StarTram: An Ultra Low Cost Launch System to

Enable Large Scale Exploration of the Solar System

James Powell, George Maise, and John Paniagua

StarTram, Inc., PO Box 547, Shoreham, NY 11786,

631-744-5707; maise@optonline.net

Abstract. StarTram is a new approach for low launch to space using Maglev technology. Spacecraft are magnetically levitated and accelerated without propellants to orbital speeds in an evacuated tunnel at ground level using only electrical energy. The cost of the electric energy for acceleration to 8 kilometers per second is only 60 cents per kilogram of payload. After reaching orbital speed, the StarTram spacecraft coast upwards inside an evacuated levitated launch tube to an altitude, of 10 kilometers or more, where they enter the low-pressure ambient atmosphere. The launch tube is magnetically levitated by the repulsive force between a set of high current superconducting cables on it and oppositely directed currents in a set of superconducting cables on the ground beneath. High strength Kevlar tethers anchor the launch tube against crosswinds and prevent it from moving laterally or vertically. A Magneto Hydro Dynamic (MHD) pump at the exit of the evacuated launch tube prevents air from entering the tube. Two StarTram systems are described, a high G (30G) system for cargo only launch and a moderate G (2.5 G) system for passenger/cargo spacecraft. StarTram’s projected unit cost is $30 per kilogram of payload launched, including operating and amortization costs. A single StarTram facility could launch more than 100,000 tons of cargo per year and many thousands of passengers. StarTram would use existing superconductors and materials, together with Maglev technology similar to that now operating. The StarTram cargo launch system could be implemented by 2020 AD and the passenger system by 2030 AD.

Keywords: space launch, Maglev, Maglifter PACS: 07.87.+v, 85.70.Rp, 85.71.Ba

INTRODUCTION

The Moon-Mars Initiative calls for completing the International Space Station (ISS), phasing out the Space Shuttle, establishing a permanent human base on the Moon, and manned expeditions to Mars by 2030 AD, a dramatic expansion of the human exploration of space (Bush, 2004). Since the last manned landing on the Moon three decades ago, humans have not gone more than 300 miles above the Earth. The ISS is undermanned and not fully operational. Shuttle flights are restricted, budgets are tight, and public interest in space is tepid. Given the major problems facing the World, including widespread poverty, military conflict and terrorism, shrinking oil resources, drought and water scarcity, etc., it is unrealistic to expect large dramatic increases in space exploration funding, if that is the only justification for it.

The best hope to dramatically increase space exploration is to radically reduce the cost of launching payloads and people into space. Placing a kilogram of payload in Low Earth Orbit (LEO) presently costs or the order of $10,000 (Futron Corporation, 2002), while placing the space tourist, Dennis Tito, human in the International Space Station (ISS) costs 20 million dollars (Russian News Agency NOVOSTI, 2005). The unit costs for placing payloads and people on the Moon would be an order of magnitude greater. The manned Mars missions, proposed by the Space Exploration Initiative (SEI) in the early 1990’s, were estimated to cost on the order of 400 billion dollars, based on existing technology (NASA, 1989). The cost in current (2004) dollars would be considerably greater. Over the last 30 years, many have tried to develop lower cost launch systems, involving such approaches as fully reusable launch vehicles, scramjets, single stage to orbit, etc. As yet, the cost reductions are marginal. No practical approach for major reductions in launch cost, i.e., by a factor of a least 10, have been identified. This is not surprising. Systems

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based on the combustion of chemical propellants, whether rockets or combined rocket/air breathing vehicles, deliver only a very small fraction of their takeoff weight into orbit, and are very expensive to build and operate. The launch vehicles have many complex systems that operate near their failure point, with very limited redundancy. For a major reduction in launch costs, the radically new approach that does not depend on the combustion of propellants is needed.

This new approach is StarTram. In StarTram, spacecraft are magnetically levitated and accelerated to orbital speeds in a long evacuated tunnel on the ground. They then enter an evacuated launch tube that is magnetically levitated, and ascends to a high altitude, e.g., 10 km or more, where the atmospheric density is a few percent of that at sea level. At this altitude, the aerodynamic drag forces and heating rates are much less than at sea level. The spacecraft

coasts upwards using a small ∆V burn from an on-board rocket to establish Earth orbit, or to travel directly to the Moon. The evacuated launch tube is levitated by the magnetic repulsion force between high current superconducting cables attached to the launch tube, and superconducting cables located on the ground underneath. Superconductors can carry enormous currents, e.g., millions of amps with no electrical losses. Some electric power is required for the refrigeration system that maintains the superconductors at low temperature. This power is quite small, because the superconductors are thermally well insulated from the outside ambient environment. The magnetic levitation force at altitudes of 20 kilometers is several tons per meter of launch tube length. The technology needed for StarTram already exists. High Speed Maglev (magnetic levitation) trains are already operating in Japan. The superconductors, cryogenic refrigeration equipment, and structural materials for the levitated launch tube are commercially available. Building StarTram will be one of the World’s major construction projects, requiring extensive engineering development; however, all of the needed technology already exists, and no breakthroughs are required.

In the following sections, the design and technology of StarTram is described in detail together with projections of its construction and operating costs. The projected costs, together with projections of the annual amounts of payload that could be launched by StarTram, enable a very low unit launch cost, on the order of $30 per kg of payload.

