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SpaceX Capsule Explosion



 
 
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  #31  
Old July 20th 19, 01:54 PM posted to sci.space.policy
Jeff Findley[_6_]
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Default SpaceX Capsule Explosion

In article ,
says...

I suppose they could still go for propulsive landing over water. At sea
and then move to a large fresh water tank on dry ground? Or if
up-welling steam is a problem maybe a high boiling point oil?


When Soyuz lands on ground, are the engines that fire at last second
roughly equivalent to Draco or Super Draco in terms of power ?


Not really. Soyuz uses solid rocket engines for its propulsive
"landing". These engines are triggered by radiation detectors which
have a corresponding radiation source. The sensors detect radiation
reflecting off of the ground (or water) as the capsule comes close to
landing. It's essentially a switch activated by radiation.

So, the system is designed to reduce the velocity at landing. It
doesn't reduce the velocity to zero for a truly "soft" landing because
that would require an active control system (otherwise it might thrust
too much, making the craft go back up a bit).

If Dragon were to land propulsively in water, are there things it could
bring back that it can't bring back now because of the impact on water?
If not, is there any point in firing engines to land?


NASA doesn't care, so it doesn't really matter.

If He2 enters tanks from the top, then as long as you are on earth,
there is no reason for NTO or MMH to flow up through a faulty backflow
valve and onto titanium tubing to the He tank.

But once that capsule travels to space, in 0G, any deceleration would
make either NTO or MMH want to flow "up" and a faulty backflow valvce
would then let it pass and move towards the He tabnk in tha titanium tubing.

This might explain why all the tests on ground had worked well, but the
one test after the capsule had flown went "kaboom".


No, SpaceX has already said the NTO got into the helium line during
ground (re)processing of the system.

Jeff
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  #32  
Old July 20th 19, 01:59 PM posted to sci.space.policy
Jeff Findley[_6_]
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Default SpaceX Capsule Explosion

In article , says...

On 7/19/2019 2:43 PM, JF Mezei wrote:
On 2019-07-19 12:05, David Spain wrote:

presume the only method to relieve the pressure is through combustion,
but there may also exist a pressure relief valve that vents off the
helium without need to run the engines. Without hard data this is just a
WAG but not a SWAG.



You can vent off the Helium between the Helium tank and the
Fuel/oxydizer tanks. But the pressure inside the later tanks can't be
vented otherwise you are venting uncombusted NTO and MMH which may
combust if they meet after having been ventet and remain highly toxic if
they don't meeet to combust.


You close the Helium pressurization valve, and de-press through another
valve and coupling perhaps one at the top of the helium tank.

The NTO and MMH would be drained via separate plumbing connections,
which already must exist to fuel it anyway.

Then you purge the system with helium to remove the trace elements of
NTO and MMH from the pressurization lines. Yeah if you do it together
you stand back, otherwise you do them singly with lots of venting to
allow it do disperse.

I can make up a lot of stuff too w/o data it's a WAG (Wild Ass Guess)
but not a SWAG (Silly Wild Ass Guess).


SpaceX has said they designed the system according to industry
standards. What could those be? For example, here is a plumbing
diagram of the space shuttle OMS system:

https://www.orbiterwiki.org/images/8/8e/OMS_diag.png

Note that on this diagram, there is no isolation valve in the helium
plumbing between the check valve and the NTO tank. The gas isolation
valves are between the check valve and the helium tank.

So the arrangement that SpaceX used is not new. That's why they said
that what they encountered was "unexpected". The space shuttle flew
dozens and dozens of times without this happening.

Jeff
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  #33  
Old July 20th 19, 03:11 PM posted to sci.space.policy
Jeff Findley[_6_]
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Default SpaceX Capsule Explosion

In article ,
says...

On 2019-07-20 08:47, Jeff Findley wrote:

It wasn't. NASA has prohibited SpaceX from performing Dragon 2
propulsive landing testing on returning ISS cargo flights.



Since the BFR/BFS is allegedly going to service the space station, NASA
will have to rethink its policy on propulsive landing.


Dragon and Dragon 2 are the only SpaceX vehicles that NASA has agreed to
let berth/dock to ISS. Anything beyond that is "just a pretty render".

The policy was sound in early days of programme when SpaceX hadn't yet
demonstrated ability to land Falcon9. But with landing reliability now
seamingly very good, I have to wonder if NASA would warm up to land
landings. (researchers really want this because they get quick access to
experiments being returned (think live cultures, animals).


