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Falcon 1 Staging Recontact - Engine Burp



 
 
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  #21  
Old August 7th 08, 04:27 AM posted to sci.space.policy,sci.space.history,sci.space.shuttle,sci.space.station
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Default Falcon 1 Staging Recontact - Engine Burp

Excess Thrust Led To SpaceX Booster Loss

See:

http://www.aviationweek.com/aw/gener...&channel=space
  #22  
Old August 7th 08, 05:47 AM posted to sci.space.policy,sci.space.history,sci.space.shuttle,sci.space.station
snidely
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Default Falcon 1 Staging Recontact - Engine Burp

On Aug 4, 11:05 pm, Pat Flannery wrote:
richard schumacher wrote:
Or something as simple as thrust created by gas exhausting from the
(new) cooling system. Geez Louise. Does Falcon 1 use anything other
than explosive bolts and springs for stage separation? How many more
basic errors can they afford to re-discover?


That's their problem; they are basically rediscovering every problem
that rockets had in the mid-late 1950s.
They should have hunted down retired steely-eyed missile men who worked
on vehicles like Jupiter, Thor, Titan I, and Delta and pooled everything
they learned from those programs as how to do and not do things.
Propellant oscillation was a big problem in the early days, particularly
for Jupiter.


Per the SpaceX website:

"The problem arose due to the longer thrust decay transient of our new
Merlin 1C regeneratively cooled engine, as compared to the prior
flight that used our old Merlin 1A ablatively cooled engine. Unlike
the ablative engine, the regen engine had unburned fuel in the cooling
channels and manifold that combined with a small amount of residual
oxygen to produce a small thrust that was just enough to overcome the
stage separation pusher impulse. "

/dps

  #23  
Old August 7th 08, 01:52 PM posted to sci.space.policy,sci.space.history,sci.space.shuttle,sci.space.station
Pat Flannery
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Posts: 18,465
Default Falcon 1 Staging Recontact - Engine Burp



Brian Gaff wrote:
That is what I was thinking, hence my thought on the deceleration motors,
but this is weight taken away from payload, I suppose.

Whichever way you look at it, you cannot just assume that the two bodies
coasting for a short time will give the desired separation. If you coast
too long, in order to protect your first stage from plume damage, you run
the risk of sloshing in the upper stage suddenly released from thrust with
no continuation within the time you have before it goes float about in the
tank.
Brian


There are two ways {at least) around that problem.
1.) Use ullage rocket engines on the upper stage to seat the propellants
before engine ignition.
2.) Use some sort of a membrane inside the tank that separates the
propellant from the tank proper and which allows gas to fill the area
between the tank wall and the membrane - squeezing the propellant toward
the feed pipe rather than letting it float around in the tank.
SpaceX's report still doesn't explain the roll oscillations on the video
during ascent.

Pat
  #24  
Old August 7th 08, 02:03 PM posted to sci.space.policy,sci.space.history,sci.space.shuttle,sci.space.station
Jeff Findley
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Default Falcon 1 Staging Recontact - Engine Burp


"snidely" wrote in message
...
On Aug 4, 11:05 pm, Pat Flannery wrote:
richard schumacher wrote:
Or something as simple as thrust created by gas exhausting from the
(new) cooling system. Geez Louise. Does Falcon 1 use anything other
than explosive bolts and springs for stage separation? How many more
basic errors can they afford to re-discover?


That's their problem; they are basically rediscovering every problem
that rockets had in the mid-late 1950s.
They should have hunted down retired steely-eyed missile men who worked
on vehicles like Jupiter, Thor, Titan I, and Delta and pooled everything
they learned from those programs as how to do and not do things.
Propellant oscillation was a big problem in the early days, particularly
for Jupiter.


Per the SpaceX website:

"The problem arose due to the longer thrust decay transient of our new
Merlin 1C regeneratively cooled engine, as compared to the prior
flight that used our old Merlin 1A ablatively cooled engine. Unlike
the ablative engine, the regen engine had unburned fuel in the cooling
channels and manifold that combined with a small amount of residual
oxygen to produce a small thrust that was just enough to overcome the
stage separation pusher impulse. "


From what I can tell, stage separation events are one of the hardest things
to get right on a launch vehicle.

