A concentrated beam of particles and photons could push us toward Proxima Centauri

Getting to Proxima Centauri b will require a lot of new technology, but there are still exciting reasons to do so. Both public and private efforts have begun to seriously look for ways to achieve this, but until now there has been one significant obstacle in the way – propulsion.

To solve this problem, Christopher Limbach, now a professor at the University of Michigan, is working on a new type of beam drive that uses both a particle beam and a laser to overcome the technology’s biggest weakness.

Let’s first look at why conventional propulsion systems would not work to get the craft to Proxima b. Conventional rockets are out of the question because their fuel is too heavy and burns too quickly to get the probe anywhere near the speed it would needed to reach Proxima b. Conventional solar sails also fail because once they are far enough from the Sun, there is only minimal pressure on them.

Other unconventional solutions, such as nuclear propulsion or ion propulsion, could also work. But they fall victim to the tyranny of the rocket equation – because they have to carry their fuel, they have to carry more mass to go faster, eliminating much of that advantage.

That leaves the beam drive – essentially creating a giant beam in space that continues to push the spacecraft with a collector on it that can continue to push the entire time the spacecraft is en route to its destination. Typically, two types of beams are used in these systems – particle beams and light beams. However, each of them has a weakness – diffraction.

Both light and particle beams tend to spread over long distances, making them much less effective at focusing on a single small object that may be light years away. Even lasers, if allowed to aim far, will eventually dissipate into unusable light. However, there is a way around this.

Recently, optics research has developed a method of combining particle and laser beams that, when used simultaneously, eliminates diffraction and beam propagation. This would allow the beam propulsion system to continue to focus its beam in exactly the right place without slowly losing its thrust as the probe moves away.

Dr. Limbach used this basic technology to develop what he calls PROCSIMA, a new propulsion method that used a coherent combined particle and laser beam propulsion system.

Calculations by Dr. Limbach and his collaborator, Dr. Ken Hara, now a professor at Stanford, show that creating a coherent beam that can effectively last all the way to Proxima b while bending only about 10 m is possible, at least in theory.

According to their calculations, a 5g probe like the one Breakthrough Initiatives is working on could be pushed up to 10% of the speed of light, allowing it to reach Proxima b in 43 years.

Alternatively, they also calculated that a much larger probe of around 1 kg could reach the system in around 57 years. This would allow for much more exciting payloads, even if the probe would bring the Proxima Centauri system a significant fraction of the speed of light.

There is still some work to be done, including developing things like cold atom particle sources and improving the functionality of the beam systems.

However, the project has not yet been supported by another grant, although the laboratory of Dr. At UM, Limbacha continues to work on similar ideas, such as the nanoNewton propulsion system. Development continues on a stellar shot method to eventually get a probe to another star, and it looks like, for better or worse, beam propulsion is the way we’ll get there.