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"Flight proven" is the new "Certified Pre-Owned"



 
 
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  #21  
Old September 1st 16, 03:19 PM posted to sci.space.policy
Fred J. McCall[_3_]
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Default "Flight proven" is the new "Certified Pre-Owned"

Rick Jones wrote:

Jeff Findley wrote:
The "violence" of a launch is largely a myth for liquid fueled
launch vehicles.


Myth or "history"? eg pogo/whatnot.


Pogo means the rocket has a problem. It's not a 'normal' liquid
rocket effect. The vibe environment from a solid is much, MUCH worse
than from a liquid.


--
"Millions for defense, but not one cent for tribute."
-- Charles Pinckney
  #22  
Old September 1st 16, 03:27 PM posted to sci.space.policy
Fred J. McCall[_3_]
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Default "Flight proven" is the new "Certified Pre-Owned"

JF Mezei wrote:

On 2016-08-30 15:01, Rick Jones wrote:
It would seem that "flight proven" is now "officially" to used rockets
what "certified pre-owned" is to used cars:

http://www.marke****ch.com/story/spa...ets-2016-08-30


I wonder if Cape Canaveral will be *totally* business as usual, of if
they will move all equipment out, batten down the hatches if they think
higher risk of failure, just in case.


If they thought they needed to do that they just wouldn't allow the
launch.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn
  #23  
Old September 1st 16, 03:33 PM posted to sci.space.policy
Vaughn Simon
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Default "Flight proven" is the new "Certified Pre-Owned"

On 9/1/2016 6:32 AM, bob haller wrote:
perhaps the solution to make many flights with a reusable booster is simple and affordable.
as easy as launching all payloads with a launch boost escape system.


It's actually not that "simple" because, assuming all else stays equal,
every pound devoted to the escape system subtracts a pound from the
payload capacity.

Now if you get innovative, the above need not be written in stone! For
example; SpaceX hopes to get double duty from its Dragon capsule escape
system because it will also be used for landing and possibly for other
purposes.

And surely I'm not the only person to wonder if there is a way, later in
the launch when it is no longer needed for escape, to use the impulse
from an escape system as added propulsion. Think of it as small solids
added to the thrust of the second stage. That extra thrust should
recover at least some of the payload capacity lost to the mass of the
escape system.




  #24  
Old September 1st 16, 07:59 PM posted to sci.space.policy
Fred J. McCall[_3_]
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Posts: 10,018
Default "Flight proven" is the new "Certified Pre-Owned"

William Mook wrote:

On Thursday, September 1, 2016 at 6:42:40 AM UTC+12, Fred J. McCall wrote:
You appear to be repeating yourself (yet again), MookBot.

William Mook wrote:

snip echo


I deleted one post with a mathematical error and reposted the same post with the error corrected. Blowhard.


No need to sign your posts, Mookie. We know you're a blowhard. You
really need someone to explain standard Usenet NEWS practices to
you...


--
"Ignorance is preferable to error, and he is less remote from the
truth who believes nothing than he who believes what is wrong."
-- Thomas Jefferson
  #25  
Old September 1st 16, 08:46 PM posted to sci.space.policy
Fred J. McCall[_3_]
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Posts: 10,018
Default "Flight proven" is the new "Certified Pre-Owned"

Jeff Findley wrote:

In article ,
says...

On Thursday, September 1, 2016 at 6:42:40 AM UTC+12, Fred J. McCall wrote:
You appear to be repeating yourself (yet again), MookBot.

William Mook wrote:

snip echo


I deleted one post with a mathematical error and reposted the same post with the error corrected. Blowhard.


You can't delete posts from Usenet News you dolt. You've been told
repeatedly why this is the case. You can try to cancel a post, but many
(most?) newservers will already have propagated the post to other
servers by then. And many (most?) servers simply ignore the cancel
request anyway.

So your math error will be preserved in perpetuity.


And this is precisely why normal Usenet NEWS practice is to just
follow up your original article with ONLY the correction. It's about
the only time following up your own post is acceptable. However, as
we've seen, Mookie follows up his own articles just to hear himself
talk some more and now we see that his method to 'correct errors' is
to repeat an entire posting.

What a maroon...


--
"Ignorance is preferable to error, and he is less remote from the
truth who believes nothing than he who believes what is wrong."
-- Thomas Jefferson
  #26  
Old September 1st 16, 08:49 PM posted to sci.space.policy
Fred J. McCall[_3_]
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Posts: 10,018
Default "Flight proven" is the new "Certified Pre-Owned"

bob haller wrote:

perhaps the solution to make many flights with a reusable booster is simple and affordable.

as easy as launching all payloads with a launch boost escape system.

that way if a booster has a bad day, the payload will be safe and can be retrieved and reused.

launch boost escape will add some costs but save money when a booster fails


If this was an economically reasonable practice everyone would already
be doing it. There are two problems with the idea:

1) Just 'escaping' isn't enough. You now need to give up a bunch of
cargo space to hold parachutes or some other way to get the payload
down 'soft'.

