Maglev Assist for Space Vehicle Launching

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A
SEMINAR REPORT
ON
“Magnetically Launching of Space Vehicle in Earth’s Lower Orbit”
In partial fulfilment of requirements for the degree of
Master of Technology
In
Instrumentation and Control Engineering
(Specialization - Process Instrumentation)
Submitted By:
BHASE PRASAD SHASHIKANT
MIS NO: 121416017
Under the Guidance of
Dr. S.B. PHADKE
DEPARTMENT OF INSTRUMENTATION AND CONTROL ENGINEERING
COLLEGE OF ENGINEERING
SHIVAJINAGAR, PUNE-411005
2014 - 2015

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CERTIFICATE
This is to certify that the Seminar titled “Magnetically Launching of Space Vehicle in Earth’s Lower Orbit” has been submitted by BHASE PRASAD S. under my guidance in partial fulfilment of the degree of Master of Technology in Instrumentation and Control Engineering with specialization in “PROCESS INSTRUMENTATION” of College of Engineering, Pune during the academic year 2014-2015 (Sem-I) .
Date:
Place: Pune
Guide Head, Instrumentation Department
(Dr. S.B.Phadke) (Dr. S. L. Patil)

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ACKNOWLEDGMENT
I would like to thank all those who have contributed to the completion of the seminar and helped me with valuable suggestions for improvement. I would like to thank Dr. S. B. Phadke, my guide and Dr. S.L. Patil, Head, Department of Instrumentation and Control, College of Engineering, Pune, for all help and support extend to me.
I am extremely grateful to Dr. S.B. Phadke, for providing me with best facilities and atmosphere for the creative work guidance and encouragement. I thank all staff members of my college and friends for extending their cooperation during my seminar. Above all I would like to thank my parents without whose blessings I would not have been able to accomplish my goal.

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ABSTRACT
A Maglev system uses magnetic fields to levitate and accelerate objects along a track, potentially providing initial vertical velocity prior to rocket ignition allowing for smaller, lighter rockets. Previous tests have demonstrated that Maglev technology could accelerate a spacecraft up to 600 mph, and then switch to a conventional rocket propulsion system near the endpoint of the track. Maglev launch assist provides many advantages over the conventional rocket launch and the report presents a system approach documenting the launch assist and compares both systems, essentially asking the question “would the investment be feasible compared to conventional solid/liquid rockets?” The report continues analysing the system by considering engineering challenges of construction, maintenance and power supply. A case study is performed comparing conventional rocket launch to Maglev launch assist on the basis of payload lifting capabilities, cost and environmental impacts.

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CONTENTS
1. Introduction ………………………………………………….….. 1
2. Maglev Technology ………………………………………………3
2.1. Basic Terms ……………………………………………..3
2.1.1. Permanent Magnet ………………………………..3
2.1.2. Electromagnet ……………………………………..4
2.1.3. Superconductive Magnet …………….....................5
2.2. Maglev Principle ………………………………………..6
2.3. Working of Maglev Vehicle …………………………...7
2.3.1. Propulsion Force…………………………………..7
2.3.2. Levitating Force…………………………………...9
2.3.3. Lateral Guidance………………………………….11
3. Design Concepts of Maglev Launch Assist……………………..12
3.1. StarTram Gen-I ………………………………………...12
3.2. StarTram Gen-II ………………………………………..13
3.3. Maglifter ………………………………………………..15
4. Cost Analysis…………………………………………………….17
5. Environmental Impact ……………………………......................19
6. Summary & Conclusion …………………………………………20
7. References ……………………………………….........................21

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LIST OF FIGURES
2.1 Permanent Magnetic Field…………………………………3
2.2 Electromagnet……………………………………………...5
2.3 Propulsion Force…………………………………………...8
2.4 EDS System………………………………………………..9
2.5 EMS System……………………………………………….10
2.6 Combined Sketch of Propulsion, Levitation
and Lateral Guidance……………………………………...11
3.1 StarTram Gen-II Levitation Tube…………………………14
3.2 StarTram Gen-II Launch ………………………………….14
3.3 Maglifter Launch Assist Designed at NASA...……………16
LIST OF TABLES
4.1 Cost Analysis of Gen-I,II, Maglifter and Space Shuttle…..17

