|
|
Thread Tools | Display Modes |
#112
|
|||
|
|||
Towards routine, reusable space launch.
JF Mezei wrote on Mon, 25 Jun 2018
12:48:25 -0400: On 2018-06-25 07:15, Jeff Findley wrote: That's exactly what JF is doing. He's and waving away the modal behavior of a cable like structure that is instantaneously released from extreme tension. You are the one who pointed at a simulation showing the cable floating freely and snaking in space. I argued this wouldn't be the case because of orbital mechanics. Yes, he pointed at a simulation that presumably takes some of those dynamics he keeps trying to explain to you into account. You pointed to handwavium. -- "Some people get lost in thought because it's such unfamiliar territory." --G. Behn |
#113
|
|||
|
|||
Towards routine, reusable space launch.
JF Mezei schrieb:
On 2018-06-20 16:42, Sergio wrote: Carbon nanotubes. they are held in a matrix of epoxy glue. your 10,000 km of glue wont support itself. Carbon nanotubes do not replace the primary carbon fibre structure. They are mixed with the epoxy to add strength to the matrix. Or another material... With the problem of disentangeling the tubes, of binding the tubes to the matrix material (pulling out the fiber from the matrix is a common failure mode), and of course the fibers may have imperferfections which can _drastically_ (by quite a few orders of magnitude) reduce their strenghts. Is anybody aware of actual application of CNTs for materials, an application which has made it into the marketplace and that I could order today? I'm not, but I have not followed that field for some time. |
#114
|
|||
|
|||
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 |
#115
|
|||
|
|||
Towards routine, reusable space launch.
(Steve Willner) wrote on Mon, 25 Jun 2018
21:17:06 -0000 (UTC): In article , Fred J. McCall writes: Oversize fairings are easy. No doubt the JWST engineers wish you had told them that. Well, someone should have if mirror size alone was the reason for making it folding. [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? What do you think they hide them behind? I think it's complete because lots of people put lots of effort into it. And it takes a telescope and some time to measure their size. This may be rocket science, but it's EASY rocket science. 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.) You can only 'mitigate' so far. Are you one of those people who believes the movies that you can make out faces from orbit and that you can 'improve' an image with processing beyond the information that it contains? 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.) Sources aren't hard to find. Here's one. https://spaceflightnow.com/2015/05/0...ching-in-2018/ 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. 'Temporal resolution' is difficult, given that both the satellite and the Earth's surface are moving relatively rapidly with regard to each other. Increased sensitivity means increased image noise. Distance matters. That's why as newer satellites launch the older ones are moved to lower orbits. -- "The reasonable man adapts himself to the world; the unreasonable man persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." --George Bernard Shaw |
#116
|
|||
|
|||
Towards routine, reusable space launch.
JF Mezei wrote on Mon, 25 Jun 2018
18:29:22 -0400: On 2018-06-25 14:31, Fred J. McCall wrote: Yes, he pointed at a simulation that presumably takes some of those dynamics he keeps trying to explain to you into account. You pointed to handwavium. "presumably". So you take some random animation off the web that doesn't consider orbital mechanics as science, despite neither material nor structure of the space elevator being known and thus elastic proporties that can't be simulated. You need to stop making **** up. Yet, you choose to ignore orbital mechanics that apply to all matter is orbit that is brought down and consider that to be "handwavium" You wouldn't know an orbital mechanic if one tuned your car. -- "Ignorance is preferable to error, and he is less remote from the truth who believes nothing than he who believes what is wrong." -- Thomas Jefferson |
#117
|
|||
|
|||
Towards routine, reusable space launch.
