Buoyancy rockets!?

[kerbiloid]

Spoiler

WaterDragForce = LiquidDensity * CrossSectionArea * DragCoefficient * Velocity^2 / 2;
GravityForce = TotalMass * g;
ArchimedesForce = LiquidDensity * TotalMass * g / RocketDensity;

WaterDragForce + GravityForce = ArchimedesForce;

LiquidDensity * CrossSectionArea * DragCoefficient * Velocity^2 / 2 + TotalMass * g = LiquidDensity * TotalMass * g / RocketDensity;

LiquidDensity * CrossSectionArea * DragCoefficient * Velocity^2 / 2 = LiquidDensity * TotalMass * g / RocketDensity - TotalMass * g;

LiquidDensity * CrossSectionArea * DragCoefficient * Velocity^2 / 2 = TotalMass * g * (LiquidDensity / RocketDensity - 1);

Velocity^2 = 2 * TotalMass * g * (LiquidDensity / RocketDensity - 1) / (LiquidDensity * CrossSectionArea * DragCoefficient);

Velocity^2 = 2 * TotalMass * g * (1 / RocketDensity - 1 / LiquidDensity) / (CrossSectionArea * DragCoefficient);

Say, LiquidDensity >> RocketDensity.

Velocity^2 ~= 2 * TotalMass * g / (RocketDensity * CrossSectionArea * DragCoefficient);

Velocity^2 ~= 2 * Volume * g / (CrossSectionArea * DragCoefficient);

Velocity^2 ~= (2 * g / DragCoefficient) * (Volume / CrossSectionArea);

Volume = CrossSectionArea * Length

Velocity^2 ~= (2 * g / DragCoefficient) * Length;

Velocity ~= sqrt((2 * g / DragCoefficient) * Length);

Velocity ~= sqrt(2 * g / DragCoefficient) * sqrt(Length);

Say, DragCoefficient ~= 0.1..0.3

Velocity ~= 10 * sqrt(Length);

Say, Length = 100 m.

Velocity ~= 10 * sqrt(100) ~= 100 m/s;

Something like that.

[Arugela]

Could you combine the concept of vacuum and bubbles to reduce drag? Say you have a rocket with a tip that creates a bubble all around the rocket after it picks up speed. It could create a lesser amount of friction and work like the tube with vaccum concept. Then you could have it work where it either drops the top parts off for normal air travel or also works in air to reduce drag. The kicker would be if you can make it vacuum enough air from the bubble and air to make a bubble of vacuum? Especially if it can be done with simple shaping of a rocket tip and some strong vacuum forces. Either produces with energy or mechanical forces cleverly built in. How much of a bubble would you need? If you could could you make one very thing around the rocket to minimize needed forces to make it easier.

And as is probably smart, try to utilize as many of the forces exerted on the rocket to try to aid in these endeavors. Like the generic concept of the put put motor. Take heat and cold and other things to try to create the effects basically passively. Put put motor is just an example. Same concept with something like a sterling engine by taking it and producing electricity to drive things during flight. then you can either save electricity from the motors for something else or use a greater amount of electricity to get a desired effect. Especially if in as simplistic a manner as possible.

Yes, I know, simpler overall design is probably better. 8)

I wonder if you could use underwater differences in pressure to power an electric motor for underwater travel? If you are protecting something from pressure that is an already created difference. So why not use it to create thrust or other effects passively. It must be utilizable.

Edited October 7, 2018 by Arugela

[kerbiloid]

9 hours ago, Arugela said:

Say you have a rocket with a tip that creates a bubble all around the rocket

But how then the Archimedes force could appear? 

Or if consider the whole thing as a single bubble, the equations look same for me, just average rocket (or bubble) density varies.

Edited October 8, 2018 by kerbiloid

[magnemoe]

On 10/8/2018 at 6:15 AM, kerbiloid said:

But how then the Archimedes force could appear? 

Or if consider the whole thing as a single bubble, the equations look same for me, just average rocket (or bubble) density varies.

This would require you to run an gas generator in the nose I think. And it already way to complex to be useful then you can simply add more boosters who is less complex. 
Only use would be to launch missiles while dived deep but even here I think it would be better to release an tube with the rocket. so you did not have to design the rocket like an submarine. 
 

[KSK]

On 10/7/2018 at 7:29 PM, Arugela said:

Could you combine the concept of vacuum and bubbles to reduce drag? Say you have a rocket with a tip that creates a bubble all around the rocket after it picks up speed. It could create a lesser amount of friction and work like the tube with vaccum concept. Then you could have it work where it either drops the top parts off for normal air travel or also works in air to reduce drag. The kicker would be if you can make it vacuum enough air from the bubble and air to make a bubble of vacuum? Especially if it can be done with simple shaping of a rocket tip and some strong vacuum forces. Either produces with energy or mechanical forces cleverly built in. How much of a bubble would you need? If you could could you make one very thing around the rocket to minimize needed forces to make it easier.

And as is probably smart, try to utilize as many of the forces exerted on the rocket to try to aid in these endeavors. Like the generic concept of the put put motor. Take heat and cold and other things to try to create the effects basically passively. Put put motor is just an example. Same concept with something like a sterling engine by taking it and producing electricity to drive things during flight. then you can either save electricity from the motors for something else or use a greater amount of electricity to get a desired effect. Especially if in as simplistic a manner as possible.

