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SpaceX Dragon 2 In Flight Abort Test



 
 
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  #1  
Old January 14th 20, 01:04 PM posted to sci.space.policy
Jeff Findley[_6_]
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Posts: 2,057
Default SpaceX Dragon 2 In Flight Abort Test

Currently the SpaceX Dragon 2 In Flight Abort Test is scheduled for this
Saturday at 8:00 a.m. There is a four hour window for the test. The
reason there is a four hour window is that since it's not going into
orbit, it's not critical they launch "on time". I'm sure this will be
live-streamed by people like @EverydayAstronaut
https://everydayastronaut.com/
https://www.youtube.com/channel/UC6u...J1R2HMTY3LIx5Q

Hopefully it will be on NASA TV and possibly a live stream from SpaceX
as well.

Cites:

SpaceNews.com
SpaceX ready for Crew Dragon in-flight abort test by Jeff Foust
https://spacenews.com/spacex-ready-f...ht-abort-test/

SpaceX on final lap in the commercial crew space race
Rachael Joy, Florida Today
https://www.floridatoday.com/story/t.../01/14/spacexs
-flight-abort-test-final-milestone-before-crewed-flight/2835391001/

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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  #2  
Old January 15th 20, 03:45 AM posted to sci.space.policy
Greg \(Strider\) Moore
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Default SpaceX Dragon 2 In Flight Abort Test

"JF Mezei" wrote in message ...

On 2020-01-14 07:04, Jeff Findley wrote:
I'm sure this will be
live-streamed by people like @EverydayAstronaut


Wouldn't SpaceX live stream it? I would expect nothing less than views
from many on-board cameras. A good disaster movie :-)


I assume SpaceX will have a feed. But as I recall @EverydayAstronaut often
has better commentary.


I take it the ejection will happen at MaxQ? At that altitude, can
aircraft assets film the event?


Yes, it will happen at MaxQ.



Will Stage1 come back to land?


Only if any pieces wash up on shore.


What is the impact on Stage1 upon Dragon2 popping out? Is it a
survivable event where Stage1 could cut off engines, start falling and
then aim for the drone ship?


No, this is expected to be a "rapid scheduled disassembly event".

If "firing in the whole" (not really) doesn't break it up, atmospheric
disturbances will.

And if it survives that, hitting the water will ensure an RSDE.

Or does separation happening in "thick" atmosphere result in Stage1
hitting atmosphere in the wrong angle and causing breakup and fireworks?

Or are they actually going to detonate Stage1 prior to the abort and
also test the software/sensors that will automatically trigger the
Dragon abort?


No. We've been over this.




--
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CEO QuiCR: Quick, Crowdsourced Responses. http://www.quicr.net
IT Disaster Response -
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  #3  
Old January 15th 20, 01:39 PM posted to sci.space.policy
Jeff Findley[_6_]
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Posts: 2,057
Default SpaceX Dragon 2 In Flight Abort Test

In article ,
says...

On 2020-01-14 07:04, Jeff Findley wrote:
I'm sure this will be
live-streamed by people like @EverydayAstronaut


Wouldn't SpaceX live stream it? I would expect nothing less than views
from many on-board cameras. A good disaster movie :-)

I take it the ejection will happen at MaxQ? At that altitude, can
aircraft assets film the event?


I understand that the abort will actually happen at the time of maximum
drag, which isn't exactly maximum aerodynamic pressure. But, the two
are "close enough" that people just keep saying MaxQ.

Will Stage1 come back to land?


Absolutely not. It will be destroyed by the test. The first stage has
no grid fins or landing legs.

The Falcon 9 first stage will be simulating an abort, which means that
its engines will all shut down. So it will have little control
authority when Dragon 2 aborts. This will expose the (blunt) top of the
2nd stage directly to airflow, including exhaust from the Super Dracos.
This will no doubt cause the booster to tumble. It will therefore break
up quite quickly due to aerodynamic forces because launch vehicles that
are very tall and thin (fineness ratio) are simply not designed to fly
sideways through the air near the portion of the flight where it
experiences maximum aerodynamic pressure.

What is the impact on Stage1 upon Dragon2 popping out? Is it a
survivable event where Stage1 could cut off engines, start falling and
then aim for the drone ship?