In article ,
says... On 2018-06-25 07:15, Jeff Findley wrote: That's exactly what JF is doing. He's and waving away the modal behavior of a cable like structure that is instantaneously released from extreme tension. You are the one who pointed at a simulation showing the cable floating freely and snaking in space. I argued this wouldn't be the case because of orbital mechanics. You replied "because of the wind". There is no wind in space, and this was about the cable breaking at geostationary altitude with over 38,000km of cable falling down and how it would fall on earth (east, west, or all in one pile). I suppose Google is broken again, SMH. Oh well, it's working for me: Dynamics of Space Elevator after Tether Rupture Vladimir S. Aslanov1 and Alexander S. Ledkov2 Samara State Aerospace University, Samara, 443086, Russian Arun K. Misra 3 McGill University, Montreal, H3A 2K6, Canada and Anna D. Guerman4 University of Beira Interior, Covilhã, Portugal http://aslanov.ssau.ru/papers/Aslanov_JGCD_2013b.pdf You can skip past the math right to: Fig. 13 Formation of a loop Fig. 14 Profile of the tether at t=3500s From above: Analysis of space elevator dynamics after failure presented here shows that the problem is rather complex and worth studying in detail. We focus on the case when the tether is destroyed by space debris in the vicinity of the geostationary orbit, and consider motion of the upper and lower parts of the system after rupture. The mathematical model developed for this purpose represents the flexible heavy tether of circular cross-section as a set of massive points connected by massless viscoelastic bars. The model takes into account the interaction of the tether with the Earth atmosphere during the fall. The approximate expression (18) for boundary value of distance to the center of mass of the top part was obtained. If the distance to the center of mass of the upper part surpasses the boundary value, this part will escape the Earth on a trajectory close to hyperbolic. For lower part numerical simulations show that the aerodynamic force changes significantly the tether behavior. After the tether enters the atmosphere, most of it slows down and falls smoothly; however, one can notice also quite unexpected motions, such as formation of large loops that can get out the atmosphere. Analysis reveals that some segments of the tether reach the ground with rather large velocities. One can conclude that the rupture of the space elevator ribbon can jeopardize both spacecraft and objects on the Earths surface located close to the equatorial plane. So, atmospheric effects taken into account and the thing exhibits "quite unexpected motions, such as formation of large loops that can get out the atmosphere". Jeff -- All opinions posted by me on Usenet News are mine, and mine alone. These posts do not reflect the opinions of my family, friends, employer, or any organization that I am a member of. |
#118
|
|||
|
|||
Towards routine, reusable space launch.
JF Mezei wrote on Tue, 26 Jun 2018
00:55:02 -0400: On 2018-06-25 21:19, Jeff Findley wrote: lower parts of the system after rupture. The mathematical model developed for this purpose represents the flexible heavy tether of circular cross-section as a set of massive points connected by massless viscoelastic bars. So virtual thing made of unobtainium and which has elements without any mass. So a model that behaves the way something real would behave. Do you not have a single clue about how simulation and modeling work? hyperbolic. For lower part numerical simulations show that the aerodynamic force changes significantly the tether behavior. After the tether enters the atmosphere, most of it slows down and falls smoothly; The simulation showed the upper sections of the tether where it broke off near geostationary altitude. It showed it snaking, floating in space. Meaningful atmosphere is roughly 20m in altitude, or if you want to include stratosphere, 50km in altitude. You say all that like it means something. So, in the cable falling because it broke at geostationary orbit scenario, you have some lateral forces in the first 50km and eventually, so air resistance to the structure falling sideways or diagonally with perhaps a terminal velocity. But it will fall, and it will pull down on all the rest of the 39,000 of cable. But that cable will first and foremost be affected by orbital mechanics since it is way above atmosphere. And pulling down an object that has forwrad motion causes it to accelerate that forward motion. So in space, that should be the primary factor to affect cable behaviour. And since the cable is going down, any motion imparted in the first 50km of cable will be 1-dampened by the anchor point (or drag on ground) 2- have very little chance of "snaking up" the whole length of the 39,000km of the cable. Once the cable has mostly fallen to the ground and all you got left is a few hundred km of cable left, then yeah, atmopshere will play a large role because it affects a large part of the cable. Of course you're absolutely correct, Mayfly, and everyone else is wrong and dynamics from things like elasticity are just irrelevant. Keep flapping. -- "Ignorance is preferable to error, and he is less remote from the truth who believes nothing than he who believes what is wrong." -- Thomas Jefferson |
#119
|
|||
|
|||
Towards routine, reusable space launch.
JF Mezei wrote on Tue, 26 Jun 2018
03:49:31 -0400: On 2018-06-26 01:09, Fred J. McCall wrote: Of course you're absolutely correct, Mayfly, and everyone else is wrong and dynamics from things like elasticity are just irrelevant. Keep flapping. Am I incorrect in stating that as the cable is pulled down, the higher end portions will accelerate horizontally? Depends on what you mean by 'accelerate'. You've been incredibly sloppy in differentiating angular acceleration vs linear and tangential acceleration. If I am so far off, why are you not able to explain why orbital mechanics don't play a role in this? Nobody said that, that's why. They just don't play the only role, which is what your argument assumes. -- "Ignorance is preferable to error, and he is less remote from the truth who believes nothing than he who believes what is wrong." -- Thomas Jefferson |
#120
|
|||
|
|||
Towards routine, reusable space launch.
|
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Reusable Launch Vehicles - When? | [email protected] | Policy | 4 | December 1st 09 12:10 AM |
AFRL To Develop Reusable Launch Capabilities | [email protected] | Policy | 1 | December 21st 07 05:03 AM |
Is anything on this new launch system reusable? | Ron Bauer | Policy | 10 | September 22nd 05 08:25 PM |
Suborbital Reusable Launch Vehicles and Emerging Markets | Neil Halelamien | Policy | 5 | February 24th 05 06:18 AM |
Space becomes routine. | Ian Stirling | Policy | 24 | July 5th 04 11:21 PM |