Every 2 minutes you can right click on ore in your cargo and jetison the ore into space. This will create a cargo container close to your ship. Typically you will then use this cargo container to add more ore into it. The container will last for minimum 1 hour, maxium 2 hours - so typically dont use it more than 1.5 hours before hauling the ore back or move it to a new one.

PS! Watch out for can-flippers, pirates that steals your ore. So it's good to watch local and haul in the ore from time to time.

/MegaThordin

Also, if you rename the cargo container it will last longer in space. But again, just to be safe you should probably haul it every 2 hours at least. Putting the time you jettisoned the can into the name will help remind you when to haul.