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#21
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Michael Smith wrote:
(Allen Meece) wrote: Because nasa designed it as a Mack truck with little wings instead of going with the ultralight Rogallo Wing re-entry vessel. The Rogallo Wing is a modified parachute. It was developed as a steerable recovery system for Gemini before finding a use as a hang glider wing. It has no role in reentry. No role? It could have a role in civilian CATS [cheap access to space] vessel reentry. The reason nasa didn't go with it was because it was too slowly developing a folding/deployment system for the wing and it was holding the Gemini program back. It wasn't meeting the program's schedule. So there you go. Institutional priority results in bad technology. What Michael means is that the Rogallo wing can be deployed at low speeds, as in the final landing phases of a return from orbit, but not at the hypersonic speeds Gemini (and the Shuttle) experienced during "entry interface" and the upper atmosphere. It would be a major engineering challenge to develop a deployable structure of significant span that *could* take hypersonic speeds -- we're having enough trouble with fixed structures. /dps |
#22
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"Ash Wyllie" wrote in message ... Aerodynamic lift simply isn't enough. It always comes packaged with a certain amount of drag, and at hypersonic speeds actually quite a bit of it. When you do the numbers, it just doesn't work. If the drag is low enough to stretch the deceleration out that long, you don't have enough lift to hold you up. Period. Full stop. Does that also mean that the Sanger skip bomber would not work? Yes, but did you really expect scientists of that era to truly understand hypersonic aerodynamics? It's a tricky field, even today. Jeff -- Remove icky phrase from email address to get a valid address. |
#23
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"Rodney Kelp" wrote in message ... They could send up some solid fuel boosters that the shuttle could dock with and use for braking. How how long would it take to brake from 18k mph to about 200mph without exceeding 2 G's? That would be insane. You'd need "solid fuel boosters" with very nearly as much energy as the SRB's and the ET used to *launch* the shuttle in the first place (the gravity, altitude, and drag losses are far less than the energy needed to get to orbital velocity). To get your "solid fuel boosters" into orbit would require a launch vehicle bigger than any ever built. Jeff -- Remove icky phrase from email address to get a valid address. |
#25
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"william mook" wrote in message om... "Anthony Garcia" wrote in message m... "william mook" wrote in message om... http://science.ksc.nasa.gov/shuttle/...s/gidefinl.pdf Here's some information on what goes into reusable spacecraft design. http://www.astronautix.com/lvs/shuenara.htm Here's a picture of an alternative to the Shuttle, that in my estimation would have been better than the Shuttle's present delta wing. An even better version would have been a slender cylinder with straight wings deployed at subsonic speeds. Think of a tomahawk cruise missle. This was proposed for the Russian PKA [snip] How are these alternatives any better? They're less costly and safer. Are they truely safer and less costly? How do we know this? [snip] There are no free lunches. You had it right the first time. Cross range is reduced with the proposed wing structures. The footprint of allowable landing sites from a given deorbit burn is reduced as a result. So what? We have the ability to precisely control orbital parameters of the deorbit burn and hit the landing site even with reduced cross range. So, the issue is, should we keep cross range far in excess of what we need to accomplish the mission, or reduce the size of the wings and improve all the factors you mentioned? The choice is clear, we should reduce cross range and make a smaller less expensive and safer vehicle capable of carrying more payload. I do see your point. Perhaps if one presumes that the deorbit burn can provide a large component of the cross range requirement then yes, you have a very good point. |
#26
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They could send up some solid fuel boosters that the shuttle could dock
with and use for braking. How how long would it take to brake from 18k mph to about 200mph without exceeding 2 G's? That would be insane. You'd need "solid fuel boosters" with very nearly as much energy as the SRB's and the ET used to *launch* the shuttle in the first place This is the second poster who erroneously contends that it takes as much to brake an empty shuttle out of orbit as it did to get the fully fueled orbiter into orbit. C'mon guys, it only takes a fraction of the launch fuel to brake the empty craft. But there's no need to "send up" an SRB to brake it, just hang onto the ET and use its spare liquid fuel for braking and then cut it loose. ^ //^\\ ~~~ near space elevator ~~~~ ~~~members.aol.com/beanstalkr/~~~ |
#27
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Isn't the quantity of energy being shed going from orbit to ground the
same regardless of the angle of reentry? The energy to be shed is determined by the orbit and the spacecraft mass right True, Brute force reentry sheds it faster with a steep plunge while the elegant lifting body approach is to shed the same energy over a longer time using suitable heat radiators, flying and skipping rather than diving. |
#28
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Incorrect. The space shuttle re-enters at a flight path angle typically
between -1 and -1.5 degrees. That's hardly "steep". Also incorrect. The shuttle's flight path angle in the atmosphere is 20 -- 25 degrees. You're thinking about the initial orbital departure angle, not the average sink rate along the entire descent. The shuttle's reentry path IS STEEP. It is a high wing-loading, controlled brute force reentry. Hardly as graceful as a good lifting body like the cancelled [!?] X-38 would do. ^ //^\\ ~~~ near space elevator ~~~~ ~~~members.aol.com/beanstalkr/~~~ |
#29
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If your TPS can't shead the heat while out of the atmosphere, the "skipping"
trajectory will be worse in terms of total heat load than a "traditional" re-entry. Well, yes, of course the heat will have to be radiated away at the top of each skip. Later, when the ship has lost the speed necessary to skip out of the atmosphere, it will have to shed head via convection. Maybe copper heat pipes from the nose connecting to some fins or feathers in the slipstream to transfer the nose's heat to the ambient frigid air which is about -75C. ^ //^\\ ~~~ near space elevator ~~~~ ~~~members.aol.com/beanstalkr/~~~ |
#30
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It would be a major
engineering challenge to develop a deployable structure of significant span that *could* take hypersonic speeds -- we're having enough trouble with fixed structures. But how do we know that? Especially since it depends on the flight profile. Look, there's hypersonic speed in the atmosphere where the air is dense and there's hypersonic speed in the stratosphere where there are scattered molecules. There's no reason why a well-designed Rogallo Wing would not deploy in the stratosphere, and provide lift for a slow descent. ^ //^\\ ~~~ near space elevator ~~~~ ~~~members.aol.com/beanstalkr/~~~ |
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