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Abstract
This project aims to explore the overall importance of space exploration in today’s world and society that has been growing more and more curious every decade that passes and what potential benefits it can offer but also what costs this exploration can have. These benefits could range from medical research using the useful aspect of zero gravity to mining asteroids that contain minerals that our world has been mined free of. However, exploring space is no easy task and many new developments in technology have been made since the first spacecraft, Sputnik 1, entered space. One of these developments has been ion drives which is a relatively unused advancement in thruster technology but what I believe to have huge potential in helping exploit the vast figurative goldmine that exists beyond our planet’s atmosphere.
Introduction
Space exploration has an undeniably huge amount of potential benefits but at what cost do these benefits come at and is it worth it to keep investing the hundreds of billions of dollars that have been invested in space exploration and other developments just from Nasa in the last decade. There are people who share the opinion that we currently have too many problems here on Earth: poverty, overpopulation, a diminishing supply of fossil fuels that we currently rely heavily on and the list just keeps going. Hence, they believe we should first focus on Earths problems before investing in space. I will assess both sides of this argument and determine whether I believe the money invested in space missions is justified or whether I think it should be adjusted. Following this I will also decide how big a role ion drives could play helping us acquire the benefits that space has to offer.
Before I begin exploring and assessing the importance of space exploration in our continuously developing world I should first define what space exploration actually is. Science Daily says Space exploration is the physical exploration of outer space, both by human spaceflights and by robotic spacecraft. . However, this definition may at first seem restricting to how many benefits space exploration but this is not the case at all. This is because it is often assumed that all space exploration can offer, in return for the billions of dollars invested, is some data and images about planets in our solar system. Although this is often the main objective/direct benefit of most space exploration missions, many other advancements and technologies that are used in everyday life can come as an indirect benefit from these missions. This is why I need to try to value all the benefits that come from space exploration and compare this to the money and resources invested into the missions in the first place.
Ion drives are a method of propelling spacecraft through space and due to their high efficiency,could help lower these costs; they also have some distinct features that could allow us to explore further into space than ever before.The idea for ion drives was conceived in the early 1900s but due to the low thrust of ion drives; they are only operable in a near, or more ideally, a perfect vacuum because an atmospheres resistance negates the thrust from the ion drive. Hence, to be able to test the thruster; a vacuum would be needed as well as, ideally, a gravity-free zone because it is best to trial technology in the place where it will be most commonly used. This of course, leads us to one solution, we would first need to be able to enter space to test the drives to their fullest extent so when we first reached it in 1957, the previous concept became a much more realistic idea and just a decade later ion drive technology was able to be tested in space. In recent years, ion propulsion has also found itself other uses; including being used to keep low earth orbiting satellites from descending into the surface.
Basic principle
Not all ion drives operate the same way and there are several different thrusters which have been engineered slightly differently, with the main difference being the field used to accelerate ions which varies from electromagnetic to electrostatic fields. The process of achieving thrust occurs when atoms are bombarded by a beam of electrons to knock out an electron from the outer shell of the atoms, hence forming positive ions, which are positively charged particles, whilst in an electrostatic field and they are guided through a grid of negative charge that accelerates the ions. Finally, a neutralizing ray is fired into the accelerated ions after they leave the thruster to stop them from being attracted back towards the grid which would prevent the thruster from accelerating. {NASA, 2019}
Chemical rockets
Again, not all chemical rockets are identical but I will explain the principle behind how they are able to achieve acceleration. At the base of the rocket, there are either multiple or just 1 large combustion chamber that is filled using pumps with propellant from the main fuel supply which is usually liquid hydrogen, however, this can vary. An oxidizer is then added which causes the fuel to ignite which forms a gas. This has a much higher volume than its corresponding mass of liquid or solid propellant and this causes a huge amount of pressure to build. Following this, the pressurised gas is ejected out of nozzles and this pushes the rocket forward due to some fundamental physics that is explained by Newtons third law, For every action, there is an equal and opposite reaction . {Grc.nasa.gov, 2019}
Why would we use ion drives rather than the most common type of propulsion system, the chemical propulsion system?
