Long Range Electromechanical Power Transmission Along Space Transportation Structures

 

J. E. D. Cline1

1141 E St. NE, Ephrata, WA 98823-1713, USA jedcline@kestsgeo.com,

 jedcline@nwi.net  http://www.kestsgeo.com

 

 

Abstract.           Although the transmission of energy across long distances is generally considered the domain of electrical conductors and electromagnetic radiation beams, in the field of very large space transportation structures it may be worthwhile to re-visit electromechanical energy transmission distribution means. Some such means include pulley-terminated tether loop space elevator as an efficient bucket-lifted conveyor belt system; fountain-like support of weight by use of continuous loop mass stream flow; wave motion power transmission along an anchored centrifugally supported tether; and delivery of electromagnetically coupled kinetic lift energy by means of high velocity electric motor armature segments sliding along embedded maglev tracks. Such electromechanical distribution of energy may be interestingly applied to the lifting of payload mass up along large space transportation structures, or to form temporary lifting structures from ground to space.

 

1. Context

 

An expanding and long term viable technology based civilization which is having a major impact on the world ecosystem which supports the civilization and is reaching limits of adequate economical energy resources, needs to reach for more resources of energy, materials, recycling systems, and room to grow. Preparing technologies which may be adequate in capacity and efficiency to do the transportation part of these tasks in the near term, is prudent for responsible leadership. The decisions as to whether or not to utilize the prepared technologies remains, of course, in the hands of the social systems active at the time and in the past.   

Space resources in high earth orbit and beyond have the potential for greatly assisting civilization's long term viability and expandability. These resources include plenty of room to build within, plenty of hard vacuum to process materials in, microgravity processing and living environment variable up to 1-g  by centrifugal action, and of course abundant 24/7 raw solar energy unimpeded by day-night cycles nor latitude nor cloud cover. Sufficiently adequate capacity and efficiency transportation between the earth surface and orbit is required for the utilization of space resources in quantities able to make significant impact on fulfilling civilization's requirements. Since existing types of space access through use of chemically fueled reaction engine vehicles expend most of their energy just in lifting the fuel and its tankage, their energy efficiency is extraordinarily poor in comparison to the actual energy added to payload mass by virtue of its being moved from the earth surface up into Geostationary Earth Orbit, which is only 15.72 kWh per kg, costing only $1.58 per kg lifted to GEO at an energy cost of $0.10 per kWh. Surely there are ways to make huge improvements in energy efficiency for transportation to and from GEO to ground. Scalable electrically operated transportation structures extending from ground to GEO seem ideally capable of providing this transportation function that could enable civilization's large scale near-future access to space resources.       

Such transportation structures as currently visualized include anchored tether structures which are supported by the outward centrifugal force of mass beyond GEO swung around by the daily rotation of the Earth, which are highly dependent on adequate strength to mass ratio tether material availability; and structures which are not dependent on extreme materials strength, but instead on the continuous circulation of kinetic energy within itself expressing as outward centrifugal force which balances the weight of the track and hard vacuum environment maintenance tubing  which constrains the path of the high velocity flowing  mass streams as they loop around the planet continuously within the structure.

            The movement of payload up and down such structures still requires adequate energy sources of lift energy delivered to the lifting vehicles traveling the structures between ground and high earth orbit. Carrying along the fuel or batteries required to provide the climb up the structure reduce the efficiency of such transportation systems, somewhat as does reaction engine propulsion systems. Potential mechanisms for delivering the transportation energy to the vehicles traveling such structures include energy which is transmitted by the structure itself, and these are explored in this paper.

            Although most tether space elevators assume a tether material inadequate for a non-tapered tether, the forms of space elevators become quite different when a tether material is strong enough to support use of a non-tapered tether structure. To error on the high side, the approximation here uses a tether divided up into 11 sections, and each section is assumed to have a constant acceleration that is equal to that found at the base of each section due to gravity and centripetal acceleration’s sum. The density of the material is assumed to be 1300 kg/m3. The stress on the tether material at GEO is found to be 80 GPa in the table below. Therefore, a tether material strength that is above this threshold of 80 GPa is assumed in the elevator forms in this paper.

