Bolonkin

Non-Rocket Space Launch and Flight is a collection and partial rewrite of many conference papers. Dr. Bolonkin discusses many megastructure alternatives for space launch, from the space elevator to dynamic structures to gas guns to electrostatic devices. Dr. Bolonkin presents many ideas, with some analysis, and focuses on what might work, not on what might go wrong, avoiding the sort of analysis engineers do before deployment.

Launch Loop uses magnetic fields and vacuum confinement. Non-Rocket... has two chapters on Kinetic Space Towers (Chapter 5, IAC-02-IAA.1.3.03 2002, JBIS 57 1/2, 2004, pp 33-39) and on Kinetic Anti-gravitator (Chapter 9, IAC-02-IAA.1.3.03 2002, AIAA-2005-4504). These are open, vertical systems, and use mechanical spinning outer rollers for turnarounds. Dr. Bolonkin does not discuss how these rollers are made, or how a roller can rotate with high edge speed without flying apart.

The launch loop pulley elevators, which raise payloads up to the stations, include tapered high-velocity pulley rollers moving at 400 meters per second. These pulleys and cables are probably far too difficult to make, and a real launch loop will raise payloads on many more, slower, elevators.

Dr. Bolonkin may be unaware of the effects of gravity on vertically moving cable velocity. The launch loop cable is moving at 14000 meters per second at 80 kilometers altitude. As it descends towards the surface, it picks up speed, adding an additional 9.7 x 80000 Joules per kilogram, raising the speed of the cable to 14055 meters per second. Since the mass flow rate is constant at 42000 kilograms per second throughout the system, this means that the density of 3 kilograms per meter at 80 kilometers altitude must be reduced to 2.988 kg/m at the surface - a 0.4 percent stretch. Payload launching results in both stretching and compression, again because of velocity changes.

Dr. Bolonkin's towers are similar heights (75km) and run at lower velocities ( 8000 m/s ) so the stretching must be larger. If the velocity is 8000 m/s at the top, the velocity at the bottom must be 8090 m/s, a stretch of 1.1 percent. If the cable is solid and made of a strong material, that stretch is associated with tensile stress at the bottom, which adds to the compression burden on the tower. If there is no tension at the bottom, then the cable at the top will meander, like a rope pushed from both ends.

This is why the launch loop rotor (performing the same function as Bolonkin's cable) has long sliding joints, which resist lateral bending but otherwise offer only slight resistance to longitudinal stress, allowing the rotor to change longitudinal density. Most of the material in the rotor is iron, perhaps with some insulation to shape the eddy currents. A solid iron rotor, and most high temperature insulator materials, will fracture if subjected to strains approaching a percent.

On page 184 of Non-Rocket..., Dr. Bolonkin briefly mentions the launch loop, quoted below:

In 2002 Loftstrom⁴ published a description of a space launcher. The offered device has the following technical and physical differences from the Loftstrom installation.

The Loftstrom installation has a 2000-km long launch path located at an altitude of 80 km, which accelerates the space vehicle to space speed. The Loftstrom space launcher is non-connected plates of complex path enclosed in an immobile tube. The plates are made from rubber-iron material and is moved using an electromagnetic linear engine. The plates are turned by electromagnets.

The idea offered in this chapter is the kinetic device which creates a push (repulsive, repel) force between two given bodies (for example, between a planet and the apparatus). This force supports a body at a given altitude. The body is connected to the cable by rollers that slide along the cable. The cable can be made of artificial fiber and moved by the rollers and any engine. The kinetic anti-gravitator supports any body at altitude (for example, towers) and may also be used to launch vehicles. The Loftstrom device is only a space launcher and cannot permanently support a body at altitude or towers (he did not write anything about this).

4. K.H. Lofstrom, "The Launch Loop: A Low Cost Earth-to-High-Orbit Launch System", 2002, http://www.Launchloop.com/launchloop.pdf

Dr. Bolonkin is referring to a 2002 paper for the International Space Development Conference. Launch loop was first published in November 1981 in the American Astronautical Society Reader's Forum. With much of the activity concerning launch loop published before his arrival in the West in 1988, and the references in the 2002 paper perhaps difficult for a native Russian speaker to parse, perhaps he does not understand that this is a much older idea.

