Elevator Friction Motors

Previous versions of the launch loop west station elevator assumed a "three stage" elevator structure. A main cable loop did most of the lifting between 4 and 76 km, at 400 meters per second, while two short segments of cable loop accelerate or decelerate at two gees.

There is an easier way. First, we assume a [[LowerWestStation | lower west station ], at 50km. Ascent speed is still 400 meters per second.

But we do not need to be so finicky about saving energy. Rather than accelerate and decelerate a loop of cable with an attached payload, we can use a "friction wheel" clamp on the main elevator cable to get up to speed. The "friction wheel" is a lightweight wheel (or wheels), a clutch, a generator, and an incandescent resistor.

At the bottom of the elevator run, the payload will be supported by a cradle with friction wheels. It will be brought up to the fast-moving elevator cable, and the unclutched wheels will be spun up, perhaps by ablative friction on the elevator cable, or perhaps by motor action. When the wheel is spinning at 400m/s, we engage the clutch and the generator until the cable is supporting the full weight of the 5 tonne cradle and payload (stationary for now). 49000 Newtons times 400 m/s is about 2 megawatts. What do we do with the heat? Waste it in a resistor! A 2 square meter incandescent tungsten band, perhaps exposed to air, inside an outwards pointing reflector. If the emissivity of the filament is 0.6 on the outward side, and 0.2 on the inward side, and there is no appreciable air cooling, it will heat up to about 2000K.

We now increase the drag to 150KN, and lift the payload and cradle with a vertical acceleration of 20m/s², added to the gravitational acceleration of 9.8m/s². That brings the emission up to 6MW, and the tungsten band temperature up to 2600K (incandescent lights run at 3300K). The payload accelerates upwards, with the drag power decreasing as the speed difference decreases. After 20 seconds, the payload and the elevator cable are moving at the same speed, and the drag power is zero. We engage a different clutch, and lock the wheel.

As we speed up, we would like the drag force to remain high while the drag power reduces. The drag force is proportional to generator current, while the velocity difference is proportional to generator voltage. So we would like some approximation of constant current operation. Fortunately, filament resistance increases as it gets hotter, and so the material itself does part of the regulation. The rest can be approximated with filament segments, and switches. We will want extra segments for reliability, anyway. With pendulum-and-spring activated switches, the entire regulation system could be non-electronic - positively Victorian! In actual fact, electronics will be more reliable, though probably more expensive. We will reuse the cradles many times per day, so we can spare some expense. Properly sized electronic switches will not dissipate much power, as they will only switch once or twice per ascent.

While the filaments are running near the ground, we can visually observe them from quite a distance, and monitor payload position and acceleration. The filaments will be brighter than noontime sunlight within 15 meters or so. At night, the light will be a bright as the full moon for 10km or more. Not as good as the rocket's red glare, perhaps, but still thrilling to watch!

At the upper end, we release the locked wheel, and coast vertically to a stop. We can take extra nudges of force from the elevator cable to rendezvous with the west station platform, but some other station-controlled rendezvous method (springs and bumpers? hoists?) might be lower energy and safer. The station should control the rendezvous, not the payload and cradle.

So, 20 seconds acceleration to speed at 4km altitude, a 95 second climb at 400m/s to 42 km altitude, and 40 seconds of weightless deceleration to arrive, at rest, at the west station platform at 50km altitude. Less than 3 minutes to space ... plus the decades needed to build this stuff!