The main advantage of an ion drive is its efficiency as the exhaust velocity of ion drives is typically 10 times that of a chemical propulsion systems exhaust velocity (Exhaust velocity is the velocity at which the propellant is expelled from the thruster). The secret to the efficiency of ion drives is actually no secret at all but it just hides behind the laws of motion discovered by Sir Isaac Newton over 300 years ago in 1686. Specifically, it’s the 2nd and 3rd law that we are most interested in here. As an example, Ill use the Dawn spacecrafts ion thruster to explain how the different newton’s laws allow ion drives to work. Dawns propellant was xenon and this was specifically chosen due to its high relative atomic mass and its inert property {Rayman, 2013} {Rayman, 2007}. Note – Lighter elements are avoided as despite the fact they are expelled at faster speeds than heavier elements, after calculations the mass has a larger impact on the resultant force applied to the spacecraft. Also, being a noble gas, it meant that xenon had a full outer shell which prevented accompanying atoms from easily forming bonds, most importantly it won’t form covalent bonds with other xenon atoms to form diatomic molecules like some elements in other groups will do, eg. Cl2, O2, F2 etc.
To start the process of generating thrust; both delocalised electrons and xenon atoms must be supplied into the ionisation chamber, then an electron which has been fired into the chamber by an electron beam will collide with a xenon ion which causes an electron to be knocked out of the outer shell of the xenon atom and this will cause a positive xenon ion to be formed. This positive ion is then accelerated out the end of the thruster by the electric field that surrounds the ionisation chamber and the negatively charged grid that the ion passes through. As these ions are accelerated, F = m * a, shows that each ion will have had a force applied to it by the ion thruster. Because the electric field and the negatively charged grid applied a force on the xenon ion to accelerate it, the xenon ion will apply an equal force in the opposite direction on the ion drive. It is this process that causes the spacecraft to accelerate but this acceleration is almost immeasurable because the mass of the ions which are expelled are so small which must mean that the force applied to the ion was also minute. The acceleration of the spacecraft is therefore very small as the force exerted on the spacecraft is extremely small and the mass of the spacecraft is large hence the small acceleration.
Lit review
The sources that I have used; have supplied me with essential information and data which have allowed me to construct arguments around my various topics within the focus of my dissertation. My sources come in a large plethora of different styles which include dissertations, scholarly articles, reliable websites and even the logs of NASA missions.
First, I had to gain a strong yet basic understanding of how both ion drives and chemical rockets work. For this, I looked at a wide array of websites until I located the most suited source which ended up being from NASAs website. I believe this to be a reliable source as they are a large and well-respected government agency that I dont believe would have a reason to be biased when explaining the mechanics of both methods of propulsion, especially as the details were not opinion based and therefore werent subjective. Furthermore, the information on their website matched with the other websites which I had previously looked at, which gives me the confidence to say the information is correct.
As I began to explore the Dawn mission as an example of how ion drives can be used in space exploration, I decided to use NASAs data that they gathered as well as some of the logs on Dawns progress. Although I have already mentioned that I believe NASA to be a reliable source, they would have a reason to be biased with this information as it would appear better for them as an agency if the mission that cost millions of dollars was a success. On the other hand, I dont think NASA has been unreliable in this situation as they have thousands of images that DAWN precured on its mission which they have made readily available to the public which they could have kept private if the images werent as successful and knowledge inducing about the orbited masses as they were claiming. There are also logs of DAWNs progress all throughout its journey which highlight what the were aiming for in the succeeding months of the mission. Marc Rayman is the author of these logs, as well as the author of another source I used during arguments surrounding ion drives. From multiple sources that agreed, I found he was the director and chief engineer of the DAWN mission in NASAs JPL (Jet Propulsion Lab). He has been very well educated and many people, myself included, trust his reports to be factually and statistically correct. Moreover, his reports published by UPI; a very successful and well established publishing agency which further supports the validity of his reports. Being enthusiastic about the mission is part of his job but from the sources I have used, I dont believe he has been particularly biased as all of the claims he made are supported by evidence and also by NASA.
