After considerable research, I have been unable to identify this book. I'm trying to find a book that I read ages ago (and have subsequently misplaced) that seems impossible to find because it has a robot in it and there are so many books with robots.
It was a short book that was definitely very old, I got it in a 2nd hand bookstore for like $2. As time goes on, I remember less of the story but this is what I've retained thus far:
There is one robot in this story, who has a bomb set up inside (I don't think it knows). The premise was that this crew of people were on a spaceship, en route to an abandoned moon or something to safely dismantle or destroy this robot but they had to do it without the robot cottoning on. The protagonist was a male who had a crush on the female scientist or doctor, who had red-hair. The lady was very close with the robot- they had been friends for a long time or something.
The robot of course soon enough realises what is happening and things start getting strange (like, people start dying or something? unsure). One part I vividly remember is the protagonist looking for the lady and he hears her voice outside (they'd landed somewhere snowy...) so he goes out and you see that the robot had imitated her voice and tricked him.
It can't have been a hugely famous book, or else it would have come up in my research. I have no idea who wrote it and I can't remember the title. I'm sorry it's so vague but it is all I can remember!
My friend read the first chapter of this book around 9 years ago and she has some other info which may or may not help. I figure I'll add it just in case (I'm unsure how correct it is, it seems vaguely similar): Humans had built a big (non humanoid) bomb and it was in space, possibly out near Mars, to do something, but it became sentient and didn't want to do its job or something (and FYI it's not that story with the Alpha Centauri Device thing).
It is not Imposter by Philip K Dick.