The Cat and Rimmer aren't human, so Asimov's First Law wouldn't apply to them.

And I was surprised that they said life signs were detected from the mechanoids. Not sure whether it's been previously established that this is the case, though?

So these Mechanoids have been wander space for millions of years.

The Cat and Rimmer aren't human, so Asimov's First Law wouldn't apply to them.

Which is why psycho droid was able to try to kill them in Last Day.