Jump to content

SpaceX Discussion Thread


Recommended Posts

12 minutes ago, mikegarrison said:

So that means that even though there are 9 engines, there is no redundancy for landing?

Here:

21 hours ago, sevenperforce said:

All nine engines are lit on the pad using TEA-TEB plumbed from the ground. Only three specific engines are plumbed to the onboard reservoir of TEA-TEB needed for in-flight restart. When the first Falcon Heavy launch failed to land the core, it was because the onboard TEA-TEB reservoir ran dry just after restarting the core engine for the second time, meaning there was not enough remaining for the other two engines to relight. They fixed this in subsequent Falcon Heavy flights by making the core's reservoir bigger.

So this is the problem. If Falcon 9 had lost one of the other four six engines on ascent, it would have been okay, but since it lost one of the intended landing engines, it was stuck. It can't choose other engines to relight because they aren't plumbed with TEA-TEB. I'm guessing they went ahead and tried to force a restart of the engine that previously shut down and its burn-through got worse.

Starship, of course, won't have this problem because all of the Raptor engines use their own internal spark igniter and can relight at any time, independent of any other engine or system.

 

Link to post
Share on other sites
31 minutes ago, mikegarrison said:

So that means that even though there are 9 engines, there is no redundancy for landing?

Nope. 

They may want to reconsider trading a bit more complexity (plumbing another pair into the ignition fluid system) for landing redundancy, or not using life-leader parts on the critical landing engines. Or accept writing off more boosters due to preventable occurrences. 

Of course, hindsight is 20/20, as usual 

Link to post
Share on other sites
1 hour ago, mikegarrison said:

So that means that even though there are 9 engines, there is no redundancy for landing?

Only whatever is afforded by by using some fraction of those 3.

So far this the first failure they've had along those lines with Merlin, though I think.

Link to post
Share on other sites
30 minutes ago, tater said:

Only whatever is afforded by by using some fraction of those 3.

So far this the first failure they've had along those lines with Merlin, though I think.

Added complexity (of more plumbing) means added weight, added cost, and potentially added failure modes. There’s something to be said from simply figuring out, through trial and error, how long X part can go before it need thorough inspection or just preemptive replacement. As this was a life leader part, that sound largely like what they’re doing. They don’t want to invest too much effort here, as Starship is right around the pike, and is planned to make Falcon obsolete. The question is, where does that balance point come?

Link to post
Share on other sites

I'm confused. I was under the impression that a hole in the engine boot allowed hot gasses to enter during reentry, which managed to kill the engine partway through its landing burn. 

*entry burn

Link to post
Share on other sites
1 hour ago, tater said:

Only whatever is afforded by by using some fraction of those 3.

So far this the first failure they've had along those lines with Merlin, though I think.

Correct me if I'm wrong, but I would think that successful restart of each engine is a single failure point for Falcon 9 recovery regardless of mission profile. If they are doing a three-engine burn it's because they don't have enough margins for a single-engine burn, so a failure of either outboard engine means they don't have the thrust they need. If they are doing a single-engine burn then they only restart the center engine, and if it fails to restart they're screwed anyway.

The reason they always light the center engine first is to avoid bad juju during startup. This isn't like KSP where the engine roars to 100% the instant you stage; they have to spin up the turbopump and then start pouring in TEA-TEB and wait for a full, good ignition. There are timing variations (which, again, is why they lost the first Falcon Heavy core when the center engine took too long to start and they ran out of TEA-TEB for the other two engines).

If they tried to light all three engines at once (or, worse, tried to light only the two outboard engines), then one of the outboard engines could reach full throttle before the other engine(s) had ignited, producing a massive amount of off-center thrust. Lighting the center engine first ensures that they have gimbal control alive and operating during startup transients.

9 minutes ago, Brotoro said:

I'm confused. I was under the impression that a hole in the engine boot allowed hot gasses to enter during reentry, which managed to kill the engine partway through its landing burn. 

*entry burn

The impression I received from the explanation was that hot gas recirculation during the ascent caused a burn-through of the engine boot and triggered a commanded shutdown of that engine, resulting in the other 8 engines completing the ascent at higher throttle. When they attempted the restart for the entry burn, the damaged boot caused a thrust shortfall on that engine which was ultimately unrecoverable.

Edited by sevenperforce
Link to post
Share on other sites

6 of the 9 engines have their TEA/TEB igniters plumbed to the pad, they can't be air-started.

The other 3 engines share an onboard reservoir. I think the centre engine must ignite for a safe landing. CofG is too low to safely land on one of the outer engines with gimbal. There *may* be some redundancy in the other 2 if there's enough propellant margin (bearing in mind a failure reduces the nominal margin) and the failure is identified really enough to swap to plan B.

