When I see the SpaceX reentry videos I see no flaming ionization from the time the reentry starts. I realize things must be getting hot at some point but its not the ball of fire I imagined . Where should I be seeing this or its probably not as I imagined. Anybody got any observations.
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3 Answers
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Assuming you are referring to videos that end with a landing, you are only seeing the first stage. Even without the boostback burn it is relatively slow - less than 2 km/s.
The second stage gets up to actual orbital speeds, around 7 km/s, and that does turn into a fireball on reentry.
answered Feb 19, 2017 at 22:38
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Quentin Clarkson's answer is correct; the first stage doesn't get fast enough to create a dramatic reentry fireball.
However, if you look at this video -- sped-up footage from the top of the first stage, looking down -- you can see at around 0:15-0:20 that the grid fins are getting charred from the heat of reentry.
In the real-time feed in a different video, the first reentry burn occurs at 7:00 to 7:19 or so. After the reentry burn shutdown call the fins are a light gray with soot. At 7:26 there's a glint on the fin at the left of the frame -- possibly burning paint. Around 7:30 the frame is starting to gray out, with black flecks hitting the camera, while the engines are not firing. 7:35 is completely grayed out. We're still far above clouds, and around 7:40 the realtime downlink is lost, I assume because of vibration. It's another full minute before the first stage landing burn.
Comparing that sequence of events to the (uninterrupted) high-speed video you can see the burn from 0:13-0:14, light gray grid fins, then the gray-out from 0:15-0:16, and blackened grid fins at 0:18 shortly after the live feed dropped out. Something blackened them and it wasn't a main engine burn!
answered Feb 19, 2017 at 23:59
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$\begingroup$ Yeah I can see the charring the grid fins but is that blowback from the rockets firing to slow the first stage down? On some of the landed first stages you can see smudging along the lower portion or some of the logo's degraded. So I am wondering is the exhaust or the friction or some combo of the two. Thanks for your reply. $\endgroup$ Feb 22, 2017 at 4:52
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$\begingroup$ I believe it's reentry heat; I'll expand the answer to explain why. $\endgroup$ Feb 22, 2017 at 5:38
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$\begingroup$ During the SES-10 launch on 3/30/2017 SpaceX said the video dropout during initial reentry was due to losing line of site communications to the Cape. $\endgroup$ Mar 30, 2017 at 22:42
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They do three burns.
- Boostback burn to cancel forward velocity (for ASDS landings) or to head back to the Cape to land at LZ-1/LC-1.
- Re-entry burn to control the speed and interface with the atmosphere.
- Landing burn.
The Boostback burn is too high usually to have much atmospheric effects.
The Re-Entry burn is the one you would likely see it, but it seems they control the speed sufficient to avoid it.
