APOD: The Falcon 9 Nebula (2018 Oct 12)

Comments and questions about the APOD on the main view screen.
User avatar
APOD Robot
Otto Posterman
Posts: 3326
Joined: Fri Dec 04, 2009 3:27 am

APOD: The Falcon 9 Nebula (2018 Oct 12)

Post by APOD Robot » Fri Oct 12, 2018 4:09 am

Image The Falcon 9 Nebula

Explanation: Not the Hubble Space Telescope's latest view of a distant planetary nebula, this illuminated cloud of gas and dust dazzled even casual U.S. west coast skygazers on October 7. Taken about three miles north of Vandenberg Air Force Base, the image follows plumes and exhaust from the first and second stage of a SpaceX Falcon 9 rocket rising through southern California's early evening skies. In the fading twilight, the reddish smoke drifting in the foreground at the right is from the initial ascent of the rocket. The expanding blue and orange filamentary plumes are from first and second stage separation and the first stage boostback burn, still in sunlight at extreme altitudes. But the bright spot below center is the second stage itself headed almost directly away from the camera, accelerating to orbital velocity and far downrange. Pulsed thrusters form the upside down V-shape at the top as they guide the reusable Falcon 9 first stage back to the landing site.

<< Previous APOD This Day in APOD Next APOD >>

Iksarfighter
Asternaut
Posts: 5
Joined: Sat Dec 24, 2016 7:13 pm

Re: APOD: The Falcon 9 Nebula (2018 Oct 12)

Post by Iksarfighter » Fri Oct 12, 2018 6:53 am

Is that illuminated by the Sun cause it is very high ?

heehaw

Re: APOD: The Falcon 9 Nebula (2018 Oct 12)

Post by heehaw » Fri Oct 12, 2018 8:46 am

Wow, at my first glance I thought that this was an ASTRONOMICAL photograph, and it had a truly weird nebulosity! Whew!

User avatar
Case
Commander
Posts: 578
Joined: Sat Jun 09, 2007 10:08 pm
Location: (52°N, 06°E)

Re: APOD: The Falcon 9 Nebula (2018 Oct 12)

Post by Case » Fri Oct 12, 2018 11:55 am

Did SpaceX time it for noctilucent vapor, or what? I don’t recall these light shows from pre-2010 launches …

User avatar
Chris Peterson
Abominable Snowman
Posts: 13965
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: The Falcon 9 Nebula (2018 Oct 12)

Post by Chris Peterson » Fri Oct 12, 2018 2:10 pm

Case wrote:
Fri Oct 12, 2018 11:55 am
Did SpaceX time it for noctilucent vapor, or what? I don’t recall these light shows from pre-2010 launches …
The plume shape with these recent launches is different, but growing up in southern California, I remember many launches from Vandenberg that produced similar noctilucent displays, going back to the late 1960s.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
MarkBour
Subtle Signal
Posts: 739
Joined: Mon Aug 26, 2013 2:44 pm
Location: Illinois, USA

Re: APOD: The Falcon 9 Nebula (2018 Oct 12)

Post by MarkBour » Fri Oct 12, 2018 7:07 pm

This is a lovely, artistic view of the launch. I'm glad for the caption, I never would have sorted it out. There are a couple of things I wonder about as I gaze at this "nebula". First, why is the most central part of the exhaust a distinct brown color, highly differentiated from the outer white and blue region? It appears that the brown exhaust is higher up (farther from the camera). Second, I did not know that the Falcon return burn involved pulsed thrusting. Why do they do that? Does it happen too fast for the naked eye to see that pattern?
Mark Goldfain

User avatar
Chris Peterson
Abominable Snowman
Posts: 13965
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: The Falcon 9 Nebula (2018 Oct 12)

Post by Chris Peterson » Fri Oct 12, 2018 7:43 pm

MarkBour wrote:
Fri Oct 12, 2018 7:07 pm
This is a lovely, artistic view of the launch. I'm glad for the caption, I never would have sorted it out. There are a couple of things I wonder about as I gaze at this "nebula". First, why is the most central part of the exhaust a distinct brown color, highly differentiated from the outer white and blue region? It appears that the brown exhaust is higher up (farther from the camera). Second, I did not know that the Falcon return burn involved pulsed thrusting. Why do they do that? Does it happen too fast for the naked eye to see that pattern?
I'm not sure that the pulsed engines seen in this image are from the landing thruster. There are small pulsed rockets used to rotate the landing stage and to maintain its attitude.

That said, the main boosters have to be capable of something like pulsed operation, because the way the landing works is that it basically falls until the last possible moment, and then blasts at extremely high thrust to rapidly bring it to zero velocity just as it reaches the ground. That requires very fast response engines.

I don't know if this is the case with the Falcon rockets, but in many control systems it is easier, more efficient, or more compatible with the hardware involved to simulate analog behavior by some kind of time modulation of a binary output. So in the case of a rocket, you could control thrust by having the engine either on or off, going quickly between those two states as necessary. This would eliminate the need for fancy throttles that can linearly modulate fuel flow, in favor of simple on/off valves. (Again, I don't know if that's what actually is done here, but it could explain the reasoning behind pulsed thrusters.)
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com