 

Radii section endpoints, in Earth radii

Radius to base of section, in meters

Gravitational – centripetal net

acceleration in m/s2

Length of tether section, in meters

Net acceleration times tether length times density, in Pascals

Sum of stresses from Earth surface to top of tether section, in Pascals

1.0 to 1.2

6.37e6

9.83 – 0.034 = 9.80

0.2 R = 1.27e6

1300 x 9.80 x 1.27e6 = 1.62e10

1.62e10

1.2 to 1.5

7.64e6

6.83 – 0.04 = 6.79

0.3 R = 1.91e6

1.69e10

3.31e10

1.5 to 2.0

9.56e6

4.36 – 0.051 = 4.31

0.5 R = 3.18e6

1.78e10

5.09e10

2.0 to 2.5

1.27e7

2.47 – 0.067 = 2.40

0.5 R = 3.18e6

9.92e9

6.08e10

2.5 to 3.0

1.59e7

1.58 – 0.084 = 1.50

0.5 R = 3.18e6

6.6e9

6.74e10

3.0 to 3.5

1.91e7

1.09 – 0.101 = 0.99

0.5 R = 3.18e6

4.09e9

7.15e10

3.5 to 4.0

2.23e7

0.802 – 0.118 = 0.68

0.5 R = 3.18e6

2.81e9

7.43e10

4.0 to 4.5

2.55e7

0.613 – 0.135 = 0.48

0.5 R = 3.18e6

1.98e9

7.63e10

4.5 to 5.0

2.87e7

0.484 – 0.152 = 0.33

0.5 R = 3.18e6

1.36e9

7.76e10

 

5.0 to 6.0

3.18e7

0.394 – 0.168 = 0.226

1.0 R = 6.37e6

1.87e9

7.95e10

 

6.0 to 6.6 GEO

3.82e7

0.273 – 0.202 = 0.071

0.6 R = 3.82e6

3.53e8

1300 x 6.146e7 = 7.99e10

 

            Table 1. Approximating non-tapered space elevator tether material stress requirement

 

2. Potential means of distributing lift energy along a space access transportation structures explored here are:

 

A. Pulley-terminated tether loop space elevator as an efficient bucket-lifted conveyor belt system, requiring tether material of around 80 GPa or greater

 

B. Fountain-like support of weight by use of continuous loop mass stream flow

 

C. Wave motion power transmission along an anchored centrifugally supported tether

 

D. Delivery of electromagnetically coupled kinetic lift energy by means of high velocity electric motor armature segments sliding along embedded maglev tracks

 

            In general, payload lift energy could be tapped from the upward moving part of each of these energy flows along the way to be used to lift payload carrying vehicles up the structure. This would deliver the energy to the captive vehicles needed to lift the payload, instead of needing to lift an energy source, or track the vehicles with laser beams, to provide lift energy to the cargo vehicles.

            Let us now look more closely at each of these means of distributing lift energy along very long space transportation structures.

 

3. Pulley-terminated tether loop space elevator as an efficient bucket-lifted conveyor belt system.

 

            This is perhaps the simplest of the systems. It requires a tether working stress material sufficient for constant cross-section construction, of around 80 GPa or more strength to mass ratio. It is slow but highly efficient, so in initial form is for lifting radiation resistant payload materials, and would be powered either directly from solar power panels in GEO, or by electric power on the earth surface. A lower payload transfer rate variation would use a shielded transfer cargo container.

 Except for the anchored tether part, it resembles ancient conveyor belt loop bucket lift systems. However, it requires the greatest strength to mass ratio tether material of any of the systems; around 80GPa. The tether needs to be in the form of not one but two belts that are connected together at the pulley ends to form a continuous closed loop. The tether material also needs to periodically endure bending around the pulley's radius. However, the material does not have to endure the friction of climbers' compression rollers moving up and down along its surface, as would some other forms of travel along a tether. The pulleys would be at each end of the tether, one at the earth surface terminal, and the other far out beyond GEO near the end counterweight. Both points are low load points, minimizing bearing stresses. At GEO, where an optimum space platform complex could be built, the belt tether could be driven by an electric motor powered by photovoltaics, providing the lift energy for the transportation system from the Sun. This configuration also has the advantage that the weight of the descending vehicles would return most of their energy received in their lift to GEO. Figure 1 shows a simplified diagram of such a mechanism.

