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  #33  
Old June 29th 19, 07:07 PM posted to sci.space.policy
Fred J. McCall[_3_]
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Niklas Holsti wrote on Sat, 29 Jun
2019 13:46:13 +0300:

On 19-06-29 07:25 , Fred J. McCall wrote:
Niklas Holsti wrote on Fri, 28 Jun
2019 22:44:30 +0300:

On 19-06-28 19:25 , Fred J. McCall wrote:


If the abort test is at Max Q I don't think this makes any
difference anyway, since you're not really 'accelerating' at Max
Q.

I don't recall seeing any pause, at Max Q, in the growth rate of
the Falcon 9 "velocity" reading in the numerous Falcon 9 launch
videos I've watched, so I find it hard to believe that the vehicle
stops accelerating at that point.


https://space.stackexchange.com/ques...y-after-launch


The acceleration graph shown there for CRS/Dragon missions never falls
below about 0.53 g, so it is indeed still accelerating at Max Q. From
the behaviour before and after Max Q it seems that without the
throttle-down for Max Q the acceleration at that altitude would still be
less than 1 g, so the throttle-down cuts acceleration in half, but not
more than that.


Whoop-d-****ing-doo! Now, what's the acceleration of the capsule on
abort?

Hint: When Dragon commands an abort the engines on the booster shut
down and acceleration is negative. Aerodynamics break up the launch
vehicle shortly after separation. Meanwhile, Dragon is capable of a
6+g slap in the ass...


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn
  #34  
Old June 29th 19, 07:09 PM posted to sci.space.policy
Fred J. McCall[_3_]
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Jeff Findley wrote on Sat, 29 Jun 2019
08:27:43 -0400:

In article ,
says...

Jeff Findley wrote on Fri, 28 Jun 2019
07:23:56 -0400:


Falcon 9 Block 5 first stages are designed for something like 100
flights. There are no Falcon 9 Block 5 first stages with 99 flights on
them.


The one thought that occurs to me (and I don't think the description
you posted of the test assets makes it clear) is that perhaps they are
NOT using a Block 5 booster set, but rather an earlier set that isn't
intended for a lot of reflights.


That would certainly be possible, but it wouldn't be as high fidelity as
a Block 5. According to NexxusWolf on Reddit, it will be a Block 5
booster. Yes, I know, not the most reliable spot for info, but it is
what it is.

https://www.reddit.com/r/spacex/comm...at_i_got_from_
my_tour/


Well, they're already removing grid fins and landing legs, so does not
having Block 5 upgrades really make that much additional difference?


--
"Insisting on perfect safety is for people who don't have the balls to
live in the real world."
-- Mary Shafer, NASA Dryden
  #35  
Old June 29th 19, 07:39 PM posted to sci.space.policy
Niklas Holsti
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On 19-06-29 21:07 , Fred J. McCall wrote:
Niklas Holsti wrote on Sat, 29 Jun
2019 13:46:13 +0300:

On 19-06-29 07:25 , Fred J. McCall wrote:
Niklas Holsti wrote on Fri, 28 Jun
2019 22:44:30 +0300:

On 19-06-28 19:25 , Fred J. McCall wrote:


If the abort test is at Max Q I don't think this makes any
difference anyway, since you're not really 'accelerating' at Max
Q.

I don't recall seeing any pause, at Max Q, in the growth rate of
the Falcon 9 "velocity" reading in the numerous Falcon 9 launch
videos I've watched, so I find it hard to believe that the vehicle
stops accelerating at that point.


https://space.stackexchange.com/ques...y-after-launch


The acceleration graph shown there for CRS/Dragon missions never falls
below about 0.53 g, so it is indeed still accelerating at Max Q. From
the behaviour before and after Max Q it seems that without the
throttle-down for Max Q the acceleration at that altitude would still be
less than 1 g, so the throttle-down cuts acceleration in half, but not
more than that.


Whoop-d-****ing-doo! Now, what's the acceleration of the capsule on
abort?

Hint: When Dragon commands an abort the engines on the booster shut
down and acceleration is negative. Aerodynamics break up the launch
vehicle shortly after separation. Meanwhile, Dragon is capable of a
6+g slap in the ass...


Probably rather less in the face of Max Q drag forces. But probably more
than 0.5 g, so ok.

--
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
. @ .
  #36  
Old June 29th 19, 09:25 PM posted to sci.space.policy
Jeff Findley[_6_]
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In article ,
says...

Jeff Findley wrote on Sat, 29 Jun 2019
08:27:43 -0400:

That would certainly be possible, but it wouldn't be as high fidelity as
a Block 5. According to NexxusWolf on Reddit, it will be a Block 5
booster. Yes, I know, not the most reliable spot for info, but it is
what it is.

https://www.reddit.com/r/spacex/comm...at_i_got_from_
my_tour/


Well, they're already removing grid fins and landing legs, so does not
having Block 5 upgrades really make that much additional difference?