See above. Or if you like here's a cite:

SpaceX test-fires rocket ahead of Crew Dragon in-flight abort test
January 11, 2020 Stephen Clark
https://spaceflightnow.com/2020/01/1...cket-ahead-of-
crew-dragon-in-flight-abort-test/

Or does separation happening in "thick" atmosphere result in Stage1
hitting atmosphere in the wrong angle and causing breakup and fireworks?


Again, the top of the 2nd stage will be directly exposed to airflow. It
is simply not designed for this.

Or are they actually going to detonate Stage1 prior to the abort and
also test the software/sensors that will automatically trigger the
Dragon abort?


I don't believe they're going to "detonate" stage 1 because it won't
have a chance to do so. On a crewed flight, the detonation would not be
commanded until after the Dragon 2 has time enough to escape. Falcon
will quite likely be torn apart by aerodynamic forces long before it has
a chance to self destruct.

Falcon 9 does have destruct devices. It also has an automated destruct
system that has been used on uncrewd flights. This article describes
that system:

https://www.floridatoday.com/story/t.../03/11/spacex-
autonomous-flight-safety-system-afss-kennedy-space-center-florida-
falcon9-rocket-air-force-military/98539952/

At the time this article was written, NASA had not yet decided if it
would use the aforementioned automated system on crewed flights. From
the article above:

NASA's Commercial Crew Program is reviewing the system and has
not yet accepted it.

"If done correctly, an automated system is actually safer,
more reliable than having a human in the loop," said Kennedy
Space Center Director Bob Cabana. "We've still got some work
to do before Commercial Crew is going to certify that this
is the way to go, but this is the future."

Cabana, a four-time shuttle astronaut, remembered how
shuttle crews before launches would meet with the Range
safety personnel who could decide their fate.

"We used to go visit the guys that sat on console that
would push the button and show them pictures of our kids
and get to know them," he said.

So, it's not clear to me whether or not crewed Dragon 2 flights will use
the automated system, or whether an actual range safety officer will
have to "push the button".

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.
  #4  
Old January 16th 20, 01:55 PM posted to sci.space.policy
Jeff Findley[_6_]
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Posts: 2,057
Default SpaceX Dragon 2 In Flight Abort Test

In article ,
says...

On 2020-01-15 07:39, Jeff Findley wrote:

I understand that the abort will actually happen at the time of maximum
drag, which isn't exactly maximum aerodynamic pressure.


is drag different because it includes drag alongside the stage whereas
MaxQ only measures pressure at the tip end of rocket ?


Pretty much.

Absolutely not. It will be destroyed by the test. The first stage has
no grid fins or landing legs.
The Falcon 9 first stage will be simulating an abort, which means that
its engines will all shut down.


Thanks. So at the time the Super Dracos lift Dragon off the stack, the
stack will no longer be producing thrust but still get a lot of drag.


Correct.

From the point of view of testing the worse case scenario, shouldn't the
capsule eject be tested at MaxQ while engines still producing thrust?
Or do all failure scenarios conjured up always involve capsule eject at
time of or after loss of thrust from lower stage?


No. In the case of any abort during first stage burn, the Falcon 9
simultaneously shuts down the engines and sends the "GTFO" signal to
Dragon 2 to initiate its abort. That's one advantage of having a liquid
fueled stage rather than SRBs (which are harder to shut down reliably
without a lot of transient forces being sent through the stack).

So it will have little control
authority when Dragon 2 aborts.


I realize this is moot because any actual abort scenario implicitely
means the lower stage has something very wrong with it, but
**theoretically**, could fins located at the top (front) control
trajectory to keep it "flying" until it has slowed enough to flip and
start to descent engine first? (theoretically)


Again, the 2nd stage isn't designed to handle the loads of being in the
atmosphere without *something* on top of it to handle the aerodynamic
forces. It will likely shred. That will make for quite an
"interesting" environment for the first stage.

Also, if something is "horribly wrong" with the first stage, trying to
land it, either on land in Florida or on the ADS, is "not a good idea".

Or is the speed/air density at that point make it impossible to even
deploy the fins ?


That too. The grid fins on the first stage are designed to deploy in
vacuum *before* first stage reentry. No doubt the actuators don't have
the strength to deploy. Also, even if they did deploy, they'd likely
rip right off anyway.