            One of the characteristics of such a payload lift system is the relative slowness of travel along the path between ground and high earth orbit, as the speed of the captive vehicles is identical to the speed of the tether ribbon on which they are attached. The speed of the tether is limited by the stresses endurable by the tether as they suddenly are turned around the pulleys, and by the speed which is endurable by the drive wheels in GEO. Thus this technique would by extremely efficient for lift of materials to GEO, but also relatively slow. Also, the captive vehicles have to get a running start to match the speed of the tether when they climb onto the tether, and when are approaching the target altitude they need to release from the tether and brake to the standing velocity at that location, such as at GEO; conceivably momentum-transfer exchange could be given for payload returning toward the earth surface could provide this function. Much of the attachment and release infrastructure that is on the tether is a static load, balanced in both upward and downward directions, but does represent extra tensile stress on the tether ribbon material.

            Although the amount of solar-sourced electric power supplied by this technique is small, using the tether to drive an electric generator at the earth surface pulley site does represent a way to transfer solar-sourced electrical energy to the earth surface without use of radiant beamed energy    Passively shielded lift for personnel and other radiation-intolerant payload, is provided by  a variation on this method. It would use a relatively massive cargo lift container attached to the tether ribbon, which utilizes several feet thickness of sawdust-reinforced water ice as a passively shielding shell. Water ice is chosen for the shielding mass for minimizing environmental damage in case the container falls to earth, disintegrating in the atmosphere. The significant added shielding mass would reduce the overall throughput of payload, and/or require more tether strength. It would also require bi-directional movement of the tether loop, along with starting and stopping the tether belt when the shielded cargo container arrives at ground or GEO terminals. However, this would eliminate the need for the running start mechanisms on the ground, and momentum transfer mechanisms at the GEO terminal..

 

            Figure 1. Schematic of a pulley-terminated tether loop space elevator as an efficient bucket-lifted conveyor belt transportation space elevator structure

 

            Note that the use of sawdust-reinforced water ice as passive shielding mass becomes feasible due to the continuous running high efficiency transportation potential of some of the transportation access lifting structures explored in this paper, and could be extensively to shield occupied areas of structures built in GEO, protecting from solar storms and cosmic radiation, as well as used for crew lift slowly through the radiation belts between LEO and GEO.

            If more than one of this kind of tether space elevator is used, one of them could be for radiation-tolerant material payloads at the slower lift speed, but higher semi-continuous throughput, and another could be for the lower throughput transfer of radiation-sensitive payloads such as personnel and biological materials.

 

.

 

4. Fountain-like support of weight by use of continuous loop mass stream flow for long range electromechanical power transmission along space transportation structures

 

            This concept is analogous to a fountain of water or air, such as once used in department store vacuum cleaner displays, where a vertical air stream supported a ball seemingly floating in mid-air; it also draws on Rod Hyde's “Starbridge” vertical tower concept. The use of continuous streams of projectiles in the form of electric motor armature segments launched upward to be intercepted at a higher platform and then bounced back to the lower site, maintaining a continuous flow of mass in both directions, the catching and reverse thrusting of the mass of the projectiles supports or lifts the upper platform. Additionally, the upward-moving mass stream could have some of its kinetic energy electrodynamically tapped off to lift vehicles along the path, as well as also to similarly provide static support to weight that is unmoving, such as that of air-excluding tubing and maglev rails. The earth  surface site needs to have strong electromagnetic means to turn the returning armature mass stream around while also restoring the kinetic energy that was used during the process.           

