Traveling the Distance Between Stars

Proposed methods of interstellar space travel which could make the stars within our reach

The Proposed ‘Helical Engine’

When it comes to interstellar travel, getting your craft to a velocity that means you can escape the solar system and propel yourself to another star system is a challenge. If you are using a form of fuel to do that, then the amount of mass required can hold back your ability to accelerate your spacecraft. But what if your method of travel did not involve fuel?

David Burns, a researcher at NASA’s Marshall Space Flight Center in Alabama, has suggested a method of interstellar travel that would not require fuel. The method involves. Ions, captured by the craft as it travels through space, would be accelerated in a loop to control relativistic speeds. As Burns explains it in a recent presentation in August 2019, moving the ions back and forth along the direction of travel would produce a slight amount of thrust.

The ions bouncing off the inside of a box at speeds well below the speed of light would entail the box remains stationary. This is the case because of the consistency in mass and momentum. But if the ions bounce off the box with relativistic effects taken into account, the box moves slightly.

Depiction of the change in mass of the ions due to relativistic effects. Credit: David Burns / NASA
Depiction of the change in mass of the ions due to relativistic effects. Credit: David Burns / NASA

Einstein’s Special Theory of Relativity explains how an object traveling close to the speed of light gains mass, becoming infinite in mass when it reaches the speed of light. The gained mass of the ion as it accelerates towards the speed of light adds on the momentum of the particles which is then transferred to the spacecraft. This can be used to accelerate its speed ever so slightly. Used over large distances it could mean a spacecraft reaches a massive speed.

However, the method is speculative. Burns admits that his work has not been reviewed by subject matter specialists. Theoretical physicists are yet to discuss and confirm the likelihood that his engine will work. Burn’s engine faces the hurdle of challenging well-established ideas within theoretical physics. Newton’s third law of motion in particular, dictates that: every action comes with an equal and opposite reaction. Although Burn’s is a researcher for NASA, his theory and ‘Helical Engine’ may not turn out to be viable.

A Possible Field Propulsion System

Takaaki Musha, a researcher at Shinshu University in Nagano Japan, discusses another possible method that could be used to accelerate a spacecraft through the vastness of space. In a publication back in 2011, he also discusses the idea of using relativistic effects.

The idea involves the use of the field of space, where the bending of space-time results in gradient stress that propels the spacecraft through the field. Within Einstein’s theory of General Relativity, the bending of space-time is used to explain the force of gravity.

The bending of space-time by mass results in a change in motion and acceleration of objects known as the force of gravity. But how might one generate this kind of change to the field of space-time and get their star-hopping spacecraft moving towards that far away destination?

Teaming up with Mario J. Pinheiro, an academic in the department of physics of the University of Lisbon, Musha explains. Superconducting coils could be used to change the field around the craft and create a sort of ‘gravity engine’. In a publication in the International Journal of Sciences back in March 2018, they explain how using an electromagnetic field generated by the coils and ‘co-axial condenser’ would create a gravitational vortex.

“By pulsing the electromagnetic field generated by the superconducting coil, a strong co-gravitational field can be generated inside the toroidal structure” (Musha and Pinherio, 2018, p. 21). Imagine a coil, flexing space and time and warping it into a bowl-like shape that the spaceship sinks to the bottom of. This is the thurst caused by the electromagnetic field bending space-time.

Both Burn’s and Musha’s method of travel involves Einstein’s work. But there are still important differences. Musha is concerned with “momentum derived from an interaction of the spaceship with external fields” (Musha, 2011, p. 35). Burn’s method is focused on the interactions between objects to bring about thrust. The distinction is critical, as relativistic field propulsion doesn’t challenge Newton’s third law and the conservation of energy and mass.

Realistic Alternatives

One criticism that can be made of theoretical methods of interstellar space travel like these is that they remain to be practically demonstrated. Even if they were shown to be experimentally verified, they would be expensive. This thinking supports realistic alternatives, like the use of solar sails and lasers as discussed by Tobias Häfner and colleagues in a recent paper in the journal Astra Astronautica backin January 2019.

But this is slightly short-sighted. Alternatives to realistic options like ‘gravity engines’ and ‘helical engines’ should not be written off so quickly. The big challenge of getting humans to the stars will be on the horizon after unmanned missions travel to the stars.

Exploring these theoretical methods and their viability may well be part of our long term vision of space exploration. Just as the invention of the steam train did not mean that dreams of the bullet train were thrown out, the use of solar sails for interstellar travel should not mean that other proposed methods of interstellar space travel are not worth exploring as well. Humans eventually being able to step on planets around other stars may well be dependent on it.

All Rights Reserved for Christopher Carroll

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