What's New ?

Go to Recent Changes for the webpages that I've been working on lately. I'm always tinkering with the design, my notebooks have a lot of information and ideas I have not formally written about and illustrated yet.

The 2009 paper was a cleanup and expansion of the 1993 AIAA paper. Since then, I've worked on many improvements:

Ambits and Bolts

Rather than "turnarounds", I shall use John Knapman's britishism "ambits". The rotor will be composed of long (10 meters?), thin (millimeters?), separable components called "bolts", using John's terminology for his own stubby and separated bolts.

The bolts will be tightly bunched throughout most of the system, but will be split into many separate small cross section streams for passage around the ambit magnets. This small cross section can scale down the ambit radius considerably.

More under the Velocity Transformer track heading below.

No Gram Left Behind

This is a guiding principle for making cis-lunar space safe for the deployment of trillions of tonnes of assets, into the distant future. Even rocket exhaust is a form of distributed space debris; the molecules will stay in orbit until they hit something (and erode it), or light pressure sufficiently modifies their orbits to re-enter. Billions of tonnes of exhaust molecules in orbit will not cause immediate macroscopic damage and penetration, but they will damage surfaces, and the atoms they knock off those surfaces by spallation will add to the problem. Gas-phase Kessler syndrome.

So, a goal is to design missions so that make clever use of orbital dynamics to minimize the need for rocket propulsion, or fire the rockets at very high apogee, with exhaust velocities exceeding escape velocity at that altitude. That will put the molecules in solar orbit, a vastly larger volume than cis-lunar space. Alternately, use high ISP electric rockets that fire their exhaust far faster than orbital velocities. VASIMR engines with argon propellant may be available someday, replacing xenon and otherexpensive and scarce electric propellants.

Reduced Rotor Velocity

Launch loop rotor velocity has been reduced to 12.5 km/s (relative to the 0.47 km/s rotating Earth), and the rotor mass increased to 4.32 km/s. This lifts 7.4 kg/m of track and stabilization cables, about the same as before, but helps reduce the radius of the ambit magnets. It also reduces the impact energy of residual gas molecules on the rotor, and the multiplication gain of hyper-velocity spalling cascades.

Velocity Transformer Track

Instead of the payload dragging magnetically on the rotor, a Halbach array is driven synchronously by motor windings that connect (with a pitch change) to other transformer windings that couple to the rotor in induction motor generator mode. The field velocity in the rotor lags its synchronous speed by tens of meters per second; while this results in very high thrust, and very brief high current pulses in the rotor windings, the slip is very small and the motor efficency very high. This velocity transformation greatly reduces rotor heating, and increases launch efficiency above 99%. However, it does create stress on the track, requiring longitudinal strain relief running the length of the track.

VelocityTransformer page, with a cross section of the segmented bolt rotor.


Segmented Bolt Rotor


Capture Rail

Some (needs reference!) have written about a tether hanging from a heavy orbiting station. An ascending vehicle matches velocity with the bottom of this rail, then climbs up, perhaps powered with acoustic energy on the tether. This will rob the station of momentum and angular velocity, but that can be added back with slow, high efficiency electric engines (VASIMR engines with cheap argon propellant, perhaps).

A CaptureRail climbing capture tether arrives with a higher velocity, and decellerates all the way up a relatively stiff rail. That can require no climb energy, and slightly less angular velocity correction at the station.

However, the LoopPort described below is probably a better idea.


Geosynchronous Construction Orbit

Before a capture system is built in a synchronous location in GEO, or for the assembly of interplanetary missions requiring a lower perigee, we can launch to multiple highly elliptical 86164 second period Construction Orbits with a perigee of 8378 km (2000 km altitude) and a perigee of 75950 km. These orbits are synchronized with the daily availability of the launch loop (within a 15 minute window) for the delivery of multiple payloads.

Interplanetary missions should start at a low perigee for maximum escape velocity. A low perigee also permits a "12 hour return" for crew rotation and medical emergencies given a relatively small 114 m/s delta V at apogee. Two more delta V's will put the vehicle into a circular geostationary orbit. However, for many missions, including crew missions, construction orbit is the final destination, or the launch point (at perigee) for interplanetary missions.

LoopPort: Construction Orbit Spaceport

A short spaceport resembling the 1979 Arnold/Kingsbury horizontal capture spaceport. The LoopPort is in a geosynchronous (but not geostationary!) high eccentricity "24 stellar hour" construction orbit, and captures incoming vehicles launched from the launch loop at perigee, with a relative delta V of 114 m/s. Like the LEO spaceport, the vehicles will be captured "retrograde", shedding energy and accelerating to the slightly higher LoopPort apogee velocity. They will decelerate relative to LoopPort; this can generate some energy, but it is probably cheaper to waste it, or use it to power passive stabilization coils that keep the vehicle centered (mad handwaving here).

A second stream of much smaller vehicles, carrying "dumb" payload that can tolerate high acceleration, is also launched from the loop into into a much higher orbit 12 hours later, putting it in an orbital plane tilted 16 degrees from the main construction orbit. At apogee, rockets boost velocity, angular momentum, and perigee to the apogee radius of the first stream. At plane crossing, another rocket firing matches the orbital plane to that of the first stream, and the vehicles arrive at LoopPort altitude to be captured prograde and restore angular momentum.

The velocity ratios and mass ratios are about 20 to 1.


80 km main acceleration track, 30 km altitude West Station

With a pointy nosecone, the hypersonic drag for an acceleration path at 80 km is acceptable, the lower altitude reduces stabilization cable weight, and the 33 times higher atmospheric density should reduce space debris flux by a corresponding factor.

Vehicle drag power and heating is proportional to velocity cubed. Vehicles will increase acceleration slowly from West Station, and increase speed as they gain altitude and encounter less drag. A lower altitude west station allows it to be heavier, makes maintenance and staff "commuting" easier, and reduces the time and expense of the west station elevators.


Acoustic Elevators from the Surface to West Station

I presented this at the 2017 ISEC Space Elevator Conference (ADD LINK to paper). If a very strong tether material ever becomes available, it will be stiff enough to make a superb "tin can telephone" high power vibration transport to an ascending climber.

A 30 km high elevator to West Station can be made from Kevlar, or from stronger (but more expensive) materials like Torayca T1100G ( ADD LINK to datasheet ). A Kevlar acoustic elevator must be much stouter, but can lift a vehicle in a few minutes. A launch loop will need dozens of these elevators.

This replaces recent "loop and pulley" elevator approaches.


Server Sky Positioning, Control Information, and Precision Debris Prediction


Return Track Bolt Acceleration and Deceleration

The return track isn't doing much, besides providing a platform for radars and measurement gear, and helping to support surface cables. It will carry a small track that will accelerate replacement bolts retrograde to very nearly rotor velocity, sending them down through a "13th channel", past the vertical deflectors, and into a horizontal switchyard where they can be swapped with defective bolts in the main stream. A sparse stream of replacement bolts may be maintained in a racetrack that loops through the west station bolt switchyard, so that bolts can be swapped as soon as a defect is detected.


Incline Lightning Protection

The inclines will be hit by lighting strokes. They should be sheathed in at least 2 kg/m of aluminum to reduce return resistance. The bolts in the rotor stream should be electrically isolated from each other (method TBD) so that they can capacitively couple to the outer tube and develop similar voltages. Hands again waving madly.