WO2006088584A2 - Superconducting magnetic suspension and electromagnetic launch accelerator - Google Patents

Abstract

Superconducting cables and coils are employed to create a high force magnetic suspension, which is used to suspend a carriage that is accelerated by a linear motor around an enclosed, evacuated circular track of large circumference. The magnetic suspension counteracts both gravity and radial acceleration to prevent the carriage from contacting the acceleration passage wall. A projectile is firmly clamped into the carriage. When the carriage reaches launch speed the projectile is released from the carriage into a tangential exit tube and launched through an egress hatch into the open atmosphere and, potentially, into orbit. The carriage continues around the track, decelerates, and is re-used to launch additional payloads. Multiple carriages and projectiles can be accelerated simultaneously. Radial accelerations exceeding 10,000 g's are achievable.

Description

SUPERCONDUCTING MAGNETIC SUSPENSION AND ELECTROMAGNETIC LAUNCH ACCELERATOR

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from United States Provisional Patent Application No. 60/645,162, filed 18 January 2005, the entirety of which is incorporated herein by reference.

[0002] This application is related to commonly-assigned United States Patents 6684794 and 6873235, the entirety of which are incorporated herein by reference.

FIELD OF THE INVENTION

[0003] This invention relates generally to apparatus and methods to magnetically suspend and electromagnetically accelerate a vehicle or object to high velocity for launch into Earth orbit or for various other purposes.

BACKGROUND OF THE INVENTION

[0004] The cost of sending a payload into orbit has been extremely high ever since the capability to do so was first created. In the early 1960's, with the development of the Saturn V and the Space Shuttle expected soon to get under way, the future cost of reaching orbit was forecast to decrease from $1400 per pound (in 1964 dollars) to $25 per pound by 1980. In fact, the cost remained virtually constant. As reported in "The Military Use of Space: A Diagnostic Assessment" by analyst Barry D. Watts, launch vehicles commercially available in 2001 had an average cost-per-pound to low-earth-orbit of over $4000. The cost of Space Shuttle flights exceeds $10,000 per pound of payload. Many organizations have tried, and are still trying, to reduce this expense and open space to more extensive commercial activities. It is clear, however, that traditional rocket-based approaches are highly unlikely to produce drastic cost reduction. [0005] Non-traditional approaches have been considered and researched as well. The High Altitude Research Project (HARP) at McGiII University in the 1960's used large-bore artillery in an attempt to reach the edge of space at low cost, and achieved limited success, but never came close to the velocities required for orbit. Light gas guns have had more success at achieving high velocities culminating in the proposal for a "Jules Verne Gun" at the Lawrence Livermore National Laboratory. This launcher would place 5 tons of payload into orbit every few hours, at cost of $5 billion for construction and operation over a ten year period. This level of funding has been an insurmountable obstacle.

[0006] Rail guns such as the UTSTAR ("The STAR railgun concept," IEEE Transactions on Magnetics, vol. 35, pp. 432-436, Jan 1999) out of the University of Texas at Austin provide another potential solution. Still to be solved are the problems of creating and controlling massive electrical power flows (a peak of 50 to 300 gigawatts or more) and achieving reliable sliding contact between the projectile and the power rails at speeds that can exceed 8 kilometers per second. Again, even if these daunting technical problems can be solved, a launcher of this type would likely be capable of firing once every few hours at most, and will have an estimated construction cost of well over a billion dollars.

[0007] Even more extreme approaches have been proposed. US Patent 4,881,446 describes a "Space Train" using electromagnetic acceleration in an evacuated tube over 1000 kilometers long. With a vehicle mass of 3 million kilograms, the peak power consumption of this system would be approximately 3 terawatts (3 x 10¹²) at launch. The cost would be truly astronomical.

[0008] US Patent 6,311 ,926 describes a "Space Tram" with an electromagnetic acceleration tube 1600 kilometers long and the launch end magnetically suspended 22 kilometers above the ground. The average power required for the nearly 7 minutes of acceleration would be 16 gigawatts (1.6 x 10¹⁰ watts). Again, construction costs and power technology, among other things, will be enormous obstacles for this project to overcome.

[0009] US Patent 5,699,779 describes an approach that attempts to reduce the size, cost and peak power requirements of an orbital launch system. In this proposal an enclosed, evacuated circular track shaped much like a hula hoop is mechanically oscillated in a circular motion to accelerate an object sliding along the inside of the track. A fairly detailed analysis of this approach by the inventor and others ("Sizing a Slingatron- Based Space Launcher," Journal of Propulsion and Power, Vol. 18, No. 2, March-April 2002) produced a specific design to launch a 1000-kg, 0.64 m-diameter projectile. The proposed hoop is 28 miles (45 kilometers) in circumference, weighs 10,500 tons, and the entire hoop must be mechanically oscillated at 75 meters per second. When the projectile reaches launch speed a section of the pipe-shaped track must be swung open, while still oscillating and without compromising the vacuum seal, to release the projectile into a launch ramp. Assuming this could be accomplished at all, any mechanical malfunction in the movement of the egress section could result in the projectile impacting it at 8+ kilometers per second. 1000 kg moving at 8+ km/sec contains a great deal of energy. The launch system would not fair well.

[0010] All of these approaches have attempted to solve a real and important problem. Low cost access to orbit is the first step in opening up the entire universe beyond Earth to routine human use. So far such access has not been technically and economically achievable. Therefore, it is an object of this invention to create an improved launch system that provides low cost access to orbit. To achieve this objective it is a further objective to create a system that requires relatively modest levels of peak and average electric power. It is a further objective to minimize the size and capital cost of this system. It is a further objective to minimize mechanical complexity in order to achieve high reliability and extremely low probability of catastrophic accident in case of malfunction.

