Starship is Go...

elderflower · 2019-01-07 04:52:19

Stainless steel is cheap and easily available in common grades, not extremely strong but sufficiently so to make large pressure vessels and the like, corrosion resistant (obviously), and performs well at both high and low temperatures. Some grades eg type 304, are easy to work and welding procedures are well established. It is consistent from sample to sample, unlike composites so can be tested with high confidence that the sample is representative of the rest of a batch. It is also unreactive to LOX, provided its surface is polished, passivated and clean.
Its main drawbacks are density, fairly low fatigue performance and relatively low strength.

GW Johnson · 2019-01-07 09:17:00

300-series stainless may be inferior to other steels in fatigue, but it is way superior to aluminum. The real shortfall is more high-temperature creep than fatigue, anyway.

The most cost-effective alloy for tank construction is usually SS 304, same as SS steel pipe fittings and pipe, but if you are welding, use SS 304L. These will go to about 1200 F without scaling. Otherwise you will experience weld cracking very quickly. If you need high temperature resistance (in the sense of not scaling, all are weak structurally when hot), I would suggest SS 316/316L (the weldable is 316L) as most cost-effective. Its max is about 1500-1600 F. SS 309/310 will go a bit hotter without scaling (close to 1900 F), but are hard to find and expensive.

The martensitic stainless alloys like 4130 will show better strengths, even hot, than the 300-series austenitic stainlesses, but do require a surface coating for higher temperature service (good to around 1200-1400 F). If you need high strength both cold and hot, you need an alloy steel like a 17-7PH, with a surface coating to avoid corrosion when hot (up to 1600 F). Even the superalloys like inconel and alloy 188 cannot do that: they are good hot (1800-1900 F), but have relatively much lower strength at room temperature than 17-7PH.

To answer the question about aluminum airplanes and fatigue, there is a plot called an S-n plot showing stress at failure vs number of cyclic loadings. It is usually a dog-leg shape on a log-log plot: decreasing slope, then flat. If your stresses in your design are about an order of magnitude under the stress shown on the ideal sample S-n diagram, your parts' fatigue life should equal or exceed the number of cycles for your factored-up stress on the S-n diagram. These more fatigue-resistant stress levels are way, way lower than the tensile yield for the material, down in the 5-10 ksi class, at most.

Plays havoc with the usually-reported strength/weight ratios, don't it? I have found that marketing hype generally sucks.

If your designs' stresses are low enough to be on the flat part of the S-n diagram, you have essentially an infinite fatigue life. That was the "secret" to the long service life of the DC-3. Most aircraft are designed to 40,000 cycles today. When they get close to that, you must inspect and repair or replace fatigue-damaged parts. They crack. Which presumes you know which will fail first. If you screw that up, people die. And they have.

The only reason Spacex gets away with re-flying boosters aluminum-lithium alloys (even worse in fatigue than 2024 or 6061) is that they only fly them 10-ish cycles, not 10,000. 100 cycles may prove safe enough from a fatigue-only standpoint. I would NOT bet on 1000, though. Actually, it will be heating damage, not fatigue, that limits these parts.

It has long been said that composites and wood "do not experience fatigue" (all metals do, but some are worse than others). I simply don't believe that. It is foolish to believe that without centuries of successful experience to back it up.

Wood comes closest: it experiences either dry rot or wet rot instead. But given enough time, it rots.

Composites have not been used long enough to tell for sure yet, being only about 5 decades old at most as fiberglass, and carbon-epoxy much younger yet. They seem resistant to fatigue damage, but I have heard some anecdotes that indicate they are not immune. They are certainly vulnerable to hidden damage, and are inherently variable enough that there is no sure way to recognize hidden damage unless you have imaging (in the same format) from when the part was made. THAT is quite expensive, by the way.

GW

Last edited by GW Johnson (2019-01-07 09:40:00)

elderflower · 2019-01-08 04:03:16

Wood only rots in the presence of water and oxygen which are required for the bacteria and fungi that can do the job. Exposed to space it won't rot, but its structural properties would be changed.
I have often wondered whether one trip heat shields could be made from natural materials like balsa, cork and white oak. They char, which protects the underlying material so you would need a way to keep the char bound to the surface.

louis · 2019-01-08 04:25:41

I had friends who used to save their wine bottle corks to throw on the fire. I don't think they were left with cork-shaped char...I can only presume it burnt like the logs.

elderflower wrote:

Wood only rots in the presence of water and oxygen which are required for the bacteria and fungi that can do the job. Exposed to space it won't rot, but its structural properties would be changed.
I have often wondered whether one trip heat shields could be made from natural materials like balsa, cork and white oak. They char, which protects the underlying material so you would need a way to keep the char bound to the surface.

elderflower · 2019-01-08 04:54:52

Now I'm thinking of shipping a few hundred bottles of wine to the ISS so we could test the idea, Louis.
On second thoughts lets just ship them to my house.

Terraformer · 2019-01-08 06:04:23

I have often wondered whether one trip heat shields could be made from natural materials like balsa, cork and white oak. They char, which protects the underlying material so you would need a way to keep the char bound to the surface.

