Exotic+Propulsion+Technologies+for+Spacecraft

toc =**Introduction **=

Propulsion is a term describing the act of pushing or driving an object forward, typically a vehicle of some sort. In the case of space travel, propulsion has mainly taken the form of chemical propulsion. In short, this means that the spacecraft in question is being driven by the production of thrust through a chemical reaction inside of an engine. The energy that this chemical reaction produces is then translated into momentum to propel the spacecraft in whatever direction desired.

=**Typical Methods of Propulsion **=

Though [|chemical propulsion] has been the propulsion method of choice since the late 1940s, scientists have occasionally opted for electrical propulsion when concerning smaller spacecraft such as satellites. Furthermore, many newer sorts of propulsion are in the beginning stages of actual implementation. These newer propulsion systems rely on other methods that also allow for energy to be translated into momentum or thrust. However, the current state of propulsion theory makes long-range space exploration unfeasible. This is a direct result of how the methods employed in space craft rely on the expulsion of mass to produce momentum [1]. This inadvertently limits the spacecraft’s maximum velocity, a limit inversely proportional to both exhaust velocity and mass of the fuel. In other words, for a spacecraft to achieve speeds that are more desirable for long range space travel, a massive amount of energy would have to be produced so that high levels of thrust can be produced while also bypassing a mass deficit. = = =**A Theoretical Solution **=

In order to circumvent the mass/energy limitation, scientists have begun to theorize on propulsion methods that do not rely on [|Newtonian Mechanics], instead focusing on what is known as field propulsion. This novel and science-fiction-esque theory of propulsion theoretically derives its momentum from the interaction of spacecraft with fields described in in quantum field theory and Einstein’s General theory of Relativity [2].

=**Field Propulsion **=

The concept of Field Propulsion functions under an assumption that Einstein theorized many years ago in his groundbreaking theories of relativity; space is not an empty vacuum, but rather it has substance and structure [3]. Thus, the interaction of a spacecraft with this space-time structure and substance allows for the space-craft to produce thrust. The nature of the “substance” that space-time holds is dependent on whether one is utilizing concepts proposed by the General Theory of Relativity or Quantum Field Theory.

=**Field Propulsion and General Relativity **=

Within the realm of [|General Relativity], field propulsion is formulated through the assumption that space is fundamentally an elastic field [4]. Given this assumption, it must be noted that space is treated as an infinitely large elastic field that, under the right conditions, can be elongated, curved, expanded, contracted and bent. In nature, space is curved by the many forces that exist within it (large masses, gravity, electro-magnetic fields). When the space-time continuum is deformed in anyway, a normal stress is generated which, in turn, creates a pressure field [5]. If the space around a vehicle were to be curved substantially, an enormous amount of surface forces could be produced as the elastic space-time continuum sets itself back into its normal place, accelerating the vehicle and any other matter around it substantially. Considering that Einstein’s General Theory of Relativity can be solved in various manners, there are accordingly multiple points of view with which to describe this phenomenon. Instead of analyzing how the space-time continuum changes through stress and strain analysis, the manipulation can be expressed as a differential of distance between the original position of space and its new position. Much like a [|spring], this change in position will generate a force as the spring, in this case space, accelerates to its original position. This phenomenon can be shown through the numerical analysis of the [|Riemann Curvature Tensors]that are a consequence of Einstein’s work. It must be noted that the manner by which a necessity for high mass is circumvented has to do with the idea that space-time can be curved through magnetism and not just mass density. This means that a strong enough magnetic/electric field would, in theory, produce the above-mentioned results if capable of curving a significant enough area of the space-time continuum.

=**Propulsion Systems Based on Relativistic Field Propulsion **=

In the late 1990s, propulsion expert Yoshinari Minami proposed the concept of a Space Drive Propulsion System. This propulsion system, based on relativistic mechanics, focuses on the principal of space time curvature. By implementing a specific solution to Einstein’s General Theory of Relativity ([|de Sitter Solution]) the acceleration of a spacecraft could theoretically be maximized by employing magnetic fields while also maximizing the size of the region of space-time being altered. Further conjoining theories that pertain to the General Theory of Relativity, a cosmological constant (which relates to the amount of energy that can be produced from the manipulation of space-time) is added so that the acceleration that this propulsion system could theoretically yield can be more accurately estimated. Considering that this cosmological constant also accounts for the consistent expansion of the universe, the potential yield of acceleration is increased by the increasing rate of expansion that the universe experiences. By default, a given region in space’s volume will expand along with the rest of the universe, meaning that the potential acceleration that can be derived from this manipulation of space is exponentially growing as time goes on with asymptotic behavior when approaching the speed of light, as relativistic mechanics hold. Relating this to the Riemann tensor equations, this cosmological constant essentially adds another tensor to the system, further adding to the thrust that space-time produces when bent. Basic laws of physics must be considered if this theory is to ever be implemented. Considering this, through [|momentum] analysis, there must be a reaction pair when the vehicle employs this form of propulsion. Momentum can be classified by two categories; momentum thrust, and pressure thrust [6]. Contemporary space crafts are built with momentum thrust in mind. By creating a chemical reaction, a reaction that produces thrust is generated. In the case of the Space Drive Propulsion System, the deformation of the given region in space serves as a sort of spring that propels the vehicle forward, producing a pressure thrust.