This will expose the (blunt) top of the
2nd stage directly to airflow, including exhaust from the Super Dracos.


Assuming for a second a more or less intact Stage 1, would the exhaust
from the Super Dracos compromise the top of Stage 1's tank and cause
some pretty fireworks? Or is the direction of the escape engines exhaust
such that impingement onto the top of Stage 1's tanks won't happen?


Again, you're forgetting there is a fully fueled *second stage* between
the two. Falcon 9 ain't an SSTO. Remember how Challenger was ripped
apart by aerodynamic forces? That's what's going to happen on this
abort to both the first and second stages of Falcon 9.

I don't believe they're going to "detonate" stage 1 because it won't
have a chance to do so.


If the trigger is shutdown of engines, then there is no need to detonate
it. Hopefully we get nice footage of the stage as it starts to veer off
course and eventually breaks off.


I'd imagine that events will unfold very quickly. Again, remember what
happened to Challenger. It ripped apart in seconds.

In the event of rocket veering off course and aiming for the White
House, when it leaves it cone of normal flight, what order are commands?

Shutdown engines, initiate eject, initiate range safety? (with shutdown
of engines possibly not happening)


First two happen simultaneously. Range safety likely comes later. NASA
and SpaceX would know the details (likely dictated by NASA for crew
safety).

Also, engine shutdown *will* happen. If you rip the engine control
module from a modern car, the engine doesn't keep running. It's a
necessary component to keep it going. A liquid fueled rocket engine
should be much the same. Absent being commanded to "keep going", I'd
imagine valves are designed to "fail safe", which means shutting the
thing down.

NASA's not going to crew rate any vehicle that doesn't have a way to
reliably terminate thrust. For liquids, that's relatively easy to
design into the system.

Shutdown engines, initiate range safety, and initiate capsule eject?


No.

Or would it be just capsule eject and then range safety ?


Yes.

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.
  #5  
Old January 18th 20, 04:17 PM posted to sci.space.policy
Jeff Findley[_6_]
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Posts: 2,057
Default SpaceX Dragon 2 In Flight Abort Test

In article ,
says...

On 2020-01-16 07:55, Jeff Findley wrote:

No. In the case of any abort during first stage burn, the Falcon 9
simultaneously shuts down the engines and sends the "GTFO" signal to
Dragon 2 to initiate its abort.


Pedantic question: You had mentioned shutdown of engines and GTFO happen
simultaneously. Is that absolutely at same time, or is there a short
pause between sending command to engines and sending command to Dragon?
(to give engines time to initiate shutdown). If not, wouldn't Drago
essentiall launch off Falcon9 with Falcon9 engines still at full thrust?


NASA knows the details of this for sure. But I believe that the Super
Draco engines are sized to pull Dragon 2 away from Falcon 9 at the same
time the engines are shutting down.

Cite:

SpaceX delays dramatic Crew Dragon abort test due to high winds and
rough seas. BY WILLIAM HARWOOD, JANUARY 18, 2020 / 7:05 AM / CBS NEWS
https://www.cbsnews.com/news/spacex-...nch-in-flight-
abort-test-to-prove-crew-ship-safe-delay-2020-01-18/

From the article:

The Falcon's engines will shut down as the Crew Dragon's
eight Super Draco abort engines ignite, pushing the capsule
away from the now-powerless booster with an acceleration a
race car driver would envy. Within just a few seconds, the
spacecraft will reach a relative velocity of some 430 mph,
subjecting two heavily instrumented astronaut test dummies
to more than four times the normal force of gravity.

Sounds simultaneous to me. Also, shutting down the liquid fueled
engines should only take a fraction of a second anyway. Also note the
acceleration of more than 4 Gs that Dragon 2 will experience while the
Super Dracos are firing at full thrust. This is much more acceleration
than would normally be experienced during that part of the flight, so
that would no doubt be sufficient acceleration to pull away from a
Falcon 9 that's still firing (even though that won't ever happen).

Also, in cases where the rocket veers off course, is range safety
totally eparate from abort and only triggered from ground? or can the
stage 1 initiate it by itself?


I posted another article on Falcon 9's automatic abort system. This
system eliminates the need for anyone on the ground to do anything as it
will terminate thrust and destruct the vehicle.

