totm nov 2023 SpaceX Discussion Thread

[Spaceception]

3 minutes ago, magnemoe said:

Its pretty sure they will test this system before they put rockets on top of it. 

Yeah, I goofed there. But is this sooner than most of us were expecting?

[tater]

live

 

[tater]

16 flown booster lands.

[RCgothic]

Wow

 

[darthgently]

For closure, the green plume from the MVAC I've seen so many times (and no one else reported) is no longer there since the stage 2 camera has been upgraded to 4k.  So it was likely an artifact of the old camera/encoding combined with the player/decoding on my end.  So everyone can relax now

[RCgothic]

200t+ to a useful orbit. That's likely 250t+ to LEO Ref. Even more expended.

These performance figures may be aspirational rather than near future. The flight cadence certainly is.

 

[RCgothic]

5 hours ago, RCgothic said:

Wow

 

20M lbfs for superheavy is ~275 metric tonnes per raptor by the way. More powerful than currently available BE-4 figures. (~250t)

[tater]

3 hours ago, RCgothic said:

200t+ to a useful orbit. That's likely 250t+ to LEO Ref. Even more expended.

ASDS landing for F9 results in a ~23% performance hit (stated max payload of 22.8t vs actual max launched where booster has been recovered, 17.4t). The heaviest RTLS might have been ~11t, I have seen 12t talked about as where they switch to ASDS. At 12t, that's a 48.6% hit, some time ago I thought 40% was the number, but it might be closer to 50%. That pushed expended performance of SS/SH towards 400t to LEO.

FWIW, that means an 80t LSS launched with booster expended can land on the Moon with residual propellants (it can do so with a LSS up to 95t dry). Our 80t LSS refilled once with an expended tanker (tanker SS can stay in LEO as a depot) and fly to the lunar surface AND return to lunar orbit—back to NRHO, actually (not quite enough to go to the surface via NRHO then back to NRHO, though, so presumably it could meet Orion at some medium orbit and do Artemis with just 1 refilling).

 

 

[RCgothic]

17 minutes ago, tater said:

ASDS landing for F9 results in a ~23% performance hit (stated max payload of 22.8t vs actual max launched where booster has been recovered, 17.4t). The heaviest RTLS might have been ~11t, I have seen 12t talked about as where they switch to ASDS. At 12t, that's a 48.6% hit, some time ago I thought 40% was the number, but it might be closer to 50%. That pushed expended performance of SS/SH towards 400t to LEO.

FWIW, that means an 80t LSS launched with booster expended can land on the Moon with residual propellants (it can do so with a LSS up to 95t dry). Our 80t LSS refilled once with an expended tanker (tanker SS can stay in LEO as a depot) and fly to the lunar surface AND return to lunar orbit—back to NRHO, actually (not quite enough to go to the surface via NRHO then back to NRHO, though, so presumably it could meet Orion at some medium orbit and do Artemis with just 1 refilling).

 

 

I made an argument like this on Twitter one time and it was suggested back to me that because Raptor has a higher ISP and Superheavy has higher temperature tolerances, it doesn't need to save as much fuel for boostback and landing, so applying a Falcon payload penalty to Superheavy probably isn't fair.

[tater]

2 minutes ago, RCgothic said:

I made an argument like this on Twitter one time and it was suggested back to me that because Raptor has a higher ISP and Superheavy has higher temperature tolerances, it doesn't need to save as much fuel for boostback and landing, so applying a Falcon payload penalty to Superheavy probably isn't fair.

As a boundary value it's useful, though.

Real performance being better just adds margin. Seems like it can do a crew lunar mission (meeting Orion) with 1 refilling to a medium orbit, possibly via NRHO if the penalty is lower. 2 refillings and it can do the entire mission from LEO, no Orion required (with margin based on how much better than a 50% penalty it gets).

[tater]

 

[sevenperforce]

1 minute ago, tater said:

 

He was speculating about gimbal clearance...this could be fixed by using SL Raptors on the outside or going to 4 RVacs and 8 SLs.

[RCgothic]

5 hours ago, tater said:

As a boundary value it's useful, though.

Real performance being better just adds margin. Seems like it can do a crew lunar mission (meeting Orion) with 1 refilling to a medium orbit, possibly via NRHO if the penalty is lower. 2 refillings and it can do the entire mission from LEO, no Orion required (with margin based on how much better than a 50% penalty it gets).

No, actually. Making up numbers here to illustrate:

If Superheavy RTLS is a 20% payload penalty (because of its superior performance ) and it can put 250t mass into LEO inc starship dry mass and reserved deorbit and landing fuel, then expending Superheavy gets ~312t to the same orbit.

If we apply a Falcon 40% payload penalty to Superheavy, that would imply 417t to LEO expended. That exaggerates Superheavy's performance by 105t.

The bigger Falcon payload penalty is not bounding for the purpose of estimating Superheavy's expendable performance.

[tater]

1 hour ago, RCgothic said:

No, actually. Making up numbers here to illustrate:

Yeah, my bad above.

Boostback on AX-2 looked like ~50 seconds of 9 engines. That's nearly 20% of the total S1 propellant mass. Entry and landing for F9 kill ~20%, so the 40% number looks like it's in the ballpark—though the real life numbers seem to show the actual RTLS penalty is closer to an additional 26% on top of ASDS losses (entry+landing).

So maybe RTLS for SH is 20-26%.

So maybe 270-340t expended? If it's closer to the upper end (26% penalty) it can still land on the Moon with no refilling (JUST), 80t dry, 420t wet  (LOL).

A single refilling would then make the vehicle 80t dry, 760t wet. ~8.3 km/s. Just shy of the 8.85 required for a direct flight to the surface, then return to NRHO, but enough for a trip from LEO—>LLO—>surface—>LLO.

Bottom line is that it only needs 2-3 refilling flights with expended boosters.

 

 

Edited July 10, 2023 by tater

[tater]

Ouch:

 

[Meecrob]

On 7/3/2023 at 2:30 PM, Pthigrivi said:

This happens on most every construction project too. Everyone is behind and its kind of a game of chicken to see who has to cop to the clients. 

I have to concede your point...I bet SpaceX is guilty of this very tactic as well.

[CatastrophicFailure]

On 7/10/2023 at 1:45 PM, tater said:

Boostback on AX-2 looked like ~50 seconds of 9 engines.

Wait, I thought only three engines were plumbed for relights?

[tater]

5 minutes ago, CatastrophicFailure said:

Wait, I thought only three engines were plumbed for relights?

Might be, I recall hearing that—but watch the vid, and the exhaust profile looks more like launch, not like the 3 engine entry burn which seems to read more linear to me.

AX-2 entry:

 

Vs latest starlink:

 

Looks like it is 3 engines, even if the pattern looked really different to me.

Interesting that residuals for a 20 second, 3 engine entry burn results in a ~20% payload loss, but a total of ~70 seconds is only a 40-50% loss.

[sevenperforce]

2 hours ago, tater said:

2 hours ago, CatastrophicFailure said:

Wait, I thought only three engines were plumbed for relights?

Might be, I recall hearing that—but watch the vid, and the exhaust profile looks more like launch, not like the 3 engine entry burn which seems to read more linear to me.

Can confirm that only three engines are plumbed for relights. The other engines (and those three, at launch) get their TEA-TEB from GSE.

Also, I'm not sure even Falcon 9 could handle running all nine engines on a nearly-empty booster. Think about it -- 9x941 kN on a ~30 tonne stage is almost thirty gees. That's really getting into ridiculous materials stress.

2 hours ago, tater said:

Interesting that residuals for a 20 second, 3 engine entry burn results in a ~20% payload loss, but a total of ~70 seconds is only a 40-50% loss.

The upper stage is really doing most of the work to get to orbit.

[tater]

1 hour ago, sevenperforce said:

Can confirm that only three engines are plumbed for relights. The other engines (and those three, at launch) get their TEA-TEB from GSE.

That's what I thought... when I pulled up the ax-2 because it was RTLS (was just wanting to time the boostback vs entry burn), I noticed the exhaust pattern was far more like the launch than the entry.

The idea was to get a ballpark for payload losses from RTLS on SH.

We had an elon figure on expended tweeted at some point, maybe with R3? 300t? Then the hot staging added 10% (on nominal reusable flights, but presumably the same).

Also:

 

[tater]

 

[magnemoe]

13 hours ago, tater said:

Looks like it is 3 engines, even if the pattern looked really different to me.

Interesting that residuals for a 20 second, 3 engine entry burn results in a ~20% payload loss, but a total of ~70 seconds is only a 40-50% loss.

I imagine SpaceX could have rebuild falcon 9 first stage to manage without an braking burn, Electron does not do it neither will Supeerheavy, but I imagine it would require some pretty significant changes and Starship is on its way. 

[mikegarrison]

On 7/12/2023 at 1:11 PM, sevenperforce said:

The upper stage is really doing most of the work to get to orbit.

I take issue with this characterization. The upper stage would get absolutely 0 kg of payload into orbit by itself. The only reason it can get any useful work done at all is because of all the energy that the first stage has invested into it.

[tater]

live

[Brotoro]

Rocket launch funtime!