Large Ship hull material

RobertDyck · 2022-02-28 11:06:24

tahanson43206 has created several discussion threads for various aspects of this project. So I'll create one myself. This is about hull material.

First starting basic principles. Aluminum has a short service life because it accumulates metal fatigue. This ship will have to endure and remain in operation for years. This ship will experience constant force from rotation to create artificial gravity, there will be acceleration for Trans-Mars Injection (TMI), aerocapture to enter Mars orbit, acceleration for Trans-Earth Injection (TEI), some sort of Earth orbit insertion, and turning forces as the ship orients both the radiation shield and light reflectors toward the Sun during transit. Modules of the International Space Station manufactured by USA are made of aluminum alloy. However, the station is already considered to be approaching end-of-life with no realistic replacement. That's not acceptable. The Large Scale Colonization Ship will be expensive, it will have to operate over many years. So a more durable material is necessary. Large ships at sea that operate over many years have hulls made of steel. Steel is a far more durable material. And Italy manufactured the Multipurpose Modules used to ferry cargo to ISS in the hold of Shuttle. When Shuttle was decommissioned, one of those modules (Leonardo) was left permanently attached to ISS. These Italy made modules are made of stainless steel. So steel is the preferred material for the hull of our Large Ship, the question is which grade.

I have also said shipping material from the surface of Earth is not practical for a ship this large. Some people have difficulty understanding this, but building a ship this large does require some new technologies. We won't introduce new things frivolously just because they're new, but do not allow the project to be scuttled simply because you're afraid of requirement just because it's new. Mining a metal asteroid for metal is necessary. It's the source of material for the hull and large structures. We won't manufacture everything in space; obviously computers and life support and other high tech equipment will come from Earth. But bulk material for the structure of the ship will be harvested and processed in space.

My starting assumption is the hull would be built based on the hull of the Leonardo module. This has a pressure hull, outside that is multi-layer insulation, and outside that is a micrometeorite shield. Multi-layer insulation is aluminized Mylar. That is thin sheet plastic with a vacuum deposited layer of aluminum. It reflects infrared light, which is radiant heat. The vacuum of space is the universe's largest Thermos bottle. "Thermos" is a brand name, the generic term is Dewar flask. In vacuum there is no heat loss due to conduction or convection, because there is no material or gas to conduct heat, and no air or gas to convect. All you have to worry about is radiant heat loss. The aluminum reflects radiant heat, the Mylar holds a very thin layer of aluminum. There are fishnet spacers between layers to minimize conduction. American modules have Orthofabric on the outside as a micrometeoroid shield, but Leonardo has thin stainless steel sheet metal. Whether we use Orthofabric or sheet metal is open for discussion.

So now what is the hull made of? SpaceX is using 304L for Starship. That's a grade of stainless steel. It gets stronger at cryogenic cold temperatures. At room temperature it appears heavier than carbon fibre, but at cryogenic temperature the metal gets so strong that the weight is not significantly different than a carbon fibre tank able to hold the same pressure, hold the same weight of propellant (fuel and oxygen) and able to withstand the forces of launch. That includes acceleration, aerodynamic stress as it flies at supersonic speed through the atmosphere, etc. Well, the hull of our ship will hold people, not cryogenic propellant. So performance at cryogenic temperatures is not an issue. Tanks of the propulsion module will be made of different material, this discussion is about the hull were people will live.

Stainless steel has the advantage that it doesn't rust. Rust will destroy a ship. The inside of the habitation ring will be filled with air, and that will have humidity. Passengers could spill drinks or food. The floor will have to be cleaned, that will involved water and some sort of cleaning fluid, probably soap. That could cause corrosion. It isn't acid, but it is normal rust caused by moisture. The outside of the ship will experience Low Earth Orbit. LEO has mono-atomic oxygen, which is extremely reactive. EMU spacesuits are the white spacesuits used for EVA on Shuttle and now ISS, they use Orthofabric. Yes, the same material that's now used for the outside of American modules of ISS. Orthofabric is a double-layer fabric, with Goretex outside and Nomex inside. Every 3/8" in each direction (warp and weave) two threads of Goretex are replaced by Kevlar. It's very strong and resistant to mono-atomic oxygen. Goretex is a fibre made of pure PTFE (PolyTetraFluoroEthylene) the same material as Teflon. It will not react to oxygen. Nomex is fireproof, used for firefighter jacket and pants, although that feature is useless in the vacuum of space. But Orthofabric is strong and able withstand cycles of heat and cold in space. The Leonardo module uses stainless steel sheet metal, which also resists corrosion from mono-atomic oxygen.

kbd512 has repeatedly recommended maraging steel ("martensitic" and "aging"), which solves some problems and creates others. The first problem is it isn't stainless, so corrosion is a major problem. kbd512 learned in the US Navy and keeps trying to do everything the way the navy does. Space is different, has different concerns. Maraging steel is something to consider, but far from a foregone conclusion. Rust is a *MAJOR* problem.

Another advantage to stainless steel 304L is that it's austenitic. I could go over the molecular structure, but the bottom line is it doesn't harden by heat treatment. Someone who makes knives would not like the fact it doesn't harden, but this is a good thing for a large ship. It means you can weld it, and the weld will not become hard. Hardened steel is inherently brittle. For some types of construction, any weld has to be heat treated to anneal. To harden you heat steel then quench it quickly. To anneal you heat it red-hot, then allow the steel to cool slowly over time. Typical to anneal martensitic steel you bury it in dry sand and let it cool over 3 days. Heat treating in space is not practical. So austenitic steel allows welding without any further treatment.

