Forget Mars, Now You Can Kickstart an Antimatter Propulsion System to Another Star!

When it comes to the future of space exploration, one of the biggest questions is, “how and when will we travel to the nearest star?” And while space agencies have been pondering this question and coming up with proposals for decades, none of them have advanced beyond the theory stage. For the most part, their efforts has been focused on possible missions to Mars and the outer Solar System.

But there are some people, like Dr. Gerald Jackson, who are working towards making an interstellar mission possible in the near future. He and his research team, which have been funded by NASA in the past, are looking to create an antimatter engine that will be capable of reaching (or exceeding) 5% the speed of light. Towards this end, they have launched a Kickstarter campaign to fund their efforts.

As advanced propulsion concepts go, antimatter has quite a lot going for it. As propulsion goes, it has the highest specific energy of any known method, 100 times more than fission/fusion reactions, and 10 billion times more than chemical propellants. It is also the most fuel-efficient, requiring mere milligrams of antimatter to produce the same amount of energy as tons of chemical fuel.

In 2002, he co-founded a limited-liability company (HBar Technologies) for the sake of developing commercial markets for antimatter. In 2002, NASA’s Institute for Advanced Concepts (NIAC) awarded Dr. Jackson and his company $75,000 to develop a mission concept that could traverse 250 AUs of space within 10 years time, and with a fuel supply of 10 kg.

These specifications essentially called for the creation of an antimatter rocket that could travel as far as the heliopause within a decade’s time. The result was a propulsion concept that relied on a beam that would fire focused antiprotons onto a sail to generate propulsion. This sail would measure 5 meters in diameter and be composed of a carbon backing on one side and uranium foil on the other (measuring 15 and 296 microns thick, respectively).

The solar system and its nearby galactic neighborhood are illustrated here on a logarithmic scale extending (from < 1 to) 1 million Astornomical Units (AU). Credit: NASA/JPL
Illustration of the solar system and its nearby galactic neighborhood on a logarithmic scale extending (from < 1 to) 1 million AU. Credit: NASA/JPL

When a pulse of antiprotons is annihilated against a small section of the uranium side, the resulting fission causes momentum. As Dr. Jackson explained to Universe Today via email:

“Note that antiprotons have a negative electrical charge, similar to an electron. When the antiprotons enter the sail, they displace an electron orbiting an uranium nucleus. Because antiprotons and electrons do not share any quantum numbers, the antiproton immediately cascades down into the atomic ground state, causing a high probability of interaction between the antiproton and either a proton or neutron within the nucleus.

“On average, a fission event results in the creation of two daughter nuclei of roughly equal mass. These daughters travel in opposite directions with a kinetic energy of 1 MeV per proton or neutron. Because the daughters are charged, the one travelling further into the sail is absorbed and transfers is forward momentum. The other daughter flies into space with an exhaust velocity of 4.6% of lightspeed. This selective transfer of momentum is thrust.”

Unfortunately, due to the budget environment of the time, the NIAC was forced to cancel its funding after a second round had been granted. Because of this, Dr. Jackson and his colleagues are now seeking public support so that they may finish their work on the experimental sail and prepare it for exposure to an antiproton beam.

Diagram showing Hbar's concept for a antimatter-driven propulsion system. Credit: antimatterdrive.org
Diagram showing Hbar’s concept for a antimatter-driven propulsion system. Credit: antimatterdrive.org

Much like Project Starshot (whom they acknowledge on their campaign page), Jackson and his team are looking to produce an interstellar mission proposal that does not involve shortcuts (i.e. warp drive, wormholes, star gates, etc.). Starshot, as you may recall, calls for a wafer craft and a laser-driven lightsail that would be capable of reaching speeds of up to 20% the speed of light, thus making the journey to Alpha Centauri in 20 years.

In the same vein, a antiproton-driven sail that could reach speeds of 5% the speed of light or more would be capable of making it to Alpha Centauri (or Proxima Centauri) in about 90 years time. All the while, the science behind it would remain within the realm of established physics, being consistent with Newton’s Laws of Motion and Einstein’s Theory of Special Relativity.

