The concept of interstellar trip is not easy, but attainable through adoption of appropriate technologies. This paper gives an overview of this possibility by discussing the main difficulties involved in such missions and a series of proposed and theoretical solutions that can be used to speed up the spaceship. It further discusses a number of future problems and the key contributions to human life that could arise once interstellar travel is accomplished. The adoption of advanced technologies will make interstellar travel a reality within the foreseeable future and will bring major benefits to the lives of humans living on earth.
The concept of Interstellar spaceflight refers to the unmanned or manned trip that takes place between stars. Nowadays, a journey into space is limited to just some spaceships visiting our neighbouring planets. However, is it possible to travel up to the nearest stars? Interstellar trip offers more challenges than interplanetary trip, but intergalactic trip, which is the voyage between various galaxies, is even more challenging. For the short term, particularly for manned travels, it may seem like a pipe dream due to the limitations on practical technology and sources. Nevertheless, in the long term, this dream may be achieved, possibly commencing with unmanned missions. In addition, once this goal is achieved, it will contribute to the discovery of the universe and human life.
One of the main difficulties of accomplishing an interstellar trip is the enormous distance that exists between the earth and the nearest star.
This implies that an interstellar ship that travels at a fast speed and that can take a long time to travel is necessary for its achievement. The period taken by the majority of propulsion methods would last for decades to millennia; therefore, a spaceship would be much more extremely exposed to the dangers present in interstellar travel such as hard vacuum, radiation, weightlessness, and micrometeoroids. The vast distance complicates the possibility of designing manned travels, and further makes the economic justification of such a trip almost not possible. This is because the advantages that do not become available for a number of years to come have a present worth close to zero (Marcvey 1977).
An important aspect contributing to the complexity arises from the energy that must be supplied to realize a practical travel time. The law of kinetic energy, e=1/2mv2 where m represents the final mass, describes the amount of energy needed; therefore, if deceleration on arrival is considered necessary and this cannot be attained by an atmosphere, then the total energy needed is even more. The speed for a manned interstellar travel of a few decades to even the nearest star exceeds by far the speed of the current propulsion methods and according to the square law, millions of times as much energy would be necessary. Moreover, this immense amount of energy has to be carried along the space vehicle since solar panels cease to function when they are far from the sun and other stars. A significant issue with the voyages at very high velocities is that interstellar dust and gas are able to impair the proper functioning of the space vehicle. This is because of the high relative velocities and huge kinetic energies involved. Larger materials, for example, macroscopic dust grains, though can cause more damage, are not very frequent. Different appropriate ways of protecting the spacecrafts from such hazards have been properly evaluated.
Another difficulty of achieving an interstellar trip is attributed to the practical speed of spaceships that move slower than the speed of light. Astronomical distances are usually given in terms of the time a beam of light moves between two places and in a vacuum, light travels at 186,000 miles per second. For example, the distance from the earth to the moon, which is about 1.3 light-seconds away, can be achieved in about three days by the use of the current spacecrafts. This implies that the speed of light is about two hundred thousand times faster than the speed of the current spaceships. It takes approximately three light-minutes to four light-hours to travel from the earth to the other planets within the solar system; therefore, a space vehicle can take about a few weeks to even many years to complete a voyage to any of these planets. The closest star to the sun is referred to as the Alpha Centuri and it takes light coming from it up to four years to reach the Earth. At present, the fastest spaceship that has been developed travels at thirty kilometres per second.
At that velocity, the voyage can last for up to 40,000 years. Moreover, the current spacecrafts are designed to have an operational lifetime of approximately forty years before they finally start to disintegrate. Therefore, major technological advances, for example, automated self-repair, may be incorporated in the design of spacecrafts to make sure they survive for a longer time. There is presently absence of adequate technological advancement to ensure that a spacecraft reaches other stars in less than five decades (Clark 1995).