GW Johnson has suggested an alternative: electron beam welding. This allows welding martensitic steel without the hardening problem. Electron beam welding requires vacuum, but space is all vacuum. An electron gun requires vacuum to form the electron beam. One researcher at Brookhaven National Laboratory in 1995 developed a "plasma window". This can hold back 1.5 atmospheres of pressure against hard vacuum. The purpose was an electron beam welder. Normally you have to put your entire piece to be welded in a vacuum chamber to use electron beam welding. But could you make a box with vacuum inside to generate the electron beam, then let the beam shine out of the box to weld a piece that isn't in vacuum. If the beam is strong enough to weld, then it'll cut a hole through the vacuum box. Once air gets into the box, the electron gun can't generate a beam any more. So how? The researcher at Brookhaven developed "plasma window" as a means to let the electron beam shine out. If the beam heats the plasma, it just gets stronger. I don't know if this is being used anywhere, but it's a way to electron beam weld very large pieces. In space, we wouldn't have to worry about this because all of space is vacuum.

Another aspect is austenitic steel can endure the heating/cooling cycles of space without developing metal fatigue. And can endure the heat of aerocapture without metal fatigue. Because astenitic steel doesn't harden, it doesn't develop metal fatigue as quickly or severely as martensitic. For extended life, fatigue is a real issue.

Another is materials. I said source will be a near-Earth metal asteroid. I use meteorites as a reasonable sample of near-Earth objects. Here are compositions of a few group IVB iron meteorites. Values are in parts per million (ppm) except nickel, which is percent. Balance is iron. It's mostly iron, with significant nickel, and third largest constituent is cobalt. There's not much chrome. This is an issue if we want to make stainless steel, because it requires a lot of chrome.

One side issue: precious metals. Mining a metal asteroid will produce precious metals as a byproduct. These can be sent to Earth and sold as a revenue stream to off-set the cost of the mining operation. Precious metal content is not a lot, but metal asteroids are true metal, not an oxide ore. That means ferrous metals can be extracted easily and cheaply using the Mond process. Once all iron, nickel, and cobalt have been extracted, everything else is concentrated. That includes concentrating:
Au - gold
Ar - silver
Pt - platinum
Pd - palladium
Ir - iridium
Rh - rhodium
Os - osmium
Ru - ruthenium
Gold is difficult to separate from silver, so you wouldn't bother at the asteroid. If a bar is gold/silver alloy with 2% industrial metals, good enough! It could be sold as 10 to 18 carrot gold, or sent to a refinery on Earth for further processing. One group has already been working on how to modify the Mond process to extract platinum group metals from a metal asteroid.

Stainless steel 304L consists of: 18% chrome, 8% to 10% nickel. That's a lot of chrome. Harvesting that would require processing a lot of metal, leaving a lot of iron and nickel behind.

Maraging steel 250 consists of: 17-19% nickel, 7.0-8.5% cobalt, 0.05-0.15% aluminum, 4.6-5.2% molybdenum, 0.3-0.5% titanium, 0.50% chrome, 0.50% copper, 0.03% max carbon. A couple other things must be less than a certain amount, but could be absent. Balance is iron. This requires aluminum, which isn't found on a metal asteroid. Realize how metal asteroids and meteorites formed. A small body formed in the early solar system, probably the size of a dwarf planet. It had to be large enough to melt the bulk of the body, and enough gravity to differentiate material. Heavy elements like iron and nickel sank to the core, while light elements like aluminum and silicon and magnesium floated to the surface to form what we call rock. Then something hit it, causing it to break up. So a metal asteroid is the core of a dwarf planet, already broken up for us. This means a stony asteroid will have aluminum and magnesium, but no heavy metals. A metal asteroid will have iron and nickel and precious metals, but no aluminum or magnesium.

There is martensitic stainless steel. This solves the corrosion problem, but to make it stainless it must have chrome. And martensitic has the issue of heat cycles causing metal fatigue.

Quaoar · 2022-02-28 11:31:38

RobertDyck wrote:

tahanson43206 has created several discussion threads for various aspects of this project. So I'll create one myself. This is about hull material.
First starting basic principles. Aluminum has a short service life because it accumulates metal fatigue. This ship will have to endure and remain in operation for years. This ship will experience constant force from rotation to create artificial gravity, there will be acceleration for Trans-Mars Injection (TMI), aerocapture to enter Mars orbit, acceleration for Trans-Earth Injection (TEI), some sort of Earth orbit insertion, and turning forces as the ship orients both the radiation shield and light reflectors toward the Sun during transit. Modules of the International Space Station manufactured by USA are made of aluminum alloy. However, the station is already considered to be approaching end-of-life with no realistic replacement. That's not acceptable. The Large Scale Colonization Ship will be expensive, it will have to operate over many years. So a more durable material is necessary. Large ships at sea that operate over many years have hulls made of steel. Steel is a far more durable material. And Italy manufactured the Multipurpose Modules used to ferry cargo to ISS in the hold of Shuttle. When Shuttle was decommissioned, one of those modules (Leonardo) was left permanently attached to ISS. These Italy made modules are made of stainless steel. So steel is the preferred material for the hull of our Large Ship, the question is which grade.

Do you know exactly which is the mass penalty for using steel instead of aluminium?

Example 1: the space shuttle external tank has an empty weight of 26.5 tons, if you made a 304L stainless tank of the same volume and the same sturdiness, how would it weight?

Example2: GW, in his mars mission study, has calculated that a 5 m diameter 14.9 m long cylindrical habitat for three people has an inert weight of 1.244 tons (the total weight is 24.88 tons): if you made it of 304L steel with the same sturdiness how would it weight?