On another list Henry Spencer pointed out that, when they developed the
Saturns, Von Braun's team was pretty much the only team on the planet who
had real experience designing large rockets.

I talked to our senior engineer here about this (he does software today, but
spent maybe 10 years working for an aerospace company doing actual designs
for certain large satellite components). His take on this sort of thing is
that in any engineering organization, there is a certain amount of
knowledge, maybe even the majority of knowledge, that isn't captured in
formally documented analysis and design processes. Furthermore, it's not
appropriate to try to capture all of that knowledge. Every project is a bit
different, so the lessons learned vary a bit from project to project. If
the formal engineering process is too rigid, you wouldn't be able to
innovate.

Space-X is innovating while at the same time they're building up their
collective engineering knowledge for the approach they're taking. While
from the outside, it may look like they're making the same mistakes made in
the past, the details of their approach may be new enough that these really
are new mistakes which have never been made in exactly the same way.

Jeff
--
A clever person solves a problem.
A wise person avoids it. -- Einstein


  #25  
Old August 7th 08, 04:11 PM posted to sci.space.policy,sci.space.history,sci.space.shuttle,sci.space.station
richard schumacher
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Default Falcon 1 Staging Recontact - Engine Burp

In article ,
Fred J. McCall wrote:

:Those are methods for cutting the stages apart. Then you need something
:to ensure that they continue moving away from each other: thrusters on
:the first stage to slow it, or firing the second stage just before
:separation.
:

Or maybe just some strong springs compressed between the stages and
some pop-out drag brakes on the first stage. Not much air up there,
but you're already moving pretty fast so maybe just a little drag is
enough...


A potential problem with single-impulse separation methods such as
springs arises if the first stage continues to generate thrust, because
it can then catch up with the second stage. This is exactly what
happened with the 3rd Falcon 1 flight.
  #26  
Old August 7th 08, 04:19 PM posted to sci.space.policy,sci.space.history,sci.space.shuttle,sci.space.station
richard schumacher
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Posts: 191
Default Falcon 1 Staging Recontact - Engine Burp

In article ,
"Jeff Findley" wrote:

I talked to our senior engineer here about this (he does software today, but
spent maybe 10 years working for an aerospace company doing actual designs
for certain large satellite components). His take on this sort of thing is
that in any engineering organization, there is a certain amount of
knowledge, maybe even the majority of knowledge, that isn't captured in
formally documented analysis and design processes. Furthermore, it's not
appropriate to try to capture all of that knowledge. Every project is a bit
different, so the lessons learned vary a bit from project to project. If
the formal engineering process is too rigid, you wouldn't be able to
innovate.

Space-X is innovating while at the same time they're building up their
collective engineering knowledge for the approach they're taking. While
from the outside, it may look like they're making the same mistakes made in
the past, the details of their approach may be new enough that these really
are new mistakes which have never been made in exactly the same way.


True. The problems they have had are maddening, but in that class of
unavoidable teething problems of a new engineering team. With any luck
this team will remain together for a long time, retaining and passing on
their hard-won wisdom as they develop successive generations of
launchers. Barring some assembly error the odds of success for the 4th
Falcon 1 flight should be pretty good.

Now, on to the bad news : the most likely failure of the first flight of
Falcon 9 will involve staging, specifically because it will be the first
attempted start of the Merlin 1C engine in flight. Will the second
stage ullage thrusters continue firing for the duration of the main
engine startup transients?
  #27  
Old August 7th 08, 04:35 PM posted to sci.space.policy,sci.space.history,sci.space.shuttle,sci.space.station
Pat Flannery
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Posts: 18,465
Default Falcon 1 Staging Recontact - Engine Burp



Jeff Findley wrote:
On another list Henry Spencer pointed out that, when they developed the
Saturns, Von Braun's team was pretty much the only team on the planet who
had real experience designing large rockets.


No, Korolev had some good sized ones, like the R-7 (built with some
German input), and Chelomei was working on the UR-500 "Proton" super
ICBM of the Saturn 1 class, a entirely home-grown Soviet design.
Von Braun's team's only real experience was in drawing big rockets, not
building them prior to Saturn I. Up till that point the largest thing
they had actually built was Jupiter, which wasn't even a ICBM.
Their multistage experience consisted of clustered solids atop the Juno
1 and 2 boosters, based on the Redstone and Jupiter respectively. I
don't know how much input they had on the V-2/WAC Corporal tests.