FIGURE 1. Trajectory of Generic StarTram Launch Tube.

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DESCRIPTION OF THE STARTRAM SYSTEM

The StarTram system (Powell, 2001; Powell, 2002; Powell, 2003) has 2 principal sections, as illustrated in Figure 1. In the first section, the acceleration tunnel, a StarTram spacecraft is magnetically levitated and accelerated using Maglev technology similar to that presently operating in Japan. In 1966, Powell and Danby (Powell, 1967) proposed using superconducting (SC) magnets to magnetically levitate (Maglev) and propel high speed passenger vehicles. SC magnets on the vehicle induce opposing currents in ambient temperature aluminum guideway loops, stably levitating the vehicle with a large clearance (e.g. 10 cm or more). AC current (~103 A) carried in separate guideway loops propels the vehicle, which is phase locked to the AC current wave [Linear Synchronous Motor (LSM)]. The vehicle speed equals the product of frequency and pole pitch, regardless of drag force variations

Based on their inventions, Japan Railways (JR) has built and is operating full size superconducting Maglev trains on a 40 kilometer test track in Yamanashi Prefecture, Japan. Single and multi-vehicle train sets operate at speeds up to 350 mph with total levitation weights of up to 200 metric tons. Since 1997, accumulated run distances of 300,000 kilometers with a total of 50,000 passengers have been achieved, with no accidents or incidents (Japan Railways Central, 2004). Since Maglev vehicles do not physically contact the guideway, the only real limit to their speed is air drag. In the open atmosphere, it is uneconomic to go beyond ~350 mph, because propulsion power increases with the cube of speed. In evacuated tunnels, however, speeds of 8 km per second can be achieved with close to 100% efficiency. At such speeds, the spacecraft would disintegrate if it entered the atmosphere at surface level, because of the intense heating and deceleration forces. If the spacecraft entered the atmosphere at high altitude where the air density is much lower, however, it could coast up to orbit without damage. To accomplish this goal after reaching orbital speed in the evacuated ground level acceleration tunnel, the StarTram spacecraft enters an evacuated launch tube that curves upwards to an altitude where entry into the low density atmosphere results in acceptable aerodynamic forces and heating rates. Although the end of the evacuated launch tube is open to the ambient atmosphere, the rate of air leakage into the tube is controlled and limited to an acceptably low rate using a combination of high velocity gas jet ejectors and an MHD pump. The gas jet ejectors positioned around the circumference of the launch tube reduce the atmospheric density at the exit point by factor of 10 below the already low ambient atmospheric density.

(a) Launch tube (b) Levitation/tether system

FIGURE 2. Cross Sectional View of StarTram Launch Tube and Levitation/Tether System.

The air leakage rate into the evacuated tube is further reduced by using an MHD pump inside the final section of the tube in which air is ionized and pushed outwards by interaction of an applied DC current with a transverse magnetic field. After entering the atmosphere, the StarTram spacecraft coasts upwards through the remaining low density

atmosphere until it reaches the desired orbital altitude. At that point, a small ∆V burn of several hundred m/sec from an attached chemical engine places the spacecraft into its final orbit. A major factor in the design of StarTram is the effect of launch altitude on the currents required in the superconducting cables attached to the launch tube as well as the ground cables. The magnetic force (N/m) on a levitated SC cable is

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with the opposite directed ground (IG) and levitated (IL) cable currents in amps, and the height (HO) of the levitated cable above the ground in meters. The factor (fGL) reflects the geometric effects of finite length and positioning. For infinite parallel cables positioned with aligned magnetic and gravitational force vectors, fGL = 1. For finite length, multi-cable systems, fGL is ~0.8 to 0.9. The magnetic levitation forces on the launch tube support its weight, the weight of the superconducting cables, and the momentary weight of the spacecraft as it coasts up the launch tube to plus a net magnetic levitation force that is strong and upwards. Accordingly, the launch tube is anchored to the ground beneath to hold it in place. Figure 3 shows the system of vertical and angled tethers that holds the launch tube in place, both vertically and laterally, against the upwards magnetic force and cross winds.

The primary tethers shown in Figure 2, which reach down to ground level, are spaced at intervals of 1 kilometer along the launch tube. Not shown is the network of shorter and smaller secondary tethers that are attached to the launch tube and SC cable at intervals of 20 meters, and connect to the upper portions of the more widely spaced primary tethers. Spectra (oriented polyethylene) has extremely high ultimate strength of 3 GPa (450,000 psi) and low density (910 kg per m3). As an example, operating at 0.6 GPa (90,000 psi), 20% of ultimate strength, a network of vertical and angled primary and secondary tethers can anchor a net lift force of 1 metric ton per meter at 20 km altitude above ground level, with a total weight of 0.6 metric ton per meter of launch tube length. The force balance is then FMAG -FLT- FT -FSC = FNET. (2)

Table 1 shows the total magnetic lift force, FMAG, and the net upwards magnetic lift force, FNET, on the launch tube as a function of the total SC current carried by the SC cables. The total SC current would be carried in a number of independent cables to ensure reliability and redundancy, with multiple parallel SC conducting units in each cable. For example, a total current of SC megamps could be carried by 10 separate SC cables, each of 5 megamps capacity, with 100 individual SC conductor units each carrying 50,000 amps, inside each SC cable cryostat. The individual SC sub-unit could be connected either in series at the end of the SC cable, or operate in parallel or be connected in series parallel combinations. The total area of the SC in each of 10 separate cables would be only 25 cm at present conservative current densities of ~200,000 amps per cm2. With further development the SC area will become even smaller.

