totm nov 2023 SpaceX Discussion Thread

[wumpus]

7 hours ago, kerbiloid said:

Superdraco requires udmh+at, two more substances in their own tanks, incompatible with the main engine. While using kerosene, which is already onboard + htp which makes it hypergolic, allows to add just one small tank with htp and to choose whether you will burn all kerosene in a one-way flight, or reserve a little to return and land.

So, unless the falcon is udmh+at, this looks like a lesser evil.

Isn't Kestel pressure fed?  A Kestel needs its own tanks that are far heavier than a super Draco.  This really looks like a job for a Draco.  If it were heavier or needed more kick, I'd recommend adding SRBs, but you still need something for control and enough Dracos for control (of a Falcon upper) are enough Dracos to land.

I'd imagine a raptor upper stage would land on Merlin engines, but the Kestel doesn't seem to fit.  If they were playing KSP, they would likely be using Ruthorford engines, but this isn't KSP.

[Racescort666]

6 hours ago, Rakaydos said:

you may notice that Raptor isnt flying yet. neither is BE4, or the SLS engines.

Designing a new engine is not a lesser evil compared to adding more tanks. especially if the extra tanks add flexibility by being removable if you arnt landing on a mission.

I have a dumb idea: run the SuperDraco on RP-1 and some other storable oxidizer. I have been thinking about this and there have been rocket engines that have been converted from RP-1/LOX to Hydrazine/NTO. I don't know the specifics of the SD but I guess I could do the math to design a hypergolic engine and switch the fuel to RP-1 to see what the performance looks like. The question is whether its worth saving the weight of an extra fuel tank and just using whats left over from the fuel margin of the main mission.

[IncongruousGoat]

12 minutes ago, Racescort666 said:

I have a dumb idea: run the SuperDraco on RP-1 and some other storable oxidizer. I have been thinking about this and there have been rocket engines that have been converted from RP-1/LOX to Hydrazine/NTO. I don't know the specifics of the SD but I guess I could do the math to design a hypergolic engine and switch the fuel to RP-1 to see what the performance looks like. The question is whether its worth saving the weight of an extra fuel tank and just using whats left over from the fuel margin of the main mission.

As far as I know, RP-1 isn't hypergolic with any storable propellant. There are probably additives that'll make it hypergolic with N2O4, but after digging through Ignition! I can't find reference to any that don't substantially alter the composition of the propellant, and thus mess up the fuel you're trying to burn in the MVac. So it would seem that swapping the propellants around like that isn't really possible, at least not in any useful way.

[Rakaydos]

Why is everyone trying to make the landing engine run on cryogenic fuel? You want the landing engine to be reliable after a week out and back on GTO, and cryo fuels just dont work that way.

Separate, storable fuel in an optional module you can remove if you want to fly expendable.

Edited June 13, 2017 by Rakaydos

[KSK]

11 hours ago, kerbiloid said:

Superdraco requires udmh+at, two more substances in their own tanks, incompatible with the main engine. While using kerosene, which is already onboard + htp which makes it hypergolic, allows to add just one small tank with htp and to choose whether you will burn all kerosene in a one-way flight, or reserve a little to return and land.

So, unless the falcon is udmh+at, this looks like a lesser evil.

It's a close run thing though. I don't think HTP is quite monomethylhydrazine levels of nasty but it's not exactly safe or easy to handle either. Also SpaceX would need to build the pad infrastructure for handling HTP as well as their other hypergolics and as well as RP1 and LOX. I doubt it's going to happen, given that this is the company that deliberately uses the same propellant combo on both stages of their workhorse booster in the interests of keeping costs down.

Again, I think @Rakaydos has the right answer here.

[insert_name]

6 hours ago, wumpus said:

Isn't Kestel pressure fed?  A Kestel needs its own tanks that are far heavier than a super Draco.  This really looks like a job for a Draco.  If it were heavier or needed more kick, I'd recommend adding SRBs, but you still need something for control and enough Dracos for control (of a Falcon upper) are enough Dracos to land.

I'd imagine a raptor upper stage would land on Merlin engines, but the Kestel doesn't seem to fit.  If they were playing KSP, they would likely be using Ruthorford engines, but this isn't KSP.

