Starship Prototype Unveiled • Hacker News Board

Re: Starship Prototype Unveiled

#161

Post by hollerith » Mon, Sep 30, 2019, 1:19 AM UTC

wongarsu wrote: post #158

computerex wrote: post #80

I just want to point out that SpaceX has not yet successfully put a human in LEO. The moon seems well beyond their technical capabilites at the moment and Mars seems like a fools dream at this point in time.

Getting anything, including humans, to LEO is the hard part though. Once they have brought crew to the ISS and have demonstrated a spaceship flying to the moon, landing and returning to earth they will have solved most of the challenges of bringing humans to the moon. And they make good progress on both fronts.

The other hard part is keeping the health of humans from declining rapidly in zero g.

I don't know whether the surface of Mars (.378 g) or the Moon (.165 g) will prove any less destructive to human health.

Re: Starship Prototype Unveiled

#162

Post by frankharv » Mon, Sep 30, 2019, 1:22 AM UTC

brandonjm wrote: post #101

frankharv wrote: post #93

Earlier quoted context omitted.

Well when you tell a customer you will have all hands on deck and then are out back playing with your go-kart then expect your billion dollar customer will say something.

I imagine all the necessary hands are already on deck for Crew Dragon. Starship wasn’t built by the Falcon or Crew Dragon manufacturing teams, and the vast majority of the design and engineering currently happening for Starship has long been completed for Crew Dragon. Let’s also remember that NASA is hardly the only company that pays SpaceX, they have other income sources and what they do with that income is ultimate…

From this[1] article:

"Musk said in 2018 that SpaceX was “all hands on deck for Crew Dragon,” and it would be making trips to the ISS by December 2018.

After that, he said, “most of our engineering resources will be dedicated to BFR, and I think that will make things go quite quickly,” he said. BFR was the earlier name for Starship."

"All hands on deck" is not some subjective term, it is naval and means get everyone on deck now to repel boarders.

[1]https://kfor.com/2019/09/28/nasa-administrator-tells-elon-mu...

Re: Starship Prototype Unveiled

#163

Post by XorNot » Mon, Sep 30, 2019, 1:27 AM UTC

elif wrote: post #105

Blakestr wrote: post #97

Earlier quoted context omitted.

Not a metallurgist but doesn't tempering make steel stronger? (As long as it is quenched properly?)

Stronger is not a specific enough term with metal, but tempering is the opposite of what you described, which is hardening. Steel becomes harder and more brittle if quenched (hardening), and softer and less brittle if cooled slowly (tempering). Cold Rolling steel is done to avoid the heat cycle which would otherwise result in tempering, which is why its specific stats don't strike me as particularly relevant past the…

Uh what? This is exactly the inverse of what happens. Quenching leads to stronger, more flexible steel. Slow cooling leads to harder, but more brittle steel. The reason is grain structure - slow cooling allows larger grains, which don't allow the movement of dislocations as freely, but the loss of flexibility costs in ultimate tensile strength.

Re: Starship Prototype Unveiled

#164

Post by [deleted] » Mon, Sep 30, 2019, 1:29 AM UTC

martythemaniak wrote: post #21

That was a very dense an informative presentation last night, but I think the main take away is that rapid reusability is a game changer. In fact, game-changer is probably an understatement, basically every intuition and rule-of-thumb we have about space launches and travel will have to be rethought. And this will be true even of SpaceX falls well short of meeting their stated targets (2020 orbit, 150t capability, mu…

[deleted]

Re: Starship Prototype Unveiled

#165

Post by elif » Mon, Sep 30, 2019, 1:29 AM UTC

XorNot wrote: post #163

elif wrote: post #105

Earlier quoted context omitted.

Stronger is not a specific enough term with metal, but tempering is the opposite of what you described, which is hardening. Steel becomes harder and more brittle if quenched (hardening), and softer and less brittle if cooled slowly (tempering). Cold Rolling steel is done to avoid the heat cycle which would otherwise result in tempering, which is why its specific stats don't strike me as particularly relevant past the…

Uh what? This is exactly the inverse of what happens. Quenching leads to stronger, more flexible steel. Slow cooling leads to harder, but more brittle steel. The reason is grain structure - slow cooling allows larger grains, which don't allow the movement of dislocations as freely, but the loss of flexibility costs in ultimate tensile strength.