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CHAPTER -1
INTRODUCTION
Achieving orbit in space, for both cargo and people is still considered a great achievement, but in a time of limited budgets the use of conventional rockets might not be the most efficient method. Placing a kilogram of payload into space can reach $10, 000[1]. Considering the global economic crisis, space exploration will be reduced if lower cost technologies fail to replace the current ones. There are multiple technologies being proposed for space transportation and one of the most realistic options is magnetic levitation (maglev) launch assist. A maglev system uses a spacecraft that is magnetically levitated on a track to reduce friction, and is propelled along the track to high speeds. A maglev train in Japan, used for passenger transportation can achieve top speeds registered at 581 kilometres per hour (kph). The train’s success demonstrates that the technology is available, and has the potential to provide an alternative for space exploration. Compared to conventional rocket launch, the maglev spacecraft launch assist seems to offer numerous advantages; this report examines the following three:
1) It works on electricity, which significantly reduces the operating costs.
2) It locates its equipment on the ground, which allows placing more payloads into space.
3) It releases very few chemicals in the atmosphere.
The report presents three existing maglev designs, two developed by StarTram and NASA’s MagLifter. The report then continues with a comparative case study of maglev spacecraft system vs. conventional rocket launch. The report compares these systems based on cost efficiency and environmental footprint. It then discusses which system is the preferred based on these criteria. The analysis is not just theoretical, but also describes the exact criteria for a practical maglev system. The report touches the current global problems: the economic crises and

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the alarming negative environmental situation. This type of analysis is important for space exploration because it can demonstrate whether the maglev launch assist approach is cost feasible compared to traditional rocket launch, and how it meets the challenges of current environmental challenges.

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CHAPTER-2
MAGLEV TECHNOLOGY
The creation of magnetic forces is the basis of all magnetic levitation. The creation of a magnetic field can be caused by a number of things. The first thing that it can be caused by is a permanent magnet. These magnets are a solid material in which there is an induced North and South Pole. These will be described further a little later. The second way that magnetic field can be created is through an electric field changing linearly with time. The third and final way to create a magnetic field is through the use of direct current.
2.1 Basic Terms
2.1.1 Permanent Magnet: -
The first type of levitation is the implementation through permanent magnets. These magnets are made of a material that creates a north and a south pole on them.
Fig.2.1 Permanent Magnet Field

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The formal definition of a permanent magnet is “a material that retains its magnetic properties after and external magnetic field is removed.”
The whole idea behind permanent magnets is that like ends will repels and opposite ends will attract. Permanent magnets require very little if any maintenance. These magnets do not require cryogens or a large power supply for operation. The magnetic field is measured vertically within the bore of the magnet.
Disadvantages: -
1. Cost of the magnet is very high when put into large scale systems
2. Varying changes in the magnetic field
3. The ability to control is a constant magnetic force from a permanent magnet is an ongoing problem
Different applications that use these types of magnets can be found in a number of different areas. Examples of these applications are compasses, DC motor drives, clocks, hearing aids, microphones, speedometers, and many more.
2.1.2 Electro Magnet: -
The basic idea behind an electromagnet is extremely simple. By running electric current through a wire, you can create a magnetic field. When this wire is coiled around a magnetic material (i.e. metal), a current is passed through this wire. In doing this, the electric current will magnetize the metallic core.

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Fig.2.2 Electromagnet
By using this simple principle, you can create all sorts of things including motors, solenoids, heads for hard disks, speakers, and so on. An electromagnet is one that uses the same type of principles as the permanent magnet but only on a temporary scale. This means that only when the current is flowing is there going to be an induced magnet. This type of magnet is an improvement to the permanent magnet because it allows somebody to select when and for how long the magnetic field lasts. It also gives a person control over how strong the magnet will be depending on the amount of current that is passed through the wire.
2.1.3 Superconductive Magnet: -
Superconductive magnets are the most common of all the magnets, and are sometimes called ‘cryomagnets’. The idea behind the superconducting magnets is that there is a material which presents no electrical resistivity to electrical current. Once a current has been fed into the coils of this material, it will indefinitely flow without requiring the input of any additional current. The way that a material is able to have such a low resistivity to current is that it is brought to very low temperatures. The temperatures that are commonly found in superconducting magnets are around -258oC. This is done by immersing the coils that are holding the current into liquid Helium; this also helps in maintaining a homogenous magnetic field over time. The advantage to the superconducting magnet is that they don’t require constant power from a source to keep up the