Baked by the Chinese.

https://vintagespace.wordpress.com/2016 … ally-work/
https://www.newscientist.com/article/mg … -oddities/

louis · 2019-01-08 09:27:37

elderflower wrote:

Now I'm thinking of shipping a few hundred bottles of wine to the ISS so we could test the idea, Louis.
On second thoughts lets just ship them to my house.

louis · 2019-01-08 19:41:48

The Big Hopper is ready!

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

Hope all goes well from here on...

Looks a bit vulnerable out there.

Wonder when they might start tests and will the tests be from that location ?Looks like they might be. One obvious thing I've noticed of course, there isn't a support gantry...kind of weird to see it standing there like it's out of a 1950s sci-fi movie.

I'm guessing tests by first week of February. Anyone else care to guess? Or is this an assembly test? And have they got to unpack it and then fill it up with stuff?

SpaceNut · 2019-01-08 20:19:57

Something not a video...

Elon Musk aims to test SpaceX’s Starship hopper next month, tweets mock-up

la-1546722618-mcey3av6uf-snap-image

Elon Musk is aiming to test SpaceX’s Starship hopper in the next four weeks, “which probably means 8 weeks, due to unforeseen issues,”

The engines currently on the Starship hopper are a mix of Raptor development and operational parts,

This initial trip will be the rocket’s first “hopper test,” a short test run. Later tests, expected to take place in 2020, will be performed at higher altitudes and at higher velocities.

Both SpaceX’s Starship vehicle and the Super Heavy rocket will use the company’s Raptor engine, which is still in development.

louis · 2019-01-09 04:39:40

SpaceNut wrote:

Something not a video...
Elon Musk aims to test SpaceX’s Starship hopper next month, tweets mock-up
https://www.latimes.com/resizer/OkZmCgq … snap-image
Elon Musk is aiming to test SpaceX’s Starship hopper in the next four weeks, “which probably means 8 weeks, due to unforeseen issues,”
The engines currently on the Starship hopper are a mix of Raptor development and operational parts,
http://blogs.discovermagazine.com/d-bri … spacex.jpg
This initial trip will be the rocket’s first “hopper test,” a short test run. Later tests, expected to take place in 2020, will be performed at higher altitudes and at higher velocities.
Both SpaceX’s Starship vehicle and the Super Heavy rocket will use the company’s Raptor engine, which is still in development.

louis · 2019-01-09 04:49:24

Well we are now beyond a "mock up", it seems. We can see what the real hopper looks like.

So, if all goes well,a test by mid March 2019.

Hopper tests of the cargo version by 2020?

Test flight to Moon in 2021?

Cargo flights to Mars in 2022...?

kbd512 · 2019-01-09 14:06:13

More like 1 year of hopper testing, 1 year of suborbital flight testing to confirm full scale vehicle control behaves the way the simulations predicted, another 2 to 4 years to build and test the booster, 1 year of interplanetary reentry testing to confirm that the heat shield withstands interplanetary reentries as well as was expected, and then a lunar landing test to confirm low gravity stability and the ability to directly return to Earth from the surface of the moon. After another 2 to 4 years of long duration life support and ISRU testing and integration work, then we can do a crewed Mars free return while the robotic mission on the surface works out the propellant production challenges. At the following opportunity, then it can land on Mars.

louis · 2019-01-09 15:39:45

I am more optimistic. The Apollo Mission really began in late 1961 with a bidding process based on an inhouse NASA concept. By 1969 they had landed a man on the moon. So I'd say 8 years is our standard, for want of anything better. Interestingly, that's pretty much bang on with the Musk Mars Mission - which I'll dub "Triple M" (since Space X don't seem to have given it a moniker yet): 2016 announcement for a 2024 landing.

I'd make a couple of observations about the Apollo Mission:

1. It was a highly complex mission with a three stage rocket, a lunar orbiter, a lunar lander, lunar ascender and a return capsule. On balance, I'd say that was a lot more complex in principle than Triple M.

2. The Apollo programme was having to "invent the wheel" as it went. There were lots of unknowns. Space X is standing on the shoulders of a lot useful giants.

Then there's really the question of when Triple M really began. Mars has truly always been the goal for Musk and Space X. Space X was founded in 2002. So we could say the mission has been running since then, but then you could say Apollo had its roots in Gemini. But an important point is that we know the Starship's rocket engines have been in development since 2013.

Musk says work on construction of the Super Heavy will begin in Spring 2019.

