SpaceX Starship/Super Heavy Engineering General Thread 4

[equiserre]

Why would anyone watch something that is advertised as almost 100% speculation?

An engineer puts in a lot of effort to make educated guesses, explaining his reasoning, and calls it 100% speculation? that´s pretty good for some Youtube entertainment

[Tangilinear Interjar]

Why would anyone watch something that is advertised as almost 100% speculation?

Why would anyone read a Space forum where everything is pretty much 100% speculation? 🙄

[Robotbeat]

LOL, that’s a totally fair point.

My real gripe is with the annoying click-bait tactics. Regular old forum speculation is fine, and CSI_Starbase is often pretty informative.

[OTV Booster]

What are the chances these ports have something to do with controlling spinup gasses?

[livingjw]

What are the chances these ports have something to do with controlling spinup gasses?

I am pretty sure spin up gases exit the main chamber. Maybe CH4 chill down exhaust gas?

John

[sdsds]

Summary of the theory Zack Golden is proposing:

It appears Booster 7 may have been reconfigured so that methane produced during spin prime testing will now be recaptured.  This could eliminate the need to redirect LOX from raptor chill sequence.

More on this later once I’m able to verify this change.

https://twitter.com/CSI_Starbase/status/1612327585857392646

[OTV Booster]

I've got a question that came to me while formulating a post in the refueling thread.


The reason for putting the header tanks in the nose is CG issues during EDL. A crewed ship will have the habitat mass up in the nose. Would the header tanks still need to be there for balance?


Not having the headers and plumbing sorta in the crew quarters sounds like a good idea if it could be made to work. Where would they go? Maybe back to earlier designs with the headers in the tanks? The down side would be human rated ships not having tank commonality with other variants.


Personally, I think commonality does not mean slavishly copying, and in something as tricky as human rating, it can be sacrificed in part when it gets in the way.

[BT52]

Honestly. I think SpaceX calculates CoP, CofG with crew in mind already. I cannot think more smart way to include" nosecone" as useful space as it is in current design.

But what i know. Elon said in interviews that the CofG is scuffed already.

Maybe 2 variants will be way to go as u said.  I suppose they can produce easily 2 different aero flap geometries (surface area and CoP bias adjustment). That sort of things is not unknown in racing (aircraft) industry.

Soo atm they just keep waiting too see if drag and flaps can keep it stable as it is. So i think everything is in limbo and in anticipation of orbital test and real data.  I suppose we can say SpaceX is no afraid too ditch current iteration in split second if necessary. 

[kevinof]

SpaceX website (https://www.spacex.com/vehicles/starship/) now saying 150t reusable and 250t fully exepnded. This is a change from the previous and a (big) increase?

"SpaceX’s Starship spacecraft and Super Heavy rocket – collectively referred to as Starship – represent a fully reusable transportation system designed to carry both crew and cargo to Earth orbit, the Moon, Mars and beyond. Starship will be the world’s most powerful launch vehicle ever developed, with the ability to carry up to 150 metric tonnes to Earth orbit reusable, and up to 250 metric tonnes expendable."

[Alberto-Girardi]

SpaceX website (https://www.spacex.com/vehicles/starship/) now saying 150t reusable and 250t fully exepnded. This is a change from the previous and a (big) increase?

"SpaceX’s Starship spacecraft and Super Heavy rocket – collectively referred to as Starship – represent a fully reusable transportation system designed to carry both crew and cargo to Earth orbit, the Moon, Mars and beyond. Starship will be the world’s most powerful launch vehicle ever developed, with the ability to carry up to 150 metric tonnes to Earth orbit reusable, and up to 250 metric tonnes expendable."

Yes, but it seems that they haven't updated all the page since in the "Starship" section of the slide it still says `100-150+ t`.  AFAIR the general consensus was that the 100 tons number was a sort of "guaranteed performance" and that the final payload mass once the system is up and running and has been optimized would be higher.

[InterestedEngineer]

SpaceX website (https://www.spacex.com/vehicles/starship/) now saying 150t reusable and 250t fully exepnded. This is a change from the previous and a (big) increase?

"SpaceX’s Starship spacecraft and Super Heavy rocket – collectively referred to as Starship – represent a fully reusable transportation system designed to carry both crew and cargo to Earth orbit, the Moon, Mars and beyond. Starship will be the world’s most powerful launch vehicle ever developed, with the ability to carry up to 150 metric tonnes to Earth orbit reusable, and up to 250 metric tonnes expendable."

100 – 250+ t (orbit dependent)

Polar satellites probably 100t.   Most efficient orbit, fuel only, closer to 150t.

I wonder if there's any dependency on SH return to launch or land downrange.

Has anyone looked at launches from BC with SH return to KSC in Florida?  Is that trajectory possible?

[steveleach]

SpaceX website (https://www.spacex.com/vehicles/starship/) now saying 150t reusable and 250t fully exepnded. This is a change from the previous and a (big) increase?

"SpaceX’s Starship spacecraft and Super Heavy rocket – collectively referred to as Starship – represent a fully reusable transportation system designed to carry both crew and cargo to Earth orbit, the Moon, Mars and beyond. Starship will be the world’s most powerful launch vehicle ever developed, with the ability to carry up to 150 metric tonnes to Earth orbit reusable, and up to 250 metric tonnes expendable."

