Red Dragon Discussion Thread (1)

[Dave G]

That doesn't look very rigid, can anyone explains how this works?

Also from the same link:
http://www.spacex.com/updates_archive.php?page=0205-0505

The subtitle of the picture reads:
"A 12 ft diameter barrel section with stir welded stringers (rounding hoops to be added) "

[mmeijeri]

Rounding hoops, that's it? Amazing.

[SpacexULA]

Rounding hoops, that's it? Amazing.

Mmeijeri why is that amazing?  Worst thing around this place, you get impressed by unimpressive things, and things that don't sound impressive are.   Why would Rounding hoops be amazing?

[mmeijeri]

Well, I'm amazed adding rounding hoops is enough to make this thing stiff enough.

[krytek]

I'm more amazed by how simple (or unimpressive) it all is. Most of it is just standard engineering and manufacture, a lot of this can be done in a standard factory without any huge investments in special tooling.

Personally I dislike aluminum (wonder if they use any special alloy?),
a lot of this can be made from steel, 3 times as cheap and 4 times stronger.

[Jim]

Personally I dislike aluminum (wonder if they use any special alloy?),
a lot of this can be made from steel, 3 times as cheap and 4 times stronger.

Too heavy. I guess your opinion doesn't matter, aluminum is the metal of choice for launch vehicles, save Centaur. 

[mmeijeri]

Too heavy, Aluminum is the metal of choice for launch vehicles.

Wasn't the old Atlas made from steel?

[Dave G]

Too heavy, Aluminum is the metal of choice for launch vehicles.

Wasn't the old Atlas made from steel?

Sea Dragon was supposed to be steel:
http://en.wikipedia.org/wiki/Sea_Dragon_(rocket)

"To lower the cost of the rocket itself, he intended it to be built of inexpensive materials, specifically 8 mm steel sheeting. The rocket would be built at a sea-side shipbuilder and towed to sea for launch."

"TRW conducted a program review and validated the design and its expected costs, apparently a surprise to NASA. However, budget pressures led to the closing of the Future Projects Branch, ending work on the super-heavy launchers they had proposed for a manned mission to Mars."

[krytek]

Personally I dislike aluminum (wonder if they use any special alloy?),
a lot of this can be made from steel, 3 times as cheap and 4 times stronger.

Too heavy. I guess your opinion doesn't matter, aluminum is the metal of choice for launch vehicles, save Centaur. 

You're right probably as much as 3 times heavier. But is it more economical?
We know of too many times when aerospace companies made absurd or irrational design decisions as seen through the eyes of the average engineer.

[baldusi]

Personally I dislike aluminum (wonder if they use any special alloy?),
a lot of this can be made from steel, 3 times as cheap and 4 times stronger.

Too heavy. I guess your opinion doesn't matter, aluminum is the metal of choice for launch vehicles, save Centaur. 

You're right probably as much as 3 times heavier. But is it more economical?
We know of too many times when aerospace companies made absurd or irrational design decisions as seen through the eyes of the average engineer.

Look at the rocket equation. It's more like twice as heavy for the same strength. Which would mean that instead of 1% of your rocket gross mass being tanks, you'd get 2%. That's definitely not good. You'd need a bigger rocket for the same payload and thus bigger/more engines. That's what would kill your cost.
Trading the engines cost for vehicle size might be economically sensible, since the engines might cost many times the cost of the structure. Avionics and such stay basically the same in that range.
In other words, maximum efficiency in tanks and structure is way cheaper than maximum efficiency in engines. Guess which SpaceX trades.

[docmordrid]

http://www.spacex.com/falcon9.php

The Falcon 9 tank walls and domes are made from aluminum lithium alloy. SpaceX uses an all friction stir welded tank, the highest strength and most reliable welding technique available.
>

[Prober]

isn't photoshop wonderful?

You're hilarious.

Thx, at least one person got my warped humor.

[krytek]

Al-Li sounds really expensive.
Not saying they're wrong either, just an interesting experiment- lets say a Falcon 9 Block III can deliver 16 mass tonnes to LEO, and it's structural loads coefficient is 1.4.
Say you increase the coefficient to 4-5, and mass to LEO drops to 10 mass tonnes. Basically not only does the stage handles reentry loads, it can also be dropped into the ocean pretty roughly.

How much 5 tonnes to LEO worth? probably around 20 Million dollars...
How much is the first stage worth? unknown, probably a lot less than above.
What are the other factors at play here and how do they effect cost?

