Why Elon Musk is tweeting about a stainless-steel starship | Hacker News Reader

Why Elon Musk is tweeting about a stainless-steel starship

arstechnica.com

87 pointskristianp63 comments

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Ars Technica has a great comment section on its space articles, be sure to check that out too.

Ars is probably the best tech site on the web.

So the image of it in 2 pieces outside in the desert.

I have visions of rockets being constructed in clean hangars. That looks more like some mining set up.

They wouldn't have constructed it outside, unprotected already would they?

This is a testing setup for in-atmosphere flights, so it does not need to be space rated.

But still, if it fails a test you want to be sure it's because of something you did, not just dust/ or an animal chewing through something etc etc.

"That looks more like some mining set up"

As an aside, that reminds me of the early designs for Orion ships which had to be fairly robust and weight wasn't really an issue so they thought they'd use naval shipbuilding techniques rather than those we normally associate with aerospace - steel plate and rivets!

The Orion ships as in the nuke powered theoretical ones or something else.

I think you meant Sea Dragon, not Orion.

Link: https://en.wikipedia.org/wiki/Sea_Dragon_(rocket)

I did mean the nuke powered ships from Project Orion:

https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...

The ships that this is prototyping will need to be able to land on Mars, have any needed maintenance or repairs done in-situ, and return to Earth. No clean rooms allowed. They need to be both tough and hack-able; more like an A-10 than an F-35. So even though this is obviously a fairly crude mockup, there are probably some useful operational learnings from building it in the field.

What's an A-10? Please tell me it's a sweet hackable truck!

It's a big autocannon with wings: https://en.wikipedia.org/wiki/Fairchild_Republic_A-10_Thunde...

BRRRRRRRRRRRRRRRRRRRRRRRRT

A gun with wings attached.

https://en.wikipedia.org/wiki/Fairchild_Republic_A-10_Thunde...

Once the shell is sealed the rocket becomes its own clean room. They have access ports for workers to climb through and for air conditioning ducts, and the 9m diameter interior should provide few restrictions for workers.

What are the characteristics that make stainless steel a better choice than carbon fiber for the BFR ? Is it just tensile strength ?

> Usable strength/weight of full hard stainless at cryo is slightly better than carbon fiber, room temp is worse, high temp is vastly better

https://twitter.com/elonmusk/status/1077111607564464129

Also:

SS has longer service life than composites or aluminium due to being less susceptible to fatigue. This is important on a spacecraft intended to be reusable, and

SS is highly reflective to infrared aka heat, which is important for handling reentry heating which is mostly radiative heating from the bowshock.

TL;DR

I could not find the answer directly in the article but in spotted it in the URL: elon-musk-is-really-really-excited-about-his-starship

Edit: typo

The answer is “because SpaceX is actually building a stainless-steel starship, with first test flights planned for March”.

Unless they have quietly invented warp drive, no they aren’t.

They are calling it Starship, so the parent isn't entirely wrong.

It's just pedantry about the name, must really hate the Starliner too, or the Starfighter, or anything else with the word star in it, if it can't physically get there.

I will establish a new small company, focused on innovating hygienic facilities for starships. I will call it Startubs.

Starshits?

If it can get to Mars then it could certainly fly itself into the sun too. Possibly wouldn't be the best use of SpaceX money, though.

This is a common misconception. It requires much much more energy and delta-V to send a craft on a collision course with the sun than to send it to Mars, or even to send it outside the Solar system altogether[1][2].

1. https://www.reddit.com/r/askscience/comments/5lt50r/why_does...

2. https://en.wikipedia.org/wiki/Delta-v_budget#Interplanetary

Not technically true. To dive into the Sun requires a much higher delta-v then to transfer to Mars. If you look at the Parker Solar Probe it is using a 7 year flightpath getting multiple gravity assists of Venus to miss by 6Gm at 200km/s.

Nope. It takes far more delta-V to get to the Sun than to get to Mars.

To get to Mars you need to change your solar orbit from that of Earth to match that of Mars. The difference is a small fraction of Earth's orbital velocity.

By comparison, you only need to add about 41% of Earth's velocity to escape the solar system entirely.

But to get to the Sun, you need to subtract 100% of Earth's orbital velocity. It's a colossal amount of delta-V.

