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Space Solar Power * Recent Conceptual Progress
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Space Solar Power ? Recent Conceptual Progress
On Jun 21, 7:50 pm, Jeff Findley wrote:
snip Henry Spencer has posted specific stages which meet the above criteria in postings to these newsgroups. A Google search of these newsgroups ought to turn up these postings. Of course, these stages were all expendable. Making a reusable SSTO is quite a bit more difficult. Jeff Taking "orbit" as 9,000 m/s and SSME as 4,500 m/s, the mass fraction is 1/7.4 or 13.5% Gary Hudson has informally said that a mass fraction of 15% is about as low as you can go for "reusable." Skylon C1 design was 17.8% structure, (and ~4% payload) but they cheat. Counting the rotation of the earth, they get to 1/4 of orbital speed with an equivalent exhaust velocity of 10.5 km/s. I have a graph of beamed energy exhaust velocity vs cost if I can figure out how to make it into something I can put on a wiki. Keith |
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Space Solar Power ? Recent Conceptual Progress
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Space Solar Power ? Recent Conceptual Progress
On Jul 12, 7:59 pm, Jeff Findley wrote:
In article , says... Nothing would ever get built if nothing was ever built before it had been built. On paper, Sabre has the characteristics required for an SSTO, and Skylo n itself isn't designed around unobtanium. So far no show stoppers have been identified. On paper. The show stoppers are the flight rate and reliability of bleeding edge technologies. In order to make a profit (and pay off development costs), Skylon will have to fly quite often and have an extremely high reliability (hardware losses will be very expensive for such a complex engine/vehicle). The engine doesn't have any more moving parts than a conventional aircraft turbine. True, the vehicle is big, but not as heavy as a 747. A more conventional approach to reusable SSTO using VTVL and plain old liquid fueled rocket engines would be a far more sane approach when you take into account economics. How do you get it back? If you put wings on it and land, then the structure mass eats the whole mass budget. That said, even SpaceX didn't use this approach, instead choosing to build an expendable in order to minimize development costs and time. There are no existing markets which would require the high flight rates needed to justify the development costs for Sabre and Skylon. I agree entirely with you statement. There is only one projected market I know about where Skylon makes sense (SBSP) and even for that market it takes something extreme for the second stage. Power satellites really need $100/kg to GEO to make economic sense. Keith It's a research project which belongs in Popular Science magazine. Jeff -- " Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/2011 |
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Space Solar Power ? Recent Conceptual Progress
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Space Solar Power ? Recent Conceptual Progress
On Jul 14, 7:26 pm, Jeff Findley wrote:
In article 01609aef-2c20-43b4-a553-9c84cb346892 @m3g2000pre.googlegroups.com, says... On Jul 12, 7:59 pm, Jeff Findley wrote: In article , says... Nothing would ever get built if nothing was ever built before it ha d been built. On paper, Sabre has the characteristics required for an SSTO, and S kylo n itself isn't designed around unobtanium. So far no show stoppers ha ve been identified. On paper. The show stoppers are the flight rate and reliability of bleeding edg e technologies. In order to make a profit (and pay off development costs), Skylon will have to fly quite often and have an extremely hig h reliability (hardware losses will be very expensive for such a comple x engine/vehicle). The engine doesn't have any more moving parts than a conventional aircraft turbine. True, the vehicle is big, but not as heavy as a 747. Development costs are still high and it's very unlikely that a Skylon would have the high flight rate of a 747. The 747 needs that high flight rate in order to justify the high development and operational costs of its engines. A more conventional approach to reusable SSTO using VTVL and plain ol d liquid fueled rocket engines would be a far more sane approach when y ou take into account economics. How do you get it back? If you put wings on it and land, then the structure mass eats the whole mass budget. I said VTVL: vertical take off and vertical landing. In other words, land the thing like DC-X on liquid fueled rocket engine power and on vertical landing gear. This approach is simple (no wings needed) and has been proven to work "in the real world". That's not entirely true. Nobody has ever gone to orbit with a DC-X approach. It's possible new materials like carbon nanotubes or graphene would get the structure fraction down far enough to have some payload. That said, even SpaceX didn't use this approach, instead choosing to build an expendable in order to minimiz e development costs and time. There are no existing markets which would require the high flight rat es needed to justify the development costs for Sabre and Skylon. I agree entirely with you statement. There is only one projected market I know about where Skylon makes sense (SBSP) and even for that market it takes something extreme for the second stage. Power satellites really need $100/kg to GEO to make economic sense. Even then I'm not sure they make sense. They've got to compete with al l other alternative sources of terrestrial power. As fossil fuel prices continue to rise, terrestrial alternatives become more attractive and investment in them may yield reductions in cost such that space based power never makes economic sense. That's possible. But it will take a conceptually different approach, like solar collectors that grow themselves like Kudzu. It seems unlikely that earth based solar power will ever get down to 2 cents per kWh, and that's the target I set for power satellites. (StratoSolar might be an exception.) Keith Jeff -- " Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/2011 |
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Space Solar Power ? Recent Conceptual Progress
On Jul 15, 8:25 pm, Jeff Findley wrote:
In article 41f2ea4f-47ee-4f68-b980-399f7e714df0 @j14g2000prn.googlegroups.com, says... On Jul 14, 7:26 pm, Jeff Findley wrote: In article 01609aef-2c20-43b4-a553-9c84cb346892 Even then I'm not sure they make sense. They've got to compete wit h all other alternative sources of terrestrial power. As fossil fuel prices continue to rise, terrestrial alternatives become more attractive and investment in them may yield reductions in cost such that space based power never makes economic sense. That's possible. But it will take a conceptually different approach, like solar collectors that grow themselves like Kudzu. It seems unlikely that earth based solar power will ever get down to 2 cents per kWh, and that's the target I set for power satellites. (StratoSolar might be an exception.) Perhaps advances similar to this? Photovoltaic Breakthroughs Brighten Outlook for Cheap Solar Power Novel materials might make harvesting sunlight for electricity affordable http://www.scientificamerican.com/ar...=photovoltaic- breakthroughs-brighten-outlook-for-cheap-solar-power Frankly, no. This is not particularly reliable information. Shame too, I grew up on Scientific American, started reading it in 1957, read back issues to 1948 and read every issue till the editorial policy changed and it got "fluffy." And there are always other renewable sources, like wind, wave, hydroelectric, thermal, and etc. Wind will not scale large enough, wave is much worse. Hydroelectric is mostly exploited. Geothermal isn't large enough either. You might want to look he Sustainable Energy — Without the Hot Air. http://en.wikipedia.org/wiki/David_J._C._MacKay It's available online. Keith Jeff -- " Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/2011 |
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