Author Topic: FAILURE: Astra Rocket 3.3 – STP-27AD1 – Kodiak – August 28, 2021 (22:35 UTC)  (Read 73092 times)

Offline joek

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What Astra just showed is why you need to thoroughly check that all your engines are running correctly before liftoff. If you do that correctly, then the failure Astra had isn't possible, no matter how many engines you have.

Astra stated the engine failed less than a second after liftoff--which I take as after all engines were verified to be performing nominally prior to clamp release (liftoff). Engine failure could happen to any LV, whether 1ms, 1 second, or 1 minute after release. Maybe Astra needs to improve verification of nominal engine performance prior to release; maybe it was GSE-related. We don't know enough to say at this point.

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What Astra just showed is why you need to thoroughly check that all your engines are running correctly before liftoff. If you do that correctly, then the failure Astra had isn't possible, no matter how many engines you have.

Astra stated the engine failed less than a second after liftoff--which I take as after all engines were verified to be performing nominally prior to clamp release (liftoff). Engine failure could happen to any LV, whether 1ms, 1 second, or 1 minute after release. Maybe Astra needs to improve verification of nominal engine performance prior to release; maybe it was GSE-related. We don't know enough to say at this point.

They scrubbed the day before because of a slow startup of one or more engines.

Explanation for yesterday’s abort: engines appeared to start-up a little slower than expected, so vehicle aborted. Today they’ve preconditioned the vehicle (in an earlier hold) which should resolve the issue for today’s attempt.

Edit to add:

https://twitter.com/nasaspaceflight/status/1431724835571474443

Quote
Astra has made some operational adjustments to counter yesterday's abort (slow engine ramp up), including a reconditioning hold earlier in today's count (thus the more to the right for the T-0).

T-55 mins.

➡️youtube.com/watch?v=O8Tdm7…

So they did check and something was off.  They "adjusted" things and tried again.  The engine tried to warn them the first time in my opinion.

Can anyone verify if the slow startup engines was the one that died?

Offline chrisking0997

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so the consensus seems to be that this was an acceptable anomoly profile, lateral movement until vertical velocity occurred vs FTS activation.  So were they just lucky that the engine that failed caused to vehicle to pitch in probably the most optimal direction to allow that path (which you have to wonder if they put the gate there for that very possibility?) or do we think the vehicle commanded that movement?  Would be interesting to know, and if its the later then that is pretty darn impressive
Tried to tell you, we did.  Listen, you did not.  Now, screwed we all are.

Offline darkenfast

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so the consensus seems to be that this was an acceptable anomoly profile, lateral movement until vertical velocity occurred vs FTS activation.  So were they just lucky that the engine that failed caused to vehicle to pitch in probably the most optimal direction to allow that path (which you have to wonder if they put the gate there for that very possibility?) or do we think the vehicle commanded that movement?  Would be interesting to know, and if its the later then that is pretty darn impressive

There seem to be three sections of fencing removed just before launch because of the way the pad diverts the jet.
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Offline launchwatcher

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so the consensus seems to be that this was an acceptable anomoly profile, lateral movement until vertical velocity occurred vs FTS activation.
Earlier posts on this thread suggest that Astra does not have a pyrotechnic FTS; the "FTS" just cuts the engines.
No doubt there's enough wide open unpopulated space around their launch area in on Kodiak Island that this is sufficient to keep regulators and insurers happy.

Offline SpeakertoAnimals

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There could be some very relevant data on the effect of ground plume impingement on unprepared surfaces.  I think I can see in the video the moment it slides/flies off the concrete over bare earth.  The plume gets dirtier.   Lucky it didn’t hit a tree.
Cool, we are entering a new age. If I may paraphrase, "We are lucky our orbital rocket didn't hit a tree."

Offline AstroDave

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  Looking at Astra wiki page, it showed a tentative schedule of two more flights (#7 & #8) before year end. Launch schedules are always optimistic, but with the anomaly on this past flight does Astra attempt another launch again before year end? Or, is their next attempt pushed into 2022? Is there any good information about status of hardware for future orbital attempt?
  Aware there are lots of unknowns here, but was interested in some informed opinions.

Offline savantu

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Someone was smart enough to open the perimeter gate so the rocket could escape out.;-)

That's the understatement of the month. Probably without that , it would have tumbled immediately after hiting the fence.