“The revolutionary aspect of the antimatter-driven sail is that the antimatter is not the fuel, but rather the spark plug that initiates fission reactions,” said Jackson. “Because the fission reactions can produce thrust without heavy shielding or other structures, the mass of the propulsion system can be comparable to the mass of the instrument package.”

Project Starshot, an initiative sponsored by the Breakthrough Foundation, is intended to be humanity's first interstellar voyage. Credit: breakthroughinitiatives.org
Project Starshot, an initiative sponsored by the Breakthrough Foundation, is another concept for making humanity’s first interstellar voyage. Credit: breakthroughinitiatives.org

To see their project through, Jackson and his colleagues are hoping to raise $200,000. Should they prove successful, they hope to mount follow-up campaigns to finance a series of validation experiments, storage demonstrations, and mission details. In the end, their goal is nothing less than making antimatter propulsion a reality, which they hope will one day lead interstellar mission.

“We expect that these campaigns will provide the data needed to convince people to fund full scale antimatter production and an actual mission to a nearby solar system,” Jackson added. “The goal of those early interstellar missions is to provide information about these other solar systems, such as whether they are habitable or inhabited.  If the latter, we will want to study or interact with those life forms in follow-on missions.  If habitable and not inhabited, we need sufficient information to assure the success of a manned migratory mission.”

As of the penning of this article, Jackson and his colleagues have raised $672 of their $200,000 goal. However, the campaign launched only a few days ago and will remain open for another 25 days. For those interesting in following their progress, or have an interest in donating to their cause, check out the links below.

Building an Antimatter Spaceship

If you’re looking to build a powerful spaceship, nothing’s better than antimatter. It’s lightweight, extremely powerful and could generate tremendous velocity. However, it’s enormously expensive to create, volatile, and releases torrents of destructive gamma rays. NASA’s Institute for Advanced Concepts is funding a team of researchers to try and design an antimatter-powered spacecraft that could avoid some of those problems.

Most self-respecting starships in science fiction stories use anti matter as fuel for a good reason – it’s the most potent fuel known. While tons of chemical fuel are needed to propel a human mission to Mars, just tens of milligrams of antimatter will do (a milligram is about one-thousandth the weight of a piece of the original M&M candy).

However, in reality this power comes with a price. Some antimatter reactions produce blasts of high energy gamma rays. Gamma rays are like X-rays on steroids. They penetrate matter and break apart molecules in cells, so they are not healthy to be around. 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.

Antimatter is sometimes called the mirror image of normal matter because while it looks just like ordinary matter, some properties are reversed. For example, normal electrons, the familiar particles that carry electric current in everything from cell phones to plasma TVs, have a negative electric charge. Anti-electrons have a positive charge, so scientists dubbed them “positrons”.

When antimatter meets matter, both annihilate in a flash of energy. This complete conversion to energy is what makes antimatter so powerful. Even the nuclear reactions that power atomic bombs come in a distant second, with only about three percent of their mass converted to 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.

The NIAC research is a preliminary study to see if the idea is feasible. If it looks promising, and funds are available to successfully develop the technology, a positron-powered spaceship would have a couple advantages over the existing plans for a human mission to Mars, called the Mars Reference Mission.

“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.

Another significant advantage is speed. The Reference Mission spacecraft would take astronauts to Mars in about 180 days. “Our advanced designs, like the gas core and the ablative engine concepts, could take astronauts to Mars in half that time, and perhaps even in as little as 45 days,” said Kirby Meyer, an engineer with Positronics Research on the study.

Advanced engines do this by running hot, which increases their efficiency or “specific impulse” (Isp). Isp is the “miles per gallon” of rocketry: the higher the Isp, the faster you can go before you use up your fuel supply. The best chemical rockets, like NASA’s Space Shuttle main engine, max out at around 450 seconds, which means a pound of fuel will produce a pound of thrust for 450 seconds. A nuclear or positron reactor can make over 900 seconds. The ablative engine, which slowly vaporizes itself to produce thrust, could go as high as 5,000 seconds.

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.

If this is so, perhaps the first humans to reach Mars will arrive in spaceships powered by the same source that fired starships across the universes of our science fiction dreams.

Original Source: NASA News Release