This article also said NASA was still evaluating its use on crewed
flights. So you'd have to ask NASA.

And theoretically, can ground initiate range safety with the crewed
capsule still attached? or would range safety command, ujpon reception
by the Falcon 9, initiate the abort if it wasn't fonr already and then
light up the fireworks?


No one in their right mind would destruct a vehicle with a crewed
capsule still attached (automated or manual). But to verify, you'd have
to ask NASA.

or is range safety such that once triggered, Falcon9 will detect
anomaly, initiate the abort and Dragon 2 will be out before the
fireworks have reached the top of the stack?


Thrust termination and destruction are two separate events. No doubt on
a crewed flight thrust termination would come first (simultaneous with
telling Dragon 2 to abort). Destruction of Falcon 9 would happen later.
But destruction of Falcon 9 will likely be moot since aerodynamic forces
will rip it apart before the deliberate destruct happens.

Remember Challenger. It was ripped apart *very* quickly by aerodynamic
forces. Falcon 9 will face the exact same fate.

Out of curiosity, how do they measure how much thrust is produced by
each engine? A sensor that measures pressure against the wall of the
engine bell? An electronic scale measuring "weight" of engine against
the mounting brackets of the stage?

Or is thrust assumed from speed of turbopumps (fuel flow)?


You'd have to ask SpaceX. But suffice it to say that there are enough
sensors such that there are many ways you'd verify the engine is working
properly. When something goes wrong with a first stage engine, the
Falcon 9 computers will know this and shut down that one engine,
compensate for loss of thrust with the other engines, and the flight
will continue. An upper stage engine failure is different since there
is only one Vacuum Merlin on the upper stage.

Abort for Dragon 2 during first stage burn (which is what this abort
simulates) will only happen for some sort of massive failure.

I assume that thrust from each engine is a huge component for the "abort
scenario" software in terms of not only detecting non-nominal engine,
but also deciding if flight can continue? ex: loss of 2 engines on
same side vs loss of 2 engines opposite each other).


You'd have to ask SpaceX. Since there has only been loss of thrust on
one Merlin engine in flight on all of the flights of Falcon 9, I'd say
the demonstrated reliability of the engine (and the armor between them)
makes failure of more than one engine on the first stage *very*
unlikely. Still, the Dragon 2 abort system is there in case of such an
unlikely event.

That's one advantage of having a liquid
fueled stage rather than SRBs (which are harder to shut down reliably
without a lot of transient forces being sent through the stack).


I take it the SLS SRBs have "zipper" explosives similar to shuttle?


For range safety, one would hope so.

Once
SLS is put out of its misery, is it safe to bet that we won't see SRBs
used for manned flight anymore, or would NASA still be open to the idea?


Note that Atlas V will use solids on the crewed configuration used for
Starliner launches. They're much smaller solids, but they are still
there.

Again, the 2nd stage isn't designed to handle the loads of being in the
atmosphere without *something* on top of it to handle the aerodynamic
forces. It will likely shred.


I hadn't realised there was a 2nd stage. Thansk for clarification. I
though it was Dragon, its service module and Falcon 9 first stage.


Test as you fly; fly as you test. Not having an upper stage on this
flight would violate that principle. The mass and aerodynamics of the
launch vehicle would be all wrong and would have to be compensated for.
Because of this, it's just easier to stick a real upper stage on the
stack and fully fuel it, just like a real commercial crew launch.

From the animatiosn I have seen, Dragon ejects with its service module
still attached (apparently for aerodynamic purposes), and only at apogee
does it detach, capsule uses thrusters to set descent attitude , deploys
parachutes


Yes. The fins on the trunk aren't there to look pretty. They keep the
capsule stable during the abort, up to max altitude (essentially zero
velocity).

If there is a second stage, would this be a dummy one just for mass
equivalence, or would they have a real McCoy that is destroyed without
having done anything ?


It's a real, fully fueled, Falcon 9 upper stage. Only the Vacuum Merlin
is a "dummy" mass simulator on this abort test since the upper stage
won't need to be fired on this flight.

Again, test as you fly; fly as you test.