 * Field Propulsion and Quantum Field Theory **

<span style="font-family: &#39;Times New Roman&#39;,serif; font-size: 12pt;">Where Einstein’s General Theory Relativity takes a macroscopic approach when analyzing the nature of space-time, [|Quantum Field Theory] views the universe on a microscopic level. In this theory, space is characterized by a very different sort of structure. In substance, the universe is filled with zero-point electromagnetic fields [7]. This means that the entirety of empty space is in the lowest energy that a system can have. As a result, gravity is a phenomenon that is produced by changes in energy within these electromagnetic fields. Generating electric fields would, thus, alter the energy in a given region of space and produce a gravitational field that would similarly produce an accelerating force. It is also observed that space is characterized by an elasticity not in space itself, but in its entropy (measure of a system’s disorder). This entropy is expounded by a set of energy strings that are all intertwined. As with Relativistic theory, if these strings can be altered or deformed, when they return to their original level of energy they will yield a gravitational field and acceleration induced by the excitement of their fundamental particles and how these particles interact. = = =**<span style="font-family: &#39;Times New Roman&#39;,serif; font-size: 12pt;">Propulsion Systems and Quantum Field Theory **=

<span style="font-family: &#39;Times New Roman&#39;,serif; font-size: 12pt;">Many of the theoretical propulsion systems that adopt Quantum Field Theory draw their propulsion from the generation of gravitational fields and the extraction of energy from the emptiness of space itself. This energy can then be translated into thrust to accelerate the vehicle profusely. One such proposed system involves disturbing the emptiness of space with electric fields. The high-energy electric fields produced by the space craft causes for oscillations in the “energy-strings” that the vacuum is comprised of. <span style="font-family: &#39;Times New Roman&#39;,serif; font-size: 12pt;">By controlling how the vacuum oscillates by means of the application of the theories of quan <span style="font-family: "Times New Roman",serif; font-size: 12pt;">tum [|optics], pressure gradients can be created as desired. A pressure field then envelops the spacecraft and the differences in pressure gradients around the vehicle allow it to be accelerated in the desired direction, as the pressure behind the vehicle will be significantly higher given that the strings of energy in space have been excited while the particles in front of the spacecraft remain near a zero-field state.


 * <span style="font-family: &#39;Times New Roman&#39;,serif; font-size: 12pt;">Conclusions **

<span style="font-family: &#39;Times New Roman&#39;,serif; font-size: 12pt;">The current limitations of propulsion technology make deep-space travel lack the efficiency necessary when conducting long range missions in space, as these would cost massive amounts of money while consuming significant amounts of time. The above theories, which are at the forefront of scientific study in the realm of propulsion, though promising have not truly been subject to experimentation, with the exception of the effect of squeezing light in order to manipulate a vacuum. It can thusly be said that any implementation of these, as effective and appealing as they may seem, will not be seen for years to come.

**<span style="font-family: &#39;Times New Roman&#39;,serif; font-size: 12pt;">References **

<span style="font-family: &#39;Times New Roman&#39;,serif; font-size: 12pt;">[1] Y. Minami, "Space Propulsion Physics toward Galaxy Exploration," Journal of Aeronautics & Aerospace Engineering, vol. 4, (2), 2015. <span style="font-family: &#39;Times New Roman&#39;,serif; font-size: 12pt;">[2] T. Musha and Y. Minami, Field Propulsion System for Space Travel: Physics of Non-Conventional Propulsion Methods for Interstellar Travel. 2011. <span style="font-family: &#39;Times New Roman&#39;,serif; font-size: 12pt;">[3] Y. Minami and T. Musha, "Field propulsion systems for space travel," Acta Astronautica, vol. 82, (2), pp. 215-220, 2013. <span style="font-family: &#39;Times New Roman&#39;,serif; font-size: 12pt;">[4] U. Yurtsever and S. Wilkinson, "Limits and signatures of relativistic spaceflight," Acta Astronautica, vol. 142, pp. 37- 44, 2018. <span style="font-family: &#39;Times New Roman&#39;,serif; font-size: 12pt;">[5] M. Alcubierre, "The warp drive: hyper-fast travel within general relativity," Classical and Quantum Gravity, vol. 11, (5), pp. L73-L77, 1994;2000; <span style="font-family: &#39;Times New Roman&#39;,serif; font-size: 12pt;">[6] M. Fil'chenkov and Y. Laptev, "Galaxy travel via Alcubierre's warp drive," Acta Astronautica, vol. 139, pp. 254-257, 2017. <span style="font-family: &#39;Times New Roman&#39;,serif; font-size: 12pt;">[7] O. Semyonov, "Relativistic rocket: Dream and reality," Acta Astronautica, vol. 99, pp. 52-70, 2014. <span style="font-family: &#39;Times New Roman&#39;,serif; font-size: 12pt;">[8] B. N. Cassenti, "Mass Production of Antimatter for High-Energy Propulsion," Journal of Propulsion and Power, vol. 16, (1), pp. 119-124, 2000. <span style="font-family: &#39;Times New Roman&#39;,serif; font-size: 12pt;">[9] G. Vulpetti, "On the viability of The Interstellar Flight," Acta Astronautica, vol. 44, (7), pp. 769-792, 1999. <span style="font-family: &#39;Times New Roman&#39;,serif; font-size: 12pt;">[10] P. Marquet, "Exotic Matter: A New Perspective," Progress in Physics, vol. 13, (3), pp. 174, 2017.