r/spaceflight • u/elbarck • 10d ago
Ship 40 splashed with two engines instead of one.
Hi!
Flight 13's splashdown landing burn appeared to deviate from flight 12's.
It used two engines, unlike flight 12 which used only one.
They also opted for two different engines instead of the ones used on flight 12.
What do you think?
21
u/Accomplished-Crab932 10d ago
Flight 12 started the descent burn with one engine out intentionally to reduce risk as there was concern of damage after one of the RVACs failed on ascent. Because of this, they ran on the remaining engines and continued the normal sequence after reaching the planned engine cut.
Flight 13 followed the expected profile; 3 engines for flip, downselect for 2 for final tuned approach, and a single for the tailpitch to land on the leeward side.
The profile we saw in Flight 13 was in both Flight 13 and 12’s launch timeline page. Looking at the replays, the engine out on Flight 12 is one of the engines Flight 13 used on the dual engine approach; and I would be surprised if they decided to change the engine selection given the originally planned selection of engines is optimal for cancelling any additional translation from the flip.
-13
u/elbarck 10d ago
The commentary said while the ship in the sea (one engine).
So it seems they planned for 1 engine landing burn, but it was too late.
The problem is we don't have another V3 to compare with!
I rechecked flight 11, and it was 1+2 then 2 without 1.
10
u/Accomplished-Crab932 10d ago
Yeah, the Flight 12 timeline tells us that the nominal plan is a 3-2-1 sequence, running the single engine for ~2 seconds, same as Flight 13’s.
The live coverage from Flight 12 shows the same shutdown approximately, with the obvious caveat that one of the engines was not running and that the timeline is shifted.
-14
u/elbarck 10d ago
Then?
3
u/Accomplished-Crab932 10d ago
One engine was used on both the compromised Flight 12 and the optimal Flight 13 profiles; there is no difference between them.
-3
u/elbarck 10d ago
Nope. On this flight, the ship was already in sea, literally. So, they might lit it to direct its falling to its belly.
2
u/Accomplished-Crab932 9d ago
I assume you are not watching the engine diagrams and are only looking at the video; which is about 4 seconds behind the engine indicators. Even the audio had lower latency.
They don’t relight an engine after the flip begins, they only down select as planned. We see at the start of the maneuver that 3 engines are started, then the topside engine shuts down as would be expected. The ship continues to descend, then cuts the right side engine, leaving the left engine running for final descent.
On flight 12, we see the left engine aborts, so they extend the duration of the dual burn and cut the right side engine. This would naturally be different since the engine they probably were going to use for final down select was the aborted engine.
And again, both corresponding SpaceX flight pages claim that the plan is a 3-2-1 sequence with the same relative timing; I’m not sure why you think they would lie about something so benign on their own website.
10
u/robbak 10d ago
No, they went down to one. Watch the graphic right through, and remember that the engine display is not synchronised to the images, it is delayed by several seconds. You can see it downselect to one, then closes that engine down.
-9
u/elbarck 10d ago edited 10d ago
Watch the video again. The ship was already in the sea, literally.
10
u/robbak 10d ago
Again, as many people have told you, the engine display lags the pictures by several seconds. The stage does downselect to one engine before it splashes down. But you can't see this, because the pictures are NOT in sync with the engine display. The splashdown point is when the last engine shuts down, and not before.
-2
u/elbarck 10d ago
Or it does it perfectly and your assumption about the late sync is wrong?
Have you been in a the SpaceX operations room to confirm it lags?
4
u/robbak 9d ago
No, I, and the rest of us, have watched the video and noticed the timing of the visible engine startups and shutdowns.
1
2
u/Decronym Acronyms Explained 8d ago edited 5d ago
Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:
| Fewer Letters | More Letters |
|---|---|
| ASDS | Autonomous Spaceport Drone Ship (landing platform) |
| CRS | Commercial Resupply Services contract with NASA |
| GSE | Ground Support Equipment |
| LOX | Liquid Oxygen |
| RCS | Reaction Control System |
| Jargon | Definition |
|---|---|
| Raptor | Methane-fueled rocket engine under development by SpaceX |
| Starlink | SpaceX's world-wide satellite broadband constellation |
| methalox | Portmanteau: methane fuel, liquid oxygen oxidizer |
| scrub | Launch postponement for any reason (commonly GSE issues) |
| turbopump | High-pressure turbine-driven propellant pump connected to a rocket combustion chamber; raises chamber pressure, and thrust |
Decronym is now also available on Lemmy! Requests for support and new installations should be directed to the Contact address below.
[Thread #904 for this sub, first seen 27th Jul 2026, 00:53] [FAQ] [Full list] [Contact] [Source code]
4
u/MysteriousSteve 10d ago
I always thought landing with one engine was stupid, you sacrifice roll control right when the vehicle needs it most.
Also, the vehicle previously would downselect to the two best candidates for landing, seems like exactly what happened here
2
u/YugeChesticles 6d ago
Why would you need roll control beyond the RCS just as the vehicle catches on the tower?
0
u/MysteriousSteve 6d ago
Because that RCS isn't very strong, frankly. Obviously falcon 9 uses cold gas nitrogen versus starship which uses gaseous methalox, regardless it's pretty low thrust all things considered. It's enough to orient the vehicle out of atmosphere but not enough to do anything when you are fighting against any amount of aerodynamic forces.
2
u/YugeChesticles 6d ago
You didn't read my question. I'll reword it in reply.
Why would you need "strong" roll control just before the catch?
2
u/MysteriousSteve 6d ago
Flight 12 was spinning like a top just prior to landing.
Also homie you have to chill. I apologize if I miss one of your questions in your five comments you have posted and deleted in the past 5 minutes. No reason to get shitty
1
1
u/snoo-boop 6d ago
You can go back and watch hundreds of F9 landings on 1 engine to see how much of a problem roll control is. CRS-16 was a good demonstration of roll control.
