NASASpaceFlight.com Forum
NASA Shuttle Specific Sections => Atlantis (Post STS-135, T&R) => Topic started by: Hotdog on 06/24/2007 10:38 am
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Hi Chris
That picture of the shuttle in your 'Atlantis avoids early retirement - will keep flying to 2010' article is fantastic. Do you have a high resolution version you can post?
Thanks
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Hotdog - 24/6/2007 12:38 PM
Hi Chris
That picture of the shuttle in your 'Atlantis avoids early retirement - will keep flying to 2010' article is fantastic. Do you have a high resolution version you can post?
Thanks
Here you go: http://mediaarchive.ksc.nasa.gov/detail.cfm?mediaid=4720
Edit: Corrected the link, thanks to ShuttleDiscovery for letting me know.
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I think you've got the wrong picture Dave! That one's a shuttle crew in the white room at the pad...
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Wow. Thanks. It really is a great picture isn't it?
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Images like this one are what make me hate film with the passion of a thousand burning SRBs!
I've attached a cleaned-up version.
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Hotdog - 24/6/2007 5:38 AM
Hi Chris
That picture of the shuttle in your 'Atlantis avoids early retirement - will keep flying to 2010' article is fantastic. Do you have a high resolution version you can post?
Thanks
The image is explained (and a full size desktop version) here. http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=7708&start=1
And yes, it's real. :)
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The image is from film; it's a still from a videofilm tracking camera.
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Is it actually the point at which the stack is breaking the sound barrier? Is that what we see with the bow wave?
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Yes, Carl. She's about to go through the sound barrier, and keeps on truckin'
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No, technically the shockwave happens at or near breaking the sound barrier but it is not correlated with the instant it does. That's why you see it last as long as ten seconds sometimes.
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Lee, thanks for your cleaned-up version of the picture... my first thought upon looking at the "original" large size on the NASA website was "Darn it! Can't put that on my desktop", but yours is already there...
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a stunning picture indeed. We are extremely lucky to be able to witness such an incredible aerodynamic phemnomena. Often misinterpreted and ill-explained, what you are really seeing is a Prandtl-Glauart Singularity cloud caused by the amplification of pressure disturbances at or near the speed of sound. I looked into the math and confirmed it theoretically. Under the right conditions the Singularity can be visualized by the human eye as a result of the reduction in local pressure caused by the amplification. With the drop in pressure at points around the vehicle, there is a corresponding drop in local temperature leading to condensation (assuming the air is near the saturation point) causing a cloud. for us to see this on the Space shuttle, there has to be sufficient moisture at the altitude where the shuttle goes transonic.
Often assumed, the outline of the cloud DOES NOT define the edge of the shockwave (shockwaves cause an INCREASE in pressure and temperature across them). The shockwave and PG clouds are not related and caused by two different aerodynamic mechanisms.
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That image is "desktopped" as of now!
Raw power defined!!
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This is the best image http://forum.nasaspaceflight.com/forums/get-attachment-big.asp?action=view&attachmentid=20526 the ones on the NASA site are wrong way around (compared to this image that is) and the one here has better colors.
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terynd - 24/6/2007 1:14 PM
a stunning picture indeed. We are extremely lucky to be able to witness such an incredible aerodynamic phemnomena. Often misinterpreted and ill-explained, what you are really seeing is a Prandtl-Glauart Singularity cloud caused by the amplification of pressure disturbances at or near the speed of sound.
I agree that the cloud is a Prandtl-Glauart Singularity. But the rainbow looks to me more like a shock visualized in more of a Schlieren sort of way by the lighting. What do you think?
Lee Jay
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Good point. We'll assume at the moment that we don't have any optical illusions/effects going on here. If that rainbow-colored cloud was the actual shock, then I dont believe that you would see it through condensation because the pressure increases through the shock (pressure has to drop to support condensation). If there's a rainbow, then there must be condensation or water vapor droplets to create the rainbow. This condensation is only created by a drop in local pressure. So, all this doesn't support that we are seeing the shock in this image. Plus we don't see the bow shock which would also be seen if there was a Schlieren effect here.
I look forward to hearing more ideas on this.
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Ben - 24/6/2007 5:37 PM
The image is from film; it's a still from a videofilm .
Thats an oxymoron i feel
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Not from video but from a 35mm cinema film reel.
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terynd - 24/6/2007 10:44 PM
Good point. We'll assume at the moment that we don't have any optical illusions/effects going on here. If that rainbow-colored cloud was the actual shock, then I dont believe that you would see it through condensation because the pressure increases through the shock (pressure has to drop to support condensation). If there's a rainbow, then there must be condensation or water vapor droplets to create the rainbow.
