for Advanced Concepts (NIAC) is funding a team of researchers working on a new design for an antimatter-powered spaceship that avoids this nasty side effect by producing gamma rays with much lower energy.
Previous antimatter-powered spaceship designs employed antiprotons, which produce high-energy gamma rays when they annihilate. The new design will use positrons, which make gamma rays with about 400 times less energy.
Ryan Weed and his team at Positron Dynamics are creating the spacecraft that could loop Earth in three seconds and reach Mars in weeks. NASA spacecraft are currently powered by ion thrusters, which have top speeds of 200,000mph. The antimatter rocket could hit speeds of 72 million mph, Weed claimed.
Positronics Research, LLC’s rocket powered by a positron reactor consists of storage unit of Positrons, which are directed to the attenuating matrix, where they interact with the material and release heat as reported by Bill Steigerwald of NASA Goddard Space Flight Center. Liquid hydrogen (H2) circulates through the attenuating matrix and picks up the heat. The hydrogen then flows to the nozzle exit, where it expands into space, producing thrust.
“The most significant advantage is more safety,” said Dr. Gerald Smith of Positronics Research, LLC, in Santa Fe, New Mexico. The current Reference Mission calls for a nuclear reactor to propel the spaceship to Mars. This is desirable because nuclear propulsion reduces travel time to Mars, increasing safety for the crew by reducing their exposure to cosmic rays.
Also, a chemically-powered spacecraft weighs much more and costs a lot more to launch. The reactor also provides ample power for the three-year mission. But nuclear reactors are complex, so more things could potentially go wrong during the mission. “However, the positron reactor offers the same advantages but is relatively simple,” said Smith, lead researcher for the NIAC study.
Also, nuclear reactors are radioactive even after their fuel is used up. After the ship arrives at Mars, Reference Mission plans are to direct the reactor into an orbit that will not encounter Earth for at least a million years, when the residual radiation will be reduced to safe levels. However, there is no leftover radiation in a positron reactor after the fuel is used up, so there is no safety concern if the spent positron reactor should accidentally re-enter Earth’s atmosphere, according to the team.
It will be safer to launch as well. If a rocket carrying a nuclear reactor explodes, it could release radioactive particles into the atmosphere. “Our positron spacecraft would release a flash of gamma-rays if it exploded, but the gamma rays would be gone in an instant. There would be no radioactive particles to drift on the wind. The flash would also be confined to a relatively small area. The danger zone would be about a kilometer (about a half-mile) around the spacecraft. An ordinary large chemically-powered rocket has a danger zone of about the same size, due to the big fireball that would result from its explosion,” said Smith.
One technical challenge to making a positron spacecraft a reality is the cost to produce the positrons. Because of its spectacular effect on normal matter, there is not a lot of antimatter sitting around. In space, it is created in collisions of high-speed particles called cosmic rays. On Earth, it has to be created in particle accelerators, immense machines that smash atoms together. The machines are normally used to discover how the universe works on a deep, fundamental level, but they can be harnessed as antimatter factories.
“A rough estimate to produce the 10 milligrams of positrons needed for a human Mars mission is about 250 million dollars using technology that is currently under development,” said Smith. This cost might seem high, but it has to be considered against the extra cost to launch a heavier chemical rocket (current launch costs are about $10,000 per pound) or the cost to fuel and make safe a nuclear reactor. “Based on the experience with nuclear technology, it seems reasonable to expect positron production cost to go down with more research,” added Smith.
Another challenge is storing enough positrons in a small space. Because they annihilate normal matter, you can’t just stuff them in a bottle. Instead, they have to be contained with electric and magnetic fields. “We feel confident that with a dedicated research and development program, these challenges can be overcome,” said Smith.
Air Force Institute of Technology (AFIT) study
In late 1994 Air Force Institute of Technology (AFIT) study was chartered to find ways to launch payloads from the Earth’s surface to low-earth orbit without the use of conventional chemical combustion (fuel and oxidizer). The study considered Antimatter Propulsion or enormous energy released from matter-antimatter annihilation as one of their approach.