Pat
  #28  
Old August 7th 08, 06:21 PM posted to sci.space.policy,sci.space.history,sci.space.shuttle,sci.space.station
[email protected]
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Default Falcon 1 Staging Recontact - Engine Burp

On Aug 7, 11:19 am, richard schumacher wrote:

Now, on to the bad news : the most likely failure of the first flight of
Falcon 9 will involve staging, specifically because it will be the first
attempted start of the Merlin 1C engine in flight. Will the second
stage ullage thrusters continue firing for the duration of the main
engine startup transients?


What ullage thrusters?
  #29  
Old August 7th 08, 07:21 PM posted to sci.space.policy,sci.space.history,sci.space.shuttle,sci.space.station
Jeff Findley
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Posts: 5,012
Default Falcon 1 Staging Recontact - Engine Burp


"richard schumacher" wrote in message
...
A potential problem with single-impulse separation methods such as
springs arises if the first stage continues to generate thrust, because
it can then catch up with the second stage. This is exactly what
happened with the 3rd Falcon 1 flight.


On another discussion forum, Henry Spencer said this is almost exactly what
nearly happened during Apollo 15's S-IC separation, so naturally I went
digging for details.

http://history.nasa.gov/alsj/a15/a15mrp6.pdf

Quote from above:

Four of the eight S-IC retromotors and all of the S-II stage
ullage motors were removed for this flight; therefore, the
S-IC/S-II separation sequence was revised. This sequence change
extended the coast period between S-IC outboard engine cutoff
and S-II engine start command by one second. The S-IC/S-II
separation sequence and S-II engine thrust buildup performance
was satisfactory.

From what I understand, the above deleted motors were added back for
subsequent flights, but I can't find a PDF online to confirm this.

Jeff
--
A clever person solves a problem.
A wise person avoids it. -- Einstein


  #30  
Old August 8th 08, 01:22 AM posted to sci.space.policy,sci.space.history,sci.space.shuttle,sci.space.station
Jorge R. Frank
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Posts: 2,089
Default Falcon 1 Staging Recontact - Engine Burp

Jeff Findley wrote:
"richard schumacher" wrote in message
...
A potential problem with single-impulse separation methods such as
springs arises if the first stage continues to generate thrust, because
it can then catch up with the second stage. This is exactly what
happened with the 3rd Falcon 1 flight.


On another discussion forum, Henry Spencer said this is almost exactly what
nearly happened during Apollo 15's S-IC separation, so naturally I went
digging for details.

http://history.nasa.gov/alsj/a15/a15mrp6.pdf

Quote from above:

Four of the eight S-IC retromotors and all of the S-II stage
ullage motors were removed for this flight; therefore, the
S-IC/S-II separation sequence was revised. This sequence change
extended the coast period between S-IC outboard engine cutoff
and S-II engine start command by one second. The S-IC/S-II
separation sequence and S-II engine thrust buildup performance
was satisfactory.

From what I understand, the above deleted motors were added back for
subsequent flights, but I can't find a PDF online to confirm this.


Apollo 16 press kit:

http://history.nasa.gov/alsj/a16/A16_PressKit.pdf

p. 140 (144 of the PDF):

Significant Vehicle Changes
Saturn vehicle SA-511 is similar in configuration to the
Apollo 15 launch vehicle. The first stage (S-1C) has eight retrorocket
motors, double the number on the SA-510 vehicle, because
flight evaluation of the Apollo 15 mission revealed that the
separation distance between the first and second stages was
less than predicted. Eight retrorockets will give a greater
safety margin should one motor fail during separation.

Apollo 17 press kit:

http://history.nasa.gov/alsj/a17/A17_PressKit.pdf

p. 94 (146 of the PDF):

The first stage has eight solid-fuel retro-rockets that
fire to separate the first and second stages. Each rocket
produces a thrust of 337,000 newtons (75,800 pounds) for
0.54 seconds.
 




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