The novel - ahh, now I get it !
Having recently acquired and read the novel of the movie, I found a number of small differences and more detailed explanations of the events that happen.
Firstly, the thing you see flying overhead at the start of the film is not a ship at all, but an orbital platform that orbits Saturn.
Captain James is late simply because his alarm clock didn't go off. He looses his hand after the force of the air rushing out of the airlock pulls him into space, but he doesn't get sliced by any wires like in the movie. The novel does describe a catwalk being suspended by cables though, and it was these cables that James was hanging on to as his hand was sliced off. Benson swapped his and the Captain's uniform round so that if the body is found, they would assume Benson had committed suicide after failing his exam. The exam was to test how well Benson could control the brain-interface, and since he was marked as "potentially unstable" was unfit to carry out the assignment of building Hector. James got what should have been Benson's promotion to Captain Handler - the novel goes into detail that Benson wanted to kill James so that he could prove to himself that he was good enough to build the Demigod after all.
There is no debris of Adam during the explosion at the end of the film simply because he was disintegrated by the blast.
The novel doesn't end the same way as the film in that on Alex's return to Earth, she decides to go back to Saturn 3 on completion of Handler exam and brain-link implantation to build another Demigod. Adam's mind survives in some way after being downloaded into Hector and is placed in the station computer just before Hector is blown to bits - the novel implies that Alex wants to return to Saturn 3 to download Adam's mind into a new Demigod so that she can be with him again - I think I'll stick to the movie's version of the ending.
Some of the dialogue was changed for the film and a lot of detail missed out, which leaves a lot of questions if you have only seen the film.
That's all I can remember from the top of my head and there is more, if you want to understand the film in more detail then you might be able to find a copy of it on ebay, which is where I got my copy from - although it was the only one I came across under the search of "Saturn 3 Movie Book."