Arugela

Buoyancy rockets!?

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I just had a fun idea. The though came to me randomly that sometimes maybe you need to go down to go up... Stupid random thought, but.. What about making rockets that use buoyancy and water to make them go faster to help get out of the atmosphere. They could use, buoyancy, and things like, hopefully light/redundant, electrical systems to do what a jetski does or similar and maybe loose the bottom part or separate near the surface in order to reuse it. This part could be collected.

Example. A rocket dives very deep(maybe the water thrusters in reverse.) then go upwards at a speed to seperate the above rocket in order to make it separate like navy/sub missile and bounce into the air and then use that momentum to maximum upward thrust and then ignite the rockets and get into orbit. Could you make more interesting rockets or more efficient ones. I imagine they could be larger to fit in gasses or things for upward thrust or use compressed air or a vacuum to create things to aid in rocket propelled ascent partially. How feasible is this and has this been considered over land rockets.

Also a mid stage filled with helium or vacuum could be either made to land (possible similar to a blimp, or at least to minimize descent forces) Or if filled with viable materials used as part of the rocket stage as fuel.

Has this been attempted or proposed before?

I was also looking at something about vacuum blimps recently. The blimp stage could either just aid the water ascent and stay when reaching the surface or it could help propel actual rocket stage higher in order to gain altitude to lessen the overall craft fuel needs. I imagine for a designer it would be nice to add negative weight to a craft for once. I imagine one problem could be getting the potential lighter than air stage to not hit he other one. Maybe you would need it to be on the nose and come off and float at a different trajectory than the main stage. It could also have some rockets to help pull it away and in a different direction before attempting to land. And with it being a water based rocket it could potentially just land in the water nice and soft like. 8)

We don't have any lighter than air portions for rockets in stock to do we?!

Either way, how high could you get a rocket before igniting main thrusters? Could this sort of hybrid design save on launch costs or allow new things to be done?

You could also add in blimp like negative air aspects to staging to make the stages land softer or have a slower natural decent to save on fuel if using reusable stages. At least hypothetically. What if fuel tanks were make to fill with negative air vacuum after being spent on top of any additional outer vacuum chambers. If this could be done while expending fuel you could increase air buoyancy while ascending. Maybe this could be used to increase efficiency of the rocket.

Edited by Arugela

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This is a lot (a *lot*) of effort for maybe an extra hundred metres per second, which is at best what drag would afford you.

Saturn 5 is over 100m tall. The crush depth of most submarines is under 1000m. So you can go under 10 body lengths deep and in order to do so you have to build your rocket like a submarine.

You'd lose any benefit from poor dry mass.

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So basically you are proposing using buoyancy as a catapult launch mechanism.

I'm not sure how much speed you could gain like that, or if it would be sufficient to overcome the added launch cost.

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Could you dual purpose things enough to not add extra weight. Or get enough vacuum to compensate for the extra weight on the bouyancy stagings? A vacuum would be made from a pump and you already use pumps for fuel don't you? You'd just have to make it well enough to not add mass overall. Outside of any structural increase needs. Could you get anything from current structural uses with just adding vacuum to current stages? Maybe it could be added to lighten the current rockets a little with current equipment. Or is that not realistic? If you could take current equipment and apply the principle to current empty compartments could you within the current structure of a rocket hypothetically get any significant gains? Even for a land based rocket?

I'm also proposing entire stages dedicated to being a blimp to get the rocket higher before launch to reduce overall fuel payload. Assuming that is even possible meaningfully. If added to current units without adding much mass could you get more efficiency with the current easily safe structural integrity.

Maybe the principle could be applied to eak out enough performance for things that are currently just barely not possible. Or to help stabilize rockets in some way. If it's applied to a side, given balance and other considerations, maybe the concept could be used to aid in flight.

That or maybe it's useful for smaller rockets as proposed. Say, super cheap fresh pizza delivery to the ISS.

Edited by Arugela

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@Arugela

Buoyancy assist, whether water or air, I think is a blind alley for this (adding deltaV) unfortunately, but I like how you're thinking.

