Curious Phenomena In Shuttle Launches Options

[ugordan]

The arm-waving speculation I've had for these features is that they're due to the line-of-sight from the tracking camera to the shuttle is crossing some overhead wires some tens of meters from the camera.

How would that explain that the lines are perpendicular to the shuttle motion and the fact they seem to dance around themselves as well?

[Bob Shaw]

I'd say that the bright lines and spikes are created by internal reflections in the optical tracking system, and that they move around because the optical elements also move in order to track the Shuttle stack. The flaws in the image are only seen where there is very bright light, unlike in the Thrust SSC photo. You might well, for example, be seeing light reflected off cross-hairs in an off-axis aiming device.

Bob Shaw

[ugordan]

I'd say that the bright lines and spikes are created by internal reflections in the optical tracking system, and that they move around because the optical elements also move in order to track the Shuttle stack. The flaws in the image are only seen where there is very bright light, unlike in the Thrust SSC photo. You might well, for example, be seeing light reflected off cross-hairs in an off-axis aiming device.

Again, why would the lines be perpendicular to the shuttle motion vector?
The "flaws" are seen regardless of the brightness and they very much look like refraction patterns. I could buy the idea of optical artifacts if the lines behaved more orderly, however, they seem to follow the shuttle one moment and start to lag behind or overtake the orbiter the next (simultaneously with other lines appearing and NOT doing the same thing).
One thing's for sure: they appear to be located much closer to the camera as they aren't suffering from atmospheric turbulences as much as the actual orbiter is.

At what time after liftoff does the shuttle actually become supersonic? It would be a big benefit if there were another long range tracker footage that could show the same effect from a different angle.

[helvick]

I could buy the idea of optical artifacts if the lines behaved more orderly, however, they seem to follow the shuttle one moment and start to lag behind or overtake the orbiter the next (simultaneously with other lines appearing and NOT doing the same thing).
One thing's for sure: they appear to be located much closer to the camera as they aren't suffering from atmospheric turbulences as much as the actual orbiter is.

These are tracking cameras and they are not absolutely perfect in their targeting - the position of the orbitor within the frame will move as will the orientation of the camera relative to the orbiter so the effect as you describe it could be artifacts of the lens optics.

[ugordan]

Sorry for resurrecting a long-dead thread, but I've just been watching the STS-115 chase plane footage (found on www.insideksc.com) and I saw what undeniably have to be shockwaves. Below's a screenshot from an enhanced clip, the clip's a bit noisy due to contrast enhancement, but refraction (shock "hooks") of the background clouds is readily apparent. This happened some time after Mach 1 transition and some condensation can still be seen sticking to the orbiter and SRB nosecone.


Click on the image for a short, slowed down Quicktime clip.
It would thus appear the groundtracker views showing the same effects are not artifacted.

How cool is this?

[helvick]

Seems like pretty compelling evidence that what we saw before actually are sonic\transsonic\supersonic shock waves. I suppose these are a sort of standing wave supersonic shock front ?

[stevesliva]

Made me think of "vapor cones"
http://en.wikipedia.org/wiki/Prandtl-Glauert_singularity

[ugordan]

Nope, Prandtl-Glauert singularities have a very narrow Mach range when they can occur, something like Mach 0.95-1.05 so for a rapidly accelerating vehicle they're very shortlived. In most shuttle launches it can't even be seen if the air isn't humid enough. During this launch, the singularity came a while earlier:

That's actually the point I referred to as the Mach 1 transition in the previous post.

A rare image showing the singularity as a faint disc:

[stevesliva]

Neat! Conclusively something else.

[helvick]

Seems to be an attached supersonic shock wave made visible because of the effect it has on the refractive index of the air rather than the condensation cloud that makes the Prandtl-Glauert singularity visible.

Wikipedia's Shock Wave Entry:

Attached shock

• These shocks appear as "attached" to the tip of a sharp body moving at supersonic speeds.
• Examples: Supersonic wedges and cones with small apex angles
• The attached shock wave is a classic structure in aerodynamics because, for a perfect gas and inviscid flow field, an analytic solution is available, such that the pressure ratio, temperature ratio, angle of the wedge and the downstream Mach number can all be calculated knowing the upstream Mach number and the shock angle. Smaller shock angles are associated with higher upstream Mach numbers, and the special case where the shock wave is at 90 degrees to the oncoming flow (Normal shock), is associated with a Mach number of one. These follow the "weak-shock" solutions of the analytic equations.