There's an interesting photo at http://mit.zenfs.com/1555/2013/10/Hopkins-Space-Cloud.jpg. (Story at http://ca.news.yahoo.com/blogs/geekquinox/strange-space-cloud-turns-russian-ballistic-missile-launch-151349176.html)
The Russians were testing a Topol ICBM and the exhaust plume was seen and photographed from the ISS, so this is a shot of the expansion of a rocket plume in vacuum as seen from space. Given it's a modern ICBM and likely quite fast-burning, odds are we're seeing the final propulsive stage burn here. (There would likely be later fine correction guidance burns.)
I think this image can be viewed to a considerable extent as a velocity profile for the exhaust plume of the stage in vacuum.
Look at the photo and you can see a distinct four-lobed structure, along with a central void. I speculate that the central void is because the stage cut off shortly before the photo was taken - the expanding gas should behave mostly ballistically in vacuum; the inner surface of the void (and the forward surface of the cloud in general) plausibly is the gas from the very end of the burn expanding away from the point in space where it came from the nozzle.
The four lobes are probably from the guidance system - from http://en.wikipedia.org/wiki/RT-2PM_Topol, "During first stage operation the flight control is implemented through four aerodynamic and four jet vanes. Four similar trellised aerodynamic surfaces serve for stabilization. During the second and third stage of flight gas is injected into the diverging part of the nozzle for flight control."
Topol is a 3-stage solid fuel rocket; it seems reasonable to assume that the gas injection for upper-stage steering is also quadrilateral, for guidance electronics compatibility with the first-stage steering system. The four lobes visible in the plume are thus likely an artifact of the steering system.
(And what does this have to do with ARocket? Well, you can sometimes tell a surprising amount about what a rocket engine is doing from the right plume imagery; it can be a useful tool. And, well, it's a cool rocket photo, something I think is its own justification...)
Henry hvanderbilt@xxxxxxxxxxxxxx