If a spacecraft could average just ten percent of the velocity of light, it would take less than fifty years to reach the nearest star. Therefore, a series of proposed solutions have been proposed to overcome the difficulties and achieve the dream of interstellar travel. These include development of the nuclear pulse propulsion, fusion rockets, the bussard ramjet, antimatter ramjets, and the beam-powered propulsion.
The construction of spacecrafts by the use of nuclear pulse propulsion technology has been achievable from the 1960s. The spacecrafts are driven by a series of nuclear explosions that propels them at very high speed; hence, they are able to reach the nearest star in decades rather than centuries. The building costs of such crafts were estimated to be equal to those of crafts build by means of chemical rockets technology. Suggested interstellar spaceship travel by means of nuclear pulse propulsion technology includes Project Orion and Project Longshot. The former used nuclear bombs as propellant while the latter used inertial confinement fusion explosions. Project Orion is one of the few interstellar travel suggestions which can be achieved through the modern technological advancement. Interstellar trip would only be achieved by means of advanced derivatives of the design with cruising speeds of eight to ten percent metres per second; however, versions investigated during the exercise had too low exhaust velocities of twenty to thirty kilometres per second.
The project was under intense criticism because of the dangers involved in using nuclear explosives as fuel for spacecrafts. The use of the fusion rockets have also been proposed as a means of speeding up the spaceship. The technology employs foreseeable fusion reactors that have the capacity to attain about ten percent the speed of light. Fusion reactors “burn” such light elements as helium or tritium to yield one percent of the mass of the nuclear fuel as released energy. On the other hand, fission is less preferred because it releases approximately 0.1% of the fuel’s mass energy.
Nevertheless, the most realizable fusion reactions give out a huge portion of their energy as high-energy neutrons that are complicated to use. One suggestion of employing this technology is Project Daedalus. A hindrance of the traditional ways of propelling rockets is that the spaceship would have to be loaded with its fuel, therefore increasing its mass. The use of bussard ramjet, antimatter rockets, and beamed propulsion methods has been proposed as probable solutions to this problem. The proposal of the bussard ramjet for an interstellar propulsion system was made by Robert W. Bussard in 1960. He suggested that a large scoop would gather the diffuse hydrogen in space, consume it during the interstellar flight by means of proton-proton fusion reaction, and then force it out. As the fuel would be gathered on transit, a spacecraft could travel at a speed near that of light.
Later computations with more precise approximations indicate that the force produced would be less than the drag resulting from any possible scoop design. The proposal of an antimatter rocket would have an increased energy density and specific impulse that would exceed any other suggested interstellar propulsion system. Major progress can be made if energy resources and sufficient ways of manufacturing are discovered to formulate antimatter in the quantities desired.
This would make it possible for the spacecrafts to reach velocities near that of light. However, time dilation would be more evident where time would pass at a slower rate for the voyagers as alleged by an outside observer. Finally, the proposal of beamed propulsion, would potentially reach even higher velocities surpassing those of the rockets or pulse propulsion methods. This is because it uses a light sail or magnetic sail driven by an enormous laser or particle accelerator in the home star system. Moreover, since it would not carry its own reaction mass, it would only need to propel the spaceship’s payload. Robert L.
Forward suggested a method for decelerating an interstellar light sail in the destination star system devoid of a laser array by the use of a smaller secondary sail and a larger secondary sail. The smaller secondary sail is placed at the back of the spaceship whereas the larger primary sail is separated from the spaceship in order to keep moving forward on its own, and light is reflected from the latter to the former sail. The reflected light is used to decelerate the secondary sail and the spaceship’s load.
It is also possible for a magnetic sail to decelerate at its destination minus relying on fuel carried on the way. The magnetic sail interacts with the plasma present in the destination star and the interstellar medium since in contrast to the light sail system; this would not need the action of the particle beam employed when starting the voyage of the spacecraft. On the other hand, it is possible to increase the speed of a magnetic sail by means of particle beam or a plasma beam.