Yes, I know, simpler overall design is probably better. 8)

I wonder if you could use underwater differences in pressure to power an electric motor for underwater travel? If you are protecting something from pressure that is an already created difference. So why not use it to create thrust or other effects passively. It must be utilizable.

Not sure if it’s exactly what you had in mind but this sounds a bit like supercavitation. From the Wikipedia article, it’s been shown to work with torpedoes and in principle could be used on larger vessels too.

I don’t think it would be practical for vertically launched buoyancy rockets, simply because you run out of water too quickly at the speeds needed to sustain the supercavitated bubble. But the basic idea of using a bubble to reduce drag is sound, so far as I know.

Edited October 9, 2018 by KSK

[kerbiloid]

19 minutes ago, magnemoe said:

This would require you to run an gas generator in the nose I think.

This can decrease the drag force and the bubble density.
But in the estimation I've already presumed the water density much greater then the bubble density.
An SLBM runs up not because of Archimedes force but due to a kick from below.
And how could an Archimedes force appear if the rocket is flying up in the middle of a gas cloud? The rocket will fall down to the bubble bottom.

[Arugela]

Could you use vacuum pressure instead of gas if you can pull the air out fast enough? Either via some motor or by using forces in play?

That is also why I wondered if you could use a non vertical takeoff by using speed to build up underwater and/or by launching at a none straight up angle. Maybe you could run it around in circles for a bit then launch at high speeds and/or use an angle to increase the distance and possibly avoid going deeper in the ocean. If you can go in circles or along a long path horizontal under the water you could potentially get a longer run time. I would think you would want a reusable base for the rocket underwater that uses electricty or some other cheaper/renewable force for the underwater speed build. Like the put put motor or some odd concept, assuming it can lower fuel needs or be used with something to generate electricity for cheap and thus thrust. Maybe combined concepts could create a relatively fuel cheap form of underwater motion. Especially if you try to maximize forces actually taking place underwater during the process. Say pressure differences or temperature differences etc.

I was thinking a specially shaped nose cone could help create the bubble or something. Unless you used the water to create gas for you. And couldn't the nature of the rocket itself be used to help get other energy out of the rocket. Say as a conduit of temperature like a giant peltier or various other things. You might be able to reduce expensive equipment of the ships hull or parts are used to gain resources.

https://www.dailymail.co.uk/sciencetech/article-3664723/US-Navy-developing-supersonic-submarine-cut-ocean-speed-sound-using-bubble.html

Now the question is can you make the gas by using the water or use vacuum pressure in place of gas.(unless you can generate the resource in the field.) Is the gas used for the same reason it is inside of a blimp?

And if you used this and only used the rocket in shallow water could you remove most of the need to build it like a sub. You can fly/swim horizontally and then pull up potentially as to not deal with heavier pressures. Heck, if you can avoid the same thing after going into the atmosphere you could hypothetically remove the need to fly vertically at low altitudes.

If needed, maybe you could collect or change water during flight/swim to separate into 0^2/0^1(for water) and hydrogen(for air) particles. Use it to release under water and then in air after getting into atmosphere to either get out of the low altitude air easier or ease the transition from water to air.

Fun thought. If you are already using vacuum and positive pressure on fuel. Why not use the water to make a chamber to continually fill and pressurize like those toy water rockets. You could just use the ocean itself. Then you just need to find a way to power the pressurization as lightly as possible. You could try to use basic principles like I mentioned with put put motors or peltier like concepts(tempurature differencitals), especially if you are using the existing materials and not adding weight, and possibly the pressure difference itself. Could a put put motor create sufficient pressure difference and other conepts help generate electricity or other things for enhancements or backup power/resources? There have to be convenient low cost ways. By cost I mean rocket resources.

Maybe you can use air from the bubble to pressurize some incoming water to create a jetstream to push the rocket and some other things to jumpstart or aid in gaining speed. Kind of like a combined giant toy water rocket.

If you could power a rocket with little more than water, air, air pressure, and accompanying things that would be awesome. And use nothing but resources and energy transfered from the rockets use to power it. You could even use vacuum and some popout wings and try to land it for reuse if possible. A sort of blimp vacuum winged reentry mode.

https://www.extremetech.com/extreme/188752-chinas-supersonic-submarine-which-could-go-from-shanghai-to-san-francisco-in-100-minutes-creeps-ever-closer-to-reality

That is very much like a rocket(spacebound rocket). I wonder if it could be used as one? In fact if it's a missile it would already have to deal with low altitude air pressure transition to hit it's target more than likely. So, this would already be being researched by governments. So it's not out of the possibility for future rockets potentially. Maybe future reusable rocket designs. Now if you can generate all resources needed from use so it' doesn't officially need fuel.

https://www.businessinsider.com.au/hypersonic-jet-airbus-paris-air-show-2011-6

Similar concept. I wonder if the stored gasses are capable of aiding flight. If so then vacuum also could to some extent. Either in and/or around the ship. I wonder if this would fill the tanks with vacuum afterword to help with re-entry?

Edited October 9, 2018 by Arugela