For the cargo launch systems, the cargo craft enters the atmosphere at an altitude of 10 km above local ground level; for the passenger plus cargo launch system, the spacecraft enters the atmosphere at an altitude of 20 km above local ground level. Launch tube weight is taken as 1 metric ton per meter, and the superconducting cable system is 0.6 metric ton per meter. The tether system weight is taken as 0.4 metric ton per meter at the exit of the cargo launch system, and 0.8 metric ton per meter at the exit of the passenger plus cargo system. The geometric lift factor, fGL, is taken as 0.8.

TABLE 1. Magnetic Lift Force on StarTram Launch Tube. Lift Force, Metric Tons/Meter

Cargo Launch Passenger Launch

Total Superconducting

Cable Current

Megamp Turns Total Lift Force Net Lift Force Total Lift Force Net Lift Force

20 Megamps Turns 0.64 < 0 0.52 < 0 30 Megamps Turns 1.44 < 0 0.72 < 0 40 Megamps Turns 2.56 < 0 1.28 < 0 50 Megamps Turns 4.00 2.00 2.00 < 0 60 Megamps Turns 5.76 3.76 2.88 0.48 70 Megamps Turns 7.84 5.84 3.92 1.52

The magnetic forces are shown as a function of SC current where the levitated and ground cables carry equal currents – that is, they form a simple dipole loop. The exit end of the cargo launch system is taken as 10 km above local ground level and the passenger launch system as 20 km above local ground level. For a local ground level altitude of 2 km, the actual exit altitude would then be 12 km and 22 km. The passenger launch system requires a considerably higher exit altitude in order to have aerodynamic deceleration forces that are acceptable for passengers.

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Based on a structural mass of levitated launch tube, SC cable, and tethers that is in the range of 2 to 3 metric tons per meter of length, the net upwards lift force (magnetic lift minus structures mass) should be in the range of 1 to 2 metric tons per meter. This provides a good safety margin in case of a possible – through unlikely – failure of a portion of the SC conductor units. At 50 megamps, the levitated cable for the cargo launch systems has a net upwards magnetic force of 2 metric tons per meter at an altitude of 10 km above ground. The net upwards magnetic force for a section of ascending launch tube at an altitude of 5 km would be 6 metric tons per meter, enabling a very strong and rugged structure at lower altitudes where storm effects would be stronger. For the passenger launch system with an exit altitude of 20 km above ground, the net upwards magnetic force is 1.5 metric tons per meter at the exit, and 5.4 metric tons per meter at 10 km, the halfway point up the launch tube. Because the lift force is proportional to (current)2, a relatively small change in current will compensate for a relatively large change in structural weight. For the cargo launch system, for example, if the launch tube were to weigh 2 metric tons per meter instead of 1 metric ton per meter, the SC current would have to only increase from 50 megamps to 56 megamps to maintain a net upwards lift force of 2 metric tons per meter.

The same levitation force can be achieved with a smaller SC current in the levitated cable, if the current in the ground cable is correspondingly increased. For example, for the cargo launch system, reducing the levitated SC current to 25 megamps and increasing the ground cable current to 100 megamps would provide the same lift force. The total amount of superconductor required would essentially double, however, because of the extra SC in the main ground cable for levitation, plus the need for additional SC cables on the ground that would be needed to return the extra current. High wind speeds are rare at high altitude, and due to the low air density, wind forces relatively modest. At 50 meter/sec (110 mph), for example, a very infrequent wind speed at 20 km, the wind force is only 50 Newtons per meter, negligible in comparison to the magnetic and tether forces. Higher wind forces can occur at lower altitudes, but with additional tethers, the StarTram launch tube, SC cable, and tether system appears capable of withstanding all conceivable wind forces. The following sections describe two versions of StarTram systems. The first is a cargo only, high G system that would launch payloads using expendable spacecraft at an altitude of 10 km above local ground level. The second is a dual passenger/cargo system that would launch re-usable spacecraft to carry passengers as well as cargo at an altitude of 20 km above local ground level. The passenger/cargo system would operate at a modest g level, e.g., ~2 g, while the cargo only version would operate at a g level of ~30 g.

THE STARTRAM-C CARGO LAUNCH SYSTEM

Figure 4 shows a layout of the StarTram cargo craft and magnetic levitation geometry. The cargo craft has a nominal diameter of 2 meters and an overall length of 8 meters, with a total weight of 20 metric tons, including the cargo, structure, superconducting cables, and cryogenic refrigeration. Overall mass density is 800 kg per cubic meter, with an actual cargo capacity of ~15 metric tons. The L/D of 4 reduces aerodynamic drag when it enters the upper atmosphere. The cargo craft has 12 lines of superconducting (SC) loops spaced around its circumference, with each line occupying a 30 degree section. Each line is a series of separate SC loops that alternate in magnetic polarity along the length of the cargo craft. Each SC loop is 1 meter long, so that a given point on the wall of the acceleration tunnel sees an alternating magnetic field as the cargo craft moves past. The effective AC frequency is 1/Vc Hertz, where Vc is the speed of the craft in meters per second. At 8 kilometers per second, the frequency is 4 kiloHertz.

