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You would think that nobody knew anything about cryogenic tanks and that no such thing had ever been built before. Meanwhile LNG is shuttled around the world by ship and every hospital and innumerable labs and industrial undertakings have LOX and LN2 tanks and vaporisers.
GW Could the Mars performance of Starship be improved with a fly by of the moon?
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So liquid CO2 can exist at pressure above about 5 Bar.
T A Hanson. Some thoughts about underground habs.
Spray concrete reinforced with stainless whiskers or maybe asbestos fibres is probably one answer but it lacks the true circularity of a sectional concrete liner and the fibres are not aligned and therefore it cant be loaded to the same degree. Consequently it uses more material for the same duty than the precast sectional liners commonly used, which will efficiently support very large loads, even though the spaces between the rings and the tunnel walls must be filled with grout. Note that the grout is not reinforced. At Mars temperatures thick steel sections will be embrittled and may fracture so large steels should not be relied on unless specifically formulated for extreme low temperatures. Note that 300 series stainless does not suffer from this. Neither do 6% and 9% Nickel steel, which are popular for LNG tanks (where corrosion is not an issue, so stainless is not needed). 3% Nickel is also resistant but when welded it's resistance can fail.
It is the requirement for insulation which prevents you from using bare concrete for your hab. It could be used as is if you don't mind extreme cold and a vacuum but that doesn't suit everybody. You can spray insulation quite easily and I suppose a formulation for that spray process could be made to work in a near vacuum. It may need temporary heating of the surface to enable it to stick but that would be OK for short duration. Alternatively insulation could be made up off site and installed in sections. Insulation tends to be light weight but quite weak so separate supports must be provided for the liner. There is an exception to this which applies when the insulation is a completely evacuated powder or fine particles. You will be used to powders like graphite or talc which are quite fluid, but their fluidity is due to the layer of gas adsorbed onto each particle, which lubricates them. In a good vacuum the particles become immobile and the insulation can then support quite large loads. I doubt that the 11 mBars at Mars is sufficiently low for this immobilisation to occur.
When you have insulation it must be prevented from getting damp as this severely impacts its effectiveness so you must provide a barrier on the warm side to keep moisture vapour from getting into the insulation. At some point on the temperature gradient in the insulation, moisture would fall to its dew point and from there onwards your insulation layer would become wet, reducing the effectiveness. In really cold conditions it freezes and becomes a moderately good conductor of heat and quite rigid (remember the frozen foam insulation that resulted in the loss of a shuttle). This process occurs with anything that will condense at or above the temperature of the cold side of the insulation layer, so cryogenic insulation is always evacuated, either as a Dewar vessel or as particulate insulation. Otherwise any gases would be liquified in the layer.
The condensation issue is one reason you need a liner membrane. The other is to take wear and tear and transmit loads from the activities inside the hab/tunnel. The supports have to carry those loads to the concrete casing without also carrying too much heat. They must also carry the self weight of the liner and allow for differential expansion between liner and tunnel.
Since Mars has quakes you will have to design for dynamic loads, and since you don't know much about the ground conditions, you will have to allow for some subsidence. Your design will need to be fault tolerant, which means sectionalising it to allow a fault in one zone to occur without jeopardising the entire structure.
My conclusion would be that it will be a long time before we can design a secure bored tunnel hab
A cut and cover design would be somewhat easier and could be fabricated offsite either whole or in sections from a material like GRP sandwich, but this would limit the depth of burial. Such a structure can be laid down on a sand bed and be inherently flexible so unlikely to fail in modest quakes or subsidence and would be my favoured solution. The issue of condensation doesn't arise because the insulation is entirely encapsulated in GRP. Fibres might be basalt and resins might be made from CO2, Nitrogen and water, not easy but possible given sufficient power and a chemical plant.
Concrete, especially steel reinforced concrete, is brilliant stuff in compression. Not so good in tension! If you want to make up rings to support external loads such as an overburden of regolith, you are essentially talking about tunnel liner sections. If you then want to pressurize your tunnel/ concrete sectional hab, you will need a pressure rated membrane inside it. This will be elastic material such as Aluminium alloy, Stainless steel, GRP etc which will expand under pressure- even just a little bit so it cannot be applied directly to the concrete sections. Additionally it will need to be insulated to prevent heat loss to the surrounding ground and possible destabilisation due to migration of ice away from the warmth. This means that your stainless or aluminium liner becomes almost an independent structure attached to the concrete by flexible supports to preserve the insulation and to allow expansion. If you use GRP that isn't quite such an issue as it isn't very stiff, so can be deformed quite readily and the supports can be more solid.