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.
  #7  
Old January 18th 20, 11:53 PM posted to sci.space.policy
Niklas Holsti
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Posts: 128
Default SpaceX Dragon 2 In Flight Abort Test

On 2020-01-19 0:11, JF Mezei wrote:
On 2020-01-18 10:17, Jeff Findley wrote:

NASA knows the details of this for sure. But I believe that the Super
Draco engines are sized to pull Dragon 2 away from Falcon 9 at the same
time the engines are shutting down.


Media articles tend to "Readers Digest" what is given to them by
authorities which are already a Reders Digest version of reality.

Say an abort happens for causes other then engines. If engines are
already giving astronauts a 3G acceleration, and you fire the Super
Dracos that give 4G, the crew would go from 3G to 7G


No. If the Dragon is still attached to the launcher when the Dracos
fire, the acceleration would only increase a little, as the Draco thrust
is added to the Merlin thrust to accelerate the launcher+Dragon assembly.

If the Dragon is not attached to the launcher when the Dracos fire, the
Dragon will simply pull ahead of the launcher, at 4G, losing contact
with the launcher which will fall behind, the distance increasing at 1G.
In theory, the launcher's acceleration might increase a little when the
Dragon pulls away, because the launcher no longer has to accelerate the
Dragon's mass, but I believe that the control SW keeps the launcher's
acceleration at its programmed value, and the Dragon's mass is anyway
only a fraction of the mass of the launcher and its fuel.

Also, I believe that typically Falcon-9 will accelerate at much less
than 3G around Max-Q. In an earlier discussion, numbers in the range
0.5G - 1G (on top of gravity) were used, taken from some time-velocity
diagrams of actual launches.

--
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  #8  
Old January 19th 20, 01:18 AM posted to sci.space.policy
Alain Fournier[_3_]
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Posts: 416
Default SpaceX Dragon 2 In Flight Abort Test

On Jan/18/2020 at 17:53, Niklas Holsti wrote :
On 2020-01-19 0:11, JF Mezei wrote:
On 2020-01-18 10:17, Jeff Findley wrote:

NASA knows the details of this for sure.* But I believe that the Super
Draco engines are sized to pull Dragon 2 away from Falcon 9 at the same
time the engines are shutting down.


Media articles tend to "Readers Digest" what is given to them by
authorities which are already a Reders Digest version of reality.

Say an abort happens for causes other then engines. If engines are
already giving astronauts a 3G acceleration, and you fire the Super
Dracos that give 4G, the crew would go from 3G to 7G


No. If the Dragon is still attached to the launcher when the Dracos
fire, the acceleration would only increase a little, as the Draco thrust
is added to the Merlin thrust to accelerate the launcher+Dragon assembly.

If the Dragon is not attached to the launcher when the Dracos fire, the
Dragon will simply pull ahead of the launcher, at 4G, losing contact
with the launcher which will fall behind, the distance increasing at 1G.
In theory, the launcher's acceleration might increase a little when the
Dragon pulls away, because the launcher no longer has to accelerate the
Dragon's mass, but I believe that the control SW keeps the launcher's
acceleration at its programmed value, and the Dragon's mass is anyway
only a fraction of the mass of the launcher and its fuel.


Yes. Note also that even if the Dragon capsule did experience 7g for a
few seconds, that wouldn't be a problem. Such an acceleration is a
problem if it is sustained but for a few seconds 7g is uncomfortable but
not really dangerous.


Alain Fournier
  #9  
Old January 19th 20, 03:57 PM posted to sci.space.policy
Jeff Findley[_6_]
external usenet poster
 
Posts: 2,057
Default SpaceX Dragon 2 In Flight Abort Test

In article ,
says...

On 2020-01-18 10:17, Jeff Findley wrote:

NASA knows the details of this for sure. But I believe that the Super
Draco engines are sized to pull Dragon 2 away from Falcon 9 at the same
time the engines are shutting down.


Media articles tend to "Readers Digest" what is given to them by
authorities which are already a Reders Digest version of reality.

Say an abort happens for causes other then engines. If engines are
already giving astronauts a 3G acceleration, and you fire the Super
Dracos that give 4G, the crew would go from 3G to 7G and drop to 4G.


That's not how acceleration works. In the case you state, Falcon 9
would continue to accelerate a 3G, but the Dragon 2 will accelerate at
4G. So, Dragon 2 still pulls away from the Falcon 9.