RobertDyck wrote:

I have also said shipping material from the surface of Earth is not practical for a ship this large. Some people have difficulty understanding this, but building a ship this large does require some new technologies. We won't introduce new things frivolously just because they're new, but do not allow the project to be scuttled simply because you're afraid of requirement just because it's new. Mining a metal asteroid for metal is necessary. It's the source of material for the hull and large structures. We won't manufacture everything in space; obviously computers and life support and other high tech equipment will come from Earth. But bulk material for the structure of the ship will be harvested and processed in space.
My starting assumption is the hull would be built based on the hull of the Leonardo module. This has a pressure hull, outside that is multi-layer insulation, and outside that is a micrometeorite shield. Multi-layer insulation is aluminized Mylar. That is thin sheet plastic with a vacuum deposited layer of aluminum. It reflects infrared light, which is radiant heat. The vacuum of space is the universe's largest Thermos bottle. "Thermos" is a brand name, the generic term is Dewar flask. In vacuum there is no heat loss due to conduction or convection, because there is no material or gas to conduct heat, and no air or gas to convect. All you have to worry about is radiant heat loss. The aluminum reflects radiant heat, the Mylar holds a very thin layer of aluminum. There are fishnet spacers between layers to minimize conduction. American modules have Orthofabric on the outside as a micrometeoroid shield, but Leonardo has thin stainless steel sheet metal. Whether we use Orthofabric or sheet metal is open for discussion.
So now what is the hull made of? SpaceX is using 304L for Starship. That's a grade of stainless steel. It gets stronger at cryogenic cold temperatures. At room temperature it appears heavier than carbon fibre, but at cryogenic temperature the metal gets so strong that the weight is not significantly different than a carbon fibre tank able to hold the same pressure, hold the same weight of propellant (fuel and oxygen) and able to withstand the forces of launch. That includes acceleration, aerodynamic stress as it flies at supersonic speed through the atmosphere, etc. Well, the hull of our ship will hold people, not cryogenic propellant. So performance at cryogenic temperatures is not an issue. Tanks of the propulsion module will be made of different material, this discussion is about the hull were people will live.
Stainless steel has the advantage that it doesn't rust. Rust will destroy a ship. The inside of the habitation ring will be filled with air, and that will have humidity. Passengers could spill drinks or food. The floor will have to be cleaned, that will involved water and some sort of cleaning fluid, probably soap. That could cause corrosion. It isn't acid, but it is normal rust caused by moisture. The outside of the ship will experience Low Earth Orbit. LEO has mono-atomic oxygen, which is extremely reactive. EMU spacesuits are the white spacesuits used for EVA on Shuttle and now ISS, they use Orthofabric. Yes, the same material that's now used for the outside of American modules of ISS. Orthofabric is a double-layer fabric, with Goretex outside and Nomex inside. Every 3/8" in each direction (warp and weave) two threads of Goretex are replaced by Kevlar. It's very strong and resistant to mono-atomic oxygen. Goretex is a fibre made of pure PTFE (PolyTetraFluoroEthylene) the same material as Teflon. It will not react to oxygen. Nomex is fireproof, used for firefighter jacket and pants, although that feature is useless in the vacuum of space. But Orthofabric is strong and able withstand cycles of heat and cold in space. The Leonardo module uses stainless steel sheet metal, which also resists corrosion from mono-atomic oxygen.
kbd512 has repeatedly recommended maraging steel ("martensitic" and "aging"), which solves some problems and creates others. The first problem is it isn't stainless, so corrosion is a major problem. kbd512 learned in the US Navy and keeps trying to do everything the way the navy does. Space is different, has different concerns. Maraging steel is something to consider, but far from a foregone conclusion. Rust is a *MAJOR* problem.
Another advantage to stainless steel 304L is that it's austenitic. I could go over the molecular structure, but the bottom line is it doesn't harden by heat treatment. Someone who makes knives would not like the fact it doesn't harden, but this is a good thing for a large ship. It means you can weld it, and the weld will not become hard. Hardened steel is inherently brittle. For some types of construction, any weld has to be heat treated to anneal. To harden you heat steel then quench it quickly. To anneal you heat it red-hot, then allow the steel to cool slowly over time. Typical to anneal martensitic steel you bury it in dry sand and let it cool over 3 days. Heat treating in space is not practical. So austenitic steel allows welding without any further treatment.
GW Johnson has suggested an alternative: electron beam welding. This allows welding martensitic steel without the hardening problem. Electron beam welding requires vacuum, but space is all vacuum. An electron gun requires vacuum to form the electron beam. One researcher at Brookhaven National Laboratory in 1995 developed a "plasma window". This can hold back 1.5 atmospheres of pressure against hard vacuum. The purpose was an electron beam welder. Normally you have to put your entire piece to be welded in a vacuum chamber to use electron beam welding. But could you make a box with vacuum inside to generate the electron beam, then let the beam shine out of the box to weld a piece that isn't in vacuum. If the beam is strong enough to weld, then it'll cut a hole through the vacuum box. Once air gets into the box, the electron gun can't generate a beam any more. So how? The researcher at Brookhaven developed "plasma window" as a means to let the electron beam shine out. If the beam heats the plasma, it just gets stronger. I don't know if this is being used anywhere, but it's a way to electron beam weld very large pieces. In space, we wouldn't have to worry about this because all of space is vacuum.
Another aspect is austenitic steel can endure the heating/cooling cycles of space without developing metal fatigue. And can endure the heat of aerocapture without metal fatigue. Because astenitic steel doesn't harden, it doesn't develop metal fatigue as quickly or severely as martensitic. For extended life, fatigue is a real issue.
Another is materials. I said source will be a near-Earth metal asteroid. I use meteorites as a reasonable sample of near-Earth objects. Here are compositions of a few group IVB iron meteorites. Values are in parts per million (ppm) except nickel, which is percent. Balance is iron. It's mostly iron, with significant nickel, and third largest constituent is cobalt. There's not much chrome. This is an issue if we want to make stainless steel, because it requires a lot of chrome.
https://d3i71xaburhd42.cloudfront.net/47e9348e661466d188203d9045554f8493ba9a43/36-Table2-1.png
One side issue: precious metals. Mining a metal asteroid will produce precious metals as a byproduct. These can be sent to Earth and sold as a revenue stream to off-set the cost of the mining operation. Precious metal content is not a lot, but metal asteroids are true metal, not an oxide ore. That means ferrous metals can be extracted easily and cheaply using the Mond process. Once all iron, nickel, and cobalt have been extracted, everything else is concentrated. That includes concentrating:
Au - gold
Ar - silver
Pt - platinum
Pd - palladium
Ir - iridium
Rh - rhodium
Os - osmium
Ru - ruthenium
Gold is difficult to separate from silver, so you wouldn't bother at the asteroid. If a bar is gold/silver alloy with 2% industrial metals, good enough! It could be sold as 10 to 18 carrot gold, or sent to a refinery on Earth for further processing. One group has already been working on how to modify the Mond process to extract platinum group metals from a metal asteroid.
Stainless steel 304L consists of: 18% chrome, 8% to 10% nickel. That's a lot of chrome. Harvesting that would require processing a lot of metal, leaving a lot of iron and nickel behind.
Maraging steel 250 consists of: 17-19% nickel, 7.0-8.5% cobalt, 0.05-0.15% aluminum, 4.6-5.2% molybdenum, 0.3-0.5% titanium, 0.50% chrome, 0.50% copper, 0.03% max carbon. A couple other things must be less than a certain amount, but could be absent. Balance is iron. This requires aluminum, which isn't found on a metal asteroid. Realize how metal asteroids and meteorites formed. A small body formed in the early solar system, probably the size of a dwarf planet. It had to be large enough to melt the bulk of the body, and enough gravity to differentiate material. Heavy elements like iron and nickel sank to the core, while light elements like aluminum and silicon and magnesium floated to the surface to form what we call rock. Then something hit it, causing it to break up. So a metal asteroid is the core of a dwarf planet, already broken up for us. This means a stony asteroid will have aluminum and magnesium, but no heavy metals. A metal asteroid will have iron and nickel and precious metals, but no aluminum or magnesium.
There is martensitic stainless steel. This solves the corrosion problem, but to make it stainless it must have chrome. And martensitic has the issue of heat cycles causing metal fatigue.

