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The Atlas V that carried the Solar Dynamics Observatory into orbit on 11 Feb. 2010 created shockwaves that rippled through a cloud layer. I’ve counted 11 distinct shockwaves, marked by arrows in this image.

Ok, this has little if anything to do with security or arms control (well, perhaps a little) but it is such fun that I couldn’t resist writing about it. And it is certainly very educational. There is a very fun video of the Solar Dynamics Observatory launched on February 11, 2010. In that video (and in the image above) you see the SDO’s Atlas V launch vehicle passing through a cloud layer, with shockwaves radiating out. Of course, the shockwaves are generated by the missile and the cloud layer is only providing a way of seeing them. In fact, what is visible is not a single shockwave radiating through the cloud layer but rather multiple shockwaves passing through the layer. As these shockwaves “follow” the missile, each point of intersection with the cloud layer moves outward. I’ve tried to indicate this with the cartoon below:

Shockwaves are formed at “discontinuities” along a rocket’s airframe. They radiate energy away from the point on the missile where they are created. As the missile moves along, this constant creation of shocks form what appears to be a continuous “cone” that trails along the rocket. The angle the cone makes with the rocket is therefore related to the rocket’s speed. Of course, the more discontinuities there are on the airframe, the more shockwaves are formed and the more energy is radiated away. That, by the way, explains why the “baby-bottle nose cone” of the Ghadr (also sometimes know as Shahab-3B and various other names, I wish we could all agree on names) has a higher drag coefficient than the simple cone on a Nodong or Shahab-3. Of course, as my friend and fellow former UNMOVIC inspector, Mike Elleman points out, the baby bottle shape allows the weight to cross sectional area of the detached warhead to be increased. This ratio is also know as the ballistic coefficient or Beta of the warhead and allows both a faster reentry and a more stable trajectory.

I’ve been able to make a rough correspondence between the number of discontinuities on the Atlas V and the number of shockwaves visible in the cloud layer. (See the image at the top of this post as well as the images to the left.) Of course, not all discontinuities make shockwaves that are visible around the entire vehicle. For instance, the vehicle’s airframe shields a whole hemisphere from a shockwave caused by a pipe sticking out on one side. But this correspondence is close enough to really illustrate this physical process.

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