But this *can't happen*. If Dragon 2 aborts, the engines will stop.
That's how the abort system is designed.

If the capsule ejects after engines have ended thrust, then crew go from
3G to 0G to 4G.


These numbers are correct.

So it would seem to me that the sequencing becomes important. And I
suspect that a command to shut down engines doesn't result in immediate
end of thrust.


Not immediate, but quite quick. However fast the input valves leading
to the gas generator can be shut dictates how quickly the engines will
stop. No gas generator means no power for the pumps.

Since these engines are designed to not get damaged when
stopped, I would assume there is a smooth progressive shutdown as
opposed to abruptly ending fuel/oxydizer flow or abruptly putting the
space equivalent of a pump through a bike wheel's to stop the turbopumps.


Firstly, Merlin engines are designed to throttle. They can already
adjust thrust quickly. Shutting down simply uses the same
actuators/valves as throttling. It therefore follows you can shut them
down very quickly as well.

Also, in an abort situation, you don't care one bit if you destroy the
engines (i.e. turbopumps) in the process of quickly shutting them down.
If you're in an abort situation, you're *already* having a "bad day" and
are trying to save the crew's lives! So, you don't care that the Falcon
9 first stage will be lost. This simply isn't the same situation as
carefully shutting down the Merlins when landing a Falcon 9 in order to
prevent engine damage.

This is akin to ejecting from a fighter jet. No one gives a damn about
the fighter jet "surviving" an ejection. Same thing with a Falcon 9
during an abort.

that would no doubt be sufficient acceleration to pull away from a
Falcon 9 that's still firing (even though that won't ever happen).


And if Stage 2 is exploding while Stage 1 is intact, then super Dracos
firing ASAP is more important than waiting for Stage 1 to shut down.


Regardless of the situation, Dragon 2 will leave *immediately*. Which
is to say it will start pressurizing the tanks for the Super Dracos the
instant that it receives the abort signal. Once the pressure is
sufficient, the Super Dracos fire. This happens in fractions of a
second, but it's all carefully sequenced.

Simultaneous with the above, Falcon 9's engines will be shut down.

Since the Super Dracos have variable thrust, I wonder if at ejection
time, the initial thrust would be adjusted based on how many G2 the crew
are experiencing already and trhen quickly increase to max in order to
make the "jolt" more survivable.


Dragon 2 under power of the Super Dracos will generate more than 4 Gs of
acceleration. The idea is to save the crew's lives. The human body can
take that jerk to 4 Gs. Look up the USAF ejection seat tests done
decades ago. This acceleration is quite tame compared to what e-seats
expose USAF pilots to.

I posted another article on Falcon 9's automatic abort system. This
system eliminates the need for anyone on the ground to do anything as it
will terminate thrust and destruct the vehicle.


When you had aexplained it I though you refered onto to abort, didn't
realise it also included range safety.


Obviously the two systems are related. If you abort, obviously range
safety comes next. But in many cases, like this abort test, the abort
will result in the destruction of the Falcon 9 launch vehicle before the
range safety system attempts to fire.

No one in their right mind would destruct a vehicle with a crewed
capsule still attached (automated or manual). But to verify, you'd have
to ask NASA.


NASA wouldn't admit to it. But consider a rocket headed directly to
Disneyworld. Two crew abord, abort fails. Thousands on the ground.
Someone would have to make a hard decision. pretty sure NASA would have
to press the big red button.


This situation simply *can't* happen. Dragon 2 would abort *long*
before "imminent danger" to anyone on the ground. Also, this is why
Falcon 9 flies *east* out over the ocean. Nothing launched from KSC
flies towards Orlando.

making sure the Abort works is this very very important to avoid NASA
ever having to make that decision.


Which is why the abort system needs to be as simple as possible. This
is why both Dragon 2 and Starliner use a pressure fed system using
hypergolic propellants. It's about as simple as it can be.

telling Dragon 2 to abort). Destruction of Falcon 9 would happen

later.
But destruction of Falcon 9 will likely be moot since aerodynamic forces
will rip it apart before the deliberate destruct happens.


Range safety had been initiated for a Cygnus launch as its engine
failed seconds after clearing tower. At that moment, there woudln't be
aerodynamic forces to break the stage apart.