As an alternative, we can use the iron and the nickel of the asteroids and bring the chrome from Earth: chromium is only 18% in 304L so is a big mass saving anyway.

Last edited by Quaoar (2022-02-28 13:34:11)

tahanson43206 · 2022-02-28 19:38:51

For RobertDyck, Quaoar and all who may be following this new topic ...

This item showed up in a tech newsletter today. If anyone is interested I saved the email and can investigate further:

A Path to a Better High Frequency (HF) Weld
from Inductotherm Group
Attendees will learn the physics behind the HF welding process, the definition of weld heat input and how to control it, as well as how the mechanical setup affects the quality of the finished product.

However, it is possible the snippet contains all the information you need to learn more about this form of welding.

(th)

Quaoar · 2022-03-01 04:02:19

There are also a new class of alloys of austenitic aluminium stainless steel with ultra high strenght (1 GPa), high elongation 35%, 17% lower density (6.64 g/cm3) and lower chromiun content (almost 5%).

https://www.nature.com/articles/s41598-020-69177-7

with these new alloys a stainless steel spacecraft would be really lighter than an an aluminium one of the same size

Last edited by Quaoar (2022-03-01 04:04:41)

tahanson43206 · 2022-03-01 07:43:39

kbd512 wrote:

Robert,
It looks like Vascomax sells C250 maraging steel plates, measuring 12mm by 1000mm by 2000mm, for $55.65USD per square meter. If your large ship had a surface area of 20,000m^2 and was made from 12mm thick plates machined into isogrid structures, similar to the Aluminum "potato chips" that ULA carves into isogrid plates to fabricate Atlas V propellant tanks, then you're looking at $1,113,000USD in terms of materials. This material comes from India.
C250 has a YS of 250ksi, UTS of 255ksi, and requires heat treatment at 900F to achieve those properties. 304L stainless, which also has excellent weldability like C250, has a YS of 25ksi and UTS of 70ksi. The same company sells 304L for $2/kg or $2,000/t, whereas C250 is $577.52/t. In terms of yield strength (YS), you have approximately 10X the strength for about 3.5X less cost. Once the structure yields, failure will likely progress until it completes, so ultimate tensile strength (UTS) figures are only interesting from the standpoint of understanding when a total failure will occur. 316L, which is even more expensive has a 30ksi YS. What this really means is that you can use much thinner and therefore lighter maraging steel structures, as compared to 304L. Within its temperature limits, maraging steel is extremely tough and strong, unlike any stainless that isn't also very brittle. The primary advantage is no Chromium at all. It's also corrosion resistant, but not a true stainless, so polishing or surface treatment will be necessary to inhibit corrosion. This material could be painted, ceramic coated, powder coated, or a Nickel-based finish applied. The Nickel finish would be pretty durable and shiny / slick. The powder and ceramic coatings require heat. White Titanium-based paint would be cheapest and probably easiest to remove, although it would burn in a fire. C250 is semi-magnetic, unfortunately, unlike non-magnetic stainless.
You need a lot of steel plate, it needs to be cheap / ductile / easy to machine and weld / resistant to impacts / dimensionally stable, so C250 fits the bill. You may also get away with even cheaper materials with appropriate surface treatments, but they won't be nearly as strong and will be strongly magnetic (may or may not be an issue for the EM shield).
My advice would be to use the 304L for cryogen tanks only, prevent the C250 from getting too cold, and you get a very tough and durable steel that is easy to repair by welding. Machine the potato chips here on Earth, roll them, heat treat them, then weld them together in orbit using EBW.

kbd512 · 2022-03-01 08:25:13

Robert,

Corrosion is less of an issue than starting out with a 10X strength deficit. It'll take quite a lot of corrosion before 304L catches up with C250 in the yield strength department. Ships rust. It's a fact of life. You do what you can to minimize it and move on from there.

tahanson43206 · 2022-03-01 09:00:11

For what it's worth ....

The advice offered to RobertDyck would help with both issues, if he were to accept it.

He's been counseled multiple times to put a thick layer of material on the outside of the hull, to keep heat inside the vessel and to keep radiation out.

Properly designed material would adhere to the metal hull despite extremes of heat encountered in space.