 

Sea-launch *has* been investigated for various things, just not in the way you are imagining.

Firstly theres the Sea-Dragon (http://www.projectrho.com/public_html/rocket/surfaceorbit.php#seadragon) which uses open water as a transport/launch platform for a really, ridiculously large rocket. IIRC the maths on it is actually pretty good.

Then theres Quicklaunch (https://en.wikipedia.org/wiki/Quicklaunch) a space-gun concept that uses buoyancy to support a large gun barrel (and possibly as a heat sink)

Quicklauncher.jpg

 

There are some more esoteric hypothetical methods as well, that have been investigated in some detail - one method suggests using very large, tall balloons filled with a light gas mixture. The idea being you launch the rovcket through these ballons, inside which is reduced atmospheric drag due to the lower molecular weight of the gas mixture. Another slightly more ambitious idea is to build an enormous hollow tower and evacuate the inside, so that a rocket can be launched all the way from the ground to orbit whilst in vacuum, with obvious reductions in drag.

Those two are quite out-there, google around the terms and you are sure to find something.

 

Now a little surprise titbit I found just now: a study on using an evacutated tube to propel an atmospheric sounding rocket. Not quite in the way you originally envisaged, but not a million miles away either. The idea is you have a long evacuated tube with the rocket fitting snugly inside, forming the bottom seal. Once you release the rocket, atmospheric pressure pushes on the lower part of the rocket forcing it up the tube at speed, exiting the top with some positive velocity and altitude, whereupon the rocket firs with a boost to speed and height. 

This is pretty similar to using buoyancy, and therefore a direct confirmation that you are not crazy! (the caveat is that the benefits may not scale up to full-size space rockets)

http://www.dtic.mil/dtic/tr/fulltext/u2/715350.pdf

 

 

 

Edited by p1t1o

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Not exactly the same thing, but some sounding rockets used balloons to gain extra altitude before lighting their engines. They're dubbed, "Rockoons".

Spoiler

 

The Wikipedia article also features one of the most ridiculous cases of, "citation needed," I've ever seen.

Quote

A serious disadvantage is that balloons cannot be steered[citation needed] and consequently neither the direction the launched rocket moves[citation needed] in nor the region where it will fall is easily adjustable[citation needed]. Therefore, a large area for the fall of the rocket is required for safety reasons.

I mean... I guess you can steer blimps and zeppelins. Which are basically really sophisticated balloons.

 

 

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Those are interesting. I always liked the idea of getting into atmosphere before launch. I was at one point working on an electric ascent for eve but It never got fully of the ground. It got a ways up there but It was tedious. Although it looked like a potential for in game.

The other idea with water is the fact you are in a space like environment. You hypothetically are giving launch a full 3d 360 infinite runway with virtually no limitations on distance and other factors. Or like the long balloon idea make something so large the bottom is in one region and the top in another. 8)

The other thing I was thinking is like sub missiles but not necessarily going straigth up. If you encapsulate them you can literally make a sub carrying a traditional rocket(or any rockets. use it deal with underwater pressures and make it reusable. Then it and the underwater stage basically stay in or on the water surface and you collect them afterwords. on top of this use lifting body concepts to get more out of the normal rockets via adding to the current rockets or via a stage on top or on the bottom to give extra life. Or like you mentioned it could be like a water based firing chamber using negative pressure. Maybe it could be run from the deep or use ti to gain momentum and fire like a plane firing a gun. If you are getting enough re usability out of it then maybe it would help. If not maybe the buoyancy issues and lighter than air stuff could help lower fuel a little in order to need less full for things like the reusable parts from spacex or similar. if it helps at all it could get more efficiency out of stages from it potentially. If you already have air pumps and can make pump it all out fast enough you could make it ascend better on the way down by using it's existing structure to some extent to remove air.