Please cite your correction or delete it if you find you are in error. I have provided my 2 sources which are in addition to my peer and personal experience in blacksmithing.

Re: Starship Prototype Unveiled

#166

Post by ryanmarsh » Mon, Sep 30, 2019, 1:33 AM UTC

How do they plan to get 100 tons of cargo from atop the starship down to the surface of Mars? Do you use a crane? I mean, cranes are heavy, right?

Re: Starship Prototype Unveiled

#167

Post by NortySpock » Mon, Sep 30, 2019, 1:36 AM UTC

davidivadavid wrote: post #133

vermontdevil wrote: post #124

Earlier quoted context omitted.

Steel was used before for the early Atlas rocket models. But the skin was too thin and collapsed on its own weight. You can see YouTube videos of this.

Did any new process/invention make it viable to use steel today that wasn't available before?

Not your parent commenter, but SpaceXs innovations start with pulling most design and fabrication in-house, rather than NASA relying on (multiple levels of) defense contractors redesigning ICBMs. ICBMs are single-use only and cost is no object when you're fighting WW3. Similarly, cost was no object for launching military spy satellites, so there was no reason to reduce the launch cost of a $1B recon satellite.

Here, specifically, with regard to steel rockets? SpaceX stopped optimizing for weight and used thick steel. SpaceX optimized for cost and practicality. Brute force rocket engineering, rather than "the best performance numbers on paper" which is where a lot of rocket designs seemed to get lost in the weeds of some component that ends up being a massive maintenance mess but gives you "the best performance".

The steel tanks that collapsed in the sixtys? They were so thin they needed pressurization at all times or they would collapse. SpaceX realized that was a design and maintenance risk, and just built thick tanks.

Re: Starship Prototype Unveiled

#168

Post by ryanmarsh » Mon, Sep 30, 2019, 1:39 AM UTC

strainer wrote: post #159

elif wrote: post #92

Earlier quoted context omitted.

I know there are 1000 of them 100x smarter than me at all of this, but I have my doubts that the specs for "cold rolled" stainless will hold up after tens of re-entries, as it is effectively being tempered over and over.

From the sounds of it steel structure can basically handle much greater temperatures routinely and also even more in rare situations that might mean retiring the ship afterward but not losing everything. In his presentation Elon says that aluminum alloy or carbon fiber structure is basically done for at 300 to 400 Celsius, well that's the temperature at which stainless steel can just begin to get conditioned by heat,…

it doesn't structurally 'melt' until over 1000 Celsius

Is this why jet fuel can't mel..... ah never mind.

Re: Starship Prototype Unveiled

#169

Post by iblaine » Mon, Sep 30, 2019, 1:40 AM UTC

hoorayimhelping wrote: post #20

380s for ISP for the Raptor vacuum engine seems durn good, considering the tradeoffs between hydrogen and methane. The most efficient engines we've flown, the RL-10 [0] (used on the Delta IV and Atlas rockets as part of the Centaur Upper Stage) and the RS-25 [1], (the Space Shuttle Main Engine) get around 450-460s for their specific impulse. These engines use liquid hydrogen and liquid oxygen. The issue with liquid h…

Musk thinks like a software engineer. Create simple, reusable, components that can scale efficiently. I’m taking some liberties in saying this, but the gist remains the same. Musk keeps it simple and focused.

Re: Starship Prototype Unveiled

#170

Post by ryanmarsh » Mon, Sep 30, 2019, 1:43 AM UTC

hinkley wrote: post #117

tlb wrote: post #71

Earlier quoted context omitted.

Spiral tube are a bad choice for a rocket. Because rolled steel has the grains largely aligned with the direction of rolling, it is stiffer and has less thermal expansion in one axis than the other. Large forces and temperature changes therefore cause a twisting motion, which can put weird strains on the internal components.

Pillsbury rolls come to mind. The tube is under pressure from the leavening agent, and you apply torsion on the tub until the can ruptures along the spiral seam.

That would not go over well with the occupants.