Does anyone know the T/W of Astra ? I mean it perfectly hovered sideways which is really strange, what's the likelyhood of that ?
« Last Edit: 08/30/2021 10:39 am by savantu »

Online Yggdrasill

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That's the understatement of the month. Probably without that , it would have tumbled immediately after hiting the fence.
Probably not, imho. I think the fence would lose that encounter.

The rocket could have hit the masts for cameras/lights/etc, though, not to mention the launch tower, so it was quite lucky that it didn't explode right next to the pad.

Does anyone know the T/W of Astra ? I mean it perfectly hovered sideways which is really strange, what's the likelyhood of that ?
Scott Manley mentioned a T/W of 1.25, which makes perfect sense. Losing one out of five engines would then drop the T/W to exactly 1. And then it would climb from there as it burns though propellant and gets lighter.

I think for this specific design, it's maybe not that unlikely. Typical T/W is often around 1.2-ish, so this scenario where you lose an engine and end up with a T/W of approximately 1 is really only likely to occur on a vehicle with 5-6 engines. That excludes every(?) other launch vehicle.
« Last Edit: 08/30/2021 11:00 am by Yggdrasill »

Offline niwax

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Does anyone know the T/W of Astra ? I mean it perfectly hovered sideways which is really strange, what's the likelyhood of that ?
Scott Manley mentioned a T/W of 1.25, which makes perfect sense. Losing one out of five engines would then drop the T/W to exactly 1. And then it would climb from there as it burns though propellant and gets lighter.

I think for this specific design, it's maybe not that unlikely. Typical T/W is often around 1.2-ish, so this scenario where you lose an engine and end up with a T/W of approximately 1 is really only likely to occur on a vehicle with 5-6 engines. That excludes every(?) other launch vehicle.

1.2 is very much at the low end. Saturn V was around 1.2, and they were really pushing the mass as far as they could while bumping against the limits of 1960s engine technology. The Falcons are over 1.4, even Electron is well over 1.3, not to speak of solids. Atlas exceeds 1.6 with only two solids. The Russians like to go over 1.5, as high thrust and good density play into the strengths of kerolox.

At 1.2, gravity losses become more noticeable and more importantly for an early attempt, they will need to uprate their engines or put in more for any stretch or payload increase.
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Offline Ken the Bin

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Chris Kemp provided this information about the TWR:

https://twitter.com/Kemp/status/1431831601445425157

Quote from: Chris Kemp
Five engines is 1.25:1 by design, in case this exact scenario happened.  With one out ~1:1 - for a few seconds - until some fuel is burned.

Offline meekGee

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Someone was smart enough to open the perimeter gate so the rocket could escape out.;-)

That's the understatement of the month. Probably without that , it would have tumbled immediately after hiting the fence.

Does anyone know the T/W of Astra ? I mean it perfectly hovered sideways which is really strange, what's the likelyhood of that ?
It was too precisely balanced..  If the T/W ratio was 1.24 or 1.26, it would have crashed in seconds or taken off..

Not to mention that propellant was being expended, and 10 seconds of almost full thrust is a lot of weight.

I think it was a sort of ground effect, even though the traditional type is not possible with a supersonic exhaust.  Call it blow back.  Just enough to balance the books.
« Last Edit: 08/30/2021 12:11 pm by meekGee »
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Online Yggdrasill

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1.2 is very much at the low end. Saturn V was around 1.2, and they were really pushing the mass as far as they could while bumping against the limits of 1960s engine technology. The Falcons are over 1.4, even Electron is well over 1.3, not to speak of solids. Atlas exceeds 1.6 with only two solids. The Russians like to go over 1.5, as high thrust and good density play into the strengths of kerolox.

At 1.2, gravity losses become more noticeable and more importantly for an early attempt, they will need to uprate their engines or put in more for any stretch or payload increase.
Fair enough. My point was really that there is a limited number of launch vehicles with 3-6 engines, which is where the scenario is most likely to occur. The number of engines must match the T/W of the launch vehicle, to drop down to a T/W of exactly 1 in the event one engine dies.

1. A LV with three engines needs a T/W of 1.5 to drop down to a T/W of 1 in the event one engine fails.
2. A LV with four engines needs a T/W of 1.33 to drop down to a T/W of 1 in the event one engine fails.
3. A LV with five engines needs a T/W of 1.25 to drop down to a T/W of 1 in the event one engine fails.
4. A LV with six engines needs a T/W of 1.2 to drop down to a T/W of 1 in the event one engine fails.

