Wiki Super Heavy/Starship - General Development Discussion

[ecarfan]

(Edit: sorry, I see much of this information is in the thread dedicated to the Raptor)

SpaceX CEO Elon Musk reveals photos of Starship's first completed Raptor engine

This is interesting:
—————————————————————————————
“Initially making one 200 metric ton thrust engine common across ship & booster to reach the moon as fast as possible. Next versions will split to vacuum-optimized (380+ sec Isp) & sea-level thrust optimized (~250 ton).”
— Elon Musk (@elonmusk) February 1, 2019
—————————————————————————————

So the first Raptors, that will be used for the Dear Moon flight, will be a compromise between sea-level and vacuum optimized designs to reduce development and construction costs and speed up the timeline. Clever approach.

Quote from the article: “Musk indicated that the sheer value of 31 advanced Raptor engines also means that the first Super Heavy flights may only feature a partial complement of engines in case the vast booster experiences a failure, far from uncommon during the first few launches of a new rocket.”

So the first Super Heavy booster may launch with less than the planned number of engines because for the Dear Moon mission the full number of engines won’t be needed, and if the first test launch (without crew, I assume) has a RUD fewer engines will be lost.

 

[mongo]

(Edit: sorry, I see much of this information is in the thread dedicated to the Raptor)

SpaceX CEO Elon Musk reveals photos of Starship's first completed Raptor engine

This is interesting:
—————————————————————————————
“Initially making one 200 metric ton thrust engine common across ship & booster to reach the moon as fast as possible. Next versions will split to vacuum-optimized (380+ sec Isp) & sea-level thrust optimized (~250 ton).”
— Elon Musk (@elonmusk) February 1, 2019
—————————————————————————————

So the first Raptors, that will be used for the Dear Moon flight, will be a compromise between sea-level and vacuum optimized designs to reduce development and construction costs and speed up the timeline. Clever approach.

Quote from the article: “Musk indicated that the sheer value of 31 advanced Raptor engines also means that the first Super Heavy flights may only feature a partial complement of engines in case the vast booster experiences a failure, far from uncommon during the first few launches of a new rocket.”

So the first Super Heavy booster may launch with less than the planned number of engines because for the Dear Moon mission the full number of engines won’t be needed, and if the first test launch (without crew, I assume) has a RUD fewer engines will be lost.

Tweet quote:

Still up to 31. Will probably fly with fewer initially in case it blows up.

I think that refers to inital testing of the full system, not the moon mission itself with people on board. Unless the article had more info from Elon.

 

[ecarfan]

In new Starship details, Musk reveals a more practical approach

Eric Berger’s usual insightful analysis of the latest developments with Starship and Raptor.

 

[e-FTW]

In new Starship details, Musk reveals a more practical approach

Eric Berger’s usual insightful analysis of the latest developments with Starship and Raptor.

"Idealism is great and all, but engineers work best in the real world." Heh!

Financial pressures are definitely driving most if not all of these decisions. Having a customer (aside from #DearMoon) at this point would be fantastic. Blue Origin got that for New Glenn, and that is a massive positive.

 

[mongo]

First test fire has occurred, videos in Twitter thread.
Spark plugs-> dual methox torches for engine and pre burner -> main engine

Twitter

Video:
Twitter

 

[Yggdrasill]

I find it amazing just how much effort and thought SpaceX is putting into making the Super Heavy/Starship propulsion system simple, reusable and reliable, something that is needed for Mars. Some observations:

- Liquid methane/oxygen can be stored at higher temperatures than hydrogen, reducing boiloff in transit to a minimum. While still allowing for pretty good specific impulse. And being relatively easy to produce on Mars.
- Methane/oxygen combustion has no issues with coking, which means you may be able to reuse the engine many times without refurbishment.
- Autogenous pressurization mens no helium needed, which may be hard to come by on Mars.
- Full flow staged combustion cycle, with two separate turbo pumps for fuel and oxidizer means no issues with seals between fuel and oxidizer side, reducing the amount of refurbishment needed. Also great for specific impulse, and simplifies injector design (as no liquid enters combustion chamber, only gaseous methane/oxygen plus some CO2 and H2O from preburners).
- Spark plug ignition means basically unlimited engine restarts. Not limited by the amount of TEA-TEB carried.

They were also planning on using methane/oxygen thrusters in the reaction control system, but it looks like they're going for regular cold gas thrusters. Possibly using nitrogen, which is 2.7% of Mars atmosphere, so should be possible to refuel on Mars relatively easily, and is needed for the crew anyway. I guess they could also simply use methane, which has a bit higher specific impulse than nitrogen.