And the other advantage of water, although what i already mentioned, is that you can go from the waters surface at any angle. You are not stuck with an initial vertical launch if it's helpful. And you don't need to take straight launches. You can use any convoluted path you want potentially. Even a circle to gain speed and try to breach like a whale to gain max altitude and velocity. Could you use the water speed and lighter than air concept(or reduction of effective mass) to get it in the air without thrusters with enough momentum? I would imagine there is a way to calculate how much speed would be needed to get to a certain altitude. I'm asuming you can reduce drag more with shape and things. Although i have no idea how much. with separate stages you could specialize the shape. If the underwater one is literally a sub made out of engines and a sheath around the entire rocket you could customize pretty nicely. At least hypothetically.

I didn't think about the heatsink part. If it helps you could use more powerful or smaller engines on the underwater portion.

I was basically thinking of a rockoon with a stiff body, or applied to a stiff body, like a zeplin body, being projected from underwater, via a distinct underwater phase, and then made more efficient on the way up. Plus I was wondering if the lighter than air applied underwater could enhance the water breaching stage to increase the height or velocity. Then you use a more powerful underwater stage to pull it or keep it under at a safe depth and then launch. if you can even stay at a shallow depth but move horizontally underwater you could then pull up with the right depth launch at a steeper angle. But I'm guessing it would depnd on the struture, which is why a dedicate shell around the entire rocket as an underwater stage might be good.

You could make a speedy submarine that shoots out a rocket from it's length/nose instead of it's top and use that vacuum tube concept. 8) It's a bit extreme but potentially reusable... ><

Then fire a special rocket with lighter than air enhancements to get more lift. I still wonder if there is a speed to get to maximize the gain in height before igniting the main rockets. If needed use an inner tube in the submarine to help protect the rocket or a shell to make it like a giant bullet to maximize air speed or something. The shell could eve hold the lighter than air properties or a large portion to enhance the rocket ascent.

AKA this is now a bullet/rocket/zeppelin shot from a submarine/gun. 8) AKA firing a large navy shell with a giant rocket in it that when the shell seperates leaves you with a rocket to ignite in the air. And it's enhanced with lighter than air properties to make it go higher!

Edited by Arugela

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Thing is, unless you are getting YUGE gainz, its much, much easier and cheaper to just build a slightly larger (or even very much larger, still cheaper and easier) KeroLOx rocket.

Ask yourself "Why am I adding deltaV in this way?"

HOWEVER, launching to orbit from submarines....has actually been done.

Not to benefit from buoyancy but there is a big advantage in being able to steam the launch platform to differrent parts of the globe (to reach various inclinations etc.) especially for military use.

https://en.wikipedia.org/wiki/Submarine-launched_satellite

Edited by p1t1o

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Or could make a speedy submarine that shoots out a rocket from it's length/nose instead of it's top and use that vacuum tube concept. 8) It's a bit extreme but potentially reusable... ><

Then fire a special rocket with lighter than air enhancements to get more lift. I still wonder if there is a speed to get to maximize the gain in height before igniting the main rockets. If needed use an inner tube in the submarine to help protect the rocket or a shell to make it like a giant bullet to maximize air speed or something. The shell could eve hold the lighter than air properties or a large portion to enhance the rocket ascent.

AKA this is now a bullet/rocket/zeppelin shot from a submarine/gun. 8) AKA firing a large navy shell with a giant rocket in it that when the shell separates leaves you with a rocket to ignite in the air. And it's enhanced with lighter than air properties to make it go higher!(possibly both the rocket and the shell.)

^ this is basically what I edited after you posted. 8)

I'm just seeing how far it can be taken logically. Even jokingly.

I imagine any such sub would either not need to go very fast or be built like a giant tuna.

https://physics.stackexchange.com/questions/74240/what-happens-if-a-rocket-is-filled-with-a-vacuum-instead-of-high-pressured-air/74243

This is interesting. 8)

Could this be used to help expel fuel and then fill the chamber with a vacuum to create bouyancy in air. Maybe to help gain lift as it empties or to help ascending reusable parts land more safely? Or am I misunderstanding the concept? Maybe if it has the next stage lighting it up with fire on the outside to help get the last of the air out to help it get down to earth again for reusable stages. If it needs it.

https://www.youtube.com/watch?v=0ki9Kta8g14&feature=youtu.be

I found this also. It looks like fun.