Also kestrel is a vacuum engine and has an ablatively cooled throat, not good for reusability

[wumpus]

9 hours ago, Rakaydos said:

Why is everyone trying to make the landing engine run on cryogenic fuel? You want the landing engine to be reliable after a week out and back on GTO, and cryo fuels just dont work that way.

Separate, storable fuel in an optional module you can remove if you want to fly expendable.

I thought we were discussing the second stage of the booster.  Cryogenic isn't an issue there, and it will certainly use them for any burns still done in vacuum via the merlin engines.  If you want to land the Dragon[2], you are already insisting on hypergolics.  You will also expect to use hypergolics for the second stage of the booster, but only because the merlin engine won't work at sea level.

[Rakaydos]

1 hour ago, wumpus said:

I thought we were discussing the second stage of the booster.  Cryogenic isn't an issue there, and it will certainly use them for any burns still done in vacuum via the merlin engines.  If you want to land the Dragon[2], you are already insisting on hypergolics.  You will also expect to use hypergolics for the second stage of the booster, but only because the merlin engine won't work at sea level.

and yet people are talking about using the kerlox main tank for fuel "to save tank mass."

[CatastrophicFailure]

My money remains on them re-using a Dragon propulsion system/subframe with heat shield, maybe upgraded with SuperDracos, mounted upside-down on the inaugural FH upper stage.  Simple, modular, an expansion of existing components and a testbed for D2 landing procedures as well.

 

On another note, BulgariaSat is still on tap for the 17th, but no word on a static fire. Um... should we be getting nervous?

[kerbiloid]

Though, Buran orbital engines were LOX powered, with LOX tank for 15-20 days flight without active cooling and 30 days - with active cooling

https://translate.google.ru/translate?sl=ru&tl=en&js=y&prev=_t&hl=ru&ie=UTF-8&u=http%3A%2F%2Fwww.ciam.ru%2Fabout%2Fhistory%2Fnovember-15-1988-saw-the-first-and-only-flight-of-the-reusable-orbiter-ok-buran%2F&edit-text=.

with a skimmer inside

Spoiler

 

Edited June 14, 2017 by kerbiloid

[magnemoe]

1 hour ago, CatastrophicFailure said:

My money remains on them re-using a Dragon propulsion system/subframe with heat shield, maybe upgraded with SuperDracos, mounted upside-down on the inaugural FH upper stage.  Simple, modular, an expansion of existing components and a testbed for D2 landing procedures as well.

 

On another note, BulgariaSat is still on tap for the 17th, but no word on a static fire. Um... should we be getting nervous?

As an first version this makes lots of sense, you would need to add fins at the rear but no other changes. 
Later they can think of an more integrated system but they will probably keep it as bolt on. 

[Skylon]

With front-mounted engines where would the landing legs go, and what would they look like? Could a scaled down first stage landing leg work? I guess not, partly because of aerodynamic problems on launch

[kerbiloid]

And heatshield. Will it be cheap and heavy or light and expensive? Tiles or ablator? Don't forget, it must shadow all the stage.

 

[CatastrophicFailure]

10 minutes ago, Skylon said:

With front-mounted engines where would the landing legs go, and what would they look like? Could a scaled down first stage landing leg work? I guess not, partly because of aerodynamic problems on launch

IIRC plans for the D2 have very short legs that just kinda pop out of the heatshield. Could be a test of that mechanism, too. 

[kerbiloid]

D2 is short and wide

[Brotoro]

They should have the second stage land onto a support cradle...no need for legs. They want to do that eventually with gigantic ITS boosters, so start small with the second stage landing that way.

[RedKraken]

Maybe :

[KSK]

1 hour ago, kerbiloid said:

And heatshield. Will it be cheap and heavy or light and expensive? Tiles or ablator? Don't forget, it must shadow all the stage.