In a simple picture, antiprotons and positrons would be slowed, trapped, and recombined to form a charged anti-hydrogen cluster. This antimatter cluster forms one part of a bipropellant fuel, the other being ordinary hydrogen. The antimatter cluster is then reacted with ordinary hydrogen and almost completely converted into energy.
The energy density of a propellant is linked to the characteristics of the reaction producing the energy release. Chemical reactions swap bond energies, with the energy released being of the order of electron volts per reaction.
Nuclear reactions swap nuclear bond energies releasing energies of the order of millions of electron volts per reaction. Similar to nuclear reactions, antimatter reactions swap rest mass energies, releasing energies of the order of a billion electron volts per reaction.
The concept, in essence, is beautifully simple yet implementation eludes our current understanding and capabilities when we consider the requirements facing any high-energy-density fuel. “Any HED fuel must be able to be economically produced in quantity, stored, reacted in a controlled manner, and permit efficient utilization of the energy released to directly or indirectly produce thrust. ”
Antimatter fails each of these requirements. While very small amounts of antimatter would be required to provide the necessary heat source, current methods of producing and storing antiprotons provide trillions of times (12 orders of magnitude) less capability than what is needed.
Even assuming that the host of difficulties associated with production and storage are surmountable, one faces the fundamental problem that the reactions themselves are extremely complex, and the products of the reaction include both high-energy radiation and elementary particles. These products are not terribly useful for propulsion since they are not easily converted to thrust (they are moving very fast and pass right through all but the heaviest materials without depositing their energy).
The environmental and safety concerns are similar to those associated with nuclear propulsion. Even if adequate shielding against the gamma radiation can be provided, temperatures will likely be so high as to require magnetic confinement to prevent meltdown of the reaction chamber.
“From an operational standpoint, the failure of such a containment system will be catastrophic, resulting in a meltdown of the reactor and release of extremely radioactive by-products. Presently, there does not appear to be any way to make such a magnetic confinement system fail-safe. Therefore, antimatter propulsion systems and fusion reactors, which will also require magnetic confinement systems, were dropped from further consideration.”
Antimatter-catalyzed fusion.
Scientists are researching other designs for an antimatter engine that could generate enormous thrust with only small amounts of antimatter fueling it. Antimatter-catalyzed fusion would require smaller amounts of antimatter than pure antimatter-matter annihilation propulsion, however with lower performance.
Antimatter Ablated Light Sail
Given how expensive it is to create antimatter, we have to work with vanishingly small amounts. One possibility, analyzed by physicist Steve Howe (Hbar Technologies, LLC) is to store anti-hydrogen aboard the spacecraft and let it be released so that it interacts with a small (five-meter) sail impregnated with U-238. The antimatter reacts with the uranium to produce neutrons and various secondary emissions, fission fragments that leave the sail at enormous speeds. The push is essentially a nuclear-stimulated ablation, one that can produce specific power on the order of 2000 kilowatts per kilogram. 30 milligrams of antimatter would enable missions to the outer planets with round trip times on the order of 2-3 years, but an Alpha Centauri mission will still require tens of grams.
One possibility: Harvesting naturally occurring antimatter around the outer planets, as investigated by NASA’s Institute for Advanced Concepts, or the Van Allen radiation belts around Earth, which have much less abundant antimatter, but are a lot closer.
Antimatter-catalyzed Fusion
No nuclear fusion reactor has yet been built that is capable of generating more energy than what is needed to operate the reactor. One proposed solution to this is to use antimatter-catalyzed fusion. In this concept, a small number of antiprotons are injected into a fusion fuel, which then undergoes annihilation. The large amount of energy released from this reaction generates plasma which then initiates fusion reactions within the rest of the fuel. Theoretically, this could enable fusion more economically than any of the other fusion ignition concepts currently being explored. The major disadvantage to this is that producing antimatter is an extremely expensive and inefficient process.