Edit: Oh, I read something wrong. I was thinking the vacuum tube was to create propulsion to launch like a bullet into air(The first one that is.). Misread that. that would be cool to see a balloon space elevator. 8)

If it doesn't scale then at least we have hope for the future of SSPPppAAaaACCEeeEE PPIiiiZZZAaaaaA!!!!! We could even use the atmosphere and other heat sources to cook the pizza on the way up!(or down.) Actually in this case it would be like a vacuum oven. I think those cook pizzas.

Edit2: That underwater gun concept is conveniently hooked onto a large drilling platform. You could so easily just hide that and wait till night and secretly launch from your, "Underwater drilling equipment!" Maybe BP has a secret space service and those oil spills are to cover up the equipment. I wonder how many of those oil platforms are conveniently on really good launch sites along with all of those oil pocket discoveries...(GB: We do not have any mysterious launch sites near the american coast. Oh look a spill... Oh god the environment! What will we do!? We shall get the first boats there to help clean up and help remove that drilling equipment and plug that nasty hole up!)

Edit3: And trying to use vacuum(or gas) would be the same as the parachutes for the airplane dropped rocket(assuming you can get anywhere near the same performance.). Except it might give some aid beyond the parachute deployment. I also wonder if that could be useful for reentry. If you could slow the decent a little would it help with safer returns to use vacuum chambers. You would even easily get vacuum chambers from space by letting out oxygen or things on the way back. If drag is not so much an issue on the way back from space why not Zeppelin landers. You could make the structure capable of deploying to larger sizes for returns to hold vacuum to slow down/aid in descent. If larger sizes are needed. Maybe sent up some heavy stuff and empty the cargo hold and fill with vacuum to slow down return trips. Or do we do this already?

https://en.wikipedia.org/wiki/Vacuum_airship

According to this it could potentially lift 1.28g for every liter of vacuum air. How much could you potentially lighten a normal rocket? Could you simply vacuum out those large orange tanks and not separate quite as quickly from the space shuttle and get a little extra oomph?(obviously structure and other issues aside.)

https://en.wikipedia.org/wiki/Space_Shuttle_external_tank

LOX tank: 553,358 liters?! I'm assuming this is not straight forward. But if it was that is:

553,358.24*1.28=708,298.24grams= 0.78076516146US tons?

58,500lbs(empty)=29.25tons; 0.78076516146/29.25=2.67% of it's weight Not including the shuttle.

I'm assuming that in no way works as i'm using fuel amounts and not air in liters. Anyone know how to convert fuel in liters to how much air would fit? Does this include all the space as that is only for the LOX tank? let alone the wrong values from pressure etc of fuel to vacuum.

LH2 tank: 1,497,440 l. This added with the same math would be about 10% gain.

If you could somehow gain that in flight while the fuel is draining then it could be useful I would imagine. You would in essence reduce your dry mass in flight.

Edit4: Oddly that sea dragon fits my other notion. Super large rockets. Although having one where the top of the rocket is in lesser depth compared to the bottom would make a rocket of a few thousand feet long(or even a few hundred.). Although I bet the numbers would be interesting on how that affects launch. I think I saw a post on that once about super high in the atmosphere to avoid fuel use or something. But I have no idea how it went or how it would work starting in water. Water would support more types of structures until you got into the air. The blimp concept and other things could be applied to actually aid structure instead of primarily lifting if it's something that is better off in ocean/space compared to water. And if something goes from water to air it could easily inflate under the difference and use this to launch if it doesn't add drag sufficiently. maybe it gets longer and is loose like a deep see fish and inflates with hot air on the way up. That would be a undersea launched hot air balloon rocket. I guess that would be a more pure rockoon but from water and it has to inflate on the way up. It's either hot air or a structure that can inflate but still hold a vacuum. Maybe a metal structure(like a round tomato cage) with fabric held taught enough?!

