When playing through the space missions, you may notice that two of them do not seem have the gold brick to start the mission. Many people get confused about this so I thought a quick post might help everyone.
For these two space missions, you have to do something first that will trigger the appearance of the gold brick. For the Ryloth space mission, you need to aboard the Resolute and locate the room with the turrets in. To find this, go through the brig and use the lift at the end. Cross the large hanger from right to left and use another lift here. When you are in the turret room, jump into one and start shooting the floating debris you can see. When you have shot enough the space mission will unlock, meaning the gold brick will now be there when you want to start the mission.
Maridun is the same deal. This time, on the Invisible Hand, find the turret room. To get there, head to the left when you dock and go through the double doors into the bounty hunter room. In here there is another lift which will lead you to the turrets. When you arrive, jump in one and start shooting the broken red ship in front of you. When you destroy it, the mission will unlock.