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Feb
6
Written by:
admin
2/6/2010 2:18 PM
We've been highlighting groups of abstracts for Space, Propulsion, and Energy Sciences International Forum (SPESIF) for about a week now, so it's time to start moving into detail on some of the more interesting ones.
James Powell, George Maise, and John Rather have an abstract in the mix entitled "Maglev Launch: Ultra Low Cost Ultra/High Volume Access to Space for Cargo and Humans" which looks interesting. In the abstract, they propose a 100 km long evacuated tunnel within which a magnetic levitation system would accelerate a spacecraft to orbit speeds. Upon reaching the end of the tunnel, which would be roughly 5 kim above sea level, the craft would coast into orbit, using a small rocket thruster to even out its orbital path.
Based on their estimates of current costs for construction and operations, it would be possible to launch a 40 ton, two meter diameter spacecraft into orbit for $43 per kilogram. A second generation system would have the tube itself elevated such that the opening would be 70,000 feet above sea level where the air would be thin enough that the deceleration upon exiting the evacuated tube would be less harmful to human passengers.
The air would be kept out of the evacuated tube by means of an electrically-powered magnetohydrodynamic window, basically an electromagnetic field strong enough to prevent air molecules from passing through.
I have not read the entire paper yet (although I would like to). It seems to me that you could implement a series of MHD windows with gradually increasing air pressure in each one so that the transition to full atmospheric pressure would be less of a sudden shock on the craft. You would lose a bit of velocity in trade off, but but extending the initial launch tube by a relatively small amount, you would likely be able to launch passenger spacecraft using the initial system without having to resort to a tube 14 miles above the ground.
Initial construction costs are projected to be high (~$20 billion), which puts this kind of system out of reach unless a major corporating wants to stake its future on the project or a coalition of governments decides to get involved. Without seeing the plan, I cannot say whether there are opportunities to reduce the estimated costs. It is somewhat likely that the costs would increase. Plus, finding a 100 km long stretch of land where you would be able to construct the tunnel would be challenging.
The abstract points out that for polar orbital paths, potential launch sites exist in Alaska, Russia, and China, and for equatorial orbitals, sites exist in South America and Africa. I would think, though, that more launch sites are feasible if you're willing to put just a little more oomph into the orbital insertion thrusters and launch at an angle toward the equator. With that kind of design, you may be able to launch from Hawaii, for example, by starting your launch tube beneath the ocean and running up the side of Mauna Kea.
Additionally, if you put a series of transfer tethers in orbit and fired at them as they came around, you could put your launcher pretty much anywhere you want, as long as it can target a transfer tether.
One major problem would be the sonic and shock waves emanating from the end of the launch tube, which I expect would be quite significant. That means you would want to launch far from any inhabited area.
Also, is a maglev the right way to go, or would a type of rail gun or gauss cannon work better? I'm not an expert on any of these technologies, so let's have some feedback.
The complete abstract follows:
Despite decades of efforts to reduce rocket launch costs, improvements are marginal. Launch cost to LEO for cargo is ~$10,000 per kg of payload, and to higher orbit and beyond much greater. Human access to the ISS costs $20 million for a single passenger. Unless launch costs are greatly reduced, large scale commercial use and human exploration of the solar system will not occur. A new approach for ultra low cost access to space – Maglev Launch – magnetically accelerates levitated spacecraft to orbital speeds, 8 km/sec or more, in evacuated tunnels on the surface, using Maglev technology like that operating in Japan for high speed passenger transport. The cost of electric energy to reach orbital speed is less than $1 per kilogram of payload. Two Maglev launch systems are described, the Gen-1System for unmanned cargo craft to orbit and Gen-2, for large-scale access of human to space. Magnetically levitated and propelled Gen-1 cargo craft accelerate in a 100 kilometer long evacuated tunnel, entering the atmosphere at the tunnel exit, which is located in high altitude terrain (~5000 meters) through an electrically powered “MHD Window” that prevents outside air from flowing into the tunnel. The Gen-1 cargo craft then coasts upwards to space where a small rocket burn, ~0.5 km/sec establishes, the final orbit. The Gen-1 reference design launches a 40 ton, 2 meter diameter spacecraft with 35 tons of payload. At 12 launches per day, a single Gen-1 facility could launch 150,000 tons annually. Using present costs for tunneling, superconductors, cryogenic equipment, materials, etc., the projected construction cost for the Gen-1 facility is 20 billion dollars. Amortization cost, plus Spacecraft and O&M costs, total $43 per kg of payload. For polar orbit launches, sites exist in Alaska, Russia, and China. For equatorial orbit launches, sites exist in the Andes and Africa. With funding, the Gen-1 system could operate by 2020 AD. The Gen-2 system requires more advanced technology. Passenger spacecraft enter the atmosphere at 70,000 feet, where deceleration is acceptable. A levitated evacuated launch tube is used, with the levitation force generated by magnetic interaction between superconducting cables on the levitated launch tube and superconducting cables on the ground beneath. The Gen-2 system could launch 100’s of thousands of passengers per year, and operate by 2030 AD. Maglev launch will enable large human scale exploration of space, thousands of gigawatts of space solar power satellites for beamed power to Earth, a robust defense against asteroids and comets, and many other applications not possible now.
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