Attached to the wall of the acceleration tunnel are normal temperature aluminum loops. The magnetic fields from the moving SC loops generate currents and magnetic forces in them that levitate and stabilize the craft. The aluminum loops are arranged in pairs, with the two halves of the pair on opposite sides of the acceleration tunnel. The two-halves form an electrical circuit, in which the net magnetic flux is zero when the cargo craft is centered in the tunnel. If the craft moves closer to the tunnel wall, the loop closest to the craft will experience a magnetic flux that is greater than the flux through its partner loop on the opposite wall. The net magnetic flux through the loopcircuit will then be non-zero, causing an induced current to flow. The magnetic interaction between the induced currents and the SC loops on the cargo craft then pushes the craft back towards its centered position. This restoring force capability is inherent and automatic against any displacement, whether lateral or vertical, from its centered position. The restoring force for the cargo craft is very strong, 2g (20 m/sec2) per centimeter of displacement, for a current of 1 megamp in the superconductor loops. Since the physical clearance between the cargo craft and the surface of the tunnel is 10 centimeters, the levitated cargo craft is extremely stable.

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To provide a centered position for the cargo craft even though it weighs 20 tons, the bottom halves of the null flux loop circuits have slightly more turns than the top halves. This results in a small non-zero net flux and current through the null flux loop circuits, that levitates the craft at the center of the tunnel. The induced current is small, only about 7000 amps for a restoring force of 2 g. The conductor packs that make up the null flux loops can be small, typically 1 inch x 1 inch square (2.5 cm x 2.5 cm). I2R losses in the aluminum conductors are only about 100 kilowatts, and the temperature rise in the conductor is less than one degree Kelvin, when the cargo craft passes the loop. The set of superconducting loops on the cargo craft also magnetically accelerate it. Aluminum conductor loop windings on the walls of the acceleration tunnel carry an AC current that magnetically pushes on the superconducting magnets on the craft. The AC current synchronously propels it forward at the same velocity as the AC current wave. The craft in effect thus “rides” the current wave, much as a surfer rides a water wave. The LSM is similar to conventional rotary synchronous motors, except that the stator is a long continuous ribbon along the guideway, instead of a closed circumferential path. The cargo craft cannot get ahead or behind the AC current wave, but rides at a phase angle relative to the wave where the propulsion force equals the drag force. As the frequency of the applied AC current wave increases, so does the speed of the cargo craft.

The acceleration power required to accelerate the 20 ton StarTram craft is very large, with a peak power of approximately 40 gigawatts as the craft reaches its final speed of 8 km/sec. The total kinetic energy in the craft at final speed is 600 gigajoules. The cost of this energy is modest, about $10,000 at 6 cents per KWH. At a launch rate of 2 cargo craft per hour (440,000 tons per year) the average power consumption would be 400 megawatts, about 1/1000th of the US current power capacity. It is not necessary to build 40 GW of power plants for the StarTram acceleration process. Instead, a low constant power input is stored for an extended period, followed by a fast high power discharge. The most promising storage approach appears to be superconducting magnetic energy storage (SMES). A bifilar SC line carrying 10 megamps stores 200 gigajoules of energy per kilometer of length. Separate magnetic storage lines would be positioned along the acceleration tunnel, with each individual line switched in at the appropriate moment to contribute to the acceleration process.

After reaching 8 km/sec at the end of the acceleration tunnel, the StarTram cargo craft transitions into the ascending launch tube, where it coasts upwards to the high altitude point where it exits into the low density atmosphere. The launch tube is constructed from 5 shells of graphite-epoxy composite bonded together to form a rigid structure. The individual shells are ridged on their outer surfaces. When bonded together, the ridges form a honeycomb structure in which the individual empty cells are isolated radially and longitudinally from each other. If a crack occurs in the wall of one cell, any air leakage into the cell would be confined to that cell, since it does not communicate with the other cells in the structure. For air to enter the interior of the evacuated tube, all the adjacent cells at one location in the tube wall would have to fail. Since cell area is small, e.g., 10-2 m2, the probability of this occurring is infinitesimally small if cracks and failures are randomly distributed in the launch tube structure.

The inside diameter of the launch tube is 3 meters, the same as the acceleration tunnel. Attached to the walls are null flux loops similar to those in the acceleration tunnel. There are no LSM windings; however, since the cargo craft only coasts upwards to its high altitude launch point. The cargo craft experiences a strong outwards centripetal force of 30 g as it ascends along the curved first position of the launch tube. To accommodate this high outwards centripetal force and to have the cargo craft centered in the launch tube, the bottom halves of the null flux loops in the null flux circuits have more turns than the top loops, producing a net inwards magnetic force that equals the outwards centripetal force, even when the craft is centered in the tube.

