Different Space Technologies Including Ion Propulsion example essay topic

Our current means for space travel are rapidly approaching their peak, and even when our chemically powered engines reach their maximum efficiency, interplanetary travel and possible colonization in outer space would be a far fetched idea. There are many forms of interplanetary travel that are being proposed, each with great potential. Currently, nuclear propulsion is being discussed as the next conventional form of space travel. NASA has already announced that they will spend $1 billion dollars over the next five years for the advancement of nuclear propulsion technology (Shaw: 1). Methods of interstellar travel will keep improving as technology advances; nuclear propulsion is a result of these advances and seems to be the next feasible idea in space travel. There are two basic types of nuclear reactions that could be used to power space travel, fission and fusion.

Fission involves the splitting of large nuclei and fusion involves the fusion of molecules. Both of these processes dwarf the energy released by the chemical reactions we currently use for our space shuttles. These reactions produce much more energy than regular chemical reactions, but fusion is significantly more efficient than fission. In a nuclear reaction, approximately. 07% of the mass of the nucleus is converted into energy during fission, while during fusion. 7% of the mass of the nucleus is converted into energy; hence fusion is ten times more efficient than fission (Bennett: 305).

Through these nuclear reactions, our rocket ships could produce much more thrust and power than in their current form, resulting in higher speeds and less travel time. At full potential, nuclear powered rockets will be able to reach one tenth the speed of light, making it a possibility to actually reach the stars nearest Earth within the human lifespan (Bennett: 307). Nuclear fission reactors have three ways (so far) of powering themselves: nuclear explosive propulsion, nuclear thermal propulsion, and nuclear electric propulsion. Nuclear explosive propulsion is basically what it sounds like; nuclear bombs are dropped out of the back of the spaceship and detonated against a 'pusher' plate, which absorbs the force of the explosion and pushes the ship at great speeds (redcolony. com).

NASA actually experimented with this technology and dubbed the experiment Project Orion, but no actual construction ever took place due to budget cuts the nuclear test ban treaty (Bennett: 306). In a nuclear thermal propulsion engine, the traditional approach to build one is to use a solid core, heat exchange reactor. Then, "liquid hydrogen is pumped through extra-core components for cooling and then through the reactor core to be heated and expanded through the rocket nozzle to produce thrust" (web). This form of nuclear propulsion uses propellants. The propellant, which is any gaseous element, gets heated to extreme temperatures and is ejected out of the thrusters as in a regular ship. The major difference between the thermal propulsion engine and the chemical engine is that the thermal propulsion engines draws all of its energy either directly or indirectly from nuclear reactions, meaning huge amounts of energy are released (redcolony. com).

The final form of power for nuclear fission reactors is the most popular and the one that is being most aggressively investigated. Nuclear electric propulsion is similar to nuclear thermal propulsion but the purpose of heating the propellant is to ionize it so that it may be sent through an electric field and propel it at great velocities. Project Prometheus is currently developing a nuclear electric propulsion system, focusing on making current models faster and more efficient (redcolony. com). Nuclear fusion reactors are the next big step in nuclear propulsion, seeing as they are more efficient, produce more power, and are safer to use. The problem with nuclear a fusion reactors is that researchers have yet to "sustain a power-producing fusion reactor due to the extremely high temperatures required and other limitations" (redcolony. com). Otherwise, all the same techniques for the fission reactors could be applied to fusion reactors and make the power and efficiency ten times better than the fission engines.

Nuclear propulsion seems to be the most efficient and conventional way to travel our solar systems until more advanced systems are produced that would allow us to travel near or faster than the speed of light. It provides better fuel efficiency and greater power than chemical rockets and can relatively exit Earth's atmosphere easily as opposed to some other conventional forms of travel. Building a ship with nuclear propulsion would be first step in considering colonizing Mars or any other possible celestial object. Given our current technology, a trip for the colonization of a planet or moon in the solar system would be suited for a ship powered by nuclear propulsion as it will provide the best overall efficiency to make several trips back and forth.

However there are other options to choose from in near future space travel. There are 3 other forms of 'conventional' interstellar space travel aside from chemical and nuclear propulsion: ion engine, solar sails, and laser powered rockets; I say conventional to signify that these are options in the near future and not out of our reach as of right now such as warp drives or teleportation. Currently, ion engines are looking like they will hold great promise in the near future. NASA has been working with Ion Engines since back in 1959, but only recently have they put their research to the test in the form of Deep Space 1, a small space craft that tested different space technologies including ion propulsion (web). The result returned from Deep Space 1 were very positive, and it was even able to go beyond its original purpose to test the different space technologies but also was able to travel to comet Borrelly and take the best pictures and record the best data to date (Deep Space 1). The ion engine basically works by accelerating charged particles; electrons are fired from the back of a tube to the nozzle where exhaust and thrust would come from.

