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https://www.kickstarter.com/projects/1682852725/the-starfire-space-cannon
The idea is basically to shoot something into orbit, with a howitzer. Let's walk through the process here, and determine whether this guy is on the level.
The amount of energy in a kg of gunpowder is 3 MJ, according to Wikipedia and other sources: http://www.madsci.org/posts/archives/2007-11/1195506740.Ph.r.html, http://en.wikipedia.org/wiki/Energy_density.
The projectile is assumed to have a mass of 4 kg. I'm basing this assumption off of the forces it will have to endure, and the payload that it must carry. This isn't a hard and fast figure, but let's determine this as a starting point.
The amount of energy required to escape Earth's gravity well is 0.5*mass*escape velocity^2. For this particular body, the energy required to escape Earth's gravity well is 0.5*4*11200^2= 250880000 J=250.88 MJ.
Let's assume that no energy is lost to sound, or heat, or anything else. That means to propel an object out of Earth's gravity well we'd need 250.88/3 = 83.627 kg of gunpowder. You're looking at approximately 84 kg of gunpowder to propel this thing.
Gunpowder has a density of 1.7g/cm^3, which means you need 0.0494 m^3 or 3015 in^3 of gunpowder. You've got an 8 in diameter cannon, so the area of the barrel would be 3.14*4^2 or 12.566 in^2. This means you'd have to have 3015/12.566=239.9" of gunpowder. At 240" you'd have an 8" diameter cannon 20' high full of gunpowder. This isn't a howitzer, it's a pipe bomb. That sort of combustion would need an insanely thick wall just to not explode upon the first firing.
The energy is only imparted until the end of the barrel. Let's assume that the barrel is 13.716 m (he cites 45' for mobility) long. In order to reach the 11200 m/s velocity, assuming that you've got a constant linear acceleration, you're looking at a time in the barrel of 13.716m/5600m/s=0.002451s. Acceleration could be given as a=(v-v0)/t, or 11200/0.002451= 4569430 m/s^2, or 4600 km/s^2. To my knowledge, no material could withstand that kind of acceleration.
Now, let's do some creative thinking as to what is actually going to happen here. You aren't shooting the projectile out of Earth's gravity well. You might be able to get a propellant with twice the energy density of gunpowder. Both of these mean you're looking at maybe 8' of explosives in an 8" diameter barrel.
On the opposite side, you aren't getting 100% efficiency in converting gunpowder into linear kinetic energy. You have energy dissipated due to wind resistance. Finally, you've got to have a surviving barrel and projectile for multiple launches, which means a reasonable acceleration. Applying this, you'd basically be back to the 20' of propellant and a barrel an order of magnitude longer than the one cited.
So, is this guy crazy? Absolutely. Even if he built a prototype 3 times the quoted 45' size, he'd still not be able to do anything but extremely low Earth orbit. This is why NASA isn't doing this, and why the thought process of Jules Verne had a miles long track for a rocket to accelerate on in order to get to the moon. A howitzer just isn't a smart idea, and this is why Kickstarters fail. Math work. Science works. NASA and the government aren't conspiring to keep us on the Earth, the mathematics here only scratch the surface of the proposition and find the idea completely untenable. All the money in the world wouldn't help this sort of a stupid project survive.
Edit:
Thinking back on all of this, maybe the definition of space is rather pliable. Assuming that the goal was just to break into the mesosphere, we might be looking at a winner here. Of course, the difference between the mesosphere and space is rather significant (100-10000 kilometers is...significant).
I'd say this is a reasonable out for the Kickstarter, but I'd have to eat my words. The author cites instances of thousands of Gs of acceleration, but somehow links his phased combustion idea to significantly less (but more continuous) force. There is a substantial question of whether we're comparing apples to apples here, and the website linked to doesn't offer much in the way of hard science.
Consider me skeptical, but a gun without some hard science sounds pretty redneck to me. If you can't produce calculations, that others can verify, you have failed to prove your point. Requesting tens of thousands of dollars just to shoot a big gun is...not what I'd consider a fruitful endeavor.
