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.
Quote from: JEF_300 on 08/29/2021 07:31 pmWhat 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.
Explanation for yesterdays abort: engines appeared to start-up a little slower than expected, so vehicle aborted. Today theyve preconditioned the vehicle (in an earlier hold) which should resolve the issue for todays attempt.Edit to add:https://twitter.com/nasaspaceflight/status/1431724835571474443QuoteAstra 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
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 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
so the consensus seems to be that this was an acceptable anomoly profile, lateral movement until vertical velocity occurred vs FTS activation.
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 didnt hit a tree.
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 ?
Quote from: savantu on 08/30/2021 10:33 amDoes 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.
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.
Quote from: catdlr on 08/29/2021 05:40 amSomeone 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 ?
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.
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?
A launch attempt the previous day was aborted an instant after engine ignition, which Astra later said was because the engine thrust wasnt ramping up as fast as expected. Right now we have no reason to believe these are related, Kemp said.
Quote from: savantu on 08/30/2021 10:33 amQuote from: catdlr on 08/29/2021 05:40 amSomeone 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?
Quote from: Lars-J on 08/30/2021 05:42 pmHuh? 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? 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.
Quote from: trimeta on 08/30/2021 06:03 pmQuote from: Lars-J on 08/30/2021 05:42 pmHuh? 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? 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.