Is it due to energy demand or acceleration damaging the cargo/humans or something else?
In: 6
On earth? Atmosphere and the stresses induced in the frame of the rocket. More accurately though, they are. Spin launch is relatively new and has been using a scaled down test mass driver, before ~upgrading~. As to why is not used more, probably difficult to do. We as a species ever plan on staying on the moon or mars, there will definitely be more generalized usage of mass drivers.
Okay so.
Your statement of energy requirement is likely one.
However what exactly would propel the spaceship? Because if you intend to shoot the ship with the cannon energy is the least of your concerns. Beginning with the enormous amount of interference thanks to magnetic waves basically making all the electronics break. And the speed wouldnt last long enough to break atmosphere.
Now lets say you try to use the cannons to launch stuff down to propel the rocket. That also wouldnt work as reloading them takes time, and likely cant be done fast enough to capitalise on the distance you make.
So it is just worse in practise to a rocket
Apart from other concerns, reaching earth orbit from the surface requires acceleration of 3000 G kms. For example, you could accelerate at 1 G along a 3000 km long cannon, or accelerate at 3000 Gs with a 1 km long cannon. Sending most cargoes requires an impracticality large cannon.
Contrary to popular belief, going to orbit isn’t a “shoot straight up” affair, it’s more a “go so fast sideways that you miss the ground when you fall”. However, we see pretty much every rocket launch start off straight up and only start turning way up high. Why is this?
Well, turns out air drag is exponentially harder the faster you go. That means if you are going really fast where the air drags you, you’re wasting a LOT of energy to it. So it’s actually cheaper, energy-wise, to spend some energy “unproductively” going to where the air is thinner and THEN start making progress to orbital ‘lateral’ speeds.
Where the heck do mass launchers figure into this? Well, if your cannon is on the ground, you can’t shoot up and expect orbit, you have to shoot sideways into a lot of air. That’s wasteful as hell. On top of that, if you do manage to launch at enough speed to overcome the loss, you’ll basically heat your vehicle exactly like reentry does, BUT VERY CLOSE TO THE LAUNCH SYSTEM. That’s probably not good to any of the equipment.
some good answers already about the problems of using a mass driver to launch from the surface of the Earth into orbit. there’s a secondary question about the use of mass drivers as propulsion once the vehicle is already in space (microgravity, no atmosphere, etc.).
propulsion in space requires reaction mass because the only way you go forward is by pushing something out of the back of the ship. the forward momentum is a result of Newton’s Third Law. No forward momentum for the ship without backward momentum from the propulsion system expelling reaction mass.
so you have to carry mass on the ship in order to shoot it out the back. that’s mass that the ship has to haul around until it’s used. if you’re using a mass driver and shooting out *inert* mass then you also need some other kind of fuel source to generate the power for the mass driver. so now you’ve got a ship with a really large electrical generator (and it’s own fuel source) as well as some inert mass to shoot out the back with the mass driver. the weight problem is starting to add up here.
chemical fueled rocket engines are more efficient here. they don’t use inert mass as fuel, they use mass that is a very dense store of chemical potential energy. it requires minimal energy to ignite, so the ship won’t need a large power system dedicated to the engines. the engine power is stored in the fuel itself. that’s efficient. the energy density of rocket fuel is really just extremely high. it’s going to be extremely hard to beat with anything like the technology we’ve currently got.
You could technically use an AK47 shooting down as a rocket. The recoil exceeds the weight of the gun.
The problem is we want the rocket to weigh as little as possible, and the rocket to NOT destroy the payload, such as a squishy human.
For example, if you threw a nuclear bomb out the back (Orion drive), you could go pretty fast, but it might also blow up the pilot.
Rockets are pretty good for this. They’re basically only fancy tubes with fuel. Compare to an AK47, they skip out on the bullet and only use the gunpowder. Rockets ARE chemical guns without bullets, because they only want recoil and aren’t trying to shoot someone.
A gauss gun require fancy magnets and a powerful generator. This is too heavy even for Earth based artillery, much less spacecraft.
For mass drivers as a specific case, the chief reasons are:
* The power demands. To get into orbit, you need to achieve a speed of around 7500 meters per second of speed. The kinetic energy of 1 kg at that speed is about 28 megajoules. Say you are going to accelerate over 10 seconds, that’s 2.8 megawatts of power. For 1 kilogram.
* Energy loss. The fastest speed that you achieve is right out of the barrel and then you lose a lot of energy to air resistance. Rockets don’t have this issue because they travel relatively slowly while they are in the atmosphere.
* G load. You need a lot of speed over a few kilometers of launch tube, so that requires a high g load.
If you want more detail about, you can see my video [here](https://www.youtube.com/watch?v=mjbuaY-psS0).
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