Several scientists have put forward theoretical solutions for achieving interstellar trip. The concepts of traversable wormhole and warp drive have been proposed as possible means of surpassing the speed of light.
A traversable wormhole refers to a theoretical topological feature of space-time that scientists postulate could connect two arbitrary points in the universe. Although wormholes are valid solutions in general relativity, it has not been established whether they exist in practice. They can be of benefit only if exotic matter can be used to stabilize them. Warp drive is a faster-than-light (FTL) interstellar travel theoretical solution that equips a spaceship with a system that enables it to travel much faster than light by numerous orders of magnitude, while avoiding the difficulty of time dilation. The warp drive does not allow instantaneous movement between two places, but it forms an artificial “bubble” of normal space-time which envelops the spaceship.
It does not go into a different realm or dimension like hyperspace. As a result, a spaceship travelling at a warp velocity is able to maintain normal interactions with objects in normal space.
Once interstellar travel is happening, scientists would have to deal with the problems of time dilation and universe expansion.
Time dilation is one of the most enthralling aspects of relativity that refers to the slowing-down of the passage of time as witnessed by individuals or objects moving at a substantial fraction of the velocity of light. The two types of time dilation are gravitational time dilation and velocity time dilation. Both of them can operate together.
Velocity time dilation occurs when an individual or an object travels at near the velocity of light and time tends to slow down as compared to the rest of the universe. In other words, for a stationary observer, time passes slower. Even though the object is moving fast, the observer would see it as slowing down its activity. Gravitational time dilation refers to the phenomenon of time passing at different rates in areas of different gravitational potential and it has been confirmed by tests of general relativity. This means that the lower the gravitational potential of an object, the slower the clock runs. This effect is evident in accelerated frames of reference, for example, an accelerating spacecraft, or by virtue of the equivalence principle. Another problem arises from the possibility of universe expansion. It has been suggested that dark energy is slowly driving the universe in the direction of increasing rates of expansion as expressed by the Hubble Constant.
The current expansion of the universe makes astronomers to be puzzled at the possibility of an interstellar travel because of the errors that arise from computations.
Although interstellar travel is a capital intensive exercise that is full of challenges, its achievement can bring major beneficial contributions to the human life on earth. It would need advanced technology to explore the extreme conditions of interstellar space. Therefore, the technology developed in realizing this can be successfully implemented in the making of life-saving and enhanced medical equipment. Moreover, man would discover the universe and maybe establish contacts with aliens.
Interstellar travel would also make more energies and resources available to man. Fossil fuels and minerals on Earth could soon get depleted and the consequences can be worst if no reserves are available. As more people are being born on Earth, the effects of overpopulation could soon become unbearable. But, with the achievement of interstellar travel, scientists can discover methods to terraform the Mars or the moon to support human life.
This achievement would make it possible to establish another civilization that would be having adequate quantities of energies and resources to benefit the individuals habiting on it as well as the individuals on Earth (Thomas 1989).
Although there are difficulties in achieving interstellar travel which arises from the vast distance between the earth and the nearest star and the slow speed of the current spaceships, a number of proposed solutions and theoretical solutions can make this goal to be realized in the near future. The proposed solutions for realizing this include development of the nuclear pulse propulsion, fusion rockets, the bussard ramjet, antimatter ramjets, and the beam-powered propulsion. Furthermore, proposed theoretical solutions include the use of traversable wormhole and warp drive.
The possibility of interstellar travel started over 50 years ago. It has been marred by controversies from scientists, religious leaders, media and the common person. It is important therefore to review critically the available information to determine what the truth is about the possibility of such missions. This is because the inexhaustible region of interstellar space is lying before us, awaiting discovery and colonization to bring major benefits to our lives on this planet. Therefore, we should not rest until this reality is achieved by us, if not by our children.
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Thomas, McDonough. 1989. Space: the next twenty five years. New York: Wiley.