The idea is basically to shoot something into orbit, with a howitzer. Let's walk through the process here, and determine whether this guy is on the level.
The amount of energy in a kg of gunpowder is 3 MJ, according to Wikipedia and other sources: http://www.madsci.org/posts/archives/2007-11/1195506740.Ph.r.html, http://en.wikipedia.org/wiki/Energy_density.
The projectile is assumed to have a mass of 4 kg. I'm basing this assumption off of the forces it will have to endure, and the payload that it must carry. This isn't a hard and fast figure, but let's determine this as a starting point.
The amount of energy required to escape Earth's gravity well is 0.5*mass*escape velocity^2. For this particular body, the energy required to escape Earth's gravity well is 0.5*4*11200^2= 250880000 J=250.88 MJ.
Let's assume that no energy is lost to sound, or heat, or anything else. That means to propel an object out of Earth's gravity well we'd need 250.88/3 = 83.627 kg of gunpowder. You're looking at approximately 84 kg of gunpowder to propel this thing.
Gunpowder has a density of 1.7g/cm^3, which means you need 0.0494 m^3 or 3015 in^3 of gunpowder. You've got an 8 in diameter cannon, so the area of the barrel would be 3.14*4^2 or 12.566 in^2. This means you'd have to have 3015/12.566=239.9" of gunpowder. At 240" you'd have an 8" diameter cannon 20' high full of gunpowder. This isn't a howitzer, it's a pipe bomb. That sort of combustion would need an insanely thick wall just to not explode upon the first firing.
The energy is only imparted until the end of the barrel. Let's assume that the barrel is 13.716 m (he cites 45' for mobility) long. In order to reach the 11200 m/s velocity, assuming that you've got a constant linear acceleration, you're looking at a time in the barrel of 13.716m/5600m/s=0.002451s. Acceleration could be given as a=(v-v0)/t, or 11200/0.002451= 4569430 m/s^2, or 4600 km/s^2. To my knowledge, no material could withstand that kind of acceleration.
Now, let's do some creative thinking as to what is actually going to happen here. You aren't shooting the projectile out of Earth's gravity well. You might be able to get a propellant with twice the energy density of gunpowder. Both of these mean you're looking at maybe 8' of explosives in an 8" diameter barrel.
On the opposite side, you aren't getting 100% efficiency in converting gunpowder into linear kinetic energy. You have energy dissipated due to wind resistance. Finally, you've got to have a surviving barrel and projectile for multiple launches, which means a reasonable acceleration. Applying this, you'd basically be back to the 20' of propellant and a barrel an order of magnitude longer than the one cited.
So, is this guy crazy? Absolutely. Even if he built a prototype 3 times the quoted 45' size, he'd still not be able to do anything but extremely low Earth orbit. This is why NASA isn't doing this, and why the thought process of Jules Verne had a miles long track for a rocket to accelerate on in order to get to the moon. A howitzer just isn't a smart idea, and this is why Kickstarters fail. Math work. Science works. NASA and the government aren't conspiring to keep us on the Earth, the mathematics here only scratch the surface of the proposition and find the idea completely untenable. All the money in the world wouldn't help this sort of a stupid project survive.
Edit:
Thinking back on all of this, maybe the definition of space is rather pliable. Assuming that the goal was just to break into the mesosphere, we might be looking at a winner here. Of course, the difference between the mesosphere and space is rather significant (100-10000 kilometers is...significant).
I'd say this is a reasonable out for the Kickstarter, but I'd have to eat my words. The author cites instances of thousands of Gs of acceleration, but somehow links his phased combustion idea to significantly less (but more continuous) force. There is a substantial question of whether we're comparing apples to apples here, and the website linked to doesn't offer much in the way of hard science.
Consider me skeptical, but a gun without some hard science sounds pretty redneck to me. If you can't produce calculations, that others can verify, you have failed to prove your point. Requesting tens of thousands of dollars just to shoot a big gun is...not what I'd consider a fruitful endeavor.
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