totm nov 2023 SpaceX Discussion Thread

[Scotius]

You sure it's not Bigfoot's footprint?

[kerbiloid]

Just now, Scotius said:

You sure it's not Bigfoot's footprint?

Based on its size, Brobdingnag's.

[magnemoe]

5 hours ago, insert_name said:

COPV from Falcon upper stage recovered from Washington state

 

What happened here? I assume they lost control over upper stage after satellite deploy but before it was in position to do its reentry burn over south pasific. 

 

[Elthy]

Ive heard it didnt have enough fuel for a safe reignition to deorbit, trying with to little fuel could result in an explosion. So they decided to let it decay on its own.

[RyanRising]

I’d certainly want to keep the thing if it showed up in my backyard, but I suppose that’s not for everyone and if it took out some of my stuff I’d have to relinquish it in order to claim damages.

[sh1pman]

11 hours ago, Lewie said:

Do you guys think SN15 will stick the landing or RUD?

I’m betting on a landing

Not betting, but expect a RUD (80% chance). The other 20% is either a delayed RUD (like SN10) or a good landing.

[kerbiloid]

Btw, after that tank landing on the farmer's farm.

FAA knew it best...

Edited April 3, 2021 by kerbiloid

[sevenperforce]

11 hours ago, Lewie said:

Oh, the Falcon 9 upper stage is pressure fed? Huh. I knew krestel was, but not the V-Merlin.

As @insert_name said, that COPV isn’t for pressure-feeding. It looks too large to be the nitrogen tank for the cold-gas thrusters so it has to be the helium ullage tank.

The Merlin Vacuum engine uses the same gas generator turbopump as the Merlin SL engine, but you still need something to replace the lost volume in the tanks, and so they use a helium tank. The helium passes through a heat exchanger near the engine to warm up before being exhausted into the tanks to maintain ullage. Both stages of the Falcon 9 use this system.

This was the cause of the failure that exploded AMOS-6.

Starship won’t use helium COPVs because it uses autogenous pressurization — a small portion of the LOX and liquid methane are vaporized in a heat exchanger downstream of the turbopump outlet and routed back into their respective tanks. You can’t do this with kerosene because kerosene doesn’t vaporize as nicely as methane. 

Starship will, however, use COPVs to hold gaseous methane and GOX to supply the pressure-fed hot-gas thrusters and to restart the engines after coast.

[Lewie]

2 hours ago, sevenperforce said:

As @insert_name said, that COPV isn’t for pressure-feeding. It looks too large to be the nitrogen tank for the cold-gas thrusters so it has to be the helium ullage tank.

The Merlin Vacuum engine uses the same gas generator turbopump as the Merlin SL engine, but you still need something to replace the lost volume in the tanks, and so they use a helium tank. The helium passes through a heat exchanger near the engine to warm up before being exhausted into the tanks to maintain ullage. Both stages of the Falcon 9 use this system.

This was the cause of the failure that exploded AMOS-6.

Starship won’t use helium COPVs because it uses autogenous pressurization — a small portion of the LOX and liquid methane are vaporized in a heat exchanger downstream of the turbopump outlet and routed back into their respective tanks. You can’t do this with kerosene because kerosene doesn’t vaporize as nicely as methane. 

Starship will, however, use COPVs to hold gaseous methane and GOX to supply the pressure-fed hot-gas thrusters and to restart the engines after coast.

Thanks! I knew that gases such as helium were used for tank pressurization. Thanks for the insight!

[SOXBLOX]

12 hours ago, kerbiloid said:

Based on its size, Brobdingnag's.

LOL. I'd almost forgotten about that book...

[tater]

Why they are moving Dragon.

Also, 90% go for Wednesday's Starlink launch.

 

[tater]

 

[tater]

To build starlink hardware.

[tater]

 

[RealKerbal3x]

I love how transparent Elon is about the Starship program as a whole.

Edit: New NSF Starship article as well, with a nice shot of Vacuum Raptor SN2 as well as a regular sea level Raptor on the McGregor test stands:

Edited April 5, 2021 by RealKerbal3x

[Kartoffelkuchen]

Holy moly that thing is enormous.

[JoeSchmuckatelli]

2 hours ago, RealKerbal3x said:

I love how transparent Elon is about the Starship program as a whole.

Edit: New NSF Starship article as well, with a nice shot of Vacuum Raptor SN2 as well as a regular sea level Raptor on the McGregor test stands:

 

1 hour ago, Kartoffelkuchen said:

Holy moly that thing is enormous.

I can't tell from the picture - but is that just a regular Raptor with a larger bell slapped on the end - or is it a wholly different build with larger pipes and everything?

[sevenperforce]

2 hours ago, RealKerbal3x said:

I love how transparent Elon is about the Starship program as a whole.

Bingo.

I just knew it was the CH₄ turbopump that ultimately failed and precipitated the RUD.

I wonder what their fix is, though.

[RealKerbal3x]

Just now, JoeSchmuckatelli said:

I can't tell from the picture - but is that just a regular Raptor with a larger bell slapped on the end - or is it a wholly different build with larger pipes and everything?

The powerhead appears to be largely the same but because Raptor uses a regeneratively cooled nozzle, they can't just tape an extension to the normal sea-level nozzle - the piping inside the nozzle has to be fully plumbed in to allow the excess propellant to flow throughout for cooling.

[JoeSchmuckatelli]

Just now, JoeSchmuckatelli said:

I love how transparent Elon is about the Starship program as a whole.

It's pretty much marketing genius.  I get frustrated looking at NASA slowly slog along (when I shouldn't be) and forgive SpaceX every stumble (which I probably should, anyway) in large part because of how they interact with the public.

 

 

[sevenperforce]

3 minutes ago, JoeSchmuckatelli said:

I can't tell from the picture - but is that just a regular Raptor with a larger bell slapped on the end - or is it a wholly different build with larger pipes and everything?

The vacuum Raptor uses the same turbopump assembly as the SL Raptor but the engine bell is larger. I think there are changes to the regenerative cooling loops, too, so that they cover a larger area.

[tater]

SN15 presumably to the pad today.

[tater]

 

[RyanRising]

3 hours ago, RealKerbal3x said:

 

Raptor still has a ways to go, obviously, and I'm not sure if I should, but I feel kinda glad this wasn't some issue with propellant flow again due to the bellyflop. SN8 had its partial ullage collapse, SN10 had its methalox cocktail fizzy with helium, so while obviously a leak in an engine is no good, it's got to be slightly vindicating that the problem wasn't something that resulted from the patches they needed to make the bellyflop work.

1 hour ago, sevenperforce said:

I wonder what their fix is, though.

There probably won't be one silver bullet, based on "getting fixed 6 ways to Sunday." I have no real insight into this, but it sounds like the fix would involve both updating the plumbing or procedures to make sure that specific leak can't happen, and improved placement of redundant sensors and controllers such that a similar fire would leave the avionics with enough information and brains to try startup anyway.

[magnemoe]

1 hour ago, RealKerbal3x said:

The powerhead appears to be largely the same but because Raptor uses a regeneratively cooled nozzle, they can't just tape an extension to the normal sea-level nozzle - the piping inside the nozzle has to be fully plumbed in to allow the excess propellant to flow throughout for cooling.

Yes, most vacuum engines including merlin don't use cooling on the nozzle extension. Perhaps some ablative in the nozzle else its large size radiate lots of heat. 
However as raptor vacuum is inside the skirt it needs active cooling so some methane has to be diverted to cool it.