- The main engine throttles down during Max-Q: I would love this explanation because I think it is a great, visual demonstration of the concept - but I'm afraid that the main engines blue flame is too dim compared with the SRBs to have such a big effect.
- The angle of the shuttle trajectory changes: This makes the most sense, the change in angle makes the shuttle appear to move slower across the sky (even though it is moving faster), leaving more time to illuminate the film (or ccd) and a resulting brighter spot. An angle change could also make the flame look brighter or dimmer.
Any other ideas? Leave them in the comments.
The photo is by James Vernacotola and it won an honorable mention in the 2012 National Geographic photo contest.
To make my question a little clearer I've added this photo showing the confusing increase in brightness.
Edit: Not even 12 hours after posting we have an answer, thanks to a suggestion by Luke and a helpful link from Eli (see comments). The height of the shuttle at the point of extra brightness was about 20,000 ft. which puts it right in the middle of tropical cirrus cloud altitude resulting in a bright spot even though the actual rocket was not any brighter (likely dimmer).
As this appears to be a long exposure shot, the shuttle would be going significantly slower to start. This would correlate to there being fire in the lower portion of the launch for a longer period of time.
ReplyDeleteIt's moving much, much faster at the top of the curve. You don't even need to think about angle change relative to view direction (though this is probably at play too), just think of it as a parametric curve where the parameter is a function of speed. Also the rockets seem (in my observation) to burn more cleanly at higher altitudes, but that could also be a function of increased speed of the shuttle and decreased resistive force from the atmosphere.
ReplyDeleteHey everyone, the confusing part is the *second* bright peak at high altitude.
DeleteAh, that? That's probably the engines lighting up local cloud cover as the shuttle passes through. Something like the effect shown here https://plus.google.com/u/0/photos/+TreyRatcliff/albums/5623042490481885105/5795228684127618706 but more localized. You can see the thin cloud layers in the sunset. See also http://www.travelimg.org/space-shuttle-launch-kennedy-space-center-nasa-usa.html , http://www.floridatoday.com/content/blogs/space/uploaded_images/crb020810-shuttle-2-736500.jpg
ReplyDeleteSomeone else noticed this, too. Check out the discussion (and a labeled picture) on his blog. http://mechanicalintegrator.com/2010/space-shuttle-mystery/
ReplyDeleteAlso, at first I was going to try and estimate the exposure time (and hence when in the flight the second flare up happened) by the movement of the stars across the sky, but then I figured the more sensible thing to do was to look up the exposure time...
ReplyDeleteI plugged in the Google earth file the Nathan found and estimated that the height of the shuttle at that point was about 20,000 which puts it right in the middle of tropical cirrus cloud altitude - so Luke I think you are correct here.
ReplyDelete"Nathan
ReplyDeletePosted February 16, 2010 at 1:33 pm | Permalink
It's about 44 km in altitude at burnout. That's well above 99% of the atmosphere. The brighting continues to maybe about 50km. I can't think of anything off the top of my head that would make any difference at that altitude. It's still not rarefied enough to be super ionized. I have watched SRB videos a lot. But I never saw anything that looks like it would be really bright.
The one thing that I did notice is that separation happened a little later than I thought. I didn't get exact number for this flight for some reason, but it nominally happens at t+2:00 and it looked 5 or 10 seconds late which would put separation right at the brighting in the image. I still don't really have a mechanism for the brightening though, just a correlation."
I couldn't find his file, but his altitude estimate diverges greatly from yours. Though it is the right order of magnitude.
It could be a byproduct of the expansion of the rockets exhaust. The main engines will likely be optimized for full vacuum or very close to it. At launch the exhaust will be under expanded when leaving the nozzle. However, at higher altitude where the pressure drops the exhaust will expand more, possibly resulting in what we are seeing. It could also be a combination of this, the cloud layer it was passing through and other light scattering effects.
ReplyDelete