"tadchem" wrote in message news: snipped-for-privacy@d21g2000prf.googlegroups.com... | On Feb 1, 1:27 pm, Robert Clark wrote: | > I discussed a method for surrounding large ground based telescopes | > with a vacuum shroud reaching to the stratosphere in a post to | > sci.astro: | >
| > Newsgroups: sci.astro, sci.physics, sci.engr.mech, sci.space.policy | > From: "Robert Clark" | > Date: 29 Apr 2005 09:55:15 -0700 | > Local: Fri, Apr 29 2005 11:55 am | > Subject: An atmospheric envelope for ground-based telescopes.http://groups.google.com/group/sci.astro/browse_thread/thread/d7661ed...| >
| > For telescopes of the liquid mirror type arbitrarily large mirrors | > could then be used without the restrictions on the size of liquid | > mirrors caused by the winds produced by the rotating surface. | | Rotating pools of liquid will develop spiral standing waves (even in a | vacuum) due to imperfections in the bearings and alignment of the | rotating plane WRT to the ever-changing local gravity gradient (you | forgot about the moon's and sun's gravity, didn't you?). | | > Liquid mirrors telescopes have the limitation that they have to be | > upward pointing. However, they are much cheaper than a comparable | > sized solid mirror scope, perhaps by a factor of a hundred. There have | > been proposals for a 100 meter solid mirror telescope, costing in the | > range of a billion dollars. A liquid mirror telescope of this size | > might cost $10 million. | > My suggestion for raising the vacuum chamber walls to high altitude | > was to have them held in place dynamically with continuously supplied | > pressurized fluid. However, after a web search I found a report on | > creating inflatable vacuum chambers, where the walls are filled with | > pressurized gas for strength. Such chambers could even be buoyant if | > the walls were filled with a lighter than air gas such as helium: | | Air has about 7.25 times the density of helium at the same pressure. | The gas laws imply that when helium is pressurized to 7.25 times the | pressure of the air it becomes neutrally buoyant - any more and it | becomes negatively buoyant (it sinks). | | Your vacuum chamber will need an optically flat and transparent lid. | This is impossible to achieve in a gravity field. Even a 1 meter span | of glass will sag under gravity, resulting in a hopelessly distorted | image. | | Keck-style mirror arrays is the wave of the future of light-gathering | power in earth-bound optical astronomy. The only question will be | over how many kilometers will the mirrors be spread out. VLB | interferometry is SOO good at improving resolution... |
Not mention his vacuum holding bouncy castle reaches stratosphere. Lordy knows what a hurricane would do to it.