This concept would consume continuous energy in the process of supporting air-excluding tubing in the atmospheric portion, as well as in the balancing of platform mass somewhere above the ground. It has the advantage that, once air-excluding tubing was extended to above the atmosphere, and using adjustable angle tubing, the height of the supported platform could be raised or lowered by the raising of the upward velocity of the supportive armature mass streams.            


 


Figure 2. Basic principle of support of weight by use of continuous loop mass stream flow

 

 

Conceivably this principle could be used to form temporary lifting structures from ground to space, or to provide support between a lower orbiting mass and a higher altitude smaller mass that is moving at the same angular velocity as the lower mass and held stationary or being lifted higher thereby.

 

 

5. Wave motion power transmission along an anchored centrifugally supported tether

 

            Use of a single-band tether itself as a transmission line for energy, brings the thoughts of electromechanical vibration of one end of the tether and having the mechanical wave motion propagate along the structure; and of using conductivity along a tether as a waveguide for electromagnetic wave propagation. These methods of delivering energy along a tether are highly dependent on the characteristics of the tether material chosen.

            Potential techniques requiring electrical conductivity of the tether material would depend on the carbon nanotube fibers being well woven together before being matrix bound by a non-conductive encapsulating material. The resistivity of carbon nanotubes would control this aspect.

            If the resistivity of a tether extending far beyond GEO is high, as would be expected at this point, then the possibility of using extremely high voltages might be considered, using two widely spaced tethers so as to provide a continuous loop for the current. The voltage drop across any small segment of the tether could be small enough as to be fairly safe for occupants riding a vehicle up and down such tethers. Re-examination of Tesla's concepts might provide some additional approaches to this technique. This possibly could provide end-to-end electrical energy delivery; and with sufficiently spaced roller electrical contactors of a vehicle so as to provide enough voltage drop potential along the tether to power on-board electrical lift motors.


 


            Figure 3. Principle of lift energy transfer along tether by wave transmission along tether itself

 

            Rolling a band or ribbon cross-section tether into a circular or rectangular cross-section tube might be explored as a waveguide for electromagnetic wave transmission along the enclosed tube thus formed, for end to end power transmission. Again, the efficiency of such a method would be highly dependent on the resistivity of the tether material. Maintaining a constant tubular cross-section along a constant-stress tapered tether would eliminate many construction technique possibilities, and seems difficult when utilizing scalable construction techniques, unless the conducting channel part of the tether is added as a step after a tapered cross-section scaled up tether of sufficient strength were previously built. If constant cross-section tether material, of about 80GPa were used, the overall tether could be formed into a RF waveguide after scaled up to sufficient girth so as to provide the internal volume for the RF wavelength chosen for electrical power transmission.

            The need to deliver lift energy to vehicles climbing up and down a tether means energy needs to be tapped off by the vehicle wherever it is along the tether. Mechanical wave motion seems better suited for the task of delivering useful energy all along the tether. Wave modes that are lateral, as in a vibrating string, or longitudinal tension waves, would require a vehicle to have an overall length of one or more wavelength of the tether wave motion, and probably use the inertial mass of the captive spacecraft as a reference for extracting some of the energy contained in the passing wave motion of the tether. To avoid standing waves along the tether, all remaining wave energy would be needed to be extracted at the far terminal, absorbed into a load of the same characteristic impedance as the tether. The efficiency of mechanical wave motion along such a tether is highly dependent on the modulus of elasticity and damping factor of the stretched material. If the tether material is of sufficiently strong material as to have a constant cross-section, even then the tension along the tether would vary widely and thus similarly the propagation characteristics would vary. Such a tether would, however, be amenable to scaling construction techniques, and be able to deliver lift energy all during construction.

 

6. Delivery of electromagnetically coupled kinetic lift energy by means of high velocity electric motor armature segments sliding along embedded tracks


 


    Figure 4.   Delivery of lift energy to captive spacecraft by sliding armatures along linear track   

 

            This means of energy delivery to captive spacecraft vehicles could be applied to both the linear anchored tether configuration, and to the planet-encircling loop structure configuration. Such

high velocity armatures, operating at tens of km per second velocities, sliding along either a linear or loop structure, would yield up a small portion of their momentum to the vehicles they pass, through electromagnetic inductive braking against the rising direction armature mass streams.     