Do we have any clues as to how much of the extra 100t is propellant (entry/landing burns) and how much is unnecessary hardware removal (flaps, tiles, etc)? Or even whether it includes expending the booster?

[su27k]

Elon has been saying 150t fully reusable and 250t expendable for a while now, so not exactly new information.

Some obvious deduction from this:

https://twitter.com/Robotbeat/status/1619811705672073216

This is perfectly in line with what you’d expect based on past figures on their website. Full expendable should do roughly SLS block IB through TLI IIRC.

More like Ares V.

Comparable to SLS Block 2 w/ SH recovery.

Would blow past both w/ a third stage.

https://twitter.com/Devintcotter/status/1619742402713116672

So I’m going off a simple Dv online calculator but it looks like it could get 80-85 t to NRHO, 45t to lunar surface. I could be horribly wrong, I usually hope that someone like @BellikOzan or @DJSnM does the math. Maybe they can look at the new specs of 250t to orbit.

60-80t to TLI if you have 250t to LEO. But you can increase that dramatically with a third stage (you're limited by high stage burnout mass).

That'd let you get to your NRHO figures.

I wonder if this new info is because of all the “in one launch” bs. Sure looks to me like Starship could do a single launch lunar mission with a landing in one launch.

Might be.

Oh it definitely could with the right lander and Orion. (Or better yet w/ a different crew vehicle -- but w/ the right vehicle even much smaller LVs could do that).

It’s more mass than Saturn V could throw TLI. If you stick with Orion 21 day mission capability & NRHO 7 day orbit than you can only have crew on the moon for 3-5 days. You don’t need a big lander for boots, flags and light experiments.

Right. This could throw an Orion and an ILV or fully filled ALPACA in a single launch, unlike any SLS variant.

[OTV Booster]

John Livingston did some ullage calcs that are a bit disturbing. They show a full LOX tank having a bottom pressure of 6.664 bar at ignition. This is over the 6bar tank rating.


The 6bar rating was for SS, IIRC. Is SH rated higher? If it's only rated to 6bar the tank would have to be 100% full with zero ullage space, or the common dome is going to blow out.


A related question. How sensitive is a turbopump to variations in inlet pressure (assuming it stays above minimum necessary pressure). With an FFSC engine this question gets really interesting.

[DanClemmensen]

John Livingston did some ullage calcs that are a bit disturbing. They show a full LOX tank having a bottom pressure of 6.664 bar at ignition. This is over the 6bar tank rating.

If that's at ignition (at 1 g) then what is it immediately after the clamps release (at 1.5 g)?

[InterestedEngineer]

John Livingston did some ullage calcs that are a bit disturbing. They show a full LOX tank having a bottom pressure of 6.664 bar at ignition. This is over the 6bar tank rating.

6 bar was for Starship.

SH has a lot of stringers.  I suspect it can go over 6 bar at the base

I doubt the pumps on the Raptors will care

[greybeardengineer]

John Livingston did some ullage calcs that are a bit disturbing. They show a full LOX tank having a bottom pressure of 6.664 bar at ignition. This is over the 6bar tank rating.

6 bar was for Starship.

SH has a lot of stringers.  I suspect it can go over 6 bar at the base

Stringers help with buckling resistance, especially when not pressurized, not burst strength. Failure from overpressure could be hoop stress failure in the walls, or more likely based on history, failure in the bottom dome to wall welds.

Pressure at the base is the sum of propellant head pressure and ullage pressure. The difference in tank height between SS and SH can be countered by difference in ullage pressure to make inlet pressure similar.

[warp99]

John Livingston did some ullage calcs that are a bit disturbing. They show a full LOX tank having a bottom pressure of 6.664 bar at ignition. This is over the 6bar tank rating.

If that's at ignition (at 1 g) then what is it immediately after the clamps release (at 1.5 g)?

The tank pressure is calculated at launch when accelerating at 1.5g.  Static head values at engine ignition a few seconds before launch are around 66% of the given figures. 

Note that a usually reliable Reddit source has said that the booster tank walls are 4.6mm not 4.0mm like the ship.  The ship fairing seems to be 3.6mm.  Certainly Elon did originally say that they would use thicker tank walls at the bottom of the stack and use thinner walls further up.

[InterestedEngineer]

John Livingston did some ullage calcs that are a bit disturbing. They show a full LOX tank having a bottom pressure of 6.664 bar at ignition. This is over the 6bar tank rating.

6 bar was for Starship.

SH has a lot of stringers.  I suspect it can go over 6 bar at the base

Stringers help with buckling resistance, especially when not pressurized, not burst strength. Failure from overpressure could be hoop stress failure in the walls, or more likely based on history, failure in the bottom dome to wall welds.

Pressure at the base is the sum of propellant head pressure and ullage pressure. The difference in tank height between SS and SH can be countered by difference in ullage pressure to make inlet pressure similar.

I might have used the wrong term.  There are "hoop stringers", if that's the right term, even on Starship.  They run around the circumference.   See pic.

I'm still looking for the equivalent pic for Super Heavy

[livingjw]

John Livingston did some ullage calcs that are a bit disturbing. They show a full LOX tank having a bottom pressure of 6.664 bar at ignition. This is over the 6bar tank rating.

If that's at ignition (at 1 g) then what is it immediately after the clamps release (at 1.5 g)?

At launch, 1.5 g's

John