They could be EMP devices that could detonate when passing over US.
I have no actual knowledge of this but I strongly suspect the X-27B is used to check these sats for neutron emissions.
To shield the neutron emissions would require a thick covering of water...the hydrogen in water is what blocks neutrons....they could not orbit something so heavy.
They wouldn’t have to send up the satellite filled with water at the same time. They could do one, then the other.