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value of the current in the coils. Although a disadvantage is that they require an expensive cryogen such as helium to operate correctly. The magnetic field is in the direction of the long axis of the cylinder or bore of the magnet. Since the resistance in the coils can cause the current to decay, cryogens reduce the resistance to almost zero, which will help maintain a homogenous magnetic field over time.
2.2 Maglev Principle: -
Maglev is short for magnetic levitation, which means that these trains will float over a guide way using the basic principles of magnets.
There are two types of Maglev's: ones that use like magnets which repel each other and ones that use opposing magnets that attract with each other. Ones that use repelling magnets are called Superconducting Maglev's. The magnets allow the train to float. Electromagnetic Maglevs use opposing magnets.
Superconducting Maglevs use very cold temperature magnets in order to make electricity without any opposition. The magnets are then put on the bottom of the train. When the train moves, it forms currents from the magnets in the aluminium sheets placed in the guide way. Because of the repelling force, the vehicle rises. Also in the guide way, separate electric currents pass through which push the train forward. This system is also called as ‘ElectroDynamic System.’
Electromagnetic Maglev's go under the guide way. They use opposing magnets that attract with each other. This allows the Maglev to pull upward towards the guide way. Like the superconducting Maglev's, separate currents make magnetic fields shift which allows the train to move forward. These Maglev's travel about 3/8's of an inch away from the guide way. In order for the magnets from not hitting the guide way, the lifting current must keep being fixed. This system also called as ‘ElectroMagnetic System.’

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The main parts of the Maglev:
1. Guide way and guide rails - keep the train to on track
2. Landing wheels
3. levitation coils - run along the base of the guide way (used in superconducting maglevs)
4. Emergency landing wheel
5. superconducting magnets and propulsion coils - run along the base of guide way (used in electromagnetic maglev's)
6. Linear induction motor - moves and brakes the vehicle on the track.
2.3 Working of Magnetic vehicle: -
Basically the construction depends on 3 different working forces.
i. Propulsion Force
ii. Levitating Force
iii. Lateral Guiding Force
2.3.1 Propulsion Force
This is a horizontal force which causes the movement of train. It requires 3 parameters.
i. Large electric power supply
ii. Metal coil lining, a guide way or track.
iii. Large magnet attached under the vehicle.

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Fig.2.3 Propulsion Force
A linear motor or linear induction motor is essentially a multi-phase alternating current (AC) electric motor that has had its stator "unrolled" so that instead of producing a torque (rotation) it produces a linear force along its length. Many designs have been put forward for linear motors, falling into two major categories, low-acceleration and high- acceleration linear motors. Low- acceleration linear motors are suitable for maglev trains and other ground-based transportation applications. High-acceleration linear motors are normally quite short, and are designed to accelerate an object up to a very high speed and then release the object, like roller coasters.
Maglev vehicles are propelled primarily by one of the following three options:
a. Linear synchronous motor (LSM) in which coils in the guide way are excited by a three phase winding to produce a traveling wave at the speed desired; Trans Rapid in Germany employs such a system.
b. Linear Induction Motor (LIM) in which an electromagnet underneath the vehicle induces current in an aluminium sheet on the guide way.
c. Reluctance motor is employed in which active coils on the vehicle are pulsed at the proper time to realize thrust.

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2.3.2 Levitating Force
The levitating force is the upward thrust which lifts the object/vehicle in the air.
There are 3 types of levitating systems
i. EDS system
ii. EMS system
iii. INDUCTRACK system
Levitating force is produced due to the eddy current in the conducting ladder by the electromagnetic interaction. At low speed the force due to induced poles cancel each other. At high speed a repulsive force is taken place as the magnet is shifted over a particular pole.
A. EDS System: -
In EDS both the rail and the train exert a magnetic field, and the train is levitated by the repulsive force between these magnetic fields. At slow speeds, the current induced in these coils and the resultant magnetic flux is not large enough to support the weight of the train. For this reason the train must have wheels or some other form of landing gear to support the train until it reaches a speed that can sustain levitation.
Fig.2.4 EDS System