The fuel used for Deep Space 1 was Xenon, a gas with a much greater mass than air, but and ion engine is not limited xenon as a variety of gases could be used in place such as argon, cesium of hydrogen. When the engine begins to run, electrons are emitted from a hollow tube called a cathode. These electrons enter a magnet-ringed chamber, where they strike the xenon atoms. The impact of an electron on a xenon atom knocks away one of xenon's 54 electrons. This results in a xenon atom with a positive charge, also known as an ion (web). At the back of the chamber there are grids that are positively and negatively charged.

The electric charge in both of these grids exerts a strong pull on the xenon ions through electrostatic forces. The force is strong enough to get the atoms to shoot out of the engine at speeds up to 60,000 miles per hour. One drawback of the ion engine is the small amount of thrust it generates compared to even small chemical rocket engines. The engine puts out about 1/50th of a pound of thrust. Even though that is a minute quantity compared to other forms of propulsion, the ion engine is capable of running for years on end, meaning that the constant thrust would eventually add up to great speeds.

Ion Engines are ten times more efficient than chemical rockets and much more durable seeing as how the Deep Space 1 spacecraft launched in 1998 is still going strong. Seeing as 95% of the mass of a rocket at launch is fuel, there is much incentive to create a means of propulsion that is much more fuel efficient than our current means of travel (web). There are a couple of drawbacks to using an ion engine besides the fact that is generates a very low thrust. Seeing as how an ion engine is based on electric propulsion which can not generate enough thrust to lift off of the Earth, the help of a launch vehicle is necessary to carry the ion propulsion powered vehicle into space. Also due to the low thrust the ion propelled engine might not be able to drag or carry large payloads, which would be necessary in colonizing other planets. Ion engines may be the ideal mode of transportation for satellites and orbiters to reach other planets, but they may not provide the necessary requirements in the effort to colonize planets.

The next conventional form of space travel to be discussed is solar sails. Solar sails are basically huge sails that can be up to hundreds of kilometers in size; they are pushed by the pressure exerted on them by the sunlight in outer space. Since there is no friction in outer space, even a slight force can get an object moving. The solar sail would basically be constructed a huge ultra thin mirror reflecting the light shined on it. NASA is currently investigating what materials to use for the solar sail, but has been looking into a rigid lightweight carbon fiber to be used in the construction of the first solar sail. The carbon fiber being looked at is very light weight with a very light density woven together in a criss-cross pattern; the fact that the sail is made of carbon will make it possible to withstand the extreme heat from the sun (How Solar Sails will Work).

The fact that the solar sail is powered by sunlight means that there is an infinite amount of 'fuel' to be consumed, or at least until the sun dies out. The closer the sail is to the sun, the more speed it will pick up. Although the ship that is being pushed by the solar sail would have a small acceleration, it would eventually reach a great speed, likely to be five times that of a conventional rocket. NASA makes a comparison of solar sails and conventional rockets to: the tale of the "Tortoise and the Hare", with rocket-propelled spacecraft being the hare.

In this race, the rocket-propelled spacecraft will quickly jump out, moving quickly toward its destination. On the other hand, a rocket less spacecraft powered by a solar sail would begin its journey at a slow but steady pace, gradually picking up speed as the sun continues to exert force upon it. Sooner or later, no matter how fast it goes, the rocket ship will run out of power. In contrast, the solar sail craft has an endless supply of power from the sun. Additionally, the solar sail could potentially return to Earth, whereas the rocket powered vehicle would not have any propellant to bring it back. (How Solar Sails Will Work).

Scientists have also been discussing the possibilities of using microwaves or lasers to give solar sails a big boost in thrust in addition to the sunlight that would propel them. Either microwaves or lasers would provide the sail with an extra source of light that increase the solar sail's velocity significantly. A solar sail running on light from only the sun would be able to reach a speed of about 56 miles / second, roughly a little more than 200,000 miles per hour; if there was extra thrust added by a laser or magnetic beam transmitter that figure would move up to roughly 18,600 miles per second which is 1/10 the speed of light (How Solar Sails Will Work). By being inexpensive and not needing any propellants to run besides sunlight, solar sails are gaining attention in the world of propulsion systems, they do however have several faults. One problem with solar sails is that as they get further from the sun, their speed begins to drop, with no means of accelerating again since they are far from the source of light. Without a source of light, the ships are basically immobile.