RobertDyck has been counseled numerous times to forget about the impractical and dangerous idea of flying 1060 people in a harebrained scheme to aerobrake at a planet with atmosphere. He's been counselled that the precision of flight required to fly the narrow zone at Mars is beyond the capability of humans even augmented with the most advanced computing equipment. A 5000 ton rotating vessel is not a runabout on a small lake. Precision is not in the repertoire of such a vessel. It must be kept far away from atmosphere at all times. Anyone (other than members of this forum) hearing a proposal to fly 1060 people through the atmosphere of any celestial body will immediately recognize the speaker is not serious, and not to be taken seriously.

RobertDyck has been counseled numerous times to keep the floor of the hull clear. He has studiously ignored this advice. If he gets around to accepting the advice, then the hull can be kept free of moisture or oxidizing materials or anything that would damage whatever coating is placed on the interior.

There MUST be ample room for humans to enter every compartment below the passenger deck, to plug holes that are inevitably going to appear in the hull, despite the outer protection, because space is full of flying objects, and that will most certainly be true when Large Ship ventures near an inhabited body.

The Large Ship idea started out as a fantasy, and would have remained a fantasy, if members of this forum had not appeared to pull it toward an achievable reality.

(th)

RobertDyck · 2022-03-01 12:18:04

tahanson43206, what you just said is condescending and insulting. You have strongly encouraged development of this project, but refused to understand certain basic concepts.

I have lectured you several times that the pressure hull is on the inside, thermal insulation goes on the outside, and micrometeoroid shield is outside that. That's how ISS modules are built, that's how the Apollo Command Module was built, that's how it has to work. Insulation for space does not work the same as here on Earth. Space has vacuum. I have explained it many times, now you are trying to claim that you have "counseled" (sic) me. I have said the hull of this large ship will be made based on the technique of the Leonardo Permanent Multipurpose Module. That's a module attached to ISS right now. And yes, it's made of stainless steel.

kbd512 (Brian) has talked many times of his time as a sailor working on a Nimitz class aircraft carrier. He learned from the navy how things are done on a Nimitz class aircraft carrier, and keeps claiming everything has to be exactly the same as a Nimitz class aircraft carrier. We're talking about a spacecraft, not a navy ship at sea. There will be several things different.

For one, Brian doesn't understand the extreme oxidizing environment of mono-atomic oxygen in Low Earth Orbit. People think LEO is nothing but vacuum, and it is partial vacuum, but it's not completely free of atmosphere. Mono-atomic oxygen is extremely reactive. This has been a consideration since the early days of the space program. Apollo spacesuits were covered in beta fabric, fibreglass coated in Teflon. The Teflon is specifically to protect against mono-atomic oxygen. EMU suits used for EVA on Shuttle and ISS have an outer layer of Orthofabric. That's a double layer, the outer layer is Goretex, a fibre of PTFE, made by a different company but chemically the same as Teflon. Again, corrosion from mono-atomic oxygen. ISS modules are either covered in Orthofabric or stainless steel. Beginning to get it? Using the same material as the hull of a Nimitz class aircraft carrier will not work.

This is a very large ship. Do you not understand the propellant required to move such a thing? Interplanetary travel requires very high speed. Even a Hohmann transfer is extremely fast, the slowest for a thrust-and-coast engine. A ship of this size will require extreme propellant. You can't be wasteful. Aerocapture has been a basic fundamental of space travel for a very long time. Mars has been called "closer" to Earth than the Moon in terms of propellant. That means it takes less propellant to go from Earth to the surface of Mars than it does to the surface of the Moon. The reason is using the atmosphere of Mars to slow down. If you abandon basic fundamentals, you end up with a very bad design.

Robert Zubrin's Mars Direct was designed to use aerocapture to enter Mars orbit. Then use the atmosphere to slow from orbital speed to landing. Do I need to detail the whole atmospheric entry process? This is an example of what you are doing. Cost estimate for Mars Direct was $20 billion for development, construction of infrastructure, and the first mission to Mars. Plus $2 billion for each mission thereafter. If you commit up front to 7 missions, total would have cost $30 billion. All in 1989 dollars, so it could be compared to the "90 Day Report on Human Exploration of the Moon and Mars". Many people in NASA got excited, people who were part of Apollo so knew first-hand what can be done. Unfortunately some others in NASA had the attitude of "Not Invented Here". They came up with Mars Semi-Direct (NASA Design Reference Mission). They made changes resulting in cost increase to $55 billion. Congress saw the extreme increase in cost, and this was while it was still a study on paper, before any hardware was built. So they refused to approve it. This is what happens when you do stupid things like deleting aerocapture or ISPP.

Mars Climate Orbiter was supposed to demonstrate aerocapture. The problem was a US measure to metric conversion error. That was stupid! The orbiter dipped too deeply into the atmosphere, couldn't get out and crashed. A math error that severe would cause any orbit insertion method to fail. Or any landing attempt. The correct response was to correct the error, and try again. Doing it with an unmanned probe, and doing it over and over until it's a mature reliable technology before doing it with people. But some people who don't understand technology had the same attitude you just demonstrated. They thought there was something fundamentally unsafe about aerocapture, so it's never been done again.

Also realize this attitude. I attended symposia (plural of symposium) in the early 2000s. At the Canada Space Exploration Workshop I met several scientists. They treated engineers as if they were janitors. Go watch the TV show "The Big Bang Theory", the way the character Sheldon treated Howard Wolowitz. That was their attitude, but a whole room full of them. They did not want any new engineering technology on "their" mission. This attitude also exists in USA. There have been proposals to send a Mars sample return mission. Someone would notice that using ISPP for return propellant, the mission cost is affordable. They would pitch the idea, it would be approved, the project would start. Then some scientist who doesn't understand engineering would say "no new technology on *MY* mission"! Of course it wasn't his/her mission. Removing ISPP would dramatically increase cost. When politicians saw how much more money the project team demanded, the politicians cancelled the whole project. It would die with no prospect of sample return until someone else noticed ISPP, and the whole cycle started again. This cycle has happened 3 times that I'm aware of, and probably more.

