New Mars Forums

In Putin,  you are not dealing with any normal human personality,  not even one of the psychopathic types.  You are dealing with a clone of Adolf Hitler.  There is no rationality,  there is only ambition.  And a total disregard for others.  He will not stop until he is dead.  We've seen this before,  many times.

GW

It will be interesting indeed to see if this could be developed into a piece of technology ready-to-apply. 

GW

which pushes up the required enrichment level.  By encasing the fissile fuel in discrete tungsten spheres, the designer must accept limits on the burn up of the fuel and power density.  Beyond a certain burn up, the fission gases will burst the cladding.  The need for heat transfer across the cladding, also limits power density.  The alternative is to put the Uranium particles within the graphite moderator and allow a large fraction of fission products to leak out.  That wouldn't be acceptable for Earth take off.  But it may be acceptable for purely orbital transfers.  Like Robert's large ship.

For Quaoar re new topic...

Thanks for this update!  it looks important, and worth keeping this topic updated.

Out of curiosity, since you would have considered the four existing related topics before creating this new one, how does the INsTAR initiative compare to these?

Nuclear Pulse Propulsion starship. by Rune
Interplanetary transportation    16    2022-02-21 12:34:35 by SpaceNut

Nuclear Thermal Propulsion Module by Oldfart1939
Interplanetary transportation    1    2022-02-12 19:11:05 by Oldfart1939

A revival of interest in Nuclear Thermal Propulsion? by Oldfart1939 [ 1 2 3 ]
Interplanetary transportation    57    2021-12-18 09:34:39 by Mars_B4_Moon

Nuclear Ion Propulsion by Antius [ 1 2 ]
Interplanetary transportation    28    2021-12-11 13:52:35 by Mars_B4_Moon

Thanks again for the update!

(th)

These sorts of problems lead me to wonder if a molten salt reactor or aqueous homogenous reactor would be a more appropriate choice for a commercial ship.  These do not require HEU as fuel and can refuel continuously, without an extended shutdown period for refuelling.  Unfortunately, this would mean starting from scratch when designing a commercial ship propulsion system, as the military technology is not suitable.  But AHR is such a simple technology with a long history in isotope production.  It would be easy to design and build.

No doubt some idiot will chime in calling me a racist.  But the fact remains that all successful civilisations have basically been mono-racial.  We ignore that at our peril.  There is no nobility or morality in believing in an unworkable idea.

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.
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.

Your post #19 reveals that you do not realize that the idea of bringing a 5000 ton ship full of 1000 passengers and crew anywhere near an atmosphere of ANY celestial body is tantamount to giving a kilogram of fentanyl to a patient, when 10 ml at 50 micrograms per ml is a medically advisable dose for surgery.

Happily, the work of Dr. Johnson is available for your study.  You will see his most recent draft of a document on chemical propulsion for Large Ship if you visit the topic GW Johnson Postings, and look for the most recent post.  You will find a link to a document stored in the NewMars Dropbox

Please ** do ** take a bit of your (I understand limited) time to better understand the concepts in play for management of the flight of a 5000 ton space vessel between Earth and Mars. 

(th)

For Quaoar re 5

Thank you for your helpful addition to the topic.

I agree that the proposal of RobertDyck to position mass along the sun-facing side wall of the habitat, addresses part of the problem.

Your observation about particles arriving from directions not aligned perfectly with the center of the Sun seems right, and you've provided a reference to study.

The current work of SpaceNut in one of the Radiation topics (with your guidance for which we thank you) may help to address that problem.

Since ** this ** topic is about navigation and pointing, please keep an eye out for the kind of RCS management software needed for this application.

I am confident RobertDyck will pinch every penny he can, so avoiding brand new development of software to manage the flight of the ship will keep costs down.

While buying/leasing software is not ** always ** the cheapest/best solution, exceptions are (in my experience) very rare.

It is ** good ** to have your support of the Large Ship endeavor!  We (I'm speaking now of the Mars Society) will be representing our best efforts to the National Space Society on March 12th, so the more details we can have readily at hand for RobertDyck to handle questions, the better.

The audience will understand that the work of RobertDyck is published in a facility of the Mars Society, and with support and occasional contributions by members of the Society, as well as by non-member friends of the Society.

Edit a bit later: Quaoar, this topic is about navigation as well as pointing.  In GW Johnson, this forum is fortunate to have expertise in flight management (propulsion, ellipse planning, propellant requirements) but we do not currently have a member who is familiar with celestial navigation. 

If your circle of friends includes someone able to provide advice on where to point Large Ship when it makes one of GW Johnson's prescribed burns, that person would be most welcome to join the Large Ship team.

We know from experience with Apollo, that even lay people can perform celestial navigation when they are supported by a cast of thousands on Earth.  The Apollo astronaut navigator was able to point the vessel at a prescribed star, and to set up the automation to perform a burn for a prescribed period.  These skills, limited as they may have been, were sufficient to bring all the crews home safely, because the selection of the target star was worked out by the support team on Earth.

The large Ship navigator needs to be able to perform all those computations while in flight, without a support team on Earth, much as an airline pilot today plans the details of a flight from one airport to another without a ground support team.  The task of celestial navigation is far more difficult, of course, but modern computer systems are available to assist the celestial navigator.

If your (hypothetical) friend is willing to provide advice on how to acquire skills our (hypothetical) navigator will need, that advice could fit smoothly into this topic.

(th)

RobertDyck wrote:

This is why we've spoken a lot about the need to orient the ship. The aft end must be precisely aligned with the Sun, not angled at all. The axis of rotation is a line perfectly pointed to the Sun. So as the ship rotates, the aft end is always perfectly toward the Sun. Yes, that means the bow is not pointed in the direction of travel, but when ship is coasting does it matter?

If the bladder of the water wall extends down to the hull, but hull isogrid stiffener depth is 0.5" (12.7mm), and flooring thickness is 1/2" (12.7mm). That means the water wall extends 25.4mm below the walking surface. Over 19 metres that allows an angle of 0.0766° without exposing passengers to radiation.

With the aft side of the face of the ring perfectly perpendicular to the Sun, that provides full Sun so full solar power.

https://i.imgur.com/Uq9F6Sb.png

https://marsbase.org/sites/default/medi … ission.png

So lay the end of the hub on the sun and roll along the line keeping the end pinned at the sun.

Normally we use a siting star to hold course as true but sin we are rotating that may prove much harder to do.

A there is no "fission gas core NTR" for propulsion or for power to supply a super conductor that requires cooling and is a ceramic in nature.

We do not need a 20T field which is Strength enough to levitate a frog...

10^−7 Magnetic field produced by residential electric distribution lines (34.5 kV) at a distance of 15 m

The field needs to be away from the hull for starters so that we get the benefit of distance to make the radiation go around it.