What is it? Where are the rules for it? If Void Born are immune to it then it MUST have some effect on other PCs. No one else seems to have this question on the whole of teh interwebs so I must be missing it somewhere. Thanks for the help.

I may be wrong but I don't think there are any rules for "Space Travel Sickness". It just seems like one of those concepts thrown out there for more sadistic, or realistic, GMs to impose on their party to make their early days of service a little more colourful. The same description made it into Rogue Trader and there doesn't seem to be anything in that rulebook either.

I'd say something like sea-sickness from Maggots in the Meat:

Toughness tests, with some positive modifier, to avoid fatigue, with bad failures meaning the person causes an incident by throwing up on someone or ends up in sick-bay. It's entirely up to you, really.