SpaceX Falcon 9 FT - ORBCOMM-2 - Dec. 21, 2015 (Return To Flight) DISCUSSION

[Jim]

Is there any possibility the in flight abort for Dragon 2 to be the RTF mission ?
The real question is will it be ready on time.
If it is, it poses the least demand on the F9R booster:
 1 - Its only until MaxQ
 2 - It offers the maximum fuel margins for recovery
 3 - It's planned to reuse the already used Dragon V2
On the downside, as a partial mission, it wouldn't test F9R on a complete mission but it should increase confidence for more takers to go on the follow on mission.

It doesn't use a second stage which is the part that failed, so it would not be an RTF mission.  So it does not do anything for confidence building.

[Steven Pietrobon]

e a second stage which is the part that failed, so it would not be an RTF mission.  So it does not do anything for confidence building.

Aren't the same struts used on the first stage to hold the Helium bottles? I would have thought flying the new struts on the first stage would have added some confidence.

[rpapo]

e a second stage which is the part that failed, so it would not be an RTF mission.  So it does not do anything for confidence building.

Aren't the same struts used on the first stage to hold the Helium bottles? I would have thought flying the new struts on the first stage would have added some confidence.

Same struts, but a very different stress profile.  In the first stage, by the time the G forces get high, the bottles are no longer submerged in LOX nor fuel, and the bottles are more than half empty, and therefore lighter.  In the second stage, during the same time, the bottles are completely submerged, and therefore more and more buoyant as the acceleration mounts.  The stresses are much greater in the second stage, and in the opposite direction.

[kdhilliard]

Same struts, but a very different stress profile.  In the first stage, by the time the G forces get high, the bottles are no longer submerged in LOX nor fuel, and the bottles are more than half empty, and therefore lighter.  In the second stage, during the same time, the bottles are completely submerged, and therefore more and more buoyant as the acceleration mounts.  The stresses are much greater in the second stage, and in the opposite direction.

I'm not proposing the In-Flight Abort Test as a RTF mission, but according to Musk the first stage COPVs were still submerged at the time of the CRS-7 anomaly.

33:40 Elon Musk: Yeah. They were all at the same g-levels. Now the buoyancy force, once the liquid level drops below the position of the helium bottle, the buoyancy force drops dramatically, of course, but that was not the case at that point. All the helium bottles were experiencing approximately the same buoyancy force for the upper and lower stage.

~Kirk

[rsnellen4]

Is there any possibility the in flight abort for Dragon 2 to be the RTF mission ?
The real question is will it be ready on time.

In addition to the technical aspects already covered, the visuals wouldn't be helpful - even with all the publicity in the world, casual observers will only see video of the "latest SpaceX launch abort".




(Oh by the way, it was planned that way)

[Kabloona]

Is there any possibility the in flight abort for Dragon 2 to be the RTF mission ?
The real question is will it be ready on time.

In addition to the technical aspects already covered, the visuals wouldn't be helpful - even with all the publicity in the world, casual observers will only see video of the "latest SpaceX launch abort".

Especially not the visual of stage 1 breaking up from aero loads after Dragon sep.

[yokem55]

Especially not the visual of stage 1 breaking up from aero loads after Dragon sep.

It was probably a combination of the aero loads (relatively weak at that altitude, but unbalanced) and a vastly higher G loads from the higher TWR of burning near full throttle a mostly empty first stage with no dragon and mostly empty stage 2 (no lox, rapidly leaking rp1 tank).

Any guesses on what the TWR was before the first stage broke up?

[Greg Hullender]

It was probably a combination of the aero loads (relatively weak at that altitude, but unbalanced) and a vastly higher G loads from the higher TWR of burning near full throttle a mostly empty first stage with no dragon and mostly empty stage 2 (no lox, rapidly leaking rp1 tank).

Any guesses on what the TWR was before the first stage broke up?

Zero. The vehicle sharply throttled down at the first sign of trouble.

http://forum.nasaspaceflight.com/index.php?topic=37954.msg1401452#msg1401452

Supposedly, that's a sign the FTS was activated, and I was pretty sure it was the FTS that destroyed the vehicle a few seconds later. What makes you think it had anything to do with aerodynamics?

[Jim]

Zero. The vehicle sharply throttled down at the first sign of trouble.


Supposedly, that's a sign the FTS was activated,

Neither are true.  There is nothing in the vehicle that would sense the problem and issue commands to the booster. 
Where is the info that states that the FTS was activated?  The ground command was sent more than 70 seconds after the vehicle was gone.

[Kabloona]

Especially not the visual of stage 1 breaking up from aero loads after Dragon sep.

It was probably a combination of the aero loads (relatively weak at that altitude, but unbalanced) and a vastly higher G loads from the higher TWR of burning near full throttle a mostly empty first stage with no dragon and mostly empty stage 2 (no lox, rapidly leaking rp1 tank).

I was commenting on the likely outcome of the future in-flight abort test, which will be done at near max-Q, not the CRS-7 failure.

[Greg Hullender]

Zero. The vehicle sharply throttled down at the first sign of trouble.


Supposedly, that's a sign the FTS was activated,

Neither are true.  There is nothing in the vehicle that would sense the problem and issue commands to the booster. 
Where is the info that states that the FTS was activated?  The ground command was sent more than 70 seconds after the vehicle was gone.

So how do you explain the velocity graph?

[Jim]

So how do you explain the velocity graph?