2) It's going to land in water, which means it's mostly wrecked from
salt exposure anyway.


--
"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
  #27  
Old September 2nd 16, 05:06 AM posted to sci.space.policy
William Mook[_2_]
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Posts: 3,840
Default "Flight proven" is the new "Certified Pre-Owned"

On Friday, September 2, 2016 at 2:19:19 AM UTC+12, Fred J. McCall wrote:
Rick Jones wrote:

Jeff Findley wrote:
The "violence" of a launch is largely a myth for liquid fueled
launch vehicles.


Myth or "history"? eg pogo/whatnot.


Pogo means the rocket has a problem. It's not a 'normal' liquid
rocket effect. The vibe environment from a solid is much, MUCH worse
than from a liquid.


--
"Millions for defense, but not one cent for tribute."
-- Charles Pinckney


Pogo oscillation is a self-excited vibration in liquid propellant rocket engines caused by combustion instability. The unstable combustion results in variations of engine thrust, causing variations of acceleration on the vehicle's flexible structure, which in turn cause variations in propellant pressure and flow rate, closing the self-excitation cycle. The name is a metaphor comparing the longitudinal vibration to the bouncing of a pogo stick. Pogo oscillation places stress on the frame of the vehicle which, in severe cases can be potentially dangerous.

The nature of the pintle fed engine is such that Pogo oscillation does not occur.

https://www.google.com/patents/US7827781

In general, pogo oscillation occurs when a surge in engine pressure increases back pressure against the fuel coming into the engine, reducing engine pressure, causing more fuel to come in and increasing engine pressure again. Flexing of fuel pipes can also induce fluctuations in fuel pressure as well. If the cycle happens to match a resonance frequency of the rocket then dangerous oscillations occur through positive feedback, which, in extreme cases, tear the vehicle apart.

Another situation in which pogo oscillation occurs is when the engine is moving longitudinally with fluctuating speed. Owing to inertia, if the speed of the vehicle suddenly increases, the fuel inside the fuel tank tends to 'fall behind' and is forced into the turbopump, a situation somewhat similar to the slosh of liquid inside a tanker. This creates excess pressure to the turbopump and causes unintended excessive fuel to be delivered. This in turn creates excessive thrust and causes the vehicle to accelerate which leads to further increase in turbopump pressure and an unintended increase in fuel delivery. This can set up a vicious circle, and can result in structural failure in the vehicle.

The most famous pogo oscillation was in the Saturn V first stage, S-IC, caused by the cruciform thrust structure. This structure was an "X" of two I-beams, with an engine on the end of each beam and the center engine at the intersection of the beams. The center of the cruciform was unsupported, so the central F-1 engine caused the structure to bend upwards. The pogo oscillation occurred when this structure sprang back, lengthening the center engine's fuel line bellows (which was mounted down the center of the cruciform), temporarily reducing the fuel flow and thus reducing thrust. At the other end of the oscillation, the fuel line was compressed, increasing fuel flow.. This caused a sinusoidal thrust oscillation during the first stage ascent..

If the oscillation is left unchecked, failures can result. One case occurred in the middle J-2 engine of the second stage, S-II, of the Apollo 13 lunar mission in 1970. In this case, the engine shut down before the oscillations could cause damage to the vehicle. Later events in this mission overshadowed the pogo problem. Pogo also had been experienced in the S-IC first stage of the unmanned Apollo 6 test flight in 1968. One of the Soviet Union's N1-L3 rocket test flights suffered pogo oscillations in the first stage on February 21, 1969. The launch vehicle reached initial engine cutoff, but exploded 107 seconds after liftoff and disintegrated. There are other cases during unmanned launches in the 50s and 60s where the pogo effect caused catastrophic launch failures.

Modern vibration analysis methods accounts for the pogo oscillation during design to ensure that it is far away from the vehicle's resonant frequencies. Suppression methods include damping mechanisms or bellows in propellant lines. The Space Shuttle Main Engines each had a damper in the LOX line, but not in the hydrogen fuel line. In a pintle fed engine, pogo oscillations are detected in the engine and pintle geometry adjusted to instantly damp excursions in acceleration.
  #29  
Old September 2nd 16, 06:16 AM posted to sci.space.policy
William Mook[_2_]
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Posts: 3,840
Default "Flight proven" is the new "Certified Pre-Owned"

On Friday, September 2, 2016 at 7:49:40 AM UTC+12, Fred J. McCall wrote:
bob haller wrote:

perhaps the solution to make many flights with a reusable booster is simple and affordable.

as easy as launching all payloads with a launch boost escape system.

that way if a booster has a bad day, the payload will be safe and can be retrieved and reused.

launch boost escape will add some costs but save money when a booster fails


If this was an economically reasonable practice everyone would already
be doing it.


