In the spaceship, the astronauts have normal gravity though the ship is not spinning to create it. In the spacewalk scenes, they are weightless.
When David is being attacked in his home & somehow loses the link with his replica self, he should have contacted Earth from the spaceship to send someone to help at his house instead of immediately trying to go back into his replica on Earth that had already been subdued.
When David chose to transfer his consciousness back to Earth he didn't know that his replica had been tied up and incapacitated. Even if a message from the spaceship reached Earth immediately it would take at least minutes for help to be sent to his house. By returning to Earth he was attempting to protect his family immediately.
When David chose to transfer his consciousness back to Earth he didn't know that his replica had been tied up and incapacitated. Even if a message from the spaceship reached Earth immediately it would take at least minutes for help to be sent to his house. By returning to Earth he was attempting to protect his family immediately.