totm nov 2023 SpaceX Discussion Thread

[Minmus Taster]

Rewatching the feed from the booster it looks like it was intact up until the end and smacked into the water at over 1100 KM an hour, yikes.

[Deddly]

4 minutes ago, Ultimate Steve said:

no explicit confirmation of successful payload door closing

A short time later, the door could be seen flopping about. Seems it failed to close.

[AckSed]

Side benefit: SpaceX have also proved that you can use Starlink for spacecraft leaving and entering the atmosphere at orbital velocity. *Ka-ching* goes the space-internet contracts.

[Exoscientist]

47 minutes ago, .50calBMG said:

My best guess is that it's fuel slosh from the booster wobbling and spinning so much. That's solvable with tweaked control algorithms, not a failure of the engines. Seriously, with the number of test firings, I don't understand why you automatically jump to engine failure

 It should be noted the Starship during tests of the landing procedure, that at least one Raptor always leaked fuel and caught fire.

 

Note even in the last two shown here, SN10 and SN15, there were engine fires on landing. For SN10 the engine fire led to the vehicle exploding a few minutes after landing. For SN15 the fire was extinguished before it caused an explosion. SN15 was called  a “successful” landing test because it did not explode. But a Raptor still did catch fire also during this test requiring a relight.

And SN11 experienced a catastrophic explosion after a fuel leak and engine fire after engine relight:

.

  Bob Clark

 

Edited March 14 by Exoscientist

[Minmus Taster]

Watching the starship footage back it was clearly tumbling, you can see the rotation in the the little graphic below. Looks like the main issue was actually controlling the ship and not just the tiles.

[tater]

5 minutes ago, Exoscientist said:

 It should be noted the Starship during tests of the landing procedure, that at least one Raptor always leaked fuel and caught fire.

Keep beating this dead horse about Raptor versions that don't even exist any more.

3 minutes ago, Minmus Taster said:

Watching the starship footage back it was clearly tumbling, you can see the rotation in the the little graphic below. Looks like the main issue was actually controlling the ship and not just the tiles.

Yeah, attitude control needs work. Given no payload, and loads of room (and mass margin) add some real RCS.

[Minmus Taster]

You can see here the ship isn't entering with it's tiles facing the "wind", it's actually coming in by the engine bay in a sort of pencil dive. Maybe the extra weight of the engines is a factor in all this? Either way this explains why this is the end of the video, the camera was probably melted but they still seemed to be getting telemetry back, the last of the graphic showed the ship was actually recovering from this slightly but was still clearly tumbling with the tail being pushed forward. The end would have probably come when the plasma finally wore through the tanks and the remaining fuel detonated. I am curious if anyone caught views of the breakup, maybe a satellite or an asset down below.

[.50calBMG]

"something something landing test", those tests were 2-3 years ago, they've had that issue fixed for a minimum of a year and a half. That was two engines ago. I doubt sls will have an engine failure because an rs-25a test failed on the test stand 

[Exoscientist]

 

16 minutes ago, tater said:

Keep beating this dead horse about Raptor versions that don't even exist any more.

Yeah, attitude control needs work. Given no payload, and loads of room (and mass margin) add some real RCS.

 You can’t ignore a major issue for Raptor engine reusability. If the Raptor can not be made to relight reliably then reusability absolutely can not work. After SN15 test where it managed to land without exploding, SpaceX called the landing tests successful even though there was still a fuel leak and fire on relight, and conducted no more landing tests.

 Based on the Starship landing tests, a Raptor always leaked fuel and caught fire after a relight.

 Based on actual SuperHeavy/Starship flights a Raptor always fails at some point after relight, whether or not a fire and RUD occurred.

In fact, SpaceX still has not proven the Raptor can reliably relight while in flight without failing.

  Bob Clark

Edited March 14 by Exoscientist

[AckSed]

We'll just have to wait and see.

[.50calBMG]

But it does relight successfully. The failures on the last flight were due to the fuel system, not the engines. The failures in this test were attitude control and fuel systems, not the engines. Raptor 1 fixed the fuel leak issues 2 years ago with sn-15. The first one to land landed hard and cracked a tank bulkhead, leading to an explosion, so another fuel system problem. No ship other than ift-1 was lost to engine issues, and that engine design has been retired. The issue you keep bringing up has been fixed. 

[StrandedonEarth]

4 hours ago, cubinator said:

It also spent a lot of time with the heat shield only halfway in the plasma at the start there.

I had to watch the flight while also trying to work, and doing neither particularly well. Now I can catch up on the thread and post…

What I did notice doing during reentry, after plasma started up, was “wait, now it’s moving sideways?   …. Now it’s upside down?” 

Whoops, back to work, break was longer than it should have been…

Edited March 14 by StrandedonEarth

[.50calBMG]

Here, a test from a year and a half ago. Seemed to work fine, and I don't think we've seen any RUDs from these kinds of tests since then. Issue solved

Edited March 14 by .50calBMG

[Exoscientist]

11 minutes ago, .50calBMG said:

Here, a test from a year and a half ago. Seemed to work fine, and I don't think we've seen any RUDs from these kinds of tests since then. Issue solved

 

 Actually, that relight lasted only about 2 seconds. We don’t know if the relight was planned to last that long or SpaceX ended it early or it ended itself because it failed.

 If SpaceX wants to prove the Raptor can relight reliably they need to redo another Starship landing test and ensure you get relights with no engines leaking fuel and catching fire for the full length of an actual burn. As I said SN15 still had a fuel leak and engine fire on relight.

