# Galilean cannon

Do you think that Galilean Cannon can be somehow useful in rocket industry during space exploration, example to launch rocket from the Earth or from the orbit to far space? The mass of ball might be replaced by any incremented electromagnetic force, pressured gas, etc.

A Galilean cannon is a device that demonstrates conservation of linear momentum.1 It comprises a stack of balls, starting with a large, heavy ball at the base of the stack and progresses up to a small, lightweight ball at the top. The basic idea is that this stack of balls can be dropped to the ground and almost all of the kinetic energy in the lower balls will be transferred to the topmost ball - which will rebound to many times the height from which it was dropped.

• I would say it's impossible even theoretically. Deformations in rubber should spread with velocity of sound. The velocity is about 1000 m/s. (see here: ncbi.nlm.nih.gov/pmc/articles/PMC5126009). It's much less than orbital velocity 8 km/s. – Heopps Sep 22 '18 at 18:45
• I might think about it to use in space and not to launch from the Earth, so any speed will be better than no speed at all. – Luke Sep 22 '18 at 21:54

To expand out Heopps comment, any mechanical launch method runs into limits with the speed of sound in the material. As a general rule you can assume that anything that requires passing a force through an object faster than the speed of sound for the material will either deform the material or break it. See light gas gun for the current state of the art. You might be able to do this with stacked magnets, which are not depending on atom to atom forces but if you are doing that you might as well make a coil/rail gun and simplify things.

Note that this is acceleration only, if you spread the speed change out in time mechanical methods can still achieve potentially useful velocities at the cost of longer physical travel, a long armed (several km) catapult could do that on a small enough moon, not seeing any way for the Galilean Cannon to be modified that way though.

This device has the same basic problems as other cannon launch methods:

1. a very high initial acceleration (hundreds of G) requiring a very sturdy payload

2. ... followed by a long journey through the atmosphere with nothing to compensate for atmospheric drag. This means you lose a lot of speed along the way, lots of heating of the capsule etc.

3. and it fires mostly vertically, while a rocket mostly needs lots of horizontal speed, so you still need a large rocket stage to circularize your orbit.

There are a bunch of cannon-related questions here which have more detail on these points.

A Galilean cannon, specifically, is difficult to scale up. You want nice inelastic collisions between the balls, but at the speeds and weights you need here, the largest ball in the stack ends up deforming the ground underneath, reducing the kinetic energy transfer to the balls above.

• In this case maybe just use it in space and not to launch from the Earth + use it just to transport materials not humans. – Luke Sep 22 '18 at 21:57