PJ2
At 1:20 in the video with the aft-looking camera linked in the post above there's a crew remark, "auto-dump" and a cloud of gas is seen leaving the ship; it occurs again at 02:30 into the video and I suspect that's unburnt fuel and/or oxidizer. It doesn't appear to be dumped from the engine from from behind the tail-camera.
Thanks, triggered me to looking further into that.
( video
https://www.youtube.com/watch?v=0mCFxAsmnk0 )
This is what I see and what I think I hear.
0:44 End of motor burn observed
0:53 "There comes ullage"
Fumes observed on centre line, appear to be coming from rotor nozzle
(flushing motor fuel grain clean? dumping of remaining oxidiser?)
1:15 "Feather up"
1:18 Feathers observed coming up
1:20 "Feather dump"
A cloud observed escaping on port side for next 3 seconds
(venting of air from pneumatic feather actuator?)
(with water vapour condensation?)
!:47 "OK feathers down"
2:11 Feathers observed coming into view
2:17 Feathers observed down
2:26 "Autodump are on"
Cloud observed escaping on port side until end of video
Fumes appearing to come from nozzle may actually be excess oxidiser being dumped through the motor (without burning the fuel, flow started well after end of motor burn).
The oxidiser is nitrous oxide, liquid or gaseous.
The fuel is a solid.
BTW the plume from the motor burn can be observed around 0:50 just after end of motor burn, with a slight cork-screw twist due to roll oscillation in last stage of the burn.
At 1:26 the plume can be seen again, twist seems to have further expanded.
Around 2:00 the plume top is seen rising through the horizon, that 1:15 of coasting parabolic flight at that time.
Amazing footage.