Edit5: Final note, if I can stop editing. What about a water bottle rocket that the fills with air in a vacuum to get as high as possible. 8d If anything it might make a cool toy. If you are already using vacuum why not increase pressure then do the opposite and maybe add a balloon concept like above(tomato cage that inflates and holds taught fabric to hold vacuum.). Might win a model rocket contest with it or something if it works well. 8)

Edit6: Maybe if a descending vehicle can be made it can work like a boat that rides on the layers of the atmosphere. Maybe if done right it can be made into a space rescue vehicle in case of accidents in space and collect crew if they get detached in a worst case scenario. Or just a really cool descent vehicle. Think a boat descending through the atmosphere that is also a blimp lie inflatable structure and can ride the clouds and atmospheric layers. Maybe enough stuff could be added to the ISS to safely bring it back from orbit without it burning up to reuse or put in a museum. Same for some of the russian stuff.

Edited by Arugela

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If you put balloons on your rocket, you're going to get a lot of drag because balloons are big.

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I was thinking you could make thin long ones that are the shape of a rocket or similar to reduce drag. Maybe rigid body if absolutely needed. I was hoping you could choose your dimensions well to get the same result. that or a long thin flying wing concept but more like a tear drop with points on both side or similar that is aerodynamic enough... Or a long cylinder. Those are the worst designs aren't they. Make it like a specialized bullet or something. If you can make it big enough why not float and use reduced thrust to go up like a rocket propelled blimp.

If not maybe a cool lighter than air reentry vehicle.

http://highpowerrocketry.blogspot.com/2012/01/can-lighter-than-air-spacecraft-enter.html

https://www.seeker.com/airships-offer-alternative-stairway-to-space-1765492330.html

Here's is an example. Obviously not a rocket design but...

Another idea. If you are going with vacuum and loose fabric and frame could you design a morphing shape body that can change in flight to meat various needs. It's not necessarily hard to design wires potentially with curves or other things to change shape logically.

https://geekswipe.net/research/engineering/supersonic-bi-directional-flying-wing-html/

combine with this concept maybe.

Edited by Arugela

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A giant pool of mercury with a strong hollow cylindric rocket-holder.
Pull it to the bottom with tethers, then release.

Edited by kerbiloid

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Can this be done in stock to any degree. I never figured much about the buoyancy side of the game. Besides that going below like -300 automatically blows you up for some stupid reason and doesn't let me explore even when I successfully make a craft that can go where ever I want... I was hoping there were easter eggs down there. 8\

Edited by Arugela

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On 9/25/2018 at 9:02 AM, RCgothic said:

have to build your rocket like a submarine.

First: The AJ260 (solid rocket booster 21 feet in diameter and built for Apollo) *was* built like a submarine.  Although that was to hold pressure in.  Maybe you could build it lighter if you light it and then launched it through the water.

Second: I'm fairly sure no sub-launched missile has positive buoyancy.  Certainly somebody might have thought of that (I'll admit that "compactness" is a critical sub-launched missile virtue).

Third: There exists a (now sadly in bureaucratic limbo as of 2015) amature rocket attempt (to orbit?) that is balloon based.  https://www.theregister.co.uk/Tag/lohan

Scott Manley link on the AJ260: https://www.youtube.com/watch?v=UfMPgAQD420

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Submarine-launched rockets don't use bouyancy to get out of the water. They use solid rockets. Those things are pretty heavy solid boosters.

Adding the structural reinforcements to make your rocket withstand underwater pressure, plus the complexity of the thing and all the additional failure modes would take away any benefit of extra delta-v if there was any (but there isn't).

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1 hour ago, Nibb31 said:

Submarine-launched rockets don't use bouyancy to get out of the water. They use solid rockets.

For US/UK ballistic missiles...  Well, they're technically solid fuel rockets, yes.  But they're not used for thrust, they're used as gas generators and the resulting gas (and steam from the water used to cool the gas) pressure fires the missile from the tube like a bullet from a gun.

And they couldn't use buoyancy anyhow, as they're considerably denser than water.

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Rocket engineerers are always attempting to cram more stuff into less space.

Ever heard of mercury fueled engines?

So, buoyancy will not work, unless it is a hydrogen nuclear rocket. Or hydrolox rockets.

 

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8 hours ago, Nibb31 said:

Submarine-launched rockets don't use bouyancy to get out of the water. They use solid rockets. Those things are pretty heavy solid boosters.