I am amazed by individuals who are members of the Mars Society, yet still do not understand Mars Direct. The whole society was founded by Robert Zubrin to push Mars Direct. The society has built 2 analogue research stations, with proposals or more. The analogues are simulations of the Mars Direct habitat. Not something else, they're Mars Direct. I suggest you re-read "The Case for Mars".

RobertDyck · 2022-03-01 12:19:40

As for the floor: on a ship with gravity you don't walk directly on a thin-wall pressure hull that is the only thing keeping in air you need to breathe. That hull must be protected. You must have easy access to the hull, but you must not walk on it directly. A pressure hull with isogrid is actually less than 0.040" (1 millimetre) thick. The stiffeners provide strength. If the isogrid were exposed as the floor, you would be walking on the isogrid risers directly, which would trip people. And the flat sheet between risers is less than 1mm thick! You do *NOT* want to puncture that!

ISS covers the hull. Below is a picture of the real ISS. Notice the hull is completely covered. Science racks are arranged in 4 "walls" that completely cover the cylindrical inside hull. They can be unlatched and swung inward to gain access to the hull. But normally the hull is covered.

tahanson43206 · 2022-03-01 13:09:03

For RobertDyck re clarifications....

It is a failing of text communications that points made by one party can be missed by another.

I was stunned by the discovery, revealed by an innocent observation by Quaoar, that you were still planning to have your ship's Captain steer a fragile vessel weighing 5000 tons, filled with 1060 people, through the thin almost non-existent atmosphere of Mars.

It is entirely possible you have posted clarifications about the hull, but there have been ambiguous posts as well that may have (and probably did)_ lead to confusion.

In any case, thanks for your patience in dealing with the inevitable buffeting that comes with taking a leadership position. Because you are noted for your culinary talents, I am sure you are familiar with the expression.... if you can't stand the heat, stay out of the kitchen.

The problem for me is that as we come closer and closer to the moment of truth, when your work is presented to an audience of people who are not part of the NewMars family, I am worried that problems will show up that will detract from the basic solidity of the concept.

A member of the Board of the chapter has agreed to join us for a Dress Rehearsal on Saturday the 5th of March, exactly one week before the actual event, at the same time: 2 PM Houston. If you are interested in doing a dress rehearsal, it is possible the entire NewMars Sunday Zoom team can be enlisted to cheer you on.

Please let us know if this would be of interest.

(th)

SpaceNut · 2022-03-01 18:37:34

The ship is made from the same materials that have entered mars atmosphere so its not fragile in any word of it.

The issue is giving the ADAPT heat shield materials a supporting frame to be held against.

I gave mass estimates based on similar materials from the starship in the large ship topic for the ring, connecting tunnels and for the central hub.

flooring post in topic

tahanson43206 · 2022-03-01 18:52:29

For SpaceNut re #11.... It's not the material that is fragile ... it is the entire ship.

RobertDyck has designed a massive ring held onto a central shaft by three spindly pipes. The ring will be ripped away from the central shaft by the least acceleration. The ship ** may ** be able to handle the gentle 1/10th G thrust that GW Johnson is planning. The ship would not last ten minutes if flown through an atmosphere of any planet.

The ship must be kept well away from atmosphere in all it's travels. That is why GW Johnson kindly performed the computations needed to support propulsion solutions for Large Ship. You can see those solutions coming along as he works on his document. The latest version is available for viewing and for study in the GW Johnson Postings topic.

(th)

SpaceNut · 2022-03-01 19:01:22

The what you are calling spindly will be reinforced due to spin up and spin down of the rings. It is what is done with the riggers of design for mechanical connectivity. These will be extra thick connects not only at the inner ring but at the central hub as well. The mass statements that I gave for the construction has built in extra mass just for that purpose of double layering of materials to keep stress from those areas.

The main thing is to keep the un-necessary mass in the hub rather than in the ring until its needed moving waste back out as its used and consumed.

As far as the aerocapture a phenolic heat shield of PICA x would be capable of not only being light mass but easy enough to build on orbit like a hub cap to top from the hub out over the ring.

RobertDyck · 2022-03-01 19:40:35

tahanson43206, Tom: my skills at Blender aren't that good. The upper level is shown as solid glass, not glass windows with air inside. And although observation rooms and the Mars simulation room will extend the full width of the ring, the greenhouses will not. The habitation ring should have small porthole windows, each with a shutter that can cover it like the covers of the Cupola on ISS. Windows will help show scale. Most importantly, the diagonal braces are missing.

Your concerns are valid, but I have written this in text a few times. A diagonal brace will extend from the ring to the hub, where the propulsion stage connects to the hull surrounding the control moment gyros. 3 braces, one for each spoke. Should the brace connect at the base of the spoke? Or the aft end of the ring, behind the spoke? The spoke, brace, and skin of the hub form a triangle. Truss structures are based on triangles; they are very strong.

SpaceNut · 2022-03-01 20:02:48

Thing roof rafter inside the roof joists not only from the rings upper and down under to the central hub but the same to the ring from the hub much like the spokes on a bicycle rim.

kbd512 · 2022-03-02 01:31:33

Robert,

Stainless is corrosion resistant because it forms a passivating oxide layer on its surface, same as Aluminum. There's no more magic to it than that. You can achieve superior corrosion resistance to any stainless using an appropriate oxide-based coating. Weldable stainless isn't very strong or impact resistant relative to other types of steels, which means it will be significantly heavier than it would be using other steels providing greater strength, fatigue and impact resistance, etc. Iron-based alloys will become silly putty at the temperatures generated during an atmospheric reentry, so all steel ships will require ablative thermal protection.

You stated that there was very little Chromium present in the types of metallic asteroids you intended to mine, so a steel like C250 is a compromise (apparently a dirty word here, where some engineering pragmatism should be applied, IMO) that just so happens to have superior mechanical properties, relative to stainless, at the expense of some corrosion protection, which can just as easily be provided by various coatings.