I tend to agree that it shouldn't matter, but since the customer is
NASA...

Of course, Orion's abort test won't happen on an SLS, but NASA has more
"insight" into that design. Same as flying crew on the 2nd flight of
SLS but SpaceX had to have something like 7 launches of the Block 5 with
the upgraded COPVs to prove that design for Dragon 2 crew.

So, yes, there is a pattern of NASA making SpaceX jump through hoops
that it doesn't make Boeing and the other big contractors jump through.

Jeff
--
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These posts do not reflect the opinions of my family, friends,
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  #37  
Old July 5th 19, 11:14 PM posted to sci.space.policy
Fred J. McCall[_3_]
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JF Mezei wrote on Fri, 5 Jul 2019
14:29:16 -0400:

On 2019-06-27 14:50, Fred J. McCall wrote:

No. The capsule accelerates away from the stack. That's sort of the
point.


When the stack explodes, there may be portions of the stack propelled
forwards. So the question is whether the capsule will eject at speed
equal to or greater than any debris that could be pushed forward by
explosion.


If you look at the explosive velocity of the propellants, anything is
possible except accelerating humans as fast as a tiny bit of debris
could be accelerated (unless you put a whacking great motor on it and
are willing to get the crew back as jam). However, you have to look
at the odds. First, keep in mind that if there is significant
acceleration toward to capsule from the explosion that the capsule
will also be accelerated by that. Second, remember that the capsule
is a pretty robust pressure vessel while boosters are mostly made out
of aluminum. Third, remember that there is a pressure structure, an
entire second stage, and a payload adapter between the first stage and
the capsule.


(or would explosions generally push debros downward (at engine) or
outwards (at tanks) and not much going forward ?


Explosions go in the direction of least resistance. In this case that
is out the sides, as there are pressure walls and heavy structure at
the ends of the booster.


They have no such rockets. Nothing is anywhere near flight limits.


SO far, they have only re-used 3 times. Surely they have rockets with 3
uses that could be used a 4th time. Even though they may have a goal of
10000 re-iuses (or whateber the number is), the current limit appears to
be 3.


You're really 'stuck on stupid' on this issue, aren't you? Go check
the mileage on your car. Is it your contention that the current limit
on your car is that figure and that if you drive another mile it will
blow up or fail? I'll merely point out that your moving of goalposts
from your original question (cleverly deleted by you) doesn't prove
jack **** and the current limit does NOT appear to be 3.


So pushing the ebveloppe with non-commecial tests may allow SpaceX
to raise the limit of commercial re-uses.


Nope, since they're not planning on recovering the booster from the
Max Q test.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn
  #38  
Old July 5th 19, 11:16 PM posted to sci.space.policy
Fred J. McCall[_3_]
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JF Mezei wrote on Fri, 5 Jul 2019
14:35:31 -0400:

On 2019-06-28 07:26, Jeff Findley wrote:

This. I honestly don't know why NASA agreed to let Boeing only simulate
a max-Q escape with its Starliner capsule. IMHO, this is a case where
you really want a real world test. Orion will do a max-Q abort, so if
NASA doesn't trust Orion to a simulation, why trust Starliner to the
same?


Is it possible that there are enough similarities between Orion and
Starliner that the abort tests for Orion can be used to validare Starliner?


Other than the two vehicles being totally different, flying on
different boosters, and using totally different abort systems, yeah,
that makes perfect sense.

[That was sarcasm, in case you didn't get it.]


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn
  #39  
Old July 5th 19, 11:21 PM posted to sci.space.policy
Fred J. McCall[_3_]
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Posts: 10,018
Default Commercial Crew

JF Mezei wrote on Fri, 5 Jul 2019
14:44:17 -0400:

On 2019-06-28 12:25, Fred J. McCall wrote:

If the abort test is at Max Q I don't think this makes any difference
anyway, since you're not really 'accelerating' at Max Q. And wouldn't
part of the 'normal' abort sequence shut down the booster anyhow?


If you get in a situation so dire that you must eject in flight, can you
really expect that a shutdown command of liquid fueled engines will work?


Will you please stop misusing 'eject' for this situation? To answer
your question, yes, you can.


Say there is an explosion near top of Stage 1. This would sever
connection between capsule and the engines at bottom of stage 1.
Capsule could eject, but not send shutdown command to engines. Would
they shutdown within milliseconds of losing data link to capsule or
would they run till told otherwise?


They would 'shut down' when the explosion occurs because the
propellant tanks would lose pressurization. Liquid rockets do not
both blow up AND continute to boost.


Seems to me that a capsule eject system, is designed to handle worse
case scenario, would have to consider possibility of stack still getting
propulsion as it explodes. (even if the odds are that explosion would be
at engines and thus kill propulsion).


Please go read up on how liquid fuel rockets work.


--
"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
 




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