SpaceX Starship - Integrated Flight Test #2 - Starbase TX - Including Post Launch Dissection

[Ben W]

Did the booster slow down when Starship lit up its engines?
I seem to remember seeing a graph put together by someone that showed that it did, in which case negative acceleration was definitely occurring and maybe screwed up the fuel feed.
I am not trained in these sciences

Starship's exhaust certainly reduces Booster's forward acceleration. The question is whether it's strong enough to cancel it out entirely. Booster's three center Raptors combined can produce anywhere between about 270MT and 675MT of thrust, depending on throttle. Starship's six Raptors can produce between about 540MT and 1350MT of thrust, again depending on throttle. The critical question (answered by IFT-2) was: what fraction of Starship's thrust is transmitted to Booster at the moment of separation? Clearly this value was higher than SpaceX anticipated, enough to momentarily cancel out the thrust of Booster's 3 Raptors, resulting in transient negative acceleration. (This effect is independent of Booster's mass at separation, which incidentally was about 500MT.) Slightly increasing Booster's throttle and/or decreasing Starship's throttle at separation in IFT-3 should be enough to solve this; it shouldn't require a hardware redesign, although of course the hardware will continue to be iteratively refined.

Interestingly, the fact that the exhaust had a stronger-than-expected effect on the booster is promising toward using a similar strategy to deorbit space junk that can't be grappled; simply blow on it (gently, from a distance) with a rocket engine! (Though that would probably involve a Draco-sized engine, not Raptor-sized!)

 

[Buckminster]

https://twitter.com/x/status/1727675831399395408

 

[Buckminster]

https://twitter.com/x/status/1727967723806761343

V2 is longer?

 

[Electroman]

https://twitter.com/x/status/1727675831399395408

Do we see a lot of venting from all the outermost ring of engines at MECO ?

 

[JB47394]

Do we see a lot of venting from all the outermost ring of engines at MECO ?

I believe that's the CO2 system working to purge methane from the engine bays. I never did understand why there was so much venting at that point, but this shot makes it clear that the venting is coming from the skirt. I guess turning an engine off tends to dump a lot of gas in there. On this iteration of the booster and engines, anyway.

 

[mongo]

I believe that's the CO2 system working to purge methane from the engine bays. I never did understand why there was so much venting at that point, but this shot makes it clear that the venting is coming from the skirt. I guess turning an engine off tends to dump a lot of gas in there. On this iteration of the booster and engines, anyway.

Or are those the LOX vent connections which normally route to the OLM for disposal in the evaporation pit?

 

[JB47394]

Or are those the LOX vent connections which normally route to the OLM for disposal in the evaporation pit?

Towards what end? Cycling LOX to keep the engines cool for relight?

 

[mongo]

Towards what end? Cycling LOX to keep the engines cool for relight?

Yeah, the usual prechill before lighting.

 

[JB47394]

Yeah, the usual prechill before lighting.

The ports certainly seem low enough to be on the engine housings. I'm having difficulty reconciling the venting sequence (which seems to correlate vents with engines) with the restart sequence. That is, they were immediately cooling the outermost ring, but those engines weren't being restarted. Perhaps they always cool engines to "ambient" after firing, and we were seeing that.

 

[mongo]

The ports certainly seem low enough to be on the engine housings. I'm having difficulty reconciling the venting sequence (which seems to correlate vents with engines) with the restart sequence. That is, they were immediately cooling the outermost ring, but those engines weren't being restarted. Perhaps they always cool engines to "ambient" after firing, and we were seeing that.

I think the dump ports are all on the outer surface to mate with the OLM quick disconnects, not related specifically to the outer engines. They also added CH4 vent ports that get hose whips after the energetic OLM test event.

No need to stabilized engines that aren't going to fire soon.

 

[JB47394]

Zach Golden of CSI Starbase presenting his summary of the problems with IFT-1 and the engineering changes for IFT-2, focusing on engine fire and engine explosion containment. Note that he believes that the venting before hot staging was the CO2 system, and that he also believes that the booster was destroyed by the flight termination system. There will be at least one more video talking about hot staging.

 

[JB47394]

Marcus House doing his weekly summary. The focus is on IFT-2 and the information that has become available since the launch. Lots of nice visuals.

 

[ecarfan]

Zach Golden of CSI Starbase presenting his summary of the problems with IFT-1 and the engineering changes for IFT-2, focusing on engine fire and engine explosion containment. Note that he believes that the venting before hot staging was the CO2 system, and that he also believes that the booster was destroyed by the flight termination system.

(I know you know this) SpaceX has stated that the booster experienced a RUD and the ship was destroyed by the FTS.

I don’t take Zach too seriously. Seems like a nice guy, but…

 

[JB47394]

SpaceX has stated that the booster experienced a RUD and the ship was destroyed by the FTS.