            Such armature mass streams flowing along linear long transportation structures would need significantly less maglev track field strength than would a loop structure, as they would not need to do anything except to deliver some of their momentum to vehicles traveling the structure while lightly following the track. But there would need to be relatively enormous maglev field strength at the ends of the structure to turn around the armature segments. The re-accelerator would presumably be part of such a turn around structure at the power input end of the transportation structure. However, such upward lift energy could also be coupled over to the structure itself so as to augment support for the structure's weight, reducing the tensile strength needed for the tether material; but this would involve a lot of power lost just to support the structure. Might be useful temporarily during elevator construction, however.


 

 

 


    Figure 5.   Delivery of lift energy to captive spacecraft by sliding armatures along curved track

 

            The planetary loop form of structure involves use of the planetary gravitational field to bend the high velocity mass stream around to form continuous closed loops in which to travel up and down from the earth surface to high earth orbit. Thus there is no need for powerful turn around magnetic fields at the transportation terminals. However, since the high velocity armature segments are not only functioning to deliver lift energy all along the structure to lift captive spacecraft along the structure between ground and orbit, but also to support the weight of the track and tubing structure through their supra-orbital-velocity outward centrifugal force exerted against the path-defining planet-encircling maglev track so as to balance the weight of the track structure with its live loads, the strength of the maglev track field has to be greater than that of the linear form of structure.

            Since the weight of the track structure is borne by the centrifugal force of the armature segments as they are bent around the planet, the structures can be made of common materials instead of requiring the extreme strength to mass ratio materials needed for linear tether space elevators.

            In either case, vehicles conceivably could be lifted up along, and gently lowered, by lightly dragging against the high velocity armature mass streams racing past them in the upward direction. This would distribute the lift force all along the long transportation structure to wherever the point of need for captive vehicular lift energy would be as they travel along.

            As these captive vehicles could slide along their own maglev inductive tracks, their velocity through the radiation belts make heavy shielding of crew carrying vehicles much less necessary.

            In the case of the linear tether structure, the elements of the maglev track would need to be attached to, or embedded within, the tether material. The tether would need to bear the weight of this maglev material. As the stresses to the maglev field are minimal in the linear configuration, the mass of such track material would likewise be minimal.

            The form of the maglev track needs significant research, as it would be quite different from existing maglev track systems, such as those used on massive relatively slow maglev railroad trains. The space transportation maglev track would need to be inductively energized by the passing armature segments, for one thing. This becomes conceivable due to the fact that the armatures are traveling at tens of kilometers per second in a hard vacuum, and inductive coupling goes up as the cube of the velocity differential. This maglev track design for the armature segments ought to be an interesting project, since it would be easier to test it in orbit where there is abundant hard vacuum and plenty of room to build the track in the form of a huge loop. However, on the ground where it needs to be at least initially developed, it would require many km of hard vacuum enclosing tubing as the loop, and much greater maglev track field strength so as to bend their path into a closed loop. For testing the linear tether track, a horizontal test facility could employ the same high field strength turn around magnetic fields as would be used for the actual tether armature turn-around re-accelerators, so the whole system could be tested together to a large extent, to characterize the parameters. Note that such a horizontal test facility would also provide experience needed for the “fountain-like” lift technique mentioned above.

 

7. Conclusions

 

       Although electromechanical means of energy transmission may seem a giant step backwards in the present day, re-visiting the subject while including contemporary technology may provide uniquely well suited means for captive vehicular lift or support of mass across large distances in the space environment, as well as non-beamed energy transfer between space and the Earth surface, to provide transportation systems between the Earth surface and high earth orbit that are sufficiently efficient and of ample average lift throughput to be able to support the enormous construction projects needed in high earth orbit so as to sustain a vigorous civilization; and for electrically lifted linking to spaceports in GEO for very large scale ventures further into the solar system.

 

References

 

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