SUMMARY OF THE INVENTION [0011] Superconducting cables and coils are employed to create a high force magnetic suspension, which is used to suspend a carriage that is accelerated by a linear motor around an enclosed, evacuated circular track of large circumference. The magnetic suspension counteracts both gravity and radial acceleration to prevent the carriage from contacting the acceleration passage wall. A projectile is firmly clamped into the carriage. When the carriage reaches launch speed the projectile is released from the carriage into a tangential exit tube and launchecfthrough an egress hatch into the open atmosphere and, potentially, into orbit. The carriage continues around the track, decelerates, and is re-used to launch additional payloads. Multiple carriages and projectiles can be accelerated simultaneously. Radial accelerations exceeding 10,000 g's are achievable. [0012] According to one aspect, the present invention includes a magnetic suspension system, including: at least two parallel stationary superconducting cables carrying electrical current in opposing directions; and at least one movable superconducting coil adjacent to and largely parallel with the stationary superconducting cables and capable of - traveling substantially parallel to the superconducting cables; wherein the superconducting coil is cooled to the superconducting state to create a high-force magnetic suspension.

[0013] According to another aspect, the present invention includes a circular acceleration system, including: a circular track containing at least two stationary superconducting cables extending around the circumference of the track and carrying electrical current in opposing directions; and a carriage disposed adjacent to the track and capable of traveling adjacent to the superconducting cables; and at least one superconducting coil disposed within the carriage and largely parallel to the superconducting cables; wherein the superconducting coil is cooled to the superconducting state to create a high-force magnetic suspension and the carriage is accelerated to high speed around the circular track. [0014] According to still another aspect, the present invention includes a launch system, including: a circular track containing at least two stationary superconducting cables extending around the circumference of the track and carrying electrical current in opposing directions; and a carriage disposed adjacent to the track and capable of traveling substantially parallel to the superconducting cables; and at least one superconducting coil disposed within the carriage largely parallel with the superconducting cables; and a projectile attached to the carriage; wherein the superconducting coil is cooled to the superconducting state to create a high-force magnetic suspension, the carriage is accelerated to high speed around the circular track, and the projectile is released from the carriage. [0015] According to yet still another aspect, the present invention includes a method of magnetically suspending a movable object, the method including: disposing at least two parallel stationary current-carrying superconducting cables, the cables carrying electrical current in opposing directions; and disposing at least one movable superconducting coil adjacent to and largely parallel with the superconducting cables and capable of traveling substantially parallel to them; cooling the superconducting coil to the superconducting state to create a high-force magnetic suspension.

[0016] According to yet still further another aspect, the present invention includes a method of accelerating a carriage around a circular track, the method including: disposing at least two stationary superconducting cables around the circumference of the track, the superconducting cables carrying electrical current in opposing directions; and disposing a carriage adjacent to the track such that the carriage is capable of traveling adjacent to the superconducting cables; and disposing at least one superconducting coil within the carriage and largely parallel to the superconducting cables; cooling the superconducting coil to the superconducting state to create a high-force magnetic suspension and accelerating the carriage to high speed around the circular track.

[0017] According to still again a further aspect, the present invention includes a method of launching projectiles, including: disposing at least two stationary superconducting cables around the circumference of a circular track, the superconducting cables carrying electrical current in opposing directions; and disposing a carriage adjacent to the track such that the carriage is capable of traveling adjacent to the superconducting cables; and disposing at least one superconducting coil within the carriage largely parallel with the superconducting cables; and attaching a projectile to the carriage; and cooling the superconducting coil to the superconducting state to create a high-force magnetic suspension, accelerating the carriage to high speed around the circular track, and releasing the projectile from the carriage.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1a shows a cross-sectional view of a permanent magnet repulsive suspension system.

[0019] Figure 1b is a graph of the vertical and lateral force characteristics versus lateral offset of the suspended object in Fig. 1 a.

[0020] Figure 1c shows an alternate embodiment of the suspension system of Fig. 1a with the permanent magnet assemblies replaced by current-carrying conductors.

[0021] Figure 1d shows the suspension system of Fig. 1c with the current configured to provide attraction rather than repulsion. [0022] Figure 2a shows a generalized electromagnet assembly for creating positive or negative vertical or lateral force.

[0023] Figure 2b shows the electromagnet assembly of Fig. 2a with the moving element offset YA. wavelength to the left.

[0024] Figure 2c shows the electromagnet assembly of Fig. 2a with the moving element offset Yz wavelength to the left.

[0025] Figure 2d is a graph of the vertical and lateral force characteristics versus lateral offset of the moving element in Fig. 2a.

[0026] Figure 3 illustrates electromagnet assemblies of the type shown in Figure 2a arranged on four sides of a square object inside a square tube such that they all provide force in the same direction.

[0027] Figure 4 shows an example of the magnitude of force achievable with superconducting cables.

[0028] Figure 5a shows how the current changes in a superconducting coil as it moves away from stationary superconducting cables. [0029] Figure 5b shows how the current changes in a superconducting coil as it moves closer to stationary superconducting cables.

[0030] Figure 5c shows how the stationary superconducting cables of Fig. 5a and Fig. 5b can be combined to increase current and force levels in a moving superconducting coil. [0031] Figure 6a shows superconducting magnet assemblies of the type shown in Figure

5a and 5b arranged on the four sides of a square object inside a square tube, with the object at rest and no current flowing in the superconducting coils within the object.

[0032] Figure 6b illustrates the current flow in the superconducting coils within the square object of Figure 6a as the object moves linearly through the tube and centrifugal force offsets the object to the left.

[0033] Figure 7a shows a cross-sectional view of a repulsive centrifugal compensator using two superconducting stator cables and a single superconducting carriage coil.

[0034] Figure 7b is a perspective view of the centrifugal compensator of Fig. 7a showing the superconducting stator coils and the superconducting carriage coil.

[0035] Figure 7c shows the superconducting coil from the moving object in Fig. 7a with the end turns configured for use as the moving part of a linear synchronous motor.

[0036] Figure 8 is a plan view of a launch accelerator system.

[0037] Figure 9 is a perspective view of the launch accelerator system of Fig. 8. [0038] Figure 10 is a close-up cutaway view of the launch system of Fig. 8 in a surface installation.

[0039] Figure 11a is a side cutaway view of a launch projectile and its protective encasement for use in the launch accelerator of Fig. 8.

[0040] Figure 11b is a cross-sectional view of a launch ramp tube, projectile, and projectile encasement according to a first embodiment of the launch ramp.

[0041] Figure 11 c is a cross-sectional view of a launch ramp tube, projectile, and projectile encasement according to a second embodiment of the launch ramp.