The description of the rotor is plainly incorrect. There is no rubber in a launch loop. With the rotor core heated to 600C by payload drag, rubber would not survive. The "plates" (actually tubes) are connected with sliding joints in order to accomodate stretch. The launch loop does include "towers" - west and east stations are large 5000 ton stationary platforms at 80 km altitude, supported by the 8 degree deflection forces of the east-bound and west-bound rotors.

There is not high friction at the ground in a launch loop. Bolonkin exposes his moving cables to atmosphere, resulting in high turbulent drag (and yes, it will be turbulent, the unguided cable will vibrate laterally and stir the air). The launch loop assumes that the rotor is continuously guided by actively controlled electromagnets inside a tubular vacuum sheath. Active guidance is necessary to keep the spacings small, especially where the rotor approaches the main deflection magnets. A lot of electronics is needed. Fortunately, we know how to make a lot of electronics, cheaply and reliably. The electronics power, responsible only for correcting lateral vibration, is a tiny fraction of the drag power of a high-speed cable in air. If the double-walled launch loop sheath is breached, air will flow in and cause drag, lots of it. Internal air will be pulled by the moving rotor to the next vacuum pump station. The section subjected to air drag will be short, Hopefully, the breach will be patched quickly.

Why not towers?

While the launch loop paper does not describe the use of the technology for towers only, this is not an oversight. To provide the lift force, the launch loop stores an enormous amount of energy and momentum, and that momentum is directed horizontally for part of the rotor's path. When (not if) the launch loop breaks, some rotor material will be flung horizontally, acting like hypervelocity penetrators. This is incredibly dangerous. The nearest vulnerable target (besides the launch loop itself) should be hundreds of kilometers away, allowing the rotor sections to disintegrate and the fragments to slow down to safe speeds. Launch loop technology should not be used near large populations, and is best deployed at sea. It is also most easily deployed from a flat surface, and the ocean approximates that.

With a cheap space launcher available, altitude is best achieved by launching into orbit. Tall towers don't get built, not because we can't, but because there is usually no reason to. As towers get taller, wind speeds increase, and the lever arm of the tower increases, requiring a larger and larger base (partly achievable with guy wires for stabilization). Euler column instability limits slenderness, again requiring guy wires. As the wires get longer, they must get thicker to maintain the same stiffness to lateral variations in the column. In general, even with very strong materials, the cost of adding height goes up as at least the square of the height. Dynamic structures are not immune to these problems, they just appear differently in the equations.

At lower speeds, a dynamic structure can be partly guided by tension. If the cable is moving faster than the speed of sound in the material, then tension will not guide the cable onto the next roller or magnet, and small lateral velocity deviations at "launch" will result in large distance variations at the next "arrival". For example, if a tower is 100km high, and the cable is moving at 10km/second, then a 10cm/sec (0.001% ) variation in lateral velocity will result in a 1 meter "miss" at the top deflector. If the deflector is made with "magic" rollers with a 100 meter diameter, then that velocity variation could result from a change in separation angle of only 10 microradians, or only 0.5 millimeters of change along the circumference of that giant roller. This is impossible to achieve without precision electronic control.

Electronic controls work at a large fraction of the speed of light. Variations can be measured and corrected at many places along the path of the cable, especially with moving counterweights and actively controlled guy wires connected to the static structure. Assume a cable weighing 10kg/meter moving at 10km/second. A small lateral perturbation of 10cm/sec, corrected with an acceleration of 10cm/sec² over a 10 km length, requires about 1000 watts of distributed control. Trying to correct the same perturbation at the arrival deflector would require huge amounts of power and energy control, because the accelerations and decelerations would be enormous. This kind of control is possible because mechanical objects move so slowly compared to electronic signals. As Dr. Ivan Bekey teaches us, "Move information, not mass". When the imaginative Dr. Bolonkin adds this principle to his designs, I'm sure he will invent some wonderful new ideas.