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On board magnets and large margin between rail and train enable highest recorded train speeds (581 km/h).This system is inherently stable. Magnetic shielding for suppression of strong magnetic fields and wheels for travel at low speed are required. It can’t produce the propulsion force. So, LIM system is required.
B. EMS System: -
Maglev concepts using electro -magnetic suspension employ attractive forces. Magnetic fields inside and outside the vehicle are insignificant; proven, commercially available technology that can attain very high speeds (500 km/h); no wheels or secondary propulsion system needed.
Fig.2.5 EMS System
The separation between the vehicle and the guideway must be constantly monitored and corrected by computer systems to avoid collision due to the unstable nature of electromagnetic attraction.
C. Inductrack System: -
The inductrack guide way would contain two rows of tightly packed levitation coils, which would act as the rails. Each of these “rails” would be lined by two Halbach arrays carried underneath the maglev vehicle: one positioned directly above the “rail” and one along the inner side of the “rail”.

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The Halbach arrays above the coils would provide levitation while the Halbach arrays on the sides would provide lateral guidance that keeps the train in a fixed position on the track.
The track is actually an array of electrically-shorted circuits containing insulated wire. In one design, these circuits are aligned like rungs in a ladder. As the train moves, a magnetic field repels the magnets, causing the train to levitate.
2.3.3 Lateral Guidance Force: -
Guidance or steering refers to the sideward forces that are required to make the vehicle follow the guideway. The necessary forces are supplied in an exactly analogous fashion to the suspension forces, either attractive or repulsive. The same magnets on board the vehicle, which supply lift, can be used concurrently for guidance or separate guidance magnets can be used. It requires the following arrangements:
• Guideway levitating coil
• Moving magnet
Fig.2.6 combined sketch of Propulsion, Levitation and Lateral Guidance

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CHAPTER-3
DESIGN CONCEPTS OF MAGLEV LAUNCH ASSIST
The two developed concepts of maglev launch assist are StarTram and MagLifter.
StartTram is an innovative lunch concept that proposes levitating the launching track tube high above the earth surface where the air has low density and allows for lower air drag. The spacecraft placed inside the tube will accelerate at 8 km per second (kps) enough to place it into the Lower Earth Orbit (LEO). This is the second generation of StarTram – Gen II – which transports passenger into space. Gen I is theoretically designed for cargo transportation, and it does not require a launch tube. Instead it uses a track to be launched from the top of a mountain at velocities greater than Mach 8. Because Gen II transports passengers it takes into account the high heating and increased friction, and requires launching the vehicle at high attitude in a long magnetically levitated tube. Estimated an elevation of approximately 18 km. [1]
MagLifter is another maglev launch assist concept and was part of the NASA reusable launch vehicle system. Small scale experiments were conducted at the NASA Marshall Space Flight Center in Huntsville, USA (Figure I). The MagLifter spacecraft is escalated on a magnetically levitated sled on a track, and like Gen I it does not require a tube. The two concepts are described in more detail below.[3]
3.1 StarTram Gen-I
Gen I system is designed for cargo only, and as mentioned it requires an acceleration tunnel only. The cargo craft is 2 meters in diameter, 13 meters long and with a 40 metric ton weight. It is intended to accelerate the craft at 30 G in a

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~ 100-km length tunnel that is evacuated of air with the help of Magnetic Hydro Dynamic “window”. The high G level allows building a short acceleration tunnel and therefore reduces the cost of building the system. The biggest challenge with operating a short tunnel to high acceleration of 8 kps is the large power storing and quick power delivery. A good system for electricity operation that allows both a very short delay between charge and discharge and high power generation is the superconducting magnetic energy storage (SMES) system. This system can be designed to include 60 loops of 250 meters in diameter that will allow the storage of 3,000 Gigajoules (GJ), more than enough to accelerate the 40 metric ton craft of 1280 GJ. [1]
According to Powell and Maise(Scientists), the potential launch sites for Gen I have to be close to a low populated area with the minimum flight over land. This will create a more secure area and less noise disturbance. They also suggest that the launch attitude is preferable to be at least at an attitude of 4 km in order to contribute to lower air drag and heating. The last criteria proposed by the author is a launch into the polar orbits that allows high resolution environmental monitoring and better survey of all areas around the Earth. The potential launch site that would meet all the above criteria would be Antarctica.[1]
3.2 StarTram Gen-II
Gen II vehicle is launched from an elevated tube at an altitude of 18 km. Superconducting wires are buried into the ground and placed on the launch tube. The repulsive force levitates the tube attached to the Kevlar cables as shown in the Figure II. The level of 2-3 G is significantly lower than the cargo craft G level and allows passenger transportation. Because of the slow acceleration Gen II requires a long track of up to 1600 km as sketched in Figure III. The accelerating track tube seven meters in diameter consists of the acceleration tube (1280 km long) at the ground level and the elevated launch tube (281 km long). The current