[0042] Figure 11d is a plan view of one of the magnetic suspension coils of Fig. 11c.

[0043] Figures 12a-12e show a sequence of cross-sectional views of the system of Fig. 7a as a projectile is released from a maglev carriage at launch and enters the launch ramp.

[0044] Figure 13a shows a cross-sectional view of an acceleration tube and carriage according to a second embodiment of the suspension, which employs attractive suspension. [0045] Figure 13b is a perspective view of the accelerator system of Fig. 13a showing the superconducting stator coils and the superconducting carriage coils.

[0046] Figure 13c shows a cross-sectional view of the system of Fig. 13a soon after the projectile has been released from the carriage. [0047] Figures 13d-g show cross-sectional views of the system of Fig. 13a as the carriage and projectile enter a dump tube in the event of a failure of the maglev suspension.

[0048] Figure 14 is a plan view of the launch accelerator system of Fig. 8 with the addition of 2 dump tubes.

[0049] Figure 15a is a cross-sectional view of an acceleration tube and carriage according to a third suspension embodiment, which employs shear-force suspension.

[0050] Figure 15b is a cross-sectional view of the accelerator system of Fig. 15a with the carriage approaching launch speed. [0051] Figure 15c is a cross-sectional view of the system of Fig. 15a soon after the projectile has been released from the carriage.

[0052] Figure 16 is a plan view of the launch accelerator system of Fig. 14 with the addition of a second launch ramp and segmented linear motor.

[0053] Figure 17 is a graph of launch trajectories that may be achieved with different embodiments of the launch ramp and projectile.

DETAILED DESCRIPTION

[0054] The present invention improves upon previous suspension systems through various aspects including, but not limited to, utilization of superconducting suspension. [0055] With reference to the drawings, Fig. 1a shows a cross-sectional view of a magnetic suspension system 10 as described in US patents 6684794 and 6873235. Magnet array 16 in stationary element 14, typically part of a track or roadbed, faces magnet array 18 in moving element 12, typically part of a vehicle, assuming the motion direction is into or out of the page. The resulting vertical and lateral forces upon array 18 are depicted in graph 20 of Fig. 1b. When array 18 is centered above array 16, as shown, a large upward force acts to repel array 18 from array 16 and the lateral force is zero. If array 18 moves laterally to the right or left, the vertical force decreases and the lateral force increases in absolute value. If array 18 moves closer to array 16 the vertical force increases and the lateral forces remains at zero. Thus the position of array 18 is vertically stable but laterally unstable. An electro-magnetic stabilization system (not shown) as described in the reference patents interacts with the magnetic field produced by stationary array 16 in response to position changes detected by position sensors (not shown) to counteract the lateral instability and produce stable suspension. This system provides high suspension force at any speed, exhibits low eddy current drag, and requires little power for stabilization. [0056] Figure 1c shows a cross-sectional view of variation 40 of this suspension system using electromagnetic coils in place of the permanent magnets of Fig. 1a to create magnetic repulsion. Stationary element 42 containing cables 44a and 44b sits below moving element 46 containing coil 48. Cable 44a of the stationary element carries an electric current moving into the page (denoted by the X inside the coil) and thus repels left side 48a of the moving coil, which carries an electric current moving out of the page (denoted by the dot inside the coil). Cable 44b of the stationary element repels right side 48b of the moving coil. Control coils (not shown) interact with the magnetic fields produced by stationary cables 44a and 44b to produce stable suspension, as described above.

[0057] Figure 1d shows another variation 60 of this suspension system using electromagnetic coils to create magnetic attraction. Stationary element 62 containing cables 64a and 64b sits above moving element 66 containing coil 68. In this variation the cable and coil currents are moving in the same direction, and thus cables 64a and 64b attract moving coil 68. A control system (not shown) may be employed to vary the current in either the cables or the coils to produce stable suspension, as is generally known in the art.

[0058] Figure 2a shows a more generalized configuration 80 of the suspension of Fig. 1c, now using electromagnetic coils to create positive or negative vertical or lateral force. With the relative position shown, array 82 is strongly repelled by array 84 due to the opposite current directions in adjacent coils. As the lower array 84 moves laterally to the left or right, the vertical and lateral forces due to array 82 will change as shown in graph 100 of Fig. 2d. For example, if array 84 moves left by % of a wavelength, as shown in Figure 2b, the vertical force upon it will change from strongly negative (repulsion) to zero and the lateral force upon it will change from zero to strongly negative (leftward). If array 84 continues to the left by another ^ΛA of a wavelength, as shown in Figure 2c, the vertical force upon it will change from zero to strongly positive (attraction toward array 82) and the lateral force upon it will change from strongly negative (leftward) to zero, and so on. Electronic stabilization of the type discussed previously can be added to either of the array pairs in Fig. 2a to produce vertically and/or laterally stable suspension.

[0059] Variations of the array configuration of Fig. 2a can be combined to counteract substantial inertia! forces on a moving object. Figure 3 illustrates generally how this can be accomplished. Acceleration compensator system 120 consists of square containment tube 122 with square carriage 124 moving inside it. If carriage 124 is moving at high speed into the page, and tube 122 is curved to the right, a strong force is required to counteract inertia and move carriage 124 to the right. Unless otherwise prevented, this force would normally be provided by contact between carriage 124 and the left wall of tube 122, which would be detrimental at high speed. In acceleration compensator 120, electromagnet arrays 126 and 128, of the type shown in Fig. 2a, both provide force on carriage 124 directed to the right. Array 130, of the type shown in Fig. 1c, and array 132, of the type shown in Fig. 1d, both add to the rightward force on carriage 124.