For the high altitude portions of the launch tube the overall thickness of the launch tube wall is 10 centimeters, with an internal solid fraction of 30% of graphite-epoxy composite. This produces an extremely strong structure, with a collapsing pressure that is 200 times greater than the ambient pressure of 0.24 atm at 13 km altitude. Since the magnetic levitation force is considerably greater at lower altitudes, the tube wall thickness could be even thicker there without penalizing levitation capability. The weight of the graphite epoxy launch tube is 1 metric ton per meter. Adding in the weight of the aluminum null flux loops and internal structure, total weight would be 1.2 tons per meter. The motion of the cargo craft in the curved launch tube will cause a momentary small displacement of the launch tube at the point of passage, because of the outwards centripetal force on the null flux loops. Since the passage time of the cargo craft past a given point is very short, about 1.5 milliseconds, the displacement of the launch tube will be very small, i.e., a few millimeters. After the craft passes, the magnetic levitation force on the tube will quickly return it to its normal position.

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The cargo craft exits through the open MHD window at the end of the evacuated launch tube. The outside ambient atmosphere is prevented from entering the evacuated tube by a combination of high speed gas ejectors positioned on the periphery of the launch tube and an MHD pump located inside the end of the tube. The gas jet ejectors reduce the pressure at the entrance to the pump kg a factor of ~10 from the ambient outside pressure, down to a level of ~0.02 atm. This low density air is then ionized by an RF power source, and prevented from flowing into the tube by an applied JXB MHD force in the MHD pump. The MHD pump is similar to an MHD generator, with the difference that instead of an ionized gas or conducting liquid flowing through a magnetic field to generate a DC electric current, in the MHD pump the DC current is applied from an external source to produce a body force on the ionized gas or conducting liquid. There will be a residual small leakage of neutral air molecules into the evacuated launch tube, but this leakage can be handled by conventional vacuum and cryopumps.

When the cargo craft enters the ambient atmosphere it will experience a short period of intense heating on the nose surface, and a substantial deceleration force. However, the heating pulse can be readily handled using ablation or transpiration cooling, since there is no significant penalty in payload capability or launch cost. If substantial amounts of protective cooling material (e.g., ablative carbon layers, or water for transpiration cooling) are carried by the cargo craft during the acceleration phase. At a nominal launch altitude of 13 kilometers (10 kilometers above local ground at 3 km altitude) the peak nose heating rate at the exit point from the launch tube is 12 KW/cm2, a level comparable to that for high performance re-entry vehicles. As the cargo craft coasts upwards at a launch angle of 20 degrees, it reaches an altitude of 40 km in only 10 seconds, and the peak nose heating rate is then just 0.4 KW/cm2. The peak deceleration force in the craft is 3 g at the exit point, decreasing in 10 seconds to 0.1 g. The associated V loss is small, only a few hundred meters per second.

The principal parameters for the StarTram cargo launch system are summarized in Table 2.

TABLE 2. Baseline Parameters for Unmanned StarTram Cargo Launch System. Cargo Craft Parameters

8 km/sec after acceleration 20 metric ton total weight, 15 metric ton payload 2 meter diameter, 8 meter overall length 12 lines of SC loops around circumference, 0.5 megamp SC current in each loop

Launch Tube and Tether Parameters

93 km total length 13 km launch altitude (10 km above ground) 1.2 metric ton per meter launch tube 4 metric ton per meter levitation force 1.8 metric ton per meter net upwards force 0.6 GPa (90,000 psi) stress in Spectra tethers

Levitation/Acceleration Parameters

15 centimeter clearance from tunnel wall Aluminum loops on wall for levitation 2 g per centimeter, radial centering force 30 g acceleration 40 gigawatts peak acceleration power Superconducting magnetic energy storage 600 gigajoules kinetic energy at 8 km/sec 2 launches per hour maximum launch rate 106 kilometer acceleration tunnel length 26 seconds acceleration time

Nose Heating Rates and Deceleration Forces

12 KW/cm2 and 3 g at 13 km altitude (t = 0 sec) 0.4 KW/cm2 and 0.1 g at 40 km altitude (t = 10 sec)

THE STARTRAM PASSENGER AND CARGO LAUNCH SYSTEM

The StarTram cargo launch system has a high G level, e.g., 30G, to level enable a relatively short acceleration tunnel and launch tube, and reduce capital cost. For this reason, and because the principal near term need cargo launch, it is likely to be the first StarTram system built. In the longer term, however, if there are to be large numbers of persons going into space for tourism, manufacturing, and exploration, a StarTram system that operates at an acceleration level acceptable to human passengers will be needed. StarTram is the only possibility for a system that could launch thousands of passengers annually at a reasonable cost. The StarTram passenger system would use the same superconducting materials, and Maglev technology as the StarTram cargo system. The main differences between the two systems are the much lower G level for passenger launch, e.g., 2.5 G compared to 30 G for cargo only system, and the use of re-usable spacecraft instead of expendable cargo craft. Table 3 summarizes the basic parameters for the StarTram system.

