According to this site [2] that's equivalent to around 200 kg of TNT. Even with the counterweight being mostly water, that's quite a lot of energy to disperse. How does one evenly spread out the water to a surface the size of a football field? Would that even be enough area to prevent a shock wave being reflected back at the launch equipment?
[1] https://calculator.academy/joule-calculator/#f1p1|f2p0
[2] https://www.convert-me.com/en/convert/energy/tntkg.html?u=tn...
* 5 metric tons TNT
* 1/3000 Little Boy atomic bomb
* 4 barrels of crude oil (!)
* Boil 2,300 gallons of water
* 0.25 mg of matter converted to energy
* Enough energy to melt two 11,000 kg iron counterweights, with 2 GJ left over
* A magnitude 3.7 earthquake [1]
[1] https://www.volcanodiscovery.com/earthquakes/energy.html
> Although not shown in the previous figures, the circular mass accelerator structure 150 may comprise a second exit port directly opposite the exit port 115 to capture the counterweight 135 that is released simultaneously with the launch vehicle 105 to minimize an imbalance on the motor at the time of release. The counterweight 135 may be a solid material, or a liquid such as water.
The use of a liquid is a curious idea. Perhaps it could be dispersed in such a way as to spread the force of the counter weight being released across a wide surface area? Like a small explosive forces the liquid out in all directions?
https://patents.google.com/patent/US10202210B2/en