 

[mongo]

- Autogenous pressurization mens no helium needed, which may be hard to come by on Mars.

I guess they could also simply use methane, which has a bit higher specific impulse than nitrogen.

With a large supply of liquified methane on board for engine and heat shield purposes, it seems like using electric heaters to gassify and pressurize the CH4 would provide an effectively limitless supply of cold(ish) gas for the reaction control system. The fins provide most maneuvering control (when maneuvering is really needed).

Run a feed line off the gas side of the main tank, through a one way valve, into a heater chamber, to another valve, and you have control via a high power gas called methane, Master Blaster would be proud.

Spoiler: what?

In Mad Max Beyond Thunderdome, Bartertown runs on methane collected from pig feces. "Not *sugar*, energy!"

From Elon's twitter feed :

Cold gas thrusters only. Will use body flaps & main engines for landing orientation, so won’t need high thrust reaction control. Simplifies things considerably.

 

[spacex'er]

Saw this. I want one.

 

[ecarfan]

Spark plug ignition means basically unlimited engine restarts. Not limited by the amount of TEA-TEB carried.

I guess I missed this: the Raptor ignites the fuel mixture electrically?

 

[mongo]

I guess I missed this: the Raptor ignites the fuel mixture electrically?

Yep, see my post #285 it links the Elon's tweet on the subject.

 

[ecarfan]

Yes I saw Elon’s tweets and watched the video but don’t see any information there about “spark plugs”.

First test fire has occurred, videos in Twitter thread.
Spark plugs-> dual methox torches for engine and pre burner -> main engine

Twitter

Video:
Twitter

 

[Yggdrasill]

Yes I saw Elon’s tweets and watched the video but don’t see any information there about “spark plugs”.

Twitter
Twitter

This is similar to how the space shuttle main engines are ignited.

 

[ecarfan]

Twitter
Twitter

This is similar to how the space shuttle main engines are ignited.

Thanks. Now I get it.

 

[RDoc]

"Idealism is great and all, but engineers work best in the real world." Heh!

Financial pressures are definitely driving most if not all of these decisions. Having a customer (aside from #DearMoon) at this point would be fantastic. Blue Origin got that for New Glenn, and that is a massive positive.

IMHO it's going to be a very long time before carrying passengers into space makes a significant amount of profit and I doubt NASA is going to use BFR for astronauts due to the lack of an escape system. However, the BFR system may very well turn out to be the lowest cost satellite launcher when it becomes available. Elon has said it would be cheaper than F9 or F9H.

Between the Starlink constellation, and lower commercial satellite launches driving innovation, that may be the financial imperative driving development.

 

[mongo]

and I doubt NASA is going to use BFR for astronauts due to the lack of an escape system

While the escape system of Crew is the capsule, the shuttle had only itself. Why can't Starship do likewise?

 

[ecarfan]

I doubt NASA is going to use BFR for astronauts due to the lack of an escape system.

I am confident that SpaceX will have an inflight abort esacape mechanism for the Starship that will enable it at any point from on the pad to during and after MaxQ rapidly separate from the Falcon SH booster and protect the occupants from booster failure/RUD.

It would make no sense to design a vehicle like FSH/Starship that can carry up to 100 or more crew and a lot of cargo and not include that capability.

 

[Yggdrasill]

Should be possible for Starship to return to launch site at basically any point, if there is a fault with the Super Heavy. But it would need to be able to get clear of the Super Heavy really quick. Maybe have some small solid rocket boosters to get it clear, before lighting up all 7 Raptors.

Issues with the Starship itself would be more problematic. Though I'm not sure if it's unsolvable.

 

[Grendal]

The Everyday Astronaut asked a good question of Elon and he answered:
Everyday Astronaut on Twitter

 

[ecarfan]

What are longitudinal “hat stringers”. I understand the “longitudinal” part, I think: they are oriented along the long axis of the vehicle. I found this US8714485B2 - Method of fabricating a hat stringer - Google Patents . So they are internal structural pieces attached to the wall of the vehicle?

 

[Grendal]

What are longitudinal “hat stringers”. I understand the “longitudinal” part, I think: they are oriented along the long axis of the vehicle. I found this US8714485B2 - Method of fabricating a hat stringer - Google Patents . So they are internal structural pieces attached to the wall of the vehicle?

View attachment 375396

I could be wrong but I'm picturing the interior of a Zeppelin airship. An internal framework that gives support.
Watch the very beginning of this and you'll see what I mean: