 Why did Peter choose to break all the mirrors inside the ship?
Then there would remain only the task of blasting the great, shining ship out into the carefully-calculated orbit that would be its home. He could see, too, the level on level of laboratories and storerooms that filled its interlocking segments; the meteor deflectors, the air renewal system, the mighty engines at the stern—all the children of his brain. Not only our individual lives are threatened, but our existence as a race. Peter took it in fifteen seconds, running, and stumbled to a halt in front of the door marked "Radiation." It was a street scene in the Science City of Manhattan, flooded by the warm spring sunshine. There aren't going to be any noncombatants, this time.
 He didn't want to see the changes to himself due to the rays.
 The mirrors were harmful to the embryos  The mirrors reflected too much light.  He needed his full attention on the task at hand.  He didn't want to see the changes to himself due to the rays.