Russian R7 (Soyuz) Exterior Launch Footage

[Eric Mc]

First time this type of video footage has been possible from an R7 as far as I know. Watch for the separation of the sustainer rockets - even more spectacular than the SRB sep on the Shuttle.

http://spaceflightnow.com/soyuz/vs07/video/

[rufusruffcutt]

Thanks for posting that up Eric. I find it remarkable how stable the camera is with all the vibrations of a launch. Also, how the exhaust plume changes colour and shape the higher the rocket climbs through the atmosphere.

[Fugazi]

rufusruffcutt said:

Also, how the exhaust plume changes colour and shape the higher the rocket climbs through the atmosphere.

In a nutshell, the pressure of the flow right at the exit of the nozzle and the ambient air will change as the rocket climbs through the atmosphere. At launch the flow tends to be slightly 'over-expanded' so that the pressure of the gas at the exit is below ambient whereas at higher altitudes the flow is 'under-expanded' so when it leaves the nozzle it immediately expands and so the plume looks bigger.

The only way to compensate for this is to change the rocket nozzle geometry during the flight, but the operating conditions are awful and doing this mechanically is very difficult. There are very, very, very high flow speeds and temperatures that you have to deal with while also trying to keep the engine weight and complexity down, so it's just something that you put up with. If you look at the latter stages of something like the Apollo rockets, the rocket nozzles had huge exit diameters in comparison to the throat (narrowest section of the nozzle), unlike the first stage which is more modest, due to the different operating ambient pressures that each engine will experience.

There was/is some research on a type of rocket nozzle called an Aerospike, which is self compensating when it comes to the change in pressure ratio between the nozzle and the ambient pressures, but nothing beyond a few test engines and some sounding rockets have ever been built.

[rufusruffcutt]

Cheers for that Fugazi