Nonsense.

There are two problems with the idea:

1) Just 'escaping' isn't enough.


If you have a recoverable upper stage it is.

You now need to give up a bunch of
cargo space to hold parachutes or some other way to get the payload
down 'soft'.


You dolt, a reusable upper stage, like the Dragon capsule, that already executes a powered touchdown,

https://www.youtube.com/watch?v=07Pm8ZY0XJI

Is perfectly capable of aborting off the launch vehicle and being recovered..

https://www.youtube.com/watch?v=1_FXVjf46T8

We can run some numbers and see what a stage is like. A two stage system with 3.8 km/sec exhaust speed and 4.6 km/sec per stage for a total ideal delta vee of 9.2 km/sec can be estimated with a 54 tonne payload.

http://www.spacex.com/falcon-heavy

Payload: 54.0 tonnes

Stage Two: 37.0 tonnes - structure
305.3 tonnes - propellant

Stage One (x3) 57.4 tonnes - structure
473.6 tonnes - propellant

Thrust at Lift Off: 24,681.0 kN
Total Mass at LO: 1,420.8 tonnes
Acceleration LO: 1.77 gees.

The system boosts at maximum thrust at lift-off and the center core is throttled back after Max-Q. The side mounted elements are dropped and the first stage core continues at increased thrust. The second stage core is lit and carries the payload to orbit.

Now, the Merlin 1C Vacuum engine is throttled back to 411 kN thrust with a high expansion nozzle compared to its sea level counter part's 914.1 kN thrust on the first stage. The engine weighs 0.68 tonnes.

A Falcon heavy carries 54 tonnes into LEO.

Two sea level Merlins with shortened nozzles, tuned to produce 1,000 kN of thrust each, with 2.2 tonnes of propellant, and 0.44 tonnes of structure - reduces the payload to orbit by 4 tonnes from 54 tonnes to 50 tonnes. This can be picked up by a slight improvement in propellant density - which SpaceX is perfecting.

The stage at lift off with two Merlin escape engines lit boost the payload at 3.77 gees or 2.77 gees above 1.00 gee (27.2 m/sec2 movement straight up)..

This system has the capacity to accelerate the payload through a delta vee of 0.158 km/sec (569 kph, 353 mph). Terminal speed of a falling payload is 0.054 km/sec (195 kph, 122 mph) This means that 0.104 km/sec (or 0.100 km/sec with reserve) is available (360 kph, 223 mph) for escape! (allowing an abort at any stage of the flight!) This boosts 2.705 seconds. Boosting straight up this achieves 0.0735 km/sec (264 kph, 164 mph) over a 99.4 meter (326 ft) length.

https://www.hq.nasa.gov/alsj/CSM15_L..._pp137-146.pdf

This compares favourably with the Apollo Launch Escape Subsystem in terms of performance. This is due primarily to the vastly improved specific impulse of the liquid fuels, as well as the throttability of the liquid fueled engines. As in the Apollo system, several abort modes are possible. Unlike the Apollo, this system would have the ability to recover the entire payload on land or a recovery platform. An abort to recovery platform is an interesting capacity.


2) It's going to land in water, which means it's mostly wrecked from
salt exposure anyway.


Not if it lands at the launch center or a recovery platform.

The four tonnes the system requires could easily be won back in a vehicle the size of a Falcon Heavy through propellant density increases.

http://ntrs.nasa.gov/archive/nasa/ca...9790004067.pdf

--
"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



  #30  
Old September 2nd 16, 06:18 AM posted to sci.space.policy
William Mook[_2_]
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Posts: 3,840
Default "Flight proven" is the new "Certified Pre-Owned"

On Thursday, September 1, 2016 at 11:00:28 AM UTC+12, JF Mezei wrote:
On 2016-08-30 15:01, Rick Jones wrote:
It would seem that "flight proven" is now "officially" to used rockets
what "certified pre-owned" is to used cars:

http://www.marke****ch.com/story/spa...ets-2016-08-30



I wonder if Cape Canaveral will be *totally* business as usual, of if
they will move all equipment out, batten down the hatches if they think
higher risk of failure, just in case.

The damage at Wallops was fairly extensive and took quite a while before
site became functional again. I am sure the Cape launch facility doesn't
want to be down for that long.

(not saying that the "flight proven" rocket has higher risk, but
wondering what Cape folks think).


If this was done before the FTS failure today, its prescient don't you think? This is the sort of publicity that could kill SpaceX and maintain the artificial scarcity I spoke of yesterday, particularly if the alliances with insurers is tested.

 




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