All in all I would say that currently Triple M is on course for a human landing in 2024. To stay on course probably requires everything to go right and nothing (at least major) to go wrong.

kbd512 wrote:

More like 1 year of hopper testing, 1 year of suborbital flight testing to confirm full scale vehicle control behaves the way the simulations predicted, another 2 to 4 years to build and test the booster, 1 year of interplanetary reentry testing to confirm that the heat shield withstands interplanetary reentries as well as was expected, and then a lunar landing test to confirm low gravity stability and the ability to directly return to Earth from the surface of the moon. After another 2 to 4 years of long duration life support and ISRU testing and integration work, then we can do a crewed Mars free return while the robotic mission on the surface works out the propellant production challenges. At the following opportunity, then it can land on Mars.

kbd512 · 2019-01-09 16:08:22

Louis,

By 2030, they'll be completely ready to go to Mars to stay. There's no need to rush things. They're going to get there. Once SpaceX starts working on something, they never stop until they get it to work well. This vehicle can't simply work. It has to work exceptionally well.

louis · 2019-01-09 18:15:41

And that can be proven in test flights just as with Apollo, which didn't take 14 years to complete as you are suggesting for the Triple M mission.

You will see if everything works perfectly in relation to the cargo Starships before you risk humans - another advantage over Apollo.

kbd512 wrote:

Louis,
By 2030, they'll be completely ready to go to Mars to stay. There's no need to rush things. They're going to get there. Once SpaceX starts working on something, they never stop until they get it to work well. This vehicle can't simply work. It has to work exceptionally well.

SpaceNut · 2019-01-10 21:12:49

I am not sure if this is intended to be a floor layout but its sort of simular to another one from Mars Society.

louis · 2019-01-11 03:35:46

Where's this from? Is it supposed to be a Starship floor plan?

SpaceNut wrote:

I am not sure if this is intended to be a floor layout but its sort of simular to another one from Mars Society.
https://pbs.twimg.com/media/C6QNo6LWQAE3Ls8.jpg

louis · 2019-01-11 05:37:19

"Obviously it needs to be more pointy..."

https://twitter.com/elonmusk?ref_src=tw … r%5Eauthor

Is the cargo hold at the bottom more about providing low ballast to improve the stabiity of a "more pointy" Starship?

Is there an issue with those fins? I can see them providing stability on landing with less than say a 3% slope ...but I can also seem them, with 100 plus tonnes (let's say 120 tonnes, with excess fuel) of mass pressing down (is that 40 tonnes per fin? I presume so), digging into the ground. The fins appear to be flattened out where they make contact with the ground but at about 60 cm x 15cm (as best as I can guess from the pics) = 900 sq cms does that mean there's about 33 kgs per sq cm? Is that a lot or a little? Or just about right?

SpaceNut · 2019-01-11 18:20:34

I am sure GW ran the calculations in this topic Looking at the Mars Colony's development, based on Space X & BFR

louis · 2019-01-11 19:19:12

Footprint of fins has definitely come up before. But if there is a figure in the thread no doubt you can pick it out and reproduce it here.

I don't think anyone's analysed the latest pics.

SpaceNut wrote:

I am sure GW ran the calculations in this topic Looking at the Mars Colony's development, based on Space X & BFR

Last edited by louis (2019-01-11 19:19:38)

louis · 2019-01-11 19:29:32

Latest vid from Mic of Orion. Some interesting observations and speculation. He seems v. optimistic in the short term but more pessimistic in the long term - thinks Space X will get the (real) Starship flying by Sept 2019 but that it will miss the humans to Mars target of 2024 by two years. There seemed to be something missing in his reasoning for me...

https://www.youtube.com/watch?v=xgmRYoFWqw8

SpaceNut · 2019-01-11 20:20:02

Th latest pic are artist renderings and are not to scale of the expected rockets final form. The mock up is not the total deal either for its more about other stuff as the legs are different again as its a shorter hieght of the rockets final size.

The fuel level would need to be more than what is remianing for a landing of a falcon 9..

But to answer the dead weight of landing the rocket for earth is taking off from a concrete pad and its going to need something close to the value for the landing even empty.

louis · 2019-01-11 20:27:42

"Mock-up"? Do you mean the actual existing hopper?

SpaceNut wrote:

Th latest pic are artist renderings and are not to scale of the expected rockets final form. The mock up is not the total deal either for its more about other stuff as the legs are different again as its a shorter hieght of the rockets final size.
The fuel level would need to be more than what is remianing for a landing of a falcon 9..
But to answer the dead weight of landing the rocket for earth is taking off from a concrete pad and its going to need something close to the value for the landing even empty.

SpaceNut · 2019-01-12 12:32:24

https://en.wikipedia.org/wiki/Mockup

First sketch, wireframe, mockup or prototype, initial test article, a partial or full-scale model, which includes the assembling of a shiny steel "test hopper" to collect data for use in a final design and even that will have trial balloons of testing.

https://phys.org/news/2019-01-elon-musk … ocket.html

louis · 2019-01-12 17:16:18

I would say it's an initial test vehicle. I wouldn't call it a prototype, because I think they know what they are building.

SpaceNut wrote:

https://en.wikipedia.org/wiki/Mockup
First sketch, wireframe, mockup or prototype, initial test article, a partial or full-scale model, which includes the assembling of a shiny steel "test hopper" to collect data for use in a final design and even that will have trial balloons of testing.
https://phys.org/news/2019-01-elon-musk … ocket.html

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