Centauri Dreams reports that Dana Andrews proposes a lunar sling for launching metal products to Earth, but goes into greater detail on what any space infrastructure requires going out of the gate: A simple and inexpensive way to get to Earth orbit, what he calls FRETOS — Fully Reusable Earth-to-Orbit Systems. A fleet of five launchers supporting a flight rate of 1000 launches per year using four tethers is at the heart of the proposal. On the space side, a Skyhook capture device located at 300 kilometers orbital altitude is part of a picture that also includes a Low Earth Orbit station at 1000 kilometers, a powered winch module at 1700 kilometers and a counter-balance at 2400 kilometers. The total mass of the space segment is estimated at 190 metric tons, including 2100 kilometers of tether lines, high-speed winches, power generation arrays, counter balances and station-keeping components, all to be launched separately and docked together for assembly.
What kind of resources are we talking about? Andrews enumerates quite a few, a list on which items like rhenium — used in fuel-efficient aircraft engines — stand out. The price of rhenium is now over $11,000 a kilogram, twelve times what it was just four years ago. Reserves of indium, which is used in solar cells and LCDs, are forecast to run out within ten years, and so is the hafnium we use in computer chips and nuclear control rods. Such shortages and accompanying price increases can be the driver for space commercialization. Andrews proposes moving the mining and smelting of key non-renewable resources to the Moon, providing access to high grade ores and transferring potentially polluting mining operations away from our planet.
Many asteroids are richer in most of these precious metals than the richest Earth ores which we mine. Further, these metals all occur in one ore when it comes to asteroids, not in separate ores.
As for getting to orbit, the launch segment is envisioned as a first stage subsonic carrier/aircraft with onboard hybrid rocket motor to achieve altitude for release of a second stage at 12.6 kilometers, with the second stage delivering a 13-ton payload to the capture point at the bottom of the 2100 kilometer long tether system. After payload capture, the second stage re-enters and glides to a landing at the launch and recovery base. Andrews’ assessment is that the entire recovery, turn around, launch and tether lift cycle could be completed within 24 hours, which works out to 1000 missions a year with the proposed fleet of 5 launchers and four tethers.
To get equipment to the Moon, outgoing payloads are released from the tether every day or so and transported to a lunar transfer station at L1, where they are assembled into lunar lander packages and then delivered to individual mining sites or research centers. The L1 station also collects and processes propellants for lunar landers and, possibly, deep space exploration missions, its operations almost entirely automated but allowing for the presence of a small crew as needed.
The economic model Andrews built of the entire infrastructure as operational over a twenty year period shows the cost of rare metals brought back to Earth at about $2600 per kilogram, an investment he notes is ‘fairly lucrative’ given current costs, and while a flow of materials from the Moon will lower the price, demand should also increase assuming we find momentum to reduce our use of fossil fuels, leaving a sizable potential for profit.
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