Bad data. Do you know that the source is valid?  There was no second stage avionics <0.5 seconds after the plume.

[kraisee]

Jim is right that the velocity data should be considered 'suspect', as should all vehicle data after the LOX began to leak around the avionics bay.   It all needs to be examined and verified before anyone can determine its veracity -- and we here on a public forum just aren't ever going to get to see the results of that data analysis!

Do we even know that the velocity data you have seen actually came from vehicle telemetry?   Could it have been ground radar?   Could that have been picking up the rapidly decelerating plume cloud following the vehicle, not just the rocket?   Can anyone prove it didn't?

But even if were to make the assumption that it is correct, the event itself can still easily explain the numbers.   One possibility:   The loss of the aerodynamic Dragon capsule on top, left the vehicle completely un-aerodynamic.  A dramatically higher Cd would result in significantly lower acceleration.

In such a situation it is not wise to get attached to personal theories.   It tends to be little more than a great recipe for missing something else, often something important.   Even the brilliant Richard Feynman famously did that, much to his own embarrassment!

Ross.

[dorkmo]

(homeless "RTF party thread" post)

just remembered this scene from independnce day. a prelaunch conversation between the autonomous spaceport drone ship and the falcon9 rocket.

https://www.youtube.com/embed/OYSRthKDYEc

i miss the thrill of landing attempts. heres to picking up where we left off.

[mlindner]

It was probably a combination of the aero loads (relatively weak at that altitude, but unbalanced) and a vastly higher G loads from the higher TWR of burning near full throttle a mostly empty first stage with no dragon and mostly empty stage 2 (no lox, rapidly leaking rp1 tank).

Any guesses on what the TWR was before the first stage broke up?

Zero. The vehicle sharply throttled down at the first sign of trouble.

http://forum.nasaspaceflight.com/index.php?topic=37954.msg1401452#msg1401452

Supposedly, that's a sign the FTS was activated, and I was pretty sure it was the FTS that destroyed the vehicle a few seconds later. What makes you think it had anything to do with aerodynamics?

I wouldn't trust a rendered number on a web stream to provide accurate data. There could easily be smoothing algorithms being run over the raw data being sent back for display in the live video to prevent spiky numbers and if the feed suddenly cut off and the code kept reporting the same value then it would gradually decelerate just as shown in the graph generated from the video frames. You shouldn't draw any conclusions from the numbers in the video or from that graph.

[Jet Black]

Zero. The vehicle sharply throttled down at the first sign of trouble.


Supposedly, that's a sign the FTS was activated,

Neither are true.  There is nothing in the vehicle that would sense the problem and issue commands to the booster. 
Where is the info that states that the FTS was activated?  The ground command was sent more than 70 seconds after the vehicle was gone.

So how do you explain the velocity graph?

It doesn't matter for the sake of his answer; the fact which we know is that the ground command for FTS was sent 70s later, so any theory that has FTS being activated well before then is wrong (unless you want to say that the FTS system is faulty)

[Sesquipedalian]

It doesn't matter for the sake of his answer; the fact which we know is that the ground command for FTS was sent 70s later, so any theory that has FTS being activated well before then is wrong (unless you want to say that the FTS system is faulty)

Supposedly the onboard FTS activated when it detected the disintegration of the second stage, independent of any ground command.

I say "supposedly" because I was fairly certain Gwynne Shotwell said this in one of the press updates, but I can't find the quote.

[PreferToLurk]

It doesn't matter for the sake of his answer; the fact which we know is that the ground command for FTS was sent 70s later, so any theory that has FTS being activated well before then is wrong (unless you want to say that the FTS system is faulty)

I am less certain than Sesquipedalian that we have a quote on the activation of the FTS, however in theory he is correct.

We know for certain that the ground control FTS was not activated in the timeframe of vehicle destruction, but that does not rule out an FTS destruction of the first stage. IIRC, the stage is capable of triggering the FTS all by itself.  I don't believe we have a statement confirming automated FTS, but I am also pretty sure that it has not been ruled out.

That being said, using the on-screen velocity figure as evidence of ANYTHING is silly - we have no idea how that graphic is created nor the source of the data.

The exact mechanism behind the first stage destruction is (IMHO) still up to speculation, and any statements of a definitive cause should be presented with a link to the proof. Even if its paywalled or L2 - link it up and at least claim a definitive answer so that we can know and move on.

[the_other_Doug]

Kim Keller has stated here that since the S1 engines were observed to continue to fire right through the RUD of S2, that the FTS was never activated, because the first thing the FTS does is shut down the engines.  Since the engines were observed to continue to fire right up to the point where S1 came apart, he concluded that the FTS never activated.  Since Kim is one of the stalwart pros here, I tend to believe him.

[PreferToLurk]

Kim Keller has stated here that since the S1 engines were observed to continue to fire right through the RUD of S2, that the FTS was never activated, because the first thing the FTS does is shut down the engines.  Since the engines were observed to continue to fire right up to the point where S1 came apart, he concluded that the FTS never activated.  Since Kim is one of the stalwart pros here, I tend to believe him.

Yup, that's plenty good enough for me. Now that you mention it, I do recall that discussion. So outside a direct contradiction from SpaceX, I think that is settled.

Now I have heard that there are break-wires between the stages that are supposed to trigger the FTS. So, should have the FTS fired? Is this a secondary failure that no one is talking about, or is the first stage supposed to ignore a disintegrated second stage?