Falcon first stage finished

Brett Buck wrote:
Recontact at staging - which definitely left a mark. It also
appeared to dislodge something at the flange of the bell which flew
off around the time of fairing sep. It seemed to be an issue with
the first stage whipping out of line rather than a start transient
on the second stage.

I was wondering about that - it did look like it made the second stage
bell move. Is it common to separate like that - the whole
stage+interstage together? The only other staging I've seen is some
old SaturnV stuff where it appeared the stage went, then the
interstage.

rick jones
--
Process shall set you free from the need for rational thought.
these opinions are mine, all mine; HP might not want them anyway...
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

Damon Hill wrote:
Stills from the rocketcam indicate there was a "dirty" staging in
which the first stage contacted the second stage engine bell. The
second stage apparently corrected for the nudge, but may have
developed control problems a minute or so later which may not have
been due to the bump.

Good thing for the rocket cam and the clear images it was able to
convey; it will help with the failure analysis. It looks as though
the second stage engine itself was working okay up to the moment of
loss of signal.

I wonder if it is just coincidence that the bump happened on the side
where the camera happened to be? I wonder if the camera was present
in the sims...

rick jones
--
The glass is neither half-empty nor half-full. The glass has a leak.
The real question is "Can it be patched?"
these opinions are mine, all mine; HP might not want them anyway...
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

On Mar 21, 5:32 pm, Rick Jones wrote:
Is it common to separate like that - the whole
stage+interstage together? The only other staging I've seen is some
old SaturnV stuff where it appeared the stage went, then the
interstage.

If you only have a single engine, yes. The SIVB separation on both
Saturn 1b and Saturn V left the interstage behind.

The SII stage took the interstage along in case of serious thrust
fluctuation between different engines on startup or a total engine
failure, which could cause the engine bells to hit the interstage if
it was left attached to the SIc stage instead. With one engine it
either starts and runs or it doesn't.

Mark

On Mar 21, 11:15 am, Fred J. McCall wrote:
"Jeff Findley" wrote:

:
:"Fred J. McCall" wrote in message
.. .
: Of course, we're all just guessing based on one optical video...
:
:True. Hopefully they've got some good 2nd stage telemetry which will point
:them to the root cause. But this wouldn't be the first time that the
:simulations all looked o.k. but something unforeseen turned up in the flight
:test. It's the unknowns that get you.

Yep. This is why I lean toward it being an actual aerodynamic
instability that is increasing during the flight rather than a pure
G&C 'lag' issue.
The problem got worse later in flight when the rocket was essentially
out of the atmosphere. No 'aerodynamic' there. Could have been
sloshing of the propellant or some other part of the hardware behaved
differently then in the simulator. Still, G&C should have been more
robust - it was obvious long before the end that something is wrong
and getting worse.

Btw, after seeing the build-up of the oscillations, could they command
from the ground the G&C to swith to a different, 'backup' mode, since
the primary mode is obviously not working?

The latter sort of problem DOES tend to show up
during simulation, while finding the former relies on the fidelity of
the aero model and flow fields that you have for your vehicle (which
you have to fly to get and prove out).

--
"The reasonable man adapts himself to the world; the unreasonable
man persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man."
--George Bernard Shaw

On 3/21/07 8:15 AM, in article ,
"Fred J. McCall" wrote:

"Jeff Findley" wrote:

:
:"Fred J. McCall" wrote in message
.. .
: Of course, we're all just guessing based on one optical video...
:
:True. Hopefully they've got some good 2nd stage telemetry which will point
:them to the root cause. But this wouldn't be the first time that the
:simulations all looked o.k. but something unforeseen turned up in the flight
:test. It's the unknowns that get you.

Yep. This is why I lean toward it being an actual aerodynamic
instability that is increasing during the flight rather than a pure
G&C 'lag' issue. The latter sort of problem DOES tend to show up
during simulation, while finding the former relies on the fidelity of
the aero model and flow fields that you have for your vehicle (which
you have to fly to get and prove out).

No aerodynamics involved, it's far too high. After watching it several
times, I would have to guess that it's a fuel swirl/slosh issue.

It was clearly stable at separation and not later. This is not all that
unexpected. The stability margins typically go down as the fuel runs out,
because the inertia goes down, and the gimbal torque/angle ratio goes up
(since the CG moves forward as the stage gets lighter). Both of these raise
the effective system gain, and anything like this will certainly go unstable
if the gain goes up sufficiently. Of course you design it for adequate
margin at the worst-case condition, but if you miss something, like the fuel
slosh "swirl" mode that couples the axes together, you may go unstable. I
would guess that's what happened here.

I would disagree that this couldn't or even wouldn't likely have been
found in analysis. It's a well-understood problem and while it's non-trivial
to come up with a good linear stability model, it's certainly well within
the state of the art. What I suspect, and once again, not to cast any
aspersions on anyone, is that all they did was a bunch of time-domain
simulations. This is very common these days, and very appealing to newbies
since you have enough computing power available to do thousands and
thousands of them in a Monte Carlo procedure. But that's also how you get
caught on stuff like this, as many people have found (the hard way) before.
That's why they call them "start-ups", not an unexpected situation. I have
access to some great reports from the late 50's/early 60's about stuff like
this, let's say they aren't the first people to run into problems like this!
All "not for public discussion" of course.

It's also not all that trivial to solve. It's not insoluble but from
experience it's not as easy as Mr. Musk seems to want to imply. I wouldn't
be surprised if they end up needing more tank baffles. Just dropping the
gain might be possible, but if you didn't see the problem the first time,
you won't know how much to drop it. The first step needs to be to modify the
analysis so it accurately predicts the problem.

I have no idea why they are referring to it as a roll control anomaly. It
was quite obviously going unstable in pitch/yaw long before roll gave up the
ghost.

