Do segundo livro, Guerra de Caliban, capítulo 48:
“Okay,” Holden said. “That was bad.”
“What?” Avasarala said. “What was bad?”
“One of the Earth ships just took three torpedo hits.”
“It that a lot?”
“The PDCs (Point Defense Cannons) aren’t stopping them,” Naomi said. “Those UN torpedoes all have transponder codes that mark them as friends, so they’re sailing right through. They typically don’t expect to be getting shot at by other UN ships.”