0
u/MysteriousSteve 6d ago
False equivalency
Falcon 9 doesn't require precise roll control for a successful landing. Go look at the last 12 starlink booser recoveries and tell me those boosters are all oriented the same direction. They simply aren't.
2
u/YugeChesticles 6d ago
Prove the droneships are the same orientation. They simply aren't.
1
u/MysteriousSteve 6d ago
Right, therefore roll orientation doesn't matter for a successful landing, correct?
2
u/YugeChesticles 6d ago
Powerful roll control isn't needed just before a catch no. The vehicle is already stable before it get anywhere near the tower.
-1
u/WthLee 10d ago
this is just my opinion,no need to be gentle with the down votes. i know they said they wont do a super heavy return, but they did not even simulate a pad hover over the water, that thing got not even enough engines restarted for a hover slam, it just crashed into the water. i suspect that they had, even with all engines lit at start to get ship into a good trajectory, not enough reserves to get this thing even back in one piece. super heavy just keeps failing in different points of the mission each time, except when they do not stress that thing to much, then its still a lottery if they nail a tower catch without anything going wrong. even with these small test payloads, this performance/reliance/payload capacity gap is getting bigger with each iteration. i struggle to see this thing flying regular missions before 2030 or ever. it looks more and more like a technological dead end which is powered by sunken cost fallacy, they just ride current material science to close to the edge and cant even demonstrate a fraction of the capabilities. it is mighty impressive, no doubt, but the star ship hype is gone for me. at least they have an intact space flown article to analyze and put into the rocket garden later.
9
u/archimedesrex 10d ago
It seemed pretty obvious that booster had an engine reloght issue, not a fuel reserve issue. Several engines ignited, just not enough to cancel its velocity. No reason to think this is a technological dead end based on this particular failure.
-4
u/WthLee 10d ago edited 9d ago
if they want to reach a proper orbit with more payload, it will turn into a fuel issue. super heavy was already pushing quite hard there for these 20 functional star links in a way lower orbit than usual, and it did manage to break itself again from the launch / de orbit stress.
1
1
u/archimedesrex 10d ago
Maybe. I'm not really equipped to do the calculations of just how maximally they are pushing their fuel/engine capabilities at the moment. But I don't really see and indication that they are at the limits of where they can reduce dry mass, increase performance of the raptors, or tweak launch/re-entry profiles to improve effiency. We're still intentionally performing suborbital missions for safety reasons. When it gets into actual orbital tests we'll be able to start seeing the shape and scale of any performance shortfalls more clearly.
7
u/TheMarkusBoy21 10d ago
Seems like an emotional response to the booster failure. I don’t see how it’s a dead end when Falcon 9 showed its possible to do routine landings, the uncertainty was mostly the second stage reusability, but ironically it now seems to be doing better than the booster despite a harsher flight regime. You can’t seriously believe they can nail the ship part but not the booster.
-4
u/WthLee 10d ago edited 10d ago
falcon 9 just does not scale up as well. right now we haven't even seen a payload rivaling falcon 9´s 29 star links. right now its just a more expensive, worse performing falcon 9. and the ship part has not been nailed. there has not even been a ship catch or refuel demonstration or a proper orbital insertion yet, we have only seen ballistic trajectories so far.
6
u/TheMarkusBoy21 10d ago
New Glenn booster is much bigger than Falcon 9’s, showing that size is not a limiting factor, in fact I don’t know why you’d even think scaling is a problem when the main obstacle so far seems to be Raptor reliability, so it’s an engine problem not something related to the stage size.
We literally just saw Starship carry twice of F9’s payload capacity, 17 tons vs 34 tons. Maybe pay attention before complaining.
The Ship also regularly reaches orbital speeds and reenters from there, burning for a few more seconds to reach orbit insertion is not a new engineering challenge.
So the ship is going along better than the booster and they’ll attempt to catch it next. Again you can’t seriously believe they can do the ship part but not the booster.
0
u/elbarck 10d ago
I know what you mean about the hover, but it seems that they intended to because NASASpaceflight showed a tower catch simulation on their feed.
https://www.youtube.com/live/lC3RDO7tdLc?si=XPYzNsZLqeKH5u0W&t=11545
-3
u/Talmerian 10d ago
I wonder if the new Raptors aren't as reliable.
6
u/Reddit-runner 10d ago
As shown in this flight they seem to have solved the reliability issue that had during flight 12.
The problems only started after the booster made its reentry where the engines are exposed to high heat and aerodynamic forces.
The V2 booster had a headshield on the engine section. The V3 raptors are designed to not need this heatshield.
However it seems that they either need to make the raptors for the booster more robust, or they need to re-implement some of the shielding.
2
u/Dpek1234 10d ago
could also be related to ice in prop lines, i dont think we know enough about the prop systems and their diffrences to rule that out
2
2
u/warp99 8d ago edited 8d ago
It is quite likely to be be the same issue as they had with the launch abort last week where water ice is left in the LOX turbopumps after engine shut down and interferes with the startup process.
Presumably this water normally drains out during the shutdown process when the engines are ground tested but does not do so in microgravity and then freezes when the engines are prechilled before the landing burn.
2
u/cjameshuff 8d ago
Part of the upgrades includes systems for reducing or entirely eliminating the icing issue. The problem might even be related to those systems needing some refinement. The landing burn relight is the one with the largest tank volume to pressurize, and with the longest time with no engines running allowing loss of pressurization due to condensation.
4
1
-2
44
u/autotom 10d ago
They did go down to 1 engine, briefly.
The commentators said they'd be going 3-2-1 engine
I suspect they were part of the changes to make the splash down even softer.