Brett

On Mar 21, 8:52 pm, Brett Buck wrote:
I have no idea why they are referring to it as a roll control anomaly. It
was quite obviously going unstable in pitch/yaw long before roll gave up the
ghost.

This is odd, and a little disturbing. Also the reference to "clean
staging", when most everyone watching the webcast could see the
interstage hit the Kestrel nozzle and put a pretty big rate on the
second stage.

Surely even if they weren't watching the video, they'd see the pitch/
yaw excursions in the attitude telemetry, right? ITAR restrictions on
discussing failures, perhaps?

I also wonder how much the guys in the sixties would have given for
this level of video coverage of their rockets...

- jake

On 3/21/07 10:11 PM, in article
, "Jake McGuire"
wrote:

On Mar 21, 8:52 pm, Brett Buck wrote:
I have no idea why they are referring to it as a roll control anomaly. It
was quite obviously going unstable in pitch/yaw long before roll gave up the
ghost.

This is odd, and a little disturbing. Also the reference to "clean
staging", when most everyone watching the webcast could see the
interstage hit the Kestrel nozzle and put a pretty big rate on the
second stage.

I'll have to go check, but it think the recontact actually reduced the
rate, which was slewing off very quickly right from separation. It was a
VERY hard hit. If I we knew the exit plane diameter we could estimate it,
but to my eye it looked to bend the nozzle out-of-round something on the
order of an inch or so. It appeared to spring back most of the way, but in
any case, very bad. I would have to assume that something hung up in the
separation system, but finding it and correcting it may be a challenge.


Surely even if they weren't watching the video, they'd see the pitch/
yaw excursions in the attitude telemetry, right? ITAR restrictions on
discussing failures, perhaps?

Not a chance! I can't see why it would in any way fall under ITAR to
discuss failures. I would say marketing/spin doctoring. Read their website
about how much economy and reliability they are gaining with their
revolutionary features - like holding the rocket on the pad until the system
reports back that it is running correctly. That wasn't revolutionary in
1944, much less 2006. It borders on arrogance, but that's hardly a new
feature in rocket science. Usually, after a few decades, that gets beaten
out of you. It's a very humbling business.


Brett

On Thu, 22 Mar 2007 05:27:37 GMT, Brett Buck wrote:

On 3/21/07 10:11 PM, in article
.com, "Jake McGuire"
wrote:

Surely even if they weren't watching the video, they'd see the pitch/
yaw excursions in the attitude telemetry, right? ITAR restrictions on
discussing failures, perhaps?


Not a chance! I can't see why it would in any way fall under ITAR to
discuss failures.

Huh?

ITAR in its present form was *motivated* by discussion of failures. The
1995 and 1996 Long March failures, to be precise. As both launchers were
carrying US satellites, Hughes and Loral participated in the subsequent
investigation, and co-authored the "Why Chinese Rockets Blow Up and How
To Make It Not Happen Again" report. Copies of which went to the Chinese,
with full Commerce Department approval.

Since the Commerce Department is an executive branch agency, which in
1995-6 was run by the Clinton Administration, and since Congress in that
era was suffering a severe case of Clinton Derangement Syndrome, this was
construed as, "Traitorous Clinton Administration Conspires to Help the
Commie Red Chinese Build Better Nookyuler Missiles With Which to Murder
God-Fearing Americans", which brouhaha ended with A: ITAR in its current
form, with satellite and launcher technology on the Munitions List and the
State Department in charge, and B: tens of millions of dollars in fines to
Hughes and Loral for, essentially, having talked about why rockets blew up
in a forum where Evil Furriners were listening.

I don't think ITAR has much to do with what Musk has or has not been
saying recently, but the suggestion isn't absurd and I can certainly
see how discussing failures in public might fall under ITAR.


--
*John Schilling * "Anything worth doing, *
*Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" *
*Chief Scientist & General Partner * -13th Rule of Acquisition *
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* for success" *
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On 3/21/07 11:21 PM, in article ,
"John Schilling" wrote:



Huh?

ITAR in its present form was *motivated* by discussion of failures. The
1995 and 1996 Long March failures, to be precise. As both launchers were
carrying US satellites, Hughes and Loral participated in the subsequent
investigation, and co-authored the "Why Chinese Rockets Blow Up and How
To Make It Not Happen Again" report. Copies of which went to the Chinese,
with full Commerce Department approval.

I understand all that - but as far as I can tell this doesn't apply at
all. They can publish all their telemetry files, plus analysis, on the
internet if they want, near as I can tell. They aren't telling the Iranians
how to debug Iranian ICBMs.

Brett

Brett Buck wrote:

I have no idea why they are referring to it as a roll control anomaly. It
was quite obviously going unstable in pitch/yaw long before roll gave up
the ghost.

Just watched the video, missed the launch because I turned of the feed after
the first engine start. Nice turn key and go vehicle they have.

Lack of Helium seems to be what finished it off. No roll control, tank
pressurization went down, and no settling burn.

Your right it's obviously pitch/yaw, maybe a slosh problem. As the tank
empties and the vehicle accelerated the the pitch/yaw gimbal began to move,
ever so slightly. Like the control system was coming up on a resonate
frequency with a slosh mode. It really looked like the vehicles attitude
was solid, when the engine began pitching and yawing slightly. Fighting and
exciting the liquid in the tank.

The Space Shuttle worries about slosh, especially during RTLS with the pitch
over maneuver just prior to MECO. Large pitch maneuver, too much LOX in the
tank and it will recontact after separation.

SpaceX really should have thought about using auto-gains in their flight
control system (attitude control). Too much gimbal movement, adjust the
gains. Too much attitude error, adjust the gains the other way.