Adding the structural reinforcements to make your rocket withstand underwater pressure, plus the complexity of the thing and all the additional failure modes would take away any benefit of extra delta-v if there was any (but there isn't).

That is why I thought separate stage to simplify. If you build the first stage like a giant bullet/sub but built to withstand pressure you could have it help the initial staging from underwater pressure. This could then be reusable. Or be a modified submarine. Basically launch the submarine nose up and make the middle of the sub like a giant gun or missile silo and get momentum. Although if using a real modified sub it would limiting to the size of the rocket. Else like a giant reusable outer casing and base.

Of course of your normal rocket is designed to use vacuum already... You could pack as much buoyancy into the rocket to get more momentum on launch. Could current fuel tanks hold a negative buoyancy when empty? I was kind of assuming those were already fairly strong by design as they have to deal with positive pressures. If you designed a rocket around a positive and negative pressure fuel tank then you might be able to do this. Maybe give it various section so that when one empties it is then drained of oxygen for a buoyancy assist. I don't see why, if that is feasible, that could not help with reusable rocket designs like the spacex stuff. Maybe you could get some extra fuel efficiency or less overall fuel needs overall. Or do things strong for positive pressure not work out to being strong against negative pressure?

Edited by Arugela

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An interesting idea but, as others have pointed out the extra mass of making a rocket that can go underwater and catapult itself out would FAR outweigh one that just does a normal surface launch. The drag in water alone is several times higher.
The closest to this idea that has been considered is something like jet-launched rockets that already get it out of the majority of the atmosphere. There have been concepts before for blimp-launched rockets before but, blimps and rockets are kinda polar opposites, rocket-fuel is absurdly heavy, and i don't think blimps/airships have a boyancy ratio much greater than 1 so you'd need something probably city-sized to even get something like a Falcon 9 off the ground.

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It wouldn't necessarily be to get it off the ground. it could be applied to other things. I was also thinking using normal internals designed to take the negative pressure and positive pressure to in essence decrease the empty weight of the vehicle artificially with a blimp like negative pressure chamber in any empty fuel tanks. It could help improve performance if accounted for if it sufficient buoyancy in air.

What if the orange tank could go from holding compressed fuel to holding a negative vacuum in all empty stages at it empties. How much could that improve overall performance if engineered correctly? Could it get enough buoyancy(in air not water) before hitting a weak enough part of the atmosphere or could it be useful for making such a tank reusable in concept. Maybe as a modification or whatnot. Then apply this to purposely designed reusable rockets.

Edited by Arugela

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If your building a multi-stage rocket and it starts underwater, ALL the stages are going to need to deal with the extra pressure. that's more mass for everything. Even if your not bringing everything extra with you. It would probably be more effective to load the rocket in a giant slingshot. XD

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I'm also thinking normal rockets. The idea of using a blimp concept could be applied to enhance a normal rocket like space x or a modified shuttle tank. Could you take solid rocket tanks(or any tanks) and then make them hold a negative pressure(after a chamber is emptied of fuel.) to help bring them down with a secondary fuel source. Maybe to offset the weight and reduce the fuel for recovering the part in a usable form. I would think the best chance of this working would be on large fuel tanks with lots of empty space. Or things with large cargo holds. Especially ones already designed for positive pressure.

Or could you design a system to help with flight. If you can especially get a tank filled with negative pressure/vacuum fast enough maybe it could be used as a counter system to help in case a rocket tries to veer off course. Or as a safety system to help making stuff in a bad situation not go as out of control by having it be partially a blimp and then more predictable on failure. Maybe it could increase the chance of saving crew in a bad situation. You could design it to be a little more stable or likely to move in a certain pattern with properly place vacuum tanks or similar.

This is of course assuming it can be done in a way that doesn't increase the likelihood of failure to start.

I'm emphasizing vacuum because I assume it's more resilient as you don't need to carry resources to use it. You just need to evacuate resources already in the tank.

