totm nov 2023 SpaceX Discussion Thread

[Guest]

That's what I've been trying to say. Numbers are deceitful and looks even more so. Falcon 9 takes many tradeoffs to be able to land the 1st stage, so it uses a large 2nd stage and a rather short and weak 1st stage, in order to drop the latter early enough to land it.

32 minutes ago, RCgothic said:

If Centaur weighed 116t gross then it would need 1.46t of engine and 5.3t of tank, assuming the tank follows square cube and engine goes linearly with mass.

FUS *still* beats it by 2.57km/s at 0te of payload and 800m/s at 16te of payload.

They're roughly equivalent at 50T, though, which is what, realistically, an LH2 stage of this size would be used for. Apollo complex was around that mass. You could probably shave something off Centaur's engines. Not to mention that, realistically, an enlarged Centaur's "tank" would be lighter than that, too, since avionics, RCS propellant, payload adapters and such also figure into the dry mass. These would go up linearly or not change at all, depending on the part. I don't have RSS installed right now (best way to check is to build that thing), but I think a Centaur-style stage would win at or slightly above 50T.

Edited June 26, 2020 by Guest

[RealKerbal3x]

Here's to SN5 being the first to fly!

[RCgothic]

I retract some previous statements. My maths was wrong. >.<

But the FUS's mass fraction *is* incredible.

[sevenperforce]

11 hours ago, AngrybobH said:

looks like the worlds largest beer keg.

Stan rocket kegstands?

5 hours ago, Dragon01 said:

That's what I've been trying to say. Numbers are deceitful and looks even more so. Falcon 9 takes many tradeoffs to be able to land the 1st stage, so it uses a large 2nd stage and a rather short and weak 1st stage, in order to drop the latter early enough to land it.

They're roughly equivalent at 50T, though, which is what, realistically, an LH2 stage of this size would be used for. Apollo complex was around that mass. You could probably shave something off Centaur's engines. Not to mention that, realistically, an enlarged Centaur's "tank" would be lighter than that, too, since avionics, RCS propellant, payload adapters and such also figure into the dry mass. These would go up linearly or not change at all, depending on the part. I don't have RSS installed right now (best way to check is to build that thing), but I think a Centaur-style stage would win at or slightly above 50T.

I'm really looking forward to Vulcan because as far as propellant allocation choice goes, it's pretty close to optimal. Solids to get you off the pad quickly and kill gravity drag, a high-performance methalox sustainer that has good mass fraction AND good specific impulse, and Centaur on top. No energy penalty for recovery because there's no boostback; just a little extra dry mass for the heat shield and chute (which, again, doesn't kill you because it's first-stage).

The only thing better would be to swap in Raptors for the BE-4 (better thrust and better specific impulse) and something like a stretched Falcon 1 first stage with the Merlin1Ds to replace the solids. 

[RealKerbal3x]

8 minutes ago, sevenperforce said:

The only thing better would be to swap in Raptors for the BE-4 (better thrust and better specific impulse) and something like a stretched Falcon 1 first stage with the Merlin1Ds to replace the solids. 

If you have Raptors and Merlin 1Ds on the same rocket then you'd have to worry about loading both liquid methane and RP-1. 

[sevenperforce]

4 minutes ago, RealKerbal3x said:

If you have Raptors and Merlin 1Ds on the same rocket then you'd have to worry about loading both liquid methane and RP-1. 

Vulcan already has to worry about loading both liquid methane and liquid hydrogen.

[RealKerbal3x]

5 minutes ago, sevenperforce said:

Vulcan already has to worry about loading both liquid methane and liquid hydrogen.

Fair enough. Though the LH2 is for the upper stage, right? A lot of launch vehicles use different fuels for their first and upper stages, but I can't think of one that uses different fuels for its centre core and liquid boosters. I'm not sure if that would make a difference.

[SOXBLOX]

How are we certain on the BE-4's numbers? Blue could be adjusting the mass and Isp  for secrecy. Sounds like something they would do. 

[sevenperforce]

1 minute ago, RealKerbal3x said:

Fair enough. Though the LH2 is for the upper stage, right? A lot of launch vehicles use different fuels for their first and upper stages, but I can't think of one that uses different fuels for its centre core and liquid boosters. I'm not sure if that would make a difference.

China does it. Long March 5 uses kerolox boosters, a hydrolox core, and a hydrolox upper stage.

Apart from China, the only operational rockets with liquid boosters are Falcon Heavy, Delta IV Heavy, and Soyuz-2, all of which use a single prop for the entire rocket (I am treating the Soyuz-2 kick stages as part of payload). Technically, India uses liquid (hypergolic) boosters on its first stage, but the core is a solid rocket and the boosters do not separate, so it's more like a cluster stage than proper boosters.

Energia used RD-170s for its boosters and an RD-120 for its center core, so that's a mix of kerosene and hydrogen. The Pyrios booster proposal for SLS would have used kerolox boosters with a hydrogen core. 

5 minutes ago, SOXBLOX said:

How are we certain on the BE-4's numbers? Blue could be adjusting the mass and Isp  for secrecy. Sounds like something they would do. 