[0060] The force produced by the coils in arrays 126, 128, 130, and 132 can be greatly increased, and resistive power dissipation reduced to zero, by fabricating these coils of superconducting wire. Superconducting cable arrangement 140 of Figure 4 illustrates by example the level of force achievable. Two superconducting cables 142 and 144, each 2.5 cm in diameter, carry current with the current flowing in opposite directions, as shown. Magnetic fields produced by the cables repel each other with a force F per unit length (in Newtons/meter) determined by the equation: rr — f ^o ^?i^?2 2π w where: f_GL is a geometric length correction factor (assumed to be 1 for long cables); μo is the permeability of free space (4π x 10^'7 Henrys/meter); J₁ is the current through conductor 1 (in amps); I₂ is the current through conductor 2 (in amps); and w is the gap width between the two conductors. If J₁ and i₂ are both 509,000 amps and w is 10 centimeters, the resulting force is approximately 52,000 kg-force per meter of cable. This current density and force is well within the capability of low temperature niobium-titanium (NbTi) superconducting wire. Other superconducting materials are capable of even higher current densities, with correspondingly higher levels of force. [0061] Superconducting coils exhibit another characteristic very different from coils using conventional conductors, as illustrated in Figures 5a and 5b. Attractive suspension system 160, shown in the cross-section of Figure 5a, consists of two long stationary or "stator" cables, 162 and 164, with currents flowing in the direction depicted. These cables may be conventional conductors, but more typically would be superconducting cables to allow high current levels and field strengths. Superconducting coil 166, is placed adjacent to cables 162 and 164 and cooled to the superconducting state in a procedure known in the art as "field cooling". For NbTi superconductors this temperature is approximately 4 K. Coil 166 thus has no current flow, initially, and magnetic field from cables 162 and 164 is "trapped" within coil 166. If coil 166 is then moved leftward away from cables 162 and 164, as shown, the magnetic flux from stator cables 162 and 164 will decrease. In coils using conventional conductors, this would temporarily induce a current according to Faraday's Law (ε = -dΦ/dt), which would quickly dissipate. In a superconductor, however, ε (the EMF or electromotive force) is zero, so dΦ/dt (the rate of change in magnetic flux) must also be zero. Thus a current appears in coil 166 sufficient to maintain the magnetic flux within the coil at constant levels. This flux in coil 166 interacts with flux from stator cables 162 and 164 to attract coil 166 back toward its original position. [0062] Repulsive suspension system 170, shown in Figure 5b, operates in a similar fashion. Stator cables 172 and 174 carry high current, as shown, with superconducting coil 176 placed nearby and cooled to the superconducting state. Coil 176 initially carries no current. If coil 176 is then moved closer to stator cables 172 and 176, as shown, Faraday's Law again comes into play and a current appears in coil 176 sufficient to maintain the flux within the coil at constant levels. This flux now opposes the flux from stator cables 172 and 174, repelling coil 176 back toward its original position.

[0063] Attractive and repulsive suspension can be combined, as shown in Figure 5c. Here superconducting coil 190 is field cooled between stator cable pair 182 and 184 and stator cable pair 186 and 188, with currents flowing in the stator cables as shown. When coil 190 is then moved leftward, as shown, current flows in the coil to maintain flux. This flux attracts the coil to stator cables 182 and 184 and repels it from stator cables 186 and 188.

[0064] A third form of suspension uses shear force, as described in US Patent 6873235. Attractive and repulsive suspension elements, as in Figures 5a and 5b, can be combined with shear-force suspension as shown in the cross sections of Figures 6a and 6b. Combined suspension system 200 is comprised of stationary tube 202, interior tunnel

203, and moving carriage 204 enclosed within tunnel 203. Superconducting stator cables 214a, b and c interact with superconducting carriage coil 216 to form a shear-force suspension. With stator cables 214a, b and c carrying current in the directions shown, coil 216 is aligned directly below cables 214a and 214 b and cooled to the superconducting state. If carriage 204, including coil 216, is then moved leftward as shown in Figure 6b, current will appear in coil 216 according to Faraday's Law, thus keeping the flux within coil 216 constant and creating a restoring force that will act to push coil 216 and carriage 204 back to its original position. Stator cables 218a, b and c and carriage coil 220 act similarly to create additional restoring force. Stator cables 206a and b interact with carriage coil 208 to form an attractive suspension of the type shown in Fig. 5a. Stator cables 210a and b interact with carriage coil 212 to form a repulsive suspension of the type shown in Fig. 5b.

[0065] At system startup, carriage 204 is stationary upon a support system (not shown), and superconducting coils 208, 212, 216, and 220 within carriage 204 are all in the superconducting state but carry no current. Superconducting stator pairs 206a and b,

210a and b, 214a, b and c, and 218a, b and c carry current in the directions depicted. If the carriage support system (not shown) is then removed, carriage 204 will drop slightly until currents in coils 208, 212, 216, and 220 increase sufficiently to balance gravitational force. If the carriage is then accelerated through tunnel 203, with tube 202 and tunnel 203 assumed to curve toward the right, inertia will tend to keep carriage 204 moving in a straight line and the gap between carriage 204 and the left wall of tunnel 203 will decrease. In other words, centrifugal force will move carriage 204 toward the left side of the tunnel. In response, currents in all four coils, 208, 212, 216, and 220, will increase as shown in Figure 6b, producing restoring forces, until they balance the leftward centrifugal force. The restoring force produced by superconductors in this manner can be extremely large. For example, with a carriage 2 meters long weighing 100 kg, restoring forces sufficient to balance lateral accelerations exceeding 10,000 G's can be achieved, using NbTi superconductors in the stator cables and high temperature superconductors such as YBCO in the carriage coils. By changing the direction of the electrical current in the stator coils or by rearranging their alignment or configuration, powerful acceleration forces to compensate for left, upward, and/or downward turns could be produced just as well. Applications of this "acceleration compensation" may use attractive, repulsive and shear-force suspension individually or in any combination. [0066] Figures 7a, b and c depict an accelerator and "acceleration compensator" according to the first embodiment of the suspension. In the cross-sectional view of Figure 7a, accelerator system 240 comprises acceleration tube 242 and carriage 244 contained within acceleration tunnel 243: Superconducting stator cables 246a and 246b interact with superconducting vehicle coil 248 to create a repulsive suspension system. Projectile 250 with protective encasement 252 is carried within carriage 244. A perspective view of stator cables 246a and 246b is shown in Figure 7b, with the acceleration tube and carriage structure removed for clarity. As depicted in Figure 7b, stator cables 246a and 246b are arranged in a circle, and coil 248 travels around the inside diameter of this circle. Magnetic fields emanating from stator cables 246a and 246b interact with the magnetic field of carriage coil 248 to prevent carriage 244 from contacting the walls of acceleration tunnel 243, even with carriage 244 moving at high speed. As depicted in the perspective view of carriage coil 248 in Figure 7c, end turns 254 and 256 may be arranged to interact with stationary coils 258, as is generally known in the art, to form a linear synchronous motor. This motor can be used to accelerate and decelerate carriage 244. In a typical implementation, stator cables 246a and b are cooled to 4 K to achieve high current carrying capability. Carriage coil 248, typically fabricated with high temperature superconducting wire such as YBCO, operates at higher temperatures such as 30 to 40 K. Carriage coil 248 can thus be cooled by radiating heat across levitation gap 247 to the 4 K surfaces of stator cables 246a and b. Damping elements (not shown) such as conductive coils may be added in or nearby acceleration tube 242 to prevent unacceptable lateral or vertical motion of carriage 244. These damping elements would be configured as is generally known in the art such that only vertical or lateral motion of carriage 244 would induce current in the elements and thereby suppress undesired motion without producing excessive drag.

