Same query pertains to movement into a system you have settled that is hazardous. Sending ships for space defence runs the risk of them being destroyed before they can orbit?
You could always build a Starbase there. Ships built in the system don't have to roll for the hazard, nor do they roll when they leave the system. Only arriving ships that stop there have to brave the hazard.
Just for clarity, we are all referring to systems that have a hazard printed on them. You might pull an exploration card that has a hazard on it which will disappear after the card conditions have been met. So there is a possible situation where someone might roll for a hazard when first encountering a system, but then won't have to roll for it again.
(Just trying to head off any potential confusion down the road.)