Falcon 9 and Dragon 2 aren't the same. Just because one usually lands
intact, doesn't mean the other is going to be reliable enough for NASA
to trust with irreplaceable cargo like a returning EMU. The EMUs are
the same ones that NASA has used since the first space shuttle EVAs.
There literally are no other certified EMU suits besides those.

Jeff
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These posts do not reflect the opinions of my family, friends,
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  #34  
Old July 20th 19, 03:16 PM posted to sci.space.policy
Jeff Findley[_6_]
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Default SpaceX Capsule Explosion

In article ,
says...

On 2019-07-20 08:54, Jeff Findley wrote:

No, SpaceX has already said the NTO got into the helium line during
ground (re)processing of the system.



Would this have involved purging the tanks and refilling them with new
hydrazine? Or did the processing just clean up the outside and fired the
engines in the same state thay came in at landing?


They have not provided details other than what I said above.

Scott Manley's video showed springs pushing valve down (to illustrate
the backflow prevention). Is this how the real valve would function?


Yes.

Or are we talking about a motor controlled valve that only opens valve
when pressure on He2 side is greater than pressure on the fuel/oxydizer
side?


No.

It is correct to state that the root cause is the failure of that
valve to prevent the liquid from flowing past it towards the He2
tank?


We don't know for sure, since SpaceX has not provided enough details.
But I find it possible that liquid leaked past the check valve (again,
no details, so we can speculate all we want).

That said, what others online (who know more about these sorts of
systems than I do) speculate is that (relatively warm) gaseous NTO snuck
past the check valve and then re-condensed to liquid in the (relatively
cold) helium plumbing. If that is the case, it's not a failure of the
check valve to prevent liquid from leaking past. That actually seems
more likely, IMHO.

Jeff
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  #35  
Old July 20th 19, 07:23 PM posted to sci.space.policy
Niels Jørgen Kruse[_2_]
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Default SpaceX Capsule Explosion

Jeff Findley wrote:

Note that on this diagram, there is no isolation valve in the helium
plumbing between the check valve and the NTO tank. The gas isolation
valves are between the check valve and the helium tank.

So the arrangement that SpaceX used is not new. That's why they said
that what they encountered was "unexpected". The space shuttle flew
dozens and dozens of times without this happening.


Perhaps it did happen, but the valve didn't explode because the helium
pressure was lower.

--
Mvh./Regards, Niels Jørgen Kruse, Vanløse, Denmark
  #36  
Old July 20th 19, 08:11 PM posted to sci.space.policy
Niklas Holsti
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Default SpaceX Capsule Explosion

On 19-07-20 15:40 , Jeff Findley wrote:
In article ,
lid says...

On 19-07-19 14:06 , Jeff Findley wrote:
In article , says...

I couldn't find a definitive reference. But the abort system is simply
not needed for a cargo flight. It could be that the parts will still be
on the Dragon 2, but the abort system's propellant tanks and high
pressure helium tanks simply won't be filled. That would also save a
lot of mass while minimizing the modifications needed to turn a crew
Dragon 2 into a cargo Dragon 2.


They might even use propulsive landing for cargo flights.


No, they won't. NASA has definitively nixed that idea. NASA does not
want irreplaceable returning cargo (e.g. EMU suits) splattered all over
a concrete landing pad when the inevitable "oopsie" happens.


If an EMU is irreplaceable, and is being sent back to the ISS on a cargo
Dragon2, by the same logic the abort system should be included and
active on launch, no? In case the launcher has an "oopsie".

NASA is requiring SpaceX to parachute all Dragon 2 capsules into the
ocean.


If commercial use of the ISS takes off, perhaps some cargo missions will
be non-NASA.

But (as I said in an earlier reply/correction to myself) propulsive
landing probably needs legs, which are no longer in the Dragon2 design,
so it won't happen.

--
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
. @ .
  #37  
Old July 21st 19, 02:48 PM posted to sci.space.policy
Jeff Findley[_6_]
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Posts: 2,307
Default SpaceX Capsule Explosion

In article ,
says...

On 2019-07-20 10:16, Jeff Findley wrote:

Scott Manley's video showed springs pushing valve down (to illustrate
the backflow prevention). Is this how the real valve would function?


Yes.


systems than I do) speculate is that (relatively warm) gaseous NTO snuck
past the check valve and then re-condensed to liquid in the (relatively
cold) helium plumbing.



