h a l f b a k e r yLeft for Bread
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The idea is, instead of having 1 fuel tank per engine, you have huge amounts of small tanks. These tanks will each be drained individually, and then released. This will not increase tank weight as tank weight is proportional to volume (and psi), and the total volume stays the same, as compared to single
tank.
This will greatly decrease the after-burn mass, but will (basically) decrease the ISP - (dependant on the _average_ exhaust speed - dropping tanks this often basically makes them exhaust). However, because of the insane mass ratio, scary speeds can be obtained. For an ISP of 125 (LOW) and a finishing mass ratio of .99, speeds of 18,420 ft/s (~LEO to mars, without mars capture) or so are obtainable in a single stage. Increase The ISP and the terminal velocity increases proportionally.
This can be done in 3 basic ways:
1 - Containers like stackable cups are connected though hoses to top, angled out (yes, bad for efficiency) and dropped from the bottom when dry.
2 - Tanks around a spike, allows bottom (higher efficiency) rocket engines, but will probably increase weight.
3 - Micro-solids with shared nozzle have a whole bunch of armature-sized rockets and line them up, one by one with a multiuse nozzle - kind of like a gun, then discharge.
[link]
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My only concern: The extra mass of all the extra tanks. |
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// there is no atmospheric friction to speak of after T minus thirty seconds. // |
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Presumably you mean T plus 30? |
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Very little at minus thirty too, though, methinks. |
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1, you don't have to expend energy to lose a tank - in the first example, you simply realese the coupelings, the tank falls away. In the third mode you could use springs or simply push them out of the compustion chamber. |
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Don't have to worry about terminal velocities? So I guess speed dosn't matter? - I ment burn out velocities - sorry for the miss-use of wording! |
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ISP has little to do with final speed? For a given mass ratio, Isp is porportional to final speed. |
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And all your comments about tank parts are voided if you use the micro-solids anyway. And this was mostly intended as a orbit changing device - so use low acceleration and you only need 1 pump, smaller pipes - valuves... |
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Plus, use of low mass ratio (cheaper) tanks is still quite effective in this scheam. Thease could be filled with low-tec fules such as (self pressurizing!) propane and nitrogen oxide, there by eliminating the expensive pump! |
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Nitrous oxide as propellant ? That makes me laugh.... |
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1 - //RELITIVE to you// That's the point - you speed up, (using the next tank) not the tank! This is relitive velocity, even if the tank didn't change speed! Don't get it? Walk away from computer! |
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Yes, not the most pratical with "fancy" tanks but wit the heavy russian aproch...it becomes more likable. |
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3 - Don't want use those proplents? Use something else! |
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doan't yoew wont tu youse a ditcionery? |
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Lots of small tanks = large surface area of tank per unit volume of propellant. |
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One big tank = small surface area of tank per unit volume of propellant. |
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Given an approximately equal wall thickness for a given propellant initial pressure then your many small tanks, including propellant, will weigh much more than one big tank. I guess that is why NASA, the Russians, ESA etc., use one or two big tanks instead of lots of small tanks... |
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Wall thickness, if I remember right [suctionpad] is equal to " 1/2 Pie*diameter*psi/material strength. |
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So, volume is *porportional* to tank mass. |
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your'e getting *proportional* mixed up with the mathematic term proportional. |
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You mean "increses as the other does" whereas the math term means "as this doubles, so does that" |
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Volume is very much not proportional to tank mass. |
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In a complex piped, pumped system, multiple tanks is many orders of magnitude less efficient as compared to a single large tank. |
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Custardguts, my-nep didn't confuse proportional with "directly related"; he said thickness of the tank winds up proportional to radius as well. Since surface area is proportional to the square of the radius, tank mass is then proportional to the cube of the radius -- as is tank volume. So multiple tanks would be around the same mass of one larger tank. |
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But, as you suggest, it may be that the extra equipment to support multiple ejectable tanks per engine wipes out the mass savings you get from jettisoning spent tanks, except perhaps where only low thrust is needed, as in his orbit-changing example. |
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I think the only advantage of having more stages is that you don't have to accelerate as much mass for as long. The disadvantages are presumably increased complexity (decreasing reliability), and additional weight of the separation equipment. |
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I think that there's also optimum engine designs for varying speeds and ambient pressure. |
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Ideally, you would jettison the tanks using
explosives, so that the final velocity of the tank was
zero (relative to the ground) until it started to fall
under gravity. In that way, you haven't left any
valuable kinetic energy in the empty tanks, and the
tanks instead become very efficiently-used reaction
mass. (On the downside, though, you'd have some
high acceleration spikes at every tank jettisoning.) |
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Ideally the thrust engine would be entirely consumed as reaction mass; jettisoning wouldn't be an issue. |
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mmm, edible rocket engines... |
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