And at this point in design you wouldn't necessarily increase the size of teh tank. Just use the tank as it already is to increase performance if it's possible. Maybe even vacuuming it out to a current safe amount and not acheiving perfect vacuum. Outside of structural issues. Logically it should increase performance to some degree. Else I wonder how hard it is to make a purposely design vacuum tank that goes from strong positive to negative pressure on purpose. I would think it could be useful for something.

Separately, what about the buoyancy water rocket idea as a way to get more launch windows. It could be an emergency vehicle for rescues potentially. Even if less efficient. Not sure if that opens up enough things for practical use. If it helps with landing issues because of the problems of air space etc. Maybe it could also open up more flights in general if we start doing more in the future. Mainly with an emphasis on where you can land if you fail to get all the way up for some reason but can still manage to land in friendly territory. If the world becomes a harsher place or it's just practical for other reasons it could be useful one day.

 

Why can't you design an underwater vehicle that takes off all the pressure from the outside so the rest of the rocket doesn't have to take it. It's the same as protecting a person from pressure underwater. Then you make an expensive underwater shell that can be used and repaired as long as possible. Not saying it's necessarily practical but I would imagine it's possible.

156436main_image_feature_648_ys_4.jpg

And I am not against the concept of a giant slingshot. ;d

 

Edit: I would think a positive/negative pressure tank would be build by adding or design around a cylinders with half spheres in it(And on each end of the cylinder). A giant cylinder could have half spheres put in it to make chambers. The cylinder would have the top be a half sphere for max structural strength(assuming) and then another half sphere on the bottom with a whole for the positive pressure to force out fuel and them a plug that negative pressure would/could cap when applied and other holes, if needed, for getting all the air out(probably redundancy for safety). then you only need downward facing half circles put in the rest of the cylinder to for any other desired chamber space. You could have as many negative pressure half sphere/cylinder spaces as desired for either for maximizing negative pressure or to get as much fuel as possible. Or even to aid in the overall strength of the cylinder.

The inside would only have half spheres in it to maximize fuel space. These would be half spheres facing downwards to let gravity or pressure push the fuel out. The only upward facing sphere/half sphere would be on the top of the cylinder. Although you could simply make the very top a full sphere with a hole in the bottom.

You could also add other internal or external structural strength with beams or other arched beams, or the like, inside the empty spaces. Maybe with a tapered widening joint that spread out along the inner or outer skin of the tank. This would allows a wide joint and a much smaller  beam in the middle for maximum strength to the walls. Although I don't know if that helps maximize fuel or tanks space. At least not if it's inside the tank. But that, on the outside of the tank, could be done to aid both negative and positive pressure. I would assume it would look alot like how it's presumed cells are attached organically with a wide connection and potentially thinner, but maybe flexible, connection point. Just a matter of doing it efficiently. Or am I think of drawing of neurons? I'm also thinking wide as in 3d wide in all direction. a joint covering a wide potentially hexagonal or pentagonal surface. Very thing at the edged and thicker as it gets to the center where it goes into a long tube(s) to attach to another surface. These could be tightly packed. Also potentially making room for thinner inner tank. Or one designed to counter the outer surface joints to equal out the strength of the surface.

I wonder if you could make a thinner tank(designed around total weight.) and an outer layer of a material that can be worked like sodder(but at higher tempturatures likely.) and then pulled to a second outter layer in multiple strands to make joints. The outside layer on the inner tank could be this material in hexagon/pentagon shapes along it's surface. This could be used to make the tank somewhat cheap to replace. it could also have the inner tank also make of similar shapes underneath(and in the same spots or purposely misaligned) so they can be replaced easily and cheapy. Just a matter of shaping them then. Which I would think could be done with heat and negative/positive pressure designs of the tank. Although the spheres would probably need to be solid. Unless also made the same way with inner joints.

I wonder if you could make the joints by taking physical thin(relatively) lines of material and heating them to sufficient heats to make a material draw up a wick to positions. Maybe this could be perfected to be done in space for repairs in orbit or something odd.

Again, the point of this is to achieve better overall performance if possible or for functionally aiding in the recovery of said parts. Assuming it can be done efficiently. Or possibly to make the tanks continuously repairable.

 

Edited by Arugela

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