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required to levitate four tons per meter is 14 Mega-amps (MA) in the levitated
cables and 280 amps (A) in the ground cables [5]. At a first glance, Gen II seams
to face more engineering challenges then Gen I considering the elevation of a
long tube above the ground. Nevertheless, using Ampere’s force law, the amount
of current needed in the ground superconductors to elevate the tube (around 280
x 106 A) at an attitude of 20-km is 20 times more than current on the tube.
Niobium-titanium superconductors can be resistant enough to deliver this amount
of current with its conventional critical current density of 5 x 105 A/cm2. Because
the power supply required is more than the usual power grid, a power generation
facility is located nearby. The reusable vehicle would return on a horizontal
guideway in the same manner like the Space Shuttle.[7]
Fig.3.1 StarTram Gen-II Levitated tube supported by Kevlar Cable [5]
Fig.3.2 StarTram Gen-II Launch System sketch divided into the long
acceleration tube located on the ground and the elevated part tube 18 km above
the ground [7]

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3.3 Maglifter: -
The MagLifter is a spacecraft launch system to the LEO created by the NASA program on Highly Reusable Space Transportation. Compared to other maglev launch concepts MagLifter does not require extremely high accelerations and high rates to achieve economical operations. The MagLifter is the next generation of many “gun” assists ideas, and it consists of launching the vehicle from a sled that is accelerated on a three to four mile track. The design was invented, as mentioned, by Mankins who was the manager of Advanced Concept Studies at NASA in 1994. The architecture of MagLifter system consists of the following major substructures: the catapult, power systems, structural support systems and supporting systems:
i. Catapult: - The catapult includes the maglev guideway, the accelerator- vehicles and the accelerator-carrier staging facility. The accelerator will be enclosed in a tunnel and will be filled with a helium gas that would allow low drag forces.
ii. Structural Support: - The structural support will require complicated engineering design and will depend on whether the guideway is placed on the exterior of the mountain, on the side of the mountain or in a tunnel inside the mountain.
iii. Power System: - A substantial local power supply system is needed to provide enough launch energy that would charge from the local power grid.

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Fig. 3.3 MagLifter Launch Assist designed at NASA
Marshall Space Flight Center, Huntsville, USA[4]
The reusable vehicle accelerates at 550 miles per hour (885 kph) and at the end of the guideway, ascends to the Earth orbit and separates from the sled. The 3 G acceleration will allow passenger transportation similar to Gen II. The vehicle is accelerated efficiently because of the absence of friction between the sled and the guideway created by the superconducting magnets lined on the sled bottom and the conductive plates on the guideway. After the launch the sled returns to the starting point and is reused again for the next launch. Argus, the MagLifter vehicle is powered by two supercharged ramjet and rocket-based combined-cycle engines that use liquid hydrogen and liquid oxygen fuels. Argus can be designed from 170 to 225 feet (52 to 67 m) in length with a 51 to 60 foot (16 to 18 m) wingspan. The vehicles weights run from 600,000 to 1 million pounds (273,000 kg to 455,000 kg) and can deliver up to 20,000 pounds (9, 000 kg) into the LEO. Argus returns back as a glider in the same way as the Space Shuttle. The possible location for the launch facility of MagLifter is the Kennedy Space Center since it one of the closest U.S. locations to the equator and facing East to the Ocean. [3], [4]

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CHAPTER-4
COST ANALYSIS
One primary element of these studies is comparing the investment budget and the operational costs associated with placing a kilogram of payload into space. This cost comparison is essential to possible future investment due to the current global economy.
A detailed cost for StarTram system is proposed by Powell and it is important to mention that the cost for Gen I includes building two acceleration tunnels (operational and reserve). The length of both tunnels is twice as long (260 km), therefore the budget for excavating the tunnel will double. In the Gen I system the spacecraft and the Magnesium diboride (MgB2) are non-recoverable, so we will move the cost of the MgB2 superconductors to the operational costs for the final calculations. The detailed budget description of Gen I and Gen II estimated by Powell is presented in Table I. The MagLifter program estimates a cost of 2 billion for a large scale project. [6],[7]
The payload delivered to LEO by Endeavour is 24,400 kg and will be used as the average payload for U.S. Space Shuttle in further calculations.
Table 4.1: Gen I, Gen II, MagLifter and Space Shuttle
Launch Cost/kg of Payload.