With oxygen-rich staged combustion, I don't think the BE-4 can ever reach the same raw chamber pressure as the Raptor, which is the primary driver of the Raptor's ridiculous TWR and Isp. Full-flow staged combustion is a beast.

5 hours ago, Dragon01 said:

They're roughly equivalent at 50T, though, which is what, realistically, an LH2 stage of this size would be used for. Apollo complex was around that mass. You could probably shave something off Centaur's engines. Not to mention that, realistically, an enlarged Centaur's "tank" would be lighter than that, too, since avionics, RCS propellant, payload adapters and such also figure into the dry mass. These would go up linearly or not change at all, depending on the part. I don't have RSS installed right now (best way to check is to build that thing), but I think a Centaur-style stage would win at or slightly above 50T.

The other variable is the size of the payload and where you are sending it. With a very small payload going to a high-energy orbit, a low-thrust hydrolox stage suffers less than it would with a larger payload and LEO or MEO. Of course a kerolox stage is still going to deliver more total dV but if the hydrolox one is staged high enough and fast enough it doesn't matter.

[Guest]

Actually, according the computation I made, hydrolox becomes preferable with larger payloads. This makes sense when you consider that the bigger the payload is, the less influence the stage's mass fraction has on the whole thing, and the more important Isp becomes. However, all things equal, a hydrolox upper stage will be optimized for a larger payload than a kerolox stage of similar mass. Compare S-IVB to FUS, for instance. The latter tops out at 24T (FH), while the former was designed for a 47T class payload.

BTW, by all accounts, designs like Energia, LM5 and all variations on Shuttle tanks with liquid boosters should be treated as conventional two-stage rockets, just with an LH2 upper stage so huge that the first stage needs to be mounted around it. Same goes for Ariane 5 and every hydrolox core design but H-2 and Delta IV. The latter is an oddball design brought about by desire to reuse some of the SSME technology, and I don't know about the former, but it's a pretty weird rocket, too (might be that Mitsubishi only ever made LH2 engines and solids). 

Edited June 26, 2020 by Guest

[tater]

 

[mikegarrison]

2 hours ago, SOXBLOX said:

How are we certain on the BE-4's numbers? Blue could be adjusting the mass and Isp  for secrecy. Sounds like something they would do. 

They can't be too secretive about an engine they are selling to other companies.

[CatastrophicFailure]

[screaminFizgig.gif]

 

[tater]

56 minutes ago, mikegarrison said:

They can't be too secretive about an engine they are selling to other companies.

They are selling to ULA, it's not like the information is entirely public. Look how hard it is to find out what an RL-10 costs.

I'd trust numbers given to us by Blue, with the understanding that they would (just like SpaceX) be constantly working to improve them as they gain more experience firing them.

[mikegarrison]

3 minutes ago, tater said:

They are selling to ULA, it's not like the information is entirely public.

Oh believe me, I know. I work with proprietary information all the time. But they still can't be too secretive about something as fundamental as mass or Isp.

Probably a bigger issue is that undoubtedly they have negotiated performance guarantees with ULA. They will probably try to have some margin to them. Both parties will probably keep the guarantees proprietary, and the margins will be proprietary information for Blue. But they won't be too far off from stated "brochure" numbers.

[tater]

2 minutes ago, mikegarrison said:

Oh believe me, I know. I work with proprietary information all the time. But they still can't be too secretive about something as fundamental as mass or Isp.

Probably a bigger issue is that undoubtedly they have negotiated performance guarantees with ULA. They will probably try to have some margin to them. Both parties will probably keep the guarantees proprietary, and the margins will be proprietary information for Blue. But they won't be too far off from stated "brochure" numbers.

Agreed—and they have room to improve towards whatever the theoretical maximum is for their engine cycle.

Edited June 26, 2020 by tater

[StrandedonEarth]

 

[CatastrophicFailure]

And the official: 

 

[tater]

 

[CatastrophicFailure]

Hmm. If it holds, GPSIII-3 launches on the 30th around 3:55 local. So that would be two launches within almost 48 hours from the same coast, that’s gotta be a new record for SpaceX. 

[CatastrophicFailure]

In the “also interesting, not really discussed” pile, I just came across this: the first Dragon 2 Cargo mission in October of this year will also carry an airlock.  In the trunk. 

(it’s that little doodleybop on the far left)

It will serve to deploy cubesats for Nanoracks, and I do mean serve. There won’t be any hatches, sats will be loaded from the berthing hatch on Harmony, then the RMS will just pick the airlock shell off like, “bon apétit, space, hon hon hon!”

Edited June 27, 2020 by CatastrophicFailure
argh,.

[tater]

The growth of Boca Chica is amazing. We often see ground level images that make it look like "rockets in the dirt." Aerial shots make it look less... dirty.

 

 

 

 

[Raven Industries]

It's very strange to watch a full blown manufacturing plant spring from the ground, more or less. 

[tater]

Seems like they are gonna push it right farther:

 

 

[Elthy]

On 6/25/2020 at 4:25 PM, tater said:

Would love to see an image with both F9s vertical.

 

I guess it wont get much better than this...