I still can't get over that front flap burning through, being shredded/burned lube on camera and still working when the time came. How did that still work?

[–] gressen@lemm.ee 18 points 5 months ago* (last edited 5 months ago)

Parts of the flap got burned and/or taken away with the airflow but majority of the control surface was left intact leaving enough manouverability to continue the mission. The electric drive obviously survived the reentry and continued operation of the flap and the control software was probably able to adapt to the partial loss of available aerodynamic surface.

In terms of test data this sequence of events was way better than nominal mission flight. Now they know how much surface then can lose and still have a successful touchdown.

[–] atocci@lemmy.world 12 points 5 months ago* (last edited 5 months ago)

I wonder how much was left of it, and I also wonder if the damage was symmetrical on the other side's flaps. As soon as the flames appeared I was sure the whole ship would be lost but it just kept going. How?

[–] Thorry84@feddit.nl 10 points 5 months ago (3 children)

I'm not sure it did actually work. When the landing burn kicked in it folded all the way over, so the movement we saw earlier might not have been intentional movement but just the thing moving as the atmosphere was pounding it.

This was the most sci-fi shit I ever saw in my life and it was real, it was a great thing to see. Hopefully next flight it can fly to an actual location and have it land within sight of a fleet of ships.

[–] shadowtofu@discuss.tchncs.de 8 points 5 months ago (1 children)

I expect the flap on the opposite side of the ship experienced a similar level of destruction. Well, that depends on whether the damage occurred because of a general loss of structural integrity because of excessive heating, or if specific localized damage on that flap allowed plasma to penetrate the heat shield, resulting in the damage that we observed. So, general structural failure vs. random damage at that location cascading into a hole in the flap.

Anyways, I am pretty sure that the complete loss of control authority on one of the flaps would be catastrophic. But the movement that we observed seemed pretty deliberate and consistent to what we saw during the suborbital test flights. Especially the unfolding of the flap at the T+01:05:42 mark is EXACTLY what we saw during the high-altitude flights, e.g., see SN8 @ T+6:33 or SN9 @ T+6:18. The forward flaps are folded back at first, and then rotate into a position perpendicular to the surface of Starship. The movement (for IFT-4) is precise, consistent with previous flights, and stops abruptly in the correct position.

[–] Thorry84@feddit.nl 6 points 5 months ago* (last edited 5 months ago) (1 children)

True, but it was definitely broken by the time the landing burn commenced. So it's hard to see where it failed. I think the other fins must have done much better, otherwise it would have totally lost control. The telemetry did get weird at one point, but it's hard to say if that was just an error in the data or actually happening.

Note that besides the fins they added more cold gas thrusters this time, so a loss of one or more fins wouldn't mean loss of control like with the previous attempt.

I also think the connection between the fin and the inside didn't fail and held up well. I remember from Space Shuttle that a small defect in the heatshield meant a stream of superheated air blasted in like a plasma cutter and destroyed the insides, even in parts where the heat shield was just fine. But with this flight on Starship it seamed like the fin burned away, but the inside was fine, otherwise I think it would have blown up. It even seamed like the fin moves after a lot of it was burned up, so that would mean the motors and control systems were still working. But I'm still not sure at what point it failed, some of the movement could be due to atmosphere with it hitting the end stops, so it looked like a controlled movement to a certain point.

Very interesting and cool nonetheless.

Edit: Just rewatched and you can see at 1:04:22 it makes a move which is very fast. At this point I feel it's broken and every movement we see is due to the thing shaking around in the atmosphere. But somehow with the thrusters and other fins that may have faired better it maintains control. It really was the little Starship that could.

[–] shadowtofu@discuss.tchncs.de 4 points 5 months ago

I just compared the footage from various points in time. The flap positions for T+00:48:12 (pre-entry) and T+01:05:41 are almost the same, then it rotates about its rotation axis until T+01:05:44, but suddenly it starts to rotate about ANOTHER axis, and at T+01:05:47, its at a completely new angle. I think T+01:05:44 is the point where the flap finally breaks (after touchdown, but before splashdown).

I think we have seen motion as fast as the one at T+01:04:22, but the subsequent bounce is surprisingly strong. I still think that the flap was still under some control at that point.

I heard rumors on reddit that SpaceX deliberately removed a single tile on this flap for testing purposes, but I could not find any reliable confirmation for this. They deliberately removed tiles on the engine skirt, though.

[–] kokesh@lemmy.world 4 points 5 months ago

I think the control mechanism must have been nackered, but it still seemed to move.

[–] BastingChemina@slrpnk.net 4 points 5 months ago

I would not have believed it in a Sci-Fi movie. Having the heatshield failed on the flap for most of the descent, seing the flap burning in flame and still managing to land softly after that !

What kind of plot armor is that ?

It is incredible that the ship survived that and really shows the kind of resilience starship has !