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Post by The Astronomer on Aug 19, 2018 2:53:44 GMT
Tanks should be rated for a certain amount of G loading and stress; I know my MPD-only ship tanks should be fairly thin but a 50g terminal stage missile shouldn't have paper thin fuel tank walls... Considering real life orbital rocket boosters sometimes come in "balloon" type, which can't even stand themselves without the fuel inside, that would be feasible I guess. You know that many orbital injection rocket stages' initial TWR are less than 1, right? Have we ever build any orbital rocket stage with final TWR over than 10, much less balloon ones?
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Post by The Astronomer on Aug 19, 2018 4:02:58 GMT
One impressively tough balloon you have there, to be able to withstand both its own weight, upper stage+payload weight and aerodynamic heating! Sources?
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Post by anotherfirefox on Aug 19, 2018 4:06:34 GMT
Considering real life orbital rocket boosters sometimes come in "balloon" type, which can't even stand themselves without the fuel inside, that would be feasible I guess. You know that many orbital injection rocket stages' initial TWR are less than 1, right? Have we ever build any orbital rocket stage with final TWR over than 10, much less balloon ones? I meant booster stage, saying Atlas. Never reached over 10, but it withstand more than 5g iirc.
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Post by anotherfirefox on Aug 19, 2018 4:07:22 GMT
One impressively tough balloon you have there, to be able to withstand both its own weight, upper stage+payload weight and aerodynamic heating! Sources? en.wikipedia.org/wiki/Balloon_tankI expected more than this from your nickname, bro...
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Post by The Astronomer on Aug 19, 2018 4:12:58 GMT
One impressively tough balloon you have there, to be able to withstand both its own weight, upper stage+payload weight and aerodynamic heating! Sources? en.wikipedia.org/wiki/Balloon_tankI expected more than this from your nickname, bro... It's 'The Astronomer', not 'The Rocket Scientist' nor 'The Rocket Engineer'.
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ghgh
Full Member
Still trying to make kinetics work.
Posts: 136
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Post by ghgh on Aug 31, 2018 14:17:06 GMT
I don't know about dimensions but I do know that diamond is the best for low density propellant (Hydrogen, Hydrogen-Deuteride and selenium is good for high density propellant (decane, methane, etc.) as far as cost and mass go. If you want redundancy on tanks, having a flat (I mean flat compared the pencils normally suggested) tank will allow you to store it more efficiently and effectively for broadside combat. Kinda pointless to have long skinny tanks if 3 can get pierced by a laser burning through to a turret on the other side.
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Post by AtomHeartDragon on Aug 31, 2018 16:01:00 GMT
I don't know about dimensions but I do know that diamond is the best for low density propellant (Hydrogen, Hydrogen-Deuteride and selenium is good for high density propellant (decane, methane, etc.) as far as cost and mass go. Why not VCS?
Also, I'm still suspicious of long, skinny tanks being efficient and will remain so until I'm shown the math or at least sources - a lot of early and small rocket tankage was downright spherical.
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Post by Rocket Witch on Aug 31, 2018 18:54:07 GMT
The biggest factor I've found in optimising propellant tanks is the armour the craft carries over them. Longer tanks may be more efficient in and of themselves, but longer thinner craft will have more armour mass (given same thickness/protection level) than one with an ideal lengthways aspect ratio. For there seems to be an ideal overall craft length ratio where both tank mass ratio and armour surface area coincide, depending on the desired performance of the craft. This is analogous to the relationship between combined reactor and radiator mass optimising around 2500K with the available materials, but is harder to compute due to there being varying mission requirements and no consensus armour scheme. As, indeed, we disagree on whether armour should be used at all, but this also applies to any kind of aeroshell or skin around a craft, and/or truss network within it, which it must have for structural integrity under thrust; so there comes such a point for any craft where infinitely long tanks are not desirable, similar to how infinitely long rocket nozzles aren't. Packing lots of small long tanks is realistically infeasible due to the complex and massive plumbing requriements, especially when trying to meet the mass flow requirements of a warship.
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Post by AtomHeartDragon on Aug 31, 2018 20:04:45 GMT
Packing lots of small long tanks is realistically infeasible due to the complex and massive plumbing requriements, especially when trying to meet the mass flow requirements of a warship. You could effectively make your tankage a large blob of thin-walled honeycomb structure with very long cells and common drainage. My main concern is that COADE's model seems to think that such a tank would be inherently more mass efficient than a conventional spherical one - like the ones actually used in many space vehicles - which I still doubt would be a case (granted they might have enough of other advantages to make them highly desirable for a warship).
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ghgh
Full Member
Still trying to make kinetics work.
