(Badwater Bill) wrote in message . ..
Not knowing the particular vehicle, we can only speculate, but it's
fairly common to use verniers - nozzles mounted at an angle - for
steering and control. Fins don't do much at that altitude.

That's what I was thinking. It was a minuteman rocket. Does the
Minuteman have four nozzels?

Not according to this:
http://www.wpafb.af.mil/museum/engines/eng66.htm

Other launch photos:
http://pirlwww.lpl.arizona.edu/~jscotti/rocket.html
http://home.earthlink.net/~kd6nrp/msls-ift-3-3.htm shows the X-shaped
plume

According to this: http://www.designation-systems.net/dusrm/m-30.html
the Minuteman has a single engine in each stage.

That's all I can find. The photo at earthlink confirms the X-shaped
exhaust, but I can't find a reason for it.

But hey - this is interesting (adding 'steering' to the google
search-term list) http://groups.yahoo.com/group/space-.../message/32302
:

""The Rocket" by David Baker say Nitrogen Tetroxide ... is injected
into
the SRB nozzle to change the shockwave pattern and therefore the
exhaust
plume to give a limited thrust-vectoring for steering. "

So maybe that's it!