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Returning StarTram spacecraft would land at the StarTram Spaceport. After landing, the StarTram spacecraft would be inspected and necessary maintenance/repair operations carried out. The turnaround time for a StarTram spacecraft is projected about one day. Including the loading and unloading time at the Spaceport and in orbit, plus the time to ascend to and descend from orbit, a StarTram spacecraft could then make ~100 flights per year. Because the components of the StarTram spacecraft are not highly stressed and driven by weight limitations - for example, since the V’s for orbit insertion and de-orbiting are small, the engines can be conservatively designed and operated - maintenance and repair operations should be simple. The departure port connects to the StarTram acceleration tunnel. At an average launch interval of 1 hour; for example, a single StarTram Spaceport could carry out 8800launches to orbit per year. At 70 ton payload or 100 passengers per launch, this would correspond to almost to a half million tons of cargo and a half million passengers annually. The deployable wings are folded back against the body of the spacecraft, so as to allow efficient magnetic coupling of the superconducting magnets along its sides with the guideway loops on the sides of the tunnel. The spacecraft wings remain retracted as it travels upwards in the evacuated launch tube, and also after it enters the atmosphere at ~22 kilometer altitude. Control actions as it flies upwards to orbit through the residual atmosphere would be performed by small rocket thrusters positioned at various points on the spacecraft. After the spacecraft achieves orbit, the wings would be deployed in preparation for the return flight to Earth.

TABLE 3. Baseline Parameters for the StarTram Passenger and Cargo Launch System. Spacecraft

Launch Velocity Launch Altitude (Above Sea Level) Gross Weight Empty Weight Payload in LEO Overall Dimensions Launch Kinetic Energy Atm Deceleration at Launch Exit of Launch Tube

�V Loss Thru Atm

�V Burns in LEO

Nominal Values

8 km/s 22 km 200 MT 100 MT 70 MT 5 Meters diameter 1.8 Gw Hr (7 m/sec2)0.05 km/s 0.35 km/s

Acceleration Tunnel

Tunnel Length Ground Elevation (Above Sea Level) Longitudinal Acceleration Velocity at End Time in Tunnel Acceleration Drive Power (Avg.)

Nominal Values

1250 km 3 km 25 m/sec2 (2.5 g) 8.02 km/sec 5.3 Minutes 28 GW

Launch Tube

Total Length Length of Levitated Ground Elevation (Above Sea Level) Trajectory Slope Launch Angle Centripetal Acceleration Time in Tube

Nominal Values

282 km 220 km 3 km@ Start; 4 km/@ End Recurve 5 Degrees 25 m/sec2 (2.5 g) 0.58 minutes

Commercial airliners have fast turn around times, with thousands of operating hours between major maintenance

activity. Since StarTram rocket engines only operate for a very small �V burn, it appears reasonable that they could function like jet engines, with conservative operating parameters and many hours between overhauls. The only system requiring close inspection after each flight would appear to be the Thermal Protection System (TPS). Since takeoff weight is not an issue with StarTram, the TPS can be very rugged and use transpiration cooling, eliminating the need for replacement of thermal tiles.

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MAGLEV AND SUPERCONDUCTOR TECHNOLOGY FOR STARTRAM SYSTEMS

The necessary Maglev and superconductor technology needed for StarTram already exists. The basic Maglev technology including inherent stable magnetic levitation and propulsion has been demonstrated at full scale by Japan Railways (JR). JR Maglev vehicles have achieved 350 mph, a practical limit in the open atmosphere. Using consists of up to 5 vehicles weighting 200 metric tons, over 50,000 passengers have been carried, with cumulative distances of over 200,000 kilometers. Maglev can achieve StarTram speeds in an evacuated tunnel. Swiss Metro proposes building Maglev lines in evacuated tunnels in Switzerland. The principal challenge is the energy storage system to accelerate the spacecraft. The components commercially exist; but, a system of the required scale has not yet been built. Initial StarTram designs used conventional niobium-titanium (NbTi) superconductor. NbTi superconducting systems have operated successfully for many years, and there is a very well developed commercial industry. The Japan Railways Maglev vehicles use superconducting NbTi loops, as do thousands of MRI (Magnetic Resonance Imaging) medical devices in widespread use around the World. The current densities in NbTi are very high, on the order of 300,000 amps per cm2 and higher. The principal drawback of NbTi is its need to operate at ~4 degrees Kelvin. Using multi layer vacuum insulation, heat leaks into the superconducting enclosure can be very low, 1 watt (thermal) per square meter. However, refrigerators at 4 degrees Kelvin require 300 watts of electric power per watt of heat leak.

New superconductors have been recently developed that operate at much higher temperatures than NbTi with high current density capability and are less sensitive to small motions and thermal fluctuations. YBCO (Yttrium Barium Copper Oxide), can operate at 77 Kelvin (liquid nitrogen temperature) and MgB2 (Magnesium Diboride) can operate at 20 Kelvin. Both use much less refrigeration power than NbTi. YBCO requires only 1/20th as much refrigeration power as NbTi while MgB2 requires only 1/5th as much. When StarTram is built, it probably will use MgB2. It will require much less refrigeration power than NbTi, be lower in cost, and less sensitive to small movement and thermal fluctuations. However, any of the 3 superconductors, i.e., NbTi, MgB2, and YBCO can enable a practical, cost- effective StarTram system. Table 4 compares superconducting parameters cargo launch system using NbTi and MgB2 superconductor. The cost difference between MgB2 and NbTi, for the cargo craft itself, are minor only a few dollars per kg of payload. The big difference between the two conductors is the construction cost and refrigeration power of the superconducting cables on the launch tube and on the ground beneath. MgB2 superconductor would save approximately 2 billion dollars on construction cost and over 300 megawatts in refrigeration power input. While NbTi would still be practical there is a strong incentive to use MgB2 superconductor.