Posts: 136
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Post by ghgh on Aug 31, 2018 21:25:15 GMT
I don't know about dimensions but I do know that diamond is the best for low density propellant (Hydrogen, Hydrogen-Deuteride and selenium is good for high density propellant (decane, methane, etc.) as far as cost and mass go. Why not VCS?
Also, I'm still suspicious of long, skinny tanks being efficient and will remain so until I'm shown the math or at least sources - a lot of early and small rocket tankage was downright spherical.
VCS might overtake selenium and diamond at a midpoint given certain dimensions. Those dimensions will be as near a sphere as a cylinder can get with equal diameter to height. My issue with spherical tanks is that unless the ship has thrusters on all sides the design will be inefficient because the nozzle will be forcing a single point on the ship not the entire body.
Like this =O Whereas a cylinder would be like this ====
Basically more of the thrust is dedicated to pushing the train along.
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Prancer
Junior Member
Jousting in space. We're all Knights of the Stars.
Posts: 57
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Post by Prancer on Sept 1, 2018 2:13:06 GMT
It would be nice to have toroidal tanks; those should be right by the ultimate limit for an extended cylinder, since the end caps disappear into each other. And then slide the crew modules/reactors/ammo through the hole down the center. It would essentially be an optimized version of how I lay out my ship designs.
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Post by Apotheon on Sept 1, 2018 7:06:11 GMT
Hey! I've also started customising the propellant tanks and the "other" modules. I’ve opted not to change any materials since I don’t know what’s actually realistic and I’ve been meaning to ask. The lowest density materials are lithium, lithium-6, potassium, polyethylene, and UHMWPE… but would building a tank out of these materials and filling it with methane really work, all things considered? Probably no? Also, what’s the default propellant tank thickness? Dynamic? Because the tanks must be able to hold a certain amount of pressure and if they’re transparent, I guess radiation can affect the contents? All things considered, what’s a good material for containing methane or oxygen? By default it’s aluminium zinc magnesium and aluminium copper lithium, which sounds like some thought was put into the decision. Anyway, the reason why capsules are more mass-effective than spheres is because while spheres have a greater surface-area-to-volume ratio, capsules have a greater outer-volume-to-inner-volume ratio and possibly for all capsules with a shell, there’s an aspect ratio above which they are superior to spheres and that depends on the thickness of the shell… is my theory. I’ve done a few maths and it appears with an aspect ratio of 20, which is the highest available, a capsule is more effective than a sphere if the armour is at least 1% of the radius of the capsule. Capsules are still more effective than spheres if the armour is at least 10% of the radius of the capsule and the aspect ratio is at least 13… but since you cannot make a sphere in the game and for other reasons the exact numbers I have made here are probably not accurate in the game.
In fact, in game it appears an aspect ratio of about 1 is best as soon as you start adding any armour... I guess?
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ghgh
Full Member
Still trying to make kinetics work.
Posts: 136
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Post by ghgh on Sept 1, 2018 11:07:40 GMT
lithium prop tanks need to be packed so thick to hold the gas down that they are uneconomical anyways..
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Post by apophys on Sept 1, 2018 20:59:56 GMT
The lowest density materials are lithium, lithium-6, potassium, polyethylene, and UHMWPE… but would building a tank out of these materials and filling it with methane really work, all things considered? Probably no? Also, what’s the default propellant tank thickness? Dynamic? Because the tanks must be able to hold a certain amount of pressure and if they’re transparent, I guess radiation can affect the contents? All things considered, what’s a good material for containing methane or oxygen? What you need is a high strength to weight ratio, not low density. The tanks need to be pressure-tight. Tank thickness is dynamically modified to be the minimum that holds the pressure. Materials that are not directly outclassed by any other for tanks, from lightest to cheapest, are vanadium chromium steel, diamond, or selenium. The mass increase with selenium isn't ever really worth it, imo.
I use diamond tanks for all fluids with the density of around methane or better.
There is no need to add armor to prop tanks. Your armor should be wrapped around the outside of and in front of the ship, not wasted inside between tanks.
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Post by bigbombr on Sept 2, 2018 5:06:29 GMT
What you need is a high strength to weight ratio, not low density. The tanks need to be pressure-tight. Tank thickness is dynamically modified to be the minimum that holds the pressure. Materials that are not directly outclassed by any other for tanks, from lightest to cheapest, are vanadium chromium steel, diamond, or selenium. The mass increase with selenium isn't ever really worth it, imo.
I use diamond tanks for all fluids with the density of around methane or better.
Vanadium chromium steel is the lightest stock material. If you have mods, it's obviously vastly outclassed by nanomemes. Of the more realistic modded materials, I've found that high grade epoxy carbon fiber composite is even better than VCS (it has a lower yield strength, but is much less dense, resulting in overall lighter tanks).
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