Discussion
About half a century ago, the first ion drive was built and yet only in the last decade or so has this method of propulsion started to become more widely recognised. A reason for this could be that despite some useful properties, including efficiency, the very small thrust prevents them being used when acceleration is required to be large. It isnt just the low thrust that has stopped ion drives becoming a more conventional method of propulsion. Although many tests have been carried out, it isnt cheap to put ion drives in practice and just like lots of other technologies; the risk that potential adopters perceive can delay the progress. However, once this barrier has been overcome and the technology is first tested then the risk of failure is seen as far less; resulting in a much faster development in this technology. For ion drives a big step in its development was the agreement reached in the early 1990s between Russian, European and American space industries to give chase to the advancement of ion propulsion technology.
Not everybody believes that the benefits we get back from space exploration is worth the cost and in a survey conducted in 2018 carried out by the Pew Research Center in the US found that over a quarter of those surveyed believed that it was not essential for the US to stay a world leader in space exploration. {Pew Research Center Science & Society, 2019}[image: ]
I understand their viewpoint as the only direct benefit we get back from space exploration is scientific knowledge and it is practically impossible to place a price on this knowledge. Depending on your view on space exploration and similar topics you will value this data at different values which would leave the question of Are the benefits of space exploration worth the cost unanswered. For example, I can understand why the DAWN mission that cost $500 million in total would not be seen by everybody as a worthwhile investment as all it returned were some images of a couple of asteroids in the asteroid belt. However, these images accompanied by other data gathered by the other scientific instruments aboard DAWN allowed scientists at NASA to come to these conclusions, Among its accomplishments, Dawn showed how important location was to the way objects in the early solar system formed and evolved. Dawn also reinforced the idea that dwarf planets could have hosted oceans over a significant part of their history and potentially still do. {NASA Solar System Exploration, 2019}. This knowledge represents something much greater than just another fact about our solar system. It shows how much progress the human race has made to be able to travel to other planets and gather information on them that can help us picture what they looked like millions of years ago.These successful missions can help motivate global culture . It is this type of innovation that can inspire new generations to quite literally reach for the stars .
One benefit of exploring deep into space is that we create the first line of defence for Earth. Although unlikely it isn’t impossible that a large asteroid could cause some serious damage to Earth, for example, something similar to the dinosaur extinction that happened 66 million years ago could happen. If probes deep into space could identify large asteroids then their path could be calculated and a collision course could be predicted and then from there, we can work on disrupting its course to miss Earth. Although this may sound far fetched, appear to be something seen in a sci-fi movie and you may just assume we would be safe; this has actually become a genuine plan to combat this potential hazard. The Double Asteroid Redirection Test or DART for short is a plan announced by NASA to be launched in 2021 and in 2022 it is set to collide with its targets a binary asteroid systemthat is, a double asteroid. This system, named Didymos, has a main body ( Didymos A ) about 750 meters (2,460 feet) in diameter and a satellite ( Didymos B, though it also has an extremely informal nickname of Didymoon ) 160 meters (525 feet) or so in diameter. {NASA, 2019 [2] }.
Nasa has decided to utilise the use of Solar electric propulsion in the form of ion thrusters which has been developed from Dawns ion thruster design to achieve a velocity of around 6.6km/s at the point of impact, Nasa believes at this speed and with a mass of 500kg the test should be able to alter the speed of the moonlet in its orbit around the main body by a fraction of one percent, but this will change the orbital period of the moonlet by several minutes – enough to be observed and measured using telescopes on Earth. {NASA, 2019 [2]}. Although this change in speed may seem irrelevant to the overall speed of the system: if this change occurred a year before a potential collision it could be enough to divert the asteroids path to miss Earth.
