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Towards routine, reusable space launch.
At least three observatories with seven telescopes in active use will
be surprised to learn [that making a 6.5-m primary mirror is impossible] That should have been five observatories and ten telescopes. I forgot some. I won't swear I'm not still forgetting others. In article , Fred J. McCall writes: You can do things with earthbound scopes that you cannot do with something you're going to shoot into space. How does that apply to the current discussion? Launching a 6.5-m mirror monolithic should in principle be easier than having the same size mirror deploy to the required precision. The problem is making it fit into the payload fairing. I wouldn't be surprised if there are "black" programs with the same difficulty. Nope. They use a mirror roughly the size of Hubble's. The ones we know about used mirrors that size. Anyone who actually knows the current situation -- I don't -- wouldn't be allowed to say. Remember, they're looking at something relatively close as such things go. 6.5-m mirrors would have advantages over smaller ones. (I don't see what distance has to do with anything.) I've seen hints that some have been built and deployed, but that may be salemanship. Companies vying for the JWST contract would have had an incentive to drop such hints whether true or not. The point is that a balloon does NOT replace a 'first stage'. We agree on that. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
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Towards routine, reusable space launch.
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Towards routine, reusable space launch.
In article ,
Fred J. McCall writes: Oversize fairings are easy. No doubt the JWST engineers wish you had told them that. [mirror size of reconnaissance satellites] You can see the bloody things from Earth, after all. See some of them, sure. Why do you think the census is complete? What observations (equipment) are needed to measure their sizes? Past a certain point a bigger mirror doesn't help you for Earth observation. Atmosphere speckle becomes the driving parameter and a bigger mirror doesn't help that. Are you assuming LEO and visible wavelengths? I don't see why either one necessarily represents all reconnaissance satellites. And even with those assumptions, what about temporal resolution? Taking short exposures most certainly helps mitigate seeing effects. ("Atmospheric speckle" is only one of those effects.) No, they wouldn't. The next generation of recce satellites will use a mirror right around 2.4 meters; the same size used since KH-11. Source? All of them or only some? Other than better sensors and onboard processing, how do newer telescopes differ from the older generation? (As you no doubt know but some readers may not, two of those were declared surplus and delivered to NASA.) Distance has a lot to do with everything when it comes to telescopes. What did you have in mind? I'd have said the key parameters are angular resolution, temporal resolution, and sensitivity. Distance affects requirements on those parameters, but I don't see that distance _per se_ matters. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
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