# Can anyone help me?



## Damian12612 (Dec 2, 2021)

I'm writing a sci-fi book, and I want to calculate the weight of a 153 cm caliber projectile for a magnetic cannon, which is the main weapon in side-by-side artillery duels, the projectile is made of depleted uranium (density 19.1 g/cm³) is spherical in shape, its length is 30 centimeters, can anyone help me calculate the weight?


----------



## Biskit (Dec 2, 2021)

What shape is your projectile?
If spherical, then the volume of a sphere is 4/3 x π x r xr x r where r is the radius = half the diameter.

The mass of the projectile will then be volume x density.

If you're using other than a spherical projectile, then you will need to calculate the appropriate volume.

However, if your projectile is made of uranium, how are you launching it using magnetic fields? Uranium is paramagnetic not ferromagnetic. Some sort of magnetic accelerator would be very inefficient.

ETA - Sorry, missed that you actually specified spherical


----------



## Valtharius (Dec 2, 2021)

By length you mean the diameter?


----------



## Foxbat (Dec 2, 2021)

As far as I know, depleted uranium shells are used up to 30mm. It appears they weigh almost 0.66 pounds (1.32kg?) With that in mind, your 30cm (300mm) round would roughly be around 13 kilograms?


----------



## Venusian Broon (Dec 2, 2021)

Biskit said:


> However, if your projectile is made of uranium, how are you launching it using magnetic fields? Uranium is paramagnetic not ferromagnetic. Some sort of magnetic accelerator would be very inefficient.



You could coat the uranium in steel/iron?

A ball though seems the wrong shape for a projectile, if you want to use the heaviness of the Uranium to penetrate 'armour'. You'd probably want a dart-like object to penetrate, though - perhaps with a steel sheath that gets discarded after being accelerated that then launches a solid uranium 'dart'. Like this, say (although this is a cut through of a depleted uranium round with explosives to propel it):







Or something more bullet-like and 'solid' with no propellent (if it is to copy an old cannon) rather than a sphere.


----------



## Biskit (Dec 2, 2021)

Venusian Broon said:


> You could coat the uranium in steel/iron?
> 
> A ball though seems the wrong shape for a projectile, if you want to use the heaviness of the Uranium to penetrate 'armour'. You'd probably want a dart-like object to penetrate, though - perhaps with a steel sheath that gets discarded after being accelerated that then launches a solid uranium 'dart'. Like this, say (although this is a cut through of a depleted uranium round with explosives to propel it):
> 
> ...


My understanding (and this is well away from my techy comfort zone) is the projectile either needs to be a sabot-style round where the sabot shell is steel, or you use a steel projectile, perhaps with a uranium tip for penetrating power. Using the denser uranium means packing more kinetic energy into the projectile on launch for a given velocity, but higher velocities might be easier to achieve with a steel projectile. 

I seem to recall that there are all sorts of tricks with composite projectiles combining materials of different mechanical strengths to create better penetrating power, so a simple uranium sphere might not be the most effective design.

The other big factor in all of this is whether the battle is occurring in space or in atmosphere. Spherical projectiles are not very accurate in atmosphere but I've no idea how they perform in vacuum. Without atmospheric friction to disturb them they perhaps don't need axial spin from a rifling system to keep them flying true.


----------



## Venusian Broon (Dec 2, 2021)

Biskit said:


> The other big factor in all of this is whether the battle is occurring in space or in atmosphere. Spherical projectiles are not very accurate in atmosphere but I've no idea how they perform in vacuum. Without atmospheric friction to disturb them they perhaps don't need axial spin from a rifling system to keep them flying true.



Good point. If they are going fast enough in a vacuum, all that matters may be just the kinetic energy transferred on a hit. However, a bit like a mace, a tiny tip on the leading edge of projectile would still probably increase penetrability of the round. 

An advantage of a projectile that is fully Uranium, apart from its mass and therefore increase in kinetic energy, could be if the target has 'shields' or protective magnetic fields that are there to deflect ferromagnetic objects, they wouldn't really be deflected much. I mean, it might not really matter if the projectile is going at 10 km/s   and thus a shield like this really be worthless, but this is fiction...


----------



## Foxbat (Dec 2, 2021)

For firing electromagnetically and keeping up efficiency, how about a kind of catapult just like launching a plane from an aircraft carrier (I’m thinking DU projectile sits in a cradle, which is accelerated along an electromagnetic rail). This would mean the magnetic characteristics of the projectile for launch wouldn’t matter.


----------



## CupofJoe (Dec 2, 2021)

Practicalities aside, my rough maths on a sphere as you describe [30 cm across made of DU] makes it about 270 kg. But that doesn't take into account any shaping or rifling there would be.


----------



## Venusian Broon (Dec 2, 2021)

Foxbat said:


> For firing electromagnetically and keeping up efficiency, how about a kind of catapult just like launching a plane from an aircraft carrier (I’m thinking DU projectile sits in a cradle, which is accelerated along an electromagnetic rail). This would mean the magnetic characteristics of the projectile for launch wouldn’t matter.


Could be a good idea for a very large projectile and a target that can't move much. 

But if you're in "open space" and firing against something moving reasonably fast, you might want a large volume of projectiles to make a 'spread' to try and ensure some hits.

(Although if you fired this in orbit, depending on the velocity of the projectiles, you might end up with 'instant kessler syndrome'!)