So not economical under these imaginary numbers, but you can try to play with them and somewhere in there will be a limit which will make sense.

[corrodedNut]

That doesn't look very rigid, can anyone explains how this works?

I'll give it a try.

Much like a traditional aircraft fuselage, Falcon 1 (shown in the previous poster's photo) and Falcon 9 fuel tanks are built with longerons and stringers. It is very lightweight and strong, but unlike aircraft manufacturing, which typically rivets or screws these components together, SpaceX welds them. Their cost effective, high-tech take on this method is to use automated friction stir welding, mainly for accuracy, consistency and speed.

The oxidiser tank is pressure stabilized (like a pop can), these two tanks together are described by SpaceX as their own "graduated monocoque design".

Li Aluminium flat rolled stock is welded into a barrel segment, then stringers are stir welded to the inside of the barrels, and then barrels are stir welded end to end (see top photo). At some point, either before or after the barrel sections have been joined, longeron hoops are attached perpendicular to the stringers. Spun domes are stir welded to the ends (including the common one) and you have a first or second stage tank.

[Jim]

Our barrel sections are constructed from rolled aluminum sheet with stringers stir welded in for stiffness. This method yields substantial cost savings over the conventional launch vehicle approach of using machined isogrid. With isogrid and its variants, you start with a plate of aluminum that can be as thick as two inches and then machine away up to 90% of the material, leaving behind sheet with integral stiffeners. This is obviously very inefficient use of material and requires thousands of hours of machining time.

Doubtful.  .  NC machining is easy, set it and forget it.  Welding stringers and hoops takes more touch labor.

[docmordrid]

Might be useful to think of it as similar to a car with modern unibody construction instead of using a box steel frame and heavy body panels  like a 1955 Buick.

The sheetmetal in a unibody is so thin you could easily bend it, sometimes by hand, but welded up it can protect you in a car crash while still being very light - much lighter than that Buick.

Make it out of lithium-aluminum and you're on the bleeding edge of light & strong.

Next stop: someone builds a booster out of composites.

[Jim]

Next stop: someone builds a booster out of composites.

Delta IV payload payload fairing, interstage, second stage intertank, first stage intertank and aft aeroshell.  Composites for cryogens is some years away or not at all.

[baldusi]

Next stop: someone builds a booster out of composites.

Delta IV payload payload fairing, interstage, second stage intertank, first stage intertank and aft aeroshell.  Composites for cryogens is some years away or not at all.

Falcon 9 also has composite intertanks and fairings. I would even guess the aeroshell in the back, too. What's more, even Proton-M block III, have those parts made out of composites. I know that the Polish Stako company does 300Bar SCUBA tank out of composite (not aluminum lining with composite reinforcement, pure composite).
Obviously a SCUBA tank and an RP-1 are orders of magnitude differente sizes. But they SCUBA tank had a proof pressure of 450bar, while the Falcon 9 has what, 3.3Bar? I mean, eventually we might see or not cryogenic composite tanks, but non cryo should be seriously studied.
The other thing that I would study (and I guess was already but nothing came out of this) would be fibre reinforced cryogenic tanks. With some kevlar mesh around, should be able to support quite a bit of extra pressure, which should save on the wall thickness. It would most certainly require to be kept slightly pressurized for structural stability. But something like 1.2Bar of air should do it.

[RocketEconomist327]

Al-Li sounds really expensive.
Not saying they're wrong either, just an interesting experiment- lets say a Falcon 9 Block III can deliver 16 mass tonnes to LEO, and it's structural loads coefficient is 1.4.
Say you increase the coefficient to 4-5, and mass to LEO drops to 10 mass tonnes. Basically not only does the stage handles reentry loads, it can also be dropped into the ocean pretty roughly.

How much 5 tonnes to LEO worth? probably around 20 Million dollars...
How much is the first stage worth? unknown, probably a lot less than above.
What are the other factors at play here and how do they effect cost?

So not economical under these imaginary numbers, but you can try to play with them and somewhere in there will be a limit which will make sense.

This has to be the most absurd post of the day.  Falcon is the cheapest EELV out there and you are saying it is not economical?

This isn't even comical.  This is just stupid.  About $65 is not economical.  Dear Lord.  Just stop.

[krytek]

Have you actually read the post?
try re reading it and post again.

*edit* If it wasn't clear, I was talking about the economics of first stage recovery under hypothetical conditions.
This isn't 4chan, try to keep things civil and/or think a bit before responding with crap. Thank you.