[0067] Figure 8 is a plan view of an electromagnetic "launch ring" 260 designed to exploit the capabilities of accelerator system 240 of Figure 7a. The accelerator loop consists of evacuated acceleration tube 242 constructed in the form of a large circle, typically up to several kilometers in diameter. Carriage 244 travels inside acceleration tube 242, as described previously and shown in Fig. 7a. Acceleration tube 242 bifurcates at point 262 with launch ramp 264 capped by egress door 268. Launch ramp 264 typically would be constructed up the side of a hill or mountain to provide an elevated launch angle, and may gradually straighten, as shown in Fig. 8, may form a completely straight tangent line from the accelerator loop, or may curve all the way to egress door 268.

[0068] In operation, carriage 244 is loaded with projectile 250 contained inside protective encasement 252, placed inside acceleration tube 242, and coil 248 is cooled to the superconducting state as described previously. A linear motor (not shown) gradually accelerates carriage 244 over a period of minutes or hours. During the acceleration interval stator coils 246a and 246b interact with carriage coil 248 to counteract radial inertia and preventing carriage 244 from contacting the inside wall ofacceleration tube 242. When carriage 244 attains the desired speed, projectile 250 and protective encasement 252 are released from carriage 244 a short distance before they arrive at bifurcation 262. Encasement 252 protects projectile 250 from contact with the inside wall of acceleration tube 242. Radial inertia), or centrifugal force, carries projectile 250 and encasement 252 into launch ramp 264 where it continues toward egress door 268. Egress door 268 is opened just as projectile 250 arrives. Egress door 268 can be augmented by a plasma window, as described in U.S. Patent 5,578,831, to prevent external air from entering the vacuum in the launch ramp while letting encasement 252 and projectile 250 freely pass. Projectile 250 exits into the open atmosphere where encasement 252 splits and falls away as projectile 250 proceeds. Carriage 244 continues around acceleration tube 242 where it is decelerated to a halt and, if desired, loaded with the next projectile to be launched. [0069] With a loop on the order of one to eight kilometers in diameter and an acceleration compensator constructed with presently available superconducting wire, launch speeds in excess of 9 kilometers per second - well above orbital velocity of ~7.8 km/sec. - are attainable in launch ring 260. Because the acceleration period can extend for minutes or hours the linear motor employed in launch ring 260 does not require the enormous power output of previous electromagnetic launch system designs. Rather than gigawatts or higher, a motor of a few megawatts or less will suffice, avoiding the technical difficulty and expense of extremely high power. For example, if carriage 244 and its payload have a total mass of 2000 kg, a 20-megawatt motor (net output) would accelerate them to 9 kilometers per second in 67.5 minutes. Motors of approximately this power level have been in use on high-speed electric railroads for decades. By "linear motor" we mean linear motor technology curved to fit around a circle. Electrodynamic drag due to conductive materials in or around acceleration tube 242 may increase the required motor power, depending upon details of particular implementations. [0070] Figure 9 is a perspective view of a launch ring 260 in a typical installation site such as a dry lake, with acceleration tube 242 constructed on the flat lake bed and launch ramp 264 constructed up the side of adjacent ridge line 270. [0071] Figure 10 is a close-up cutaway view of launch ring 260 installed just below ground level. Ring structure 272 is typically constructed of concrete reinforced with non- conductive materials such as fiberglass. Pressure wall 282 is a vacuum vessel to prevent atmospheric gases from entering the evacuated acceleration tube 242. Heat shield 284 is cooled by liquid nitrogen, typically at 77 K, and constructed with a low emissivity, highly reflective surface to prevent infrared heat from traveling from pressure wall 282 to the 4 K stator cables in acceleration tube 242. The stator cables (not shown) in acceleration tube 242 are themselves typically cooled with liquid or gaseous helium, if low temperature superconductors are employed, or may be cooled with other cryogenic fluids if high temperature superconductors are employed. Support struts 280 keep acceleration tube 242 in position, are sufficiently strong to withstand the high forces generated by a carriage passing at high speed, and are constructed of a heat insulating material such as fiberglass to prevent excessive heat flow from pressure wall 282, through heat shield 284 to acceleration tube 242. Linear motor drive coils 258 are mounted outside pressure wall 282 for easy installation and maintenance and to prevent heat from coils 258 from entering cryogenic acceleration tube 242. The high flux field produced by carriage superconducting coil 248 allows a large gap between motor drive coils 258 and carriage coil 248. Passage 286 provides space for cooling pipes, power lines, and communication wires. Cover 288 allows access for installation and maintenance. Although launch ring 260 is shown just below grade level in Fig. 10, it may also be constructed farther below ground for safety and/or security reasons. [0072] Figure 11a shows a cutaway side view of launch package 300, comprising projectile 302 and protective encasement 304. Protective encasement 304 must exhibit sufficient strength to support projectile 302 under high lateral acceleration before release from carriage 244. Projectile 302 is shown with the highly streamlined conical shape typical of re-entry vehicles designed to penetrate the atmosphere at hypersonic speeds, but may also be a lifting body or any other appropriate shape, and is constructed of carbon-carbon or other materials capable of withstanding the extreme temperature of hypersonic flight in the lower atmosphere. An electronic control unit (not shown) within the carriage activates the release mechanism (not shown) when it is time to drop launch package 300 out of the carriage and into the launch ramp. Rocket engine 306 provides thrust to modify the orbital trajectory after projectile 302 leaves the atmosphere. If projectile 302 is accelerated to less than orbital velocity by launch ring 260, rocket engine 306 can be used to provide the final acceleration needed to reach orbit. Smaller reaction engines (not shown) stabilize projectile 302 outside the atmosphere and allow orbital maneuvers in the conventional manner.

[0073] Figure 11b is a cross-sectional view showing launch ramp 264, projectile 302, and protective encasement 304. Like acceleration loop 242, launch ramp 264 is an evacuated tube. Launch ramp 264 is constructed of high strength material such as concrete or steel and the exterior surface of protective encasement 304 is constructed of polycarbonate or another similar material that will vaporize upon high-speed contact with the tube wall. This vapor serves to create a gas bearing to separate protective encasement 304 from the wall of launch ramp 264, in the same manner as is commonly used in rail guns, to reduce friction and minimize loss of velocity. [0074] Fig. 11c is a cross-sectional view of launch ramp 320 according to a second embodiment. Launch ramp 320 is constructed of a non-conductive high strength material such as fiber-reinforced concrete. The external surface 324 of protective encasement 326 is constructed of a highly conductive substance such as copper or aluminum. Lateral suspension coils 322a, b, c and d in the wall of launch ramp 320 are energized with an electric current to provide an intense magnetic field, and may be fabricated using superconducting wire. A plan view of a suspension coil 322 is shown in Figure 11d. When the highly conductive surface 324 of protective encasement 326 passes suspension coils 322, a powerful repulsive force will be generated through sheet levitation, as is generally known in the art, thus preventing contact. This prevents projectile 302 from losing significant speed during the short period, typically less than one second, required to transition launch ramp 320 and exit into the atmosphere. [0075] Figures 12a through 12e show cross-sectional views of acceleration tube 242 and launch package 300 as they progress through release at accelerator bifurcation 262. In Figure 12a, carriage 244 is at launch speed with carriage coil 248 interacting with stator cables 246a and 246b to prevent contact with outer wall 330 of acceleration tunnel 243 just before release of launch package 300. In Figure 12b launch package 300 has begun sliding out of carriage 244 and has made initial contact with tunnel wall 330. Ablation creates a gas bearing. In Figure 12c bifurcation 262 has been encountered, with wall 330 receding from acceleration tunnel 243. In Figure 12d launch package 300 is fully separated from carriage 244 and accelerator bifurcation is nearly complete. In Figure 12e bifurcation of accelerator tunnel 243 from launch ramp 264 is complete.

[0076] Figures 13a through 13c show a launch accelerator system according to a second embodiment of the suspension. In the cross-sectional view of Figure 13a accelerator system 400 comprises acceleration tube 402 and carriage 408 contained within acceleration tunnel 406. Superconducting stator cables 404a-d interact with superconducting carriage coils 410 and 412 to create an attractive suspension system. Launch package 414 is carried within carriage 408. A perspective view of stator cables 404a-d is shown in Figure 13b, with the acceleration tube and carriage structure removed for clarity. As depicted in Figure 13b, stator cables 404a-d are arranged in a circle, as before, but carriage 408 now travels around the outside diameter of this circle. Carriage 408 carries four superconducting coils 410a & b and 412a &b, which interact with magnetic fields emanating-from stator cables 408a-d to provide an attractive suspension that is stable in roll, pitch, and yaw. The end turns of carriage coils 410 and 412 may be used as the moving component of a linear synchronous motor, as before. Figure 13c is a cross-sectional view showing launch package 414 soon after release from carriage 408 and as launch package 414 is entering the launch ramp. The suspension embodiment of accelerator system 400 allows the stator current to be spread out over more than two stator cables while still keeping carriage 408 short in the vertical dimension, which makes it possible to construct a relatively compact and lightweight carriage capable of withstanding high lateral G-forces. [0077] The cross-sectional views of Figures 13d-g illustrate another advantage of the embodiment of accelerator system 400. In Figure 13d the attractive suspension has failed, which could be due to a "quench", or loss of superconductivity, in superconducting stator coils 404a-d or in carriage coils 410 and 412, for example. Inertia has moved carriage 408 leftward with respect to wall 420 of accelerator tunnel 406 where it has made contact. Ablation begins where carriage 408 contacts wall 420. If carriage 408 is traveling at high speed and the stator cables were located in wall 420, as in a repulsive suspension, this contact could damage or destroy the stator cables. In the embodiment of Fig. 13d, however, inertia has moved the carriage away from the stator cables, rather than closer to them, providing a protective effect. In Figure 13e, carriage 408 has been pulled down by the force of gravity into contact with floor 422 of acceleration tube 406. [0078] Carriage 408 could not remain intact with such contact for long, and disintegration of carriage 408 could produce flying debris that could damage stator cables 404a-d on the opposite side of acceleration tube 406. To prevent this, accelerator tube 402 may include "dump tubes", as depicted in Figures 13f, 13g, and 14. In a dump tube a bifurcation in the acceleration tube, similar to the launch ramp bifurcation, provides an escape path for both the launch package and the carriage. As shown in Figure 13f, acceleration tunnel 406 begins widening, carrying the failed carriage farther from the stator cables. In Figure 13g dump tube 430 has separated from acceleration tunnel 406 entirely. Figure 14 shows a plan view of launch ring 450, including dump tube 430. When carriage 408 enters dump tube 430, blast door 434 closes and carriage 408 proceeds into dump chamber 432, which is designed to allow carriage to impact without damaging launch ring 450. A second dump tube 436, with dump chamber 438 and blast door 440 as shown in Figure 14, decreases the distance a failed sled must travel before escaping the launch ring. More dump tubes may be included, and dump tubes can be directed downward, instead of or in addition to the tangential arrangement depicted in Figures 13f, 13g, and 14.

[0079] The cross-sectional views in Figures 15a through 15c show a launch accelerator system according to a third embodiment of the suspension. In Figure 15a accelerator system 500 comprises acceleration tube 502 and carriage 508 contained within acceleration tunnel 506. Superconducting stator cables 504a-f interact with superconducting carriage coils 510 and 512 to create a shear-force suspension system of the type described previously. Launch package 514 is carried within carriage 508. Carriage 508 carries four superconducting coils, 510a & b on the top of carriage 508, one in front of the other, and 512a &b on the bottom of carriage 508, one in front of the other. Magnetic fields from carriage coils 510 and 512 interact with magnetic fields from stator cables 504a-f to provide a shear-force suspension that is stable in roll, pitch, and yaw.

High power linear motor drive coils (not shown) to accelerate and decelerate carriage 508 may be placed outside acceleration tube 502 to reduce the incident heat load. Low power linear motor drive coils for use when the magnitude of current in carriage coils 510 and 512 is low may be placed closer to carriage 508, or even inside acceleration tube 502. [0080] In Figure 15a carriage 508 is stationary at the startup point, with carriage coils

510 and 512 vertically aligned with stator coils 504a and b and stator coils 54Od and e. Carriage coils 510 and 512 initially carry no current. As carriage 508 accelerates it moves leftward with respect to the stator coils and current appears in carriage coils 510 and 512, counteracting the leftward force of centrifugal force, until it approaches left wall 520 of acceleration tunnel 506, as depicted in Figure 15b. [0081] Figure 15c is a cross-sectional view showing launch package 514 soon after release from carriage 508 and as launch package 514 is entering the launch ramp. The suspension embodiment of accelerator system 500 allows the stator current to be spread out over more than two stator cables while still keeping carriage 508 short in the vertical dimension, as in accelerator system 400, but also allows coils 510 and 512 to remain close to their respective stator cables, where the field strength is highest, even at maximum carriage speed. This configuration provides higher peak force per amp of stator current than accelerator system 400, while retaining all of the advantages of accelerator system 400, thereby decreasing the amount of superconducting material required in the stator cables and reducing the cost of the system. With 2 million amps of current in each stator cable, a vertical separation of 45 cm between stator cables, and a vertical separation of 25 cm between the carriage coils, restoring forces exceeding 10 million Newtons per meter of carriage length are achievable. This is sufficient to compensate for lateral acceleration exceeding 10,000 G's on a 100 kg carriage. [0082] Figure 16 is a plan view of launch ring 600 according to a further embodiment of the invention. Here launch ramp 620 is identical to launch ramp 264 of Fig. 8, but now a second launch ramp 630 has been added to the system. Projectiies may be released through either of these launch ramps to provide different launch azimuths for different mission requirements. Additional launch ramps can be added as well, giving mission planners a variety of launch azimuths to choose from without otherwise affecting the operation of launch ring 600. The acceleration motor is also subdivided into 12 segments, 601 - 612, which are individually powered and controlled. This allows multiple acceleration carriages and their projectiles to be accelerated simultaneously and in synchrony. Up to one carriage per segment, for a total of 12, can be accelerated together. If the launch ring linear motor is further subdivided the maximum number of carriages and projectiles could be further increased. This has the potential to multiply the launch rate and capacity, at the relatively small cost of increasing total power requirements. For example, a launch ring 8 kilometers in diameter, or roughly 25 kilometers in circumference, with motor segments 250 meters long, would allow up to 100 carriages to be accelerated simultaneously. If each projectile weighs 1000 kg and each motor segment supplies a net power of 20 megawatts, for a total of 2000 megawatts, in excess of 50 metric tons per hoυr could be launched into orbit at a variety of orbital inclinations.

[0083] Figure 17 is a graph 700 of three different types of launch trajectory that may be achieved depending upon the characteristics of specific implementations of launch ramps and projectiles. Trajectory 710 is a flat or purely ballistic trajectory characteristic of a projectile with no aerodynamic control surfaces. The elevation angle of trajectory 710 is determined by the elevation angle of the launch end of the launch ramp. Angles up to 60 or more degrees from horizontal are feasible. Trajectory 720 begins as a ballistic trajectory with a high elevation angle, then curves toward horizontal in response to the action of aerodynamic control surfaces on the projectile. This allows the projectile to reach high altitude quickly, reducing aerodynamic heat load, and then maneuver into a trajectory closer to the final orbit without the use of rocket fuel to affect the change. Trajectory 730 begins with a low elevation angle, reducing the launch ramp elevation required, uses projectile control surfaces to climb into a high angle of attack for low heat load, then maneuvers closer to orbital trajectory as in trajectory 720.

[0084] A variety of high force magnetic suspensions, electromagnetic accelerators, and launch rings may therefore be implemented in accordance with various embodiments of the invention. In general terms, such structures are implemented as an accelerator tube of circular configuration containing superconducting magnetic suspension cables and a carriage traveling within the accelerator tube and having at least one superconducting magnetic suspension coil, such that the suspension cables and suspension coils interact to produce horizontal and vertical forces that suspend the carriage as it is accelerated through the accelerator tube until it reaches high speed. [0085] It will be apparent to those having ordinary skill in the art that the structures described herein are not necessarily exclusive of other structures, but rather that further structures and structural features may be incorporated into the above structures in accordance with the particular implementation to be achieved. Therefore, while the embodiments illustrated in the figures and described herein are presently preferred, it should be understood that these embodiments are offered by way of example only. The invention is not limited to a particular embodiment, but extends to various modifications, combinations, and permutations that are encompassed by the claims and their equivalents.

Claims

WHAT IS CLAIMED IS:

1. A magnetic suspension system, comprising: at least two parallel stationary superconducting cables carrying electrical current in opposing directions; and at least one movable superconducting coil adjacent to and largely parallel with said stationary superconducting cables and capable of traveling substantially parallel to said superconducting cables; wherein said superconducting coil is cooled to the superconducting state to create a high-force magnetic suspension.

2. The magnetic suspension as claimed in Claim 1 wherein said superconducting coil is capable of moving closer to or farther from said superconducting cables to create repulsive or attractive force while traveling substantially parallel to said superconducting cables.