----------



## Danny McG (Dec 2, 2021)




----------



## Damian12612 (Dec 5, 2021)

Biskit said:


> What shape is your projectile?
> If spherical, then the volume of a sphere is 4/3 x π x r xr x r where r is the radius = half the diameter.
> 
> The mass of the projectile will then be volume x density.
> ...


i dont know uranium dont is ferromagnetic  


Venusian Broon said:


> You could coat the uranium in steel/iron?
> 
> A ball though seems the wrong shape for a projectile, if you want to use the heaviness of the Uranium to penetrate 'armour'. You'd probably want a dart-like object to penetrate, though - perhaps with a steel sheath that gets discarded after being accelerated that then launches a solid uranium 'dart'. Like this, say (although this is a cut through of a depleted uranium round with explosives to propel it):
> 
> ...


I forgot to say that there are also other types of ammunition, like grapeshots and arrows, I read on atomic rocket that darts act as bombs and big bullets as penetrators, darts are to long range or close, sphere to medium range to "soften" the armor or destroy the soft places from darts and grapeshots to completly shred the hull close range


----------



## Damian12612 (Dec 5, 2021)

Venusian Broon said:


> Could be a good idea for a very large projectile and a target that can't move much.
> 
> But if you're in "open space" and firing against something moving reasonably fast, you might want a large volume of projectiles to make a 'spread' to try and ensure some hits.
> 
> (Although if you fired this in orbit, depending on the velocity of the projectiles, you might end up with 'instant kessler syndrome'!)


like i reply Venusian there very much class of ammunition, firing with 2000 kilogram roller to planet or orbital fort is in my universum endless stupid 'cuz fort or PMF (Planetary Militia Force) plaser (plasma laser) can destroy this in little time with beam, firing to planet or planet with relativistic missle is a one a war crime, for this you will in a mining-prison asteroid or agri-world next month, kessler syndrom is regulated by Orbital Security Force (OSF), 
so most orbital clashes are sieges, the decisive battles are usually when the two fleets meet in transit, between jump points, or in transit while using the Alcubierre drive, when the two fleets in interstellar space meet, and they come within 20 light hours of each other and turn off the Alcubierre, of course, there's the points where the jump points intersect so they're very important systems, or the wormholes which are within a star system and allow you to bypass dozens of transit points.


----------



## Damian12612 (Dec 5, 2021)

Danny McG said:


> View attachment 84355


?


----------



## Damian12612 (Dec 5, 2021)

Venusian Broon said:


> Good point. If they are going fast enough in a vacuum, all that matters may be just the kinetic energy transferred on a hit. However, a bit like a mace, a tiny tip on the leading edge of projectile would still probably increase penetrability of the round.
> 
> An advantage of a projectile that is fully Uranium, apart from its mass and therefore increase in kinetic energy, could be if the target has 'shields' or protective magnetic fields that are there to deflect ferromagnetic objects, they wouldn't really be deflected much. I mean, it might not really matter if the projectile is going at 10 km/s   and thus a shield like this really be worthless, but this is fiction...


Im my world, shields not reflect bullets but plasma laser


----------



## Damian12612 (Dec 5, 2021)

Foxbat said:


> For firing electromagnetically and keeping up efficiency, how about a kind of catapult just like launching a plane from an aircraft carrier (I’m thinking DU projectile sits in a cradle, which is accelerated along an electromagnetic rail). This would mean the magnetic characteristics of the projectile for launch wouldn’t matter.


this idea I already use, in drones of the class "Lancer" which are such torpedo boats, but instead of rockets, they use darts


----------



## Damian12612 (Dec 5, 2021)

Valtharius said:


> By length you mean the diameter?


diameter is caliber


----------



## Damian12612 (Dec 5, 2021)

Biskit said:


> What shape is your projectile?
> If spherical, then the volume of a sphere is 4/3 x π x r xr x r where r is the radius = half the diameter.
> 
> The mass of the projectile will then be volume x density.
> ...


xr?


----------



## Biskit (Dec 5, 2021)

Damian12612 said:


> xr?


Sorry, I was struggling to persuade it to do:






Damian12612 said:


> diameter is caliber



If diameter = calibre = 153cm  and length = 30cm then the geometry is not spherical.


----------



## Damian12612 (Dec 5, 2021)

Biskit said:


> Sorry, I was struggling to persuade it to do:
> View attachment 84465
> 
> 
> ...


so I have to reduce the caliber, let's say, half of 153 cm, so 76.5 cm and 76.5 cm length


----------



## Damian12612 (Dec 5, 2021)

Biskit said:


> Sorry, I was struggling to persuade it to do:
> View attachment 84465
> 
> 
> ...


thats what i get

































do i do something wrong? because i think with this weight i can destroy Pluto with speed 10 m/s


----------



## Eternity_TARO (Dec 5, 2021)

I just wanted to say that whenever you are doing any calculation for a fictional thingy, as long as you are within the ball park, you are fine, it doesn't have to be exact.

So, you can use simple shapes and simple geometry to get 95% there and that is good enough.

THere is a brilliant black-and-white Twilight Zone in which an alien is visiting Earth unbeknowst to us of course.  During the story, a small circle of people discover he is an alien.  One of the people in this circle is a PhD Astrophysicist professor at some college.  The Professor is standing in front of a board filled with equations, this board represents his life's work as he is trying to deduce some formula for something astrophysics related.

The alien looks at all the math and writes the last line of the equation, a line that has stumped the professor his entire life.  

The professor looks at the solution and says, "That easy, I could do that, but that isn't a solution, it is only an approximation."
THe alien shrugs and says, "Yeah, this problem is unsolvable, but that approximation is good enough to get you across the galaxy..."


----------



## Danny McG (Dec 6, 2021)

Damian12612 said:


> ?


It's a picture of Gumby from Monty Python.
Commonly identified as "My brain hurts!'


----------