Link to post
Share on other sites
5 minutes ago, RCgothic said:

6 of the 9 engines have their TEA/TEB igniters plumbed to the pad, they can't be air-started.

Aren't all nine lit together from pad plumbing, to make the onboard TEA-TEB reservoir smaller?

5 minutes ago, RCgothic said:

There *may* be some redundancy in the other 2 if there's enough propellant margin (bearing in mind a failure reduces the nominal margin) and the failure is identified really enough to swap to plan B.

They've never lit two outboard engines alone without first lighting the center engine to give them gimbal control during startup transients. I wonder if they wrote the code to attempt a two-engine relight and hoverslam if the center engine fails to restart for a single-engine landing burn. That's the only time they'd have sufficient propellant margin.

Link to post
Share on other sites
55 minutes ago, sevenperforce said:

Correct me if I'm wrong, but I would think that successful restart of each engine is a single failure point for Falcon 9 recovery regardless of mission profile. If they are doing a three-engine burn it's because they don't have enough margins for a single-engine burn, so a failure of either outboard engine means they don't have the thrust they need. If they are doing a single-engine burn then they only restart the center engine, and if it fails to restart they're screwed anyway.

Yeah, given timing constraints, if they need only 1 engine, by the time they determine it's time to rtry another it's too late.

You'd need a landing profile where you light all redundant engines that seem nominal before startup, then shut off any you don't need (shutting off any that are not nominal after the start attempt first).

57 minutes ago, sevenperforce said:

The impression I received from the explanation was that hot gas recirculation during the ascent caused a burn-through of the engine boot and triggered a commanded shutdown of that engine, resulting in the other 8 engines completing the ascent at higher throttle. When they attempted the restart for the entry burn, the damaged boot caused a thrust shortfall on that engine which was ultimately unrecoverable.

Was it just shy of MECO at that point?

Link to post
Share on other sites

 

If someone gave me a ride on NS flying tomorrow I'd go (only about a 5 hour drive from here). Starship in 2023 with EDL? LOL, no.

 

Link to post
Share on other sites

I'm not currently comfortable enough with Starship that I would ride one back down to Earth. Maybe from the Moon to LEO, and then dock with a Dragon to come home, but I don't know if I'd be willing to trust my life with the bellyflop and flip even after a few years...That said, everything else about the moon mission sounds perfect for me.

Link to post
Share on other sites

It's certainly interesting that this announcement has come just a day after the closure of the Inspiration4 seat raffle. It makes it seem like this sort of thing will be getting more common.

Link to post
Share on other sites

I would love a seat, and I'd fly in 2023 given a chance. Such an incredible experience is surely worth a chance of it being ultimate.

But I'm not a creative type, and not really in a position to be meaningfully supportive of the other passengers, so I'm not eligible alas.

Link to post
Share on other sites
35 minutes ago, RCgothic said:

Such an incredible experience is surely worth a chance of it being ultimate.

Not if you want to go to Mars after! :D 

Link to post
Share on other sites
4 minutes ago, Elro2k said:

Looks like some new official renders for starship are on the Dear Moon website.

https://dearmoon.earth/starship-suit.html

Right off the bat it looks like that main observation deck window has gotten smaller. Anything else you guys can notice?

starship_0_pc.jpg

 

starship_2.jpg

 

starship_3.jpg

 

starship_4_pc.jpg

 

starship_6_pc.jpg

 

 

starship_5_pc.jpg

 

Link to post
Share on other sites
3 hours ago, tater said:
If someone gave me a ride on NS flying tomorrow I'd go (only about a 5 hour drive from here). Starship in 2023 with EDL? LOL, no.

Uh, no.

I'm going.

I'm definitely going.

That is now my plan. I'm going.

Offer me a space on a lunar free-return in Starship? Hell yes; I'm in.

I don't actually know anyone who is better at explaining science and spaceflight and the wonders of the universe than me. Nye, Tyson, and everyone else included.

 

Link to post
Share on other sites

Of course the odds of acceptance are essentially zero, but I'm decent artistic at least in the music department so I'll give it a shot, there's not much to lose here.

Link to post
Share on other sites
52 minutes ago, sevenperforce said:

I don't actually know anyone who is better at explaining science and spaceflight and the wonders of the universe than me. Nye, Tyson, and everyone else included.

Your better elevator pitch might be writing space chanties.

Just sayin'.

(Elon likes chanties)

SN10-vertical-0223.jpg

Starship page updated for hop.

Link to post
Share on other sites
3 hours ago, StrandedonEarth said:

Hoo boy. Has somebody been into the Ambien again? :joy:

I can personally attest that a bit too much of that can lead to staying up all night designing crazy rockets that actually work and occasionally founding vast empires from a single city... but don’t ask how I know.... :blush:

But more than likely, someone probably just told him that he couldn’t... :wacko:

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...