Re: Three Axis Control with a Two Axis Controller (Re: Falcon first stage finished)

.... and, some more on Three Axis Control with a Two Axis Controller;

....In a nutshell, the data shows that the increasing oscillation of the
second stage was likely due to the slosh frequency in the liquid oxygen
(LOX) tank coupling with the thrust vector control (engine steering)
system. This started out as a pitch-yaw movement and then transitioned
into a corkscrewing motion. For those that aren't engineers, imagine
holding a bowl of soup and moving it from side to side with small
movements, until the entire soup mass is shifting dramatically...
http://www.spacex.com/updates.php#demoflight_2_prelim_review_2
"corkscrewing motion", looks like it was a Vortex Slosh Mode that
overpowered the roll control thuster. Now, move the bowl of soup in a
circle and add a hole in the bottom of the bowl.

Just prior to T+5:00 minutes the Slosh Vortex overpowered the Helium Roll
Control Thrusters. The vehicle was out of Roll Control Authority. Maximum
Helium Thruster Roll Moment = Vortex Slosh Rolling Moment. After that, the
Slosh Vortex was in control of the Vehicle. Notice the Islands begin to
roll and accelerate in roll at T+5:00 minutes. Loss of control in Pitch and
Yaw occurring 10-15 seconds later at >180 degrees roll. Kind of makes me
wonder if the flight control switched directions and started commanding the
Helium roll thruster in the direction of the Vortex Slosh moment. 180
degrees is where the Roll Attitude Error would switch signs. But, the Roll
Attitude Rate Error should have been huge and prevented the Roll Command
from switching signs. If the Roll Command did switch signs with the Roll
Attitude Error, they should probably fix that too. Loss of Pitch and Yaw
Control should have been due to the gimbals running out of control
authority (banging the hard stops, or maximum gimbal rate exceeded), not
the Roll Command switching signs.
http://youtube.com/watch?v=by-iwbgkaIA
Also, at T+4:09 it looks like a piece of the ablative throat falls off.
Another right next to it at T+4:12, and then they merge together. Note the
growing (glowing) hot spot on the nozzle near the throat. Possibly due to
the nozzle impact, delamination/damage to the ablative?

--
Craig Fink
Courtesy E-Mail Welcome @ WeBeGood@xxxxxxxxx
--

john hare wrote:

Actually I don't have the time, inclination, and communication
skills to post and defend them.

Like laser launch from asteroids for bulk material
return. A case could be made for it, but why.

Sounds interesting. Maybe someday we'll talk about my super light weight
rocket engine, it's similar to your turbojet. Just a guess, but has the
potential to double (possibly more) the thrust to weight of a conventional
rocket engine. Also, has a bunch of technical (real world) issues, but the
concept looks good to me. The super light weight rocket engine has about a
half a dozen new (or not so new) concepts in it. I was going to go the
Space Access for the first time this year (that would have been an
interesting discussion), but when you and Henry weren't going, I had no
reason to, and decided not to. Meeting people in person is important, to
see if they are real people. Our perception of others is shaped by many
things, USENET discussions are quite limiting.

.

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