Notes from a presentation by Larry Bartoszek at Capricon 45, Chicago, Feb. 8, 2024. Any mistakes are mine. The speaker is not responsible for any errors here.

A recent International Space Elevator Consortium (ISEC) study showed that a 20 ton Space Elevator climber needs tens of megawatts of electrical power to begin climbing from the surface of the Earth, but the power required falls off as 1/r2, as gravity does. This talk will look at options for delivering the large amount of power to get started and the design of a laser power beaming system to power the climber at higher altitudes. Non-laser options will also be discussed.

The Space Elevator is a concept that has been around since 1895. It was popularized about 1980 by the novels The Fountains of Paradise, by Arthur C. Clarke and (independently) The Web Between the Worlds, by Charles Sheffield. I first encountered it in those books.

• Reference: The Space Elevator: A Revolutionary Earth-to-Space Transportation System
• The “ribbon” (the cable on which the “climber”) ascends and descends needs to be of some material that does not exist yet. However, new materials are constantly being developed, so something strong enough may come along in the not too distant future.
• The Climber-Tether Interface of the Space Elevator
• Climber motor characteristics: Bus is 1/2 of the climber. 7 KAmps current.
• Most of this is about powering the space elevator by surface based lasers.
• Atmospheric windows
• There is diffraction of laser light in a vacuum.
• Power drops off with altitude, but power needs also drop off with altitude.
• Laser light that misses the climber can be collected.
• Dangerous near the base.
• The atmosphere absorbs at least 32% of the power.
• Military lasers use infra-red, not needing long range.
• Various green laser choices. Free electron lasers with green light.
• Receiver tech. Not the same goal as solar cells, which want capture a wide range of wavelengths. Here we want to optimize for the wavelength our laser emits.
• Need to keep our PV (photovoltaic_ array cool.
• System efficiency about 10%. So for 11 MW on the climber we need 110 MW on Earth. This is possible with naval nuclear reactors.
• Efficiency goes down with altitute but so do our power needs. When the climber is low we need the most power. Hence surface based lasers.
• Shadowing by multiple climbers on the same tether is a problem.
• Deployment of the the tether will be from GEO (Geostationary orbit)
• Disposal of waste heat is a problem.
• Microwave (1 mm-1 m) power diverges much move than optical lasers.
• The climber needs a 100m (diameter?) receiver for power.
• What about power lines from the surface to the climber?
• Graphene is a conductor
• High voltage reduces current
• Motors use 800V
• Conductivity of ionosphere drains power.
• For DC you have to worry about discharge between the + and – cables.
• AC will beam away power.
• Linear inductor motors (maglev) will not work.
• Energy: 20 ton climber requires 9.7 x 10¹¹J
• Rockets have to carry all their fuel. “Rockets are wrong.” Charles Sheffield, The Web Between the Worlds.
• Think about $/kg. Compared to rockets, a space elevator has a huge initial cost but low operating cost.<
• For more information about all of this see the International Space Elevator Consortium. Larry Bartoszek is the Director and Vice President, Chair for Design. His enthusiasm for the concept was obvious during the talk and a delight to watch.

Note on the Stanford Torus. One mile in diameter. Rotates once per minute to give Earth-normal gravity on the inside of the outer ring. Would house about 10,000 people. It cannot be built with materials from Earth.