Cheap (relatively speaking) and light apparently. I'm not sure how expensive the original PICA material was but PICA-X, the SpaceX version is about 10 times cheaper. Source. It's an old article but an interesting one. I thought this paragraph was particularly prescient:

"Many of Lindenmoyer’s NASA colleagues remain skeptical—even some who have visited SpaceX. “There’s quality control in development, and then there’s quality control in production,” says one agency senior manager who asked not to be named. “The history of launch vehicle development suggests that design issues might crop up in the first or second launch, but it’s the process problems that start to show up on the sixth, the seventh, and the eighth launch.” Noting that so far Musk’s team has launched only two Falcon 9s, this skeptic asks, “How does he ever get to a rate—you know, he’s talking about flying a dozen, two dozen times a year? And as they fly their vehicle, how long before they have a major accident? And are they able to sustain a major accident and still be a viable company?”
 

Emphasis added. Yes, yes they did show up. And happily yes, yes they are still a viable company.

[magnemoe]

45 minutes ago, RedKraken said:

Maybe :

This is a lot how I see it, fairing will cover heat shield and return module, payload on top of it.
You have an option to rotate the legs, they are wrapped around the module, you rotate them so they point out with the leg pointing down. 

You would need an payload interface on top of heat shield, this will be dropped before reentry. 

[RedKraken]

1 minute ago, magnemoe said:

This is a lot how I see it, fairing will cover heat shield and return module, payload on top of it.
You have an option to rotate the legs, they are wrapped around the module, you rotate them so they point out with the leg pointing down. 

You would need an payload interface on top of heat shield, this will be dropped before reentry. 

Yep the PAF needs mounting slots in the heatshield. They need to plug closed after the PAF is jettisoned.

I suspect they will pica up the sides of the stage too. Not as thick as the main heat shield.

What g-loading do you think this will need to withstand for re-entry? 15 - 20? The tanks may need to be built stronger.

[magnemoe]

6 minutes ago, RedKraken said:

Yep the PAF needs mounting slots in the heatshield. They need to plug closed after the PAF is jettisoned.

I suspect they will pica up the sides of the stage too. Not as thick as the main heat shield.

What g-loading do you think this will need to withstand for re-entry? 15 - 20? The tanks may need to be built stronger.

The holes can be done like the dragon landing legs but smaller holes as its just brackets, you can also make the shield larger than the stage as its in the fairing. 
Don't think the g-load is an issue outside of engine, at launch it has to handle max-q and max-g with fuel, payload and faring. now its just the empty stage. 
Another related issue is if upper stage can handle the +50 ton payload of an falcon heavy in discard mode. 

[kerbiloid]

1 hour ago, RedKraken said:

Maybe :

Spoiler

1 hour ago, RedKraken said:

 

Then why D2 looks like a drop?

Spoiler

Heat shield along the body, reinforced structure to withstand acceleration, RCS, command unit, legs.

So, we now get a shuttle fuselage without wings and with fuel tank inside the cargo bay.

1 hour ago, KSK said:

And happily yes, yes they are still a viable company.

http://www.cnbc.com/2017/01/13/spacex-documents-reveal-losses-and-high-hopes-for-a-new-business.html

Quote

Internal documents obtained by the Wall Street Journal and interviews with former SpaceX employees reveal the commercial space company suffered a $260 million loss in 2015, after a rocket bound for the International Space Station exploded after launch.

However, the company enjoyed profitable years in 2013 and 2014 after contracts from NASA and satellite companies pushed revenue from $680 million to $1 billion.

So, NASA is.

25 minutes ago, RedKraken said:

What g-loading do you think this will need to withstand for re-entry? 15 - 20?

And side tensions.

11 minutes ago, magnemoe said:

at launch it has to handle max-q and max-g with fuel

I.e. 4g

11 minutes ago, magnemoe said:

now its just the empty stage.

Ten time more? 40?

Edited June 14, 2017 by kerbiloid

[kerbiloid]

(doubled)

Edited June 14, 2017 by kerbiloid

[sevenperforce]

Remember that whatever is used for recovery has to fit inside the payload fairing, with the possible exception of fold-flush grid fins. 

[Nefrums]

I highly doubt that it would be possible to reenter the second stage top first.   All the mass is at the bottom.  It would be very aerodynamically unstable.

It would require huge fins, mounted behind CoM, And CoM for an empty stage is probably not that far above the engine.