   Bob Clark

Edited March 14 by Exoscientist

[.50calBMG]

Again, I will add emphasis to test data that is A YEAR AND A HALF OLD. How many improvements were made since then? How many hundreds of tests have been done since then to verify that they work? I'm sure raptors reliability has followed the same curve that starship has from ift-1 to today's test, if not exceeds it based purely on the fact that they can and have been testing multiple times a day since the first test

[tater]

 

15 minutes ago, Exoscientist said:

 If SpaceX wants to prove the Raptor can relight reliably they need to redo another Starship landing test and ensure you get relights with no engines leaking fuel and catching fire for the full length of an actual burn. As I said SN15 still had a fuel leak and engine fire on relight.

Useless test. Any failure makes a mess at Starbase, triggers cleanup, FAA, etc. Better to test them over the ocean.

[AckSed]

Watching the massive glowing ring cluster of engines going up reminded me of Hazegrayart's render of ROOST... but it's real. We now have a SHLV. Only took 60-odd years!

Edited March 14 by AckSed

[tater]

BTW, relight for boostback was fine. They skipped relight on ship, or rather the SHIP skipped relight itself. My guess is that the lack of attitude control resulted in the ship not lighting engines. Had it been pointing the right way, it would have relit just fine.

Edited March 14 by tater

[.50calBMG]

Just because they are hardware rich doesn't mean they can afford to redo testing. All the requirements to do those tests cost time, money, and add associated risks that occur during any flight. You don't see them testing the hot staging by putting it on the SO pad with a full ship on just the hot staging ring to see if it works. They could, but they would get the same if not better data by actually flying.

Edited March 14 by .50calBMG
Can't type today

[CatastrophicFailure]

1 hour ago, AckSed said:

Oh, nothing, just a spacecraft the size of a building went through reentry.

Indeed. 
 

RIP my inbox. 

[Pthigrivi]

My wife and I were gchatting during launch and she was like "wait... Pez dispenser? Chopsticks landing? Plasma blanket? Is this a Wes Anderson movie?"

[RCgothic]

Failure of a vehicle to supply conditions condusive to raptor firings is not the fault of the raptor and it's unhelpful to insist otherwise. Distracts from the actual causes, which in these instances appear related to failures with the grid fins and tank vent RCS systems, both of which are only getting their first full up tests this flight.

[sevenperforce]

2 hours ago, .50calBMG said:

3 hours ago, Exoscientist said:

Actually, we do know definitely that the engines did not all relight during the landing burn for the booster. That proves something went wrong at this relight, and the damage could even have occurred during the first relight during boostback except that burn was not long enough to cause loss of vehicle.

 If something goes wrong with the engines during flight, and it is a known problem to have occurred before during testing the first thing to suspect is that same issue is occurring again. 

My best guess is that it's fuel slosh from the booster wobbling and spinning so much. That's solvable with tweaked control algorithms, not a failure of the engines. Seriously, with the number of test firings, I don't understand why you automatically jump to engine failure

Also possible that the booster grid fins simply don't have enough control authority to stabilize the booster. Which would mean they need larger grid fins, or more of them. Which also wouldn't be an issue with the engines.

[AckSed]

All right, let's say Exoscientist's suspicions are justified, and the Raptors, even now, are prone to exploding. Presume they are also a pain to relight and require ullage and settling of the propellant before they'll behave.

Can you make a staged combustion engine more reliable? Peter Beck of Rocket Lab says you can: by building it to withstand and run at extremes, then under-driving it, you end up in the same level of reliability as a gas-generator rocket engine. Neutron's Archimedes is ox-rich, not full-flow, but building to run at max, then under-running at a more comfortable level is a solid path to good reliability.

Can they program Starship and/or Superheavy to under-run the engines at the cost of payload? I say yes.

Will they, or is Elon cowboying ahead with demands for, "More pressure! MORE thrust! More payload! Stuff blowing up! Boom!" and laughing maniacally? I don't have that insight, but they are complying with FAA regulations and NASA requirements, and I do believe Musky-boy knows when not to push his engineers and the physics to make things blow up, now the basic stack mostly works.

On relight: How many flight tests would it take to uncover all the quirks in handling the stack, and implement the necessary hardware and software changes to make relight reliable? We have at least four more planned, because that's how many boosters are being built right now. There are more on the way.

SpaceX has been using Falcon 9 Starlink launches to hone reuse parameters, learn more about the airframe and where its margins are e.g. jettisoning the fairings half a second earlier each flight. It's clear they intend to do the same with Starship/Superheavy. They will have at least four more attempts to relight engines in orbit and on landing, and test heatshields further.

Starships and Superheavies can and have been modified, or scrapped entirely, thanks to their stainless steel construction. The engines are the most expensive part and apparently problematic, but I have outlined a path to making them more reliable. If the engine design is fundamentally flawed and cannot relight at all without a forest of proper ullage thrusters they may have to add them. And that's fine. They will do that.

When I look at SpaceX and what they've achieved, I'm reminded of Parson Gotti, in the webcomic Erfworld: "We try things. Occasionally they even work."

[sevenperforce]

1 hour ago, tater said:

BTW, relight for boostback was fine. They skipped relight on ship, or rather the SHIP skipped relight itself. My guess is that the lack of attitude control resulted in the ship not lighting engines. Had it been pointing the right way, it would have relit just fine.

I'm guessing you're guessing right. At first I mistook RCS firing for the engine light plume, but it just kept going and going for quite a while. This may be part of the inherent limitations of "best part is no part" engineering: they might just have to add in a separate thruster system after all.