That's so counter-intuitive. It feels like the sun is a giant gravity well and we just have to give something a bit of a shove in the right direction to fall down into the well. It's not like its rocket science.

That might work if it was starting stationary, but it's not. It's starting from Earth, which has enormous orbital velocity perpendicular to the way to the sun. Everything on Earth already has that velocity too, and there's no way to get rid of it except cancel it out by burning a lot of fuel to basically go just as fast in the opposite direction.

I always hated using terms like "orbital velocity" trying to explain things to people who don't know what it means.

The analogy I use is imagine you have a ball on a string. If you spin that ball around your head, so the string is tight, how hard do you think it would be to hit a friend with it? Now how hard would it be to hit yourself with it?

A friend, you just let go! The ball is already spinning and WANTS to go flying out further away. But to hit yourself? You are going to have to first stop the spinning, then pull it toward yourself, or just pull repeatedly on the string harder and harder until it spins faster and faster until it hits you. It's a lot more effort!

It may not make sense at first, but it's easy to forget that earth is spinning around the sun pretty damn fast, and to get near it you need to first stop (or GREATLY reduce) that spin, that orbit, and only then can you start to approach it.

> A friend, you just let go!

I'm kind of in two minds about this analogy because on the one hand it does correctly explain why it's difficult to get to the sun from the earth, but on the other hand we don't get to mars by turning the sun's gravity off.

That's a fair critique, but most people (that I've spoken to about this anyway) understand that a rocket needs to "push against gravity" to go places, they just forget or don't know that orbital velocity is a thing and what it means (or that you need to cancel that orbital velocity out before you can start using gravity, and that gravity is ultimately pretty weak)

The analogy is meant to try and explain why going toward the sun might be harder, especially when it is so counter-intuitive if you've never thought about it, and it does so by taking some liberties with parts of orbital mechanics that people already instinctively understand.

I think on balance it's a definitely a decent analogy, this was just something that jumped out at me as being a possible source of confusion. If this is an analogy that you've used successfully without this confusion coming up then it's probably not too big a deal.

Surely in your analogy you would need a trained hamster sitting on the ball of wool, spinning a ball of cotton, trying to hit you, rather than you trying to hit yourself?

I suspect the analogy might break down before we got anywhere useful though?

I get that. I understand why it is this way. But it is still counter-intuitive if you don't understand the physics (or your not a rocket scientist ;-)

> But to get to the Sun, you need to subtract 100% of Earth's orbital velocity.

Yeah, one would need to substract 100% of velocity if it wanted to land on a surface of the Sun safely, bringing the ship to a full stop. But why might one bother with the slowing down, if ship will just get melted by the heat of the Sun? You need just to rotate a vector of velocity by some clever gravity assist maneuver.

Not true. To even touch the surface of the Sun you need to subtract nearly all of the Earth's orbital velocity.

Parker Solar Probe, for example, did this with a series of gravity assists off of Venus.

https://www.youtube.com/watch?v=cMNQeCWT09A

On the other hand where do you ultimately end up if you only add 40% delta V ?

This is really interesting. Is there a connection between this fact and the universe being continuously expanding?

No no, totally fine with "starter motor" and "bastard"

As Scott Manley said [1] so nicely:

If you're one of those people that wants to complain about this [name 'Starship'], please show that you're also complaining of Boeing StarLiner and at Lockheed Starfighter otherwise I'll presume you're biased against Elon Musk specifically.

[1] https://www.youtube.com/watch?v=XVgEKBwE2RM&t=41

I have never heard of the Starliner and the Starfighter went out of service before I was born but consider them both complained about too.

Test flight in this case does not equal “going to mars”, they’re doing a short 5km hop.

Should the band be called "Jefferson Band" instead then?

Are you also worried about calling people who go to space astronauts vs cosmonauts?

The frustration at the misuse of the name will only drive further attempts at building the actual thing. Except it too will likely have an exaggerated name when it comes along.

Remember, Musk is the same guy who named his lane assist and quasi-auto-braking system "Autopilot". Dude doesn't always think through his word choice all that well.

> No nation or company has ever built a single vehicle capable of flying dozens of people into space (especially deep space), landing on distant worlds, and then flying back to Earth.