Once the solar sail is around Saturn, the light intensity value of the Sun would be under 1% of what it is near earth (Bennett 308). This problem could be remedied by having a laser help propel the sail, but if the laser is obstructed for some reason and no light is able to reach the sail, the ship would be stranded. Another problem is that solar sails can end up to be hundreds of kilometers in size, depending on the amount of light to be captured by the sail. This can lead to problems by having small meteorite objects crash into the sail and cause perforations. Lastly, as with ion propulsion systems, solar sails are useless in an atmosphere, so therefore the sail would have to be carried into outer space by a vehicle other than itself (How Solar Sails Will Work).

Lastly, a laser powered rocket is an alternative that could provide a steady and continuous source of thrust for the rocket. The ship basically works by having a mirrors on the bottom of the craft to receive and focus the incoming laser beam, which in turn heats the air that is being let into the craft, the air consequently explodes due to the heat of the laser and this explosion is what propels the ship (How light propulsion will work). There are four basic components to a laser propelled space craft. First off a laser is necessary, so far only a carbon dioxide laser has been used in test flights for laser propelled vehicles. Secondly a parabolic mirror on the bottom of the ship is necessary to focus the incoming laser beam into the inlet air or onboard propellant. A similar mirror is also necessary at the site of the laser emission to direct the laser into the bottom of the space ship.

The space craft must also have an absorption chamber, in which air will be let in so that is can expand and explode as it is heated by the laser beam. Lastly, there should some form on onboard propellant because once the space craft reaches a certain altitude the air will be too thin and there will not be strong enough explosions to propel the ship upward, so therefore an onboard propellant such as hydrogen would be ideal to give the ship the extra need thrust in order to reach outer space. These four components are necessary for the laser propelled spacecraft to work (How light propulsion will work). Before liftoff, the spacecraft must be stabilized gyroscopically so that it is able to soar through the air with more stability, this is done by spinning the ship to about 10,000 revolutions per minute.

Once the ship is spinning at the right rpm, the laser is powered on and the ship goes up into the air. As the laser beam focuses on the mirror of the bottom of the ship the air in the absorption chamber is heated to up to 54,000 degrees Fahrenheit. Air that reaches this temperature turns into a plasma state, which in turn explodes to give the ship an upward thrust (How light propulsion will work). A significant difference between laser propulsion and solar sails / ion propulsion is that there is no need of a separate craft to be able to reach outer space; the ship is able to produce enough thrust to escape earth's gravity on its own. However, there are some downsides to laser powered propulsion. Although great speeds could be reached with a laser rocket, as it moved further and further away, a huge focusing mirror would be necessary in order to keep the laser pointed to the proper position.

The laser is going to be pointed from Earth, so if there is some human error in directing the laser into the ship. Also, problems would arise when it came time to stop, as the craft would be carrying great momentum after the laser stopped propelling the craft. Possible solutions have been brought up for this problem such as keeping propellant in the ship, then letting the laser heat up the propellant and then shooting it in the opposite direction of travel; natural magnetic fields in space have also been suggested as a braking method. Furthermore, for a laser to be able to lift a one kilogram satellite into low Earth orbit, a one megawatt laser would be necessary which is not yet in existence. The huge power requirement necessary for a laser powered rocket is a burden the Earth can not yet bear. To accelerate a ship to half the speed of light within a couple of years would require 1,000 times more power than all current human power consumption (Bennett: 308).

All of these methods of travel seem to possess their own advantages, and it maybe true that within a few years after the physics and details of these other modes of space travel have been optimized that they may be put into practice, but for now nuclear propulsion seems to hold an edge in its capabilities, cost, and practicality. As opposed to solar sails and ion propulsion systems, nuclear propulsion will be able to launch the spacecraft off of the ground by its own power and not have to rely on some other means to get into space such as chemical rockets. Also, building solar sails could prove to be difficult because some of the larger ones might have to be built in space just because of their sheer magnitude in size. They also have the disadvantage of being stuck in a big predicament once they too far from light as to not have a means of thrust, because once that occurs they are out of options in terms of mobility.

Ion propulsion might prove to be the wave of the future, but as stated earlier it takes time to produce a strong thrust, which might not be worth the effort if only missions to Mars or nearby satellites are planned within the next decade. Laser Propulsion may very well be the form of space travel in the future, but the fact still stands right now that for laser propulsion to work a huge power requirement is required, which as of right now the Earth is not capable of handling. Nuclear propulsion is the only feasible technology to apply for manned missions to Mars or other moons. We have the technology to build a rocket propelled by nuclear fission without eating up all the resources and money our space program has to offer. Having one billion dollars to spend over the next five years strictly on nuclear propulsion will only advance the technology and specifics that nuclear propulsion has to offer.