I don't really find this argument persuasive since there are other ways besides droplets to get scattering.
This condensation is only created by a drop in local pressure. So, all this doesn't support that we are seeing the shock in this image. Plus we don't see the bow shock which would also be seen if there was a Schlieren effect here.
On the other hand, I find this argument very persuasive. If this is a shock, where is the bow shock! Case closed in my mind - P-G singularity caused the rainbow - makes more sense to me.
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it is the classic P-G singularity
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If you take a look at the SRB aft camera films, facing forward you can see the Schlieren shadows of the shock wave forming and moving aft along the surface of the wing. It's a shadow in the form of a thin line. Not nearly as impressive as a vapor cloud.
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chksix - 24/6/2007 4:03 PM
That image is "desktopped" as of now!
Raw power defined!!
I second that.
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meiza - 25/6/2007 6:10 AM
Not from video but from a 35mm cinema film reel.
Videofilm is a term in the photo industry. It means high speed film, say 500fps. That's what this was. A still from a high speed camera.
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Ah ok, I thought video was magnetic tape, ie, versus film which is pictures.
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Lee Jay - 25/6/2007 5:54 AM
terynd - 24/6/2007 10:44 PM
Good point. We'll assume at the moment that we don't have any optical illusions/effects going on here. If that rainbow-colored cloud was the actual shock, then I dont believe that you would see it through condensation because the pressure increases through the shock (pressure has to drop to support condensation). If there's a rainbow, then there must be condensation or water vapor droplets to create the rainbow.
I don't really find this argument persuasive since there are other ways besides droplets to get scattering.
There are other ways to get scattering (dust, ice, etc) but since the scattering is localized in this case, only condensate droplets are reasonable.
This condensation is only created by a drop in local pressure. So, all this doesn't support that we are seeing the shock in this image. Plus we don't see the bow shock which would also be seen if there was a Schlieren effect here.
On the other hand, I find this argument very persuasive. If this is a shock, where is the bow shock! Case closed in my mind - P-G singularity caused the rainbow - makes more sense to me.
As far as I am aware, I don't think there is any natural "Schlieren effect." You can certainly visualize shocks (and other density gradients {technically the second derivative of density for shadowgraphs and the first derivative for Schlieren}) through the shadowgraph technique using the sun as a light source, however. Maybe this is what you are referring to.
My take on the origins of the various vapor clouds:
The shuttle is transonic in this image, meaning that the local flow over the shuttle is supersonic in some regions and subsonic in others, but the vehicle is traveling slower than the speed of sound. Because the vehicle is subsonic, there is no bow shock being generated, so even if there were some way to tell it was there, you wouldn't find one (shocks arent normally visible). Amplification of the low pressure regions (behind the cockpit windows, behind the rudder, and behind the SRB nosecones) by the Prandtl-Glauert singularity causes the condensation clouds to appear there.
The rainbow cloud is similarly formed. The subsonic/supersonic interplay generates a number of fairly weak shock waves originating at various locations on the vehicle. These shocks do induce a local rise in temperature and pressure, but because of the inertia of the gas, there is a rarefaction wave behind the shock (the rarefaction wave is necessary to cancel the shock at a finite distance from the vehicle since the vehicle is subsonic overall) that actually pulls the local pressure (and temperature) below the ambient values over a small region, before they rise back to ambient. When this low pressure is amplified by the Prandtl-Glauert singularity, it can induce condensation as is seen here, although you can compare the density of the condesation clouds behind the shock and behind the other cloud generating areas (e.g. cockpit) to get an idea of the relative pressure drop in each location and see that the pressure drop behind the shock is pretty low. I suspect the reason the fainter shock cloud is producing the visible rainbow is just that it is sparse enough to allow most of the light through and it is far enough from the vehicle to have direct illumination at the necessary angle.
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Yeah, lots of people have probably seen the pictures of a transonic hornet with the condensation clouds and mislabeled as "breaking the sound barrier".
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Worse, I had an email forwarded to me earlier that showed pictures like these, and claimed you were actually "seeing the sound barrier."
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I have seen them too. It's really sad. With these technical things, people usually grasp the easiest thing within their reach and understanding, and spread that misinformation to others which is unfortunate. Aerodynamics is far from intuitive.
Andrewwski - 26/6/2007 10:03 PM
Worse, I had an email forwarded to me earlier that showed pictures like these, and claimed you were actually "seeing the sound barrier."
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Here is a video of the same effect from youtube- identified as sound barrier. Right or wrong, still a neat video.
http://www.youtube.com/watch?v=Gn5odETw3Yc
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Yep, nice video. Shame it's surrounded by the dumbnesss of youtube. I lost brain cells reading some of the comments.