TABLE 4. Superconducting Design Parameters for StarTram Cargo Craft and Launch Tube. Type of Superconductor Used

Cargo Cart Operational Parameters NbTi MgB2

Number of SC loops on craft Loop SC current, kiloamp turns Total kiloamp meters on craft SC unit cost, $/KA meter Cost of SC on craft Heat leak into SC, watts(th) Refrigeration temperature, K Refrigeration power, KW(e) Cost of refrigeration power for 6 hours

Launch Tube System Operational Parameters

Total SC current on launch tube megamps Total SC current on ground megamps Total KA meters in SC cables on launch tube Total KA meters in SC cables on ground Cost of SC for launch tube, billion $ Cost of SC for ground cables, billion $ Electric power for refrigeration, MW(e)

1144500

200,0000.50

$100,0001504.245

$18

5050

5.5 x 109

4.5 x 109

2.82.2360

144500

200,0000.30

$60,000140208

$3

5050

5.5 x 109

4.5 x 109

1.61.470

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CONSTRUCTION AND OPERATING COST FOR STARTRAM

Table 5 summarizes and compares the projected construction and operating costs for the cargo only and passenger plus cargo systems. Each system is assumed to provide 16,000 launches per year (approximately 2 per hour). For the cargo only system, the payload per launch is taken as 15 metric tons; for the passenger plus cargo system, the payload per launch is 70 metric tons. A 10 year amortization period is assumed for the construction cost resulting in an amortized cost of $6.8 per kg of payload for the cargo only system, and $11 per kg for the passenger plus cargo system. Certain cost components, like the cost of the acceleration tunnel, superconductor, and cryogenic systems can be estimated based on existing experience. Conservative values for fabricated materials costs have been used, such as $50 per kg for the graphite epoxy launch tube and Spectra tethers. The $0.30 per kiloamp meter for MgB2

superconductor is a projected large scale production cost for the recently developed multi-filament MgB2/niobium matrix superconductor. This is an order of magnitude less than present cost; however, the production process is relatively simple, and the corresponding fabricated material cost of ~$100 per kg at $0.30 per KA meter is still well below the raw material cost. For certain cost components, such as the cost of levitating the launch tube to its operational position, there is no experience base. In such cases a best estimate is made.

With regard to the acceleration tunnel, the superconducting supercollider (SSC) tunnel was going to be ~5 meters in diameter with a total length of 76 kilometers. Total construction cost for the tunnel was estimated at approximately 1 billion dollars or about 13 million dollars per kilometer. The corresponding excavation cost of ~$700 per cubic meter is substantially greater than the $100 to 200 per cubic meter for mineral mines, reflecting the greater safety and stability requirements. Several kilometers of SSC tunnel were successfully excavated using a tunnel boring machine. The excavation cost for the StarTram tunnels is estimated based on the SSC experience, with the cost per kilometer scaled to reflect differences in diameter – i.e., the cargo launch tunnel is 3 meters in diameter, while the passenger plus cargo tunnel is 6 meters in diameter. Added to the excavation cost are the costs of the aluminum guideway loops, based on the fabricated of full scale prototypes for Maglev applications, and the costs of vacuum equipment.

The various construction component costs in Table 5 roughly scale on the length. The acceleration tunnel length for the passenger plus cargo system is approximately 13 times as long as that for the cargo only system, plus being twice the diameter. As a result, the cost of the acceleration tunnel for the passenger plus cargo system is 25 billion dollars, compared to 1 billion for the cargo only system. The levitated launch tube for the passenger plus cargo system is approximately 3 times longer than that for the cargo only launch system (281 vs 92 km). This results from the exit of the launch tube being at only 10 km above ground level, compared to 20 km for the passenger plus cargo system, plus having the cargo only tube at a much steeper angle relative to ground than the passenger plus cargo tube (20 degrees compared to 5 degrees). As a result, the components for the passenger launch tube section cost about 3 times as much as those for the cargo tube, not 13 times.

TABLE 5. Construction and Operating Costs for StarTram Construction Cost, Billion $

Component Cargo Only Passenger + Cargo

Acceleration tunnel & guideway 1.0 25.0 Energy storage @ 1 M $ /GJ 0.6 6.0 Levitated launch tube @ $50/kg 6.0 18.0 Tethers @ $50/kg 2.0 6.0 MGB2 superconductor @ $0.30/KHM 3.0 10.0 Cryo pipes for SC cables (18 units @ $1000/m each) 2.0 6.0 Refrigerator/power @ $3000/KW(e) 0.2 0.6 Erection of launch tube 2.0 6.0 Total 16.8 77.6 Amortized cost, $/kg of payload 6.8 11.0

Operating Cost Per Launch, M $

Spacecraft 0.35 1.0 (100 light/year) Energy @ 6 cents /KWH 0.012 0.12 Total 24.0 16 Total cost, $ kg of payload (Amortized + operation) 30.8 27.0

The total construction cost of the cargo only system is about 17 billion dollars, compared to 78 billion dollars for the passenger plus cargo system. These costs are high; however, compared to the cost of launching by chemical rockets,

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they are actually very low. As an example, launching 1000 tons per year of payload by conventional rocket costs about 10 billion dollars annually at a unit cost of $10,000 per kg. This is just the operating cost and does not include development and amortized construction costs. In comparison, the StarTram cargo only system could launch ~200,000 tons annually (200 times as much) at a unit cost of only $30 per kg of payload for an annual cost of 6 billion dollars. This cost includes both operating plus amortized construction cost.