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The investments cost for building MagLifter system seem very low so it is hard to make any conclusions. Gen I has high operational costs because of the non-reusable MgB2 superconductors that cost the project around 3 billion extra each launch. Gen II launch cost is the most convenient because of low operational costs which is the basic idea of potentially using the magnetic levitation launch system. Space Shuttle Launch is eight times more expensive than Gen II. However, this rate is not high enough for a big scale project like spacecraft launch, and it does not necessarily conclude the cost efficiency of one project over another. The cost predictions for maglev launch projects are very low, and so were the NASA initial predictions of Space Shuttle costs. Since Maglev is still a theoretical concept and it faces many engineering challenges, more research needs to be performed in order to make accurate final conclusions.

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CHAPTER-5
ENVIRONMENTAL IMPACT
The maglev spacecraft system’s carbon emissions occur from energy consumption at the launch stage where the power supply is vast in order to lift the tube and/or accelerate the spacecraft. Therefore, the most negative impact on the environment occurs from the emissions produced by the power source.
StarTram does not use engines for launch and so it doesn’t burn fuels [14], while MagLifter and the Space Shuttle require engines that use liquid hydrogen and liquid oxygen fuels.

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SUMMARY AND CONCLUSION
All three systems are similar and different in regards to their engineering structure and costs. Gen I launched its spacecraft from a track and is accelerated to 8 kps. The 30 G acceleration does not allow passenger transportation, therefore the spacecraft is non-reusable. Gen II is a very well though concept that can be compared to Space Shuttle best since it creates a 3 G acceleration allowing passenger transportation. The low acceleration and human transportation requires building a longer tunnel at higher attitudes. The Gen II tube is magnetically levitated 20 km above the ground where the air is less dense allowing lower heating and lower air drag. The investment costs for Gen II are higher but the operational costs lower since the spacecraft is reusable. MagLifter spacecraft is launched from a sled on a short track (3 km) at a speed of 885 kph, but it uses its engines for further ascending stages. The concept was experimented before on small scales at NASA Marshall Space Flight Center, Huntsville, USA.
The costs analysis was done assuming 135 spacecraft launches for the Space Shuttle. Gen I is a more expensive concept then Gen II because of its higher operational costs due to the non-reusable spacecraft and MgB2 superconductors
Gen II is a theoretical concept and will require further research of the engineering challenges.
Based on costs and the environmental impact Gen II is an excellent design and potentially better than the Space Shuttle. While the cost of maintaining and operating Gen II are very low.

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REFERENCES
1. Powell, J.; Maise, G., "StarTram: The Magnetic Launch Path to Very Low Cost, Very High Volume Launch to Space," Electromagnetic Launch Technology, 2008 14th Symposium on , vol., no., pp.1,7, 10-13 June 2008
2. J. R. Hull and T. M. Mulcahy, “Magnetically levitated space elevator to low earth orbit,” in Proc. 3rd International Symposium on Linear Drives for Industrial Applications, Nagano, Japan, October 2001, pp.42–47.
3. J. H. Schultz, A. Radovinsky, R. J. Thome, B. Smith, J. V. Minervini, R. L. Myatt, R. Meinke, and M. Senti, “Superconducting magnets for maglifter launch assist sleds,” IEEE Trans. Appl. Supercond., vol. 11, pp. 1749–1752, 2001.
4. NASA Marshall Space Flight Center
http://www.nasa.gov/centers/marshall/news/background/facts/astp.html_prt.htm
5. Spacedaily
http://www.spacedaily.com/news/rlv-99y.html
6. Powell, James, et al. "Maglev Launch: Ultra-low Cost, Ultra-high Volume Access to Space for Cargo and Humans." Aip Conference Proceedings. Vol. 1208. No. 1. 2010.
7. Powell, J., George Maise, and John Paniagua. "StarTram: An Ultra-Low Cost Launch System for Large Scale Exploration and Commercialization of Space."55th International Astronautical Congress 2004.