[mhandley]

I couldn't help wondering what happens to the counterweight. 100kg travelling at 5000mph works out as about 500MJ. For comparison, 1 tonne of TNT is about 4.2GJ, so the energy of the counterweight is about the same as 120kg of TNT. Looks like stopping the counterweight will produce a pretty big explosion, but probably not their biggest problem.

[avs733]

This has always been my question. In college, we built a spinning pumpkin launching appartus...the first time we had it release a 5lb pumpkin it the whole frame (about 400lbs) jumped about 2 feet in the air a split second later.

Unless they are releasing liquid, releasing two projectiles a half cycle apart (which still isn't optimal) or something similar, I can't see how the counterweight doesn't just turn the structure into dust instantly. If it isn't perfectly the vibrations will just eat the thing.

If you could guide the counterweight, maybe you could use the thing for either forging [0] or bonding of metals [1]

[0] https://en.wikipedia.org/wiki/Heavy_Press_Program

[1] http://www.explosionbonding.com/

[noitpmeder]

From the article

"a counterbalance spinning opposite the rocket gets released at the same time, preventing the tether from becoming unbalanced and vibrating into oblivion"

[viraptor]

Yes, but where is it released? Because if it's at the same time and the rocket goes up, the counterbalance goes down. And that means a big explosion right under your infrastructure.

[mhandley]

Exactly - the energy of the released counterweight will inevitably produce an explosion as it's stopped pretty quickly by something. My question was how big an explosion. The answer is pretty big, but this probably isn't their biggest problem.

[graderjs]

Liquid back stop? Ballistic jello?

[mhandley]

500MJ is enough energy to flash-boil 200Kg of water, so that might work. Would be a sizeable steam explosion, as the 330 or so cubic meters of instantaneously created steam tries to go somewhere, and an interesting pressure wave in the water tank.

[graderjs]

"interesting" -- the concussive overpressure would be brutal in water and travel further I guess, maybe you could add a bubble stream to the water like in dives to diffuse the shockwave some.

[mrfusion]

Can it regenerate energy when slowing down?