The bottom line is that a ship made from C250 could either be much stronger than 304L /316L stainless for equivalent weight or much lighter for equivalent strength. If you can come up with the Chromium to add to a maraging steel, then it will also be every bit as oxidation resistant as a 300 series stainless for the previously mentioned reason.

RobertDyck · 2022-03-02 03:58:51

Aluminum oxidizes to form a layer of aluminum oxide. If that scrapes off or gets scratched, it exposes a new layer of aluminum metal. That oxidizes to form aluminum oxide which seals the scrape or scratch. With stainless steel, the chrome forms chromium oxide. If that gets scratched, it exposes a new layer of stainless steel alloy, the exposed chrome in that alloy forms chrome oxide which steals the scratch.

Steel doesn't do that. Steel is an alloy of iron and carbon, with less than 2% carbon. Higher carbon is harder but more brittle. When steel is exposed, iron doesn't just form hematite, which is iron oxide. Instead iron reacts with oxygen and moisture to form rust. The rust is larger in volume than iron metal in the steel, so it expands to form a weak loose compound. The rust attracts more moisture which causes more iron metal to form rust. The rust grows.

Sealing steel with paint will allow it to last longer, but when that paint gets scratched it allows moisture and oxygen in. That starts a process of creating rust, which causes a simple scratch to grow to become a major rust problem.

An aircraft carrier is a lot different than a spacecraft. ISS has a small crew, with only 3 they spend most of their time maintaining equipment. They don't have time to inspect and repair rust. As it is, scientists complain that have only 1/2 the time of one crew member for actual science, the rest of the time they're all doing maintenance. The only way to get science done was to expand the crew beyond 3. This was a strong argument when the only life support was the Russian side, which only had capacity for 3. Eventually they convinced Congress to fund adding life support on the American side so crew on ISS could increase. That still means they don't have time to inspect for scratches in paint or to repair rust.

The large ship will have a small crew compliment to care for a large number of passengers. I arrived at the number of crew by looking at crew for the passenger ship SS City of New York, then updating technology from the late 1800s. Then I looked at the MS Kong Harald, which can carry 490 passengers and 60 crew.

We don't have sufficient crew to constantly clean and paint rust. And going outside for repairs is very dangerous: it requires a spacesuit and rotation means the ship is trying to fling any worker away.

Sorry but with an isogrid, the flat sheet metal between triangular risers is 1mm thick or less. That doesn't leave any margin for corrosion. I started by taking an ISS module, use that for how to build a spacecraft hull. I'm scared to move away from it. And Tom is insistent on exposing the inside hull, an issue GW Johnson raised. But the water wall has to cover one entire wall. And walking on the floor would be dangerous with artificial gravity (or any gravity). I have crawled in the attic of a couple houses here in Canada. Every house here has a basement, because the foundation must be deeper than frozen ground in winter. That means things people further south put in their attic goes in our basement. Our attic must have insulation to keep heat in. An attic here has no floor. There are floor joists with drywall nailed to the underside of the joists to form ceiling of the room below. Between the joists is nothing but insulation, either fibreglass batt or blown loose cellulose. If you step anywhere between the floor joists, your foot will go right through the drywall, through the ceiling of the room below. I expect isogrid of our spacecraft will be similar. Don't step on the 1mm sheet between risers. That means we will have to cover the hull with flooring; and not just a paper or vinyl, it will have to be something strong enough to hold a person's weight between the isogrid risers. This means the hull under the floor will be covered. Since it won't be seen, it must be durable. It has to endure everything that could be spilled on a floor.

RobertDyck · 2022-03-02 04:02:53

In case you're wondering... Wikipedia: Maraging steel - the word combines martensitic and aging.
Wikipedia: Martensitic stainless steel - yup, a stainless version of martensitic steel.

Next issue is how does martensitic steel (or maraging) accumulate stress? Can a ship operate for decades in space, with all the stress it will endure, and the temperature cycles?

kbd512 · 2022-03-02 09:08:13

Robert,

Starting with a material that's 10X stronger gives you margin that you don't have with a much weaker steel like 304L, while an oxide of Chromium can be applied to nearly any steel. The main issue is the hull flexing and creating stress corrosion cracking to begin with, which is oddly enough exactly the same problem that both civil and military ships run into. A material that's 10X stronger and 2X as hard does a lot more to prevent that than the inclusion of more Chromium in the steel itself. If you intend to get the steel from an asteroid, you don't have the Chromium to spare anyway, so it's a moot point. If you intend to get the material from Earth, then this entire argument was pointless because you can get even more corrosion resistant steels. I completely agree that nobody should be walking directly on the hull (point loads should be carefully distributed over a greater surface area), but the reason you don't even have that option with 304L is how weak it is. If the hull isn't directly exposed and appropriately coated, then it won't see much atomic Oxygen attack to begin with. Anyway, there's no point in arguing this point any further, because this appears to be about the fact that someone else proposed something different, rather than about the practical engineering aspects of what was proposed- NIH syndrome.

tahanson43206 · 2022-03-02 10:56:32

For all contributing to this important topic....

My intention in opening this post was to offer a small snippet for evaluation.

However the post by kbd512 (#19) brought into sharp focus the importance of the qualities of a leader for a project of this size.

Without naming anyone in particular, I would note that resistance to buffeting is a critical capability of a large project leader.

Setting a course and holding to it is a characteristic of large project leaders throughout human history.

However, inability to adapt *** when necessary ** is a hallmark of every massive failure ever reported, and probably most small ones.

The fact is that ** I ** cannot help any leader to make the right decision. Like everyone else, I can offer advice, such as "Look out! Iceberg dead ahead".

There are leaders who are mentally and emotionally unable to accept such advice.

On the other hand, what the junior reports is an iceberg might be an optical illusion.

Only the leader can make the right decision.

***
For anyone taking an interest in this important topic....

kbd512 just made an observation (in post #19) that combines common sense in one aspect, and lacks it in another.

This is not intended as a criticism, but is instead offered as a truism, as we humans grapple with tough problems.

