A nuclear bomb is in orbit. When it explodes some mass is converted to energy. Ok, in a real device not much mass, but some. Without breaking any laws of physics we can certainly imagine a case where there is less bulk and more fusing (or fissioning) material and the mass change is more significant. Let's say in the bomb's reference frame the explosion is spherically symmetric. With the change in mass, how is momentum conserved in the earth reference frame? I don't think the center of mass of the remaining material speeds up, so is the missing momentum all in the red shift / blue shift of the generated photons?