I can really only think of Astra that is close to one of the above scenarios. (And there are also some considerations like gimbal range that also matter. It's more likely to work with 5-6 engines than with 3-4 engines.)
« Last Edit: 08/30/2021 01:48 pm by Yggdrasill »

Offline FlatFootShift

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Will be interesting to see what caused the engine failure if it was the engine or something related to the running design changes from the previous unit that nearly reached the target. Hope Astra is ready to try again very soon. Tremendous faith in the team!

Offline Craftyatom

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So they did check and something was off.  They "adjusted" things and tried again.  The engine tried to warn them the first time in my opinion.

Can anyone verify if the slow startup engines was the one that died?
So far, this is what has been said on the matter, AFAIK (link):
Quote from: SpaceNews
A launch attempt the previous day was aborted an instant after engine ignition, which Astra later said was because the engine thrust wasn’t ramping up as fast as expected. “Right now we have no reason to believe these are related,” Kemp said.
All aboard the HSF hype train!  Choo Choo!

Offline Lars-J

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Someone was smart enough to open the perimeter gate so the rocket could escape out.;-)

That's the understatement of the month. Probably without that , it would have tumbled immediately after hiting the fence.

Does anyone know the T/W of Astra ? I mean it perfectly hovered sideways which is really strange, what's the likelyhood of that ?
It was too precisely balanced..  If the T/W ratio was 1.24 or 1.26, it would have crashed in seconds or taken off..

Not to mention that propellant was being expended, and 10 seconds of almost full thrust is a lot of weight.

I think it was a sort of ground effect, even though the traditional type is not possible with a supersonic exhaust.  Call it blow back.  Just enough to balance the books.

Huh? That makes no sense. What alternate form of physics are you using to assert that 1.26 would have been catastrophic where 1.25 was not?  :o
« Last Edit: 08/30/2021 05:43 pm by Lars-J »

Offline trimeta

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Huh? That makes no sense. What alternate form of physics are you using to assert that 1.26 would have been catastrophic where 1.25 was not?  :o

I think the claim is basically "if with 4/5 engines functioning, it had 1.01 TWR instead of 1.00, it would've ascended ("taken off") rather than hovered; that wouldn't have ultimately changed the rocket's fate, but it wouldn't match what we saw happen." However, I doubt that it was that sensitive to the exact TWR.

Online Lee Jay

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Huh? That makes no sense. What alternate form of physics are you using to assert that 1.26 would have been catastrophic where 1.25 was not?  :o

I think the claim is basically "if with 4/5 engines functioning, it had 1.01 TWR instead of 1.00, it would've ascended ("taken off") rather than hovered; that wouldn't have ultimately changed the rocket's fate, but it wouldn't match what we saw happen." However, I doubt that it was that sensitive to the exact TWR.

Yeah - it would have "taken off" at an acceleration of 0.01g = 0.098m/s^2 which means after 10 seconds it would have been ascending at a whopping 0.98m/s.  Since the smoke/dust/whatever obscured the camera view, we can't tell if it was in a perfect hover or not.  It may have descended slightly, hovered for a moment and started ascending slightly as fuel burned off, all before we saw it emerge from the smoke/dust/whatever and start picking up acceleration.

Offline TrevorMonty

Huh? That makes no sense. What alternate form of physics are you using to assert that 1.26 would have been catastrophic where 1.25 was not?  :o

I think the claim is basically "if with 4/5 engines functioning, it had 1.01 TWR instead of 1.00, it would've ascended ("taken off") rather than hovered; that wouldn't have ultimately changed the rocket's fate, but it wouldn't match what we saw happen." However, I doubt that it was that sensitive to the exact TWR.

Yeah - it would have "taken off" at an acceleration of 0.01g = 0.098m/s^2 which means after 10 seconds it would have been ascending at a whopping 0.98m/s.  Since the smoke/dust/whatever obscured the camera view, we can't tell if it was in a perfect hover or not.  It may have descended slightly, hovered for a moment and started ascending slightly as fuel burned off, all before we saw it emerge from the smoke/dust/whatever and start picking up acceleration.
May have been camera angle but after smoke cleared LV seem quite a distance away an well downhill before it started slow ascent.

I think it followed land down hill to some cliffs over the sea before gaining height. Shows negative speed ie falling in bottom right of video.


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Online Yggdrasill

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It showed negative speed while clearly ascending. So the telemetry from the feed can't be trusted.

My impression from the video is that is started climbing right from the start, although very slowly, and didn't decend (until after termination).



(Jump to 30 seconds in.)
« Last Edit: 08/30/2021 06:55 pm by Yggdrasill »

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