As shown in Table 5, the energy cost for StarTram launch is negligible. The operating cost is primarily the cost of the spacecraft launched. For the cargo only system, the 5 ton spacecraft is non-recoverable, with a fabrication cost of $50 per kg. The MgB2 superconducting loops are also non-recoverable, with a fabricated cost of $0.40 per kiloamp meter. For the passenger StarTram spacecraft, the unit cost is 800 million dollars, with 100 flights per year and a 10 year service life. The unit cost per kg of payload is calculated assuming a cargo only flight, and is slightly less than that for the cargo flights only launch system ($27 per kg of payload vs $30.8). For passengers and passenger plus cargo flights, the unit costs would have to apportioned based on some appropriate formula.

SUMMARY AND CONCLUSIONS

The StarTram concept appears to be a practical, potentially very low cost approach for magnetically launching very large volumes of cargo and passengers into space at orbital speeds of ~8 kilometers per second at very low cost, without propellants. The direct electrical energy cost to launch is less than 1$ per kilogram of payload. The total unit costs including operating and amortized capital costs in $/kg for cargo and $/passenger for StarTram, are more than a factor of 100 cheaper than the present costs based on existing rocket systems. Moreover, a single StarTram facility could launch a volume of cargo and passengers that are a thousand times greater than the total World launch capacity. The first StarTram facility to be built probably would be for the launching of cargo. Using expendable cargo craft structures, a cargo only launch system could deliver payloads into LEO at a unit cost of ~$30 per kg. In the longer term, a lower G StarTram system to launch both passengers and cargo could be built. Operating at 2.5 G, it would require a 1250 km acceleration tunnel, and could launch hundreds of thousands of passengers annually, plus hundreds of thousands of tons of cargo. The capital cost of the StarTram-C system is projected as 30 billion dollars, while StarTram-P would cost approximately 78 billion dollars. The required superconductors, materials, and Maglev technology for StarTram already exist commercially. While a challenging, complex, and unprecedented undertaking there appear to be no fundamental barriers or unknowns that would prevent StarTram from becoming a reality.

NOMENCLATURE

(Fm)L = magnetic lift force on levitated superconducting cable, Newtons per meter FMAG = magnetic lift force on levitated superconducting cable, metric tons per meter FLT = weight of levitated launch tube, metric tons per meter FSC = weight of levitated superconducting cable, metric tons per meter FT = weight of tether system, metric tons per meter FNET = net upwards force on combined system of launch tube, superconducting cable and tethers, metric tons

per meter fGL = geometric factor, lift force relative to infinite Bifilian conductor length IG = current in superconducting ground cable, Amp IL = current in superconducting levitated cable, Amp HO = height of levitated superconducting cable above ground, meters

µO = permeability of free space, 4π x 10-7 Henries per meter

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ACKNOWLEDGMENTS

The authors wish to express their deep appreciation to Ms Barbara Roland for preparation of the StarTram paper, and to Ms Judy Otto for preparation of the drawings. The authors also wish to express their gratitude to Dr. John Rather of Wayne State University and Dr. John Mankins of NASA for their encouraging and helpful comments on StarTram.

REFERENCES

Powell, J., Maise, G., and Paniagua, J., “StarTram – A New Concept for Very Low Cost Earth-to-Orbit Transport Using Ultra High Velocity Launch,” 52nd Int. Astro. Cong., Paper IAF-01-5.6.04, Toulouse, France, 2001.

Powell, J., Maise, G. Paniagua, J., and Rather, J., “StarTram: A New Approach for low Cost Earth to Orbit Transport,” 2002 IEEE Aerospace Conference, Big Sky, Montana, 2002.

Powell, J.R., Maise, G., and Paniagua, J., “StarTram-C – A Maglev System for Ultra Low Cost of Cargo to LEO, GEO, and the Moon,” 54th Int. Astro. Cong., Paper IAC-03-IAA 13.1.04, Bremen, Germany, 2003.

Powell, J.R., and Danby, G.T., “High Speed Transport by Magnetically Suspended Trains, ASME Meeting, paper 66-WA/RR-5, New York, NY. Also, Mech. Eng., 89, 3035, (1966).

Bush, President G.W., “New Vision for Space Exploration Program,” White House press release, January 14, 2004.Futron Corporation, “Space Transportation Costs: Trends in Price per Pound to Orbit, 1990 – 2000,” Futron Corportation,

Bethesda, MD, September 6, 2002. Russian News Agency NOVOSTI, “Third Space Tourist Olson Not Afraid, Believes in Soyuz,” Russian News and Information

Agency NOVOSTI, September 28, 2005. NASA, “Report of the 90-Day Study on Human Exploration of the Moon and Mars, Cost Summary,” NASA, November 1989. Powell, J.R., and Danby, G.T. “High Speed Transport by Magnetically Suspended Trains,” ASME Meeting, Paper 66-WA/RR-5,

NY 1966. Also, “A 300 mph Magnetically Suspended Train,” Mech. Eng. 89, 30-35 (1967). Japan Railways Central “Superconducting Maglev: The Review,” (2005), http://www.jr-central.co.jp/.

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