GW Johnson has advocated that the hull (pressure hull) be free of all obstructions that would prevent immediate repair in case of a holing by a random piece of space junk.

kbd512 has offered a suggestion that no one should walk on the hull (again, this is NOT a criticism)

I am countering with the observation that the repair crew MUST walk on the hull, in order to reach the damaged area from a holing.

My proposal therefore, is to make the hull strong enough to withstand constant pressure equal to Mars habitat pressure, which is 1/2 Earth standard,
and !!! be strong enough to bear the additional weight of one or more humans maneuvering in a section of hull to repair a leak.

The tradeoffs at work here involve using the 5000 tons of the model Large Ship most effectively.

The goal is to get 1060 people from Earth to Mars safely and in a modicum of comfort.

The goal here must NOT be to save money. We have seen (over the past two years) and even recently, a hint that saving money might be a motivation for some working on this project. I am advocating for safe delivery of 1060 people to Mars in a modicum of comfort, regardless of the cost.

If each of the first passengers paid $1 billion for a two year excursion, then the working budget would be $1 trillion. That sum is well within the capacity of the human race at this point,.

In my opinion (and it is no more than that) the mass allotment for the hull should be decided upon based upon:

1) Does the material lend itself well to the proposed service for an extended period, such as 50 Earth years?
2) Can the material be worked on orbit?
3) Can the material be repaired/maintained/serviced on orbit?
4) Can the material be repaired from inside a moving vessel by ordinary human beings?

There might be other questions that more knowledgeable members will offer.

(th)

SpaceNut · 2022-03-02 18:09:07

The main action is design of material with an estimated mass number of which I have been trying to work up in post 1187 using what we know for material construction and mass balancing.

We have a target value of mass total for launch of 5000 mT to balance out by area into the ring, connecting tunnel and for the central hub.
estimates using the current build of stainless outer hull parts, iso grid aluminum or stainless with the inner being aluminum.
Ring is 3450 mT with 480 mT structural
Tunnels is 425 mT with 129 mT structural
Central Hub 1125 mT with 160 mT structural

The difference in the ring mass is for all of the equipment, plumbing and electrical along with the furnishings plus tunnel inner ring reinforcing for it and the bracing spokes.

The tunnel mass difference is the elevator car and power connections plus the reinforcing spokes in ring to hub and hub to ring bracing as well as extra wall connection metal.

The central hub difference has a baseline starship plus fuel for anything that we would want to do for course or steering rotation control.

Every thing that is internal for wall or floor are mounted up off from the inner with brace standoffs that allow for the panel to attach to those. The inner water wall is mount under the false panels or plates that make up baseline construction. What we mount for equipment is with everything on rollers with latching and swing arms to these panels. Plumbing is in the floor ceiling wall of the hallways to keep the more permanent items away from anything that makes up the hull.

kbd512 · 2022-03-02 22:08:01

So anyway...

We take a strong / tough / hard steel, plasma coat it with Cr2O3, grind it smooth using diamond abrasives if so desired, and then we have a surface that's both protected from oxidation attack and exceptionally hard. We would complete this operation at the factory over all but the last quarter to half inch around the edges of the steel isogrid "potato chips" (as ULA calls them), electron beam weld them into place after laser abrading the edges to remove any oxidation or grime, and finally re-scale and protect the welds with the plasma coat. That's sufficient to get the job done.

For the floors, and to Robert's point (a very good one) about not introducing any point loads on top of a structure that thin, we can use thin stamped steel with a series of "key ring" type spring-loaded quick-disconnect twist locks weldments that will both distribute loads and provide some cushion to any shock / impact loadings such as someone dropping something heavy onto the deck. The fixtures to attach these sheets can be machined into the isogrid. This achieves GW's aim of being able to "get at" the hull quickly to repair any damage caused by debris that manages to make its way through the whipple shields (hopefully that never happens). I can't recall exactly where I saw this done, but I believe it was done to shock mount computer equipment and isolate it from the hull of the ship. It was a type of quick-disconnect mount so that the equipment could be serviced, but it serves our purpose well.

Marine Quick-Release Pins with Pull Ring

tahanson43206 · 2022-03-28 11:17:19

This image was provided by GW Johnson, following the Zoom meeting of 2022/03/27.

While this topic is dedicated to selection of "material" for the hull of Large Ship (Prime), I am hoping the topic will stretch to include design, fabrication on Earth and assembly in space.

There are separate topics for all of those, but this topic exists, so I propose we adapt it to accumulate knowledge, insight and references directly applicable to the hull.

(th)

GW Johnson · 2022-03-28 12:00:06

The bulkheads between pressure compartments must also not be flat. That introduces way too much bending in the bulkhead and the adjacent materials to which it is attached. The bulkhead needs to be a spherical segment shape, and the attachments to adjacent materials require reinforcement. That's just pressure hull and pressure vessel stuff.

GW

RobertDyck · 2022-03-28 12:56:27

Use of space works better with flat walls. I understand the curve issue. I was thinking of two sheets of flat steel with some sort of light truss in between. Something like corrugated cardboard. Corrugated steel? Remember ship pressure is half atmosphere against hard vacuum of space. Gauge pressure will be the same as an airliner hull. Yes, they're curved, but...

Floor between upper deck and lower will have the same issue. Floor must be flat to walk on. That will be the ceiling of the lower deck. Bulkhead and floor will not experience pressure under normal operation, only in case of hull breach causing a compartment to decompress.

Parts of the habitat ring without a deck above will have vaulted ceilings. From corridor wall to corridor wall. Traditional house construction in North America has weight bearing walls to hold up the upper floor or roof, ship corridor walls will be under tension rather than compression. So not "weight bearing" but "tension bearing"? Anyway, outer cabins in these areas will also have vaulted ceilings; from corridor wall to hull. My first reason for doing this is exactly what GW said. Marketing can play this up as a feature.

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#1 2022-02-28 11:06:24

Large Ship hull material

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