# How do rockets “blow” smoke rings? Did “smashing through Max-Q” really do this?

The Teslarati article SpaceX delivers largest commercial satellite in kick off of Falcon 9 marathon includes several beautiful photos, of the Telstar 19V launch, including the one below.

It shows what looks like a "smoke ring" or vortex ring. Without video though, it's hard to be sure that it's a proper vortex ring which should show some rolling motion around the circe of the torus.

While the caption for the image says:

B1047 created an extraordinary ring vortex rainbow as it smashed through Max Q, the point of highest aerodynamic stress on the rocket.

I don't see how this could be an explanation. Dramatic things do happen when one crosses mach-1 or "the sound barrier" (see image and linked discussion below, there is no "barrier", no barriers were harmed in the making of this photo) but reaching the maximum of something, or any extremum or inflection point implies a leveling off of something, where the first derivative is zero and nothing "suddenly happens". Max-Q becomes a fuzzy concept when a realistic rocket at a non-zero angle of attack is considered, and the total aerodynamic loading needs to be integrated over the entire craft, and not just the point of a theoretical nose cone.

Question: So I'd like to understand better if this is really a vortex ring to begin with, and if so, what caused it, and if the "instant of Max-Q" is really when it happened and "smashing through" it is the cause.

above: "B1047 created an extraordinary ring vortex rainbow as it smashed through Max Q, the point of highest aerodynamic stress on the rocket. (Tom Cross)" From here.

click each for full size

above left: Vortex Ring Toy. "A smoke ring being produced by a modified, smoke-filled garbage bin" from here

right: From Atlas Obscura's The Wildly Misunderstood Aeronautics Event Captured in This Photograph. See also NASA's NTRS 19950024579 Patterns in the sky: Natural visualization of aircraft flow fields.

• An additional example, with some unsupported theorizing about shockwaves illuminated by a fortunate lighting / viewing angle reddit.com/r/spacex/comments/2apsce/… – Saiboogu Jul 23 at 3:57
• @Saiboogu Interesting! Watching the launch video Max-Q happens at about T+01:17 or only about 16 seconds after passing mach-1. Since they happen so close in time, it is possible that some reporting here or there is conflagrating the two. I don't think Max-Q has any particular shock-wave associated with it. – uhoh Jul 23 at 5:38
• I agree, Max-Q is more of a milestone in the data than a physical event, but there is a lot going on around then. – Saiboogu Jul 23 at 14:03
• Everyday Astronaut just discussed this in his latest video - seems a pretty solid explanation! I can write up an answer tomorrow if nobody else fancies it – Jack Jul 23 at 21:35
• @Jack very nice find, and very nicely explained there indeed. Thank you! – uhoh Jul 23 at 22:01

This is not directly caused by 'breaking the sound barrier', and also doesn't seem to be an example of a typical vortex ring as shown in the question.

More likely it occurred as Falcon 9 passed through a particularly humid layer of the atmosphere. This, combined with the low-pressure region behind the vehicle, causes water from the engine exhaust to condense into a visible cloud.

The spectacular light show was presumably caused by the engine back-lighting being refracted through the cloud, creating a rainbow effect.

Tim Dodd gave a good explanation of the phenomenon in a video.

This is similar to a vapour or shock cone which occurs when existing water condenses in the low pressure region following the shock front of a body passing through air at transonic velocities. The main difference here is that vapour cones are always connected to the feature creating the shock wave, whereas this example is clearly detached from the vehicle.

This localised condensation in the wake of launch vehicles (and airliners) it quite a common sight since they rapidly pass through many different layers of atmosphere, therefore encountering very varied levels of local humidity.

A particular clear example of this is from the launch of the Solar Dynamics Observatory in 2010:

Image credit: Nancy Atkinson

• This looks really great, thank you! – uhoh Aug 2 at 8:26