This is why both Dragon 2 and Starliner have already performed pad abort
tests (both passed). The pad abort test covers the other extreme, which
is the one where you don't even clear the tower when the abort is
initiated.

And say Stage1 engines shut down prematurely 2 minutes before planned
MECO. High enough that aeronynamic forces no longer "Lethal" but the
inert stage might fall over Spain in a purely ballistic course. So a
decision to detonate it might be made by human.


True, but again, Dragon 2 will have aborted long before the destruct
command would need to be sent to Falcon 9. Falcon 9 destruct would
always happen after Falcon 9 thrust termination and Dragon 2 abort.

Remember Challenger. It was ripped apart *very* quickly by

aerodynamic
forces. Falcon 9 will face the exact same fate.


But only a portion of flight sees lethal aerodynamic forces. Before
that portion, not enough speed, and after it, atmosphere too thin.


True, which is why there is a huge exclusion zone during *any* launch
from KSC/Cape Canaveral. This zone is miles around the pad and
continues beneath the flight path. So even in the case of an abort
where a deliberate destruct will happen, destruct still happens after
Falcon 9 thrust termination and Dragon 2 abort.

When thrust terminates, the stack is still on a ballistic trajectory.
Thrust would be terminated long before the launch vehicle deviates from
its path enough to be outside the launch exclusion zone. That's why the
launch exclusion zone is there in the first place.

You'd have to ask SpaceX. But suffice it to say that there are enough
sensors such that there are many ways you'd verify the engine is working
properly.


Would have expected a simple answer.


It is a simple answer. Either your sensors indicate the engine is
working properly, or they don't.

It would seem to me that in a
context where software gets to decide to initiate abort, situational
awareness of health/power generated by each engine is very important.


If the sensors say the engine is going to go FUBAR, it is shut down. On
a Falcon 9 first stage, that doesn't mean the flight is over. It means
the other 8 engines take over for the one that's shut down. Shutting
down one of eight engines does not automatically trigger an abort.

Decising that loss of an engine is survivable depends on knowing the
thrust of other engines is nominal, and that loss of 2 engines does not
result in inability to keep balanced thrust to stay on course. And there
is also a decision on whether to continue with reduced thrust and
deposit Dragon and its stage2 in a sub-suborbital place where they can
then plan and prepare for de-orbit vs initiating abort.


Merlins can throttle and gimbal. Shutting down one engine doesn't mean
you shut down the opposite engine. When an SSME was shut down on a
shuttle flight (due to a faulty sensor), they didn't have to shut down
any other engines. In fact, they inhibited the faulty sensors on the
other two engines and did an Abort To Orbit.

And from a business point of view, if there is loss of engines that
prevent continuation of flight, but engines needed to land are still
healthy, it means that while the mission may have to be aborted, the
stage could land safely and Dragon perform controlled re-entry/landing.


That doesn't apply to crewed flight. If the crew needs to abort, no one
gives a rat's ass about trying to recover the Falcon 9 first stage.

Innertial measurement can be made at top of rocket to measure its
acceleration, but that doesn't give health info for each engine, just
overall thrust being generated.


Merlins have enough sensors to monitor the health of the engine. It's
how the computers decide whether or not to shut down an ailing engine.

Jeff
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  #10  
Old January 19th 20, 04:48 PM posted to sci.space.policy
Jeff Findley[_6_]
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Posts: 2,057
Default SpaceX Dragon 2 In Flight Abort Test

The launch abort test was just completed. I watched it live on the
SpaceX live stream. Everything appeared to have happened as predicted.
Thrust termination on Falcon 9 and Dragon 2 separation happened very
close to each other (I couldn't see any delay). Everything went very
smoothly. Four good main parachutes fully deployed before splashdown.

The SpaceX engineer who was one of the commentators for the live stream
said this is the Mark 3 design for the parachutes. They looked really
good. There was an awesome live camera view from the parachute
compartment on Dragon 2 looking up at the parachutes. You could see all
of the deployment steps (they don't just open all the way right away).

Congrats to SpaceX and NASA. Here's hoping that the reviews being
conducted by NASA go smoothly so that we can see a crewed demo flight to
ISS within the upcoming months.

Jeff
--
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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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