We have a ship capable of building on orbit structures to pave the way for the monster sized starship but without using the tools we have we a in a holding pattern.
Even when starship is made as light as it can the bfr first stage booster must be ever so much be capable of supporting that huge mass on its structure.
The tanks of the booster will have to be pressurised before the second stage loads come on the top, when the assembly goes vertical, in order to prevent the tank walls from buckling. That isn't difficult in principal but you need to maintain the pressure whilst fuelling and you must not contaminate the tanks.
Precipitation hardening alloys are subject to overaging at high temperatures. This is when the defect pinning deposits within the grains get larger and migrate towards the grain boundaries by diffusion, becoming less effective in hardening the material. The result is a reduction in strength and an increase in deformation. I wouldn't use them at extreme temperatures, unless someone has come up with a new type that doesn't suffer from this issue.
30 metre diameter might be a little bit ambitious. It isn't difficult to design a tank with a membrane wall that would withstand considerable internal pressure even at 30 metres diameter (100ft for the unreconstructed oldies). It is the external pressure of the regolith and the tanks weight supports that are difficult. Submarines are designed to withstand external pressure and they don't have membrane shells. Likewise LPG storage bullets are designed to be mounded, but I have never seen one that size.
There are plenty of compressors around. These include vacuum pumps and jet engine compressors. To compress a large quantity of gaseous product from low pressure, they need to be very large and therefore quite heavy, due to the low density of gas entering the machine,
Dont underestimate the power of publicity statements with no support from the numbers. People seem to love to believe that stuff.
Periods of high Oxygen concentration in the Earth's atmosphere have coincided with the evolution of giant insects. Dragonflies with wingspans measured in feet for instance. This is because the insects low performing Oxygen capture and distribution systems, along with the weight of their exoskeletons, limits their size.
Small burrowing animals seem to have survived the apocalypse of dinosaurs, along with birds. Also surviving were sharks and bony fishes, molluscs (but not Amonites), cold blooded reptiles and crocodilians.
Windmills depend on Mass flow of atmospheric gas through their blade swept area. The atmospheric pressure on Mars is very low so therefore so is its density. There would be precious little power output from even a huge machine on a windy day.
I would agree with your minimum for an effective mission, but it does depend on what you wish to do when you get there and how long you are going to stay.
A group of seven is the optimum team size for many tasks but we might need 9 or 11. Odd numbers so that group meetings don't end in deadlock.
I would suggest the use of benzene as fuel. It uses a lot less of your precious hydrogen than methane and has about the same ISp, and you don't have to refrigerate it. The main drawback is that it is a severe carcinogen.
I understand that Rocket Labs have caught returning boosters with a helicopter. Not on the most recent launch, but in a couple of earlier cases. Also that they intend this to become routine.
Congress/NASA are still clinging to technology that Musk has rendered obsolete. Why? Follow the money!
Navies have protocols for dealing with unfit commanders in circumstances where communication with higher authorities is not possible.
Louis. In the poor parts of the world infant mortality is very high compared to what happens in the developed countries. The weaker children die. Only the strong or lucky ones survive and the lucky include those who do get vaccines.
The drawback is that you are limited to line of sight working. You are limited to that anyway for communication by radio but it is much easier to have an extending aerial than to do the same with a large steerable panel.
Not all of the deep ocean floor ends up subducted into the mantle. Occasionally bits of it get shoved up or welded onto bits of continental crust. These are formations called ophiolites. There is one in Oman, another forms the Lizard peninsula in Cornwall and there is one in Cyprus, which was the main source of copper in ancient times, hence the name of the island- or maybe the other way about. Maybe one of these could have been formed from crust including rocks from before the snowball Earth episodes.
Louis, the glove boxes you see in labs are only useable because the pressure differential between the enclosure and the lab is very small. Not a couple of hundred millibars! It is much more difficult to operate with a vacuum on one side of the glove as in a space suit.
Precious little radiation protection there, by its appearance.
You have to flare it steadily. Abrupt venting of large tanks requires a flare system with condensate separators and tanks, surge capacity, igniters, pilot burners, inert purge and coolant sprays. Without that you get liquid slugs or fog resulting in loss of flame followed by a blevy.
good luck, Kbd.
Triton also has a bit of an atmosphere, Void, and is a very interesting object. It has been proposed as a captured Pluto type world, rather than a moon formed where it is currently located.
