In the Lab Rat comic Rattman was shot up by a turret. Next he climbed into a bed like the one in the start of portal one. I believe he did accually die then. This is because only the Compaion Cube is shown on the moon. If you do not know the Compaion Cube theory look it up before you read the rest of this. Because he died in the bed or somewhere else he was put in the cube. Mabey he was able to set up a program for his Compaion Cube by monoration his life signs with a computer. Then having this computer rapidly scan compaion cubes for his DNA. When it was found it was thrown to the moon( portaled) and a link with a radio was established. I am guessing GlaDos found it and put it in the garbage so Chell would not find it. When the specified radio was found Chell was told NOT to test with it. So GlaDos wanted Chell NOT to discover the lost transimission(achievement).

That conlued my theory post what ever you want. And please forgive my bad english and punctuation.