Reaching Proxima Centauri b will require many new technologies, but there are increasingly exciting reasons to do so. Both public and private efforts have begun to seriously look at ways to make this possible, but until now there has been one major roadblock on the journey: propulsion.
To solve that problem, Christopher Limbach, now a professor at the University of Michigan, received a grant from NASA’s Institute for Advanced Concepts (NIAC) to work on a new type of jet-powered propulsion, using both a particle beam like a laser to overcome that problem. the technology’s biggest weakness.
First, let’s look at why conventional propulsion systems wouldn’t work to get a vessel to Proxima b.
Conventional rockets are out of the question, because their fuel is too heavy and burns up too quickly to get a probe anywhere near the speed needed to reach Proxima b. Conventional solar sails also fail because once they are far enough away from the sun, only minimal pressure is placed on them.
Other non-conventional solutions could work, such as nuclear propulsion or ion propulsion. However, 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 beamed propulsion – essentially creating a giant beam in space that keeps pushing a spacecraft with a collector on it, which can keep pushing for the entire time the spacecraft is on its way to its destination.
Typically, two types of beams are used in these systems: particle beams and light beams. However, they all have a weakness: diffraction.
Both light and particle beams tend to spread out 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 point far away, eventually scatter into unusable light. However, there is a way around this.
Recently, optical research has developed a way to combine particle and laser beams that virtually eliminate diffraction and beam spread when both are used simultaneously.
This would allow a beam propulsion system to continue focusing its beam in exactly the right place without slowly losing its thrust as the probe gets further away. Dr. Limbach used this underlying 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 it is possible to create a coherent beam that can effectively last up to Proxima b while the diffraction is only about 10 meters, at least in theory.
According to their calculations, a 5G probe, like the one the Breakthrough Initiatives project is working on, could travel up to 10% of the speed of light, reaching Proxima b in 43 years.
Alternatively, they also calculated that a much larger probe of about 1 kg could reach the system in about 57 years. That would allow for a much more exciting payload, even if the probe zoomed through the Proxima Centauri system at a significant fraction of the speed of light.
There is still some work to be done, including developing things like cold atomic particle sources and improving the functionality of the beam systems. However, so far the project has not been supported by a new NIAC grant, although Dr. Limbach at UM continues to work on similar ideas, such as a nanoNewton propulsion system.
Development of a ‘star shot’ method continues to eventually get a probe to another star, and it appears that jet propulsion is the way we will get there.
Source: www.universetoday.com