Despite the clear benefits of preventing catastrophic damage which could almost certainly involve the deaths of millions if not billions of people varying on the asteroid’s size; the cost of said redirection is not going unnoticed. However, I will discard the cost as a discouragement because if avoiding potential extinction/global destruction is dependent on preventing the collision then it would only be logical for all of the Earths gathered resources to be used to prevent a collision as failing to do so would result in there being nobody to . Furthermore, even if explosives were taken with the rocket to further maximise the redirection of the asteroid’s path; if it wasnt identified as a threat early on enough we may not be able to generate enough disruption to the asteroids path to prevent a collision. This is a perfect example that shows us how the first step in preventing a hazard from occurring is to first identify the hazard. Now I have all these details, it is clear that to maximise our chances of avoiding a collision we need to distinguish any asteroids that present a risk to our planet. This is where I believe that the qualities of ion drives can be used. Firstly, they can be used to propel probes far into deep space to locate asteroids, which may propose a threat to earth, that we arent able to locate from current telescopes. Secondly, new ion propulsion systems, which are able to achieve much higher power outputs and therefore much higher thrust than a more common ion thruster, can be used to help accelerate the payload spacecraft (responsible for colliding with the asteroid) up to an extremely high velocity to cause a force as large as possible to the asteroid.
.There are many exploration missions within our solar system that require multiple orbits around a planet or other celestial bodies and the mission may even aim to visit multiple targets to gather information. Dawn is a perfect example of this because it visited 2 targets and also completed many orbits around both the largest and second largest asteroids in the asteroid belt found between the orbits of Mars and Jupiter. Dawn travelled a total of 6.9 billion km or 6.9 * 10^12 m. These type of missions favour ion propulsion due to a couple of main reasons. Firstly, long-distance missions take a long time to complete which suits ion propulsion as they can generate small amounts of thrust for extremely long periods of time, it can take years for ion drives to reach the maximum velocity. Despite it taking a long time to accelerate, over a mission that could take over 5 years to complete, the spacecraft using ion propulsion will have completed it faster. Also, if we were to use chemical rockets for long-distance missions, then a large proportion of the rockets velocity would have to be generated in a burst of a couple of minutes. This presents a problem in that a small error in the rockets initial angle could result in a vast change in direction needed later on in the mission. With ion propulsion, this is not a problem as the acceleration is achieved over a long time which will allow minuscule adjustments to be made to keep the spacecraft along its desired path. After considering this, it is apparent to me that ion propulsion should currently be the chosen method of propulsion for missions that are either a long distance away from Earth or that require a large change in velocity. Ion thrusters have proven to be a suitable and efficient alternative to conventional propulsion systems. {Kawnine and Kawnine, 2014}
An example of the success of ion drives is the Dawn mission that was being directed through our solar system over the span of over 11 years from Sept. 27, 2007, until its fuel supply ran out on Nov. 1, 2018, and was left in an uncontrolled but stable orbit around its second target, the dwarf planet, Ceres. It is considered a very successful mission and was able to gather data on two celestial bodies, Vesta and Ceres.
However, I have only tried to give a value to the direct benefits and I havent yet considered the indirect benefits of space exploration. Missions into space can have some very important indirect benefits because of the unique nature of space that we cannot commonly explore in many different ways here on Earth.
‘If you like spin-off products, why not just invest in those technologies straightaway, instead of waiting for them to happen as spin-offs?’ The answer: ‘It just doesn’t work that way.’ Let’s say you’re a thermodynamicist, the world’s expert on heat, and I ask you to build me a better oven. You might invent a convection oven, or an oven that’s more insulated or that permits easier access to its contents. But no matter how much money I give you, you will not invent a microwave oven. Because that came from another place. It came from investments in communications, in radar. The microwave oven is traceable to the war effort, not to a thermodynamicist. (Neil deGrasse Tyson, Space Chronicles, W.W.Norton & Company, 2012, p.210.)
