The idea of using the legs as a governor was facetious, for the record.
Designing and debugging aero surfaces that really work for controlling the reentry ( unless its passively stable, which it obviously isnt ) is no small task. "Just add fins" or "use your legs, Luke" are pretty simplistic non-answers.
Have we seen this video yet?
Thanks for posting! Mighty interesting stuff going on after stage separation....
Some insider info:
The attitude control system was railed, wanted more thrust, but engines couldn't provide anymore. Doubts that they would solve it by stockpiling more RCS fuel.
Me:
Apparently there was so much aero roll that the RCS couldn't dampen it away. They probably just need to make some changes to the outside aero surface to fix things. I doubt they'll add pop out fins though.
Wonder if forcing a slight change in AOA one way or the other would also change the aerodynamically induced roll?
Also, curious if the roll was actually helping stability during re-entry and higher in the atmosphere?
If so, it might be better to bite the mass bullet and increase RCS capability instead of aerodynamic options.
What is the current RCS implementation on F9 1.1 First stage? Cold Gas? Dracos?
Aerodynamic options are more challenging, but not impossible. This is where GH2 flights could really help.
Have we seen this video yet?
Thanks for posting! Mighty interesting stuff going on after stage separation....
Looked like first stage RCS firing maybe, for flipping over.
Have we seen this video yet?
Thanks for posting! Mighty interesting stuff going on after stage separation....
Indeed! Very cool. Also interesting how clearly visible the contrail of each outside engine is as the plume widens near stage separation.
The rapidly expanding bubble is probably the MVac ignition.
But the pulses that follow are very cool, and could be from the S1 relighting or reorienting itself. But those thruster firing are much more visible than I expected cold gas thruster to be.
It could also be some sort attitude jets on the upper stage - now that the upper stage doesn't use the turbo pump exhaust for roll control anymore.
But the pulses that follow are very cool, and could be from the S1 relighting or reorienting itself. But those thruster firing are much more visible than I expected cold gas thruster to be.
I was watching through binoculars and it seemed like the pulses continued sporadically for a while as the two dots moved apart -- I think they continued after it drifted out of frame in this video. Unfortunately, I wasn't filming, so I don't know for sure.
I was really surprised that any kind of thrusters would be visible after staging through hand-held binoculars.
Sun light glinting off of the inner stage?
Have we seen this video yet?
Thanks for posting! Mighty interesting stuff going on after stage separation....
Looked like first stage RCS firing maybe, for flipping over.
Cool - definitely RCS of the first stage controlling it after sep. RCS jet pulses clearly visible.
At the end of that video my only reaction was "why did you stop filming! the interesting bits were still to come!"
The difference in the flame on the bottom of the rocket is because this mission was such a light load for a rocket with more thrust, the rocket also accelerated off of the pad at a greater rate
Maybe I'm just "seeing things", but I got the impression that the v1.1 flame exhaust is significantly tighter (& longer) than the v1.0 flame exhaust - see attached comparison image. This would indicate the improved efficiency, right?
On the other hand the difference could be an optical illusion caused different light conditions, camera exposures, and atmospheric conditions.
Quite possibly an effect of GG exausts; dispersed outside the main flow in v1.0, inside the main flow (then forced to stay compact) in v1.1.
Maybe I'm just "seeing things", but I got the impression that the v1.1 flame exhaust is significantly tighter (& longer) than the v1.0 flame exhaust - see attached comparison image.
I'm thinking it was down to these reasons:
1) the v1.1 is sufficiently longer that the CoG shifts a bit forward away from the engine section
2) the engine section itself is less massive, additionally moving the CoG higher up the vehicle
These two things make it possible for the outboard engine vectors to point less outward than on v1.0 (watch some closeup footage of the engine nozzles before flight) in order to pass through the CoG (for control reasons). It's not clear to me if v1.1 cants the outer ring outward at all or if they all just thrust straight "up".
A third thing is the engine section is simply more tightly packet than the rectangular arrangement of v1.0
But yes, that flame is frickin' long. As long as that vehicle is, the flame is even longer
Another neat image, one of the ones that Helodriver linked to in a recent post, is very neat. It is really amazing how clearly the octaweb engine arrangement shapes the plume in such a distinctive way:
Maybe I'm just "seeing things", but I got the impression that the v1.1 flame exhaust is significantly tighter (& longer) than the v1.0 flame exhaust
Quite possibly an effect of GG exausts; dispersed outside the main flow in v1.0, inside the main flow (then forced to stay compact) in v1.1.
Bingo
These two things make it possible for the outboard engine vectors to point less outward than on v1.0 (watch some closeup footage of the engine nozzles before flight) in order to pass through the CoG (for control reasons). It's not clear to me if v1.1 cants the outer ring outward at all or if they all just thrust straight "up".
There's no need to point all (or any for that matter) engines through CG in any cluster, only resultant net force vector.
Quite possibly an effect of GG exausts; dispersed outside the main flow in v1.0, inside the main flow (then forced to stay compact) in v1.1.
I agree, it should be the GG exausts toward the inner that fully burn and "improve" the plume
There's no need to point all (or any for that matter) engines through CG in any cluster, only resultant net force vector.
There is if you don't want sudden disturbances after an engine out. Lose an engine and even though the rest of the engines are still firing up and the total vector is still up, the "hook" of the thrust vector is no longer along the vehicle centerline which means the total thrust vector is also no longer pointing through the CoG and you get a torque.
There's no need to point all (or any for that matter) engines through CG in any cluster, only resultant net force vector.
There is if you don't want sudden disturbances after an engine out. Lose an engine and even though the rest of the engines are still firing up and the total vector is still up, the "hook" of the thrust vector is no longer along the vehicle centerline which means the total thrust vector is also no longer pointing through the CoG and you get a torque.
Which would cause a sudden pitch, which would be detected and immediately countered by the control system. Something that long, with that much aerodynamic pressure can't rotate that fast.
Which would cause a sudden pitch, which would be detected and immediately countered by the control system. Something that long, with that much aerodynamic pressure can't rotate that fast.
The center of pressure for a vehicle is typically above the center of gravity, making vehicles inherently aerodynamically unstable. This sudden pitch and angle-of-attack increase can spell disaster if it happens at max-Q. Having each individual engine thrust if not through the CoG, at least *closer* to the CoG does improve controlability. If all vehicles were capable of correcting attitude disturbances that promptly, I assume they also wouldn't be worrying about things like wind shear at altitude, etc.
There is a good reason they did that on v1.0. Heck, even a Zenit vectors out the individual nozzles of the RD-171 immediately after liftoff, despite having only one engine.
Which would cause a sudden pitch, which would be detected and immediately countered by the control system. Something that long, with that much aerodynamic pressure can't rotate that fast.
What he said. Plus there's sudden disturbance, no matter what. Net vector would change even if you were pointing all engine through CG so you have to do TVC to point it towards intended trajectory.
There is a good reason they did that on v1.0. Heck, even a Zenit vectors out the individual nozzles of the RD-171 immediately after liftoff, despite having only one engine.
Sources please.
