I heard the commentators say they gimbal the sea level engines for the hot staging
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SpaceX Starship - Integrated Flight Test #2 - Starbase TX - Including Post Launch Dissection
- Thread starter Grendal
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I'd expect that, but I can think of two ways to interpret the statement in light of the vacuum engines being fired before the sea level engines:
1. The engines are gimballed and can be fired immediately but that they want a staggered start sequence, or
2. The engines are fired as soon as possible after getting some separation, and that gimballing allows them to be fired soonest
The telemetry says that there is a two second delay. I'm interpreting that as a need for a delay due to the proximity of the interstage, but it may be nothing more than a need to stagger start the engines.
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So on reflection, I think my WAG on post 321 is pretty accurate. Scott Manley added some more details as to why some engines didn't relight properly. Slowing down the stream as he did showcased the possible reason. Plumbing stress makes a lot of sense. We didn't see any eruptions or events that would have indicated significant internal disruption.
Starship ran true and smooth until it did have an event. The event didn't seem to shut down an engine but internal disruptions were likely happening until it got out of control about a minute later. All of which took it off course enough that the FTS likely kicked in.
The positive of the Starship event is that it took a while before RUD. I would expect that SpaceX has lots and lots of data of what failed and the process for the failure.
My WAG on the booster is a slightly longer delay before firing the second row of engines in the flip. Let the already firing gimballing center engines do the flip, then you fire up the second ring for the bulk of the boostback burn.
A more highlighted version of the launch:
Starship ran true and smooth until it did have an event. The event didn't seem to shut down an engine but internal disruptions were likely happening until it got out of control about a minute later. All of which took it off course enough that the FTS likely kicked in.
The positive of the Starship event is that it took a while before RUD. I would expect that SpaceX has lots and lots of data of what failed and the process for the failure.
My WAG on the booster is a slightly longer delay before firing the second row of engines in the flip. Let the already firing gimballing center engines do the flip, then you fire up the second ring for the bulk of the boostback burn.
A more highlighted version of the launch:
While there were a lot of things happening in the booster just before RUD and any of those could have been the catalyst for its RUD, the Starship anomaly is very puzzling given that it was out of the atmosphere and the engines were firing perfectly fine and smooth for quite a long time, essentially in a steady state, and with only a few more seconds to engine shutoff and start of coast phase. There is no event happening at that time to disrupt the Starship functioning at that stage of the flight.
Normally if you are that far into the flight there are not a lot of bad things that can happen.
Normally if you are that far into the flight there are not a lot of bad things that can happen.
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Agreed. When I watched Scott’s slo-mo video analysis and could easily see when and how the inner ring of engines ignited I was surprised that was occurring well before the flip was complete. Obviously I’m not a rocket scientist but I wondered why they didn’t wait a few more seconds before starting up the inner ring, closer to when the booster was fully pointed back towards the launch site. Of course they had their reasons, I just don’t understand them. Which is no surprise.
It looked to have started venting LOX (and maybe CH4?) around T+7:05 resulting in early shutdown of all engines ~35 seconds early.
Could have been issue with pressurization system like a stuck valve.
For anyone else who was curious, 1 degree of longitude at 25 degrees of latitude is 100km. So the booster debris is roughly 275 km east of the launch site and the debris field is about 100 km x 75 km.
And that lone green pixel center-left of the field... I think that's an engine. Now a marine sanctuary.
Scott Manley shows that booster may have had a bit too much Starship exhaust that induced deceleration (bad for liquid fuel location).
I’ve been re-watching the flight video and what is interesting to me is that after that initial venting the speed continues to increase but the altitude actually dropped 1km and then stayed at 148km right up to the point when telemetry was lost. At T+7:21 one of the web hosts says the ship is “still on a nominal trajectory with nominal pressures”. At 7:41 there is a big flare while Kate was speaking and she paused, as if it had caught her attention. At 7:48 there is a “terminal guidance” call out. Then at about 8:03 telemetry stops and I can faintly see in the image signs of expanding gases. At that point everyone goes quiet. I think they knew the mission was over.
It is different because they weren't going for a normal orbit. If Starship was in a flat to decending trajectory to begin with (which it was based on altitude changes) then it would accelerate due to gravity even with engines out.
Telemetry and video were ~4 seconds skewed based on staging engine readouts.
Buckminster
Well-Known Member
They need all 6 engines - more thrust means less gravity loss while fighting out of the well. Additionally, only the central 3 sea level raptors can gimbal (steer).
Long term the plan is actually 6 R-Vacs and the 3 gimballing sea level engines. Again, more thrust for lower gravity losses and greater payload to orbit.
Scott has a lengthy and detailed video analyzing the flight. Lots of interesting insights. And he noticed that on ascent before stage sep, Starship was losing tiles! It looks like SpaceX has a real challenge ahead to figure out how to reduce tile loss to basically zero before flying people.
From what I've seen of the tile images, the ones that have fallen off are primarily the ones that are hand-placed. Between barrel sections, next to fins, stuff like that. So they either need to automate more tile placement or they need to improve the hand process to ensure better quality.
dhanson865
Well-Known Member
It do. I've been scrubbing around the hour-long video just to get a sense of what his cameras saw without wading through the geekfest about the photography and how exclusive the footage is. Starship definitely went boom somewhere near the Keys. The bad news is that if the FAA sees the footage, they're going to realize that if the flight termination system was triggered, it didn't do its job. The video shows the top half of the Starship intact, complete with its control surfaces, zipping along. But how do you take apart such a huge object?
The video is pretty amazing. It's blurry and jumps around, so we'll have to wait for the stabilized version, but there are times where you can clearly make out the shape of the ship.
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