At this risk of stating the obvious, this is still the case today. SpaceX building a mockup in the desert does not mean they are anywhere close to achieving this goal.

Once the new high pressure Raptors are working, most of that dream will be a reality. The only things holding SpaceX back at this point are the heatshield, the engines and Planetary Protection.

A content-free article.

Just some ramblings of a writer about SpaceX, no new information, no answer to the question in the title.

Summarizing content from someone's Twitter posts so that I don't have to actually, you know, use Twitter, is certainly valuable content from my point of view. The bulleted list of facts about the Starship, including information about construction materials and cooling solutions, is certainly content, too.

Ars has some of the best space coverage that I have seen, thanks in no small part to the comment section. The knowledge there is amazing. Sometimes article is simply a way to start a discussion. This article is no exception.

Here's my guess: This thing, which is being assembled outdoors in the elements by dudes on mobile cherry pickers and which has low enough build and finish quality to not even make to as a temporary Epcot Center exhibit, is designed to make it to some altitude, careen sideways then EXPLODE, creating a Twitter storm and news headlines.

It exists to readjust people's expectations on how difficult the project to get to Mars is, and how likely it is people are going to die, which is something than Elon has taken some glee in reiterating over time.

Edit: Look at the third picture here and tell me this is anything other that a "rocket sketch" https://www.nextbigfuture.com/2019/01/why-is-spacex-working-...

Have you seen the grasshopper[0], which had roughly the same purpose for the early Falcons? That hardly looked like a space vehicle, but did its job quite well. I do very much agree it all feels a bit rushed (working during weekends as well), and I really do wonder why they are in such a hurry.

Also, plenty of Falcons have exploded in one way or another, I'm not sure what is new (or unexpected) about that. Things will go wrong a few times and as Elon said in SpaceX's early days "failure is an options". It will have to go right often enough before it gets even close to human-rated. I guess for Mars that means going there and back again a few times (without humans).

[0] https://i.pinimg.com/474x/44/4f/3e/444f3e51839ba246a02bd3d29...

Yes, that Grasshopper to me looks like a carefully constructed work-in-progress device whereas the the current one looks like a full scale mockup with shiny wallpaper.

Maybe I overreached with an internet explosion, but the silver craft just screams "spectacle" to me, even if, due to development progress on the Raptors it can indeed do a hop. I've been proven wrong before!

They are testing a lot of things at once - it's a new metal (for rockets, at least, it hasn't been used since the Mercury times) with new assembly techniques and new structural demands. It'll fly with new engines that have never flown before and, finally, the full-scale article will need to do something nobody has ever done before - come back from orbit and do a propulsive landing.

I dislike the active cooling part (which they'll probably start to test along the rest with this vehicle). Everything "active" will eventually fail at the worst possible time.

Since the alternative is basically use of insulating tiles, which as we know are not free of significant concerns, I have come to accept that it is required complexity.

If we had science-fiction engines, we could do a propulsive brake and skip messing with the atmosphere altogether.

Doesn't "the tyranny of the rocket equation" kind of make the idea of fully propulsive braking systems kind of infeasible?

I know it's possible, but when you have an atmosphere not using it would be just throwing away potential weight that you could be using for the mission at hand.

I'm not rocket scientist, but it sounds like solving that problem using other means (like active cooling) gives you a good amount of weight to play with before it even begins to equal the cost of propulsive braking. And that means you can have a lot of redundancy or can use less efficient but simpler to operate/manufacturer/fix.

It all depends on how much mass you can eject how quickly. If you have good enough propulsion you can save on thermal shielding (and propellant mass).

And, if you have a true science-fiction-grade engine, you may not even need propellant. ;-)

I don't think that a company that is currently actively trying to raise funds from investors[1] wants "SpaceX test rocket explodes" as a headline just to make the point of how likely human casualties are when going on missions in their new product.

It really is only designed to go up to 5km (that's their current altitude limit for the testing license [2]) and test landings. It doesn't need to be anything more than a metal tank with legs but of course SpaceX/Elon are all about style so they want it to look cool.

[1] https://www.wsj.com/articles/elon-musks-spacex-is-raising-50...

[2] https://www.reddit.com/r/spacex/comments/9z9ccn/spacex_files...

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