Shoudln't a check valve prevent passange in wrong direction on either
gas or liquid? It's not like there is a floater that rises up to close
valve is liquid rises up, is it?


You really can't rely on a check valve for this. That's why designs
also include (usually redundant) isolation valves. No, I don't know why
NASA "has always done it this way" if an isolation valve would have been
better.

Also, would the titanium tubing between the compreseed He2 and NTO tank
be at same temperature as NTO tank until the He2 valve is opened? Why
would it be colder?


Higher pressure during an event like loading the tank with NTO could
result in higher temperatures of the NTO in the tank (unless the NTO was
cooled prior to loading to prevent such a thing from happening). Higher
pressure could have been used to drain the tank as well, so we just
don't know, because SpaceX has not provided details which would have
caused such a condition.

Again, SpaceX just said that the issue was caused during "ground
processing". The only two events which might have caused this would
have been loading or draining the tank. Otherwise, the tank would have
been at ambient temperature, just like the rest of the plumbing.

If Helium is kept liquid at very high pressure,
won't it also be at room tempoerature? While being filled, I can
understand initially getting cold as liquid helium is dumped into empty
tank and can vaporize, but after a while, doesn't it get warm as they
compress that gaseious Helioum back to liquid as more liquid is pumped in?


Yes, loading the helium as a liquid could have chilled the plumbing on
the helium side. That could have caused very low pressure on the helium
side, especially if any air or nitrogen in the lines turned to liquid.

Jeff
--
All opinions posted by me on Usenet News are mine, and mine alone.
These posts do not reflect the opinions of my family, friends,
employer, or any organization that I am a member of.
  #39  
Old July 21st 19, 02:57 PM posted to sci.space.policy
Jeff Findley[_6_]
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Posts: 2,307
Default SpaceX Capsule Explosion

In article ,
lid says...

On 19-07-20 15:40 , Jeff Findley wrote:
In article ,
lid says...

On 19-07-19 14:06 , Jeff Findley wrote:
In article , says...

I couldn't find a definitive reference. But the abort system is simply
not needed for a cargo flight. It could be that the parts will still be
on the Dragon 2, but the abort system's propellant tanks and high
pressure helium tanks simply won't be filled. That would also save a
lot of mass while minimizing the modifications needed to turn a crew
Dragon 2 into a cargo Dragon 2.

They might even use propulsive landing for cargo flights.


No, they won't. NASA has definitively nixed that idea. NASA does not
want irreplaceable returning cargo (e.g. EMU suits) splattered all over
a concrete landing pad when the inevitable "oopsie" happens.


If an EMU is irreplaceable, and is being sent back to the ISS on a cargo
Dragon2, by the same logic the abort system should be included and
active on launch, no? In case the launcher has an "oopsie".


NASA has conflicting goals for cargo missions. They're supposed to be
reliable (we've lost two commercial cargo missions so far), but they're
clearly not as paranoid about "safety" for cargo as they are crew. So,
they're trading more cargo up-mass and down-mass by removing the abort
capability provided by the Super Dracos.

Note that none of the other international cargo vessels launched to ISS
have ever had an abort system. This includes the commercial Cygnus and
Dragon cargo vessels.

NASA is requiring SpaceX to parachute all Dragon 2 capsules into the
ocean.


If commercial use of the ISS takes off, perhaps some cargo missions will
be non-NASA.

But (as I said in an earlier reply/correction to myself) propulsive
landing probably needs legs, which are no longer in the Dragon2 design,
so it won't happen.


Agreed. It will never happen. The legs were deleted from the design
because NASA told SpaceX that they would not allow propulsive landing
tests using returning Dragon 2 cargo vessels. It would have been
prohibitively expensive for SpaceX to fully test propulsive landings "on
their own dime".

You see, SpaceX wanted to test propulsive Dragon 2 landings on
operational cargo missions just like they tested Falcon 9 first stage
landings on operational missions. But the key difference was that a
failed Falcon 9 first stage landing in no way impacted the primary
mission. Where a failed Dragon 2 landing would have resulted in loss of
all cargo being returned from ISS.

NASA's reasoning is pretty obvious here, IMHO.

Jeff
--
All opinions posted by me on Usenet News are mine, and mine alone.
These posts do not reflect the opinions of my family, friends,
employer, or any organization that I am a member of.
 




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