Yes, and he demurs a bit by saying that SpaceX hasn't made a public statement that the FTS fired. He goes on to back up his assertion by showing a frame where there's a flare in the location of the FTS during the RUD. I can easily imagine that the RUD was underway, but the FTS fired anyway. Because of the RUD, telemetry was lost and SpaceX couldn't know if the FTS fired. (Unless the FTS has a separate telemetry system, which I doubt.)

I don’t take Zach too seriously.

I like his videos because they talk about obscure topics. This one had a lot about engine shielding. He was of the opinion that the small glowing objects ejected out the back of the booster towards the end were a pair of engine shields. I thought they were engines, but who really knows?

I also liked the explanation of the new FTS location on the booster. Instead of trying to rupture the bulkhead between the tanks, they decided to rupture the side wall of the methane tank. That explosively depressurizes the methane tank. The oxygen tank is still under pressure which will blow the bulkhead. It's a nice use of the ship's own energy to destroy it.

I'm a little surprised they don't blow the oxygen tank. The bulkhead bulges downward, so it would seem to fail more easily downward.

 

[mongo]

CFD simulation of slosh

https://twitter.com/x/status/1729107836318163096

 

[scaesare]

Very cool simulations. I wonder if changing the thrust profile and or the turn-around timing of booster during hot staging will be sufficient, or if they'll also consider baffles etc...

 

[JB47394]

Very cool simulations. I wonder if changing the thrust profile and or the turn-around timing of booster during hot staging will be sufficient, or if they'll also consider baffles etc...

If they maintain just enough thrust through staging then they'll avoid negative acceleration while also not smacking Starship. That'll keep the propellants seated, which is the real problem demonstrated by the simulation. The oxygen sloshed (slammed?) against the methane downcomer, and then that hydraulic hammer hit once the engines started. It's a brutal environment, and a tribute to the design and construction of the booster that it lasted as long as it did. They collected lots of good data as a result.

Then they've got to keep the propellants covering the oxygen intakes and the methane downcomer during the turn. The simulation suggests that they were able to accomplish that even with the engines in the state that they were. At least one engine was out at the start, and others were possibly below their target thrust, so they were going for an even more aggressive acceleration than the simulation shows.

I figure they can sort all this out in the next launch. Beyond that, they have to flip the booster for descent, but they have experience with Falcon 9 boosters.

It was interesting that the methane in the downcomer didn't move during the negative acceleration. I assume that's because there wasn't anything that could flow in behind it, so it was stuck.

 

[scaesare]

If they maintain just enough thrust through staging then they'll avoid negative acceleration while also not smacking Starship. That'll keep the propellants seated, which is the real problem demonstrated by the simulation. The oxygen sloshed (slammed?) against the methane downcomer, and then that hydraulic hammer hit once the engines started. It's a brutal environment, and a tribute to the design and construction of the booster that it lasted as long as it did. They collected lots of good data as a result.

Then they've got to keep the propellants covering the oxygen intakes and the methane downcomer during the turn. The simulation suggests that they were able to accomplish that even with the engines in the state that they were. At least one engine was out at the start, and others were possibly below their target thrust, so they were going for an even more aggressive acceleration than the simulation shows.

I figure they can sort all this out in the next launch. Beyond that, they have to flip the booster for descent, but they have experience with Falcon 9 boosters.

It was interesting that the methane in the downcomer didn't move during the negative acceleration. I assume that's because there wasn't anything that could flow in behind it, so it was stuck.

My understanding was that the practically empty booster had 3 engines running at ~50%, and Starship had 3 SL-Raptors + 3 Vac-Raptors running at 100%.

Has anybody seen any calcs on how much additional throttle the booster would need, and what the separation profile for Starship would look like?

 

[mongo]

It was interesting that the methane in the downcomer didn't move during the negative acceleration. I assume that's because there wasn't anything that could flow in behind it, so it was stuck.

Yeah, reverse water hammer, needs to create a vacuum.
Plus, there was flow with momentum that would need to be overcome for a reversal.

 

[JB47394]

Has anybody seen any calcs on how much additional throttle the booster would need, and what the separation profile for Starship would look like?

I did rough calculations earlier in this thread and came up with a need for double the thrust. Six engines at 50%. That would maintain some booster acceleration even with Starship firing its engines. Then it's a question of how fast Starship would gain distance, how quickly the booster could turn, and how much damage the hot staging ring might take if everything happens more slowly.

It could be very touchy because the effect of Starship's engines will be dropping all through staging. It will be moving farther away, the top of the booster will be moving out of the exhaust, and the aspect ratio of the booster in the exhaust will change. It might be better to run three engines at full power, then throttle them back as the booster turns. But carefully, so as to avoid negative acceleration. Once the booster is clear of Starship, then they can start piling on the thrust for the turn.

Just. Don't. Hit. Starship.