3. The magnetic suspension as claimed in Claim 1 wherein said superconducting coil is capable of moving laterally with respect to said superconducting cables to create shear force while traveling substantially parallel to said superconducting cables.

4. A circular acceleration system, comprising: a circular track containing at least two stationary superconducting cables extending around the circumference of said track and carrying electrical current in opposing directions; and a carriage disposed adjacent to said track and capable of traveling adjacent to said superconducting cables; and at least one superconducting coil disposed within said carriage and largely parallel to said superconducting cables; wherein said superconducting coil is cooled to the superconducting state to create a high-force magnetic suspension and said carriage is accelerated to high speed around said circular track.

5. The circular acceleration system as claimed in Claim 4 wherein said carriage is capable of moving closer to or farther from said superconducting cables to create repulsive or attractive force while traveling adjacent to said superconducting cables.

6. The circular acceleration system as claimed in Claim 4 wherein said carriage is capable of moving laterally with respect to said superconducting cables to create shear force while traveling adjacent to said superconducting cables.

7. A launch system, comprising: a circular track containing at least two stationary superconducting cables extending around the circumference of said track and carrying electrical current in opposing directions; and a carriage disposed adjacent to said track and capable of traveling substantially parallel to said superconducting cables; and at least one superconducting coil disposed within said carriage largely parallel with said superconducting cables; and a projectile attached to said carriage; wherein said superconducting coil is cooled to the supeTconducting state to create a high-force magnetic suspension, said carriage is accelerated to high speed around said circular track, and said projectile is released from said carriage.

8. The launch system as claimed in Claim 7 wherein said carriage is capable of moving closer to or farther from said superconducting cables to create repulsive or attractive force while traveling adjacent to said superconducting cables.

9. The launch system as claimed in Claim 7 wherein said carriage is capable of moving laterally with respect to said superconducting cables to create shear force while traveling adjacent to said superconducting cables.

10. The launch system as claimed in Claim 7 wherein said track is enclosed within an airtight tunnel.

11. The launch system as claimed in Claim 10 wherein said tunnel is largely evacuated.

12. The launch system as claimed in Claim 11 further including: at least one bifurcation in said tunnel with at least one offshoot tunnel segment leading to at least one external door; wherein said carriage is accelerated to high speed around said circular track, said projectile is released from said carriage such that it enters said offshoot tunnel segment, said door is opened such that said projectile exits said tunnel, and said carriage decelerates for reuse.

13. The launch system as claimed in Claim 11 further including: at least one bifurcation in said tunnel with at least one offshoot tunnel segment leading to at least one chamber capable of safely containing the impact of a high-speed projectile; wherein said carriage is accelerated to high speed around said circular track, said carriage enters said offshoot tunnel segment in the event of a system failure and impacts within said chamber.

14. A method of magnetically suspending a movable object, the method comprising: disposing at least two parallel stationary current-carrying superconducting cables, said cables carrying electrical current in opposing directions; and disposing at least one movable superconducting coil adjacent to and largely parallel with said superconducting cables and capable of traveling substantially parallel to them; cooling said superconducting coil to the superconducting state to create a high- force magnetic suspension.

15. The method of magnetically suspending a movable object claimed in Claim 13 wherein said superconducting coil is capable of moving closer to or farther from said superconducting cables to create repulsive or attractive force while traveling substantially parallel to said superconducting cables.

16. The method of magnetically suspending a movable object as claimed in Claim 13 wherein said superconducting coil is capable of moving laterally with respect to said superconducting cables to create shear force while traveling substantially parallel to said superconducting cables.

17. A method of accelerating a carriage around a circular track, the method comprising: disposing at least two stationary superconducting cables around the circumference of said track, said superconducting cables carrying electrical current in opposing directions; and disposing a carriage adjacent to said track such that said carriage is capable of traveling adjacent to said superconducting cables; . and disposing at least one superconducting coil within said carriage and largely parallel to said superconducting cables; cooling said superconducting coil to the superconducting state to create a high- force magnetic suspension and accelerating said carriage to high speed around said circular track.

18. The method of accelerating a carriage around a circular track as claimed in Claim 17 wherein said carriage is capable of moving closer to or farther from said superconducting cables to create repulsive or attractive force while traveling adjacent to said superconducting cables.

19. The method of accelerating a carriage around a circular track as claimed in Claim 17 wherein said carriage is capable of moving laterally with respect to said superconducting cables to create shear force while traveling adjacent to said superconducting cables.

20. A method of launching projectiles, comprising: disposing at least two stationary superconducting cables around the circumference of a circular track, said superconducting cables carrying electrical current in opposing directions; and disposing a carriage adjacent to said track such that said carriage is capable of traveling adjacent to said superconducting cables; and disposing at least one superconducting coil within said carriage largely parallel with said superconducting cables; and attaching a projectile to said carriage; and cooling said superconducting coil to the superconducting state to create a high- force magnetic suspension, accelerating said carriage to high speed around said circular track, and releasing said projectile from said carriage.

21. The method of launching projectiles as claimed in Claim 21 wherein said carriage is capable of moving closer to or farther from said superconducting cables to create repulsive or attractive force while traveling adjacent to said superconducting cables.

22. The method of launching projectiles as claimed in Claim 21 wherein said carriage is capable of moving laterally with respect to said superconducting cables to create shear force while traveling adjacent to said superconducting cables.

23. The method of launching projectiles as claimed in Claim 21 wherein said track is disposed within an airtight tunnel.

24. The method of launching projectiles as claimed in Claim 23 wherein said tunnel is largely evacuated.

25. The method of launching projectiles as claimed in Claim 24 wherein: said tunnel includes at least one bifurcation with at least one offshoot tunnel segment leading to at least one external door; said carriage is accelerated to high speed around said circular track, said projectile is released from said carriage such that it enters said offshoot tunnel segment, said external door is opened such that said projectile exits said tunnel, and said carriage is decelerated for reuse.

26. The method of launching projectiles as claimed in Claim 24 wherein: said tunnel includes at least one bifurcation with at least one offshoot tunnel segment leading to at least one chamber capable of safely containing the impact of a high speed projectile, wherein said carriage enters said offshoot tunnel in the event of a system failure and impacts within said chamber.