This is another argument for why we should continue with missions into space as they have the potential to produce technology for a field that we werent even trying to improve. In fact, in
About half a century ago, the first ion drive was built and yet only in the last decade or so has this method of propulsion started to become more widely recognised. A reason for this could be that despite some useful properties, including efficiency, the very small thrust prevents them being used when acceleration is required to be large. It isnt just the low thrust that has stopped ion drives becoming a more conventional method of propulsion. Although many tests have been carried out, it isnt cheap to put ion drives in practice and just like lots of other technologies; the risk that potential adopters perceive can delay the progress. However, once this barrier has been overcome and the technology is first tested then the risk of failure is seen as far less; resulting in a much faster development in this technology. For ion drives a big step in its development was the agreement reached in the early 1990s between Russian, European and American space industries to give chase to the advancement of ion propulsion technology. {ISECG, 2013}
Problems with ion drives
An argument for ion drives not being suitable for exploration far away from the sun is that at this current moment, ion drives are also known as solar electric propulsion. This is because they need a supply of electricity to keep the electric field operating as well as to first the electron beam into the ionisation chamber. This electricity is generated using large solar panels that harness the light emitted by the sun. However, as we move further away from the sun towards the edge of our solar system there is a huge drop off in how much power the solar panels can generate. This is because of the inverse square law that states the intensity of an effect, in this case, light intensity, changes in inverse proportion to the square of the distance from the source. This would mean that when a solar panel at the distance Neptune is away from the sun is compared to a solar panel at the distance the Earth is away from the sun the solar panel at Neptune would receive an intensity 19^2 smaller or 391 times smaller than the intensity received at Earth.
As Earth becomes more developed, our need for resources will increase and although we may be able to find alternatives for some finite resources, there will be a limit to how many resources there will be alternatives for. For example, over the last 50 years, the world has produced the majority of its electricity by burning fossil fuels. However, as fossil fuels are a non-renewable resource; we are limited to how long we can use them as they take millions of years to form naturally. To combat this we have developed several sustainable methods of generating electricity. These include; solar, wind, tidal, geothermal and more. However, fossil fuels are not the only non-sustainable resource; there are also many valuable elements and raw materials found in our World’s crust that have become less and less expendable {Ritchie and Roser, 2019}. A perfect example of this is platinum that is used in jewellery, aeronautics, and weaponry but used even more commonly in the hard drives of computers {Rsc.org, 2019}. This makes platinum extremely valuable and millions of dollars are spent trying to mine the rare Earth metal. As we continue to mine the platinum, it is essentially used up and as we are almost always unable to find an alternative substance that can be used as effectively to the original substance that has become scarce. We are also unable to create platinum without the centre of a star and I dont think we are going to be able to find an alternative method of creating elements any time soon. This leaves us with only being able to use platinum that has already been formed within the limits of our technology. Nevertheless there has been so much advancement in our technology that space is now an available source and additionally there is a dwindling supply of platinum ore deposits on Earth which is forcing companies to look elsewhere for rare metals. As this is the case; I think it is only fair to assume that if a large deposit of platinum or other valuable substances was to be found and could be mined at a reasonable cost then it would gather attention from a lot of companies. This is indeed the case when some large NEAs (Near Earth Asteroid) were thought to have huge supplies of rare earth metals including platinum. Although it would be very expensive to mine any potential asteroid, due to the small inconvenience of not being able to drive to any mining sites, if the right asteroid could be correctly scanned and analysed then its value can be estimated to ensure that an expensive trip of transporting mining machinery is not wasted.
This is another argument for why ion drives are the key to unlocking the benefits of space as they provide the sustainable thrust that can then be used on just one spacecraft to orbit and scan the composition of multiple asteroids that are thought to have valuable content. Nonetheless, even if mining asteroids does become reality ion drives could only be used for the details I have mentioned. If it came to moving large pieces of machinery, although ion drives could be used to assist the transport, it would be primarily moved using chemical rockets that can provide high thrust and chemical thrusters would also be used to land the machinery. Therefore ion drives will only have a small use in this potential sector of the expanding space industry.
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